We are using 96.5/3.5 tin/silver solder paste on our top side and I have been noticing that on some QFPs the paste forms a heel fillet, a negligible toe fillet, and does not wick over the top of the lead "foot". I am checking to see of the components have a palladium finish (I am pretty sure they do). If it turns out they do, is there an issue with tin/silver paste and palladium coated leads? We are peaking at 230-235 C (ten zone convection Conceptronics) so the boards are getting plenty hot. Why does the paste seem to bulge up at the toe fillet, but not wick onto the lead surface?
Hey Bud: Moved from that Bi-crap to something serious, eh?
1 Get in touch with Doug Romm (firstname.lastname@example.org) at Texas Instruments. He talks palladium. 2 Review the archives on Palladium. 3 I think you're running light on temps. Eutectic is say 225. You gotta bump that by 20 to get flow and throw-in another 10 to get the palladium into solution. 4 Heel is the most important part to get strength.
So, tell me about the wetting on the toe and the sides? What does the solder look like?