Mica insulaters (insulators?),heat sinks and heat sink paste.

i'm finishing up my D-AOC build and have some question befor i go on

http://www.silentarts.de/DIY/D-AOC/D-AOC_Schematic.pdf

the lm350 will be mounted to the chassis. i am using mica insulaters and a nylon screw and nut.
my question is,do i need a heat sink at all? i have a small heatsink for the 220 case regulator and i'm thinking it cant hurt to use it. may transfer more heat to the chassis.
im not sure how to use the heatsink paste with the mica insulater do i apply it on both sides of the insulator or just one?(which one?) what is standard. any help is appreciated. thanks 

If you are heatsinking to the case then you probably don't need a heatsink.  Heatsinks only work good if you have airflow.  Having a heatsink inside of a closed chassis without active ventilation is like not having a heatsink at all.  You'll just heat up the stagnant air in the chassis until the part is just as hot as it would be without it.  Heatsinking to the chassis gives it a lot more metal to disburse heat, including the rack itself and so forth.

As far as the mica/paste, apply it to both sides of the mica.  A thin film is plenty.  zinc oxide heatsink compound (the white stuff) isn't actually a good conductor.  It's just used to fill in the microscopic cracks/dimples/imperfections between the surfaces.

I should add that if the case starts to get too hot with the part heatsunk to it, then add a heatsink on the outside of the chassis on the other side of the panel from your regulator.  You are dropping 6v as heat which could get fairly warm.

thanks. this is a tube project so there is plenty of venting (not active ventilation)on the case. lots of room in the case as well. i am using the white, zinc paste though.

seavote said:

i'm finishing up my D-AOC build and have some question befor i go on

http://www.silentarts.de/DIY/D-AOC/D-AOC_Schematic.pdf

the lm350 will be mounted to the chassis. i am using mica insulaters and a nylon screw and nut.

Click to expand...

As a suggestion,
I don't think I would use a nylon screw and nut. Use an insulating washer and steel screw.
The nylon will heat up and loosen up and cause your thermal bond between the LM350 to not work as well.

there is "high temp" nylon but I don't know if any plastic screws are made from it or not.

"don't think I would use a nylon screw and nut. Use an insulating washer and steel screw.
The nylon will heat up and loosen up and cause your thermal bond between the LM350 to not work as well."
i questioned this myself in another thread and was told it would not be a problem. i have an insulating washer and steel scew and nut. i'll try those and see if there is an isolation problem. if not, im good to go. if there is i'll try the nylon.

Svart said:

zinc oxide heatsink compound (the white stuff) isn't actually a good conductor.  It's just used to fill in the microscopic cracks/dimples/imperfections between the surfaces.

Click to expand...

Is the clear, gel type better then? Which one is 'silicone'?


Cheers, Dan

silicone is even worse as a heat transfer enabler.  The metalized heatsink compounds are the best but they are also slightly conductive too.  Not good for your application.  There is a ceramic heatsink compound that works good but is hard to find/get and expensive. 

the best possible and easy to find heat sink compound can be bought from computer stores that cater for the overclocking crowd.

for example:

http://www.arcticsilver.com/

It's not that expensive, it's insulating, and they have choices from paste to hard epoxy. I think it's completely unnecessary for regulators, but if you absolutely must..

Kingston said:

the best possible and easy to find heat sink compound can be bought from computer stores that cater for the overclocking crowd.

for example:

http://www.arcticsilver.com/

It's not that expensive, it's insulating, and they have choices from paste to hard epoxy. I think it's completely unnecessary for regulators, but if you absolutely must..

Click to expand...

Arctic Silver is great stuff.  Also, instead of using mica insulators, you could use thermal pads.  They are kind of rubbery so they won't crack.  I got a bag from DigiKey a couple of years ago, and now don't use the mica any more.
Bruno2000

those are silicone.  They aren't as heat transmissive as you would think.  They work great for mass production but not so much for high heat devices.  Arctic silver is slightly conductive too.