3 ms·
Typically, the coating is Parylene, which is a room temp vapor phase conformal coating (e.g. roughly uniform thickness independent of the contact angle of the m
by kurthr 9y ago
Typically, the coating is Parylene, which is a room temp vapor phase conformal coating (e.g. roughly uniform thickness independent of the contact angle of the materials). It's used for corrosion, moisture, vibrational. wear, and reduced breakdown voltage, etc.
It is not used for Sn (tin) whiskers at all, since it wouldn't penetrate the pads/package of the IC and wouldn't stop such a high modulus process in any case. Whiskers are most problematic with modern Pb-free solders and fine pitch SMT practices (QFNs & BGAs), but it's worth noting that other materials (like Zn) also have significant issues.
http://www.paryleneengineering.com/why_use_parylene.htm http://www.paryleneengineering.com/why_use_parylene.htm
- LeifCarrotson 9y agoFrom that page: > The coating completely penetrates spaces as narrow 0.01mm. I would have thought that would make it very effective in protecting against whiskers in QFPs that might have a lead pitch of 0.4mm or larger. There's not a lot you can do under the bodies of BGAs and QFNs, but if you're worried about whiskers you're probably using QFPs instead. This app note suggests that Parylene and a few other dip-type conformal coatings do slow down tin whiskers, but don't stop their spread: https://www.maximintegrated.com/en/app-notes/index.mvp/id/5250 https://www.maximintegrated.com/en/app-notes/index.mvp/id/52...