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Q: What is the best way to monitor microvia reliability on a lot-by-lot basis for high-volume production?
A: What I recommend, and practice, is this: Do a thorough qualification of a fabricator using a HATS Qualification Panel (an IPC PCQRR-like panel) that includes an IPC D coupon resized for the runner on your SMT panel. Run these panel coupons through IPC-TM-650-2.6.27B and then TM-650-22.214.171.124 thermal cycles for 500 cycles. This is your baseline.
Then, by incorporating this smaller D coupon on all your boards’ assembly runners—requiring each lot to have a plating process control coupon for X number of solder float tests at 288°C and then microsections to look at TH quality—you have a way of comparing that lot’s performance to your initial qualification for that vendor. This should be redone each year and kept for records on each lot in case needed later.
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