No further replies I've received so, until thenâŚ
kiriba-ru, probably I should have said âprovide better wetting abilityâ instead of âmake joining big surfaces easierâ.
In the opening post links they succesfully wet the aluminum with both fluxes without the need to scratch the surfaces. That's the main reason I am getting this stuff.
My plan is to put flux over the contact surfaces of each aluminum piece; maybe even pre-apply solder wire over it. Then use a blowtorch/hot plate to heat up the piece and, once the thing is hot, apply solder all over the desired place. This way I'll pre-wet all the surfaces which will make contact. At that point I won't be able to fit the pieces together (it's tight enough already without filling) but, as I heat one inside of the other, the solder on the piece receiving the heat directly will melt and this should provoke the melting of the in-contact solder over the other part. I'll have a good stick to push the stuff down at hand.
The solder pre-wetted alu pill should stick well to a clean and pre-soaked in alcohol/colophony underside of a copper baseplate.
Just stumbled on this link I left on my bookmark list the other day: FLUX @ Radiofun.ru
Penultimate paragraph's translated quote:
The easiest way to use special fluxing F61A - flux for soldering aluminum. Highly active flux based fluoroborates, for tinning and soldering parts and surfaces of aluminum and its alloys. Pike made of tin-lead solders Group with a tin content of more than 60% (and the best solder pure tin) at a temperature of 250-350 degrees.
InterestingâŚ
I have a roll of cheap SnCu (I think) solder, no idea about the composition, probably Sn99'3/Cu0'7. The tin pest stuff creeps me a bit, though.
I once had a flashlight with an aluminum pill that I was able to get solder to stick to it by first putting a bit of motor oil on the pill and then heating the oil with a soldering iron (while moving the tip) until it started to smoke and dry up. The solder stuck well enough to the pill and driver that I couldnât move the driver while pulling on the spring by hand.
I gave the light away several years ago but as far as I know itâs still working.
No worries The Miller, before I ended my elementary education my brother had already taught me how to etch basic one layer PCBs using a combination of muriatic acid plus 33% (yes, 33%) hydrogen peroxide⌠:FACEPALM: We were drewing the layouts by hand with an Edding 3000 permanent marker; the thing worked quite nicely, LOL!
I have a few breathing masks somewhere, you can rest easy my dear.
I'll have to trim off the inner heatsink an additional â7mm, 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. Ф61Đ, come homeâŚ
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.
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 grinderâŚ
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 itâs 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.
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 âoxygen freeâ (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 youâre sure itâs 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.
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. Iâll post up my very unscientific results at some point.
