installing TO-220 Packages

[Stuartambient]

The local hardware stores in my area carry wave washers so that is what I usually end up using if anything.  In a production environment, I would get the right parts online.

Yep, local hardware had wave washers and even Bellevilles but I went with the wave.  They even had thermal grease  Thank you!

[David Hess]

The local hardware stores in my area carry wave washers so that is what I usually end up using if anything.  In a production environment, I would get the right parts online.

Yep, local hardware had wave washers and even Bellevilles but I went with the wave.  They even had thermal grease  Thank you!

You must have better hardware stores.  Around the St. Louis area, thing are pretty stark.

Keep in mind that a single wave washer will probably not apply enough force by itself but several can be stacked to increase it.

[Stuartambient]

You must have better hardware stores.  Around the St. Louis area, thing are pretty stark.

Keep in mind that a single wave washer will probably not apply enough force by itself but several can be stacked to increase it.

Their alright, though when I needed left handed lock nuts they looked at me like I was crazy  McMaster is still a great place for all things fastening but the shipping charges can be steep. 

Well I bought a few extra so that's good. Note says 125-350 pounds (550 to 1500N) but I have no way to measure torque. I'm not sure if the wave should be depressed to any degree or just when I get to it feeling tight? 

[Paul Moir]

Well I bought a few extra so that's good. Note says 125-350 pounds (550 to 1500N) but I have no way to measure torque. I'm not sure if the wave should be depressed to any degree or just when I get to it feeling tight?

The wave washer is likely going to be fully crushed by that point.  That works out to be around 3 to 5 inch lbs on a 4-40, which is pretty snug for that little guy.  If you can figure out how to rig it up on a screw driver, that's 1 lb on a 4" arm or .5 lb on an 8" arm, etc.  Can be done with weights, fish scales, vice grips, etc.  Or for the experienced screw turner:  snugged up about all the way.

[Stuartambient]

The Caddock notes are confusing.  They say Belleville or conical washers but after stating the pressure, it goes on to say "most commonly available Belleville washers cannot provide enough force and will flatten out, rendering them useless".

Possibly the wave washer and conical (belleville) work differently and the torque needed for the later might not be necessary for the former?

[David Hess]

I would do two things:

1. Include a flat washer below the wave washer to distribute the force more evenly onto the plastic package.
2. Compress the wave washer (or washers) until just before they are fully crushed.  This will avoid the need of a torque wrench and apply the maximum force available while allowing the minimum of leeway for thermal expansion.

If your application is more critical than the above will support, then accurate torque applications and measurements will be needed to find out what is really going on.

[Simon]

What about a good old spring washer ?

[Brutte]

I was hoping to avoid having to ask another question here for a while  but I've searched pretty well on one part of the question and haven't come up with anything.

First - Any issues with soldering wire directly to the leads?

Stranded wire is more problematic than solid core during soldering. It just takes more time to assemble (adds cost). Also significantly more expensive. The worst thing is that after soldering a significant part of stranded wire sucks solder inside and a solid core wire is created there. If bent, it would crack near the stranded-solid border. Thus I would not solder stranded wire to anything. If you need stranded wire there, use clamped terminals and solder clamped terminals.

As of soldering something heavy to TO-220, these packages are made with quite long terminals (40mm?). If you put some weight at its end, you must not allow any plastic deformations of Cu or it would crack from vibrations or during installation/maintenance.

These hints apply for production of medium volume. If that is ten or million then that is a different story.

Also there are some recommendations for the washer used to mount the chip.  Recommends a Belleville, spring or conical washer but then says for this particular package Belleville's don't provide enough force and will generally flatten out.  So I'm left wondering which ones will work if anyone knows?

Everything depends on how close to the border of power dissipation you are. Is there any custom heat sink involved? TO-220 is quite popular and there are spring clips available for heat sinks. These are much easier (cheaper, faster) to install manually. You can also solder the tab to a PCB or steel case (with a serious soldering iron).

[Stuartambient]

If you need stranded wire there, use clamped terminals and solder clamped terminals.

I'm assuming you mean wire terminated with a clamped terminal like an o-ring type?

I was planning on using stranded wire, I have no solid core here and the stranded is very flexible in silicone insulation.  I'd think it would have less chance cracking.

[Brutte]

If you need stranded wire there, use clamped terminals and solder clamped terminals.

I'm assuming you mean wire terminated with a clamped terminal like an o-ring type?

I meant crimping. There are many different kinds of terminals, the most popular are blade connectors but there are also those for PCB coldering.

[Stuartambient]

I meant crimping. There are many different kinds of terminals, the most popular are blade connectors but there are also those for PCB coldering.

That makes sense, though I don't have a crimping tool but it has been on my list.  Guess it might be time to get one.

[Stuartambient]

Still thinking of the soldering.    Not that confused though.  The soldering temps for these are 250C though I can say for sure how much difference there is between the tip and dial reading. 
Usually I tin both surfaces separately and then join by applying the tip.  If I did that it shouldn't take long to make the connection.  Am I seriously better off using single core wire though?

[rs20]

The TO-220 package doesn't know nor care whether it's being soldered to a PCB, or flying leads. Unless you're doing something wildly unreasonable, it'll be fine.

[David Hess]

What about a good old spring washer ?

It will be unlikely to produce enough force.

Still thinking of the soldering.    Not that confused though.  The soldering temps for these are 250C though I can say for sure how much difference there is between the tip and dial reading. 
Usually I tin both surfaces separately and then join by applying the tip.  If I did that it shouldn't take long to make the connection.  Am I seriously better off using single core wire though?

Soldering directly to the leads is not problematical as far as temperature.  Like Brutte says, the problem is a long term reliability issue with the connection itself; in a high vibration environment, either the lead to package interface or the solid to stranded wire interface created by solder wicking tends to break.

I have lots of old equipment which has TO-3 and TO-220 parts mounted on a heat sink away from the printed circuit board and connected with stranded wire leads soldered directly to the pins of the part and there has not been a problem.  If you do this, include strain relief near the soldered junctions to minimize bending.  I usually cut off the narrow portion of the TO-220 lead when doing this but this can make things worse.

"Anti wicking tweezers" are available for holding stranded wire in place during soldering which prevent wicking of the solder up under the insulation.

For what it is worth, they make sockets for TO-3 and TO-220 parts and I do not think they are more reliable than soldering wires to the leads.  TO-3 parts soldered directly to boards can have major problems with thermal expansion causing enough force to break the solder joints.  I imagine that TO-220 parts might have the same problem if mounted vertically.