Stephane,
Whisker growth in tin and even some other metals (copper, aluminum and
silver have been reported top grow whiskers) is a result of compressive
stress. This stress can arise from high organics in the deposit, plating
factors causing stress, contamination of the plating solution, and a deposit
which is too thin. A rule of thumb is keep the organics as a %carbon less
than 0.05% by weight, and plate a minimum of 200 microinches.
Of course, if the tin is alloyed even with a small percentage of another
metal like bismuth, the whisker effect should not appear.
Good luck,
Mike Carano
-----Original Message-----
From: Stephane Menard [SMTP:[log in to unmask]]
Sent: Friday, September 03, 1999 9:30 AM
To: [log in to unmask]
Subject: [TN] Whiskers Problem on Leadframes
Hi everybody !!
I have a question regarding the well known problem of whiskers
generation on
leadframes.
With the concept of lead free deposit and the investigation of
several
alternatives (Sn-Bi, Sn-Ag, Pure Tin, etc..) to Tin-Lead, we need
to study
the risk of generation of whiskers with those substitutes.
It is generally agreed that Tin alloys (even at low percentage in
the other
metal) are not prone to this problem whereas pure Tin deposits are.
However, does anybody have a recognized method (electrochemical,
physical,
etc...) which could help in predicting the apparition, or not, of
this
problem (besides the standard aging test which sometimes can be
quite
doubtful !) ?
I am looking forward to your answers and comments.
Sincerely,
Stephane Menard
Micropulse Plating Concepts
[log in to unmask]
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