Electronic equipment has long been Sn-Pb eutectic solder as the main welding material. Now, in order to protect the environment, there are many related technologies involved in changing welding materials, which are also more difficult. under these circumstances. To replace the Sn-Pb eutectic solder lead-free solder, as much as possible to maintain the characteristics of the original Sn-Pb eutectic solder. To this end, the requirements of the study of lead-free solder characteristics are as follows:
① does not contain substances that pollute the environment, toxicity is small.
② the melting temperature of solder close to the melting point of Sn-Pb eutectic solder should be about 200 ℃.
③ has good electrical conductivity and accessibility.
④ can use the existing equipment, better wettability.
⑥ sufficient strength, good processability.
⑥ adequate supply, low cost and so on.
Requires lead-free solder alloy melting point, physical properties, chemical properties, mechanical strength and tin-lead eutectic alloys as close as possible.
① alloy composition does not contain lead or other elements of the environment pollution.
② melting point of the alloy should be close to tin-lead eutectic alloy, between 180 ~ 230 ℃.
③ a smaller solid-liquid coexistence temperature range, solidification time to be short, is conducive to the formation of a good solder joints.
④ has good physical properties, such as conductivity, thermal conductivity, wettability, surface tension and so on.
⑤ with good chemical properties, such as corrosion resistance, good oxidation resistance, not easy to produce electromigration and so on.
⑥ good metallurgical properties, and copper, silver, palladium, gold, 42 alloy steel, nickel, etc. to form excellent solder joints, solder joint leopard mechanical properties (such as strength, elongation, fatigue degree) good, and requires easy removal And repair. '
⑦ less residue generated during welding.
⑧ with manufacturability, easy processing into solder balls, solder pieces, electrodes, wire and other forms.
⑨ reasonable cost, rich resources, easy to recycle.
⑩ lead-free solder alloy composition and impurity content must be controlled.