Hello Technetters:

(Put on your metallurgical hats for a moment.)

I ran into an unusual circumstance the other day that has me baffled.  We 
soldered down a surface mount glass diode using conventional processes (Sn63 
water soluble solder paste, convection reflow).  The components were 
mis-oriented therefore had to be removed.  To our dismay, the components 
wouldn't separate from the board (polyimide multilayer).  Even though the 
solder was molten, the components wouldn't budge.  Finally, the pads lifted off 
the board so I tried to remove the pads from the component, to no avail.  

It turns out that the component's base metal is pure silver which is then 
solder coated.  The cross section looks like the silver dissolved with the 
solder, with the resultant alloy in contact with the copper pad (which was 
originally solder coated).

Could the soldering process have created a metallurgical bond between the 
silver and the copper?

Thanks for your assistance,

Jim Marsico
(516) 595-5879
[log in to unmask]
		
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