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CERSOT-23 solder on top of package

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#78498

CERSOT-23 solder on top of package | 25 July, 2017

I have some CERSOT-23 transistor packages with castellated terminals. The 4th lead (drain castellation) is electrically connected to the top of the device by the castellation. The castellation goes up the ceramic body and contacts the metal package top. The metal lid is soldered to the metal package top to provide a hermetic seal. During assembly, solder has wicked up the 4th lead castellation and is in contact with the hermetically sealed lid. Per IPC-A-610, solder is allowed to flow over the top of the castellation as long as it doesn't contact the body. Does anybody know why solder on top of a castellated terminal IC body is a defect? What should I be concerned with - reflow of hermetic seal resulting in internal solder balls?

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#78501

CERSOT-23 solder on top of package | 25 July, 2017

Looks like you have a great wetting of your paste :). Once body has been in contact with molten solder, the package could suffer damages on the body(outside and inside) and on the circuitry inside. It is considered a defect. I have seen that before and most time it comes from too much solder and the good wetting we were talking about. Decrease the paste amount on your stencil(tape apertures if possible) and try again.

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