Home made heat sink pads

[Jon Slaughter]

What I expect you to do is go away and don't come back.

HAHA. What a looser. Someone disagree's with you and you get mad. Just what
I expect from an "expert".

 

[Eeyore]

Try doing a search for silicone heat sink pad's and you might be supprised.

The only silicone pads that are any good are full of thermally conductive
fillers.

Graham

 

[Eeyore]

1mm is for 1kV+. The data seems to show that its not much worse than mica.

In other applications mica is used as a thermal *insulator* !!

real experts? How do I know they are real experts?

You've had advice already from a couple of guys designing multi-kilowatt power
amplifiers ! If anyone should know about this stuff, we should.

Avoiding the need to insulate the device from the heatsink is much, much better.

You ought to mention what dissipation you're dealing with and what package btw.

Graham

 

[JoeBloe]

Not very practical no.

That depends on the circuit, the heat sink media, and several other
factors.

No it isn't.

You're an idiot. Your responses are as retarded as it gets
considering that you claim to be knowledgeable in the realm of
electronics. The least you could do is answer the whys and
wherefores. Much less actually suggesting solutions.

You are not proud of being a stupid twit, I hope.

 

[JoeBloe]

Out of curiosity: why do you want them home-made? What would be wrong
with using some commercially-available insulators? They are not
expensive. (Ex. made from some "Boron nitride loaded silicon Elastomer")

Thanks.

-- Andy

Good point. I'm sure that ten packs from digi-key of any given form
factor can't be more than a few bucks.

 

[John Larkin]

HAHA. What a looser. Someone disagree's with you and you get mad. Just what
I expect from an "expert".

I'm not mad; you haven't anywhere near the skill to make me mad. Hell,
you can't even spell. And you're too lazy to make some simple thermal
measurements. Try starting over in sci.electronics.basics, and lurk a
while before you jump in fighting. This ain't the place for people who
know nothing but want to argue about it.

John

 

[JoeBloe]

omg, I guess that proves beyond any reasonable doubt that you are an expert
in heat sink pads of all kinds of materials?

The question is begged, if one posts a query here about a topic, why
would one reject the responses from folks having YEARS of experience
in the field? Is not the reason for the poser in this forum to garner
responses from experienced individuals?

If you want a REAL good heat sink, get one that has been properly
hard anodized. THAT surface is non-conductive, and some thermal
cream, and a direct attachment, and you are done!

BTW, the silicone (not silicon) thermal grease is ONLY there to take
up tiny, tiny crevices between the two mated surfaces. Most less than
a couple mils. The silicone grease is actually a carrier for the
powder that has the good thermal properties that get utilized here.
The grease itself is not the greatest thermal conductor.

Again, this paste is only for taking up that last 5% of non-contacted
surface. The rest of the surfaces should be in "intimate" contact,
and that is where most of the conduction work will get done.

Air is a poor thermal conductor. So it the grease, just not as bad.
Here is the proof.

Air gaps = hotter part

Grease filled SMALL air gaps maximize transfer.

A large gap between a heat generating part and its sink filled with
air is a VERY bad conductor, and the part will run away and fail.

That same part with the gap filled with grease will run away and
fail. The grease will not conduct across a large cross section of
itself (more than a few mils) as it is not meant to do so.

So. What is learned?

A heat generating part/device needs constant, intimate contact with
a thermal sinking device for any period during which it is generating
said heat in order to keep operating and not generate dangerous
temperatures at any time.

When perfect intimate contact is not possible, the space MUST be
minimized as best as possible, and any gaps should be filled with
something more conductive than mere air that is not going to dry out,
and lose its capacity to fill said gap.

You should go back through and read the responses again. Folks here
generally try to help, and you should not immediately discount Usenet
posters. Most of us here have been in the industry for a long time,
and it would serve you well to heed much of what has been iterated to
you. Ignore the DonkeyTard though.

 

[JoeBloe]

yeah. I suppose I could just test some stuff and see. Maybe burn up a few
regulators and see which ones go out first. Just not really something I'm
intersted in doing and I figured someone would know.

Keep the heat sink isolated from any other thing (ground or other
circuit nodes), and sand a surface on it smooth, and attach the thing
directly to it

BAM! Maximum heat transfer!

 

[kell]

yeah. I suppose I could just test some stuff and see. Maybe burn up a few
regulators and see which ones go out first. Just not really something I'm
intersted in doing and I figured someone would know.

Cut a piece off a mylar potato chip bag. Mylar doesn't melt easy.
You're only using 12 volts, so super-thin chip bag mylar is perfect.
Assuming it really is mylar. A commonly used dielectric. I have some
mylar sheet I use for insulators, but it's thicker than chip bags. I
can tell you, that stuff doesn't melt easy.

 

[JoeBloe]

** Typical silicone pads ( eg from Berquist) have thicknesses of 0.2mm and
quote breakdown voltages in the range of 3 to 6 kV.

Wrong. The creepage distance for 3 to 6kV is too far for the leads
and package bodies of most of the devices they cover. Regardless of
what it may take to pierce the pad, the application won't work without
arcing at those potentials. They list their breakdown Voltage at 3500
to 4500 volts for their original product. The problem is that no
unencapsulated circuit could operate at those voltages unless the pad
were several millimeters larger than the device footprint.

The word for today is "CREEPAGE".

The electrical kind.

You're just a CREEP of the net kind.

 

[John Larkin]

The question is begged, if one posts a query here about a topic, why
would one reject the responses from folks having YEARS of experience
in the field? Is not the reason for the poser in this forum to garner
responses from experienced individuals?

If you want a REAL good heat sink, get one that has been properly
hard anodized. THAT surface is non-conductive, and some thermal
cream, and a direct attachment, and you are done!

BTW, the silicone (not silicon) thermal grease is ONLY there to take
up tiny, tiny crevices between the two mated surfaces. Most less than
a couple mils. The silicone grease is actually a carrier for the
powder that has the good thermal properties that get utilized here.
The grease itself is not the greatest thermal conductor.

Again, this paste is only for taking up that last 5% of non-contacted
surface. The rest of the surfaces should be in "intimate" contact,
and that is where most of the conduction work will get done.

Air is a poor thermal conductor. So it the grease, just not as bad.
Here is the proof.

Air gaps = hotter part

Grease filled SMALL air gaps maximize transfer.

A large gap between a heat generating part and its sink filled with
air is a VERY bad conductor, and the part will run away and fail.

That same part with the gap filled with grease will run away and
fail. The grease will not conduct across a large cross section of
itself (more than a few mils) as it is not meant to do so.

So. What is learned?

A heat generating part/device needs constant, intimate contact with
a thermal sinking device for any period during which it is generating
said heat in order to keep operating and not generate dangerous
temperatures at any time.

When perfect intimate contact is not possible, the space MUST be
minimized as best as possible, and any gaps should be filled with
something more conductive than mere air that is not going to dry out,
and lose its capacity to fill said gap.

You should go back through and read the responses again. Folks here
generally try to help, and you should not immediately discount Usenet
posters. Most of us here have been in the industry for a long time,
and it would serve you well to heed much of what has been iterated to
you. Ignore the DonkeyTard though.

The regular Dow Corning thermal grease must have some very small fill
particles. With just modest pressure, I've measured its added spacing
at below 100 microinches (0.1 mils), which is the limit of the
micrometer I had at hand. It flows out of the gap. Right, it's not a
very good thermal conductor, but it does squish out very thin... a
sil-pad may be 50-100 times as thick!

Grease over flat, 0.5 mil hard anodize is about as good as it gets.

The sil-pad looking phase-change films I've tried are terrible because
they don't squeeze out thin. The wax/crayon things might, but I'd be
worried about air pockets. Silicone grease is messy but it sure works.

Eeyore is technically sound, ignoring politics.

John

 

[JoeBloe]

Trying to show your mettle, eh?

(Let me re-phrase that)

Trying to show your metal, eh?

Trying to show your meddle, eh?!


Heheheh :-]

 

[JoeBloe]

Grease over flat, 0.5 mil hard anodize is about as good as it gets.

Yep. Shame that we can't get a good high dielectric strength yet
highly thermally conductive thin film of something to bond with
copper. It conducts heat better than Al, IIRC (not gonna bother to
google it, I'm sure I'll get chastised if I err).

Oh, yeah, that silver filled stuff the CPU tweak hounds use is
awesome stuff too, and they HAVE done lots of recent research and
testing!

Try "Tom's Hardware" for reports about thermal compounds.

 

[Phil Allison]

"JoeBlow It Out His Arse FUCKHEAD "

Wrong.

** Go check the specs on their site yourself

- YOU ASININE **** HEAD




......... Phil

 

[John Larkin]

Yep. Shame that we can't get a good high dielectric strength yet
highly thermally conductive thin film of something to bond with
copper. It conducts heat better than Al, IIRC (not gonna bother to
google it, I'm sure I'll get chastised if I err).

Have you looked at aluminum nitride? It's almost as good as BeO but
it's not toxic. For high-voltage and high thermal density, I'd go for
a non-insulated copper heat spreader over an AlN insulator, all
greased... if you can stand the capacitance!

I think BeO has the best ratio of thermal conductivity to dielectric
constant, except for diamond. Or flowing distilled water.

John

 

[Eeyore]

Quite !

Keep the heat sink isolated from any other thing (ground or other
circuit nodes), and sand a surface on it smooth,

Since when did sanding produce a smooth surface Mr Blow Hard ?

Graham

 

[John Fields]

Because the there is possible contact with the heat sink and the ground. It
doesn't matter though. I didn't ask for that and I don't have to explain
those details as they have nothing to do with my original question which you
seem not to have read.

 

[ehsjr]

1mm is for 1kV+. The data seems to show that its not much worse than mica.




I didn't say they didn't. But the numbers I've seen on the internet suggest
something very different than what is suggested here. I've not seen anyone
here post any numbers but just say "Your wrong". If the site is wrong then
prove it but just don't say stupid shit without backing it up. Theres to
many "wanna-be's" here and many cannot be trusted. (Not all, there are some
good engineers here but most are not)




I dunno either, which is why I asked. I cannot seem to find any real
information on this subject on the net and you guys say what I have found is
wrong. I don't really know who to believe.




real experts? How do I know they are real experts? Do you really expect me
to take it on faith that everyone in this NG is an expert? I'm sorry. If
you want to prove you are an expert than back up what you say with data and
references. Don't just say "There wrong and I'm right" because when you do
that you look more like a cooke.

If you expect me to take everything you guys say on faith then I'm sorry. It
won't happen. I'll listen to what you guys have to say but in the end if it
doesn't add up then I'll come to my own conclusions(and if I'm wrong then
I'm wrong... atleast I'll find out for myself instead of trying to be a
mindless drone like you seem to want me to be).

Anyone can claim to be an expert and many people do it. I'm not saying there
are not experts in here or those who have replied are not experts but all I
know is that there is some contradictions between what people are telling me
and hence someone is wrong. Right now the score is against John and Eeyore
because I've found many different sites claiming that silicone works. Its
possible that all these sites are ran by the same idiot or that all of them
are created by idiots but I would imagine the odds of that happening is
pretty slim.

I think the issue you need to get over is that you don't have to take what
people anyone says on faith. Its ok to be hard headed or skeptical because
else you will be conned. Lots of people try to be experts but few are. Many
people try to impress others by acting smart but few are actually smart. Is
this happening here? I don't know. I just know that someone's wrong and it
would be nice to know if silicone is actually worth using or not so I'll
know. Probably the only way it will really get resolved is for me to test it
out on my own and see. Ofcourse thats much more work than I'd want to do
but...


Anyways, I've heard to many "You can't do this or that" type of BS from
newsgroups like this and then when you do it it works. Some people try
something once and it doesn't work and they conclude that it can't work and
then try and convince others it can't work. Those people are usually easy
to spot because they go ape shit when you don't believe them 100%.


Jon

John Larkin *is* an expert. I'm sorry if that
is painful for you, but you would do well to
listen carefully to what he has to say.

Ed

 

[David Brown]

HAHA. What a looser. Someone disagree's with you and you get mad. Just what
I expect from an "expert".

You really don't know how to use newsgroups, do you? You just wade in,
insulting people randomly just because they don't agree with something you
read on a webpage somewhere (and remember, despite being pretty
flame-proof, John et.al. are *real* people - would you talk like that face
to face?).

If you had bothered to do your homework, you'd have read some threads here
for a while, so you know who you are talking to - John really is an expert
at this stuff (as is Eeyore, and others in this thread), and I'd count his
opinion above a random webpage any time. It's lucky for you that he and
others find the problem interesting, and are therefore discussing it
despite your attitude.

 

[JoeBloe]

Have you looked at aluminum nitride? It's almost as good as BeO but
it's not toxic. For high-voltage and high thermal density, I'd go for
a non-insulated copper heat spreader over an AlN insulator, all
greased... if you can stand the capacitance!

I think BeO has the best ratio of thermal conductivity to dielectric
constant, except for diamond. Or flowing distilled water.

I'll bet the winner is still plain old mica.

For liquid try fluorinert. Much safer.