Failure analysis has played an important role in technology development for a long time. For example, black boxes have revealed the cause of numerous aircraft crashes, and the brittle nature of Titanic’s fatigued metal structure was discovered after sections of the hull were retrieved and analyzed. With data from failures like these, changes can be made in how vehicles and other products are designed and manufactured, and our technology is better and safer for it.
Circuit boards have an analysis process they can go through when they suffer a failure. Although a PCB failure doesn’t command the same amount of attention as an accident, it is still essential to understanding the error and preventing it from happening again. Here is a closer look at failure analysis in circuit board systems to better understand this aspect of PCB design and development.
Initial Analysis of Circuit Board System Failures
Circuit board testing is a normal part of the PCB assembly process. The CM will test the board to validate the assembly process and ensure there aren’t any unexpected opens or shorts in the nets, which would indicate potential soldering problems. Of the many systems and processes used for PCB testing, here are the most common:
- In-Circuit Test (ICT): Also known as a “bed of nails” test, ICT is a test system with fixed probes simultaneously contacting a matching test point in a circuit board placed in the test fixture. The board is held steady in the fixture with a vacuum drawdown while the test program sends signals through each probe, searching for assembly failures. While the ICT system requires a custom-built test fixture for each different PCB, the test itself is quick, making ICT ideal for testing production runs of boards.
- Flying probe: The flying probe system moves between two and six probes around the board, conducting tests using the same test points required for ICT. This system takes longer to run as the probes continuously move from point to point but is easier to set up and run than the ICT system.
- Cablescan: For complex interface boards with multiple connectors, cablescan can be an excellent alternative to the ICT and flying probe systems. Cablescan runs its tests through its connectors, which may require unique hardware interfaces.
- Bench testing: Many boards still need to have some or all of their testing conducted by a technician working on a test bench. Although manual testing is slower than automated systems, there also isn’t any prior setup or programming required.
If a circuit board fails, these standard testing methods are the first to look for the root of the problem.
The first step in circuit board failure analysis is for the PCB contract manufacturer to define the scope of the required work and the customer’s expectations. Next, the PCB CM will work through the first level of testing, where most problems typically lie. Often these problems stem from component issues, and the PCB CM will trace the failed part to the specific vendor that supplied it. The vendor will then conduct a failure analysis on the component to determine and resolve the problem. However, there may be times when the PCB CM must do a more in-depth analysis, and we will look at that next.
Taking Failure Analysis in Circuit Board Systems to the Next Level
When the standard testing doesn’t uncover the root of the problem, the printed circuit board contract manufacturer will take the failure analysis of the board to the next level. Primarily their concern is to meet and exceed their customer’s expectations with detailed non-conformance data. To do this, they provide ample technical documentation of their analysis and maintain open communication with all parties involved.
Depending on the specific failure, the PCB CM will use various methods to analyze the circuit board. These range from standard hand tools and measurement devices such as calipers, microscopes, LCR meters, and even video equipment to document the failure events as they happen. If warranted, the technicians also use more complex tools, including spectrum analyzers, RF meters, and various scopes and testers, to diagnose problems on the board reported by the customer.
PCB CMs can also run circuit boards through HALT and HASS testing for further diagnosis. Halt (Highly Accelerated Life Tests) and HASS (Highly Accelerated Stress Screens) include rapid changes in temperatures and vibration. The purpose is to apply a continuous amount of stress on the board until a failure occurs to determine the root cause of the problem. PCB CMs usually can do some levels of these accelerated stress testing, such as varying temperature extremes while the circuit board is powered up. However, for larger assemblies, or more vigorous testing such as shock and vibration, the PCB CM will usually work together with a third-party tester equipped for more elaborate testing.
The key is to work with a PCB CM committed to customer satisfaction, no matter how much testing and analysis is required.
The Importance of Working with an Experienced PCB Contract Manufacturer
A lot of vendors can build a circuit board, but a true partner in PCB assembly is a contract manufacturer who will guarantee quality by providing these three levels of failure analysis in circuit board systems:
- Standard PCB assembly testing: The first level of failure analysis is in the standard testing of any circuit board assembly. These include ICT, flying probe, cablescan, or regular bench testing by a technician.
- Advanced PCB testing and analysis: Armed with a variety of more in-depth test equipment, the PCB CM should be able to diagnose problems with the board down to the component level and report back with detailed non-conformance reports and data.
Networked with third-party test services: For full accelerated stress testing, the PCB CM should have access to third-party testing services equipped for this type of testing.
