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I have a flex circuit board with 5 LEDs mounted on it.

I have large copper areas attached to the LEDs for improved heat dissipation.

I read here that "With a hatched plane, the moisture can exit the flexible carrier material, whereas it is trapped under solid planes"

This is a different question because it involves LEDs that require solid copper areas for heat dissipation.

Since the copper areas are only on one side of the flex, should I still hatch the copper areas?

If hatching the areas is recommended, how can I calculate the required hatched area for heat dissipation?

Dutch2
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  • How many watt's / cm^2 ? – Tony Stewart EE75 Feb 01 '18 at 20:56
  • The hatch or diamond pattern is normally used for RF circuits only, or high-speed logic over 50 MHZ. –  Feb 01 '18 at 21:03
  • Possible duplicate of [Solid ground-plane vs Hatched ground-plane](https://electronics.stackexchange.com/questions/5139/solid-ground-plane-vs-hatched-ground-plane) –  Feb 01 '18 at 21:39
  • @Tony about 125mW per LED, anywhere from 80 to 150 mm^2 per LED copper. – Dutch2 Feb 01 '18 at 21:47
  • I'd be a bit concerned about the "flex" part. If this is meant to flex a lot and often, a big homogeneous plane may crack and split. – Trevor_G Feb 01 '18 at 22:14
  • @Trevor_G The flex is only moved during installation and then fixed but may be subject to vibration. Are hatched areas better able to withstand flexing? – Dutch2 Feb 01 '18 at 22:16
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    @Dutch2 OEM suggests 9 mm² per corner anode pad. I suggest 625 mm²/W is minimum . so 80 mm² is good or more hashed outside the 9 mm² pads with free air. Vibration or resonance and fatigue to copper must be limited in travel. THis heatsinking could be better than some cheap stripleds. – Tony Stewart EE75 Feb 01 '18 at 22:22
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    @Dutch2 a crack in the copper will propagate through a solid pour. Hatched it has rip-stops. – Trevor_G Feb 01 '18 at 22:35
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    @Tony I believe that is the answer, 9mm² solid copper per anode like the datasheet recommends and the remaining area hatched. – Dutch2 Feb 01 '18 at 22:41
  • We have designed several rigid-flex circuits and have them manufactured by a good supplier. I have never heard that hatching copper helps with moisture or crack propagation. One reason to hatch copper is to increase flexibility. I have always used solid copper planes, it has not been a problem. – EE_socal Feb 02 '18 at 17:03

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