NTS News Center

Latest News in Testing, Inspection and Certification

NTS News Center - Latest News in Testing, Inspection and Certification

MIL-STD-461G Released

MIL-STD-461 Testing at NTS

The G revision of the MIL-STD-461 standard was released in December 2015 and is available here. NTS’s Jeffrey Viel’s wrote an article for InCompliance Magazine reviewing the proposed changes which was published back in August 2015. These changes have carried into the final released standard and are worth reviewing.

A few highlights of the MIL-STD-461G standard:

  • FFT receivers are now permitted for use
  • Interconnecting cable routing now specified for floor standing equipment
  • Test method CS106 has been removed
  • Test method CS114 system check updates
  • The addition of test method CS117, conducted susceptibility, lightning induced transients, cables and power leads
  • The addition of test method CS118, personnel borne electrostatic discharge
  • Test methods RE102 and RS103 technical updates

Contact NTS today to discuss your next MIL-STD-461 test program.

Korea’s New Test Standards for 2016

Korea’s New Test Standards for 2016

Effective January 1, 2016: KN32 / KN35 to replace KN22 / KN24

Beginning on January 1, 2016, Korea standards KN32 and KN35 will be replacing the KN22 and KN24 test standards. What this means is that the KN22 / KN24 will no longer be accepted for Korea KC approval after January 1, 2016. However, permissive change applications using KN22 / KN24 reports will still be accepted until the end of 2017.

Next Steps

NTS will only be allowed to apply for Korea KC approval using the KN22 / KN24 test reports if the final report, and all accompanying documentation required for approval, are provided to NTS by December 23, 2015.

Who does this apply to?

  1. Customers with KN22 / KN24 test reports not yet submitted for approval
    If you are interested in utilizing existing reports for KN22 / KN24 approval, please contact your dedicated account manager for a quote.
  2. Customers with products that are currently being tested
    No further action is necessary if testing is expected to be complete and that accompanying documentation is provided to NTS by December 23, 2015.
  3. Customers expected to have testing done after December 23, 2015
    If testing and accompanying documentation is expected and/or provided after December 23, 2015, NTS will need to assess your project(s) and confirm if the data collected meets the KN32 / KN35 standards, test methods and limits. If necessary, additional testing may be required to meet the new requirements.

What We’re Doing

NTS recently applied for the accreditation updates. We have added the KN32 standard to our scope whereas the KN35 standard will be added later this month.

Please contact the International Approvals team and Caio Collet-Silva, International Approvals Manager at 510-570-7585 IAteam@nts.com, if you have any questions or concerns regarding the new test standards.

Technical Spotlight – Organotins Materials Testing

What are organotin compounds?

Organotin compounds have been used as heat stabilizers in PVC, biocides, wood preservatives, and marine anti-fouling agents. There are 4 classes of organotins with tri-substituted organotin compounds having the most toxic effects on the environment. These compounds are endocrine-disruptors and cause severe reproductive effects in aquatic organisms. There are also concerns in regards to neurotoxic and immunotoxic effects in higher animals.

There are laws banning the use of organotins to prevent the buildup of biological organisms (algae, mollusks, etc.) known as “fouling” on marine vessels. The Navy is required to periodically test for organotins in the waters serving as any home port for their vessels.

Several dioctyltin compounds are approved by the FDA as stabilizers in vinyl chloride plastics used in as indirect food contact additives (21 CFR 178.2650).

Who needs to test of organotins?

Manufacturers and Importers (including supply chain) of products into the EU Articles for either consumer or professional use.

Who is mandated to test for organotins?

The European Commission Decision 2009/425/EC requires:

  • Tri-substituted organotin compounds such as tributyltin (TBT) and triphenyltin (TPT) shall not be used after July 1, 2010, in articles where the concentration is greater than 0.1% by weight of tin.
  • Dibutyltin (DBT) compounds shall not be used after January 1, 2012, in mixtures or articles where the concentration is greater than 0.1% by weight of tin. Some exemptions on items such as rain gutters, PVC coated fabrics, and adhesives/sealants effective until January 1, 2015.
  • Dioctyltin (DOT) compounds shall not be used after January 1, 2012, in articles supplied to or used by the general public where the concentration is greater than 0.1% by weight of tin.

For more information concerning the chemical testing of your products, please contact us at (800) 270-2516, or email us at RFQ@nts.com.

Technical Spotlight – Phthalates Materials Testing

What are Phthalates? Phthalates Molecular Structure

Phthalates are plasticizers used to soften rigid plastics and are also used as adhesives and solvents. These compounds are present in a wide variety of products such as children’s toys, cosmetics, medical devices, pharmaceuticals, and packaging materials just to name a few. There is concern that phthalates leach out of these products and can be absorbed by various means of contact. In the human body, there is serious concern that these compounds have possible adverse effects on human development and reproduction. The FDA has made recommendations on how to reduce exposure to DEHP from medical devices and has defined a high-risk patient group would be most sensitive to exposure.

Wal-Mart, Target, and Toys R Us proactively initiated phase out of products containing phthalates prior to the required date of enforcement.

Who needs to test for Phthlates?

Manufacturers, Importers, and Crafters of:

  • Children’s toys: products intended for a child 12 years of age or younger for use when playing. General use balls, bath toys/books, dolls, and inflatable pool toys are examples of toys that are covered by the law.
  • Child care articles: products that a child 3 years of age or younger would use for sleeping, feeding, sucking, or teething. Bibs, child placemats, child utensils, feeding bottles, cribs, booster seats, pacifiers and teethers are articles that are covered by the law.

Who is mandating testing for Phthalates?

U.S. Consumer Product Safety Commission (CPSC)

  • Regulation of 6 phthalates – butyl benzyl phthalate (BBP), dibutyl phthalate (DBP), di (2-ethylhexyl) phthalate (DEHP), diisodecyl phthalate (DIDP), diisononyl phthalate (DINP), and di-n-octyl phthalate (DnOP)
  • Three phthalates (DEHP, DBP, and BBP) have been permanently banned in concentrations of more than 0.1% in children’s toys and child care articles.

U.S. Environmental Protection Agency (EPA)

  • December 30, 2009, posted an Action Plan for phthalates
  • Eight phthalates are listed on the Action Plan: BBP, DBP, DEHP, diisobutyl phthalate (DIBP), DIDP, DINP, DnOP, and di-n-pentyl phthalate (DnPP)
  • EPA intends to initiate rulemaking in autumn 2010 to add the above eight phthalates to the Concern List under TSCA section 5(b)(4)as chemicals that present or may present an unreasonable risk of injury to health or the environment.
  • In late 2010, EPA intends to initiate rulemaking to add the phthalates that have not been previously listed on the Toxics Release Inventory (TRI).

Individual U.S. States – bans and proposed laws

  • California – Prop 65 list: BBP, DBP, DEHP (among first to be listed), DIDP, and Di-n-hexyl phthalate (DnHP)
  • Connecticut
  • Hawaii
  • Illinois
  • Maryland
  • Massachusetts
  • New Jersey
  • New York
  • Rhode Island
  • Vermont
  • Washington
  • West Virginia

Outside U.S.

  • Europe – REACH; banned use of DEHP, DBP, and BBP children’s toys and childcare articles in concentrations over 0.1% by weight. Three additional phthalates (DINP, DIDP, and DnOP) have been prohibited in concentrations of more than 0.1% pending further study and review by the Commission and a group of outside experts. This interim prohibition applies to child care articles and toys that can be placed in a child’s mouth or brought to the mouth and kept in the mouth so that it can be sucked or chewed. There is an amendment (2007/47/EC) to Directive 93/42/EEC concerning phthalates and their use in medical devices (“Devices which contain phthalates, and which are intended to channel, transport or store medicines, body fluids or other substances for administration must be labeled to show presence of phthalates.”).
  • Nine other countries including Japan, Argentina, Mexico

For more information concerning the NTS chemical testing services, please contact us at (800) 270-2516, or email us at RFQ@nts.com.

Technical Spotlight – Bisphenol-A (BPA) Material Testing

What is BPA?BPA Testing

BPA is used to make polycarbonate plastics, including baby bottles, sports bottles, reusable food and drink containers, bicycle helmets, CDs and DVDs. It is also an ingredient in the epoxy resins used to line metal cans.

A number of laboratory studies have linked BPA — a synthetic estrogen — to birth defects, low birth weight, cancer, early puberty and other health problems in rats. However, 11 safety agencies around the world have said that BPA is safe for use in food-contact applications.

The U.S. Environmental Protection Agency (EPA) began a series of actions to address the potential effects of BPA and issued an action plan that concentrates on the chemical’s environmental effects. The EPA said it would look to add BPA to its list of chemicals of concern which would mandate environmental testing for BPA.

The Food and Drug Administration also reversed its long-held stance that BPA is safe for food contact applications. Regulators said they were particularly concerned about BPA’s effect on the development of fetuses, infants and young children. But the FDA did not ban BPA or require manufacturers to label products that contain BPA, saying that there is not enough information for such a requirement.

The National Resources Defense Council (NRDC) has filed a law suit against the FDA for its “failure to act on a petition to ban the use of bisphenol-A (BPA) in food packaging, food containers, and other materials likely to come into contact with food.”

Who needs to test?

Manufacturers, wholesalers, retailers

Who is mandating testing?

Individual governments – bans and proposed laws

  • Canada – Hazardous Products Act Part 1 of Schedule I amendment banning polycarbonate baby bottles containing BPA effective March 2010.
  • Denmark – Government has instituted a temporary ban beginning July 1, 2010, on feeding bottles, cups, and materials in contact with food aimed at children aged 0-3 years. It also covers those materials in the Danish order on breast milk substitutes and mixed substitutes for babies and young children and the order on manufactured food for young children and babies. The ban will be effective until new studies document that low doses of BPA do not have an impact on development of the nervous system or on the behavior of rats.
  • France – Ban on manufacturing, importing, exporting and selling baby bottles made of BPA-based products.
  • California – State Assembly and Senate passed a bill banning BPA in containers for children 3 years of age and younger. Awaiting approval from the governor.
  • Connecticut – Anti-BPA legislation that becomes fully effective in 2011. Prohibits use of BPA in all infant formula containers or baby food jars and all reusable food and beverage containers. Applies to manufacturers, wholesalers, and distributors. Sell or distribute existing inventory of infant formula or baby food containers, jars or cans as of October 1, 2011.
  • Maryland – Banned in containers for food or liquid intended for children less than 4 years of age effective January 2012.
  • Minnesota – Anti-BPA legislation becomes fully effective in 2011. Bans use in beverage containers intended for use by children 3 years of age or younger. Applies to manufacturers, wholesalers, and distributors.
  • Vermont – Ban also on sports bottles and thermoses with extension to metal cans starting July 2014.
  • Washington – House Bill 1180 passed by a vote of 95-1 that would ban the manufacture and sale of BPA in sports water bottles by July 2012
  • Wisconsin – Ban on use in baby bottles and spill-proof cups for children up to 3 years of age. Additional stipulation that these BPA-free containers must be clearly labeled as such.
  • New York – Proposed ban on use in child care articles such as sippy cups, pacifiers, teething products and baby bottles. Governor has not signed the bill into law.
  • City of Chicago, Illinois – Banned in containers for food or liquid intended for children less than 3 years of age.

 

For more information about NTS Chemical testing of your products, please contact us at (800) 270-2516, or email us at RFQ@nts.com.

Ensuring the Reliability of Products with Environmental Stress Screening

ESS is a series of tests aimed at the identification of potential manufacturing flaws. By utilizing more intense versions of temperature and vibration test methods, ESS is able to accelerate failure at weak points. This allows manufacturers eliminate units more likely to fail and ship only the highest quality products to customers.

Manufacturers are achieving significant gains in reliability through Environmental Stress Screening (ESS).

Test methods including vibration, thermal cycling, and thermal shock are utilized to run the equipment under test (EUT) through an accelerated profile. , manufacturers now can run the final product through an accelerated profile to prove out its ability to endure its intended environment and life span.

Thermal shock testing and thermal cycling are two methods used to accelerate product failures, especially for products which are intended for use in environments where extremes in temperature are encountered. Extreme changes in temperature may cause materials to expand, contract, loosen, over-tighten or simply fail.

Thermal Shock Chamber

Thermal Shock Chamber

The thermal shock chambers are generally dual zone chambers. These test chambers have either an elevator or a conveyor that transfers the samples being tested from one temperature extreme to the other. The low temperatures are achieved with liquid nitrogen, while resistance heating elements are used to achieve the required high temperatures. Temperatures typically range between -70⁰ C and 180⁰ C. The samples are transferred between temperatures in five seconds or less.

Thermal cycling chambers have a larger volume and are single zone. The temperature transition is achieved by turning off the heating elements and injecting liquid nitrogen. The transition is slightly slower than the thermal shock chamber, at roughly 60⁰ C per minute. Temperature ranges are typically between -70⁰ C and 150⁰ C. Typical volume of these chambers is 9 cubic feet.

Thermal cycling chambers have a larger volume and are single zone. The temperature transition is achieved by turning off the heating elements and injecting liquid nitrogen. The transition is slightly slower than the thermal shock chamber, at roughly 60⁰ C per minute. Temperature ranges are typically between -70⁰ C and 150⁰ C. Typical volume of these chambers is 9 cubic feet.

Following testing, reliability engineers are able to predict the actual life of a product in the real world

The ESS process identifies unanticipated flaws in design and discovers issues related to daily variations in the manufacturing process. Different environmental simulations bring to light specific failure modes in the product.

Some common techniques and their associated failures when used with electronic packages are:

  • Thermal Cycling: Cracked Traces, Under-Specified Components, Materials Failure, Solder Joint Failure
  • Thermal Shock: Discontinuity Due to Thermal Expansion, Solder Joint Failure
  • Vibration: Pad Delamination, Cable Interface Issues, Solder Joint Failure, Intermittent Connections,
    Materials Cracking, Nuts, Bolts, Screws, etc. Getting Sheared

Vibration testing is another useful tool in ESS testing. It is used to identify resonances in a product which can cause the product to self-destruct. It can also be used to accelerate metal fatigue failures. Fatigue testing has traditionally been performed using servohydraulic systems, which can be expensive and take considerable time to perform. Utilizing electrodynamic vibration systems can reduce test time because high frequencies can be used and acceleration levels can be increased. Vibration data can be collected in real world situations and replayed through the vibration table. This process can reduce the expense of field trials and predict design and manufacturing defects. Additionally, transportation vibration testing can be performed on the unit to determine if failures will occur in transport.

Vibration testing is performed on an electrodynamic shaker system. The shaker

Vibration Tables

Vibration Tables

can reproduce vibrations such as sine vibrations which occur on rotating machinery, or random vibration, such as that which occurs in an automobile driving down bumpy streets. The electrodynamic shaker operates like a giant loudspeaker system with frequencies limited between 5 and 3000 Hz. (Loudspeakers operate between 20 and 20,000 Hz, which is the range of human hearing.) There are numerous versions of vibration systems, but the most common is a system capable of performing vibration tests in three axes, one axis at a time. The vertical axis is done with the shaker in the horizontal position; the other two axes are done by rotating the vibration head 90 degrees and using a slip table. The photograph in Figure 3 shows the vibration table in the vertical position in the background. The slip table is in the foreground. It is a metal plate on a granite table which has lubricating oil continuously pumped between the plate and the granite to minimize friction.

HALT (Highly Accelerated Life Testing) is another frequently used test method.

Halt Test Chamber

Halt Test Chamber

HALT combines all of the above test methods. It is used to expose design defects and constraints in a product by accelerating stress levels. HALT primarily uses a combination of thermal and vibration step stresses to expose any latent weaknesses in a product. These primary environmental stresses may have additional stresses such as voltage and frequency added. HALT stresses a product well beyond its design specifications, up to the destructive levels of the product or the fundamental limit of the technology. It is a tool used to optimize product quality and reliability.

HALT testing does not have a specification, but instead uses guidelines. It is a five step process that starts with a cold step stress test, goes on to a hot step stress, followed by temperature cycling, then onto vibration, and finally a combination of temperature cycling and vibration. The test starts at room temperature and the temperature is lowered in 10⁰ C increments until the product fails. Once the product fails, the temperature is raised in increments until it recovers. This establishes a lower operating limit for the product. Then the temperature is successively lowered and raised to find the temperature at which the product fails. This establishes the lower destructive limit. Cooled with liquid nitrogen, temperatures in the chamber can reach -100⁰C. The next step is to do the same with high temperature. The high temperature can reach up to 200⁰ C. Then the temperature is cycled between the operating limits. The fourth step is a vibration step stress test in which the acceleration level is raised in 10G increments up to 60G. The vibration profile is pseudo-random in 6 degrees of freedom and is created using pneumatic hammers under the test table. Again the operating and destructive limits are established. Finally, all of the test modalities are combined.

In HALT testing the product usually, but not always, fails at each stage. It is up to the engineer to decide if changes should be made to correct the cause of the failure, depending on how the product will be used. The use of HALT testing can significantly reduce the random failure rate of a product during its useful life.

Another test which is an adjunct to HALT testing is HASS (Highly Accelerated Stress Screening) testing. Once the operating limits have been established in the HALT test, the HASS test can be used to screen products in which warranty returns increase after changes in components or production processes are made during the life of the product.

Testing can be performed on bare boards, populated subassemblies or full products, allowing focus on predetermined trouble areas. Depending on the level of reliability required, the number of test units can range from 100% to a few units from each vendor, manufacturing line or batch. Active monitoring can be used to track the shift in electrical properties as the circuits encounter the extremes of each test. If a measurement is found to be out of tolerance, a root cause analysis is conducted to determine the source of the problem and corrective action established.

The end product of all testing is a clearer understanding of how products will react in defined ranges of conditions. Once satisfactory results are obtained, manufacturers can confidently package these products and ship them to their customers.

 

How to Obtain FCC Authorization

FCC Authroization Process

The FCC Authorization Process

Manufacturers looking to sell most electronic products such as smartphones, vehicle remote controls, RFID sensors, low-powered transmitters, computers, networking and other telecom equipment here in the United States must ensure that their equipment won’t interfere with others or cause harm to the public.

The Federal Communications Commission oversees requirements for testing and wants to make sure goods are safe and adhere to adopted U.S. technical standards. The FCC is in charge of monitoring devices that emit information across almost any radio frequency band and governing the potential for interference.

Equipment must be tested before it can be marketed or sold in the U.S. When manufacturers sell equipment without the appropriate approval, they can be fined or even see their goods and profits seized.

What is FCC Authorization?

What Is FCC Authorization?

The FCC authorization process is a relatively simple process once your goods are ready to be mass-produced and sold to consumers.

An FCC accepted Telecommunications Certification Body or laboratory will review the technical specifications of your device and results of testing. Your device is tested to see if it may cause interference with other equipment, broadcasts in the correct radio frequency range and if it meets broader telecommunications requirements.

When you want your equipment tested and authorized, you’ll need to provide a set of technical specifications to NTS. After receiving your documentation, we’ll test the device to ensure it meets all FCC requirements.

After the testing, you may need to apply for certification authorization from a Telecommunications Certification Body, and that’s a step we at NTS can help you with as well.

What Is the Difference Between Certification, Declaration of Conformity and Verification?

FCC Verification vs Declaration of Conformity vs Certification

When you look at the FCC’s documentation covering its authorization processes, you’ve probably seen options for “Verification,” “Declaration of Conformity” and “Certification.” The guidelines can be a little vague on the difference, so let’s look into it.

Verification: Devices without radio-communications capabilities often only need to be verified and can be tested by the manufacturer or laboratory. When these devices are found to be compliant, they can be marketed and sold without FCC approval. The tests needed for verification measure how much radio frequency energy is radiated by the device when powered on, ensuring they stay below a low threshold.

The FCC lists common devices that only need verification including: Class A computer equipment, TV receivers, FM receivers, and some industrial, scientific and medical (ISM) equipment.

Declaration of Conformity: This procedure requires an accredited laboratory to measure radio frequency energy from your device to ensure that it meets relevant technical standards. Declarations of conformity don’t require you to submit any device samples or data directly to a TCB.

For Declaration of Conformity, the FCC has slightly stricter testing requirements. Your equipment must be tested by a laboratory that is accredited by an accreditation body such as:

  • National Voluntary Laboratory Accreditation Program (NVLAP)
  • American Association of Laboratory Accreditation (A2LA)
  • Foreign Accreditation body via a Mutual Recognition Agreement (MRA)

Common devices that require this declaration include Class B personal computers and peripheral devices; TV interface devices like set-top boxes and Internet-connected boxes; CB radio receivers; and super-regenerative receivers.

You should discuss your declaration needs and questions with NTS before settling on just a verification plan. Protect your company and your equipment, especially if many consumers will enjoy what it provides.

Certification: The most demanding of authorizations that we’re discussing is FCC certification. The FCC reserves this type of authorization for equipment that is most likely to interfere with other equipment, signals, and emergency information.

Devices needing certification cover a wide range of industries and use cases: from smartphones and family radios to telemetry transmitters, microwaves and ultra wideband receivers. FCC Certifications are issued by Telecommunication Certification Bodies (TCBs). Depending on the device you make, you may also need to submit devices for testing by the FCC.

What products need FCC Authorization?

What Products Need FCC Authorization?

Most products that can emit radio frequency energy need to be evaluated for an FCC authorization. Specifics for understanding FCC authorizations can be a little tricky because the law the governs it, Title 47 of CFR , is difficult to read. The best rule of thumb is that any electronics device with the ability to oscillate above 9 kHz must get an FCC authorization, but there are exempted products.

graphic3

The products that need authorization are either intentional or unintentional radiators of radio frequency energy.

Intentional radiators are devices that must broadcast radio energy in order to operate; they intentionally use the radio spectrum. Common examples of these devices include:

  • Smartphones
  • Headsets, speakers and other devices that connect via Bluetooth
  • Wireless connection devices such as Wi-Fi routers
  • Wi-Fi and Bluetooth components of Personal computers, laptops and tablets
  • CB radios
  • Walkie-Talkies
  • Short-range broadcast equipment
  • Wireless key-access systems

Unintentional radiators are electronics that can create radio signals and broadcast them through space or power lines. Their operation generates radio energy but isn’t specifically designed to transmit information through this energy. Devices created to receive radio waves fall into this category because they can often emit radio waves as a byproduct of focusing signals for reception. Many personal electronics that you’re familiar with fall into this category:

  • Digital cameras
  • TV sets and receivers
  • Game consoles
  • Older e-readers and PCs
  • Older phones and modems
  • Fax machines and other devices utilizing telephone lines

So called Digital Devices are broken down into two testing classes: Class A and Class B. Class A covers devices that are used primarily in industrial, commercial and engineering settings. These are devices that will often be used during production, testing and operation in controlled environments.

The Class B designation is reserved for consumer devices, and it is a stricter set of limits.

How do you obtain FCC Authorization?

How Do You Obtain FCC Authorization?

FCC Authorization Process

Obtaining FCC authorization can seem as straightforward as submitting your product and technical specifications to a testing lab and then sitting back to wait for the results. You can go that route, but you may risk products failing and not receiving enough information to properly fix any issue.

We recommend that you start working with a testing partner such as NTS early on, so you can begin the device optimization process early, improving your chance for testing success. This is especially true for products that intentionally use RF where a certification authorization is required. Here are some of the steps we recommend any device manufacturer take when they consider FCC certification authorization.

Step 1: Selecting Frequency and Equipment

The tests your devices are submitted to often depend on the radio frequency used. Focus on the spectrum and match your components to that spectrum to start off on the best foot.

Start by learning about what frequencies are legally open to you and your equipment. You can find the FCC’s current guidelines on radio spectrum allocation, to see what is available, what is restricted, and what is owned but has the potential to be leased.

Determine what frequencies are available to you legally and then review the FCC documentation to limit any technical concerns. Research can reveal known issues that may increase the risk of interference, inhibit range and propagation, introduce requirements around antenna length or increase power consumption.

After you’ve picked your frequency, review your designs to ensure that your antenna is optimized for the frequency. The governing sections of FCC Title 47 CFR Part 15 tell you of any harmonic or power limitations that your equipment must meet. Other FCC rules parts may also need to be consulted depending on frequency and use.

Step 2: Test When Ready

Obtaining FCC certification is difficult if you’re not working with a production-ready device. Many manufacturers have started the certification process with an early-stage prototype, only to find they needed a significant redesign to have the device operate as intended.

Your bottom line dictates that you need to move from concepts and prototypes to store shelves as soon as possible, but a major failure of an FCC certification test may send you back to the drawing board.

Once you have a production-ready model, perform as many operational tests in-house as you can. These don’t have to be FCC certification tests – the results won’t count unless performed by an accredited partner – but should include testing to ensure you’re compliant with the appropriate FCC rule parts.

Analyze output across any spectrum you can and verify that your antennas are optimally placed and designed. NTS can help you with these tests if you don’t have access to the right equipment in house. Early testing can move you through the certification process faster and help you correctly provide all of the necessary information.

Step 3: Register Your Company

You need an FCC Registration Number (FRN) if you want to obtain certification authorizations for devices that use the radio spectrum. This number establishes that you’re doing business with the FCC or using a spectrum that the FCC has regulatory authority over.

Acquiring an FRN is simple and free. Simply go to the FCC’s CORES page to register, provide your business address and contact information, and submit the document. At the end of that process, you’ll get your own FRN and have the option to request a grantee code. Grantee codes are required for certification and to sell your products, and they may be obtained for a nominal fee

Step 4: Select Your Lab Partner

When you have your FRN and grantee codes in hand, it’s time to contact an FCC registered testing facility. There are many testing partners like NTS all around the U.S. Working with us can help you achieve all of the certifications you need, including defense industry compliance and FCC certification.

Your lab partner should be able to perform as much of the testing as possible. We can help you with every aspect of testing, use our own equipment, walk you through test failures and successes, and work with you to help products pass tests.

When working hard to get your product to market, diving into FCC guidance can create an undue burden. Many manufacturers have increased their cost and time-to-market by trying to perform FCC testing themselves. Allowing a lab to perform the work they’re certified to do is a smart way to keep your prototype on track.

Lab quality, testing facilities, and capabilities can vary significantly, so we recommend working with NTS, the largest test laboratory network in North America.

Step 5: Deliver and Test

After you’ve selected a lab partner you trust, it’s time to provide them your equipment and information.

Deliver the prototype that is closest to production-ready and all of its technical specifications to your lab partner. You can also have a representative observe the tests, but it is typically not necessary.

Testing takes roughly two weeks – often less – and you can have a top estimate by reaching out beforehand and establishing a testing schedule with your lab partner. Labs will review your product and information, determine which specifications you need to have tested, and perform the tests the FCC will require. Your lab will also fill out all of the testing paperwork. We at NTS believe you should always work with a partner who has a verified process to double-check any documentation it produces.

FCC Filing and Labeling

Filing and Labeling

A TCB will issue your FCC certification. Your lab will need to provide the TCB with all of the relevant information and this body issues your certification on behalf of the FCC.

Once the TCB uploads your information to the FCC database, the FCC will list your product on its approved list. The TCB will send you your Grant of Equipment Authorization. When you receive the grant, you can legally market and sell your product here in the U.S.

Portions of the documents submitted to the FCC can be restricted. That means portions of the filing such as schematics and block diagrams don’t have to appear on the FCC site. Both your lab and FCC will want to protect your intellectual property, but you need to ask for that help.

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One extremely important thing to note is that the FCC has very specific guidelines for how your product must show its regulatory information and FCC certification number. View their guidance here, but also check with your lab partner to ensure that you’ve included all of the relevant information.

Contact NTS for Your Certification Needs

Testing with a certified partner like NTS can save you money whether you’re in need of certification or just a simple verification. Emissions monitoring, use of an anechoic chamber and filling out the documents required by the FCC can be a difficult endeavor.

Save yourself the headache and the time by working with NTS and our in-house testing equipment. Not only will we ensure that all of the tests are performed and recorded correctly, but we can even work with you to resolve any issues causing a test failure. From working with you to find the right ferrite beads and inductors or design adjustments that can reduce unintentional radiation, NTS has the facilities and know-how to get your equipment into the hands of waiting customers.

Contact NTS to learn about all of the testing facilities and capabilities NTS has to offer. Protect your bottom line and speed your time-to-market by working with us today.

The Benefits of Pre-Compliance EMC Testing

EMC Pre Compliance Testing

One of the biggest product development challenges today is ensuring electromagnetic interference is optimally controlled. With proper electromagnetic compatibility (EMC) testing and design, you can ensure the correct operation of various devices in the same electromagnetic environment. EMC is achieved by addressing both emission and susceptibility issues by taming the sources of interference and by strengthening the potential victims.

EMC Testing

A number of international EMC standards are in place to standardize product EMC performance. The FCC and CE are two of the most common EMC standards. Electromagnetic compatibility testing is broadly divided into
emissions testing and immunity testing.

EMC Emissions Testing

EMC emissions involve two types of testing: radiated emissions and conducted emissions testing. With radiated emissions tests, the goal is to check for unplanned emissions that exceed a given pass band as defined by the class of the product. Conducted emissions testing involve shorter frequency range — for example, 30 Hz to 10 KHz.

EMC Immunity Testing

Immunity testing is required for EMI compliance in the U.S. for medical devices and for a wide range of consumer products in the EU. A number of immunity tests may be required depending on the type of device and its application.

Pre-Compliance EMC testing

EMC testing is time-consuming, and failed tests can delay product launches. Your budgets will be stretched, and your reputation is at stake if you are not meeting customer’s demands. Many devices fail during EMC testing, often during radiated emissions testing.

By building EMC testing into the product design and development phases from day one, one can build a product that has a lower risk of failing EMC tests at the end. With pre-compliance EMC testing, you perform EMC tests and incorporate best practices throughout the design and development process. This allows you to meet EMC compliance more easily and effectively during your final testing.

Pre-Compliance EMC Testing Is Important

The best way to avoid expensive retesting and noncompliant EMI issues is by checking for emissions from your device throughout the product development cycle. Pre-compliance EMC testing has multiple benefits.

  • Detect Errors Upstream in the Product Development Cycle

product-development-cycle-table

The earlier in the product development cycle you can identify issues with emissions, the easier it is to correct the issues. Also, the solutions or options to correct EMI are more in the early stages of product development versus later. Correcting EMI issues after compliance testing is costly and results in loss of precious time versus fixing upstream in the design phase.

Imagine leaving EMC testing of your device at the end of the development of the product. Any issue that may have been smaller and possibly easier to isolate early on is now more complex and amplified due to more parts and subsystems within your device. For example, it’s much cheaper to make an EMC fix on a circuit board versus correcting once the design is final. As a specific example, a resistor-capacitor low-pass filter on data signals before crossing a radiating cable may cost you .1 to .5 cents per PCB. However, if the PCB is finalized and you need to solve against the radiating cables, a cable choke will cost you more than $1 per cable.

Mechanical changes, EMI shields, use of EMC foam and other design changes are made to counter emission issues. When EMC testing is done early, it allows you to make better decisions on types of changes to make to become EMC compliant.

  • Integrate Pre-Compliance Testing Into Product Development

When testing is integrated into product development, one can tap into a well-known testing company for ongoing support. It can provide testing infrastructure and subject matter experts during the entire product development cycle. This is an upfront investment that pays off by keeping your project on time and by reducing risks from noncompliance.

Experienced design engineers that offer pre-compliance EMC testing as part of their suit of services will continuously look for areas of risk during product development. For example, testing during product development can provide the designer options to add in preventative measures in the form of additional circuitry, or other mechanical or system design changes. When product designers come up with a fix, it is helpful to test it immediately before making major design changes.

  • Eliminate Overdesign

If you are not performing pre-compliance EMC testing, you may be overengineering your product to ensure it meets EMC compliance at the end. Since you are not testing along with design and development, you may be adding countermeasures which may be redundant. These measures may considerably add to your product cost.

Overdesign or overengineering is common across various industries. This can include coding for software, designing automobiles or airplanes, or design of bridges and building structures. With pre-compliance testing, you have the option to test more often and throughout the design and development. This can help you to avoid using parts with higher-than-necessary specs or even avoid parts you may be incorporating to stay EMC-compliant.

  • Design for EMC Compliance

This is not a test, but it’s one of the most ignored pre-compliance strategies. You can do a detailed and systematic schematic and layout design review as part of your pre-compliance processes. This can significantly reduce the risk of your product failing at an EMC test lab.

You can detect many potential emissions and immunity issues in a design review. A solid design review will catch many of the root causes of emissions and immunity problems even before your first test PCB is created. If you do not have in-house expertise for EMC-compliance design, work with a testing company that can provide this service. This can increase your first-time pass rate.

Pre-Compliance EMC Testing Options

Pre-compliance EMC testing can be done by hiring a testing lab or by doing it on your own once you have the right equipment and testing gear.

  • EMC Testing Lab

You can rent equipment and hire personnel from a testing company for pre-compliance testing. Professional testing labs have fully compliant test gear, which will allow you to perform tests with high accuracy. A reliable test lab will also be able to assess your test device and provide recommendations on potential root causes. This way, you can focus on addressing those as part of your pre-compliance effort. Some labs can provide turnkey pre-compliance and final compliance services as one package, which can keep your overall costs low.

Advantages to this approach include:

  • Your test results have a high level of accuracy since the same testing equipment is also used for final compliance testing
  • You don’t need to invest capital to procure test equipment
  • You get absolute measurements when performing emissions testing. If you do this on your own, you get measures which are relative

About NTS’s EMC Testing

NTS offers a wide range of services to help clients meet EMC compliance across various industries – consumer, industrial, automotive, medical, military, space, aircraft, telecommunications, etc. Our range of EMC/EMI services includes engineering, design analysis, testing and technical training.

NTS also has the largest network of commercial EMC testing labs in North America. We have a deep knowledge of various EMC compliance standards, and we are fully versed in FCC and CE standards and testing requirements.

Our labs and equipment use the latest technology and are powered by the most respected and experienced engineers and technicians. We have people, processes, tools and knowledge capabilities that allow us to test to extreme limits and complex standards.

We offer a wide array of EMC and EMI testing services:

Electrostatic discharge (ESD)

Electrostatic discharge (ESD) testing measures a device’s ability to tolerate discharge events. These events occur when a user touches the device and another metallic surface at the same time.

Harmonics and flicker

Harmonic frequencies greater than 50 Hz and voltage dips in the 5 to 15 Hz range can cause harmful interference for electronic devices. Devices need to be tested under these conditions to meet EMC compliance.

Electrical fast transients

Electrical fast transients testing (EFT) simulates a common type of real-world interference which was previously neglected. EFTs involve a high-frequency disturbance on a power line which occurs as a result of inductive loads being turned on or off.

Voltage dips and interrupts

Testing for voltage dips and interrupts (VDIs) involve simulating the conditions of voltage dips and voltage interruptions. The device is tested in the simulated environment to assess tolerance against VDIs.

Electrical surge

Surge testing is a key part of EMI analysis. NTS produces a low frequency, high energy electrical transient to simulate the effects of a lightning strike on a nearby power line. The device’s response is measured under these stringent conditions to test its tolerance against the surge.

Radiated susceptibility up to 200V/m, 10kHz to 40GHz

Military and Aerospace applications commonly require radiated susceptibility tests. NTS can perform radiated immunity testing up to 200V/m field strength in accordance with various military standards from 10kHz to 40GHz.

HIRF testing

High intensity radiated fields (HIRF) are divided into three frequency bands. HIRF-testing-frequenciesEach of these bands can affect airplane electronics in various ways:

  • Low frequency electromagnetic emissions between 10 kHz
    and 50 MHz
    — Low frequency HIRF use electrical parts like an antenna, carrying currents in the fuselage skin. These create little interior penetration.
  • High frequency electromagnetic emissions in the range of 100 MHz and 18/40 GHz — High frequency HIRF generates strong field penetration into the fuselage.
  • Medium frequency electromagnetic emissions between 30 MHz and 400 MHz — Medium frequency HIRF combine both LF and HF emissions effects. As a result, these emissions mimic both of the antenna-like performance as well as fuselage penetration.

HIRF certification generally involves measuring transfer functions to estimate the potential effects of EMI on an aircraft. NTS employs a variety of tools and techniques to produce accurate testing that is fully compliant with all required specifications.

NTS can help you meet requirements for HIRF certifications including RTCA/DO-160E/F, Boeing and Airbus requirements, and FAA HIRF Rule & Advisory Circular 20-158.

Lightning-multiple stroke, multiple burst and single stroke

NTS has lightning simulation capabilities that include:

  • Single Stroke
  • Multiple Stroke
  • Multiple Burst
  • DO-160 Section 15-22
  • Radiated Fields 200 +V/m
  • Electrostatic Discharge

We can precisely measure direct and indirect effects of a lightning strike. When it comes to direct effects, a lightning strike causes damage due to temperatures exceeding 20,000°C and electric spikes of more than 250,000 amperes. To simulate these conditions, NTS facilities have a series of high current generators and an indoor test area that measures 40 x 120 feet.

A lightning strike can also create a temporary rise in earth voltages after an impact. This indirect effect creates an intense electromagnetic field that can harm equipment up to a radius of one kilometer. NTS can run a variety of tests, including pin injections, transformer injections, and field immersions to determine the indirect effects of lightning. Together, these tests allow our engineering team to perform a thorough field and transient analysis. This further allows us to assess the indirect effects of a strike on everything from individual circuit parts to complex interconnected electronic systems.

MIL-STD-461 Testing

The MIL-STD-461 is a standard of the Department of Defense (DoD) that describes how to test equipment for electromagnetic compatibility. Even if this standard isn’t required, a device complying with this relatively strict standard will comply with most other common standards.

NTS can also help you with additional tests:

  • Magnetic susceptibility dc to 10kHz
  • Full CE immunity
  • Mode tuned chamber

EMC/EMI Engineering Services

Besides specific testing, NTS has the know-how to consult you on various engineering services related to EMC/EMI:

  • Electromagnetic environmental effects (E3) analyses of systems and platforms
  • EMC control plan
  • Independent EMI/EMC reviews
  • NARTE-certified engineers
  • Performance requirements definition and flow down
  • Requirements gap analysis
  • Risk mitigation plans
  • System EMC design
  • Test procedures and corrective action

Contact NTS for EMC Solutions

NTS testing labs can provide comprehensive HIRF and other electromagnetic interference testing for today’s most demanding clients and standards. NTS is the nation’s largest independent product testing and standards compliance organization. We regularly service the needs of military contractors, avionics manufacturers and more.

contact-nts-pullquote

NTS is renowned globally as an industry leader in providing EMC and EMI engineering and compliance services. Our experienced program managers and veteran engineers work closely with you to meet your EMC pre-compliance needs from conception, design and development to final test and production. We have expertise in various EMC/EMI engineering services to perform a variety of tests to meet standards across multiple industries and geographies.

With more than 50 years of experience, NTS has a long list of satisfied clients in our portfolio. Clients include organizations like Boeing, Cisco, U.S. Department of Defense, EMC, General Electric, Hewlett-Packard, Lockheed Martin, Microsoft, Motorola, Sony, Pratt & Whitney Rocketdyne, Texas Instruments and Tyco Electronics Corp. Contact us today to learn how we can help your business.

RoHS Recast: Is My Product Affected?

Does RoHS 2 Apply to my product?RoHS, an acronym for Restriction of Hazardous Substances, is a directive  originated in the European Union and was first brought into force in July of 2006 (RoHS 2 FAQ 28). The objective of this program is to regulate the concentration of six hazardous chemicals contained in electrical and electronic equipment (EEE). The substances included are Lead, Mercury, Cadmium, Hexavalent Chromium, Polybrominated Biphenyls (PBBs), and Polybrominated Diphenyl Ethers (PBDEs). Cadmium may not exceed a concentration of 0.01% by weight in any homogenous material, while all others may not exceed 0.1% by weight (DIRECTIVE 2011/65/EU 100).

RoHS Compliance Logos

The Birth of RoHS 2

On January 2, 2013, the original RoHS directive was repealed and has been replaced by the RoHS recast, known as RoHS 2. RoHS 2 is an updated version of the first directive and is mainly aimed at preventing the risks these hazardous substances pose to “human health and the environment, with a particular focus on workers involved in the management of electronic waste,” which is greatly increasing in volume in the European Union. It has been determined that the best way to address these concerns is to control the use of hazardous substances during the manufacturing process (RoHS 2 FAQ 5-6).

RoHS vs. RoHS 2

There are a few important differences between the first RoHS and RoHS 2. Among those differences is a gradual extension of RoHS requirements to all EEE by July 22, 2019, including all cables and spare parts (with some exclusions). Starting on July 22, 2014, Category 8, Medical Devices, and Category 9, Monitoring and Control Instruments, two new product categories that were previously exempt, will be introduced. Another significant difference between RoHS and RoHS 2 affects product marking requirements. Previously under the first RoHS directive, manufacturers would use the following markings, among others, to demonstrate compliance of their product:

Now, under RoHS 2, all EEE within scope must be CE marked. The CE mark, which stands for European Conformity, symbolizes that the responsible party has completed all appropriate compliance procedures for that product. As of January 2, 2013 the CE mark is the only mark that can be used to indicate RoHS 2 compliance (RoHS 2 FAQ 5-6).

RoHS Compliance Requirements

Does RoHS 2 apply to my product?

All of that being said, the question still lingers: “Does RoHS 2 apply to my product?” To decide, you must first determine if your product is EEE as defined in Article 3(1) and Article 3(2). Per the directive, EEE is “all equipment that has at least one intended function which is dependent on electric current or electromagnetic fields, or that generates or transfers or measures such currents and fields…” (RoHS 2 FAQ 19-20).

You may be wondering, are circuit boards considered EEE? “This depends on whether the board is placed on the market as a finished EEE product…, or it is placed on the market as a component for further production or integration in to a finished EEE product.” If the latter is true, then RoHS 2 provisions are not applicable. However, any item sold for direct use by the consumer is considered EEE. Empty, or bare, circuit boards with no components are not deemed finished EEE (RoHS 2 FAQ 18).

If your product does not meet the definition of EEE, then the provisions of RoHS 2 do not apply.

Wait! Your product may be exempt.

If your product does fall within the classification of EEE, there are additional determinations to be made. You must now ask yourself if your product falls within any of the categories excluded by RoHS 2 as specified in Article 2(4). Some of these exempt categories include military/security equipment (e.g., missiles), equipment designed to be sent into space (e.g., satellites), means of transport (e.g., cars, commercial aircraft, trains, boats), active implantable medical devices (e.g., pacemakers), photovoltaic panels, and R&D equipment. If your product falls in one of these categories, then the provisions of RoHS 2 do not apply (RoHS 2 FAQ 16-17).

If your product cannot be classified into an exempt category as listed in Article 2(4), you must now decide if any substance exemptions can be applied. In some cases, an exemption can be granted and the specific use of a hazardous substance can be justified based on certain criteria. Under the first RoHS initiative, exemptions could be granted based on overall practicability. Meaning if the result of using the substitute would be more negative to environmental and consumer safety than the use of the restricted substance, an exemption could be warranted. In addition to these parameters, RoHS 2 has also taken into account the availability and attainability of substitutes, as well as the socio-economic impact of substitution. When an exemption has been applied for, it is decided on a case-by-case basis. “Exemptions are granted for specific substances used in specific applications and not for the whole EEE, nor for a company. Therefore, whoever uses the substances in the specific application can benefit from the exemption” (RoHS 2 FAQ 25-26). As the export.gov webpage entitled, “Restriction of Certain Hazardous Substances” brings out, “these exemptions are temporary and reviewed at least every four years.”

If substance exemptions apply for your product, all provisions of RoHS 2 apply with the exception of those exempt substances. If no exemptions apply, then all provisions of RoHS 2 are applicable.

RoHS applies to my product. Now what?

So, you have determined that RoHS 2 applies to your product. Now what? There are still some important points to keep in mind before you begin testing your product for RoHS 2 compliance. If your EEE product consists of different components, it “can only meet the substance requirements if all components and parts meet the substance restriction requirements of RoHS 2, including non-electronic or non-electric components” such as bolts, wires, or plastic cases (RoHS 2 FAQ 25-26).

Each material in your product must be separated into homogenous samples and tested individually to determine full compliance. “A homogenous material is either a material with a uniform composition throughout, or a material that consists of a combination of materials” that cannot be mechanically separated in any way. In addition, it is also important to know that RoHS 2 restrictions do not apply in the manufacturing process; therefore, restricted substances can be used during production, as long as the finished EEE product does not exceed the set maximum contamination limits (RoHS 2 FAQ 27-28).

If your product currently contains restricted substances and your company needs to transition into RoHS 2 compliance, it may be necessary to perform other types of testing during this process. This will help to ensure that your product maintains the same level of quality and performance.

If your product is destined for sale in the European market, RoHS 2 should be an integral part of your quality program moving into the future. By July 23, 2019, unless your product falls into an exempt category, RoHS 2 regulations will directly affect every electrical and electronic equipment manufacturer (RoHS 2 FAQ 9). For that reason, it is encouraged to begin testing your product, and all its components, for RoHS 2 compliance as soon as possible.

What is Reliability Testing?

By Jit Gupta, Technical, Quality & Facility Manager at NTS Chicago

“How many hours, days or years will my product last in this type of environment? What’s the life expectancy if it were exposed to these specific types of conditions?”

When it comes to answering these questions, the concept of time-based quality becomes relevant with regard to Reliability Testing. Incorporating the two facilitates the process of identifying and estimating a product’s overall lifespan by exposing it to various environmental conditions. There are a number of tools and methods (statistical and non-statistical) available to estimate a product’s lifespan, but which one should you use?

The following article will answer this question and more with first explaining what Reliability testing is followed by the various types of testing involved.

Part I – Reliability Testing

We are familiar with quality control testing, where a product is subjected to quality test checks to uncover defects. However, with Reliability Testing the objective is to 1) test the endurance of a product under certain conditions, 2) identify the failure rates and 3) if applicable, propose preventative measures that can increase the product’s reliability and lifespan.

In short, Reliability Testing–like quality control testing–is performed to provide confidence that the product meets its reliability requirements. And the next step for a product to meet its reliability requirements is to go through a Reliability Test Program which consists of a series of integrated tests.

Reliability Testing Program

The Reliability Test Program integrates three types of tests: Reliability Development/Growth (RD/GD), Reliability Qualification (RQ) and Product Reliability Acceptance Test (PRAT).

Reliability Development/Growth Test

The Reliability Development/Growth (RD/GD) test attempts to achieve certain reliability goals by identifying deficiencies and systematically eliminating them through a series of tests. (This type of testing is also known as the Test, Analyze and Fix test, or TAAF test.)

Described below are two evaluation methods from the military handbook MIL-HDBK-781: Reliability Test Methods, Plans and Environments for Engineering Development and Production. The MIL-HDBK-781 specifies the use of these methods when conducting the RD/GD test. (Additional information on the MIL-HDBK-781 is discussed in Part II of this article.)

Duane Method
The Duane Method is a non-statistical method that uses graphical techniques. At each failure, the accumulated test time is calculated and the cumulative failure rate (total failures/total test time) is plotted against accumulated time. The growth rate is determined from the graph.

Army Material System Analysis Agency (AMSAA) Method
The AMSAA uses statistical method assuming that reliability growth is a non-homogeneous Poisson process, where number of failures in an interval of time (or cycles, miles, etc., as appropriate) is a random variable distributed in accordance with the Poisson distribution.

Reliability Qualification Test

During the Reliability Qualification Test phase, a product is tested under certain conditions to determine if it complies with its specified reliability requirements.

If a product is in compliance then it’s approved for production.

Note: When planning a Reliability Qualification Test, it is best to ensure that the configuration is representative of the production units.

Product Reliability Acceptance Test

Once a product is approved for production the next step is to perform the Product Reliability Acceptance Test (PRAT). The objective of a PRAT is to detect any inherent degradation in a product’s reliability over the course of production.

Note: During the PRAT, cumulative product operating time and product failures should be recorded and plotted on the chart for acceptance and rejection of the product.

 

Part II – What Test to Use and how is it Performed?

In this section we will briefly explain what type of test to perform and how it is performed.

An excellent guidance document to reference is the military handbook, MIL-HDBK-781: Reliability Test Methods, Plans and Environments for Engineering Development and Production (mentioned earlier in the RD/GD test section). Although the MIL-HDBK-781 was primarily developed for defense contracted procurements, many of the test methods, plans and environments can be tailored to suit other products and equipment.

While test conditions and the levels of test are determined by the product’s operational life profile, the MIL-HDBK-781 stipulates that a test is to be performed under the combined influence of electrical power input, temperature, vibration and humidity stress.

MIL-HDBK-781: Equipment Categories

Before deciding on the type of test to perform, it is important to identify the appropriate equipment category of the product to be tested. Defined in the MIL-HDBK-781 are six (6) broad equipment categories (see below) that help specify what operational requirements to use.

Cat 1: Fixed Ground Equipment (equipment is generally located in a controlled environment within a building)

Cat 2: Mobile Ground Equipment (includes wheeled vehicles, tracked vehicles, shelter configuration and manpack)

Cat 3: Shipboard Equipment

Cat 4: Equipment for Jet Aircraft

Cat 5: Turboprop Aircraft and Helicopter Equipment

Cat 6: Missiles and Assembled External Stores

After the equipment category has been determined, product testing can now begin.

Combined Environmental Reliability Testing

The purpose of the Combined Environmental Reliability Testing (CERT) is to evaluate the reliability of the product in the environments that they will be used. Through CERT, products are exposed to multiple environmental factors that include vibration, thermal (temperature) and humidity; the time duration and number of test cycles (fatigue testing) are dependent on the product type (i.e. equipment category).

Vibration Stress

When evaluating a vibration stress test, if the equipment is not packaged specifically for transportation, the equipment shall be subjected to single frequency sine-wave vibration at 2.2g at a non-resonant frequency between 20Hz and 60Hz for 20 minutes before start of the reliability test.

Thermal Stress

For the thermal (temperature) stress test, the equipment shall be subjected to specific ambient temperatures (no cyclic temperature requirement). Cold soak temperature of -54C and hot soak temperature of +85C can be incorporated in the profile, if needed.

Humidity Stress

Humidity testing is not performed, unless specifically required.

Electrical Stress and Duty Cycle

The equipment shall be operated at nominal voltage 50% of the time and 25% of the time each at minimum and maximum voltages. The equipment duty cycle shall be ON about 90% of the test cycle. (Learn about electrical compliance testing.)

Duration

The duration of the profile is normally 24 hours or an evenly divisible fraction thereof.

Products that are tested where the environmental conditions are elevated above the required limits can lead to finding defects and improving the product’s overall design and reliability. (The next section, Environmental Stress Screening, describes this type of testing.)

Note: The MIL-HDBK-781 specifies that CERT be performed for all six equipment categories.

 

Figure 1
CERT profile for Cat 1 equipment

1

Environmental Stress Screening

Environmental Stress Screening (ESS) is another important aspect of Reliability Testing. ESS is a process where products are subjected to higher levels of vibration, thermal, humidity and electrical stress to precipitate either design defects and/or early failure characteristics.

The concept of ESS can be explained through the Bathtub Curve shown below.

Figure 2
Bathtub Curve

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Time

In the Bathtub Curve, the failure rate is plotted over periods of time for the product population. Described below are the various time periods when testing a product’s failure rate.

Early Failure (Infant Mortality Period)
The first period is the early failure or infant mortality period, where defective or weakest products in the population have started to fail. As the failed products are being replaced or repaired, the failure rate comes down and becomes constant.

Useful Life Period (Intrinsic Failure or Constant Failure Rate)
During the useful life period, failures occur randomly. Other names for the useful life period are constant failure rate period or intrinsic failure.

Wearout Period
After the useful life period, the products start to fail more frequently due to wear and tear and fatigue. This period is called the wearout period due to the increase in failure rates.

Now from a customer point of view, the early failure will not be acceptable. The manufacturer shall eliminate the early failure, as best as possible through design, redundant component, derating, etc., and also through ESS. As stated earlier, during ESS process the product population is subjected to higher level of stress than normal operating stress to initiate early failures.

MIL-HDBK-781 specifies the sequential series of stress cycles consisting of vibration or thermal or both vibration and thermal. Another guidance document, MIL-HDBK-2164: Environmental Stress Screening of Electronic Equipment, goes into more detail about 1) the specific environmental conditions including duration, screening fixtures and monitoring as well as 2) the Failure Reporting and Corrective Actions Systems (FRACAs) of the ESS process.

Figure 3
MIL-HDBK-2164 ESS Guidance Graph

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Specific ESS Time Periods

Pre Defect Free Period

During this period, the defects found shall be repaired and counted but shall not be counted against the acceptance of product.

Vibration Stress (during Pre Defect Free Period)
With the power on, the product shall be exposed to one five-minute burst of random vibration in the axis deemed most susceptible to vibratory excitation. The random vibration spectrum shall be:

  • 20-80 Hz at 3 dB/octave rise
  • 80-350 Hz at 0.04g2/Hz
  • 350-2,000 Hz at 3 Db/octave rolloff

Thermal Stress (during Pre Defect Free Period)
With the power on, the product shall be subjected to thermal cycling for a period of 40 hours. The low and high temperature extremes are defined by equipment specifications. The dwell time at extreme temperatures shall be determined from thermal map/survey (average time over two samples cycles when 2/3rd of thermocouples reach within 100C of maximum operating temperature). The average ramp rate shall be 100C per minute.

 

Defect Free Period

After completing the Pre Defect Free Period (for a fixed duration), the product is again tested during the Defect Free Period and subjected to the same vibration and thermal cycle conditions stated above.

Thermal Stress (during Defect Free Period)
With the power on (operational), the product will be subjected to 40 consecutive defect-free hours under thermal cycling conditions within an overall screening period of 80 hours maximum.

Vibration Stress (during Defect Free Period)
Following the 40 hours of defect free thermal cycling, the product shall withstand five (5) continuous minutes of random vibration without failure within a maximum screening time of 15 minutes.

Note: In the above ESS process, vibration and thermal cycling are not applied simultaneously but in sequence.

 

Highly Accelerated Stress Screening

A new development in ESS is the Highly Accelerated Stress Screening (HASS) process. Unlike the traditional ESS process, HASS applies temperature and vibration stress concurrently with greater levels of stress.

Because HASS applies a greater level of stress for both temperature and vibration testing compared to traditional ESS testing, test times are shorter and the tests more effective at detecting early failure.

Note: The levels of stress applied for temperature and vibration during HASS are determined beforehand.

 

Summary

In determining whether or not a product will perform in a certain environment, it’s important to remember the concept of time-based quality. By subjecting a product through various types of tests, and at different phases of development, a product’s reliability can be simulated and observed of how well it will perform over time.

  • Introduced briefly in this article are the various types of tests involved when conducting a Reliability Test Program such as the Reliability Development/Growth (RD/GD), Reliability Qualification Test and the Product Reliability Acceptance Testing (PRAT).
  • Referenced also is the well-known military handbook, MIL-HDBK-781, a comprehensive guide in developing reliability test plans and environmental test profiles for defense-related equipment; the MIL-HDBK-2164 provides further guidance on the traditional Environmental Stress Screening (ESS) process. (Information contained in these military handbooks can be tailored to develop a Reliability Test Program for conventional products and equipment.)
  • Covered at the end of the article was the Highly Accelerated Stress Screening (HASS) test which is unlike the traditional ESS process.

Contact

For questions related to this article or to find out how NTS’s Chicago laboratory can help qualify your products, please call (847) 934-5300 directly or email Jit Gupta at jit.gupta@nts.com.

 

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