Hi,
I am grappling with similar issues too. I would not want to mix eutectic solder with SAC (and therefore not print eutectic solder over the BGA pads). The interface between the partially melted SAC and fully melted eutectic alloy is very weak, and will create issue with reliability.

I am still finding out info about what happens to eutectic solder if driven at SAC temps....please let me know if you find anything, I'll do the same.

Amol Kane
M.S (Industrial Eng.)
Process Engineer
Harvard Custom Manufacturing 
941 Route 38  Owego, NY 13827
Phone: (607) 687-7669 x349
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 -----Original Message-----
From:   TechNet [mailto:[log in to unmask]]  On Behalf Of Taylor, Royce
Sent:   Thursday, January 19, 2006 8:11 AM
To:     [log in to unmask]
Subject:        [TN] Building a lead free board (with PB free BGA with eutectic solder

Question(s),

I am about to build a double sided SMT board using lead free parts and eutectic solder paste, the only concern I have is that there is one lead free BGA on the board. I do not know at what temperature the balls will start to collapse (what is the normal alloy of a PB free BGA)?? AND what happens if anything to the eutectic solder if I drive the reflow temps to the needs of the BGA? Will the intermixing of the two different alloys be an issue for reliability? Would you treat this BGA like a hi temp leaded BGA and ADD solder paste volume to the land pads?

A second question is, I have a different customer that wants a eutectic BGA replaced with its PB free counterpart. Can I use just tacky flux and drive the profile hotter to get the balls to a liquidous state and get good wetting/solder joints.

Your experiences would be a huge help

Thanks
*************************************************************************
Royce Taylor
Process Engineering/Production
Suntron Corporation NEO
104 Glenn Street
Lawrence, MA 01843
(978)747-2061 voice
(978)747-2010 fax
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