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I recently come across several items employing a special type of heat sink structure .

Usually I see plate fin heat sink or pointy fin heat sink, they all have fins that are uniformly distributed.

Like this(Wakefield-Vette 655-53AB)

enter image description here

or this (Wakefield-Vette LTN20069)

enter image description here

.

But the ones listed below, however, have a non-uniform fin structure that I assume there should be some reasons behind.

Does there anyone here happen to know what's the name, origin and mechanism behind this kind of structure?
A CPU heat sink,

CPU heat sink

a high power radio device,

A high power radio device

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    \$\begingroup\$ Not sure what the "high power radio device" is doing here. I doubt that it is high power anyway. You are making too much out of the shape of the green heatsink. The reason for not having fins in the middle can be as easy as a cost reason (easier/cheaper manufacturing). There is probably no technical reason for having the shape that it has. Also, often a fan is mounted on top of such a heatsink, since the middle of the fab does not displace air there's not much advantage for having fins in the middle. \$\endgroup\$ – Bimpelrekkie Sep 14 '17 at 7:34
  • \$\begingroup\$ @Bimpelrekkie if you look closely to the surface of the "high power radio device" , you can see the same heat sink pattern shows there. It was just a little bit of surprise when noticing the green heatsink. Not until I saw the same heat dissipation pattern on the radio device (30 dBm UHF device), I start to wonder if there is something special about this pattern . That radio device sells about 4000 dollars as the demand in the market is small but high-end (It is a UHF down-converted wifi device). I think if I were the designer, I will value performance more. \$\endgroup\$ – Eagle Shou Sep 14 '17 at 7:42
  • \$\begingroup\$ ...surface of the "high power radio device" , you can see the same heat sink pattern shows there. In my opinion the pattern is a coincidence and just for decoration and/or better grip and/or making the case stronger. 30 dBm is 1 Watt, I would not call that high power. \$\endgroup\$ – Bimpelrekkie Sep 14 '17 at 8:09
  • \$\begingroup\$ FWIW, the fact that the radio is 1 W RF power does not mean it disspates 1 W of heat. \$\endgroup\$ – Vladimir Cravero Sep 14 '17 at 8:45
  • \$\begingroup\$ @Vladimir Cravero I shall bring to your attention that it is a down-converted UHF wifi module, which may imply three things 1. the power efficiency is expected to be low (in terms of unnecessary stage and high PAR due to OFDM). 2. the operating frequency and the power way exceeding 802.11 spec may implies this is an outdoor application. There shall be some sort of rugged isolation design to protect it from unfriendly environment. 3. The price should match to a high expectation for performance. Thus I conclude heat dissipation may be a concern... Though I don't know details of this thing ... \$\endgroup\$ – Eagle Shou Sep 14 '17 at 9:49
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The hole in the center is used to clamp the heatsink down and apply pressure to the IC it cools. This was a quite popular design back when thermal adhesive tape was not available or deemed not reliable enough. Today it has largely gone out of fashion but for applications where thermal tape cannot be used (e.g. high power application where the lower thermal resistance of thermal grease is needed). Incidentally, because this design was quite popular, it was available very cheap from multiple vendors. A lot of manufacturers still stick to these even though they use thermal adhesive tape, because they are cheap. Kind of an economic motivated cargo cult.

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    \$\begingroup\$ Thank you very much for your answer ! When you say the 'hole' in the center, do you mean the solid flat sqaure at the center, or you mean the hole at the side? BTW, from you mean, I would use the phrase 'llama dung' instead of 'cargo cult' :) ..... edn.com/electronics-blogs/embedded-insights/4439484/… \$\endgroup\$ – Eagle Shou Sep 14 '17 at 13:06
  • \$\begingroup\$ The 'hole' is the elongated hole/slot at the side, where you could put a clamp through to fasten the heatsink on the PCB. The Llama dung is funny. Didn't know about this. Thanks! :-) \$\endgroup\$ – Attila Kinali Sep 14 '17 at 14:05

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