Mounting & Soldering TO3's

[Screech]

Whats the procedure?

My guess is to:
Use 3mm half round bolts and nuts.
Nuts hit a step on the transistor.
Should i use a 3mm spring washer there?
3mm seems too small for a 4mm hole.
Should I solder the bolts head to the board or not?
My supplier only sells metric fasteners. Is that ok?

Am i on the right track?
thanks

 

[Nigel Goodwin]

Whats the procedure?

My guess is to:
Use 3mm half round bolts and nuts.
Nuts hit a step on the transistor.
Should i use a 3mm spring washer there?
3mm seems too small for a 4mm hole.
Should I solder the bolts head to the board or not?
My supplier only sells metric fasteners. Is that ok?

Am i on the right track?
thanks

I can't say I've ever looked what size bolts to use?, just ones that fit!.

A TO3 device is generally bolted to a heatsink, often a large one, as the case is the collector you usually require an insulating kit, consisting of a mica washer and two plastic spacers that fit in the holes of the transistor - these take up space in the holes and require a thinner bolt.

 

[Screech]

I dont nead to insulate, as the heatsink will sit on the fibreglass board.(component side).

Whats better for soldering, chrome looking bolts or the brass ones?
Do I still nead to solder the bolt to the board or not?

What do you guys do and use?

 

[Oznog]

I dont nead to insulate, as the heatsink will sit on the fibreglass board.(component side).

Whats better for soldering, chrome looking bolts or the brass ones?
Do I still nead to solder the bolt to the board or not?

What do you guys do and use?

Wouldn't use a TO-3 on a board at all! If you don't need a heatsink, then it seems unlikely you're making more heat than a TO-220 pkg can handle, and the TO-220 is far more board-friendly. Few components made only in TO-3 anymore, the pkg is becoming obsolete, partly because they're hard to mount as you note.

TO-3 is also mounted with sockets, I think Radio Shack still sells them. The pins are pressed in, not soldered. I seem to recall the bolts will hold both the socket and transistor onto the board/sink.

You never solder bolts, you'd never be able to remove them.

 

[Nigel Goodwin]

Wouldn't use a TO-3 on a board at all! If you don't need a heatsink, then it seems unlikely you're making more heat than a TO-220 pkg can handle, and the TO-220 is far more board-friendly. Few components made only in TO-3 anymore, the pkg is becoming obsolete, partly because they're hard to mount as you note.

I agree that TO3 is a strange choice for mounting on a PCB with no heatsink, as you say if you don't need the TO3's high power handling why not use a more user friendly case style?.

TO-3 is also mounted with sockets, I think Radio Shack still sells them. The pins are pressed in, not soldered. I seem to recall the bolts will hold both the socket and transistor onto the board/sink.

Sockets have been used very occasionally, but it's very rare, mostly due to the cost - plus soldering gives a better contact anyway.

You never solder bolts, you'd never be able to remove them.

It's fairly common practice with PCB mounted TO3, the bolts stick up through the board with the heads soldered to the PCB, the heatsink and transistor slide over the top, and are secured by shakeproof washers and nuts. There's never any need to remove the bolts, you just unscrew the nuts off the top. I've also seen the other way done, with the nuts soldered to the PCB, and the bolts down from the top.

For a third way, you also see just the nuts and bolts, without any soldering.

I don't think it makes a great deal of difference, just that soldering either the nuts or bolts makes it easier to assemble or replace - no fiddling about with bits in both hands (and possibly teeth!).

 

[Screech]

Thanks guys. I learnded some thing again.