How do I align these holes?

Layout 3D Models
1

I made a simple schematic using a TIF41 and a heatsink but the holes used to connect them don’t align, can I do it? How?

Capture

2

I think you mean PCB?
To adjust the TO220 transistor height, in PcbNew, edit the transistor properties. Select the 3D model tab and tweak the Z height until the holes match.

1 Like
3

Who says the TO-220 pins need to be fully seated on the PCB? Usually, space is left for tolerances and manufacturer differences. The heat tab hole is the mounting guide, not the pins.

3 Likes
4

It worked, tnks

image

5

BTW; experience tells me that using the hole for heatsink mounting of TO220 packages is not the best method and can work very poorly.

  1. The power semiconductor die is located near the center of the plastic rectangle; not at the hole in the tab.

  2. Worst situation is that you use a soft thermally conductive electrical insulator pad, and the TO220 tab is copper (softer metal). Copper sounds good because it is a great thermal conductor. But what happens is that when you tighten the screw, the insulator pad compresses and the metal tab “dishes” so that you end up with the tab contacting the insulator in only a small area around the screw. You end up with bad thermal conduction.

  3. It is not as bad if you are using only thermal grease (maybe also a thin polyamide or mica insulator) and not too much torque on the screw.

  4. Best (for thermal) mounting method is to clamp the plastic body against the heatsink. One easy way is with a metal bar and two screws; maybe with 0.5 mm of silicone rubber padding between the bar and the device plastic. Of course these methods generally require more space.

I built my own e-load ~25 years ago.

Bobs Bench Electronic Load
Bobs Bench Electronic Load2931×2739 205 KB

EDIT: I have ~half inch square steel tubing running across about 4 TO220 transistors, with screws compressing bar to rubber pads to transistors to insulators to heatsink. Screws located at the bar ends. Silicone rubber pads between the bar and each transistor body.

I used insulators of this general type:

It is still working well.

6

Just a note. When you bend the TO-220 leads be sure it is not a sharp bend but has a bend radius. Ideally the bend radius should be 3 to 5 thicknesses of the material.

1 Like
7

There are TO220 heatsinks that are specifically made to clip onto the body of the package. If space is a concern, this style may work for that application. Or use a nylon screw through the tab which will stretch/break/strip under excessive torque before the copper tab dishes. (And being nylon assists maintaining electrical separation between the tab and the heatsink if that is desired.)

8

IMHO I do not like the nylon screw. There may be some better rated ones but the first I found

are rated at 185 degrees F = 85 degrees C. That seems marginal at best, and I have seen nylon break apparently simply due to age. There are other plastics which might be better but beware of “cold flow”. None of this bodes well if you want something to work well for years.

BTW “my plant” (see link) is an heirloom tomato plant, and I did not see anything at McMaster for that.

9

This topic was automatically closed 90 days after the last reply. New replies are no longer allowed.