Why do circuit board manufacturers use lead-free soldering?

- Jan 15, 2019-

"Lead" is a compound that not only pollutes the water source, but also causes certain pollution and damage to the soil and air. Once the environment is polluted by lead, its treatment cycle and funds are enormous, and the harm to the human body is even more serious. This problem has also been increasingly valued by people. As people's awareness of environmental protection has increased, the use of lead has become more and more cautious in various industries. Among them, among the circuit board manufacturers, customers who come into contact with different industries are asked whether the soldering process has lead-free requirements, and it means that the electronic manufacturing has strict requirements on the lead-free assembly process.

multilayer pcb

First, when pcb board manufacturers use lead-free solder, they must be able to truly meet environmental requirements. They should not blindly remove lead and add new toxic or hazardous substances. To ensure the solderability and post-weld reliability of lead-free solders, And consider the cost of the customer and many other issues. In general, lead-free solders in board manufacturers should try to meet the following requirements:

First, pcb board manufacturers use lead-free solder with a lower melting point, as close as possible to the eutectic temperature of 63/37 tin-lead alloy at 183 ° C. If the eutectic temperature of the new product is only 183 ° C higher than a few degrees, it should not be very Big problem, but there is no such thing as a lead-free solder that can be really promoted and meets the soldering process requirements. In addition, before the development of a lead-free solder with a lower eutectic temperature, the temperature difference of the melting interval of the lead-free solder is lowered. Down, that is, to minimize the temperature range between the solidus and liquidus, the solidus temperature is at least 150 °C, the liquidus temperature depends on the specific application (wave soldering tin: 265 ° C or less; tin wire) : 375 ° C or less; SMT solder paste: below 250 ° C, usually requires reflow temperature should be less than 225 to 230 ° C).

Second, pcb board manufacturers use lead-free solders with good wettability; in general, lead-free solders stay in the reflow for a period of 30 to 90 seconds above the liquidus, and are used during wave soldering. The soldering pin and the substrate surface of the circuit board are in contact with the solder bath for about 4 seconds. After using the lead-free solder, it is necessary to ensure that the solder exhibits good wetting performance in the above time range to ensure high-quality soldering effect. .

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