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

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


Gold embrittlement

Jeff_Tamagi

#8583

Gold embrittlement | 11 November, 1999

Do I have to tin gold lead devices?

Can I use indium? Can I use lead-free Can I use tin-free

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#8584

Re: Gold embrittlement | 11 November, 1999

Assuming that you are going to solder them into a board rather than socket them, yes. The thickness of the gold plating in this application will usually make up a large enough percentage of the total joint to threaten enbrittlement. Use a small solder pot and monitor the gold percentage. Toss (no, recycle)the contents when the gold level gets too high. The main intent is to remove the gold (actually reduce it to a very small percentage)and any alloy that accomplishes that will do. John Thorup

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Michael Allen

#8585

Re: Gold embrittlement | 12 November, 1999

The papers I've read suggest that we need to be concerned if the weight percent of gold in the finished joint exceeds 3%. You might want to do the calculations to see where you stand, before you set up a process to "tin" the leads.

If you find that a particular joint is over this threshold slightly, you might be able to reduce the gold content to an acceptable level by printing more paste (e.g., thicker stencil or oversized aperture...the latter is a bad idea w/ no-clean).

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#8586

Re: Gold embrittlement | 12 November, 1999

Hi Michael While driving home last night I realized the omission in my response. I thought someone would call me on it. I should have clarified that the dissolution of the gold into the joint would be affected by the thickness of the gold plating, the peak and average temperatures, the time above liquidus, the solder alloy used and other factors. What is more likely to happen is that the gold will not be completely removed from the lead before the solder solidifies. The remaining gold will form an intermettalic layer between the base metal and the solidified solder. It is the arrangement of the atoms in this layer and their attachment to the other surfaces that is the real danger of joint embrittlement. For more see Klein Wassink, Soldering in Electronics and Manko, Solders and Soldering. IPC Technet also had a thread on this subject recently. John Thorup

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