A Tale of Two Mice: Sustainable Electronics Design and Prototyping [pdf]
homes.cs.washington.edu
homes.cs.washington.edu
Seems at an early stage of development (fairly low accuracy surface?), but seems it would simplify recycling a lot. Just need waterproof enclosures for more things!
If you manage to get a PCB that has all the properties of a regular PCB, but rots after a century that would probably also make recycling the other materials on that PCB less energy intensive.
A quick search shows it's about 3 times the price of common Sn60/Pb40 lead solder in small quantities: 0.3 EUR/g vs. 0.1 EUR/g.
Typical lead-free tin-copper-silver solder you find in factory mass-produced electronics is hard to work/rework manually because of its high melting point. That is the reason most hand-made and low-volume circuits still use lead solder.
Soldering temperature needs to be higher, and using one of those fancier soldering stations where the temperature sensing element is directly in the tip instead of somewhere in the shaft makes a ton of sense (to avoid temperature dips).
I think soldering with lead free can indeed be harder, but for teaching that means the people will have to learn the right technique. It is much easier to do it wrong and still get something that looks ok using leaded solder. And if they don't have the comparison they won't complain ; )
I will have to check out the bismuth solder nonetheless.
Sn/Cu/Ag solder has a narrow window where the solder is melted and wets pads but the FR4 substrate isn't yet degrading. If you have sensitive plastic parts like connectors, etc. the window is even narrower. This is doable in an industrial reflow owen. However when doing hand work or repair, it's impossible to control the temperature this well.
For example, after years of experience, I'm still unable to desolder large BGA or PGA parts without visibly degrading the board (i.e. there's usually a brown mark left on it - unfortunately the boards I commonly work with these days use white soldermask, which makes this even more obvious). That's with a temperature controlled pre-heater and a hot-air station. I won't even attempt to solder such parts manually with Sn/Cu/Ag.
I've never used bismuth based solder. Have read that it doesn't mix well with lead based solder. Last time I looked it wasn't available in flux-core. But appears to be now.
The lead/tin/antimony solder I used to use in the 80's was pretty nice.
But it has some serious disadvantages:
1. This alloy is brittle, and makes circuit boards more vulnerable to failures due to cracked solder joints than other alloys, causing long-term reliability concerns. Many industry war-stories claim users of bismuth-based solder saw significant failures in the field.
2. Backward incompatibility with leaded solder. If the solder joints are mixed with lead, the strength of the joints are seriously weakened. During the initial lead-free transition, this problem made it largely unacceptable as a replacement. But it's useful if you are reworking a board and desoldering parts...
3. Low surface tension, reducing yield. Modern surface-mount components depend on the surface tension of the liquid solder for self-alignment. Even if the chip is not perfectly aligned with the pads, the melting solder can drag it into its propel place. A lower surface tension means the self-alignment effect is weaker and increases failure rates.
Thus, bismuth-based solder has a long and established history, but it's always used only in niche, temperature-sensitive applications. Recently it saw significant uses in the LED lighting industry due to temperature-sensitive nature of the surface-mount LEDs. But I have to wonder: to what extent it's responsible for all the broken LED lamps...
For the rest of the industry, SAC305 was selected and became the standard: higher temperature, but at least it doesn't have bismuth's reliability problems. SN100C is actually slightly better than SAC305 in all aspects, but unfortunately this alloy was patented (and just expired recently).
> Typical lead-free tin-copper-silver solder you find in factory mass-produced electronics is hard to work/rework manually because of its high melting point.
Leaded solder is preferred by many in hand-made prototypes due to better the wetting properties and surface tension of the alloy, which is critical for successfully soldering surface-mount parts under non-ideal conditions. If the prototypes are assembled by reflow soldering, temperature is only a secondary concern.