Hi All, We just started build a new product and I am encountering many non-wet rejects in our new product. I need help on what should I look into to improve our Yield. Please see below back ground 1. We are using DEK Infinity as printer. 2. We are mounting our SMD's in the OSP laminates. 3. We use Sn/Ag solder paste. 4. non-wet rejects are localized on 1 specific SMD part number (0402) only. 5. In 1 circuit I use 6 SMD of this part #'s. And non-wet reject randomly occurs on any location of this specific part #. 5. I already send samples of the suspected SMD to solderability test, fedback to vendor, did SEM photo, die EDX but we found no problem on the SMD. 6. We suspect laminate, reflow and paste also but the question we have is, why only occurs on the 6 locations of this specific 0402 part #. If the laminate, reflow or paste is problem, all SMD's in my board should have rejects not only this part #. 0201's don't have this reject. 7. I tried different stencil aperture design and I improve my defect rate from ~3000 PPM to ~1000PPM in a week. 8. Also, the reject happens randomly in every lot. Like 80% of the batch processed in a week don't have this reject (PPM < 100), but 20 % of the batch processed have gross rejects. Some even have 10000PPM in one batch.
Here's my questions: 1. I wonder if my printing using DEK Infinity machine is not consistent. If not, what should I look into my program. I already invited my DEK vendor but they found no problem on DEK mechanical setup. 2. I already checked my SMD machine placement and I don't see problem also. We're Using AssemleOn in SMD placement.
Can anyone please advise me what else I need to look into to fix my non-wet problem. I am so helpless for now. I would appreciate any feedback. Thanks a lot! - Bong
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