Do i need paste?

[Doomguy42]

Hi, I've got 12v into a 5v regulator on an old an old 90's board. The heat sync bolts onto a black PCB mounted heat sync. Am I supposed to use any heat paste inbetween the joint and if so should it be insulating? Some boards I see have a bit of something inbetween. I can't tell if it's for transferring and dissipating heat or insulating any current?
Thanks

 

[KeepItSimpleStupid]

I'm guessing it's a TO-220 package. There are monting kits such as this one: https://www.newark.com/aavid-thermalloy/4880sg/mounting-kit/dp/10M7230

I'm guessing, it looks like this: https://www.newark.com/on-semiconductor/mc7805actg/ldo-voltage-regulator-5v-1a-to/dp/45J1442

The center pin is electrically connected to the tab.

Generally, in most cases, you want the tab electrically isolated, but thermally conductive.

The mounting kits allow you to do that.

If the thermal insulator can be mica or a orange color, then a thin film of thermal grease is used. The kit I linked to, does not require thermal grease.

The mounting kit also contains a shoulder washer which electrically insulates the screw.

The Belleville washer (A curved dome) is also essential. It applies constant pressure independent of thermal effects.

A picture is worth a thousand words.

What would probably be acceptable is thermal grease without a thermal insulator AND the bellville washer.
The mounting kit I linked to would be appropriate too.

 

[crutschow]

The grease is to reduce the thermal resistance to the heat sink (fills in the small air gaps than increase the the thermal resistance), it's not for electrical isolation.

 

[Doomguy42]

Hi thanks for the reply... yes its a TO200 package regulator,I'll show you exactly what I'm doing.
It's alkaline battery damage (x10 boards). The board surface becomes contaminated and slightly conductive so I'm having to scrape it back to bare copper and fiberglass whilst replacing all components with new. I've got to refit the existing heat syncs. I'm sealing the boards with UV activated masks to insulate the copper I'm also going to paint the bottom of the heat syncs with pcb mask so it's not surfaces are insulated.
I'd like to do the best job as possible fitting the new regulators.
The kits look good... I'm looking for some products I here in the UK. They're £12 on eBay so for 10 boards it's quite alot of money. What sort of thermal grease do you recommend?
Thanks again
P.s it's not the same board in pics wanted to show the mask around the heat sync bolts

 

[rjenkinsgb]

The fixing screws and copper area under the heatsink are also connected to the centre pin of the regulator, the same as the tab is anyway.

You do not need any insulator or washers, just a trace of heatsink compound on the back of the 7805 and fix it directly through the heatsink. Adding any insulator or thermal washer between the two can only reduce heat transfer.

 

[KeepItSimpleStupid]

The first pic shows a sil pad, no grease required.

This https://www.mcmaster.com/belleville-spring-washers/belleville-spring-lock-washers/ type of washer is missing.

 

[Doomguy42]

.

The fixing screws and copper area under the heatsink are also connected to the centre pin of the regulator, the same as the tab is anyway.

You do not need any insulator or washers, just a trace of heatsink compound on the back of the 7805 and fix it directly through the heatsink. Adding any insulator or thermal washer between the two can only reduce heat transfer.

I'm embarrassed I didn't notice that myself. Thanks I went and metered it and the screw buzzes with the center pin... thank you.
I was focusing on the pad under the 7805 heat sync and wanting to do the best job I could on it. Didn't seem right just not putting anything there. Something else learned. Thank you

 

[KeepItSimpleStupid]

It's sometimes "safer" electrically insulating the reguator. For the LM7805, the tab is ground.

 

[Pommie]

I have a pinball machine that had similar damage. The batteries had leaked causing a large area of corrosion.

So, I know your pain. After much cleaning and replacing some components and sockets it's all working again.

As you can see in the second photo, some tracks had complete corroded away. I had to replace them using wire wrap wire.
The batteries are used for static ram to hold high scores etc and are now in a separate holder mounted off the board with flying leads.

Good luck with your project.

Mike.

 

[Doomguy42]

Yeah cheers Mike, these are similar coin ok. They're old skool (uk)fruit machine boards all of which suffer from battery damage at some point . The sRAM holds all the book keeping and pot compensator data. On this type the battery is in a forgiving place, its out of range of the processing and mostly in the audio area, it looks slightly older than your board (86b09p cpu). The boards are HASL so the copper is covered in solder so has some protection. The solder resist on the surface is nasty though and turns conductive.
I'd absolutely love to get a pinball at some point. I'm happy the Rot didn't get to your custom chip there and yours was repairable.
Think this is a PIC of the one with the repair wires on before cleaning up

 

[Pommie]

Processor in mine (Monster Bash) is a 6809. All good now. However, the rot didn't get to the custom chip but I did!!!! Put it back in the wrong orientation and let the magic smoke out. Luckily, a replacement was available at a reasonable price. Keeping these old machines alive is a burden of love and glad I'm not the only one.

Mike.