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Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


BGA underfilling

emmanuel

#18145

BGA underfilling | 12 November, 2001

We are to use a PBGA 272 and a PBGA 388. Between 500 and 750 thermal shocks (-45�C/+125�C), we have noticed that some cracks appear in the solder joints. According to our component specialists, these cracks are due to the whole design (pcb, component,..) and not from the assembly process. I would like to know if underfilling is a solution to improve the behaviour of BGAs during thermal cycling and if somebody has yet tested it ?

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CAL

#18149

BGA underfilling | 12 November, 2001

One of the key elements you need to keep in mind......What "Contaminates" are you trapping in with the undefill. In my personnal opinion I do not think you will gain anything. I would spec a component best suited for that environment. I know ACI has written articles on this, check the Aug 2001, Jul 2001, and March 2000 and also check http://www.empf.org/html/empfset.htm.

Cal Manncorp

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#18154

BGA underfilling | 12 November, 2001

Underfill is primarily used in flip chip, CSP attach applications. It is used to balance the differing thermal expansion rates for an organic board, solder, and silicon die. There are a fair number of papers written on this in the SMTA [www.smta.org] Knowledgebase.

Although in the beginning they did, but now, BGA rarely use underfill. Some hi-rel, space, applications underfill their BGA. Maybe check NASA.

What is the correlation between failures in your stress test environment and failures in your product use environment?

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Terry Burnette

#18184

BGA underfilling | 15 November, 2001

Underfilling PBGA's will increase the PCB level solder joint life by 4x-5x but we only recommend underfill for products going into extreme environments. Normally the 272ld and 388ld PBGA's solder joints when cycled at -40C to +125C should not see any fractures up to 3000 cycles. Something is very wrong when you get fractures at 750 cycles. I believe the 272ld and 388ld PBGA's you're referring to are Motorola packages. If so contact me via email and I'll help you to get to 3000 cycles without underfilling.

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#18186

BGA underfilling | 15 November, 2001

Hey Terry. You make points that would be interesting to many here on SMTnet.

Your suggestion to take this conversation off-line and onto e-mail is not in the spirit of sharing knowledge that we on SMTnet cherish. Please keep this conversation on-line so that all can benefit, not just a few.

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emmanuel

#18220

BGA underfilling | 21 November, 2001

Yes, i confirm you that the BGA i'm refering to are Motorola BGA. The fractures that appear after 500 thermal cycles (-45�C/+125�C) are located in the solder joint/pad connection. We have been asked if this fractures are due to BGA & PCB design or to our process parameters. At the present time, we have no right answers. That's why, any hint from your side might be hepful.

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