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SAC BGA in Pb Process

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CL

#61492

SAC BGA in Pb Process | 29 March, 2010

Good Morning all,

We have successfully avoided (for the most part) the mixed alloy situation since the introducion of the RoHS directive. We are now seeing an influx of RoHS BGA components on leaded assemblies as they are no longer available in Pb and the customer does not want to reball the components. Does anyone have processing guidelines for a SAC alloy BGA in a Pb assembly? I have been experimenting with mixed results. So far, I have had what seems to be acceptable results reflowing at 210 degree C target at >60 sec. Any information on guidelines would be greatly appreciated. Thanks In Advance Chris

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#61496

SAC BGA in Pb Process | 29 March, 2010

SAC BGA In A Sn/Pb Reflow Process Conclusion: Area array components (ball grid arrays, chip scale packages, flip chip packages) with Pbfree solder sphere alloys should not be reflowed using a tin/lead reflow profile due to the resulting non-uniform solder joint microstructure and potential poor board surface finish wetting interactions. [Impact of Reflowing A Pbfree Solder Alloy Using A Tin/Lead Solder Alloy Reflow Profile On Solder Joint Integrity; D Hillman, M Wells, K Cho; Rockwell Collins] http://www.aciusa.org/leadfree/leadfree_impact_of_reflowing_a_pbfree_solder_alloy_using_a_tin-lead_solder_alloy_reflow_profile_on_solder_joint%20_integrity.html

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#61498

SAC BGA in Pb Process | 29 March, 2010

The board in the test "used an electroless nickel/immersion gold (ENIG) finish." If you are not using ENIG plating on your PCBs then you may not suffer from the same issue.

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#61501

SAC BGA in Pb Process | 29 March, 2010

SAC 305 liquidus is 219 C. A hybrid profile is often recommended with a peak of 230 C (reflow the SAC and not kill the Pb parts) with an extended liquidus of 60-90 sec to get good alloy diffusion. Or if the design (parts & pwb) can tolerate it go Pb free with the paste.

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CL

#61507

SAC BGA in Pb Process | 30 March, 2010

Thank you for the responce.

Chris

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