Cooling effect of multiple VIA ?

[DUPD]

Let's get to the point: In our Design, I placed a trace either on TOP and BOTTOM layers, 350mils width X 4.4inches long, FR-4 PCB, 2 layers, 3 oz. Have to carry 30 amps. We have a TQFP-64 CPU with 8 mils traces...

Due to high reject level from PCB manufacturers, we have to downsize to 2oz. But "power traces" will for sure overheat... We performed some tests and realized that when removing soldermask, we increase thermal transfer to air and of coarse solder helps to increase trace thickness on bottom side. But it is not enough... I would like to put a bunch of VIA to increase heat transfer between TOP & BOTTOM layers but.... Will it works ? Is this a solution or if VIA won't help ? What size of VIA should I use ? How many ???

More hints: We need a LOW COST solution, thus forget about forced convection or multilayer PCB...! Not enough space to increase trace width or bus-bar.

Thanks for helping !

[randychase]

I am not surprised you had trouble over 2 ounces.

I have done exactly this for heat dissipation. Putting in a lot of vias does work for thermal transfer, specially of those vias are flooded over with copper (or covered in copper shapes) on different layers. It also helps as you found out, to not have soldermask where you want more cooling.

What kind of vias? Whatever you are using now. How many? As many as you need.

You can calculate the current carrying ability of the vias you are using by the calculator on this site.

[robert Tarzwell]

yes extra vias help reduce the tempurature but nothing beats copper. there is manufactures out there that can produce circuit boards with as much as 20 oz of copper,,and with amasing fine line ability. Although most manufactures dont want to be bothered , there are at least 5 that will make heavy copper boards. I personaly owned a shop which specilized in weird high tech boards, and we reguialry made 10 and 15 oz boards up to 6 layers or more. And not to much higher price then 2 oz , and Randy not all circuits are etched, by combination etching and plating a 10 oz circuit can be made with 20 mil traces and spaces. In fact the best I ever produced (100's) was 20 oz with 10 mil trace and space. there are books i have writen on the subject available at megadawn.com if i can be of any help to designers you can e-mail me on this forum. robet tarzwell