High frequency on Al PCB

Discussion in 'General Electronics Chat' started by parklol, Apr 5, 2013.

  1. parklol

    Thread Starter New Member

    Aug 17, 2012
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    Hi there, I am wondering if it is possible to build a buck or boost converter on an Aluminum PCB. I know the switch frequency of these kind of converters could go up to like 1M Hz. I don`t know if the impedance of the Al PCB could be high enough so that there will not be current leakage or any other sort of chaos happening.

    Thank you.
     
  2. #12

    Expert

    Nov 30, 2010
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    Aluminum board? Not likely.
    Aluminum looking traces? Likely.
    Solder covered ground plane? Very likely.
    Can you post a photo of it?
     
  3. parklol

    Thread Starter New Member

    Aug 17, 2012
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    I don't have all the components with me yet. The PCB would look like the one showed in the attached picture (1oz copper on top, probably a 35um FR4 in the middle, and an Aluminum layer on bottom). And the chip I am going to use is from http://www.ti.com/product/LM3401.
     
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  4. #12

    Expert

    Nov 30, 2010
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    That clears up a lot. I didn't know aluminum base circuit boards existed. I also don't know why you want to use something nobody else uses and ask if it will work.

    Hello! Anybody here ever use a circuit board with an aluminum backer plate?
     
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  5. kubeek

    AAC Fanatic!

    Sep 20, 2005
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    Maybe something similar to ceramic boards for better heat transfer?
    Ok I found this http://zbpcb2008.en.made-in-china.com/product/VBQERMjYJAki/China-Aluminium-Based-PCB.html
    Thickness of the copper: 35um
    Thickness of the diclectric: 70um
    Thickness of the aluminum-base: 1.5mm

    Anyway, why do you want to use such pcb, which I guess will be very pricey and will not offer much compared to a standard fr4 board with copper on both sides in this application? Is the dissipation or working tempereature that high?

    Anyway the layout of that board looks very poor for 1Mhz switching frequency - too much loop area - the parts could be easily stuck much much closer together. You need to minimise the area of the main current loops in the circuit to minimise EMI.
     
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  6. parklol

    Thread Starter New Member

    Aug 17, 2012
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    I think aluminum PCB is mainly used in the LED lighting industry. A better heat transfer will result in a longer life time of LEDs. I am trying to mount all the components (LEDs and other parts) on the same board. I feel like a high-frequency circuit will not work properly on an aluminum pcb, even though I haven't tested it yet. I am trying to ask this question here because I could not find anyone did a similar design on google. :(
     
  7. parklol

    Thread Starter New Member

    Aug 17, 2012
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    I am trying to design some high-power LED circuits, and yes, heat dissipation is a critical part of my design.

    Thank you for your suggestion. I will make some prototypes later.
     
  8. #12

    Expert

    Nov 30, 2010
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    Congratulations, you're a pioneer in the field.
    I can understand you thinking about induced currents at near megahertz frequencies. My instinct says the aluminum will merely act as a ground plane. I guess you're going to find out for us.
     
  9. parklol

    Thread Starter New Member

    Aug 17, 2012
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    Thank you for the help. I will try it as soon as I get all the components and post the result here.
     
  10. Ron H

    AAC Fanatic!

    Apr 14, 2005
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    It will act as a ground plane. I suspect our OP is concerned about capacitance. With multilayer FR4 boards, some have internal ground planes, but, compared to the aluminum boards that parklol linked to, the dielectric layers of FR4 are much thicker, and the dielectric constant of FR4 is less than half that of alumina (if that is the dielectric layer in the aluminum boards). Since capacitance is proportional to dielectric constant, and inversely proportional to thickness, the capacitance of trace to ground would be much higher on the aluminum boards. Would that be a problem for a 1MHz converter? I have no idea.:rolleyes:
     
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  11. kubeek

    AAC Fanatic!

    Sep 20, 2005
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    I have no idea what is the price difference between an FR4 board and an alu board, nor what amount of boards you plan to produce, nor what is your target with those boards. But still, errors in the LED part of the board will be very rare, but you could need say three to five revisions of the driver board if you need to pass EMI tests. Depending on how much the non-recurring expenses are on making those boards and what the production volume is, it might be cheaper to just stick with the proven designs and do the driver on FR4 and the LEDs on the aluminium substrate.

    I also have no idea how much more the prototypes would cost, but you see you are going into unproven teritorry where only a few people have any idea what is going to happen. Also, without the real specs of the material you are going to use it is very hard to say anything, so I´d start with that - especially the dielectric thickness, dielectric constant, and the possibility of making connections straight to the alu substrate as it acts as a separate ground plane.
     
  12. parklol

    Thread Starter New Member

    Aug 17, 2012
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    My company has been using Al-based PCB for a while, and any improvement is preferred to be implemented on the original design. I proposed to use FR4 board before, but the company did not like my idea.

    Anyway, thank you for your help. Just let me try this out and see what is going on.
     
  13. kubeek

    AAC Fanatic!

    Sep 20, 2005
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    Well if you are producing something that already works and the efficiency and other parameters are tolerable, then why would you want to redesign it? Or what do you want to improve?
     
  14. parklol

    Thread Starter New Member

    Aug 17, 2012
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    For example, the power supply of an original circuit is a constant current power supply. But some customers want to use 12Vac transformer, so I have to make a new design to let it work with 12Vac.
     
  15. kubeek

    AAC Fanatic!

    Sep 20, 2005
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    You may be able to use the same circuit just with a rectifier and filter in line. Really depends on what you have now, and if you want to redesign it the properties of the ocb material.
     
  16. praondevou

    AAC Fanatic!

    Jul 9, 2011
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    Yes. We are using it for H-bridges in electric power steering.
    Frequency is only 60kHz though.

    Very good heat transfer, no need for a complicated and bulky extra heatsink because the board can be mounted directly on the EPS case ( which acts as the heatsink), easy to assemble (not the board itself) but they are more expensive than normal boards.

    I don't think it's worth it for small quantities and especially not if you enough space to mount a normal heatsink, I wouldn't use them unless it's inevitable.
    There are heatsinks you can solder directly on to SMD components.
     
  17. parklol

    Thread Starter New Member

    Aug 17, 2012
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    Adding a rectifier and filter works fine with magnetic transformer. But when using electronic transformer (probably 30k - 80kHz), the large capacitor in the filter will have a low impedance and the filter is no longer working.
     
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