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Ask the Experts

May 14, 2007 - Updated
July 4, 2007 - Originally Posted

Tin Whiskers

I have heard of tin whiskers creeping along the surface of a PCB under paralyene. Would vacuum impregnating potting 100% mitigate this disposable assembly?

J.O

Expert Panel Responses

Unfortunately, your terminology is slightly confusing. Tin whiskers can penetrate paralyene. On the other hand, if the interface is weak, it may seek a more preferential path under the paralyene. If the interface is weak, vacuum impregnation would likely have minimal effect unless it places the paralyene under stress. But, you then risk damage to your components.

Dr. Craig D. Hillman
CEO & Managing Partner
DfR Solutions

Dr. Hillman's specialties include best practices in Design for Reliability, strategies for transitioning to Pb-free, supplier qualification, passive component technology and printed board failure mechanisms.

Vacuum would help but will not prevent it. The only way to prevent whisker growth under any condition is to remove the driving force, which is the compressive stress, from the Sn coating. This can be done quite effectively by using the thin Sn (<3 um When there is a large external applied (regardless intentional or non-intentional) compressive stress, it could induce whisker growth in the Sn layer also - it is a matter of time.

Yun Zhang
R&D Director
Cookson Electronics, Enthone

Ms. Zhang has a PhD in chemistry/electrochemistry. Experiences include AT&T/Lucent Bell Labs, Technic, Cookson Electronics/Enthone. Areas of expertise include: electroplating; Sn whiskers, wafer bumping, Cu post/pillar, Cu redistribution lines and Sn and SnAg bumps.

I am not an expert on Tin Whiskers, but everything I have read or been told by experts is that there is no method to 100% guarantee that Tin Whiskers will not develop. There is detailed information on the iNEMI and many other web sites.

Joe Belmonte
Principal Consultant
ITM Consulting

Mr. Belmonte has been a process engineer and process engineering manager in the electronic manufacturing industry for over 25 years, with experience in all aspects of electronic product assembly operations. He is well-known throughout Asia and SE Asia for both his process work and teaching engagements.

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