Sometimes, you may see cracking on the coating of Vishay’s Power Metal Strip resistors such as the WSL and WSLP series. You may worry about whether this cracking will affect the performance of your resistors. Before discuss this cracking issue, let us understand the structure of Vishay’s Power Metal Strip resistors.
Generally, chip resistors consist of a ceramic substrate and a thin layer of component material on the structure. However, Vishay Power Metal Strip resistors are all-metal welded structures and do not rely on substrates. The metal resistance element is thick enough to be self-supporting. If the surface of a thick film chip resistor is exposed to the environment, then it is vulnerable; whereas the large cross-section of the Power Metal Strip® will be virtually unaffected by the environment.
The Power Metal Strip resistor family is coated with a high-temperature, silicone based coating. The purpose of this coating is:
- Mask the element of the resistor to prevent solder from being electroplated during the termination plating process
- Act as a medium for Vishay to print value, which aids in part orientation during packaging process (up and down)
- Allow for vacuum pick and placement of the part during board assembly.
Most important is that the presence of coating is not a requirement for long-term reliability or function of the part. The furthest extreme for a crack would be to entirely remove the coating.
Thus, Vishay considers these coating cracks to be a cosmetic issue only.
To learn more about cracking on WSL series parts in specific, please check: Cracking issue on Vishay WSL series Resistors