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Are thin copper tracks not allowed on Aluminium substrate PCBs?

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Flyback

Well-Known Member
Hello.

Is it true that Aluminium core PCBs for LED mounting should always be almost totally covered in copper pours?

We are doing a LED PCB using an aluminium core. It has 35um copper tracking and 100um isolation dielectric between tracking and aluminium substrate. The aluminium core is 1.5mm thick. (other dimensions are 110mm by 46mm)

The attached shows our copper tracking on this PCB? Please advise if it is totally wrong, and should instead have loads of copper pours.
 

Attachments

  • Aluminium PCB.pdf
    29.2 KB · Views: 237
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Please include the part number for the LED.
What I am trying to find out is; Is the middle leg isolated? Does the heat come mostly out of the middle leg?
 
Thanks.
LED:
**broken link removed**
..Its luxeon C color line..red green and blue ones.

Attached is same PCB but with me having added more copper pour.

I think most heat comes out of the tab
 

Attachments

  • Aluminium PCB with copper pours.pdf
    110.8 KB · Views: 252
I would go to the sch and connect the middle pad to ground. (all LEDs) (it is isolated)
Fill the board with a ground plane. Turn off "thermals".
The reason for turn off thermals is to connect the middle pad to ground with a thick trace.
 
thanks, this is an aluminium core PCB, and as you know, there can be no ground plane.
I was thinking of having a thick trace out of the thermal pad (instead of the "necked" down one that i have) but worried about wicking the heat away during soldering.
 
wicking the heat away during soldering.
You are using aluminum core and you are concerned about heat getting away from your part during soldering. It will if you hand solder one part at a time. (with or with out wide traces)

I think you will heat the entire board, aluminum and all, solder all parts at one time, and there will be no problem. I have demonstrated that there is not a problem. In my case I may have several (internal) layers of copper ground/power plain(s) and parts soldered to the top and bottom which is 85% copper. All we did was add some seconds to the heat up time in the oven. (which you would do if there are large parts)
 
Hello,
Thanks, do you think the attached is better? There is now a single copper pour connecting all LED Tabs. The isolation between this pour and other copper is 0.3mm. I hope this is OK for MCPCB? (the distance between the LED pads is in fact less than 0.3mm and is unavoidable) I presume that there will be no problems with heat being 'wicked' away by this extra thermal conenction to the LED TABS. As you say, the whole thing will be heated up ready for soldering, so heat getting 'wicked away isnt so much of a prolem for MCPCB boards?

All topcopper is 70um.
 

Attachments

  • SCHEMATIC__LED MCPCB.pdf
    71.4 KB · Views: 201
  • LAYOUT__LED MCPCB.pdf
    107.3 KB · Views: 214
I like what you did. The heat should, through copper, spread out away from the LEDs. Then the heat should transfer into the Al.
 
The layout is now as in the pdf in post #8. As you can see, there is a large single thermal copper pour connected to all the thermal tabs of each LED. This large copper pour is in fact floating. Should i tie it to some electrical node so as to stop it from floating up to some high potential, whereby it may then break over the isolation between tab and electrodes in the LEDs?


I note that our MCPCB is also actually floating, and i wonder if it is necessary to ground it with a ring terminal which gets screwed to the MCPCB, and then wire this terminal to ground?
 
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