What the Flux: How Does Solder Work Anyway?

I’ve been soldering for a long time, and I take pride in my abilities. I won’t say that I’m the best solder-slinger around, but I’m pretty good at this essential shop skill — at least for through-hole and “traditional” soldering; I haven’t had much practice at SMD stuff yet. I’m confident that I could make a good, strong, stable joint that’s both electrically and mechanically sound in just about any kind of wire or conductor.

But like some many of us, I learned soldering as a practical skill; put solder and iron together, observe results, repeat the stuff that works and avoid the stuff that doesn’t. Seems like adding a little inside information might help me improve my skills, so I set about learning what’s going on mechanically and chemically inside a solder joint.

Continue reading “What the Flux: How Does Solder Work Anyway?”

More DIY solder flux

[GuShH] wrote a guide for making your own rosin-based solder flux. According to [Stephen] — who sent in the tip and tried this method himself — is works well, it’s cheap, but you will need to clean up a bit after using it on a PCB.

Only two ingredients are necessary to make your own liquid or paste flux: rosin and a solvent. The rosin being weighed in the image above, can be found from several sources. We looked in on the same method quite recently where flux was sourced from a music store. But [GuShH] suggests that if you can find some from a hardware store it is better because the music store variety tends to be ‘molten’ and doesn’t work quite as well.

Proportions are listed on his guide for light, medium, and heavy concoctions. He recommends isopropyl alcohol as the solvent, and has stored the flux in a clear dropper bottle. We’re fans of needle bottles and asked about sourcing them in a previous post (linked in the paragraph above) so check that comments section if you don’t know where to get one.

What the flux: buy it or brew it yourself

Flux generally makes our lives easier. It’s the best bet when trying to prevent solder bridges with fine-pitch components like you see here. But it is also indispensable when it comes to desoldering components from a board (we’re talking just one component without disturbing all of the others). But have you ever looked at what it costs to pick up a syringe of liquid flux from an online retailer? In addition to the cost of the product itself there’s usually a hazardous material handling fee that is rolled into the shipping cost. So we were happy that [Christopher] sent in a link to the DIY flux page over at Dangerous Prototypes.

The concept is simple enough. Mix some rosin with some solvent. Turns out these items are really easy to source. The solvent can be acetone (which you may have on hand for removing toner transfer from freshly etched PCBs) or plain old rubbing alcohol. And an easy source for rosin is your local music store. They sell it to use on bow hair for String players. Grind it up, throw it in a bottle and you’re good to go. Now does anyone know where we can source needle-tipped bottles locally?

For those that still just want to buy flux we highly recommend watching part one and part two of [Ian’s] flux review series.

Decapping integrated circuits with sap

[James] is interested in reverse engineering some integrated circuits. One of the biggest hurdles in this process has always been just getting to the guts of the chip. He used acetone to dissolve the plastic case but had trouble getting through the epoxy blob. Commonly, the epoxy is soaked in nitric acid for a few minutes but [James] didn’t have access to that chemical. Instead he popped into the local music store and picked up some rosin (used to make violin bows sticky enough to grab the strings of the instrument). After boiling down the rock-hard rosin and the chip for 20 minutes, he got a clean and relatively undamaged semiconductor that he can easily peer into.