NASA DOD Phase 2: Copper Dissolution Testing

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Summary

Conclusions

• The amount of initial copper plated in the PTH hole may need to be increased to establish a greater margin of safety. The current requirement for 1 mil copper plating minimum may need to be increased to as high as 2.0 mils to provide this margin.
• A resultant minimum copper thickness after rework process may need to be specified and validation methods to ensure compliance would need to be established.
• Alloy selection for rework may be different than for primary attach depending on the expected number of rework cycle requirements for the given product lifetime. Some initial studies have indicated that mixing various Pb-free alloys will not degrade solder joint quality or solder joint reliability.
• Copper dissolution rates vary somewhat with the PTH diameter. This study included only two hole sizes: 0.036" and 0.015". The smaller hole may inhibit material flow up and down the PTH barrel, which affects the copper dissolution rate. Product design consideration may require some additional testing to validate product parameters and associated process requirements.
• Rework locations need to be identified by reference designator.
• Control and recording of rework exposure time may also be required to ensure the connection will meet lifetime requirements of the product.
• Tighter controls on solder pot contaminant levels and maintenance of pot composition may be required to reduce variance of the copper dissolution effect during rework operations.
• Consideration for larger component sizes with regard to nozzle design and alloy flow during the rework procedure may be necessary.

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