Well I agree in both cases.
We inspect all of our equipment on a rotating periodic basis (every 2 years) for whisker formation. When Our Supplier first issued the bulletin on whisker formation almost 20 years ago we have found numerious instances of whisker formation on tin plated leads and components. The largest I have found was possibly 34Ga and almost 3/4" long on a tin plated pot on a voltage regulator for a 48V 25amp supply, one of it's bretheren took out the voltage regulator board with catistrophic results. The rest of the two pots looked like they had hair growing on them. Our supplier recommended we install rubber heat-shrink boots on the pots, it did somewhat retard formation. All of these components are late 1960's early 1970's vintage so contain 60/40 solder for the most part and not 63/37. I do find after 2 years, growth on diode leads of around 1-2mm. We inspect every high reliability component under at least 10X, and then 40X when we find a potential issue, we document then remove the problem.
Pat
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Stadem, Richard D.
Sent: Monday, January 23, 2012 9:01 AM
To: [log in to unmask]
Subject: Re: [TN] Finally, the folly of lead-free solder is making the big time
Whiskers can be produced by several different types of alloys, including lead, silver, tin, and zinc. The most common (in electronics) are tin and zinc.
The whiskers typically take on characteristics of the metal they are borne from. For example, zinc and tin whiskers are usually straight, brittle, and break easily. Tin whiskers are shiny and do not usually branch out, but zinc whiskers often produce many branches and are black or dark gray in color. Lead whiskers, on the other hand, are curly, soft, malleable, and are fragile but can withstand some bending forces before they break.
Our Technet friend Ingemar Hernefjord once posted some incredible lead whisker photos, I believe they are in Steve Gregory's website. I think this is one of them. http://stevezeva.homestead.com/files/daniel121b.jpg
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of harvey
Sent: Monday, January 23, 2012 10:36 AM
To: [log in to unmask]
Subject: Re: [TN] Finally, the folly of lead-free solder is making the big time
Thanks.
Tin, wherever used, may form whiskers.
The list of sources would include tin plating anywhere, lead free solder, and 63-37 solder.
But I believe that lead deters whisker formation in eutectic solder generally.
That is a statement that is supported by empirical history and much more.
I'm copying Carol Handwerker for her opinion on the subject.
--- On Mon, 1/23/12, Julie Silk <[log in to unmask]> wrote:
From: Julie Silk <[log in to unmask]>
Subject: Re: [TN] Finally, the folly of lead-free solder is making the big time
To: [log in to unmask]
Date: Monday, January 23, 2012, 8:10 AM
These weren't soldered with lead-free
solder. It was tin-lead. The problem was tin-plated parts or boards (maybe both?).
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