Printed Circuit Board Assembly & PCB Design SMT Electronics Assembly Manufacturing Forum

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reflow profile

genesmelik

#6276

reflow profile | 24 August, 2000

Dr. Lee,

For Pb-free solders, will the reflow profile be similar to that of Sn/Pb, with an flux activation plateau before going to peak reflow, or will the profile be more linear in nature? Are there advantages/disadvantages to either profile for Pb-free?

Thanks,

Gene Smelik Cookson Performance Solutions

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Dr. Ning-Cheng Lee

#6277

Re: reflow profile | 24 August, 2000

The optimal profile to choose is determined by the following factors, (1) thermal mass and distribution across the board, (2) reflow temperature range needed for a particular alloy, (3) the nature of flux. When the thermal mass is small, such as cellular phone, a linear ramp up profile will be the better choice for better wetting, voiding, bridging, wicking, solder beading, and tombstoning. If the thermal mass is large, a conventional soaking zone will be recommended, due to the temperature gradient consideration. For Pb-free soldering, large temperature gradient developed across the board can really damange the board and compromise the reliability. The disadvantage of conventional profile with a soaking zone is a relatively poorer wetting, voiding, bridging, wicking, solder beading, and tombstoning. I have an article on "Optimizing reflow profile via defect mechanisms analysis" discussing the relation between defect mode and profile. You can find it in Proceedings of IPC Printed Circuits Expo �98 or website www.indium.com.

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