1. Price: Many manufacturers require that the price cannot be higher than 63Sn/37Pn, but at present, the finished products of lead-free substitutes are 35% higher than 63Sn/37Pb.
2. Melting point: Most manufacturers require a solid phase temperature of at least 150 ° C to meet the working requirements of electronic equipment. The liquidus temperature will depend on the specific application.
Wave soldering electrode: For successful wave soldering, the liquidus temperature should be lower than 265 °C.
Solder wire for manual soldering: The liquidus temperature should be lower than the soldering iron operating temperature of 345 °C.
Solder paste: The liquidus temperature should be below 250 °C.
3. Electrical conductivity.
4, good thermal conductivity.
5. Smaller solid-liquid coexistence range: Most experts recommend that this temperature range be controlled within 10 °C to form a good solder joint. If the alloy solidification range is too wide, solder joint cracking may occur, making electronic products premature. damage.
6, low toxicity: alloy components must be non-toxic.
7, has good wettability.
8. Good physical properties (strength, tensile, fatigue): The alloy must be able to provide the strength and reliability that Sn63/Pb37 can achieve without protruding fillet welds through the device.
9. Repeatability of production, consistency of solder joints: Since the electronic assembly process is a high-volume manufacturing process, it is required to maintain a high level of repeatability and consistency, if some alloy components cannot be in high-volume conditions. Repeated manufacturing, or its melting point in the mass production, due to changes in composition, can not be considered.
10. Appearance of solder joints: The appearance of solder joints should be close to the appearance of tin/lead solder.
11, supply capacity.
12. Compatibility with lead: Since it will not be fully transformed into a lead-free system in the short term, lead may still be used on the terminals of PCB pads and components. If solder is mixed, it may cause solder alloy. The melting point is very low and the strength is greatly reduced.