Flux, flux, flux

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Homemade Flux



1. Find nitrocellulose thinner (used for some paints, for some lacquers) or isopropyl alcohol or acetone (pure, not nail varnish remover filled with oil and perfume) - isopropyl alcohol is what commercial products use and should be available in 1L bottles in pharmacies (not the same as ethanol that pharmacies also sell).

2. Get yourself rosin for violin or cello or similar instrument. They use the rosin (colophony, kalafonium ... many names) to make the bow "sticky" so that it has good contact with wires hence they produce nice sound. You should be able to get this rosin in any store that sells equipment for musicians. Also beauty salons use colophony resin (for I have no idea what). http://en.wikipedia.org/wiki/Rosin

3. Put the rosin on a big sheet of thick paper, close the paper around it, and grind the rosin inside the paper (you can press it with a beer bottle for example). Do this until you have ground it to pieces smaller then 3mm x 3mm.

4. Take a glass bottle and fill with thinner/acetone/isopropyl alcohol and add the grounded rosin.

5. Mix and leave for few days for rosin to fully dissolve.

Voila - you have yourself flux :D

The ratio of thinner/rosin really depends on what kind of flux you like .. you can dissolve A LOT of rosin in nitro .. start small .. take a smaller "bottle" (I use ~30ml bottle from some nose drops) and add a tea spoon of crushed rosin to it - that's a good base point. Then, if it evaporates too quickly and does not flow nicely, add more rosin. On the other hand if it is too sticky and leaves a mess on the board, add a bit more thinner/acetone/alcohol to the mix. After 3-4 batches you will get the hang of what is the perfect mixture for you :)

If you use nitro thinner to make flux note that nitro and acetone will dissolve most plastic (ABS is vulnerable, PP and PE are safe) so you might want to try isopropyl alcohol as it is gentler on plastics. Most commercial flux mixtures are isopropyl+colophony.

Rosin: jbeale suggests avoiding "BEST SONG XIANG BEUSUTEXUZGYGABHU" rosin from Ebay: "wellparts" because it was simply poured into a box. The cardboard of the box was solidly incorporated into the block of rosin, leaving cardboard fragments in the resulting flux. Comment: DealExtreme Reviewers would seem to disagree using the "crush it up" and remove box method. YMMV.

Lead-free solder

Does anyone know how well these homemade rosin flux mixes hold up at lead-free rework temperatures (230C+) ?

In my limited experience, homemade rosin flux works better than many fluxes I have tried over time. The acetone / alcohol / nitro solvent will evaporate fairly quickly but the rosin left on the PCB will still work perfectly even at 450C. Of course the board will look super ugly and will have to be cleaned, but it does work.

Now if you use "paste like" no clean flux, it works really well and you do not need to clean the PCB. The only problem is that it's way more expensive.

Flux residue

I've been using this homemade flux for years and have never noticed any corrosive effect from the flux residue... but I can't say for sure. You can always clean the PCB with isopropyl alcohol after you finish if you want to remove the residue, and isopropyl alcohol evaporates quickly so the PCB is left clean.

PCB Tinning/Protective Coating

Rosin is also useful when you are making PCBs yourself and you do not have any chemical tinner. To prevent the copper from oxidizing when you finish etching the PCB, you clean it well, wipe it with isopropyl alcohol and then coat the whole PCB with the "stronger" mixture of isopropyl alcohol and rosin. It will dry in few minutes and you will have a thin film of rosin on the board that will protect the copper from oxidation. PCBs prepared like that which are 10-15 years old still have shiny copper.

Source: http://dangerousprototypes.com/forum/viewtopic.php?f=2&t=2305#p21898

Non-activated soldering flux (expired patent)

More detailed information for making a very similar flux to that described above may be found in the United State Patent Office expired patent 3,730,782 (May 1, 1973).

The recipe

Of particular note, the patented recipe for flux is:

  1. Isopropyl alcohol (60-70% by weight)
  2. Water white rosin (30-40% by weight)
  3. Glycerin (2-3% by weight)
  4. Cationic flurocarbon surfectant (0.01-1% by weight)

Liquid flux is produced using a 20-65% concentration of rosin; at concentrations of 65-80% of rosin, a paste flux is produced.

The glycerin is to inhibit polymerisation and retard decomposition, all of which is aimed at preventing any charred residue. The residue that does remain is so non-corrosive that it can be left on the soldered part. Chemical and corrosion analysis have shown no harmful effects from the residue.

The cationic flurocarbon surfectant lowers the surface tension of the rosin flux and provides better spreading and wetting and, for reasons unknown, reduces the need for cleaning and aids flux stability at elevated temperatures.

PCB Tinning/Protective Coating

The preferred concentration of rosin flux for a protective coating is 10 to approximately 20% of rosin flux, with alcohols or ethyl acetate as the solvent. The cationic fluorocarbon surfectant range should remain 0.01-1%.

Source: Expired US Patent 3,730,782