Aluminum soldering fluxes: The Way It's Meant to be Soldered :D

Well just keep on posting OK?
:wink:

Take a look at this pic, SIGShooter:

I'll have to trim off the inner heatsink an additional ≈7mm, or else the driver won't fit.

Anyway, this is going to be, at the very least, 150+mm² of contact surface, and no oil will stay over the aluminum while I vigorously file the alumina off all those surfaces, to start with. Ф61А, come home…

Cheers ^:)

Wow, this is getting more interesting by the moment! :partying_face:

The Biblical Magi committee arrived home today:

Drumroll!

Cheers ^:)

This stuff for al-al, al-cu, al-brass soldering. Solder paste. Same company I get Fuze Clean FS from. Not cheap but if you insist on soldering it might be the right stuff.

As is this stuff

I have some but haven’t had a chance to try it out

Da-da Da-da Da-da Da-da Da-da…

Barkuti, if you survive this… tell us how it goes!

You were reading my thoughts David. :stuck_out_tongue:

Well fellows, been doing some tests with the fluxes. I've been able to wet aluminium foil with it, that was the easy part. However, my trials over my aluminium test heatsink and over an old 16mm 7090 MCPCB have mostly been unsuccesful. The main problem is that once you make the solder stick on the alu surface (usually just a little bit), you better stop messing with the stuff because the slightest movement uncovers the surface and it insta-oxidizes. I've also tried applying solder with my iron's hot tip over the carefully pre-heated surfaces, without much success because I've had a hard time monitoring the stuff's temp (too much and the flux degrades), and of course because it's been a real mess avoiding the un-sticking of solder from the surfaces. :FACEPALM:

For my initial test I thought the flux would allow me to wet the heatsink by pre-applying a slight layer of the things; it failed, so I applied a lot more for a second test, which ended up with both FTKA and F61A mixed, in fumes & flames (a blowtorch was the heat source):

Up: FTKA; down: F61A. Solder used: mixture of Sn99'3/Cu0'7 (61%) and Sn63/Pb37 (39%).

I am seriously considering the preparation of a special soldering flux with these oily compounds. I just need to figure out how to make some finely grained solder powder. Maybe I could try on my electric coffee grinder…

Cheers ^:)

Try heating from underneath instead of direct flame, some fluxes are flammable and require indirect heat. Also. Wet sand the area using the flux as lubricant. This will clean the metal while preventing O2 contamination.

This is actually one of the tricks you can use to solder aluminium.

1. clean the area as well as possible
2. make some kind of ledge around the area you need to solder so you can cover the metal there with oil. If you can, put this aluminium thingy on a hotplate to keep it hot.
3. pick a big high-power soldering iron and sharpen and flatten the tip. Wet it with solder.
4. scrape the aluminium surface with the soldering iron until it gets tinned. Make sure it’s covered with oil all time to protect from oxidation. Add fresh solder to the soldering iron as needed.
This should tin the aluminium surface and then you can solder to it.

Pure tin or tin-zinc solders work better than normal tin-lead. Tin-indium, Tin-zinc-gallium or tin-zinc-cadmium solders are even better, though they should be pretty hard to find in hobby-scaly quantities.

Well, no direct flame was being used, I applied heat from a side but, alas, upon reaching a high temp some flux slipped down I guess.

Wet sanding may prove beneficial, I may try for testing, yet I really think I need to make that special flux if I intend to have a chance of more or less fusing my pill parts.

Cheers ^:)

Youse guys are WWAAAAYYY over my head here, but if the big problem is oxidation, can you try using a shielding gas?

CO2 is often used in welding as a shielding gas. Dry ice is a handy, fairly easily available source of CO2. The density of CO2 gas, according to Google, is 1.67, which means it should sink in air, or put another way, air floats on top of CO2. So now all you need is to place the piece inside a bucket, with dry ice at the bottom. The dry ice will off gas CO2, displacing the air, after several minutes, the bucket will essentially be full of CO2 gas, with more constantly being emitted and spilling over the top of the bucket. If the work piece is below the top rim of the bucket, it is in an “oxygen free” (well, at least very reduced) environment.

I think you would need some other heat source than your blowtorch, the lack of oxygen is likely to affect that, and the jet effect will probably cause currents in the gases. You will want to move your hands as little as possible inside the bucket to keep from causing currents.

Well, for the homemade solder paste, why not use regular solder paste? Maybe put a little into a cup or bowl and add alcohol to dissolve the regular flux that is present. Swirl it, mix it, then let it settle. Pour off the alcohol/flux and add alcohol again. Do it enough times until you’re sure it’s clean of the original flux. Then, let the alcohol evaporate out so that you have dry metal powder. Add your other flux a little at a time until the flux paste is as wet and flowing as you like it.

I think the best thing though, is going to be wet sanding with the flux, as others have said. :wink:

I like soldering emitters onto the substrate too, but after some tests i did last night I found that using a high quality thermal paste is only marginally worse than direct solder. I’ll post up my very unscientific results at some point.

mattjk, I just have some old regular thermal paste, with no plans to get some of that preppy stuff which already is more expensive than certain :P designer drugs (and certainly won't make you as happy ). Also, thermal paste is devoid of fastening properties, something which may be of value for certain hollow pills, for example.

DavidEF, no regular solder paste here. I'm going to attach a grinding bit to my high-speed multitool, and see what happens to those solder wires. ;)

Lazy-R-us, not really a bad idea but I think it needs some refinements: a badass soldering iron and some sort of anaerobic chamber. :-)

I'll be back fellows ^:)

Barkuti, if you use a grinding wheel on solder wires to make powder for your solder paste, you will be introducing lots of contamination. But, maybe contamination doesn’t really matter. Any soldering you do, even contaminated, should at least be better thermally than no solder. Hey, do you have a diamond grinding wheel? :wink:

Seriously? I was planning to use a stone grinding wheel, which definitively should be harder than the solder alloy so I don't think it'll erode & cause any contamination. In any case it shall be minimal, so no problem. 8^)

More on this later.

Cheers ^:)

A little update my dears:

I made a sort of solder blob the other day, which I proceeded to sand on my sandpaper bit equipped multitool over a small plastic box. Of course, I obtained a more or less sizeable amount of solder powder. I then poured as much as I could of it on a fancy shot glass, and added a few drops of FTKA over. Maybe I added too much FTKA, yet anyway a sort of dark coloured soldering flux appeared after stirring with a toothpick.

The trial was done with an SK68's hollow pill and an old aluminium MCPCB mounted XR-E. Cleaned the surfaces and applied plenty of flux with the toothpick over the pill's rung. Seated the XR-E board, and cooked it with my blowtorch over a small heatsink. On a hurry, I didn't grabbed my IR thermometer, overheated the whole shebang and damaged the led :(( . The flux got messily spread everywhere :UGHH: . But hey, the stuff got joined. Not very strong I must admit, I unattached the MCPCB with a good push using the stick end of a paint brush. The contact surfaces looked good. :THUMBS-UP:

My guess is this can work more or less reasonably well. I think it may be better to add a bare minimum amount of these fluxes to the powdered solder as to minimize the messy flux remainders after cooking.

I'll later post some pics of that pill I was going to un-hollow with a moulded piece of heatsink inside.

Cheers ^:)

Ersin 5 core flux solder wire is all you need. Its everywhere on ebay. Used it to solder lipo cells in various configs together, had so many fails that I wanted to build a spot welder already, they have the positive tab made of aluminium. Bought so many sorts of fluxes and solder wires that I could sell them on and make back the deposit for a house. Well…not reaally but you know. With a 100W iron (leave the sub 80W toys aside) it sticks like theres no tomorrow. Would use 130W Rub the tip of the iron on the surface to be soldered, then it will start to leave streaks of tin. From there you solder like normal. No more solder blobs (which are worse than cold solder joints). It will tear the aluminium if you pull on the wire soldered to it.