Electronic equipment for long time has been Sn-Pb eutectic solder as the main welding material. Now, for the protection of the environment, the welding materials change, implicated in the related technology is a lot of difficulties, too. In this case. The study of lead-free solders replacing Sn-Pb eutectic Solder is to maintain the properties of the original Sn-Pb eutectic solder as much as possible. For this reason, the requirements for the study of lead-free solder properties are as follows:
① does not contain substances that pollute the environment, the toxicity is small.
② melting temperature of solder to be close to the melting point of Sn-Pb eutectic solder, should be around 200 ℃.
③ has good electrical conductivity and maintenance.
④ can use the existing equipment, have good wettability.
⑥ has enough strength, machinable good.
The melting point, physical properties, chemical properties and mechanical strength of lead-free solder alloys are required to close the tin-lead eutectic alloys.
1. No lead or other elements that pollute the environment in the alloy composition.
2. Alloy melting point should be close to tin-lead eutectic alloy, between 180.
3. There is a small solid-liquid coexistence temperature range, solidification time is short, conducive to the formation of good solder joints.
4. Good physical properties, such as conductive, thermal conductivity, wettability, surface tension, etc.
5. Good chemical properties, such as corrosion resistance, good oxidation resistance, not easy to generate electricity transfer.
6. Good metallurgical properties, and copper, silver, palladium, gold, 42nd alloy steel, nickel and so on the formation of excellent solder joints, welding point Leopard mechanical properties (such as strength, tensile degrees, fatigue) good, and requirements for easy disassembly and rework. '
7. Fewer residues are generated during welding.
8. With manufacturability, easy to process into welding balls, welding pieces, welding rods, welding wires and other forms.
9. Reasonable cost, abundant resources, easy to recycle.
10. The component and impurity content of lead-free solder alloys must be controlled.
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