Best Methods of Soldering Wires to Boards? - Page 1
Forum section: electronics / projects

author: pauljmccain
author_rank: Contributor
timestamp: November 26, 2014, 03:53:23 am
content: Hello,I searched a bit and really didn't find anything regarding this, forgive me if I missed something.I develop LED boards for automotive applications. Based on my analysis of various boards from OEM vehicles and their suppliers, generally, anytime there are four or fewer wires going to a board, they are soldered directly to the board with a through-hole or surface wirepad. (Anytime there are more wires, a connector is placed, but the housing is often then molded as well in a way to secure it, and avoid disconnection from years of vibration on the road)So currently, I am tinning leads and soldering to tinned surface pads. It's not slow, but it is the slowest step of the whole process right now. I have considered switching to through-hole wirepads, but I don't think it would be much faster, especially since I'd have to trim them up. I assume larger manufacturers are not soldering wires on by hand.I have tried to search for solutions, to see how the "big guys" do it in a more automated fashion, but I can't find anything.Does anyone have any ideas, or know more about how to automate wire connection to PCBs?Thanks in advance for any feedback.-Paul

author: timb
author_rank: Super Contributor
timestamp: November 26, 2014, 04:47:36 am
content: There is automated equipment that places and solders TH components into place. I'm sure specialty equipment also exists for wiring, but it's generally done by hand. In China, unskilled labor is very cheap. Often times you'll see Chinese characters on the silkscreen of PCBs near the holes the wires go in, these are normally indicating a color so the unskilled labor can solder the proper wire in by color. You see this in Dave's recent Rigole scope teardown video when he gets to the power supply.Either use a connector or solder by hand. Those are your realistic options.Sent from my Smartphone

author: Psi
author_rank: Super Contributor
timestamp: November 26, 2014, 05:02:48 am
content: To secure it you can place 2 non-plated holes on the PCB before the main plated TH.Thread the insulated wire through one, then the other, and finally solder a small stripped section of wire into the 3rd hole.This provides some protection from vibrations and from being pulled on by the user.

author: Niklas
author_rank: Frequent Contributor
timestamp: November 26, 2014, 08:07:58 am
content: I agree with Psi. We are currently using a similar method, but the wires only pass through the PCB once before they are soldered onto a soldering pad. Put one or two vias in each soldering pad to secure it mechanically to the PCB laminate. Also think about the pad to pad distance if you are going to use Chinese labor to avoid problems with solder bridges.Also consider plating of those strain relief holes if HAL is selected as surface treatment, as the deposited solder will soften the edges of the holes.

author: coppice
author_rank: Super Contributor
timestamp: November 26, 2014, 08:16:17 am
content: Quote from: Niklas on November 26, 2014, 08:07:58 amOne hole relieves the bending stress where the solder has wicked up the wire. A second hole usually gives enough anchoring to provide some robustness against tugging the wires. I'm not sure you want these holes rounded with solder inside. The wire would slide through more easily, when you want it to anchor.

author: Niklas
author_rank: Frequent Contributor
timestamp: November 26, 2014, 05:04:13 pm
content: Quote from: coppice on November 26, 2014, 08:16:17 amWe have seen a difference in survival time on the vibration bench between the plated and unplated relief holes. The wires are also kept in place by a rubber part about 10 mm away from the relief holes, so perhaps this does some of the work as the second relief hole.

author: Yago
author_rank: Frequent Contributor
timestamp: November 26, 2014, 06:15:40 pm
content: Crimp the wire to a ferrule (bootlace?) and then solder that to the board.A soldered wire is brittle.

author: Macbeth
author_rank: Super Contributor
timestamp: November 26, 2014, 07:18:42 pm
content: When I solder directly to PCB through holes I use hot snot on the top side to provide some security and strain relief. Even the Wun Hung-Lo factories do this, so it can't be bad.

author: ajb
author_rank: Super Contributor
timestamp: November 27, 2014, 02:43:53 am
content: Notwithstanding options that don't ultimately involve soldering the wire to the board, are you using a solder pot to tin the wires, or just an iron? A solder pot will be a tremendous time saver and give more consistent results.

author: max_torque
author_rank: Super Contributor
timestamp: November 27, 2014, 12:19:48 pm
content: Only option outside of soldering is some form of mechanical "crimp" or "weld". You can get little nickle plated copper pins that can be soldered onto the pcb during production, and then take a bare wire and are crimped to capture that wire. For really high volume stuff, the copper wires can be ultrasonically or thermally spot welded directly to thick copper SMC pads on the pcb. In either case, strain rellef from overmoulding, potting, or other mechanical wire support is necessary for high vibration (ie automotive) environments.The best option of course, is to not use "wires" at all and often, automotive products that operate down at 12 or 24V will have a separate thick copper bus bar "layer" used to move power around the pcb, and that layer is injection moulded into a plastic form to keep it robust. This layer then has "pins" that can be soldered down or up to the pcb as necessary. Typically, this layer is joined to I/O connectors via welding methods.For example, in this automotive H bridge (EPAS controller):

author: nctnico
author_rank: Super Contributor
timestamp: November 27, 2014, 12:52:35 pm
content: Quote from: Macbeth on November 26, 2014, 07:18:42 pmI do the same thing. For automotive I'd use a PU based glue instead because the hot melt glue is hygroscopic.

author: calexanian
author_rank: Super Contributor
timestamp: November 27, 2014, 08:07:14 pm
content: Quote from: max_torque on November 27, 2014, 12:19:48 pmLook up the specs on those Sanken MLD685's 280 amp pulse 85 amp continuous! You could switch the starter with a couple of those, or heck, just drive electric motors directly. Sanken has always made great stuff. Too bad most of it is counterfeit.

author: pauljmccain
author_rank: Contributor
timestamp: November 28, 2014, 04:33:39 pm
content: Thank you for the replies, everyone. I'm not too worried about methods of securing the wire, we don't have any problem there- just speeding up the process. Wires are all tinned in automated fashion with a pot right now so the actual soldering is pretty quick, just was interested to hear if there were any methods for further automation. Sounds like the "weld" is the only automated solution but is not the most reliable.Thanks again for everyone's input!

author: DTJ
author_rank: Super Contributor
timestamp: November 29, 2014, 12:33:20 pm
content: +1 for solder pot. Dip in flux first.Solder to pretinned surface pads.ie tin pads, tin the leads and then for assembly you just touch on and reflow. Then take all the wires and poke them together through a suitably sized strain relief hole (or two).

author: Yago
author_rank: Frequent Contributor
timestamp: November 29, 2014, 01:07:55 pm
content: Are there some forms of "rated" hot melt glue sticks?Just all the stuff I have used is no good for anything other than temporary bodge.It does very poor in cold, vibration, it seems to like reacting with solvents or oils etc.

author: wraper
author_rank: Unknown
timestamp: November 29, 2014, 01:15:59 pm
content: Quote from: Yago on November 29, 2014, 01:07:55 pmDon't think that hot melt glue can be reliable by definition. Use neutral silicone instead.

author: Christopher
author_rank: Frequent Contributor
timestamp: November 29, 2014, 02:05:42 pm
content: Rtv silicone is good for vibrationMolexdo a range of cheap connectors with vibration latches. Crimp connection is much better than a soldered joint