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SOT-223 Flux trapped under part and lifting off pads

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MM

#62786

SOT-223 Flux trapped under part and lifting off pads | 29 September, 2010

We are Currently running a Board and it seems that the SOT-223's on the bottom side have flux and water trapped under the part. Nothing has changed in our process and this is the only board that it is happening on. We are using Kester R562 water washable paste. When we run the top side of the board, the parts sometimes fall from the pads, either tombstoned or up of the pads. When I blow air from the side of the part, there is flux/water underneath the part. My guess would be that the water and flux mixture, when heated, is what is moving the parts? Has anyone had this similar issue? We run these boards many times a month and never had an issue. I was told that no settings on the wash have changed either??? Any ideas would be greatly appreciated..

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#62787

SOT-223 Flux trapped under part and lifting off pads | 29 September, 2010

Take a few parts from the reel and look close at the parts to make sure the bottom surface of the leads is below the bottom surface of the body.

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MM

#62804

SOT-223 Flux trapped under part and lifting off pads | 30 September, 2010

> Take a few parts from the reel and look close at > the parts to make sure the bottom surface of the > leads is below the bottom surface of the body.

Yes I did that and they are below the body. I found the problem I think. The solder mask is above the pads, so when the part is placed there is no standoff. I baked the boards prior and the issue went away. Could it be that the board Manufacturer did not layer the board correctly??

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