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Solder Paste Dispensing for BGA repair

Ted C


Solder Paste Dispensing for BGA repair | 16 November, 1999

Is anyone out there using automatic despensing equipment rather than stencils for depositing paste on BGA patterns prior to placement/repair. What is minimum dot size that can be reliably applied. Pro's/con's?

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Jeff Ferry


Re: Solder Paste Dispensing for BGA repair | 23 November, 1999


We've tried using dispensing systems but without success. We either use stencils or bump the pads with solder. Stencils are messy and time consuming, but seem to be the best thing going.

Jeff Ferry Circuit Technology Center

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Re: Solder Paste Dispensing for BGA repair | 26 November, 1999

Jeff & Ted,

we have used a dispensing system too and yes, I agree, we are not too happy with the results. Not at the point that it doesn't work, though. I think our problem basicly is that we have selected an entry-level dipensing system. We are applying dots for 50 mil pitch BGAs, mostly using #23 needles. Main problems are: - clogged nozzles whenever there is a minor inconsistency in the paste (air bubbles, etc.) - solder spheres forming slivers within the archimedes screw - it takes an eternity to purge the needle every time you start or stop work - inconsistent dots whenever anything is not 100% right For many boards, we need to clean paste off and start over. However, I have heard of excellent results by people using a high-end machine (an in-line Camelot 5000, if I'm not wrong) which has more bells & whistles built-in. Details like the software control, that allows to precisely set on-, off-, and dwell times for the dot cycle, all sum up to make the difference. So I believe dispensing is still a good choice if you can afford/justify equipment that gives you enough process control and up-time. If I had to start-up again from scratch, I would invest in looking for a dispensing system with: - enough control over process parameters - a rugged construction of the "heart" (basicly the screw, and z-height control) Now a few questions for Jeff: - which BGA stencil device and/or vendor would you recommend, and why - why are stencils "messy and time consuming"? It shouldn't be such a tricky process - or not? - what is that .... "bump the pads with solder" ????? - you too heard somebody suggesting to apply paste to the component as opposed to the PCB?



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Re: Solder Paste Dispensing for BGA repair | 26 November, 1999

Jeff, Ted, Stefano

What Stefano is saying sounds reasonable. With entry-level systems its always a struggle to get sufficient results. The operators golden hand is needed. Better controlled advanced dispensing systems should do the work, unluckily I don�t have such a thing. Stencils worke quite well depending on that "golden hand" again, the work space left around the part and the equipment used. The rework equipment should be able to handle stencils that means position them safe and accurate. (could be a three head station, pick and place-, stencil- and reflow head ). It needs a bit of practice to apply the paste but after a few tries you get the feeling. Also I�ve heard of using no paste at all, only a flux paste, as long as the balls are of near eutectic solder should work. I don�t know if that is common practice. Another thing is bumb the device in paste instead of applying it to the PCB is one possible strategie but haven�t tried it and not figured out the parameters to obtain the right amount repeatedly. That�s what�s meant by Jeff, probably.

What�s the best? Wolfgang

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