Printed Circuit Board Assembly & PCB Design SMT Electronics Assembly Manufacturing Forum

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


Cracking

Views: 3155

Grant

#43790

Cracking | 7 September, 2006

Hi,

We have seen a slight rise in failures in a product, and on investigation, the BGA ball has cracked off the PCB. It's below the intermetalic layer in the ball. Reflow otherwise looks good, and the raw components are clean.

I am wondering what could cause this, and what advise people might have.

We are using flash gold on the PCB's I think, and could there be too much gold, so the intermetalic is too weak? We are running SAC solder from Koki.

Also, we are checking handling issues of the PCB, as this could be it.

Does anyone know of any other causes that I might not be thinking about?

Regards,

Grant

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#43801

Cracking | 7 September, 2006

BGA cracking is caused by mechanical stress. This may be the result of: * Rough handling of soldered board * Inadequate consideration during package design of CTE effects on BGA * Poor control of or selection of thermal ramp rates during soldering

We've talked about flash gold on SMTnet several times previously. One example is: http://www.smtnet.com/forums/Index.cfm?CFApp=1&Message_ID=38283

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#43803

Cracking | 7 September, 2006

We had similar problems with some of our products and found the root cause was our ICT fixture. The damaged balls/pads were always in a certain locations so finding the pattern helped. It also didn't help that the boards were ICT'd 10 + times.

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Bubba

#43805

Cracking | 7 September, 2006

Why 10 plus times?

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Grant

#43988

Cracking | 16 September, 2006

Hi,

Could it be shocks in transit? This is only happening on 1 product, so might point to chassis and packing design.

Does anyone know of any shock indicators that we could put inside the chassis to see if the faults are caused by this? I have seen these on shipping creates and wondered if someone made them for products.

What kind of stock can products handle safely?

Regards,

Grant

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Brad Courtemanche

#44017

Cracking | 18 September, 2006

Crazy Question, but do you know who the board house is that is making the boards. We also use alot of flash gold and have noticed many problem with one particular board house.

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#44025

Cracking | 19 September, 2006

Tom Clifford over at Lockheed put out a great Gold calculator. It works quite well in finding where you should be abd where you actually are with gold content. Is there any type of heat sink being applied to the device? Something that maybe gets screwed down to pull against the underside of the part for tension? In a past life we had that very thing happen., as the torque specs were incorrect.

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Grant

#44048

Cracking | 19 September, 2006

Hi,

Yes, we do. Above that component we have a heat-sink to the metal chassis. We are thinking shocks to the chassis could be traveling into the board from that point.

Grant

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