The 3 Reasons for PCB Failure

April 7, 2020 , in Blog

As an engineer, part of the job is expecting the unexpected. We recently installed a piece of custom production equipment that my team made at a customer’s facility. We thought of every way the system could break or fail, and when it did, we were already prepared to fix it. Heading off failure is even more important in PCB design. It can be expensive to replace a board that breaks in the field, and a customer’s wrath is often even more costly. That’s why it’s important to keep the three main reasons for PCB failure in mind during design: manufacturing defects, environmental factors, and an under-specified design. While a few of these factors may be out of your hands, many of them can be mitigated in the design phase. That’s why planning for the worst during design can help your board perform at its best.

Overloaded electrical circuit causing electrical short and fire

When it comes to PCBs you never want to make sparks fly.

Reason #1 for PCB Failure: Manufacturing Defects

One of the most common reasons PCBs fail is because of manufacturing defects. These deficiencies can be hard to detect and even more difficult to fix once they’re found. While some of them can be headed off in design, others have to be fixed by the contract manufacturer (CM).

COMMON MANUFACTURING DEFECTS AND SOLUTIONS

Defect Description Solution
Low-quality solder joint connection If solder joints are not connected well, tombstoning, where a component connection becomes disconnected on one end, may occur during operation. Misaligned pad-trace layouts result in low-quality solder joints and are susceptible to disconnecting, especially for boards that are subjected to mechanical stresses; such as vibration or motion. Design: Ensure that pads and traces are properly aligned in the PCB layout. Also make sure that your board has structural integrity, which may require testing during manufacturing.
Material degradation Board materials with low CTE can be weakened during manufacturing resulting in premature failure in the field. The most likely cause of failure is excessive heat. Design: Make sure to follow PCB thermal design for manufacturing guidelines and choose materials that are well-suited for the manufacturing situation. For example, if lead-free solder is used the temperatures that your board will be exposed to during assembly are markedly higher than for wave soldering.
Contamination Boards may become contaminated prior to or during assembly due to a lack of surface finishing and due to a lack of post-assembly protective coating. This can lead to oxidation that can cause erratic behavior and failure. Design: Make sure to specify that surface finishing be applied and that it is appropriate for your design. It is also a good idea to specify that conformal coating is used to prevent surface contamination during operation.

This is not an exhaustive list, but it gives the designer a good idea of what to expect when it comes to manufacturing defects. As you can see, the issues listed can be solved during design and/or working closely with your CM to anticipate issues that may lead to operational failure.

Reason #2 for PCB Failure: Environmental Factors

Another common cause of PCB failure is the operational environment. Therefore, it is very important to design a board and enclosure based on the environment that it will operate in.

  • Heat: Boards generate heat and are often exposed to heat during operation. Consider whether a PCB will have airflow around its enclosure, be exposed to sunlight and outdoor temperatures, or absorb heat from other sources operating nearby. Changes in temperature can also crack solder joints, substrate materials, or even enclosures. If your circuit is going to experience high temperatures you may want to look at through-hole components that can usually conduct more heat than SMTs.
  • Dust: Dust is the bane of electronics. Make sure your enclosure has the correct Ingress Protection (IP) rating and/or choose components that can handle the dust levels expected in the area of operation and/or use a conformal coating.
  • Moisture: Humidity poses a considerable threat to electronics. If a PCB is operating in a very humid environment where temperatures change drastically, moisture can condense from the air onto the circuits. Therefore, it is important to make sure that moisture protection methods are incorporated throughout the building of your board and prior to installation.
  • Physical Shock: There’s a reason ruggedized electronics commercials show people throwing them onto rocks or concrete floors. Many devices will experience physical shocks or vibrations during operation. Your enclosure, board, and components will have to be selected based upon mechanical properties to account for that.

Reason #3 for PCB Failure: Non-Specific Design

The last factor in PCB failure during operation is the most important: design. If a board isn’t designed to specifically meet its performance objectives; including reliability and longevity it simply isn’t going to go the distance. If you want your board to last a very long time make sure to select components and materials, layout your board and verify your design for the specific requirements of your design.

  • Component Selection: Over time components fail or go out of production; however, it is not acceptable for this failure to occur prior to the end of the expected lifetime for your board. Therefore, your selections should meet their performance requirements for their environment and have a sufficient component lifecycle for the lifetime of your board’s anticipated production.
  • Material Selection: Just as components performance can fail over time, so also material properties can degrade. Exposure to heat, thermal cycling, UV light, and mechanical stresses can all cause boards to degrade and fail prematurely. Therefore, you need to choose the best-printed circuit board material for your board type. This means considering material properties and utilizing the most inert materials applicable to your design.
  • PCB Layout: A less than well-defined PCB layout can also be the root cause of board failure during operation. For example, not incorporating the unique challenges for high voltage boards; such as high voltage arc tracking rate, can result in board and system damage and even injury to personnel.
  • Design Verification: This is probably the most important step in producing reliable circuits. Go through DFM checks with your particular CM. Some CMs can hold tighter tolerances and work with special materials, others cannot. Making sure your CM can make your board the way you want it before going into manufacturing will ensure quality PCBAs that are more likely to not fail.

It’s not much fun imagining the worst possible things that could happen to your PCB. The good part is sleeping well at night knowing you’ve designed a reliable board that isn’t going to fail when its deployed or in a customer’s hands. Remember the three main reasons for PCB failure and you’ll be well on your way to a consistent and reliable board. Make sure to plan for manufacturing defects, environmental factors, and focus your design decisions for your specific case from the beginning.

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It’s not much fun imagining the worst possible things that could happen to your PCB. The good part is sleeping well at night knowing you’ve designed a reliable board that isn’t going to fail when its deployed or in a customer’s hands. Remember the three main reasons for PCB failure and you’ll be well on your way to a consistent and reliable board. Make sure to plan for manufacturing defects, environmental factors, and focus your design decisions for your specific case from the beginning.

Here at Tempo Automation, we like to help our customers build things that last. And to help you get started on the best path, we furnish information for your DFM checks and enable you to easily view and download DRC files. If you’re an Altium Designer or Cadence Allegro user, you can simply add these files to your PCB design software. For Mentor Pads or other design packages, we furnish DRC information in other CAD formats and Excel.

If you are ready to have your design manufactured, try our quote tool to upload your CAD and BOM files. If you want more information on the reasons for PCB failure and how to avoid them, contact us.

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