HotLine:
Lead-free solders should first be able to truly meet environmental requirements, can not remove lead, and add new toxic or harmful substances; to ensure solderability and reliability of lead-free solders, and take into account the cost of customers and many other issues. Generally speaking, lead-free solders should meet the following requirements as far as possible:
1. The melting point of lead-free solders should be low, as close as possible to the eutectic temperature of 63/37 Sn-Pb alloy 183 C. If the eutectic temperature of new products is only a few degrees higher than 183 C, it should not be a big problem, but there is no such lead-free solders that can really be popularized and meet the welding requirements. In addition, before developing lead-free solders with lower eutectic temperature, lead-free solders should be as far as possible. The temperature difference between solids and liquids decreases as much as possible, i.e. the temperature range between solids and liquids is minimized to 150 C. The liquidus temperature depends on the specific application (solder rod for wave soldering: below 265 C; tin wire: below 375 C; solder paste for SMT: below 250 C, reflow soldering temperature should generally be below 225-230 C).
2. Lead-free solders should have good wettability. Generally, solders stay above liquidus for 30-90 seconds during reflow soldering and contact time between solder pipe pins and PCB substrate surface and tin liquid peak is about 4 seconds during wave soldering. After using lead-free solders, solders should show good wettability in the above time range to ensure high quality soldering efficiency. Fruit;
3. The conductivity and thermal conductivity after welding are close to 63/37 Sn-Pb alloy solder.
4. The tensile strength, toughness, ductility and creep resistance of solder joints are similar to those of tin-lead alloys.
5. Cost should be reduced as much as possible. At present, it can be controlled at 1.5-2 times of Sn-Pb alloy, which is an ideal price.
6. The developed lead-free solder has good solderability with copper base of circuit board, lead-free solder plated on circuit board, lead-free solder of component pin or its surface and other metal coatings.
7. The newly developed lead-free solder should match all kinds of flux as far as possible, and its compatibility should be as strong as possible. It is the future development trend that it can work with the support of active rosin resin flux (RA), and also can apply mild, weak active rosin flux (RMA) or no-cleaning flux without rosin resin.
8. It is easy to inspect and repair the solder joints after welding.
9. The selected raw materials can satisfy the long-term adequate supply.
10. It is compatible with the current equipment technology and can work without replacing the equipment.
