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    MCPCB which is double sided and with plated through vias

    Hi
    We wish to make a 6W Buckboost switch mode lighting PCB (15cm by 1.8cm) with LEDs one side and the driver electronics the other side. (everything SMD) There will also be a microcontroller to give dimming control.
    We want the PCB to be as thin as possible, but not so thin it bends easily.
    We believe that we can have two pieces of MCPCB which sandwich a plastic core. We will need plated through vias for the tracking of the driver & control electronics. We believe that plated through vias can be achieved with this setup, and can be done by simply drilling though both pieces of MCPCB where the vias occur, and then drilling through the plastic core in the same position…then plating the hole of the plastic core.
    Do you believe that this is possible?
    How expensive would you think this would be?

    Vin = 20 – 50V
    V(LEDs) = 45V

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    Re: MCPCB which is double sided and with plated through vias

    What should be the purpose of metal cladding with your board? How can it connect to a heatsink? Multilayer MCPCB can be made, although not so common. But vias go never through the metal base plate.


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    Re: MCPCB which is double sided and with plated through vias

    Question: are you using double sided MCPCB (assuming that having a core means there is layer each side of it) or are you proposing two single sided PCBs back to back with plastic between them?

    I'm not sure what you are trying to achieve here. Are you conducting heat into something else and how are the boards mounted?

    Brian.

    [Edit: sorry FvM, got distracted half way through typing and you had replied before I posted]
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    Re: MCPCB which is double sided and with plated through vias

    Thanks, its like this sort of thing
    https://www.multi-circuit-boards.eu/...-core-pcb.html

    ....we are trying to do it like this because having double sided FR4 results in too hot operation of the components/LEDs.
    We think the Al core will distibute the heat more, as in thermal spreading.
    Admittedly we are stuck on where to transport the heat away to.
    The whole thing will be in a plastic tube.



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    Re: MCPCB which is double sided and with plated through vias

    Thanks for clarification. I didn't yet see this kind of double sided MCPCB. So they manage to isolate the vias from the metal core somehow.

    Two points are unclear though:
    - What's your design idea in contrast to the MultiCB "Metal Core 2 layers plated-through" stackup?
    - Are you sure that a metal core serves a purpose for your application? You should verify that the total power can be dissipated.


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    Re: MCPCB which is double sided and with plated through vias

    So you propose something like the bottom image but made from two of the top image back-to-back with your own plastic insulator.

    Sounds unreasonably complicated and expensive to me and has no advantage over the method in the bottom image.

    Brian.
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    Re: MCPCB which is double sided and with plated through vias

    - What's your design idea in contrast to the MultiCB "Metal Core 2 layers plated-through" stackup?
    Thanks, The attached is what we did so far. It is a double sided FR4 board. As you can see, there just isn’t enough room for thermal copper pour for the LEDs (red is top and blue is bottom).
    Thanks Betwixt, yes I agree that bottom diagram is what we now are looking into.
    The MCPCB will help in thermal spreading, to prevent hotspots.

    - - - Updated - - -

    We are just wondering if our ploy of Driver electronics on the bottom, and LEDs on top is a flawed idea? But the problem of having the drivers at the ends of the tubes is that those bits then have no leds ( therefore no light shining out from the end bits.)

    - - - Updated - - -

    There are actually two 6w led drivers in the attached…..one drives a cool white branch and the other a warm white branch….total power will never be more than 6W



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    Re: MCPCB which is double sided and with plated through vias

    I see that the LEDs are populating only a small part of the top side, thus a heat spreading feature may be helpful. The through plated double side MCPCB is probably providing more thermal conductivity that a heatsink-less design can utilize and, I guess, also be quite expensive, did you ask for a quote?

    Standard 2 oz copper 4 layer PCB might be serving the purpose with lower costs.


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    Re: MCPCB which is double sided and with plated through vias

    Agreed - and what are the 'J' references to?

    Brian.
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    Re: MCPCB which is double sided and with plated through vias

    The "J"s are smd resistors used as jumpers

    - - - Updated - - -

    The problem we always are told about with 2oz copper is that it can't be used with TSSOP microcontroller packages etc.
    We always end up being stuck with a max of 1oz (35um)



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    Re: MCPCB which is double sided and with plated through vias

    I'm not sure about that TSSOP/2oz limitation. To be honest I spend little time these days on PCB development but I would have thought soldering such components was more an issue of temperature profile than copper thickness.

    Brian.
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    Re: MCPCB which is double sided and with plated through vias

    8 mil/0.2 mm clearance is industry standard with 2 oz copper, works well for TSSOP packages down to 0.5 mm pin spacing. Wiring density is nevertheless somewhat reduced.

    For your application, 2 oz inner layer and 1 oz outer could be an option.



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    Re: MCPCB which is double sided and with plated through vias

    I've definitely done boards with 2oz copper for 0.5mm pitch parts. Some fabs might charge a bit more though.

    Like you mentioned before, I'm not sure a MCPCB will matter if you then put the whole thing in a plastic tube. I would investigate that first. Strap some LEDs to something similar to the MCPCB (a strip of sheet copper?), package that in the plastic tube, and see if they overheat when driven. If they do, then you have to think of something else...



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    Re: MCPCB which is double sided and with plated through vias

    to be honest, i've seen many LED tubes with LEDs on a 1mm thick FR4 PCB, and they have a good amount of thermal copper pour on the LED side, and the bottom is just bare of copper and sits on a lonfg aluminium heatsink, and that works and has been done to around 30W for a 1 metre tube.
    The idea of the MCPCB was to prevent hotspots because as you can see from the picture, there is little room for copper pour on top or bottom, so MCPCB seemed they only resort for that methodology.



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    Re: MCPCB which is double sided and with plated through vias

    if you can solder a whole heap of QC tabs on the back side - these make great impromtu heatsinks to air ...!



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