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BGA ball vs land design problem??

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#58887

BGA ball vs land design problem?? | 25 May, 2009

Hello, recently we changed supplier of the LF BGA, we did corossection and now have doubts... previous BGA specs : pitch 1mm, ball diameter 0.6mm future BGA specs : pitch 1mm, ball diameter 0.4mm

on the crossecrion we found that one of the ball seems cracking from the package - under x-ray we saw void in other ball but this one seem quite normal, checking more BGA under x-rays show more voiding that on the opponent (previous) parts

land pad on the PCB is 0.45, profile is our standard LF and works for most of the products without any changes (12 zones myReflow) supplier of the BGA say that land pad is too big and is generating voiding problems

we will apprieciate any comments on that, as we are beginning with BGA so there is still a lot to learn - IPC 7095 is coming in the next few days

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#58980

BGA ball vs land design problem?? | 2 June, 2009

We've never heard of a situtation where oversized pads caused voiding. Your supplier is correct that the pads on the board should be the same size as the pads on the interposer, but this is to improve reliability issues.

Search the fine SMTnet Archives for more on BGA voiding.

Finally, we're not wild about your supplier using solder mask defined [SMD] pads on the interposer. * Motorola did a study in 1996 that indicated that nonsolder mask defined [NSMD] pads were significantly more reliable. * 3.1X Life Improvement of NSMD over SMD Pads [http://www.amkor.com/products/notes_papers/advpkg_appnotes.pdf]

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#59005

BGA ball vs land design problem?? | 4 June, 2009

Since posting the above comment extolling the virtues of NSMD pads and disparaging SMD pads, we've learned that the points apply to all array devices, but in spite of that some designers of fine pitch [eg, 0.4, 0.5mm pitch] array devices choose SMD with small diameter balls in order to reduce cases of bridging between balls during board assembly soldering.

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