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I'm finishing up a PCB design and it has a surface mount (TO-252) voltage regulator. I want the regulator to dissipate heat as much as possible however it will be within its thermal limit with just the top and bottom layers. So I was wondering if it will help to add a solid plane on the middle layer and/or will doing this weaken the PCB overtime or cause other issues?

Thanks

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  • \$\begingroup\$ 3-layer boards are very uncommon, and would require an asymmetric stack-up prone to warping. Do you mean a 4-layer board? \$\endgroup\$ – The Photon Nov 4 '12 at 18:15
  • \$\begingroup\$ It would help if you mention the part number and the operating conditions (Vin, Vout, Iout) \$\endgroup\$ – Oli Glaser Nov 4 '12 at 18:32
  • \$\begingroup\$ @ThePhoton your absolutely rite, 4 layers not 3, thanks! \$\endgroup\$ – Garrett Fogerlie Nov 4 '12 at 18:47
  • \$\begingroup\$ @OliGlaser the voltage regulators, input voltage, current draw, and ambient temperature vary from unit to unit, and my question is more of if this a good or bad practice. I don't have any of the numbers in front of me but I know the junction temperature in the worst cases comes close to the max (probably within 15 or 10 percent, but I don't recall for sure.) \$\endgroup\$ – Garrett Fogerlie Nov 4 '12 at 18:55
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Large copper areas on the top and bottom layers are better for heatsinking than a plane on an inner layer, because they have direct contact with the air that is the ultimate heat sink of the system.

That said, an inner layer can reduce the thermal resistance for heat to travel laterally away from the source, and allow the whole copper area of the board to provide some cooling benefit, rather than just the polygons directly connected to the hot part.

Unfortunately the net result, how much cooler will the part be with the added layer, is difficult to predict, or at least requires an expensive 3-d thermal modelling software to predict accurately.

Ultimately it's your judgement whether a modest reduction in the part's temperature (or a modest increase in the temperature range your board can be safely operated in) is worth the expense of increasing the layer count of your board. I'd think that very few situations would justify adding additional layers just for thermal reasons -- normally electrical concerns are what motivates the layer count and any thermal improvement is just a side benefit.

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  • \$\begingroup\$ Do you know if the high temperatures and changes in temperatures cause any warping or deterioration of the board over time? Also, I didn't make it clear in the question, but the board is already a multi layered board. Thanks for the quick answer. \$\endgroup\$ – Garrett Fogerlie Nov 4 '12 at 19:26
  • \$\begingroup\$ @GarrettFogerlie, Cooler is always better, but a PCB should be able to withstand, say, 80 C for extended periods without trouble. If you need more than a 10 year lifetime for this board, you should look into this more carefully. If you need to minimize warping, try to equalize the temperature between the two sides of the board as well as possible--put a polygon on the bottom side and add several large-ish (12-20 mil, maybe) vias through from the top to connect the two sides. \$\endgroup\$ – The Photon Nov 6 '12 at 17:06

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