Stephané Menard asked:

>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.

Michael Carano offered an interesting reply which concurs with my
experience, and also:

There is a method in which the electroplated coating is applied to thin
coupons which may be measured post plating for mechanical strain.

The concept is that whisker growth rate is a function of stress resulting
from the exact manner of the coating growth. Plating electrochemistry which
imparts less stress is also known to be more stable in regard to whiskers.

Sorry, I don't remember the source of these coupons, but check Metal
Finishing magazine (they used to have a website).

Plating coupons which have right angle minimum radius bends in a dry
cabinet at 120-150 degrees C will accelerate the formation of whiskers
visible with 10X magnification into the range of a few days. They seem to
form first on the outer bend radii.


regards,




Jerry Cupples
Interphase Corporation
Dallas, TX USA
http://www.iphase.com

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