| Electronics > Beginners |
| Copper bar soldering problem |
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| Bud:
when i did not have a propane blow torch i did some plumbing repair using a blow heat gun, it heated copper pipes enough to resolder joints and valves. |
| IDEngineer:
There's a reason they use propane or MAPP gas torches when soldering copper plumbing pipes. All of the above comments about the heat being conducted away are exactly correct. And your bus bar has far more cross sectional area, and is thus a better heat sink, than copper pipe. When soldering copper pipe with a torch, I usually protect the flow of heat away from the joint with wet rags. Granted in that case I'm trying to prevent the heat from spreading to and damaging sensitive and expensive components like ball valves, and what's really happening is that the water in the rags converts to steam which carries away the heat. But thinking about it, wet rags might also create a region of colder temperature and the resulting gradient might prevent heat from conducting away so easily from your work area. No matter what, though, you're going to need much more heat. And by that, I mean you need a HOTTER heat source. Equal area under the curve is not equivalent here; slowly raising the temperature with an insufficient heat source just allows the flux to evaporate, and as you've discovered solder doesn't flow well onto unfluxed bare copper. You need to properly prepare the surfaces, then quickly raise them to the necessary temperature to flow the solder so the flux is still "acting" when the solder begins to melt. I'd treat this exactly like soldering copper pipe: Sand or otherwise mechanically clean the surfaces, apply lots of flux, apply intense heat for a short time, flow the solder, and allow the joint to cool. |
| s3rkan:
Thank you all friends. I got the point. First I have tried to make a solder mask on the surface with a 200w soldering iron and thought maybe it can be more easy to solder in that way but doing this didn't make any difference. Also soldering the mosfets with a high power soldering iron could be a detrimental process for the FETs so I made the system with M3 tapping the holes and screwing the mosfets. Relevant pictures are attached. |
| JS:
Nicely done! check contact resistance if you have a way to do so, (4W measurement) so you know if you have some oxidation increasing the contact resistance or poor pressure in some contact. JS |
| Ian.M:
Solder cold-flows which will remove most of the contact pressure with time, so take it apart, heat up each copper bar with a torch or hotplate, flux it and wipe as much solder off the surface as possible so you are only left with the thinnest possible tinned surface. Then reassemble using Belleville spring washers on top of your plain washers to maintain contact pressure. Also, you need to pack* under the opposite side of the washers holding the MOSFET leads to the same thickness as the lead so they aren't sitting at an angle. * e.g an off-cut of wire, with a drop of glue to hold it in place during assembly. |
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