Electronics > Manufacturing & Assembly

Can you surface-mount components without pins?

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Hi everyone, I'm new to electronics and looking for some soldering advice.

I'm designing an EMG sensor and I'm trying to use gold-plated electrodes. The board that touches your skin is 3mm x 30mm and has three header pins at one end. At 3mm wide, I could not find surface-mounted headers narrow enough [attachimg=1]so I had to use through holes. However, that means the header pins would also stick through into your skin, creating unwanted electrical contact.

The solutions I see are
1. cover the header pins with an insulator, or
2. find gold-plated electrodes long enough to extend way past the header pins.

#1 on its own is not ideal because, if you put something taller than the electrodes next to them, it might prevent them from making solid contact on the skin.

This leaves #2. There are gold-plated contacts that can be through-hole mounted, but their "pin" is usually 1.5mm minimum which feels too big for this 3mm wide board. Regardless, none have a flange end tall enough to surpass the header pins by even 1mm.

The best fix I can think of is to solder a long, gold-plated electrode directly to a copper pad on the pcb without using a through hole, so that the solder is sandwiched between the copper and the electrode. There wouldn't be a pin to put solder on top like a surface-mount component, you'd only be able to put solder underneath. Is that possible? If so, how would you do that?

Here is a diagram of my idea.
Full-size Image [attachimg=1]

Thank you all for your time.

For hand assembly it is absolutely possible to do this. For automated assembly it might be tricky to tune the process, but still be possible. The standoff you are showing here is designed exactly for this. And spring loaded pogo-pin version of this is commonly available.

You do not want to have the hole under it though. Just keep it a plain pad and use via nearby if you need to transition to a lower level.

The issue I see here is that even 7 mm lift would not prevent your connector from touching the skin. So, you would still need to apply some insulation. Given the size constraints, epoxy may be a good option.

and trim the connector pins before soldering so they don't stick through the board

May be you can use standoffs to conduct signals instead of having a separate header.

"#1 on its own is not ideal because, if you put something taller than the electrodes next to them, it might prevent them from making solid contact on the skin."

Then make it so the electrodes are slightly taller, no? I would not want to have bare PCB sitting on my skin, I'd want it in some sort of enclosure.
Maybe look at how other devices on the market do it.



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