Ink and heat transfer?

[JeffYoung]

I mark the backs of JFETs and MOSFETs with a Sharpie. Do I need to remove this before mounting, or will the ink make no difference?

 

[Zen Mod]

no diff

 

[PRR]

Put your finger on a hot stove.

Now put Sharpie on another (unburnt) finger and put it on a hot stove.

I suspect you now have two equally burnt fingers. And are sorry you asked.

That's basic $1 Sharpie. Paint-markers can leave sensibly thick marks, and should be scraped off.

 

[xrk971]

Black Sharpie is special. Other colors are different. Black is graphite pigment based, and binder is very tough - acid resistant so black Sharpie can be used to make traces for PCB etching. When the binder is baked/cooked off, you are left with black color (and presumably carbon residue). Blue/green/red/purple are dyes and binder is not durable as the acid etchant (H2O2/HCl) eats through it, and when baked/cooked - all traces of pigment fly off as VOC vapor. Not that any of this matters for heat transfer when the layer is sub micron thin. But black may pose more of a barrier than other colors if laid on thick.

 

[JeffYoung]

It is black, but not very thick.

And I sprayed some Burn-Eze on my two burnt fingers. 😉

Cheers,
Jeff.

 

[vdi_nenna]

One thing to be aware of is, if you tap your own transistor mounting holes in a heat sink, be sure you clean away any tapping fluid or WD40 or whatever fluid used. Don't let it seep back in behind the transistor and heat sink. I'm sure this happened to me once. Doesn't take much. Results are not good.

 

[JeffYoung]

He he... you only have to get tapping fluid on the furniture once before you learn that everything goes in the parts washer after machining. 😉

 

[wdecho]

Tapping raises the hole ever so slightly so be sure and sand, file it down for proper contact.

 

[Bare]

Iso alcohol wipes off My genuine Sharpie black like it was never there... with only One swipe.
Easier done than said

 

[Mark Johnson]

I gently wipe the mounting tab on TO-220 packaged devices, across one of those DMT Diamond Whetstones. Takes off microscopic burrs and, I assume, unwanted Sharpie juices.