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Double-Sided BGA Process

Simon UK


Double-Sided BGA Process | 14 September, 2004

Hi All,

Ok, now i have hit a brick wall with our design department and due to limited space on our standard sized boards we are going down the Double-Sided route.

We have a 8 zone (4 Top/Bottom) Quad ZCR Convection (Ok! you can stop laughing!) and i dont have any experience of this type of contruction or thermal mass.

All BGA's are plastic both top and bottom. some BGA's have one directly ont he reverse side.

Any useful direction as in what i need to do to proces this new design as now im concerned over the process, im hoping it is like doing the same with QFP's, but in reality i know its not that simple..

Can anyone help please?

Thanks in advance Simon

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Double-Sided BGA Process | 14 September, 2004

Hi Simon,

Good luck mate.


PS.We try to keep all of the BGA's on side 2, and then glue spot the QFP's & other heavier components that have to go on side 1.

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C Lampron


Double-Sided BGA Process | 14 September, 2004

Hi Simon,

I would recommend a thermal profile on a BGA that is mounted directly over another one. The best way to accomplish this is to drill through the first side BGA to just break through the second side. (assuming you have a board that you can destroy) Run a thermocouiple though here and profile per your paste recommendations. You can figure that the mirrored BGA'a will be more difficult to process than ones not mounted over another one. As far as running a BGA upsidedown, there should be enough surface tension to be able to run it. If not, o drop of water soluble solder mask will hold it in place for processing.

Good Luck


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Double-Sided BGA Process | 14 September, 2004

I'm with Chris' approach as a first effort. If you don't have any luck, consider using a high (reflow)temp solder paste for the first pass reflow, and your standard solder paste for the second pass refow. Years ago I had a similiar challenge with an 8 zone oven, and 5 mirror image QFP's. We developed a reflow profile with the board sitting directly on the mesh belt. (Scary hugh!)This prevented "dropsy". May the force be with you!!

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Double-Sided BGA Process | 15 September, 2004

Hi Simon,

do not forget BGA have more surface contact ( qty off balls) then a same size of QFP. I mean, theoretically unless the BGA is very heavy, it is more simple to solder mirrored PBGA then try to have QFP on bottom side to be soldered. Are plenty of years we do assembly DIMM or similar memory cards where top side and bottom side of PBA there are mirrored PBGA (rectangular 14x22 mm). Very easy. A little more complex is the repair, but it can be done by skilled operators.

rgds GS

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