Screaming Circuits: Surface Mount EMI Gaskets


Surface Mount EMI Gaskets

Here's an interesting board.

Emi_sponges_on_board_edgeEMI gaskets have been around for a long time. Some are foam. Some are springy metal and some are wire braid. They all do the same things though - create a seal between your EMI source and your EMI shielding. We ran this board recently that uses a foam gasket from Gore Industries. It's a pretty cool product in that it can be run through our SMT machines just like any other surface mount part. No secondary or hand operations are required.

While I have the picture of the board up, there are two things I'd like to point out. (Always have to be the critic. Right?)

Emi_sponges_top_view_2 [Click the picture for a closer view] First, at the label "A", there is a part that looks to require a specific orientation. It has four leads and a directional marker on the part. You will note, however, that the board doesn't have a pin on or polarity indicator any where. We got it right - probably had an assembly drawing or illustration, but a pin one mark on the PCB would be a much more reliable method.

Second, at the label "B", you will notice that one of the pads for the little cap is in the middle of a real thick trace. The other pad has a very tiny trace connected to it. There may have been an impedance reason for doing this. I don't specifically know, but if not, you should avoid a layout like that with small parts. The thicker trace on one side can act like a heat sink and slow the paste melt on that side. Then when the solder paste on the other side melts first, surface tension can cause the part to pop up like a tombstone.

Duane Benson
EMI is mighty fine

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Comments

Thanks for the post great information, if I am not wrong this it come in use in the computer.

Thanks for the post great job keep it up....

thanks for ur presentation.nice job

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