Not soldering some pins for space

joewright
Posts: 6
Joined: Sat Jul 14, 2018 6:12 pm

Not soldering some pins for space

Postby joewright » Sat Jul 14, 2018 6:23 pm

Hi, don't know if this is a stupid question, but is it ok to leave some pins on the ESP32-WROOM-32D unsoldered so there's more space to route traces in space restricted situations?

For example, could I omit pads for pins 17-22 as these are used for the internal flash, and route spi or sdio on the top layer through the space (with the soldermask providing the separation) or would this cause problems?

Thanks, Joe

ESP_Sprite
Posts: 3610
Joined: Thu Nov 26, 2015 4:08 am

Re: Not soldering some pins for space

Postby ESP_Sprite » Sun Jul 15, 2018 3:38 am

Should be doable. However, you're relying on merely some solder mask to do the separation. If any, you may want to use the silkscreen to toughen that up a bit: effectively, make a silkscreen square under the pad to provide some extra thickness. Also, you may not want to do this with sensitive (ADC) or very high speed signals, as the pad probably will capacitively couple some noise to the trace and vice versa.

joewright
Posts: 6
Joined: Sat Jul 14, 2018 6:12 pm

Re: Not soldering some pins for space

Postby joewright » Sun Jul 15, 2018 10:26 am

Thanks, I might give it a go. I know it's a bit hacky but I just doing it as a development stage, not for later prototypes or production.

My problem is that I have a physical space requirement which means the board can't be wider than the width of the esp32 module. This means I can't route out from the sides, and I need to get SDI, SDIO, I2S and UART pins routed. I guess I should go to 4 layer but I've never done that before.

I know this is now getting very hacky but, all disclaimers apart, would I be able to route high speed signals under those pads with less risk, if I cut off the pads on 17-22, as well as using the silkscreen rectangle for added protection?

Or is that just too bad, and I should go to 4 layers?

Thanks, Joe

ESP_Sprite
Posts: 3610
Joined: Thu Nov 26, 2015 4:08 am

Re: Not soldering some pins for space

Postby ESP_Sprite » Mon Jul 16, 2018 2:44 am

The answer to that would be a very enthousiastic 'probably'; we can't really say without knowing the signals and what is on the other hand, but you'll most likely be fine, especially for prototyping purposes. I'd personally go for four-layer anyway, I've designed my share of two- and four-layer PCBs before, and it's not that different. Just make sure that you have access to any signals that may be of interest by putting in test points or leaving vias in accessible places.

joewright
Posts: 6
Joined: Sat Jul 14, 2018 6:12 pm

Re: Not soldering some pins for space

Postby joewright » Mon Jul 16, 2018 9:39 am

Thanks, I actually started giving 4 layers a go yesterday, and as you say, it doesn't seem to hard.

Thanks for the advice on my crazy ideas though :)

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