Modes of Electronic Circuit Boards
Electronic circuit boards are vital to the seamless functionality of many everyday devices. However, like any piece of technology, they can have problems from time to time. These problems can be caused by excess heat, excessive current or voltage, ionizing radiation, mechanical shock, and more. Some of these problems can occur during the manufacturing and assembly process while others may happen later on. Regardless of the cause, these issues can result in a device that no longer functions properly.
Some PCB defects are difficult to diagnose and troubleshoot. For example, brittle intermetallic layers, often due to thermal cycling, are hard to detect in an electrical test. Solder joint cracking is also difficult to identify. The mismatch of thermal expansion between the electronics board and its packaging strains solder joints. Leaded parts absorb the stress through bending, but leadless components rely on the solder to support their weight. This stress can lead to fatigue cracking in the solder joints. Various methods can mitigate this problem, including tight pattern density controls and improved wash cycles.
Another common problem is oxidation, which can lead to shorts in conductive paths. Ozone in the air can cause this issue, as can chemical contaminants such as sulfur dioxide or moisture in the air. Keeping electronics in clean, climate-controlled environments can help reduce the risk of oxidation and corrosion.
Common Failure Modes of Electronic Circuit Boards
Other common problems include pad cratering and trace fracture, both of which are associated with overstress events, such as drop or vibration. X-ray microscopy and cross sectioning can identify these failures, but further investigation is needed to determine their root causes. This is because these failures can be caused by a variety of factors, from chemical contamination to inadequate soldering pressure or improper placement of components.
Improper component spacing on the PCB can also cause overheating, which can impact the performance of adjacent components. This can be avoided by using a design tool to ensure the optimum spacing between components. Another heat-related issue is thermal runaway, which occurs when clusters of voids form in the substrate and produce more damage. These voids can be the result of incomplete soldering, electromigration effects or Kirkendall voiding.
Inappropriate soldering techniques can also result in intermittent connections on a PCB. These problems are usually caused by sloppy soldering, but can also be the result of a lack of reflow temperature control or insufficient tin/lead composition. Optimal soldering technique and tin/lead chemistry can help prevent these types of problems from occurring. During the reflow process, it is important to maintain an accurate tin/lead ratio in order to avoid overheating and oxidation. Using an accurate tin/lead analyzer can help ensure that the proper ratio is achieved.