0

I am building my first PCB ever with an ESP32. I want the PCB to be built by JLCPCB (or similar) and I am not sure what to do with the Pad39

I read these opinions:

  1. Do not add vias in pad, and if you do put more solder paste in those pads (for example this post)
  2. JLCPCB can do vias in PAD (example link - but does not mention smt assembly)
  3. Official documentation says that Pad39 does not need to be solder at all
  4. Official schematics solders it and add vias to IT

Official docs (link to page 24):

Soldering EPAD Pin 39 to the ground of the base board is not a must, however, it can optimize thermal performance. If you choose to solder it, please apply the correct amount of soldering paste.

Official Esp32 DevKit Layout (I overlapped the layers) (documents link)

enter image description here

Do I need to do anything If I add vias before sending to JLCPCB/PcbWay? Would it be better if I add the vias outside to the pad? For example:

enter image description here enter image description here

My full schematics and layout: link

TypeIA
  • 2,232
  • 1
  • 12
  • 19
Carlos Garcia
  • 1,116
  • 1
  • 7
  • 25

1 Answers1

2

You can safely do without the vias - indeed you can do without the exposed pad entirely. This is confirmed by Espressif in this thread:

If the pad is soldered then it should be soldered to Ground. If soldered then the ESP32 will run a little cooler due to heat sinking into the main board. However, this is not necessary for adequate thermal performance (for example, all the current generation development boards with ESP-WROOM32 have a solid solder mask layer under the thermal pad.)

I can also confirm this from personal experience: the module runs cool (within a few degrees C of ambient) even without the pad. Incidentally, this makes it easily hand-solderable for DIY without a hot air gun or reflow oven.

TypeIA
  • 2,232
  • 1
  • 12
  • 19
  • Note the ESP32 can get rather toasty running both cores at 240MHz and doing lots of WiFi. – Kartman Feb 07 '22 at 00:51
  • @Kartman Can you define "rather toasty" and give some detail on your application where you've seen this? It is not normal. Thorough review of the ESP32 forums confirms this. – TypeIA Feb 07 '22 at 06:32
  • @Kartman Also remember all current dev kits leave off the exposed pad (this is easy to verify). This fact together with the official manufacturer advice I linked is a solid basis for an answer, so I'd ask you to reconsider your DV. – TypeIA Feb 07 '22 at 06:41
  • Depends on how well the chip is heatsinked, but the chip will pull over 0.5W when transmitting. That equates to over 50C temp rise. Run a streaming camera and see how toasty it gets. – Kartman Feb 07 '22 at 06:53
  • @Kartman We're talking about the ESP32 module here, not the standalone chip. That 0.5 W is about right but is dissipated into the ground plane of the _huge_ (by SMT standards) module. (The ESP32 IC itself _is_ thermally soldered to the pad [pin **4**9] on the modules.) – TypeIA Feb 07 '22 at 07:15
  • Any numbers on the junction to ambient thermal resistance of the assembly? And what is 'DV"? – Kartman Feb 07 '22 at 09:43
  • @Kartman No, as best I can tell, Espressif doesn't publish thermal resistance figures for the modules. DV = downvote. I feel confident in the answer as it's based both on official manufacturer guidance and on first-hand experience. Of course, there's no requirement that everyone agree. – TypeIA Feb 07 '22 at 09:59
  • I didn't downvote. Why did you think it was me? Without any specs, it's speculation. Your test method may be totally different to mine. All i can say is the modules I've tested get toasty when worked hard. Not excessive if it is in a benign environment. In a more hostile environment, it may be an issue. – Kartman Feb 07 '22 at 10:41
  • Let us [continue this discussion in chat](https://chat.stackexchange.com/rooms/133921/discussion-between-typeia-and-kartman). – TypeIA Feb 07 '22 at 10:49