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BGA failure after coating

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#60018

BGA failure after coating | 30 September, 2009

Hi

We have a board at the moment thats passing ICT and passing functional test but its failing test after conformal coating has anyone had any experinces of this? or any idea what may be causing this?

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Pete B

#60019

BGA failure after coating | 30 September, 2009

What type of conformal coating are you using and are you allowing the coating to migrate under the device in question?

If you are allowing the coating unbder the BGA the problem could be CTE of coating is much greater than that of the BGA balls/solder joints. This can result in the BGA joints being fractured as the coating material expands under the device when it heats up in operation.

Just a thought....

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#60023

BGA failure after coating | 30 September, 2009

What does failure analysis of the BGA indicate? Is this: * ESD damage * Open circuits * Shorting

What's the problem?

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#60025

BGA failure after coating | 1 October, 2009

what we are getting is open circuits not every BGA is failing we use Humiseal 1A33 and currently there is no masking instruction for around the BGA

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#60028

BGA failure after coating | 1 October, 2009

We doubt that Humiseal 1A33 is causing opens in your assemblies. We'd guess the opens occur earlier in the process, but are not hard failures. So, you pass your tests. When applied, the conformal coat flows into the gap in the ball crack and insulates the two sides of the ball crack.

To substantiate this theory: * Fail BGA are difficult to repair [because of the Humiseal 1A33 on the pads] * Pop a failed BGA off the board and check the surface with a black light. 1A33 contains a fluorescent tracer for inspection purposes. There will be Humiseal 1A33 on the pad. * Of you really want to go full FA, do dye penetrant analysis prior to coating. Search the fine SMTnet Archives for more on this.

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#60046

BGA failure after coating | 5 October, 2009

we suggest as below : the first : check the soldering(solder ball and pad) by X-ray ; second: to do dye analyse

(note:pls confrm is there have crack )

Attachments:

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#60065

BGA failure after coating | 8 October, 2009

I have used 1A33 for many years with excellent results on through-hole pcbs in equipment subjected to very hot and very cold environments. Because 1A33 continues to harden with time, I assumed it would simply not be usable on smt boards, cracking the joints with heating and cooling cycles. I have not seen much anecdotal evidence one way or the other, except for a couple comments here suggesting this could be a problem for both polyurethanes and acrylics. For the time being, I'm using silicone because it remains flexible, but I would like to hear other's opinions, especially for arctic and desert applications. I have heard one opinion that silicone has problems in hydrogen sulfide environments, too.

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kpm

#60068

BGA failure after coating | 8 October, 2009

We've used both 1A33 urethane and 1B31 acrylic coating on our SMT assemblies with great success for many many years. This is with components of all shapes and sizes including a 9 ball micro-BGA. We apply the coating in every way imaginable and we have never experienced it hardening under a component and fracturing a solder joint.

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