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BGA shorts that can't be found.

Hon Choi


BGA shorts that can't be found. | 15 May, 2003

Dear all,

Not sure if you have this experience, but we've been seeing shorts on the BGA's from a widely known supplier "i". These shorts can not be found on the X-Ray, and when we remove the BGA, the component is ok. We peeled a few BGA's off, and could not find any shorts either. Wondering if anyone has seen this type of thing before.

Thanks, Hon

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BGA shorts that can't be found. | 15 May, 2003

Have seen similar circumstances a couple times. Possible causes:

1) PCB defect - remove the BGA and inspect/test the PCB for shorts. ( trace short, layer short etc )

2) PCB defect that only shows up when the BGA is populated - a short somewhere on the PCB, and the BGA is not the fault, but part of the circuitry. Remove the BGA, short dissapears. Replace the BGA, short returns. These are the fun ones to find

Good luck!


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David Ratte


BGA shorts that can't be found. | 15 May, 2003

Do any of the pcbs work with the bga? i.e. some work and some dont? It sounds like a layout issue.

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BGA shorts that can't be found. | 15 May, 2003

we have seen something similar,at the edge,sof the Bga the tracks were shorted with some burr and excess gold. It was very hard to find but it was root caused back to the BGA manufacturing process.

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BGA shorts that can't be found. | 16 May, 2003

Could we be seeing trapped water or flux underneath the BGAs?


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Hon Choi


BGA shorts that can't be found. | 17 May, 2003

Thanks all.

We are using no clean, so the boards are not washed. That would eliminate the trapped water issue.

We would check the PCB after dismounting the BGA, and the short would not be found. When we place another BGA on the board, the board would be okay also. We would reball the BGA and put it on a good board and it would test okay also.

I'll check into the flux issue.

Thanks for your input! Hon

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BGA shorts that can't be found. | 21 May, 2003

I need to first understand what "Peeled the BGA off" means. Was heat used? was this the pry and lift method?

We had shorts under some BGA's we have and the solder was bridging from lead to lead but not on the board level at the FR4 on the BGA creating an arch. Our x-ray has a rotating head and were able to see it at an angle. Also,I would look under the component with an endo scope. Hopefully this will show some details not seen with an x-ray. If you have no endo scope call the local reps and have them come in for a demo....they love success stories.

Cal Communications Test Design, Inc

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Neil Trelford, Nortel


BGA shorts that can't be found. | 12 September, 2003

Even though you use a no clean process, it is still possible that some type of fluid has created the "short". Production lines are notorious for using cleaning chemicals on PCBs to clean excess flux after rework on other areas. Unless this type of cleaning material is qualified so that it offers no risks, it is basically inert, it should not be used. I have seen many instances when the cleaning materials mixed with the residue fluxes & thermal transfer /heat sink materials remain on boards & create fail modes.

Regards Neil

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BGA shorts that can't be found. | 12 September, 2003

What is the surface finish of the PCB?

Tin? Imersion Silver? What flux is used in wave solder and / or SMT?

I have much experience with silver migration and tin wiskers. Both can disappear during a reqork cycle. Both can be extremely difficult to detect with x-ray. Both can cause a hard short and blow lke a fuse during test.

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