Conformal Coating Qualification and Conformance Testing
Conformal coating is applied to electronic circuits to provide a protective barrier to moisture and contamination and to provide electrical insulation. The most common specifications used for conformal coating testing are IPC-CC-830B, Amendment 1: Qualification and Performance of Electrical Insulating Compound for Printed Wiring Assemblies and MIL-I-46058.
IPC-CC-830 or MIL-I-46058
The standards established qualification and conformance requirements for conformal coatings. The standard outlines the qualification, retention of qualification, and quality conformance testing for a conformal coating. The term conformal coating within the specification is referring to a type of protective coating applied to a PCA (Printed Circuit Assembly). The coating is intended to provide protection from moisture and contamination; thus, providing confidence that the electrical properties are maintained.
The testing is conducted on the IPC-B-25A board which contains the appropriate test patterns to conduct all testing with the exception of the Temperature and Humidity Aging (Hydrolytic Stability) test which utilizes the y-pattern designed in the MIL-I-46058C, Amendment 7 military specification. With the use of the standardized test vehicles and test procedures it enables a manufacturer to qualify his product.
As of now there are five conformal coating types AR (Acrylic), ER (Epoxy), UR (Polyurethane), SR (Silicone), and XY (Paraxylylene). The coatings are classified as either being Class A (Non-Hydrolytically Stable) or Class B (Hydrolytically Stable). The hydrolytic test is designed to determine the resistance of the applied conformal coating to reverting to liquid when exposed to high humidity at a specific temperature and time.
Recently the IPC-CC-830B, Amendment 1, is scheduled to undergo a great overhaul as it has been discovered that the IPC and Military specifications (IPC-CC-830 and MIL-I-46058) are not concurrent with each other as was originally written. The IPC task group that is tasked to revise this standard will be reviewing revision of requirements specifically of the Moisture and Insulation Resistance (MIR) and Dielectric Withstanding Voltage (DWV) and the possibility of designing a new test vehicle to incorporate the easy use of automated measuring systems (i.e. AutoSIR). The committee group is working on the addition of adding Ultra-Thin (UT) coatings to the future revision of the IPC-CC-830.
IPC-CC-830 is currently broken down into three categories: Column A testing for qualification, Column B testing for retention of qualification and Column C testing for quality conformance. MIL-I-46058 is broken down into four categories: Qualification, Group A, Group B and Group C. The testing frequencies for each specification are outlined below.
|Required Initially||Column A, Qualification Testing||Qualification Testing|
|Required Every 2 Years||Column B, Retention of Qualification Testing||Group C Testing|
|Required Every Year||Not Applicable||Group B Testing|
|Required on Each Batch||Column C, Conformance Testing||Group A Testing|
Although the MIL-I-46058 document has been canceled for new design since November of 1998, the Defense Logistics Agency (DLA) still maintains a Qualified Products List (QPL) for this document because the material is still being purchased for the manufacture of products that are being built to old military contracts. NTS is a DLA-approved testing laboratory for this specification and can supply full conformal coating qualification and conformance testing including assistance interacting with DLA to complete the necessary application form.
There is currently no QPL maintained for IPC-CC-830 qualified products although one is being developed by IPC. If you, the user, are responsible for supplier surveillance, we recommend reviewing your supplier’s actual dated test reports to confirm necessary testing is being completed.
NTS supplies consultation and testing services to conformal coating manufacturers and users including root cause failure analysis for adhesion, electrical, contamination and other issues.
IPC-CC-830 Conformal Coating Guidelines for Substrate Type and Quantity
|Test||Test Vehicle||Number of Specimens|
|1) Appearance||Glass||4 coated; 1 uncoated|
|2) Fluorescence||Glass||4 coated; 1 uncoated|
|3) Thickness||Glass||4 coated; 1 uncoated|
|4) Fungus Resistance||Glass||4 coated|
|5) Flexibility||Tin Panel||4 coated|
|6) Flammability||UL 94 test strips (1/2” X 5” bare laminate strips with the sides sanded)||20 coated|
|7) Dielectric Withstanding Voltage (DWV)||IPC-B-25A test boards (with the D-pattern wired)||5 coated|
|8) Moisture and Insulation Resistance (MIR)||IPC-B-25A test boards (with the D-pattern wired)||4 coated; 1 uncoated|
|9) Thermal Shock||IPC-B-25A test boards (with the D-pattern wired)||5 coated|
|10) Temperature and Humidity Aging (Hydrolytic Stability)||“Y” shape test assembly (with the resistors, one color coded and one with numbers/alphabets, soldered)||5 coated|
IPC-CC-830 Cleaning and Coating Substrates
- Pre-Coating Suggested Cleaning Process
- Clean test lead terminals with isopropyl alcohol, and scrub with a soft bristle brush for a minimum of 30 seconds.
- During the remainder of the test specimen preparation, handle test specimens by the edges only.
- Spray rinse thoroughly with fresh isopropyl alcohol. Hold test specimen at an approximate 30° angle, and spray from top to bottom.
- Rinse cleaned area thoroughly with fresh deionized or distilled water. Hold test specimen at an approximate 30° angle, and spray from top to bottom.
- Dry test specimens in a drying oven for a minimum of three hours at an oven temperature of 50 °C ± 5 °C [122 °F ± 9 °F].
- Completely coat all sides of the test vehicles.
- Apply and cure the coating per the coating manufacturer’s instructions.