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Solder bath for pcb's

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4/30/2000 12:00 PM

Solder bath for pcb's

I'm interested in making a solder bath for pcb's. The first question I have is What temp does 60/40 rosin type solder melt at? I don't really have any way to take the temp of my soldering iron so maybe I can get the info here.
Next, Has anyone done this? I know this is the way pdb's are done in industry but they have cool machines and lots of research $$ to figure it out. I'd like to follow a tried and true example if possible.

Thanks one and all, Firefly

4/30/2000 2:47 PM

I don't want to appear too negative, but I really don't think this is a good idea. Commercial machines have a fluxer, a board preheater and a wave-solder bath, where the molten solder is circulated over a weir so it forms a wave. Solder temperature is typically about 235°C.

Leaving aside the safety implications, of which there are many, you can't used flux-cored solder in a solder pot, because the flux would burn and form crud on the surface. That's why you need a fluxer on a wave-solder machine.

Also, if you leave the board in contact with the solder for more than a few seconds, the resin in the board will melt.

4/30/2000 4:49 PM
Don Symes	Then, there are the safety implications - pounds of molten solder at or above 260C, lead fumes (airborne lead) that need to be extracted, smoky, stinky operation, little plastic toys polluting your solder (got kids?) I wouldn't (not at home) If you still care, the device is called a solder pot.

4/30/2000 8:09 PM

Well, I'm a potter so I'm versed in heat safety. My kiln fires off at about 2400F. I'm gonna have to get my book out and look a coversion from C to F but I'm thinking its roughly 500-600F for the melting point of solder. That's pretty hot for little components. You definitely couldn't take too much time with it. The thing I'm thinking about is that on a regular basis I could have a kiln at that temperature so all I would need would be a metal container of the right size and shape to hold the solder. Heat it up, pull it out of the kiln and dip. It shouldn't take more than a couple of seconds to do a whole board. So, Where would one get supplies?
I would need flux, flux free solder(do they make that?). I have all the heat resistant materials for handling the solder pot....so Lead fumes. I don't like them...

Is it safe to vent lead fumes into the air outside ones living/working area? My kiln is vented this way to expell the various gasses produced when firing. They include crbon Monoxide, dioxide and some sulpher. They stink too BTW.

I am not yet turned off of this since I have the heat thing covered..

Thanks, Firefly

4/30/2000 11:20 PM

Not sure about how to dispose of fumes, just know the industrial hygiene guys go nuts when the hear 'solder pot'.

BTW, it's not so much 'dip' as it is 'lay-briefly-on-the-hot-surface'.

Have good coats of flux on the joints, and larger non-soldered holes taped off with kapton.

With the kiln approach, you could get off with buying just the tub out of a solder pot (as a replacement item). The flux-free solder is sold in one-pound bars of whatever tin/lead mix you need.

It's a worthwhile experiment for you since you've already got the expensive and hazardous stuff dealt with. I wouldn't do it, personally, but I do wish you every success.

5/1/2000 1:42 PM

For all the reasons already noted, this is a bad idea from a safety standpoint.

However, I have seen dip soldering (that's what people used to call it) done in an old electric skillet that was never to be used for food again.

60/40 melts in the range you andicipate; most references have the exact temp. The procedure for dip soldering in a pot is to install and clinch all the leads, then brush a layer of liquid flux over the entire bottom of the board. Using high-temp tongs, you lay the board on top of the skimmed surface of the solder for no more than 2-3 seconds.

Components are usually rated for 300C for 3 seconds specifically for wave soldering.

Again, I recommend you NOT do this, as the dangers are incredible.

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