1st question…, My board has a to-220 package regulator and it lays on the PCB. I have set the mounting holes but I’m wondering if there’s a correct way of aligning the hole in the heatsink tab and the mounted hole in the PCB. I guess I have it pretty good but it seems like there would be a locking or alignment snapping feature.
2nd question…, Is there a correct way to assign the to-220 to the mounting hole? Right now when I run the error check the I’m getting “drilled holes to close” and “courtyards too close”, (sorry, don’t have computer in front of me). Well yeah, they are too close, the tab hole is literally aligned with the mounting hole. I think I could play with the clearance in both the to-220 and the mounting hole to get rid of the error but I’m assuming there’s a correct method, which I’d rather do.
There is no inherent alignment or locking feature of the TO-220 package for the tab hole in any horizontal footprint. The hole in the footprint is there for you to put a mechanical fastener (like a machine screw and nut, though I’ve seen the occasional board where they pop-riveted the TO-220s down). I hope you left clearance free of traces on the bottom side of the board for the fastener…
It isn’t dumb at all. It is used to thermally connect the package of the TO-220 to the thermal mass of the PCB, and/or sandwich an actual heatsink between the package and the PCB. It might not be what you want for your application, but it is a real and valid reason for being there.
(Also to mechanically attach the TO-220 to the PCB so impacts and vibration don’t flex and weaken the legs of the TO-220.)