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

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


Mr Mariscal

#13237

SRT BGA Rework | 18 December, 1998

I have been developing a BGA Process and are having problems with a 310 IO PBGA reflowing. I am achieving good wetting exept 2 to 5 balls on the outer perimeter I have a good profile my air flow is set per mfg spec, the strange thing is that it does not happen every time I reflow a part. the damm thing is inconsistant.

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Dave F

#13238

Re: SRT BGA Rework | 18 December, 1998

| I have been developing a BGA Process and are having problems with a 310 IO PBGA reflowing. I am achieving good wetting exept 2 to 5 balls on the outer perimeter I have a good profile my air flow is set per mfg spec, the strange thing is that it does not happen every time I reflow a part. the damm thing is inconsistant. | | Miguel: Don't bet you life on the manufacturer's spec. It's just a guess to get you in the ball park. Check the following:

1 Paste Printing: Paste will be the sparsest on the corners, then at the edges. Check stencil design, lower squeegee angle, make sure you always have 1/2 to 3/4 inch diameter paste roll. 2 Component Warping: Plastic BGAs tend to lift at the corners during reflow, both during fabrication and assembly. Check BGA incoming quality for planarity, check for warping of the BGA carrier pre and post reflow (overmold won�t warp), slow down soak on your profile, increase paste deposit slightly. 3 Board Design: Check board fab incoming quality, check for warping of the board fab pre and post reflow, check if unplugged (poorly plugged) vias attached to problem balls are starving the BGA pads of solder.

Having said that, I just noticed that the title of your quiry is: "SRT BGA Rework." Are you reflowing the BGA with a rework station or a reflow oven? If rework station, all of the above applies plus:

1 Board Preparation: Check that the under-board heater is preheating the board surface properly. Many rework stations have underside heaters that are way too wimpy for the level of patience rework people have, density of boards containing BGAs, and the components on the board. 2 Nozzel Selection: Check that the nozzel correct for the BGA, determine if the nozzel is mating to the board properly.

TTYL

Dave F

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john watt

#13239

Re: SRT BGA Rework | 23 December, 1998

| | I have been developing a BGA Process and are having problems with a 310 IO PBGA reflowing. I am achieving good wetting exept 2 to 5 balls on the outer perimeter I have a good profile my air flow is set per mfg spec, the strange thing is that it does not happen every time I reflow a part. the damm thing is inconsistant. | | | | | Miguel: Don't bet you life on the manufacturer's spec. It's just a guess to get you in the ball park. Check the following: | | 1 Paste Printing: Paste will be the sparsest on the corners, then at the edges. Check stencil design, lower squeegee angle, make sure you always have 1/2 to 3/4 inch diameter paste roll. | 2 Component Warping: Plastic BGAs tend to lift at the corners during reflow, both during fabrication and assembly. Check BGA incoming quality for planarity, check for warping of the BGA carrier pre and post reflow (overmold won�t warp), slow down soak on your profile, increase paste deposit slightly. | 3 Board Design: Check board fab incoming quality, check for warping of the board fab pre and post reflow, check if unplugged (poorly plugged) vias attached to problem balls are starving the BGA pads of solder. | | Having said that, I just noticed that the title of your quiry is: "SRT BGA Rework." Are you reflowing the BGA with a rework station or a reflow oven? If rework station, all of the above applies plus: | | 1 Board Preparation: Check that the under-board heater is preheating the board surface properly. Many rework stations have underside heaters that are way too wimpy for the level of patience rework people have, density of boards containing BGAs, and the components on the board. | 2 Nozzel Selection: Check that the nozzel correct for the BGA, determine if the nozzel is mating to the board properly. | | TTYL | | Dave F | Have you got enough solder paste there to start with ? If it's an SRT repair machine how are you applying the paste ?, if your using a miniscreen onto the board it's possible to lift paste as your moving the stencil away so lifting it straight up helps, alternatively you could paste the balls of the BGA then place it.

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