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PTH Voiding Caused by Gold Plated Leads

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SMTA-Thomas

#82592

PTH Voiding Caused by Gold Plated Leads | 21 May, 2019

Does anyone have an information or can point me to any studies which identifies any mechanisms/interactions which could explain void creation in Sn63Pb37 PTH solder joints resulting from gold plated leads?

I have been attempting to address a systemic issue with PTH voiding at the wave and selective solder process. The issue impacts multiple assemblies which run Sn63Pb37 alloy, impacts multiple surface finishes and impacts multiple component designs from multiple manufacturers.

The only commonality is that the voiding is isolated to component leads which are gold plated and do not violate J STD-001 4.5.1.a “gold must be removed: From at least 95% of the surfaces to be soldered of the through-hole component leads with >2.54 μm [100 μin] gold thickness and all through-hole leads that will be hand soldered regardless of gold thickness” (we automatically solder wash all components which violate this requirement).

In all cases we have attempted different no clean fluxes and combinations of increased and decreased process parameters (flux deposition, preheat, solder temp, dwell time, localized preheat) without eliminating the voiding. The only process so far which has been shown to completely eliminate the voiding issue is tinning the component leads and removing the gold.

If we get an alternate part which is not manufactured with the gold plating on the leads we do not have any issues with voiding.

Even though we have a solution to the problem by tinning or sourcing non-gold leaded components I would still like to understand the true root cause. This might help me to identify or develop a less time consuming and costly solution.

Has anyone else seen this issue?

If you think there is anything I might have overlooked please let me know.

This message was posted via the Electronics Forum @ SMTASMTA

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#82595

PTH Voiding Caused by Gold Plated Leads | 21 May, 2019

Voiding usually is caused by oxidation/impurities on the plating of part and or PCB. I know it is gold, but did you run any analysis for cleanliness of part plating? Couple of pictures will help everyone.

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#82599

PTH Voiding Caused by Gold Plated Leads | 21 May, 2019

Interesting problem. I've seen this before on SMT device leads (see Gold Embrittlement paper at http://www.semlab.com). The AuSn4 IMC is solid at typical reflow temperatures and traps volatiles in the solder joint. One usually cannot crank the reflow temperature high enough to avoid this.

Ed Hare, PhD VP Sem Lab Inc.

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#82638

PTH Voiding Caused by Gold Plated Leads | 23 May, 2019

Sorry for switching accounts, the SMTA interface was not giving me the option to add attachments.

Evtimor - IC testing of some samples of different assemble holes and components leads did not yield anything abnormal. SEM EDX of the unsoldered leads and barrel have not shown anything abnormal either. SEM EDX of the voids along the leads did show some organic content and a mix of Sn, Pb, Cu and Au. I will need to process an additional sample to validate what percentage breakdown was. I will attach 2 images which are representative of what we are seeing as soon as I can figure out how.

Ed Hare - Figure 3 in History Case 1 looks very similar to what our x-ray images are showing. Thanks for the information!

Attachments:

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#82684

PTH Voiding Caused by Gold Plated Leads | 1 June, 2019

Can I ask what was the organic portion and did you find any phosphorus at all as too much in the plated gold will definitely cause dewetting

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