I wrote:
> Ed W1AAZ wrote:
>
> > >The heatsink compound at RS says that it is highly conductive -- not
> > >sure if they are speaking of electrical or heat only. It is a
> > >silicon based product. Is this stuff ok?
> >
> > Many of the MOSFet's (and transistors) have their drain (or collector)
> > electrically connected to the metal tab. When fastening the tab to the heat
> > sink, the tab must be electrically insulated from the heat sink. This is
> > typically done using a thin mica insulating washer. In addition metal
> > hardware is typically used to fasten the device and a through the hole
> > washer (teflon) must also be used.
>
> I believe most heat sink compound is zinc oxide particles (which provide
> the heat transfer) suspended in a high temperature grease (usually
> silicone based). Both ZnO and silicone grease are dielectric, though
> I can not cite a breakdown voltage spec or dielectric constant. I
> know my jar of Wakefield heat sink compound claims to be electrically
> non-conductive ;-).
After prodding by Ed, it occurs to me that my message may be misleading.
I believe that one need not be concerned about the compound being conductive,
and thus shorting around a mica insulator. However, I did not intend to
suggest that an insulator was not required. I suppose I think this is
just obvious enough that it need not be said ;-)
Sorry about any confusion I might have raised.
Dana K6JQ
[
QRP-L Archive |
]
[
1993 |
1994 |
1995 |
1996 |
1997 |
1998 |
1999 |
2000
]