How to solder lots of ring terminals quickly

[loki42]

So I need to solder quite a few (750) switches with ring terminals (http://www.sci.com.tw/PRODUCTS/switch/(R13)%20PUSH%20SWITCH/R13-85.htm) to connect them to a PCB. Currently I solder wires onto them and crimp the other end with JST connectors (ZH) and connect them. I'm wondering if there is a faster way people use to solder these on or something I should search for to out source this.  Currently cutting heat shrink, soldering and shrinking takes me about 1 minute each which is 12.5 hours for 750. If I can speed that up a little it'd be great. I guess maybe something that crimps to the ring terminals or some way to stick the wires onto it while I solder.   

[DaJMasta]

Working assembly line style and preparing steps should help, also flux can make the terminals reflow very quickly (I usually use paste flux for this) vs. spending time to heat them up.  I'd do something like:
Make a jig to hold a switch (or several of them, ideally) in an easily solderable position
Precut wires with a little bend in the end to hold them in place
Precut heatshrink


Then the assembly would be:
Load switches into jig
Dip wire ends in paste flux and put in lugs
Solder all the lugs
Slip heatshrink over all wires
Shrink all heatshrink with hot air gun
Crimp connectors on the other end
Slide crimped contacts into connector housing


If you're doing them in batches of 5+ you can probably spend only a couple minutes on assembly, and while there's the prep steps to go through beforehand, they can be made pretty quick too, and the overall time savings comes from not having the overhead of switching between tools and shifting parts around for each piece.

[FreddieChopin]

Buy some colophon (kalafonia), dissolve it in denaturat alcohol and you'll have a great liquid soldering flux to apply with paintbrush.

[loki42]

This is pretty much what I'm doing at the moment. I don't dip the ends in flux though, I've realised over time that the solution to all soldering problems is more flux. Would a no clean flux be required for that so I don't need to clean off flux afterwards? Or is something like this okay: https://www.jaycar.com.au/solder-flux-paste-56g-tub/p/NS3070?utm_campaign=redirect&utm_source=NS3070r&utm_medium=web this one says "The rosin based paste is ideal for situations when post-soldering cleaning is not possible." but it's also not described as no-clean.

[reboots]

I produce a very similar assembly. I haven't found a way to optimize soldering on the switch side, but it takes less time for me than crimping the JST contacts--and you can certainly optimize there:

https://www.digikey.com.au/products/en/cable-assemblies/jumper-wires-pre-crimped-leads/453?k=jst%20zh

But while you might manage a production run of 750 in-house, this could be a good opportunity for an exercise in contract manufacturing. If your product succeeds, the next run of 1500 will be even more onerous.

[DaJMasta]

For a while, and before I knew about some fluxes that could do damage to boards, I used a Lenox general purpose soldering flux - probably not a great choice near a PCB, but did a fine job.  I think the important part is that the flux is tacky, and not just a liquid - using flux from a pen would just evaporate and have minimal effect, but recently for the lugs I've done even my regular SMD flux - Chipquik SMD291 - has done just fine.  Since you're not soldering to used switches or especially dirty joints, I think almost anything will give you faster reflow, so long as it stays on the terminals.  And dipping the switch contacts (or the wires) directly into a tub of paste flux is probably faster than using a syringe of it or something similar.