SMT components that have AgPd (silver palladium) pads require silver content
in the solder paste. The reason for this is that the silver will migrate
from the pads to the solder if there is no silver in the solder. I have only
seen this requirement on devices that are made on ceramic substrates. The
silver solder reflows at a lower temperature also and is a bit stronger
mechanically. This comes into play when the difference in the board's and
the device's tempcos get worked by heating and cooling during the life of
the end product.
If you have no AgPd pads on ceramic- and no other unknowns, there's no
reason to spend on paste with silver content, which, btw is normally about
2% silver but much higher priced. 63/37 is generally much less costly. I
would see if they are trying to sell you some silver, and check with other
distributors.

In raising this subject on the list in the past, I found that about 1/2 of
the SMTer's used wire solder and small irons, and the other 1/2 used toaster
ovens, small reflow setups and the like. So if you have good eyes and a
steady hand you may just want to try wire & iron instead of paste. I have
been able to solder .5mm pitch parts that way, and I have pretty poor
eyesight and shaky hands....Practice with scrap parts is also a good idea,
until you perfect a method that works for you.

Chris

-----Original Message-----
From: pic microcontroller discussion list
[mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of Simon-Thijs de Feber
Sent: Tuesday, February 12, 2002 11:00 PM
To: PICLIST@MITVMA.MIT.EDU
Subject: [OT]: Solder Paste


Hello all,

Since i am doing my first SMD PCB i informed about
solder paste. My local distri gave me a shocking
price;
being ~50 USD for a dsipenser of 10mg.

Is it realy this expensive ???

grtz


Simon



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