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SMT electronics assembly manufacturing forum.


BGA pad size

jdumont

#34941

BGA pad size | 14 June, 2005

Morning all, just took a look at a new board we just got in and the there are different pad areas under the same BGA. What happened is engineering uses wider trace sizes for some pads and those overlap when more than one go to the same pad. This causes there to be no pad but instead 2 thick traces act as the pad. Its hard to verballize what im seeing but basically there is a larger surface area on the pads in the center than the rest of the pads. Will this cause issues when the solder is molten and starts to spread out? I would imagine that since there is more "pad" area the ball will want to drop more than its neighbor will be able to and possibly cause issues....? I have pics if anyone is interested....

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#34955

BGA pad size | 14 June, 2005

Send the vacation pix, pls

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#34957

BGA pad size | 14 June, 2005

How do I send pics....sorry for the ignorance.

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GS

#34964

BGA pad size | 14 June, 2005

You can find useful informations also on last review of IPC-7085 : Design and Assembly Process Implementation for BGA.

Regards

GS

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#34968

BGA pad size | 14 June, 2005

click on the email link, next to the Lou Reed icon, then paste the pix in the form

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#35005

BGA pad size | 16 June, 2005

Josh: You're correct it's tough to describe the layout of the BGA pads and traces.

We wouldn't be too excited about seeing this board either. On one hand, for the obvious lack of care taken in doing the layout, this is a junk board and you shouldn't be concerned. Depending on the various layout approach taken, each ball will have different strengths and afffect on the reliability of the product. We don't think this will affect your ability to build this product.

On the other hand, if you're going to be blamed for producing schlock product, while the designer smuggly trims his fingernails, you should make your concerns known up-front. Consider using 7351 - SMT Footprint Design Guidelines as the basis for your pad design.

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#35019

BGA pad size | 17 June, 2005

Thanks for taking a look at the pics. I have made my thoughts on this type of design known to all. Im going to let this run through and have them put a note in the file for this board to reduce the trace size for the next time the board gets rev'd up. Good thing us mfg people are keeping the design guys in check!

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kenscj

#35026

BGA pad size | 17 June, 2005

Hi all, currently, we are seeing BGA problem like solder ball misalign, void, solder short (all under BGA, tested with 5DX), after reflow. We examine the solder ball (raw material of BGA), and see that the ball surface is not smooth, will that affect the solder ball problem above? How to check or measure the condition of the balls?

Any advice on these problems? Thanks.

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#35028

BGA pad size | 18 June, 2005

kenscj: Responding to your points of interest: * On the smoothness of BGA solder balls causing solder ball misalign, void, solder short after reflow: We expect the solder balls to be smooth and have no sharp irregularities. We can't recall attributing these types of failures to irregular or unsmooth balls. * On misalignment of solder ball: This may be caused by design of the board, improper placement, or handling. * On voiding after reflow: This may be caused by an improper reflow recipe. Search the fine SMTnet Archives for previous dialog. * On shorting after reflow: This may be caused by an improper reflow recipe, paste printing, or handling. Search the fine SMTnet Archives for previous dialog. * On checking or measuring the condition of the balls: Look here: http://www.reed-electronics.com/tmworld/article/CA187553.html

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kenscj

#35055

BGA pad size | 21 June, 2005

Hi dave, Thanks for the comment. I have another issue. The board already pass Test and Burn-In processes, but after 2 months the BGA contact is found open (no contact on certain balls). How can that happen? Is it during build, the solder ball already intermitant? Thanks.

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