On 05/28/99 20:02:12 you wrote:
>
>Ed,
>
>Your 2 cents worth really got me excited.
>
>I attempted to ultrasonic cleaned in a (Alkaline, PH 8 to 9) neutraliser
>for 15 mins but the stubborn white contaminants still remained.
>
>I shared your sentiment and am suspecting the contaminants to come from the
>solder. The supplier will help analyse in their lead content on the same
>batch used in production.
>
>Could you elaborate the effects of low antimony?
>
>Thanks for sharing.
>
David,
First, it seems to me that analysis of your solder pot is not a regularly scheduled item.
Several contaminants can be intoduced from the PCB's and other misc. sources such as fixtures,
tools, etc. You should not only test for lead content(actually tin content, balance lead), but
other metals such as copper, gold, silver, nickel, bismuth, antimony, zinc, cadmium, aluminum,
arsenic, iron, etc. (I did this from memory, so I probably missed a few). QQS571 spells out the
upper and (in a few cases) lower limits.
Antimony has a peculiar property in that it expands when cool and contracts when heated. I
believe bismuth is used in the equation as well, but not being a metalurgist, I am simply
repeating what I've been told, contaminated by an aging memory (it's the second thing to go,
I've also been told... I think.)
The effect is as the surface cools and freezes, the body of the joint is somewhat lagging
thermally, therefore contracting after there is a skin formed causing "wrinkles" (another sign
of aging, by the way). Antimony reduces the shrinkage in this interim stage.
Regards,
Ed Popielarski
QTA Machine
10 Mc Laren, Suite D
Irvine, Ca. USA 92618
Ph: (949)581-6601
Fx: (949)581-2448
E-Mail: [log in to unmask]
http://www.qta.net
ASK ABOUT OUR BGA REBALLER!
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