IMS pcb for output stage?

This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
Has anyone experimented with using an IMS (insulated metal substrate) pcb for an output stage (ie the aluminium-core single-sided pcb used for power dissipation in LED lighting etc). Many packages like TO220, TO264 can be modified for surface mount by forming and trimming the leads I suggest...

Effectively IMS contains its own thermal washers built in and reduces mounting hardware requirements. On the downside it makes the whole OS harder to repair.

For FET output stages it opens up the possibility of using compact SMT packages such as directFET.
Been mocking up a possible layout for this.

Still experimenting with photo-resist and etching until I get reliable results before commiting to the IMS etch. The IMS pcb I got is 2oz copper, and with protective plastic film on the aluminium side which will be useful during etching process I think.

Found these interesting looking push-in surface-mount wire connectors:


The brown rectangles are cardboard cutout representations of big SMT resistors and the brown/white of diodes. The faint rectangles are footprints for the connectors mentioned above. Two mounting holes are in groundplane polygons.
Last edited:

Rest of parts await my next Farnell order, but the big non-SMT devices survived without cracking (was a bit worried as they are not moisture-controlled, but no visible cracking and all the diode junctions test fine)

I'm so out of practice PCB etching so I did a fair bit of practice till I was happy to commit to the IMS board. Needed a little cleaning up with a scalpel as I bodged a transparency from pasting printout to acetate and cutting round the outlines (!)

I guess I'll be tempted to try a single sided SMT only full amp design next, although that I would get etched professionally(!)
Fully populated:

Alas I was a bit profligate with solder paste for the wire connectors and solder wicked inside some of them blocking the spring clips, but they can be directly soldered to at least.

The two mounting holes are in ground traces so no insulating washers are needed. The spare space in one corner should have been used for the bias Vbe multiplier in retrospect, as is close to a driver and this is a CFP OS.
I am surprised no one posted.

Well I would say its definitely worth a try because aluminum PCBs are getting cheaper, thanks to the LED industry. Have you done any thermal measurements?

Class-D amplifier would absolutely benefit from such arrangement.
Hello Mark,

interesting, suscribed.

I´ve designed a small IMS for X´s AKSA LENDER preaamplifier: unfortunately no interest in the DIY community. Not a big deal then thermal requirements low.

The component needs to be all SMD and the soldering is, without special heating bed, a pain in the a.

PS.: you could go 2 layers and more then substrat is pressed isolated in the manufacturing process (I´ve designed a military multilayer PCB mounted on a 2mm aluminium plate); it´s only a definition and sure a cost question.

PPS.: they´re a lot of SMD power connector for LED existing today on the market.

PPPS.: if you need a routed layout I would be pleased to do it for you.

Good luck, I´m curious about thermal behaviour.

Has anyone experimented with...IMS (insulated metal substrate) pcb for an output...

Hi Mark
How did this work out?
It occurred to me that it should be possible to use the substrate as an electrical power or reference plane, as a bonus to it's thermal use.
Why have 3 oz. copper when you can have 50 oz. ?
That would imply local connection to the plane but commercial PCB makers seem to have limited options for vias in their IMS boards.
Possible to do it manually to their supplied board I expect.
Did you use the substrate as a circuit element?

Best wishes
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.