I’ve been struggling with this very problem, and trying to follow the guidance on this thread.
Here’s a photo of the relevant part of my PCB:
This is the through hole that I’m using for the battery pads:
The center oval is 1.75mm x 0.75mm. The area right around it is plated, as is the hole.
The first thing I tried was using soldering paste and a hot plate. That sure got the ESP32 attached, but I think that just fried it - the CH LED didn’t light up when I plugged in a USB cable, and it didn’t talk to Arduino either.
When I tried tinning the area around the hole, the hole itself got filled with solder, and although I could get some of it to melt, it seemed to not melt all the way down to the ESP32’s pad which was tinned. (So, in practice, the ESP32 fell off when I removed the clamp.)
I also tried just putting a big blob of solder onto the ESP32’s pad and sending heat through top of the hole with the side of my chisel tip, but that didn’t seem to be enough to melt the solder on the pad - I set my Hakko to 770 degrees, and held the tip against the oval hole for 15 seconds, but no luck.
I just ordered an H18-C05 tip, since it looks like it would be small enough to actually fit through the hole and reach the solder below, but I’m pretty concerned about the tip of the tip getting hot enough to be useful here.
Anyone have other suggestions? Should I make my through holes bigger? Tagging @PJ_Glasso since you seem to have had success doing this.
Very grateful for any advice.