Board logo

Heat insulation for a PCB?
David Jenkins - 28/8/15 at 02:53 PM

Here's a test for the technically minded on this forum, even though it's got nothing to do with Locosts...

One of my interests is 3D printing, and a problem has arisen... my new printer is a 'delta', which is an upright machine with 3 arms that move around the bit that the plastic comes out of (the 'effector' ).

To avoid getting too long-winded, I have an issue with a sensor PCB that's right next to a small lump of aluminium (the 'hot-end' ) that's usually around 240C, but can get up to 280C in some circumstances. The back of the PCB has to be as close to the hot-end as possible, and at the moment I have a gap of around 3 or 4mm between the two - so I want to put some heat insulation in there. The designer suggested a couple of layers of heat-proof Kapton tape on the back of the PCB, but I have trouble getting it to stay in place, and I'm not sure how effective it will be anyway. I guess that the PCB will tolerate up to 60C, maybe a bit more.

I did a Google and found a substance called Aerogel - that's the stuff where they put a blowtorch on one side and an ice cube on the other, which survives. Trouble is, it's expensive, fragile and hard to get. I also tried a piece of exhaust wrap, but that unravelled as soon as I cut it to the required size.

So (finally) here is the question - can anyone suggest some heat-proof insulating material rated to at least 300C, that's around 3mm thick and reasonably available? I only need a piece about the size of a postage stamp!

coyoteboy - 28/8/15 at 03:37 PM

IF you connect anything between the two you'll get conductive heat transfer, you really want to have a radiative heat insulator I presume. Even something as simple as a sheet of 0.5mm foil should seriously reduce transfer to the PCB, if you could attach several you'd be better off again.

I suspect your PCB will be fine at up to ~100C as most FR4 materials (most common PCB material specification) is. At around 120ish cheaper ones will start to degrade seriously and become soft.

Any chances of a photo of the location?

What model of delta have you gone with - i've been toying with the idea for giggles.

David Jenkins - 28/8/15 at 05:39 PM

It's a design from Thingiverse called Cherry Pi IIIs. The source files for printing are on Thingiverse:

Original Cherry Pi III
Cherry Pi IIIs (the one I built)

I've got it close to working properly - but I sort-of wish I'd gone for a Mini Kossel, as there are a lot more people making them and therefore there's more knowledge around.

Here are a couple of photos:

3d printer head
3d printer head
3d printer air gap
3d printer air gap

coyoteboy - 28/8/15 at 06:11 PM

I was looking at some of the kits you can buy on Alibaba, taking a risk on the control software. Still not sure!

Looks like you could get a tiny bit of sheet Ali in that gap, mounted to the same mounting points as the pcb? That should significantly reduce pcb temp. Think I've plenty of 0.5Mm kicking about if you can't find any.

David Jenkins - 28/8/15 at 06:51 PM

Would have to be careful using metal - this is a pcb, and there are solder joints on the back!

40inches - 28/8/15 at 07:03 PM

This would probably work ok, I have a large sheet, let me know the size and I will cut a piece off.

britishtrident - 28/8/15 at 07:25 PM

What about a bit of disposable oven liner http://www.qdstores.co.uk/products/homeware/kitchenware/paper-and-disposable/-heavy-duty-oven-liner-.html?gclid=CJPPnqTAzMcCFSkYwwodCkkG8g

[Edited on 28/8/15 by britishtrident]

turbodisplay - 28/8/15 at 08:58 PM

Silicon. There is special high temp stuff for ovens and boiler flues.

coyoteboy - 28/8/15 at 09:03 PM

I was expecting you to be careful, kinda goes without saying

David Jenkins - 28/8/15 at 09:39 PM

02GF74 - 30/8/15 at 08:28 PM

quote:
Originally posted by David Jenkins
The back of the PCB has to be as close to the hot-end as possible,


Why?
Because there is a sensor on the pcb? Remove sensor, relocate board and use wires to connect.

Sounds like you want the stuff they used on the space shuttle.

How about ceramic insulators?
Mounting a tiny fan to cool the board not an option?

BenB - 30/8/15 at 08:52 PM

Silicon baking sheet? Goes up to 280degC. It's cheap, about that thick and easy to cut to size.

David Jenkins - 30/8/15 at 08:56 PM

quote:
Originally posted by 02GF74
quote:
Originally posted by David Jenkins
The back of the PCB has to be as close to the hot-end as possible,

Why?
Because there is a sensor on the pcb? Remove sensor, relocate board and use wires to connect.

The sensor has to be close so that any errors in the moving parts are minimised - the bit that holds the hot-end can tend to tilt very slightly when it moves from one side to the other, and if the sensor is too far away from the hot-end it magnifies any false readings - the control board ends up thinking that the print bed is on a slight tilt, when it isn't.

It isn't easy to take the sensor off the PCB - This board uses a pair of precisely aligned infra-red LEDs matched to a sensor that detects when the print head is a set distance from the print bed. Everything has to be held rigidly in a particular position so really has to be laid out on a PCB. The 2 LEDs and the sensor take up half the space on the existing (small) PCB, so it's not worth putting them on another.

Here's a short YouTube video from the maker of the board showing one working (it's a crummy video, so skip to 1:40 to see the thing in action).


quote:

Sounds like you want the stuff they used on the space shuttle.

How about ceramic insulators?
Mounting a tiny fan to cool the board not an option?


I ended up moving the PCB a couple of millimetres further away and put a piece of thin stainless steel sheet between the hot-end and the board. Unfortunately the new setup has caused problems with the hot-end overheating due to a bad cooling fan design (sounds daft, but only the very end is supposed to get hot, not the main body) so now I have to re-think the whole thing anyway.

So - the whole setup is back on the drawing board!

MikeRJ - 30/8/15 at 09:42 PM

Standard FR4 PCB material is good for about 100C, and up to 125C for the high temperature stuff.

Some kind of ceramic insulator would seem to be ideal, maybe something like Ceramic fibre paper.

02GF74 - 31/8/15 at 06:37 AM

Cpu cooling fan, smallest ive found is 20 x 20 x 6 or larger with ducting.

The silicone baking sheet or oven glove should work better at keeping heat away that s steel.
Careful when selecting ceramic insulators as some are made to be good thermal conductors, not what youre after.

HowardB - 14/9/15 at 02:14 PM

I asked aspen for a sample, they sent a piece about 100mm sq, 5mm thick.

Might be worth a try

HTH

David Jenkins - 14/9/15 at 05:49 PM

I've sorted it now - moved the pcb to the other side of the mounting pegs (about 3mm further away from the hot bit) and put a piece of 0.5mm stainless steel wrapped in kapton tape where the pcb used to sit.

So now it's hot-end - airgap - steel sheet - airgap - pcb

The tape was the to make sure that nothing would get shorted if the steel got bent.

I've had the hot-end up to 210C for an hour or so at a time, and the pcb has been barely warm - little more than room temp.

[Edited on 14/9/15 by David Jenkins]

coyoteboy - 14/9/15 at 08:00 PM

Awesome, now let's see some prints