Chemical Cleanliness

Cleanliness Testing

Cleanliness Testing in the printed circuit board and assembly world encompasses the analysis of a specimen to determine the “type” or “amount” of a contaminant material.

This contaminant material can be potentially anything; the material can be large or small and can be unknown, known, expected, or unexpected to the analyst or the requestor. The use of various analytical techniques for cleanliness testing can assist in determining what material is present and how much of said material exists. The following is a sampling of techniques that are available.

Fourier Transform Infrared (FTIR) Spectroscopy

Analysis via FTIR is traditionally conducted when an observed contaminant is believed to have an organic component. Commonly, these contaminant materials are an issue for assembly-level samples such as materials that could lead to corrosion, resulting in a high-resistance short. In addition to printed circuit board / assembly samples, FTIR can be used to analyze any type of sample in which an unknown material is present.

The testing program can also assist in assessing the consistency of the sample, quality level and percentage of outside components.The IR radiation is passed through the material, resulting in a spectrum that serves to illuminate the sample’s unique properties of molecular absorption and transmission. Used in conjunction with computer-generated algorithms, it’s an accurate method of quantitative analysis in identifying materials.

Fourier Transform Infrared Spectroscopy is a non-destructive technique that often provides a superior alternative to dispersive or filter methods of infrared spectral analysis. It’s more precise and offers a mechanically simply measurement process with a single piece of machinery. Additional attributes of FTIR cleanliness testing include an increased level of scanning sensitivity and much higher optical throughput that combine to reduce the presence of outside noise.

The biggest advantage of FTIR often resides in the speed of the process. Formerly, dispersive instruments used in cleanliness testing delivered a slow scanning process that impacted the rate of productivity in engineering and manufacturing. This technologically advanced method instead simultaneously measures all of the infrared frequencies through a unique signal produced by the interferometer. As the signal can be measured in a matter of seconds, the process is reduced to a fraction of the previously acceptable norm.

Although FTIR is typically a self-guided analysis, IPC has developed some test methodology to assist in the “cleanliness testing” analysis of printed circuit boards and assemblies.

  • IPC-TM-650, method 2.3.38 – Surface Organic Contaminant Detection
  • IPC-TM-650, method 2.3.39 – Surface Organic Contaminant Identification Test (Infrared Analytical Method)

Ion Chromatography

Analysis via IC provides cleanliness-related data for specific ionic species that have been selected for testing. Similar to FTIR, certain ionic species of interest can lead to corrosion or can cause electrical performance issues. The data obtained can be used for comparison to known requirements, for establishing process “control,” or for investigating a broader Failure Analysis topic.

IC cleanliness testing delivers precise qualitative and quantitative determinations regarding the material identifications of positively and negatively charged ions. It’s commonly used in trace analysis of soil, water and drinking water samples to discover contamination. IC is also an effective test used to determine halides from pyrohydrolysis extraction.

IonChromatography is able to separate and detect trace ionic species and other substances ranging from silicates and carbohydrates to amino and weak organic acids.One of the main advantages is the ability to analyze molecular species rather than focusing on present elements. With this method of cleanliness testing, it’s possible to determine the quality of all types of molecular materials and minerals as well as the purity of everything from food and drink products to soil and water samples.

At NTS, we deliver fast, highly reliable Ion Chromatography Testing for the following industries:

  • Healthcare and pharmaceutical
  • Environmental protection
  • Food production and packaging
  • Electrical power production
  • Chemical manufacturing
  • Protein purification
  • Quality control

Some industry developed cleanliness test methods for testing via IC are:

  • IPC-TM-650, method 2.3.28 – Ionic Analysis of Circuit Boards, Ion Chromatography Method
  • IPC-TM-650, method – Halide Content of Soldering Fluxes and Pastes
  • IPC-TM-650, method – Bare Printed Board Cleanliness by Ion Chromatography
  • MIL-STD-883, method 5011, section 3.5.4 – Evaluation and Acceptance Procedures for Polymeric Materials, Ionic Impurities

Using these methods, IC allows for the determination of ionic concentrations “on” or “within” a specimen for use in control / characterization studies or failure analysis based testing.

Resistivity of Solvent Extract (ROSE) Testing

Analysis via the ROSE method provides an “in-line” or, simply put, a “quick and easy” quantification of overall printed circuit board / assembly cleanliness. ROSE can be used to obtain a “singular” value for evaluators. Performed with a simple resistivity (or conductivity) meter, the ROSE test provides a “quick” assessment of overall cleanliness and is a tool that has been used by process engineers for decades to help check and/or establish process control.

ROSE cleanliness testing is typically used as a method of quality control in manufacturing printed wiring boards and printed wiring assemblies. These specific types of electronics undergo chemical and mechanical processes that have the tendency to put residual stress on the components or somehow change the characteristics of the materials. When conducted by a capable and experienced technician, ROSE testing can effectively analyze and identify any failures or unintended residues resulting from the manufacturing process.

A few facts about ROSE cleanliness testing:

  • ROSE is among the oldest and most proven testing methods utilized in the electronics industry.
  • The method involves the immersion of a sample in a room temperature isopropanol and deionized water solution at variable immersion times no less than 10 minutes in duration.
  • Used as a process control tool, ROSE measures conductive materials present after printed wiring assemblies are processed with rosin-based fluxes.

ROSE is utilized in cleanliness testing because of its many widely recognized advantages, not the least of which is its overall low production cost. It has been used successfully for decades and is among the only cleanliness test of its kind that can be efficiently relied upon as a process control tool in a production line environment. Other positive attributes of ROSE testing include the ability to demonstrate gross levels of conductive materials and its non-destructive properties when testing materials that are not susceptible to IPA or water.

The industry standard for this analysis is IPC-TM-650, method 2.3.25 – Detection and Measurement of Ionizable Surface Contaminants by Resistivity of Solvent Extract (ROSE).

Scanning Electron Microscopy / Energy Dispersive X-Ray Spectroscopy (SEM/EDS)

Analysis via SEM/EDS is typically paired with the FTIR technique described above to investigate an observed contaminant that is believed to have an inorganic or metallic component. The SEM/EDS technique provides both visual and elemental information about an area of interest. SEM gives a different view of the “unknown” material being analyzed, while EDS provides elemental information. Combined, the SEM/EDS technique is a tool that is commonly used to investigate “failures” as well as simple “unknown” material in order to determine the composition and possibly the origin of the substance.

Often used to generate in-depth, high-resolution images of surface topography, the combined SEM/EDS testing method is also valuable in a wide variety of production and engineering processes. Possible applications range from providing precision imaging of corroded copper surfaces to analyzing the composition of metallic commercial products.It’s a highly effective, non-destructive method of surface analysis that’s fast, economical and applies itself to myriad applications.

This high tech cleanliness testingis a powerful form of analysis that can provide elemental data in many different ways. Depending on the position of the electron beam, our lab can generate localized elemental information; plot proportions of identified elements along a spatial gradient or map the distribution and intensity of elements in a sample area.

Contact NTS for Cleanliness Testing and Certification Services

We’re among the largest testing laboratory networks in North America, providing a complete range of cutting edge services. We offer fast, accurate and efficient FTIR, IC, ROSE and SEM/EDS cleanliness testing delivered by our communicative and accountable team of technicians. Get in touch with us for additional information on specific test programs. We’ll be happy to assist you in analyzing your needs and provide a free, no obligation quote.

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