Welding to a PCB

[jt]

Does anyone have experience capacitive-discharge welding to a PCB?  I came across the video linked below and had a few ideas in how a similar process could benefit an application I have in mind.  I haven't had a lot of luck finding any other resources on the processes, so I was wondering if anyone knew of any application notes, or could share personal experience of any pit-falls to be wary of.  I don't really have any specific questions right now - just looking to learn more about the process.



Thanks!

[helius]

It looks similar to the welding apparatus for battery tabs. The key is very low voltage with up to a thousand amps; some people use rewound microwave oven transformers, to get very low source impedance. To get a low impedance using capacitors, a bank of ultracaps of several Farads could work:
http://www.ledhacks.com/power/tab_welder%20ii.htm has plans

[uncle_bob]

Hi

Resistance welding to copper is do-able, but it's not an ideal material to weld to. With a PCB, you normally have a very thin layer of copper. That gives you a pretty good heat impulse into the board. Coming up with a board process that does not let loose is tricky.

Bob

[jt]

With a PCB, you normally have a very thin layer of copper. That gives you a pretty good heat impulse into the board. Coming up with a board process that does not let loose is tricky.

Thanks - this is what I was mostly concerned about.  I've cap-discharge welded to Li-ion cells (like helius's mentioned application) but was concerned that the PCB features might be too thin to be reliable.   My application is high-reliability, so maybe there is a PCB fab process that can alleviate concerns (ex. hard-gold plating of some thickness)?

Thanks again for your insight. 

[T3sl4co1l]

Soldered (THT) screw terminals, with suitable hardware (star and tension washers, and strain relief for the cable) would be pretty good I think.

You can bolt directly to the board as well, but the board flows over time, so you need a lot of stiff spring washers to keep it solid.

Tim

[janekm]

I've tried it (using a discharge spot welder to weld poly batteries to a PCB, to avoid heating the batteries from soldering) but the connection was not mechanically reliable due to the thin-ness of the copper layer on the PCB.

[Neverther]

On the video it looks more like making a press fit with the spot welder as the added part is folded to touch both of the electrodes, pressed and then heated to change shape.

[T3sl4co1l]

Also looks like there's a lot of vias, which will help improve tensile adhesion.

Even just the metallurgical bond seems dubious; I'm not sure offhand how gold and nickel interact, but there are some metal combinations where that would be a bad idea, like purple gold formation against tin plated brackets.

Tim