Improving ESP32 hand soldering by adding plated through-holes under the thermal pad?

[Dr4w]

I was looking at the ESP32 section of the PCB and noticed the central GND/thermal pad area under the module.

Since this board would likely be hand-soldered by some people, what do you think about replacing or supplementing those GND pads with a few plated through-hole, so the center pad could be soldered from the backside more easily?

The idea would be:

• solder the castellated pads normally from the top,
• then heat and feed solder from the back through the holes to connect the thermal pad underneath the ESP32.

Do you think this would be a reasonable modification?

Example:

or

[jibrilsharafi]

Hi @Dr4w !

I hand soldered many of these boards, and the ESP32 is one of the few components that never gave problems.

By the way, how can you hand solder the board if it is full of SMD components?
You should be reflowing the board after pasting the solder paste with a stencil, which should be applied to the ESP32 as well.

[Dr4w]

Hi, if you mean applying solder paste with a stencil and then reflowing the board, that’s not really hand soldering in the traditional sense, which is probably why the ESP32 pads didn’t give you any issues.

A fairly common approach for these kinds of GND pads (especially on QFN-style packages) is small holes so the exposed pad can also be soldered from the back side of the PCB.

By the way, how can you hand solder the board if it is full of SMD components?

I’m not sure I fully understand the question. The PCB is currently bare, so there are no components mounted yet. But even otherwise, I don’t really see why SMD components would prevent hand assembly.

[jibrilsharafi]

The ADE7953 is a 28-lead LFCSP package. Props to you if you can solder that by hand with no reflowing! I would never be able.

In any case I would avoid modifying the pad beneath the ESP32 as it is the official footprint, and modifying it would mean for sure re-validating the PCB.

[Dr4w]

The ADE7953 is a 28-lead LFCSP package. Props to you if you can solder that by hand with no reflowing! I would never be able.

Maybe there was a misunderstanding. I'll be using a hot-air station, not a soldering iron, to solder these chips. The issue is that I don't have a reflow hot plate, so parts like the ESP32 can be more difficult to solder properly because of the large thermal pad underneath. That's the reason behind my suggested modification.

re-validating the PCB

I'm not entirely sure what you mean by that. However, after doing a bit of research, it seems that the exposed pad on the ESP32 module isn't strictly necessary to solder.

For example, in a discussion on the Espressif forum, Sprite (an Espressif employee) stated:

From the datasheet: "Soldering EPAD Pin 39 to the ground of the base board is not a must. If you choose to solder it, please apply the correct amount of soldering paste. Too much soldering paste may increase the gap between the module and the baseboard. As a result, the adhesion between other pins and the baseboard may be poor."

Based on that, it appears that soldering the exposed pad is optional rather than required, so even leaving it unsoldered shouldn't cause any issues in most applications.

[jibrilsharafi]

Maybe there was a misunderstanding. I'll be using a hot-air station

Ok got it now! I still suggest to pick up a reflow hot plate as it makes life much easier.

I'm not entirely sure what you mean by that.

I know it sounds silly, but from my point of view every minor change needs to be properly validated and tested, and since I am no EE engineer (I am self-thought on the matter) I cannot establish 100% for sure that a via that big under the ESP32 won't create production problems with the solder dripping, or something else.

Based on that, it appears that soldering the exposed pad is optional rather than required, so even leaving it unsoldered shouldn't cause any issues in most applications.

Yes I though it was something clear from the beginning, sorry for not being explicit about it!