Homebrew PCBs

I have a question to the other members in the group. 

I use alot of SMD parts, many of which have heat slugs on the bottom of 
the parts for thermal dissapation. At work, when I have a PCB made up 
by a board house, we lay these out with a large solderable pad under 
the part, then connect the top side of the PCB to the bottom side with 
numerous feed thru holes. When the part is soldered to the board this 
provides a themal path to the copper on the botom of the board. With my 
home made TT, or photo boards I can not make plated thru holes to 
provide this thermal path, but I still need to get the heat out some 
how.

I have thought of drilling many feed thru's under the part and feeding 
a thick copper wire from one side to the other, then on the compnent 
side cut or grind the surface flat so the component can still be 
soldered down.

Has any one else had to use similar parts? How have you managed to get 
the heat out of these parts? Any other suggestions?

On 6/8/07, Dave Miller <dmiller45@...> wrote:

> I have thought of drilling many feed thru's under the part and feeding
> a thick copper wire from one side to the other, then on the compnent
> side cut or grind the surface flat so the component can still be
> soldered down.
>
> Has any one else had to use similar parts? How have you managed to get
> the heat out of these parts? Any other suggestions?


I do the same as you, make a large hole and fill it with copper and solder.
If done well the solid copper slug can be better than a pro PCB, but
it's lotsa work if you compare the two. You can solder a heatsink to
the back.

ST

>Has any one else had to use similar parts? How have you managed to get
>the heat out of these parts? Any other suggestions?

Double sided thermal tape (or thermal epoxy) and heatsink.

http://www.pbase.com/eldata/image/66582088


--- In Homebrew_PCBs@yahoogroups.com, "Dave Miller" <dmiller45@...> 
wrote:
>

--- In Homebrew_PCBs@yahoogroups.com, "derekhawkins" <eldata@...> wrote:
>
> >Has any one else had to use similar parts? How have you managed to 
get
> >the heat out of these parts? Any other suggestions?
> 
> Double sided thermal tape (or thermal epoxy) and heatsink.
> 
> http://www.pbase.com/eldata/image/66582088
> 
> 
> --- In Homebrew_PCBs@yahoogroups.com, "Dave Miller" <dmiller45@> 
> wrote:
> >
>

Thanks Derek, the method you describes works great for parts where you 
have access to the heat tabs, unfortunately the parts I am describing 
have a heat slug under the part and are designed to be soldered to the 
PCB. Once the parts are soldered down, there is no access to the heat 
tab, thermal dissapation is only thru the PCB.

>unfortunately the parts I am describing have a heat slug under the 
>part and are designed to be soldered to the PCB.

If I followed the datasheet for the heatsinked component in the shot 
then there would have to be 24 vias connecting the bottom 8 sq. cm 
pad to the top 3 sq. cm pad to which the slug is soldered.

>Once the parts are soldered down, there is no access to the heat
>tab, thermal dissapation is only thru the PCB.

The case is always a viable means of heat dissipation, albeit with 
higher junction-to-whatever thermal resistance. Couple the case to a 
suitable heatsink and your junction-to-ambient resistance can be more 
than suitable.



--- In Homebrew_PCBs@yahoogroups.com, "Dave Miller" <dmiller45@...> 
wrote:
>
> --- In Homebrew_PCBs@yahoogroups.com, "derekhawkins" <eldata@> 
wrote:
> >
> > >Has any one else had to use similar parts? How have you managed 
to 
> get
> > >the heat out of these parts? Any other suggestions?
> > 
> > Double sided thermal tape (or thermal epoxy) and heatsink.
> > 
> > http://www.pbase.com/eldata/image/66582088
> > 
> > 
> > --- In Homebrew_PCBs@yahoogroups.com, "Dave Miller" <dmiller45@> 
> > wrote:
> > >
> >
> 
> Thanks Derek, the method you describes works great for parts where 
you 
> have access to the heat tabs, unfortunately the parts I am 
describing 
> have a heat slug under the part and are designed to be soldered to 
the 
> PCB. Once the parts are soldered down, there is no access to the 
heat 
> tab, thermal dissapation is only thru the PCB.
>

One thing you can do is drill holes and use small eyelets for via's. 
The only problem is the part will not sit flat on the board.

--- In Homebrew_PCBs@yahoogroups.com, "Dave Miller" <dmiller45@...> 
wrote:
>
> I have a question to the other members in the group. 
> 
> I use alot of SMD parts, many of which have heat slugs on the 
bottom of 
> the parts for thermal dissapation. At work, when I have a PCB made 
up 
> by a board house, we lay these out with a large solderable pad 
under 
> the part, then connect the top side of the PCB to the bottom side 
with 
> numerous feed thru holes. When the part is soldered to the board 
this 
> provides a themal path to the copper on the botom of the board. 
With my 
> home made TT, or photo boards I can not make plated thru holes to 
> provide this thermal path, but I still need to get the heat out 
some 
> how.
> 
> I have thought of drilling many feed thru's under the part and 
feeding 
> a thick copper wire from one side to the other, then on the 
compnent 
> side cut or grind the surface flat so the component can still be 
> soldered down.
> 
> Has any one else had to use similar parts? How have you managed to 
get 
> the heat out of these parts? Any other suggestions?
>

On 6/12/07, Brian <blue_eagle74@...> wrote:
> One thing you can do is drill holes and use small eyelets for via's.
> The only problem is the part will not sit flat on the board.
>

I doubt this would work at all with the small leadless QFN packages,
or at least soldering the other pins would be damn tricky then.
Possibly for larger parts with leads though...

ST

If the part has a "large" central heat pad you could mill out the era 
and press a heatsink on it from the back side of the board.

Edward