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non-wet on 0402 mounted on OSP & lead free paste

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non-wet on 0402 mounted on OSP & lead free paste | 17 October, 2008

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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non-wet on 0402 mounted on OSP & lead free paste | 18 October, 2008

Sounds like a part problem. You can SOMETIMES over come this with a hotter profile. We see this a lot with brokered parts. Seems like a lot of people are rejecting parts because a lot of companies haven't perfected their RoHS process, yet produce parts as compliant. Most companies reject the parts and they find their way into someone elses process. I would suggest rejecting the parts back to the vendor but then those parts would find their way into my company.

Sending the part to the vendor is useless. They NEVER find a problem with their product. Plus they probably dipped the part into a pot of solder to test solderablitity - duh! I can dip marginal parts into a pot of solder and it will cut through and solder. Reflow solder is a different process - yet no vendor tests their suspect parts with this process..... hmmmm.

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non-wet on 0402 mounted on OSP & lead free paste | 18 October, 2008

I see, maybe changing my peak temp in reflow will help. I'll try do eval again... Actually, once I did have evaluated a longer pre-heat but on my previous eval, I didn't change the peak temp. Maybe reflow can help compensate to my problem in the part.

For the SMD problem, I'll try to look for a 3rd party to test it. Does anyone know an institution or company that offers special testing for SMD solderability? And what are the tests usually done to check SMD quality? Is it only solderability, EDX, SEM photo? Or there are other special test?

thanks again... Bong

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non-wet on 0402 mounted on OSP & lead free paste | 19 October, 2008

While you're waiting for others to reply to your question on component analysis laboratories, search the fine SMTnet Archives to find posts like:

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non-wet on 0402 mounted on OSP & lead free paste | 21 October, 2008

Hi Dave, thanks for the info. I'll check the detail and try to send sample SMD's for test. - Bong

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non-wet on 0402 mounted on OSP & lead free paste | 21 October, 2008

Sounds to me like your printer not releasing paste now and again. How can you be sure that you are not getting print skips. Are you using any kind on AOI?

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non-wet on 0402 mounted on OSP & lead free paste | 21 October, 2008

Hi Shooter, we're not using AOI but we do every 30 minutes sampling Inspection on the board and we're not seeing insufficient paste deposit so far since we started.

But I agree with you that seemed my printer is not printing consistent amount of paste. I am not just sure what are the limits that I need to define in my paste deposit. Maybe my current control limits are too loose. I haven't gathered data yet to that detail on paste deposit.

I'll consider... thanks, bong

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non-wet on 0402 mounted on OSP & lead free paste | 24 October, 2008

Hello Bong,

I would make one test only. Make one batch using the problem part from a different vendor. That will answer your main question. For me the part is causing all your problems. If it is possible, change it. Last time having problem like yours I spent almost two months in looking for all possible solutions(apertures stencil calibration and parameters, reflow profiles....), and finally I changed the part. Now I forgot about the problem. Emil

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