At Foresite, we experience a great deal of satisfaction when we are able to quickly and expertly identify the root cause and get our customers back on track when they face a difficult and time-sensitive challenge. But, that is only part of the solution; we also strive, whenever possible, to share or develop knowledge that can help prevent future occurrences.
With that in mind, this blog post will briefly explore common sources of contamination throughout the fabrication and assembly processes that can potentially lead to field reliability issues.
1. PCB Fabrication
The PCB fabrication process must be tightly controlled and monitored as the chemistries used can be quite conductive and/or corrosive. If etchants are not properly neutralized and rinsed, they can provide the precursor for electrochemical migration or leakage current failures.
Additionally, poor drilling or plating of vias can result in entrapment and wicking of chemical residues within the inner layers of the substrate. It can also be difficult to clear detrimental residues from microvias, depending on factors such as heat, water quality, and use of saponifier for reducing surface tension. Subsequent cleaning steps in the assembly process can provide an opportunity to reduce or remove PCB fabrication residues, but no-clean processes are especially at risk.
2. Raw Components
Along with bare boards, raw components can also introduce contaminants that are detrimental to end-use reliability. PCBs and components use similar metallization, and therefore similar chemistries and opportunities for residues are present. Low-cost commodity chip components may not experience the levels of quality control and process monitoring that the engineer, or even the end-user, may desire.
Casting of metals and injection molding of plastics can involve a variety of different materials that may not be conducive to long-term electronics reliability. We have encountered a variety of lubricants, cutting fluids, mold release compounds, rust inhibitors, etc. that contain corrosive and/or conductive components.
These issues are commonly discovered in high humidity validation testing, where small amounts of condensation can transfer these contaminants from housing to electronic assembly.
We’ve covered a few potential sources of contamination that could contribute to reliability issues, and we haven’t even populated a circuit board yet. Check back soon for other mistakes that you can learn from!