Electronics > Beginners
false/2nd solder pad raised off pcb. what is it?
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Brian Rourke:
so i ordered a few 18650 pcm/bms.
the board has solder pads to connect wire or nickle strips but they're raised off the surface of the pcb.
when you heat and apply solder the surface slides around. at first i though i had lifted the pad.
because i have 10 and they're so cheap decided to play around with it. I pulled that pad straight off the pcb,
beneath it was another pad at the vertical level of the pcb. at 350c I left my iron on it trying to de-laminate
it, even after a dozen seconds and scraping w tweezers that second pad wasn't coming off.

I wanted to know, whats the point of these, what purpose do they serve?
What are they called?
Thanks all
Psi:
I've seen those things as gold plated SMT pads as part of a PCB switch contact.
etc.
https://www.harwin.com/product-highlights/pogo-pins-pads/

Like for example if you wanted to make your own mechanical switch using a piece of metal touching the PCB.
For the contact point you might want a hard gold plating however doing that to the entire PCB is expensive. So you use small SMT hard gold pads that can be placed and soldered to the PCB as part of the normal SMT assembly process.

I assume you have a similar thing expect it's obviously not gold. Maybe it's a silver contact.

However i cannot tell you why it's there. There doesn't seem to be a reason to use it.
Maybe that PCM/BMS is part of some bigger assembly and it clips into a holder where it touches some other contact to connect to the cells
PA0PBZ:
My guess is that it's for spot welding, you don't want to do that on a solder pad :)

Psi:
Yeah

That would make perfect sense.

Brian Rourke:
I think you may be right. I saw a battery pack advertised and it appeared as if nickle strip was spot welded to a similar pcm.
Its just a unique feature. I really want to know what they're called. After removing it i still had continuity from the pad below along the trace.
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