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BGA Voiding for RoHS

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CL

#60368

BGA Voiding for RoHS | 9 November, 2009

Good Morning,

I have seen many posts regarding BGA voiding being excessive and what can be done to better the condition. I have a customer that has an assembly that we have had a diufficult time with. We have spent a lot of time debugging the process and we seem to be heading in the correct direction. In the meantime, the customer has made the statement that our voiding is the root cause of the problem and our profile needs to be adjusted. They were in last week and we X-Ray'd several of these new assemblies. Many of the smaller BGA components exhibited small "pin hole" voiding. None of these were close to IPC reject criteria (less than 5%). I have seen many conditions like this since we have started building with RoHS. Is it common to see micro voiding with the use of RoHS chemistry? Particulars od the assembly are: SAC 305 solder paste ENIG plating .062" PCB No Via in Pad

We have spoken to the paste manufacter and they stated that we could extend the soak but could exhaust the flux activity prior to reflow if we exten it too much.

Any comments or suggestions would be greatly appreciated.

Thanks

Chris

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#60387

BGA Voiding for RoHS | 10 November, 2009

I'm curious why your customer is concerned with BGA voiding. Normal process voids, even well in excess of IPC "limits", don't effect reliability so why monkey with the process to get rid of a non-issue?

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CL

#60388

BGA Voiding for RoHS | 10 November, 2009

Good Morning,

I agree. This has been a problem job for us. They are looking for anything that could be implicated. Right now, they are focusing on the profile. My question pertains to the frequency of micro voiding on BGA devices. I have seen some degree of this on just about everything that we have built with RoHS. None of the voids exceed the IPC guidelines. Their statement is that there are voids on many of the BGA's therefore, our profile is unacceptable. I do not believe that these are a cause for concern due to their size and location. Am I correct? Is it normal to have more voiding just based on the alloy?

Any comments would be greatly appricated.

Chris

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#60430

BGA Voiding for RoHS | 13 November, 2009

Could you clear how much void content do you client required? Normally, 5% void content is permited in clients.

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CL

#60433

BGA Voiding for RoHS | 13 November, 2009

Good Morning,

The customer is looking for void free connections. They had never specified an acceptable percentage. We are reacting to the test yield. Our yield has averaged 50%. We do not test the product so we rely on feeback from the customer. Usually, we do not get any feedback for several weeks. I have profiled this job quite a few times and the profile meets the paste specifications. I have seen the voiding condition but found the voids to be less than 5%(with the exception of the LGA's). They are present in most of the connections (BGA). I have seen this type of condition since we have started building RoHS but have not thought it was problematic due to their size. We do not have a test yield problem on other jobs that exhibit this same condition. I have a new test profile with an extended soak per the paste manufacturers recommendation. I will try that and see how it affects the voids. I do not think that this is the root cause of the problem but I am willing to try anything to resolve this issue.

Thanks

Chris

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#60435

BGA Voiding for RoHS | 13 November, 2009

Your customer is very unreasonable to demand void-free BGA SJs. Minor voiding is not a condition for rejection per IPC-A-610D, J-STD-001D, or even J-STD-001DS (Space addendum). Having said that, let me tell you that the voiding has little or nothing to do with your profile, but if you want to completely eliminate even minor voiding from the BGA solder joints, simply switch to Kester R520A (SAC305, water soluble) or Kester EM907 (SAC305, no-clean). Your voids will be gone, completely. I am an engineering consultant for the industry, and I perform solder paste qualifications on a regular basis. I have seen these two products kick the fanny of every other solder paste brand in terms of open stencil life, voiding, wetting characteristics, slumping, tack time, and virtually every other solder paste characteristic, even time from refrigeration in a sealed 500 gram Nelco tube. Just get a sample and try it. And no, I do not work for Kester, nor do I get any recompense from them. I am just an engineer who needs to ensure my customers have the best possible materials they can get, and Kester provides that, every single time.

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#60450

BGA Voiding for RoHS | 16 November, 2009

I suggest you X-Ray the devices before you place them on the board we have just foun a large amount of voids on the BGA before its even placed

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#60451

BGA Voiding for RoHS | 16 November, 2009

I agree customer is being overly stringent, and that their is a possibility that BGA's have voids prior to installation. If you determine that the BGA's do not have voids prior to installation I suggest you slow down your ramp speed to allow the flux more time to evaporate. Remember that with ROHS solder paste the flux is more robust and more time needs to be allowed in the ramp speed. Also check the humidity of your facility. High humidity can cause moisture to get in the solder paste and cause voids too.

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CL

#60454

BGA Voiding for RoHS | 16 November, 2009

Thank you for your responces.

Chris

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