Heat sink attachment

[BrucieBounce]

Howdy guys,

I'm quite a newby, and have a question about heat sinks. I've seen several audio technicians saying they will tap holes in the heat sink in order to attach it directly to ICs with screws. But how does one know what type of tap to get? There are, after all, quite numerous thread specifications. Are the little screws usually used for attaching ICs of a standard thread? Does anyone know what type of tap one should buy in order to create the proper threads in a heat sink?

Thanks!

 

[rayma]

Find out what size bolt hole is spec for the device. Choose the bolt size to fit the hole.
Then drill the proper hole (see chart) in the sink to be threaded for the chosen bolt.
In the USA we usually use 4-40, or preferably 6-32 if possible. The 4-40 tap is easy to break.

Use oil liberally while tapping the hole. Then deburr the hole well and clean it out well.
Preferably use a torque wrench when mounting the device on the sink.
Check for galvanic isolation from the device tab to the sink after mounting.

Some devices, like a TO-220, require an insulating shoulder washer between the bolt head
and the device tab, in addition to the thermal pad.

 

[deadpool]

I purchased and M3 drill and tap in one package, saves on measuring and making an error...also can be used with a power drill...pretty sure you could get equivalent in the USA

https://www.bunnings.com.au/sutton-...VgghyCh2bywLvEAQYCCABEgKCKfD_BwE&gclsrc=aw.ds

 

[BrucieBounce]

Thanks Rayma and Deadpool,

That gives me answers for both English and Metric measurements. Most of the bolts I have are metric at the moment, but the English measurements will make it easier to find the proper hardware here in the US.

 

[tomchr]

A tapping block can save a lot of taps when you're tapping by hand. You can buy them or make your own. I made one from a chunk of aluminum. Making a tapping block does require that you have the ability to drill perpendicular into the block, so you'll need a drill stand or drill press. Here's an example:
https://store.curiousinventor.com/product/tapping-block/

For aluminum I recommend using some aluminum cutting fluid, such as A-9. Not to be confused with A-1 steak sauce. They don't taste the same and the sauce doesn't seem to have the same lubricating properties either. 🙂

It's important to use the correct drill bit size. For metric sizes you subtract the thread pitch from the nominal diameter to find the drill size. An M3 machine screw has a thread pitch of 0.5 mm, so 3-0.5 = 2.5 mm is the correct drill bit size. 3.3 mm for M4x0.7 mm.

Tom

Tom

 

[BrucieBounce]

Thanks Tom,

I think the last time I used a tap & die set was about 1967. And that was in shop class. At the time, I'm not sure A1 steak sauce even existed, so the risk was quite a bit lower. The use of a tapping block is a good idea, though. I was wondering how I'd make sure everything was exactly perpendicular. I do have a drill press, though.

---Bruce

 

[randytsuch]

In the long run, you may want to get a tap/die set that includes 4-40, 6-32, ...
4-40 is easier to break, you need to be careful. But sometimes only a 4-40 screw will fit.

 

[Ben Mah]

I don't have a drill press so I use a drill guide with my hand held electric drill and I also use it as a tapping block. It has worked well for me. Holes are vertical, and I don't need to store a drill press. Some may find it awkward to use but I am used to using it.

Big Gator Drill Guide

 

[vinylkid58]

I was wondering how I'd make sure everything was exactly perpendicular. I do have a drill press, though.

Use the drill press to start the tap, then continue by hand. Tom's suggestion of A9 is a good one. It works great, but I wouldn't taste it. 😉

Rapid Tap is another good one: https://www.grainger.ca/en/product/...yLWUWCMyVWfQYZMa-4BoC8uEQAvD_BwE&gclsrc=aw.ds

jeff

 

[pinholer]

For most chassis/heatsink work, I only use a few different sized taps, so I find it more economical to buy what I need at an industrial supply store. I would buy a good quality small T handle for holding the taps and a few taps of each size if you're using 4-40 and 6-32. Small diameter taps such as 4-40 are easy to break so having a spare is good. Very frustrating if you break a tap and have to run out to buy a new one.

You can also get blind hole taps to maximize the thread depth if you are tapping blind holes in a heatsink.

 

[rayma]

Yeah, avoid 4-40 taps (or similar small sizes) like the plague. You WILL break one in most every project,
even using a lot of oil. That could ruin a heat sink for your purpose, since if it breaks near the surface
of the sink, it can be impossible to get out.

 

[pinholer]

I only use 4-40 taps for 1/8 inch aluminum plate or angle so the broken tip can be easily removed.

 

[Jcris]

Not sure this has been suggested but practice on some scrap aluminum will give you a better idea of exactly what it takes to achieve a threaded hole in precisely the right spot

 

[rayma]

Definitely it takes practice and a lot of patience to get consistent results.

 

[BrucieBounce]

Is tapping the hole really better than using a nut and bolt? It seems like there are quite a few difficulties in trying to tap a hole in a heat sink, and I was wondering what the trade-offs were.

 

[rayma]

No, a tapped hole is not better than a bolt and nut. I do use a bolt and nut where possible.
With some heat sinks, only a tapped hole will work though.

 

[vinylkid58]

A "blind" tapped hole would be preferable in most heat sinks, for the obvious reasons. 🙂

jeff

 

[rayma]

If you actually have a choice, a clearance hole and keps nut will be much better.

 

[jackinnj]

In the long run, you may want to get a tap/die set that includes 4-40, 6-32, ...
4-40 is easier to break, you need to be careful. But sometimes only a 4-40 screw will fit.

Toshiba TO247 mosfets take a 4-40, but IRF 6-32

 

[dangus]

Salvaging the chuck off a dead cordless drill might be as good or better than a t-handle for 4-40; it's easier to hold perpendicular.