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PCB Reliability Testing Methods and Standards

PCB testing

PCB reliability testing is an extensive procedure that involves multiple tests. Circuit board manufacturers use it to identify design flaws, making it an essential process before using the specific circuit board. Below is an overview of printed circuit board reliability testing, the methods employed, and the testing standards in place.

What is the Reliability Testing of PCB?

PCB reliability testing is any process that seeks to identify a circuit board’s failure mode when subjected to an extreme condition. It generally involves exposing the PCB to various stress sources.

The tester takes measurements and uses the results to determine the nature and extent of damage, among other things, such as the condition levels required to cause harm. Stress sources used to simulate application conditions include:

  • Impact and vibration or shock
  • Heat changes
  • Exposure to chemicals
  • Electrical loading, such as excess voltage
  • Environmental conditions like moisture and dust
PCB testing analysis process
PCB testing analysis process
Resource: https://www.researchgate.net

Why Test a for PCB Reliability?

PCB reliability testing helps identify failure modes before mass production, their causes, and how they happen. PCB makers use it to alter flawed designs, refining them to prevent such failures from occurring in the future.

During the design stage, it’s almost impossible to determine how a printed circuit will behave in its application environment. Testing it for reliability, therefore, eliminates possible performance and aging problems.

It also ensures compliance with circuit board testing and quality standards, both regional and international. A circuit board manufacturer may carry out these tests or contract another company to undertake some.

PCB conformal coating test
PCB conformal coating test
Resource: https://www.youtube.com/watch?v=TeNN8A_GGlc

PCB Reliability Testing Methods

PCB reliability testing involves various methods and steps. That’s because the board receives different stress sources during operation. This list of PCB failure analysis techniques explains how to evaluate them for reliability, whether bare or assembled.

1. Solder Mask Hardness Test

In this test, you apply pressure to the solder mask to determine its ability to resist mechanical damage with the help of a hardness scale as specified by the IPC standards. The test requires what’s called a hardness tester or pen.

Place the PCB on an even surface. Press the solder mask using the tester and check it for deformation or other damage. Record the results and check them against a hardness scale. The hardness level should not drop below 6H.

2. Solderability Test

This PCB reliability test checks component leads for wettability and the ability to attach to the board firmly. Low wettability causes poor connections, affecting the assembly process. You can conduct it in three ways: dip and look, wetting balance, and surface mount simulation.

The dip-and-look method involves aging components, dipping them in the solder, and examining their leads for wettability. For wetting balance, age the components and insert them into soldering flux and molten solder to find the time needed to “wet” them.

Surface-mount simulation requires you to put components in the solder paste and subject them to a reflow process. In all tests, the solderability rate should be more than 95%.

3. Voltage Withstand Test

This PCB testing method measures the “breakdown voltage” or the insulation capabilities, that is, if it can handle the voltage levels of its application. It involves applying a voltage higher than its rated level for a specified period.

Ensure the board is clean and without moisture. Next, connect it to the tester and gradually increase the voltage. Check to see if the circuit breaks down at higher voltages. Based on the recorded results, confirm whether the PCB suits end-use electrical stresses.

4. Glass Transition (Tg) Test

The Tg test determines how the board responds to high-temperature levels. Glass transition, shortened to Tg, is the temperature at which a material changes to a pliable state when subjected to heat. That should not happen when using the circuit board. Here’s how to conduct the test:

Heat the board at 105 degrees Celsius for up to three hours, then cool and put it in a DSC tester. Gradually increase the temperature. Record its glass transition temperature; it shouldn’t exceed 150 ° Celsius or as specified based on the PCB’s application.

5. CTE Test

CTE, or coefficient of thermal expansion in full, is one of the most essential PCB testing techniques to confirm reliability. It measures how much the board expands (or contracts) in response to a temperature change.

Heat the sample at 105 °C for about two hours, then cool it in a dry environment. Place the board in a thermal mechanical analysis (TMA) tester to conduct the test and increase the temperature. Measure the resulting expansion at 250° C to determine if the board passes the test.

6. Heat Resistance Test

This PCB reliability testing method analyses a circuit board’s ability to endure temperature changes, ensuring its various parts can continue to function in a hot environment. In other words, it measures the board’s thermal conductivity level.

Heat the board in an oven for up to 2 hours and allow it to cool in a drier. Put the board in a TMA machine and increase the temperature to 260 °C. Observe it for damage and record the results.

7. Chemical Resistance Test

It evaluates a PCB’s ability to withstand chemical damage, including acids and alkali solutions. If passed, the board can function in its end-use environment.

Put a few drops of dichloromethane on the PCB surface. Let it sit for a while, and then wipe it using white cotton. Examine the solder mask for discoloration or damage. The layer should not dissolve or become colored.

8. Ionic Contamination Test

This PCB testing method determines if the PCB meets the required cleanliness standards. Depending on the required reliability levels, these vary across different industries—contaminants cause coating problems, electrical failure, and physical damage.

Clean the board using isopropyl alcohol to dissolve ionic contaminants. Measure the sample’s conductivity using a Rose test or ion chromatography (IC) testing. The conductivity level indicates the amount of pollutants.

9. Wire Strip Off Test

This test aims to determine the amount of force it would take to strip off copper from the PCB. You need a piece of equipment called a strip-off tester to conduct it.

Strip a section of copper on one side of the board, about 10mm. Place the stripped circuit board on the tester and strip the remaining copper. Record the amount of force used. It should not go above 1.1 N/mm.

10. Via and Microsectional Test

A via and microsection analysis inspects a circuit board’s cross-section for possible failure points and causes. The tester identifies flaws such as layer misalignment or cracks and checks vias for structural defects. This PCB reliability analysis method also checks for contamination.

Cut a piece from the sample board (about 5mm square) and secure it in a resin mold. Polish the board, starting with abrasives, to a smooth surface. Examine it using an optical or electron microscope to identify cross-section defects and other problems.

11. Impedance Test

This test verifies if the specific circuit board meets the required impedance levels. That, in turn, depends on its structure, the alignment of the layers, and other characteristics, such as electrical connectivity, trace size, and spacing.

The impedance test requires a specialized machine called a time domain reflectometer and a test board or coupon. After taking measurements, generate a report and use the data to determine if the PCB meets specifications.

IPC PCB testing standards tree
IPC PCB testing standards tree
Resource: https://circuitdigest.com

PCB Reliability Testing Standards

In addition to the various PCB analysis methods, fabricators and assemblers follow different standards when testing boards for reliability. The following is a collection of the most used standards and what they entail.

  • IPC-SM 785 and IPC 9701 standards: the IPC writes guidelines that manufacturers in the circuit board industry can use to test their products for reliability.
  • MIL-STD 202 and MIL-PRF 3102 standards: provides environmental stress tests for printed circuit boards and offers certifications.
  • JEDEC standards: a collection of testing methods for electronic circuit boards.
  • IEC 60068 standard: describes environmental test methods, including vibrations, heat, and humidity tests.

Conclusion

PCB reliability testing assesses a circuit board’s ability to resist damage, helping determine how well it can hold in its application environment. It ensures manufacturers create high-quality and dependable boards, especially those used in critical systems like the medical and aerospace industries. Overall, the tests are essential during any PCB production process.

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