Aluminum-layer PCBs

This might help with the basic questions:

I've used some boards that I was told were made using KNDJ-002 :

I also had some off-cuts of blank Al material with this stuff and copper foil laminated to it, and I have etched some of my own boards on it. That worked really well except that I have no way to make vias to the aluminium.

I turned a disc of that stuff, and soldered a bunch of SMD resistors and thermocouples on the copper side, to make a heated target for testing an IR sensor. I covered the aluminium side with Kapton tape to increase the emissivity. Kapton is slightly reflective in the thermal IR region, but available in a convenient form and temperature rating. The least reflective thing I could find in the thermal IR region was open-cell foam rubber, but it had many other disadvantages for a temperature calibration target, such as poor thermal conductivity, etc..

If cost and weight is not of too much importance, you could get the PCB house to start with a copper sheet instead of aluminium and laminate the same KNDJ-002 stuff to it. That should permit conventional methods of making vias, or for small numbers you could figure out something involving a drill and some solder.

On 8 Mar 2016 18:51:45 -0800, Winfield Hill Gave us:

Thermal conductivity of Copper is better than that of Aluminum.

On Wed, 9 Mar 2016 16:04:48 +1100, Chris Jones wrote as underneath :

What emissivity did you average on for Kapton tape? It doesnt appear in the tables I have! TIA C+

Sorry, I don't know the numerical value, and I am not confident of my ability to measure it accurately. For my purposes I just needed something repeatable.

On Wed, 09 Mar 2016 07:14:22 +0000, Charlie+ Gave us:

Search for polyimide.

Found here as "Kapton"

Hmmm...electromigration will kill vias,,,,corrosion: ditto,,,need i go further?

I have been using them on a regular basis in my hobby projects if there are bad cooling conditions and an integrated radiator is a good idea.

E.g. a stack of 3 IMS boards:

Best regards, Piotr

Uh, what current densities are you using on the poor things?!

Tim

That looks like an interesting project, Piotr, with four heavy wire tingamajibs. What is it?

Yes, but a nice thick Al substrate mates well to an Al heatsink, and hence on to fans, etc. But it appears the most common affordable usage is one copper layer only. Popular for power LEDs. I'm thinking D2-Pak transistors.

Low-cost PCB supplier pitching the technique.

Here is an ancient one from a floppy drive. No vias

More layers will add thermal resistance. We went through that exercize recently, trying to get heat through a PCB from D2PAKs to a cold plate, electrically isolated, and it was discouraging.

On Wed, 09 Mar 2016 08:24:04 -0800, John Larkin Gave us:

Large, heavy vias. Heavily populated. Like those of a large thru hole diode lead. Filled in process or not, they transfer heat quite well.

The many-vias numbers didn't work very well, and there is still the problem of electrical insulation. It's OK at maybe 15 watts per device, really nasty at 60. We stock D2PAKs rated at 300 watts dissipation, over-the-top crazy for a surface-mount part.

You can route a square cutout in the PCB and drop in an AlN insulator, and clamp-mount or epoxy the DPAK to that, but that's hardly worth the trouble. At nontrivial power, it's easier to use a TO220 or TO247, bolt that to an anodized heat sink, and lap-solder the leads to a PCB.

Hear, hear, a 300W D2Pak makes no sense.

Corn lamp:

Looks sorta lethal to me. Nice source of cheap white LEDs.

Of course it does have a CE sticker. As an Irish engineer explained to me, CE means Can't Enforce.