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IMS pcb for output stage?
IMS pcb for output stage?
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Old 4th January 2020, 12:28 AM   #1
Mark Tillotson is online now Mark Tillotson
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Join Date: May 2018
Location: Cambridge UK
Default IMS pcb for output stage?

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.
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Old 9th January 2020, 01:49 PM   #2
Mark Tillotson is online now Mark Tillotson
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Well I've just received an IMS board, time to dig out my old pcb etching kit and see if it still works
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Old 22nd January 2020, 05:00 PM   #3
Mark Tillotson is online now Mark Tillotson
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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: https://uk.farnell.com/molex/203863-...pos/dp/2885459


Click the image to open in full size.

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 by Mark Tillotson; 22nd January 2020 at 05:03 PM.
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Old 24th January 2020, 09:28 PM   #4
Mark Tillotson is online now Mark Tillotson
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Click the image to open in full size.
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(!)
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