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caps moving from pads

Views: 954

#36755

caps moving from pads | 21 September, 2005

We are having problems with a 1210 cap moving as far as a 1/4 inch from its pads during reflow. We have verified the placement before reflow. They will tombstone some of the time. There are smaller and larger parts around this location and none of them move. 85% of this part solder fine. Any suggestions? Thanks

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James

#36757

caps moving from pads | 21 September, 2005

It could be outgassing, are there any electrolitic caps or anything else nearby that may contain air or moisture? You could try baking the parts before use.

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Rob

#36762

caps moving from pads | 21 September, 2005

It's quite a big cap so try taping over about 25% of both apertures to restrict the volume of paste printed then see what happens.

Also, is anything interfering with the part during placement? or are you 100% sure it's going into the oven ok? if not try placing it last & ensure the part data (inc. height) is OK and the feeder is 100%

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PWH

#36767

caps moving from pads | 21 September, 2005

We've had parts jump off pads on occasion due to panels or boards that are restricted in a carrier during reflow. The boards/panels expand and the restriction causes them to warp thus popping parts around during cool down. Doesn't sound like your problem but just a thought. Also, maybe the "skirts" in a nitrogen chamber oven could be rubbing across the parts and moving them if they are still liquidous? Or... try changing travel directions of board in the oven as blowers could move stuff around.

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#36768

caps moving from pads | 21 September, 2005

I am going to agree with Rob a little. It is also possible that a internal ground plane might be under or connected to the pads of this cap thus causing a increase in temp to this part during reflow. This can cause parts on occasion to jump from the pads. It is also possible that some of the parts are contaminated and are rejecting solder. If so, during the liquid stage of reflow the blowers can blow the part away from its location. I think the simple fix is to possibly apply a small amount of SMT epoxy adhesive between the pads before placement. This will hold it still during reflow. Hope this helps.

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