Insulating Pads.

[castlesteve]

Where can I purchase inslating pads for a pair of LM3875 T opamps in the US?
Thanks Steve.

 

[Peter Daniel]

If you don't mind cutting them out from TO-3 sized Silpads (and the size is big enough) I can send them to you for free

 

[li_gangyi]

Or you could get those BIG sheets from farnell or RS and cut them out...and make a hole in them...

 

[castlesteve]

Thanks Peter. I`ve just Emailed you with my mailing address etc. Thanks for the kind offer.
Steve.

 

[jackinnj]

scissors work fine -- I use TO-3 pads too -- but Peter, I think that your method of mounting the device with a bar, rather than one screw probably results in a much better thermal transfer function. (oh well, lucky me, I just tapped some aluminum heat sink stock for 4-40 screws).

 

[li_gangyi]

yeah...the bar helps dissapate heat from the "front" also...guess he could only do better if he potted the whole chip in some metal or something...

 

[ronc]

Never use pads, just a very very thin coating of thermal grease and a pressure bar. Of course the H/S is isolated from the cab, for both electrical and vibration control.
ron

 

[li_gangyi]

the pads are for isolation dude....

 

[jackinnj]

the TF version is insulated -- but you will note from the apnote that it requires a bigger heat sink

 

[li_gangyi]

Unfortunately...not everyone likes the insulated version...he just asked about pads and you are tell mi the non-isolated version doesn't need pads...the original poster might get a bit confused you know...

 

[ronc]

Heat transfer is better without the pads and as my H/S is a 3/4 Lb gold plated brass bar and electrically active it is isolated and is on a nylon suspension inside the cab.
ron

 

[li_gangyi]

hmmm...maybe you should try aluminium oxide as an insulator...seriously...I mean it's just crazy to use metal to insulate...

 

[jackinnj]

Unfortunately...not everyone likes the insulated version...he just asked about pads and you are tell mi the non-isolated version doesn't need pads...the original poster might get a bit confused you know...

if you don't insulate, the heat sink is at V- so you need insulated spacers to mount the heat sink --

the thermal "cost" of insulation can be calculated explicitly, and is part of the three theta's. i don't see why it's a problem .

 

[ronc]

The gold plated brass bar is more than insulation its also the H/S.Heat transfer is greatest when you have 2 surfaces that are flat to each other( //) to within .0001". They then wring( believe thats how its spelled, its not ring) together (actually stick together without any grease).As all i use is the LM3875T version that means the bar is electrically active so i just isolate the bar.Worked very well so far with 12 different GCs.Of course i use a poly (looking at Cu though) pressure bar for clamping.
Both the block and the chip are surfaced on a granite inspection plate that is accurate to within .00001" using a plate polishing compound.
ron

 

[li_gangyi]

Yeah...good idea...but then again...if you go through so much...might as well just insulate the whole heasink and make sure it does not touch the chassis...or at least get the isolated version...

jackinnj:
I was saying that the ISOLATED version (TF) does NOT need an insulating pad...but the non-isolated version needs (T) guess must be different interpretations of my above posts...

 

[ronc]

Yea the gold plated brass bar is suspended by a poly plate and nylon bolts(brass on some config). It more or less just hangs from the roof of the cab.
ron

http://community.webtv.net/roncla/PressureLoadingBar

I am using my couch potato link as i am still trying to figure out windows 2000.

 

[jackinnj]

The gold plated brass bar is more than insulation its also the H/S.Heat transfer is greatest when you have 2 surfaces that are flat to each other( //) to within .0001". They then wring( believe thats how its spelled, its not ring) together (actually stick together without any grease).As all i use is the LM3875T version that means the bar is electrically active so i just isolate the bar.Worked very well so far with 12 different GCs.Of course i use a poly (looking at Cu though) pressure bar for clamping.
Both the block and the chip are surfaced on a granite inspection plate that is accurate to within .00001" using a plate polishing compound.
ron

In fact, the way "glues" work is to make the two surfaces absolutely smooth!

 

[quekky]

hmmm...maybe you should try aluminium oxide as an insulator...seriously...I mean it's just crazy to use metal to insulate...

do you know where to get aluminium oxide pads in singapore? something like what peter daniel had last time

 

[li_gangyi]

I'm not so sure....I just use the isolated version on my GC...makes it all so easy...I guess you can try out RS...Farnell or SLT (Sim Lim Tower) have seen insulating stuff there...but not sure if they are Aluminium Oxide though...

 

[UrSv]

Digi-Key has silpads in the MultiWatt format which means LM38xx size.