At 16:23 29.01.2004 +1100, you wrote:
I just would like to ask a question about how you handle TO-220 footprints (& the like)...

I have the three (electrical) pin device, that's fine.
I'm placing the T)-220's flat on the board.

What if I want to (selectively) put copper on the top layer under the TO-220 & have a suitable soldermask antipad? This could aid in cooling without resorting to an actual heatsink.
How should I best do that?


Do I place on the board a free pad, rectangle, with a hole the same size as the hole for the TO-220 tab? Seems a bit ugly, two holes etc etc but it should probably give me the SMask opening.

Do I make a 4pin lib part, have a 4th pin on the footprint being the large hole & add a polygon connected to that net? I suppose I'll have to add an opening for the SMask on the TO-220 footprint as well.

I do it this way. I have schematic symbol for e.g. 78M05T with 3 and 4 pins. Usually I connect this fourth pin (the tab) to the same net than the middle pin, GND in this example. The footprint will have a fourth round TH-pad for the screw. If I like to have some extra cooling, I place a fill or a poly onto the top layer and copy it also to the top solder mask.


regards
Edi



What say you?

--
Regards,

Dom 99SESP6

Dom Bragge, CID MIEEE  | Silverbrook Research PL, PO Box 207
Snr PCB Layout Engr    | Balmain NSW 2041, AUSTRALIA
Ph +61-2-9818-6633xt163| [EMAIL PROTECTED]






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