PCB Reliability Testing For Prototypes

PCBs for commercial products must pass a set of reliability tests in order to prove their capabilities, which goes well beyond the standard functional testing found in many products. Functional tests are the starting point, but reliability tests are where a design is proven for operation in its intended environment. To help designers plan a path forward for reliability assessments, we have compiled a set of reliability tests for PCBAs.

Tests For PCB Reliability

Prototypes that are being planned for scaled production need to pass a battery of tests to prove functionality and reliability. The initial round of testing is normally functional, with the testing focusing on whether the device powers up and performs some very basic function. Usually there is initial testing with a multimeter to measure input/output voltages, as well as a scope to monitor the most important signals.

Following functionality is an assessment of reliability. In reliability testing, the product must be tested against some specification or industry standard in its intended operating environment. Most reliability test programs fall into three areas:

• Mechanical Stress Tests:

  • Shock tests

  • Vibration tests

  • Drop tests

• Electrical Stress Tests:

  • ESD tests

  • Electrical over stress (EOS) tests

  • DC/AC isolation test

• Thermal Stress Tests:

  • Long-duration electrical tests

  • Thermal cycling

  • Thermal shock

There may also be more specialized reliability tests, such as exposure to certain liquids or gasses one would expect the device to encounter during operation. For example, products in industrial settings might require a PCB to withstand a possible interaction with harmful chemicals. This is not typical for most PCB assemblies, but it illustrates one of the types of specialized tests that is needed for certain products where reliability is most important.

Mechanical Stress Testing

Mechanical stress tests comprise vibration testing and shock testing. Drop testing is sometimes performed as well, although a shock test can substitute for a drop test.

Vibration testing is most important in industrial, aerospace, and automotive settings where the product can experience significant vibrations when mounted in a vehicle/aircraft/production equipment. Similarly, shock testing can be important for handheld products that might be dropped by a user, or in industrial products that can experience strong g-forces in moving equipment.

PCBA fixed on a vibration plate for reliability testing.

Vibration tests are often qualified against simulations in order to identify points where fixation should be applied. This will modify the resonant frequency profile in a PCB and can help prevent excessive vibrational motion leading to solder joint failure. Mechanical simulation tools require a lot of data regarding the weight of major components in the PCB, as well as material properties of the PCB stackup materials.

Thermal Shock

Initial thermal tests are usually performed during functional testing. One area that might need further testing is in the area of thermal shock. There are currently three major thermal shock testing standards:

• IPC-TM-650 2.6.7

• MIL-STD-202G

• MIL-STD-810 (Method 503)

• MIL-STD-883

• DEF-STAN 00-35

• IEC 60068

• AEC-Q200

Some of these apply to components or assemblies, while others apply to PCBs (e.g., IPC-TM-650 2.6.7 and MIL-STD-202G). These need to be performed with thermal chambers that provide controlled ramping of the internal temperature at a fixed rate in order to comply with standardized test methods.

Large thermal chamber for testing PCBAs, including burn-in testing.

Thermal shock tests focus on suddenly changing temperature between two extreme values and allowing the temperature to settle to its final equilibrium value. The design can be monitored during the test to check that it functions normally during the sudden temperature change. Following the test, it may be necessary to check for board failures or latent failures under thermal cycling or an internal inspection, such as a microsection test.

Electrical Overstress Testing

Overstress testing comes in many flavors, from ESD testing to verifying galvanic isolation at high AC/DC input voltages. The concept in electrical overstress (EOS) testing is simple: push the device electrically until its failure can be observed repeatedly. These various tests will evaluate the level of protection of the circuitry and the physical assembly. Once failure is observed, some failure analysis investigation will be needed to identify the specific failure mode.

Start With a Spec

The above list of tests is great to have, but the more important point is to marry the testing program requirements with the operating specifications of the device. Like most engineering projects, they only turn out the way you want when you have a great engineering specification for the end product. Make sure your team implements a specification that includes target performance values or performance-based standards a design should meet. Specs give the engineering team clear expectations for product performance and metrics for test qualification.

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