Lead Based Paste / Lead-Free BGA

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I've read all the SMTNet threads available on this topic, be... - Nov 03, 2005 by

This is what I would propose, Place and reflow the board wi... - Nov 03, 2005 by RDR

the only problem i see here is the neighboring components (d... - Nov 03, 2005 by

Thank you for the advice. I am not so concerned with the "2... - Nov 03, 2005 by

Samir Nagheenanajar

#37597

Lead Based Paste / Lead-Free BGA | 3 November, 2005

I've read all the SMTNet threads available on this topic, been to a couple seminars, and read some articles, and the general consensus seems to be "it can be done, but shouldn't."

However, at my company, we have a Pb-Free (SAC alloy) 256 IO BGA coming at us quickly. Is anyone out there successfully soldering lead-free BGA's through hotter profiles (ie getting peak reflow temps just above a SAC's eutectic 221* for slightly longer duration) with Leaded paste and just accepting the potential reliability concerns that might surface down the road?

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RDR

#37600

Lead Based Paste / Lead-Free BGA | 3 November, 2005

This is what I would propose, Place and reflow the board without the BGA with your lead process, remove the solder from the BGA pads if you cannot mask off the apertures in your stencil. Then place the BGA and reflow to SAC requirements with a rework station and paste flux.

This might get you through without reliability concerns.

I would really appreciate other opinions or facts on this proposed process for this kind of situation.

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Amol

#37612

Lead Based Paste / Lead-Free BGA | 3 November, 2005

the only problem i see here is the neighboring components (depending upon the component density) will surely undergo a second reflow during the rework stage for the BGA.

this way the only lead you will have in the BGA assembly is if you are using HASL as surface finish.

Russ puts forward a nice idea though

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Samir Nagheenanajar

#37617

Lead Based Paste / Lead-Free BGA | 3 November, 2005

Thank you for the advice. I am not so concerned with the "2nd reflow", as the same can be said for double sided reflowed PCBA's (the bottom-side parts essentially go through a 2nd reflow). As for the HASL, there is a formula in calculating how much Lead percentage will make a solder joint questionable. The formula takes into account the area of component termination, HASL-coating thickness, etc... I'd say the few microns of HASL will not do harm, versus, say, the solder paste volume on a 30-mil pad and 6-mil thick stencil, but again this has to be calculated. Russ' idea is definitely worth a try at least during the prototype stage. Doing an offline BGA placement and soldering in volume is a different story, at my company will be unacceptable.

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