TO220 , TOP3 etc mounting washers ?

[N Cook]

Not the usual nylon or whatever ones that I never trust for high
temperatures (soften and deform over time, loosening thermal connection,runs
hotter, melts more ......
Does anyone make them from whatever the plastic/mineral? is used for the
body of power transistors themselves, what is that material , what is it
called? . Maybe because of brittleness they would have to use smaller
screws/bolts allowing larger washer thickness in the hole.
I've got in the habit of cutting off the non-metal mounting parts of TOP66
type transistors, opening the holes of TO220 or TOP3 and using them as
washers.

Or any other solution, modification?

 

[N Cook]

Not the usual nylon or whatever ones that I never trust for high
temperatures (soften and deform over time, loosening thermal connection,runs
hotter, melts more ......
Does anyone make them from whatever the plastic/mineral? is used for the
body of power transistors themselves, what is that material , what is it
called? . Maybe because of brittleness they would have to use smaller
screws/bolts allowing larger washer thickness in the hole.
I've got in the habit of cutting off the non-metal mounting parts of TOP66
type transistors, opening the holes of TO220 or TOP3 and using them as
washers.

Or any other solution, modification?

a pic of the usual low temp plastic insulating bushes
http://www.maplin.co.uk/images/300/rn91.jpg
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

 

[whit3rd]

Not the usual nylon or whatever ones that I never trust for high
temperatures...

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.

 

[N Cook]

Not the usual nylon or whatever ones that I never trust for high
temperatures...

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.

 

[N Cook]

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.

 

[Ross Herbert]

::> :> > Not the usual nylon or whatever ones that I never trust for high
:> > temperatures...
:>
:> 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
http://www.richco-inc.com/group_details.asp?seccode=050&grpcode=A2390

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

 

[Eeyore]

Not the usual nylon or whatever ones that I never trust for high
temperatures (soften and deform over time, loosening thermal connection,runs
hotter, melts more ......

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

Does anyone make them from whatever the plastic/mineral? is used for the
body of power transistors themselves, what is that material , what is it
called?

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

http://uk.farnell.com/jsp/search/browse.jsp?N=500004+1000162&Ntk=gensearch_001&Ntt=mica&Ntx=

Graham

 

[Eeyore]

Not the usual nylon or whatever ones that I never trust for high
temperatures (soften and deform over time, loosening thermal connection,runs
hotter, melts more ......

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

 

[Eeyore]

Does anyone make them from whatever the plastic/mineral? is used for the
body of power transistors themselves, what is that material , what is it
called? . Maybe because of brittleness they would have to use smaller
screws/bolts allowing larger washer thickness in the hole.

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.

I've got in the habit of cutting off the non-metal mounting parts of TOP66
type transistors, opening the holes of TO220 or TOP3 and using them as
washers.

What on earth do you mean ?

Graham

 

[N Cook]

::> :> > Not the usual nylon or whatever ones that I never trust for high
:> > temperatures...
:>
:> 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
http://www.richco-inc.com/group_details.asp?seccode=050&grpcode=A2390

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

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.

 

[Ron(UK)]

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.

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

Ron(UK)

 

[Ross Herbert]

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

 

[N Cook]

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

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.

 

[Ross Herbert]

:
:The point of this thread is not the ultimate melting temperature but the
roperty 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
http://www.rtpcompany.com/info/data/1300/RTP1379.htm 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.