How to Mitigate the Risks of Tin Whiskers in Circuit Card Assembly
Tin Whiskers in Circuit Card Assembly
Tin whiskers are hair-like structures that grow out of tin-rich finishes on lead-free component terminations. They are highly conductive and can short circuit embedded electronics that need the highest levels of reliability. This can be a severe problem for systems such as life-saving defibrillators and spacecraft.
Unfortunately, tin whisker growth is difficult to prevent, especially in high humidity. However, there are some effective mitigation techniques that can be employed to prevent these problems. These include conformal coating, fusing and alloying.
While scientists have not been able to pinpoint exactly what causes the tin whiskers, it is generally believed that they are caused by internal stresses within the material of circuit card assembly. These stresses could be due to the intermetallic layer between the tin plating and the substrate, mechanical surface damage, changes in temperature or humidity, or a combination of factors.
How to Mitigate the Risks of Tin Whiskers in Circuit Card Assembly
The tin-lead alloy used in tin-lead solder can mitigate this problem, since it has properties that reduce the likelihood of whisker formation. Additionally, there are a variety of specialized tin-lead alloys that have been developed to offer a higher level of whisker mitigation. These can be used in place of pure tin plating on lead-free components.
Conformal coatings are also very effective at mitigating tin whiskers. This is because they act as a physical barrier that can physically separate components and alleviate stress. Additionally, conformal coatings can be applied to a PCB before it goes through the assembly process. This can help protect the board from moisture, chemicals and dust that would otherwise contribute to tin whisker growth.
In addition to conformal coating, fusing can also be an effective mitigation strategy for tin whiskers. However, fusing should be done soon after tin plating to avoid the formation of whiskers. Furthermore, the fusing process should be performed in a reflow environment to minimize stress on the tin-plated surfaces.
Although many different materials can be used to conformal coat a PCB, parylene is one of the most effective. Parylene is deposited in gaseous form through a chemical vapor deposition (CVD) process and seeps deep into substrate surfaces, penetrating spaces as small as 0.01mm. This allows it to effectively mitigate tin whisker growth by physically separating components and alleviating stresses that can contribute to whisker formation.
Ultimately, there are several steps in the circuit card assembly process that can cause tin whiskers. These steps include component placement, a reflow process, a conformal coating and functional testing. The best way to mitigate these risks is by working with an experienced and reliable turnkey manufacturer that can guarantee that all of the necessary processes will be conducted in a tin-free environment.
At Chemtronics, we use a tin-free production process to ensure that your mission-critical and high-performance products are free from the dangerous effects of tin whiskers. Contact us today to learn more about our services or request a quote online. We look forward to assisting you with all your electronic assembly needs. Our expertise in both tin-lead and lead-free technologies allows us to provide the best assembly services on the market.
