TO220 , TOP3 etc mounting washers ?

connection,runs

a pic of the usual low temp plastic insulating bushes

That 3.5 - 3.1 or 3.9 - 3.1mm dimension, divided into two, internal section, would probably be too breakable with that power transistor body material, if direct replacements

-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on

Mounting 'kits' for power transistors cost more than many of the transistors themselves (over a dollar for a mica gasket and some screws and washers). You can cut a small length of PTFE (Teflon) tubing for the machine screw shaft, and use a piece of fiberglass-reinforced plastic (FRP) as a washer to hold off the head, I've used polyimide (Kapton) tape for the heatsink insulation barrier.

I'm not sure where my FRP washers came from, but the Teflon tubing, about gauge #9 for 4-40 screws, is a common laboratory supply item.

Mounting 'kits' for power transistors cost more than many of the transistors themselves (over a dollar for a mica gasket and some screws and washers). You can cut a small length of PTFE (Teflon) tubing for the machine screw shaft, and use a piece of fiberglass-reinforced plastic (FRP) as a washer to hold off the head, I've used polyimide (Kapton) tape for the heatsink insulation barrier.

I'm not sure where my FRP washers came from, but the Teflon tubing, about gauge #9 for 4-40 screws, is a common laboratory supply item.

reply: I've plenty of sources of PTFE suitable for the insert part but no known sourse of suitable FRP. I wonder if fibre reinforced phenolic board would be suitable for the washer, I'll try heating some. Of course that washer part does not have to be circular and cutting it square with a hole would be easier.

-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on

be

The washer part could be a disc or 2 of that stiff plastic material found inside power supplies where there is a chance that some component will touch the casing, next to a steel washer under the bolt/screw head. For that matter I don't see a problem of using a mica disc or 2 then a steel washer for that part.

-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on

:> Mounting 'kits' for power transistors cost more than many of :> the transistors themselves (over a dollar for a mica gasket :> and some screws and washers). You can cut a small length of :> PTFE (Teflon) tubing for the machine screw shaft, and use a :> piece of fiberglass-reinforced plastic (FRP) as a washer to hold off :> the head, I've used polyimide (Kapton) tape for the heatsink :> insulation barrier. :>

:> I'm not sure where my FRP washers came from, but the :> Teflon tubing, about gauge #9 for 4-40 screws, is a common :> laboratory supply item. :>

:> reply: :> I've plenty of sources of PTFE suitable for the insert part but no known :> sourse of suitable FRP. I wonder if fibre reinforced phenolic board would :be :> suitable for the washer, I'll try heating some. Of course that washer part :> does not have to be circular and cutting it square with a hole would be :> easier. :>

: : :The washer part could be a disc or 2 of that stiff plastic material found :inside power supplies where there is a chance that some component will touch :the casing, next to a steel washer under the bolt/screw head. :For that matter I don't see a problem of using a mica disc or 2 then a steel :washer for that part.

Richco make a high temperature shoulder washer designated MNI-HT

The #4-220 is designed for the TO220 transistor mounting hole.

I can't say I've ever seen that myself.

You mean Mica. It's a natural mineral. And no, transistor bodies aren't made from mica btw.

Graham

Oh, the washer themselves ?

No, I've only ever seen nylon ones. You simply need to do them up tight with lockwashers. Personally, I prefer mounting devices 'live' or using spring clips to retain them.

Graham

Mica would simply crush.

Delrin would be nice but I don't know of anyone making washers in that.

Another way is to use nylon screws.

What on earth do you mean ?

Graham

known

would

part

touch

steel

But that is also nylon, just because they call it high temperature, does not necessarily mean it does not compress/creep in normal but highly elevated temperatures, leading to premature failure of device. The point is I'm after some insulated and mechanically strong enough alternative to plastic without having to drill into heatsinks for spring retention.

-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on

MEC make thermoplastic transistor insulators that are rated up to 180c continuous. Farnell sells them.

Ron(UK)

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On Mon, 3 Mar 2008 08:07:40 -0000, "N Cook" wrote: SNIP : : :But that is also nylon, just because they call it high temperature, does not :necessarily mean it does not compress/creep in normal but highly elevated :temperatures, leading to premature failure of device. :The point is I'm after some insulated and mechanically strong enough :alternative to plastic without having to drill into heatsinks for spring :retention.

Not all nylons are the same as you know. The normal nylon 6/6 from which the ordinary items are made should not be used over 49C but the items I mentioned are designed to operate up to 200C.

If you did some research on the material Polyphenylene Sulfide from which the Richco product is made you would find the following;

.. Plastic parts for SMD components are made of PPS (Polyphenylene sulfide) .. which is a high temperature material suitable for reflow soldering profiling. .. Temperature of operation: 200 ..C .. Flammability conformance : As per UL 94 V-O

not

the

mentioned

the

sulfide)

profiling.

The point of this thread is not the ultimate melting temperature but the property of not creeping/deforming at sustained elevated temps of say 100 to

120 deg C. eg PTFE would be fine for the internal sleeve part of such bushes unless having to resist abnormal lateral forces. But it would it be reliable as the washer part.

-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on

: :The point of this thread is not the ultimate melting temperature but the :property of not creeping/deforming at sustained elevated temps of say 100 to :120 deg C. :eg PTFE would be fine for the internal sleeve part of such bushes unless :having to resist abnormal lateral forces. But it would it be reliable as the :washer part.

One of the structural properties of PPS is "brittleness", which would indicate resistance to deformity. But don't take my word for it, take a look at a typical fibereglass filled PPS datasheet

in particular the mechanical and thermal properties. If these figures aren't good enough for you then any other superior solution is not likely to be readily available off-the-shelf.