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April 21, 2008

Eutectic reflow for Pb-free BGAs

Can I reflow Pb-free BGAs through an eutectic reflow process?

S. Y.

Expert Panel Responses

No, because the reflow temperatures in the eutectic process will not be hot enough to melt the lead free solder balls on the BGA.

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Edward Zamborsky
Regional Sales Manager
OK International Inc.
Mr. Zamborsky serves as one of OK's technology advisers to the Product Development group. Ed has authored articles and papers on topics such as; Low Volume SMT Assembly, Solder Fume Extraction, SMT Rework, BGA Rework, Lead Free Hand Soldering, Lead Free Visual Inspection and Lead Free Array Rework.

Yes you can. The most important aspect of this reflow is the melting of the Pb-free solder balls of the BGA so that there will be adequate mixing of the molten solder from the solder ball and the solder paste. The reflow temperature and time above liquidus are critical, because of the SAC bumps on the BGA. A reflow temperature of around 220-225 degree C with an extended TAL (around 75 seconds) would be helpful in melting the balls, providing sufficient time for the lead from the solder paste to mix within the bulk, and the solder to wet the PCB pads. Depending on the finish on the PCB pad, the extended TAL may form thicker intermetallic. The user needs to be aware of this.

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Bjorn Dahle
President
inspīre solutions LLC
Bjorn Dahle is the President of inspīre solutions LLC. He has 20 years experience in the electronic manufacturing industry with various manufacturing equipment companies covering pick & place, screen printers and thermal process management.
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