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The Knowledge and Know-how Connection
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May 24, 2013
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Solder Paste Volume for BGA Rework
Since rework can never be as controlled or consistent as original assembly, should we use slightly more paste during BGA rework to compensate for irregularities or flatness, pad conditions and so forth?
Board Talk is presented by ITM ConsultingVisit ITM Consulting to learn more.Phil Zarrow, ITM ConsultingWith over 35 years experience in PCB assembly, Phil is one of the leading experts in SMT process failure analysis. He has vast experience in SMT equipment, materials and processes. Jim Hall, ITM ConsultingA Lean Six-Sigma Master Blackbelt, Jim has a wealth of knowledge in soldering, thermal technology, equipment and process basics. He is a pioneer in the science of reflow.
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Views: 2106
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I personally have replaced literally hundreds of thousands of BGAs in past lives, and I have found it is better to not use any paste at all when replacing a standard BGA (this does not apply to CGAs or CCGAs, of course). Here are some of the reasons why: 1) As you stated, applying solder paste by hand is a process that is operator-variable. Some operators simply cannot perform this operation, others can do it better than the automatic printing process can. 2) Inevitably there will be smudges/smears that lead to bridging or other defects. 3) Some BGAs will not work properly with a reduction in the spacing between solderballs (high-frequency RF circuits or switching power supply components). 4)It takes a fair amount of time to set up the stencils, squeegees, paste, etc., and this adds quite a bit of cost to the rework process. 5) The solder paste often induces voids during reflow.
I find that using a good tacky flux, and placing the BGA directly onto the fluxed pads and then reflowing works far better, and will not induce the voiding into the finished solder ball that paste does. But if adding paste works for you, stick with it. I am just saying it is not a necessary practice, and going without paste will not reduce the reliability of the rework process one bit.
Richard Stadem, General Dynamics AIS