Bismuth-based solder is nice for being lead-free, having a low melting point, and being a true eutectic alloy.
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.
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.