In a message dated 8/24/98 3:19:57 PM Pacific Daylight Time, [log in to unmask]
writes:

<< My book only goes to 70/30 (tin/lead). need help. Our part supplier is
using
 90/10 rather then 63/37. The higher tin causes more oxides creating some
 cold solder joints. Supplier has brass base followed by copper flask and
 90/10 tin/lead. What is the liquidus temperature of tin/lead of 90/10 and
 has anyone had the experience. Also the feet to this part are very small and
 close to the pad. Hard to inspect. We had the supplier go to 63/37 and had
 very little problem. Supplier wants to go back to 90/10. whats the
 concensus? >>

Hi Nick!

     90/10 tin lead solder melts at 215-217° C...(finally found it! that WAS a
bit of a bear to find). There's a lot of component manufacturers trying to get
away from lead, they keep saying that we're gonna have to get rid of it too,
so might as well get used to tweeking profiles again. Ya' know, I've never
quite understood why those of us in the electronic industry get such visibilty
when it comes to lead usage...we're by no stretch of the imagination, the
largest users of lead...it's that darn pink bunny rabbit critter that keeps
going around beatin' a drum and all his buddies that hold that honor...why
don't they get the same heat that we get? Oh well, that's life...

     Back to where we were, a high content tin finish should be plenty
solderable,  although you will have to spike a bit higher than normal...it's
almost the same thing with palladium finishes too. Texas Instruments have not
been doing tin/lead finishes on their components for years.

     As to your "tin whiskers" fears, that's what alloying the 10% lead with
tin will take care of, 5% has been shown to be enough to prevent whiskers...
or you can throw a bunch of estrogen into the pot...that'll prevent whiskers
too!! HAR! HAR! (gawd, I crack myself up!)...it's getting late in the day...I
better go home...hehehe

-Steve Gregory-

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