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You shouldn't really lap solder wires to boards. They tend to pull the pads off the boards or crack. Better to use wire to board connectors or solder terminals.

by gw99 4y ago

exmadscientist 4y ago
No, you shouldn't lap join wires to surface-mount pads. But sometimes you have to. Just don't deliberately design something this way and we'll call it good. (Through holes are fine. Mostly.)
- Ao7bei3s 4y ago
  Yes, but if you do have to design a PCB for soldering wires to pads, you can increase the strength of the pad by making the pad much larger in the copper layer. You can still keep it the original smaller size in the solder resist layer; keeping the soldering area away from the pad edge and fragile traces there increases the strength further, and gives it a tidy look and a nice soldering experience. For quick one offs, simply place a normal pad, place a copper fill polygon connected to the same net around the pad, and turn off thermal reliefs / set pad connection to solid for the polygon. Obviously if you need it a lot, draw a new footprint.
  - gw99 4y ago
    You should even really do that. There are loads of nice solder in crimp terminations now that you can use for wires. Or wire to board connectors. Just stay away from any Molex crap. Tends to charcoal itself.
    - buescher 4y ago
      There are some really cool surface mount IDC things too, and push-in terminators for solid wire. Solid wire through holes is OK if the wire is never going to flex. Otherwise the stranded wire lapped to surface mount pads, or soldered into through holes, with a big blob of hot glue or epoxy for maybe-sorta "strain relief" is a great pet peeve of mine - it's ugly and it breaks. Never had a problem with Molex, myself.
      - exmadscientist 4y ago
        Molex is great if you get the reflow-compatible models. Their older lines with the non-updated parts do have some issues at high temperatures. If you really care, look for glow wire tested parts. Or just, y'know, keep your iron away from them and buy spares for when you don't....
      - gw99 4y ago
        It's the .154" Molex stuff that tends to melt after 20 years spontaneously. Not sure what plating they use bit it turns into a power dissipating resistor after a bit which is not good when you're shoving a few amps through it.
  - exmadscientist 4y ago
    Nope. Do it that way and your pad still rips off. You need to nail the pad down with a few vias (under soldermask is fine) or use a through hole. Please just use a through hole if you can. They're a lot more reliable than just about anything else. Even SMT connectors rip off boards without much trouble. (This is my job. I have seen some things.)
    - deleted 4y ago
      [deleted]
johnwalkr 4y ago
Those just starting out tend to think of solder as more direct than using a connector so therefore more secure. But it’s surprising how poor the reliability can be. Aside from your points, solder can wick up a cable, and then the cable often breaks just at the point where the solder ends since it has no strain relief and may be right in the middle of a bend. This is especially true for adding solder to a crimped connector “for good measure”. It does more harm than good. That being said it’s convenient many times especially if you don’t have connectors on hand or need to place wires in a specific orientation. Hot glue or better yet, RTV silicone can be used to make strain relief to increase the reliability. Or, when using perf board like in the post, a good technique is to drill a hole for a snug fit of the cable including insulation, then pass the cable through the hole before soldering to an adjacent hole.
- gw99 4y ago
  Good advice. It’s worth expanding on my comment now I have a few minutes. You can terminate solid core like this if it has some strain relief but not stranded!. My favoured construction method is to take a Hammond box lid and screw a piece of blank FR4 single sided copper to the inside of it leaving enough space around the edges for any (proper) connectors you need. You can then drill out anything you need, usually BNC, SMA, DC jacks, FT capacitors and D connectors for me. You build the prototype on the FR4 board dead bug and use solid core or RG174 to wire up the connectors and lap solder them to the boards or components as required. This is done carefully with thought for weight distribution and to keep the total mass of the wires low. When it works the Hammond box is closed. If it needs to withstand vibration or moisture you build it into the bottom of the Hammond box and when done fill it with potting compound.
Ccecil 4y ago
Another way is to solder direct to the board but have strain relief holes which the wire routes though. There are footprints for this in kicad.

You shouldn't really lap solder wires to boards. They tend to pull the pads off the boards or crack. Better to use wire to board connectors or solder terminals.

by gw99 4y ago

You shouldn't really lap solder wires to boards. They tend to pull the pads off the boards or crack. Better to use wire to board connectors or solder terminals.

exmadscientist 4y ago

No, you shouldn't lap join wires to surface-mount pads. But sometimes you have to. Just don't deliberately design something this way and we'll call it good. (Through holes are fine. Mostly.)

Ao7bei3s 4y ago
Yes, but if you do have to design a PCB for soldering wires to pads, you can increase the strength of the pad by making the pad much larger in the copper layer. You can still keep it the original smaller size in the solder resist layer; keeping the soldering area away from the pad edge and fragile traces there increases the strength further, and gives it a tidy look and a nice soldering experience. For quick one offs, simply place a normal pad, place a copper fill polygon connected to the same net around the pad, and turn off thermal reliefs / set pad connection to solid for the polygon. Obviously if you need it a lot, draw a new footprint.
- gw99 4y ago
  You should even really do that. There are loads of nice solder in crimp terminations now that you can use for wires. Or wire to board connectors. Just stay away from any Molex crap. Tends to charcoal itself.
  - buescher 4y ago
    There are some really cool surface mount IDC things too, and push-in terminators for solid wire. Solid wire through holes is OK if the wire is never going to flex. Otherwise the stranded wire lapped to surface mount pads, or soldered into through holes, with a big blob of hot glue or epoxy for maybe-sorta "strain relief" is a great pet peeve of mine - it's ugly and it breaks. Never had a problem with Molex, myself.
    - exmadscientist 4y ago
      Molex is great if you get the reflow-compatible models. Their older lines with the non-updated parts do have some issues at high temperatures. If you really care, look for glow wire tested parts. Or just, y'know, keep your iron away from them and buy spares for when you don't....
    - gw99 4y ago
      It's the .154" Molex stuff that tends to melt after 20 years spontaneously. Not sure what plating they use bit it turns into a power dissipating resistor after a bit which is not good when you're shoving a few amps through it.
- exmadscientist 4y ago
  Nope. Do it that way and your pad still rips off. You need to nail the pad down with a few vias (under soldermask is fine) or use a through hole. Please just use a through hole if you can. They're a lot more reliable than just about anything else. Even SMT connectors rip off boards without much trouble. (This is my job. I have seen some things.)
  - deleted 4y ago
    [deleted]

johnwalkr 4y ago

Those just starting out tend to think of solder as more direct than using a connector so therefore more secure. But it’s surprising how poor the reliability can be. Aside from your points, solder can wick up a cable, and then the cable often breaks just at the point where the solder ends since it has no strain relief and may be right in the middle of a bend. This is especially true for adding solder to a crimped connector “for good measure”. It does more harm than good. That being said it’s convenient many times especially if you don’t have connectors on hand or need to place wires in a specific orientation. Hot glue or better yet, RTV silicone can be used to make strain relief to increase the reliability. Or, when using perf board like in the post, a good technique is to drill a hole for a snug fit of the cable including insulation, then pass the cable through the hole before soldering to an adjacent hole.

gw99 4y ago
Good advice. It’s worth expanding on my comment now I have a few minutes. You can terminate solid core like this if it has some strain relief but not stranded!. My favoured construction method is to take a Hammond box lid and screw a piece of blank FR4 single sided copper to the inside of it leaving enough space around the edges for any (proper) connectors you need. You can then drill out anything you need, usually BNC, SMA, DC jacks, FT capacitors and D connectors for me. You build the prototype on the FR4 board dead bug and use solid core or RG174 to wire up the connectors and lap solder them to the boards or components as required. This is done carefully with thought for weight distribution and to keep the total mass of the wires low. When it works the Hammond box is closed. If it needs to withstand vibration or moisture you build it into the bottom of the Hammond box and when done fill it with potting compound.

Ccecil 4y ago

Another way is to solder direct to the board but have strain relief holes which the wire routes though. There are footprints for this in kicad.