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

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Double sided BGAs

Irene Taylor


Double sided BGAs | 23 June, 2005

We are defining a new assembly process for a double sided card that has 26 BGAs on the top side and 14 BGAs on the bottom side. We currently have one double sided BGA board with one BGA per side and have to epoxy one BGA (35mm X 35mm - 352 ball count)to keep it from falling off during 2nd reflow. How do you process double sided BGAs at your facility? The biggest BGA on the bottom side of the new board is 17mm X 17mm (241 ball count) Will the surface tension be enough to keep it in place during 2nd reflow?

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Double sided BGAs | 23 June, 2005

You should be fine with this if it is a plastic body, If it's ceramic or some other kind of heavy package you will probably want to check. We process PBGAs up to 35x35 with no glue on many occasions.

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Double sided BGAs | 23 June, 2005

It wouldn't surprise us [too much] if this part wouldn't stay for second sided reflow. * If the lead contact area to weight is less than 44 gm / inch^2 [we know the units are goofy, but convient], it'll stay. * Alternately, just run a scrap board and see if it stays. * Alternately, run the boards on a pallet.

The potential downside of not gluing is the weight of the component may create "elongated" solder connections that in some high reliability applications may not be acceptable.

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Double sided BGAs | 23 June, 2005

Luckily I haven't needed to do very many bottom side BGA placements.

But I have also heard of trying to use a higher temp solder for bottom side only and your normal solder for the top side. This way the bottom side solder doesn't get hot enough to melt again when reflowing the topside.

Anybody ever do it this way and were the results good?

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