The so-called lead-free soldering iron soldering means that the solder used in the soldering of the PCB is not allowed to contain Pb, and the content of Pb in the currently used solder is as high as 40%.
The key to achieving Pb-free soldering is to find a lead-free Pb-free solder that can replace lead solder. Lead solder has been used for hundreds of years because it has a range of superior properties and is inexpensive and has sufficient reserves.
At present, only a Sn-Ag-Cu alloy having a relatively good performance can be used as a temporary substitute for the Sn-Pb alloy.
The fatal defects of SAC305 and SAC405 compared with 63/37Sn-Pb solder are as follows:
1. High melting point (SAC is about 220 ° C, Sn-Pb is about 183 ° C);
2. Poor wettability (the wettability of SAC is equivalent to about 70% of Sn-Pb).
The main problem brought by the increase of the melting point of lead-free solder is to reduce the process window, that is, from 57-67 ° C (A) to 23-33 ° C (B) when Sn-Pb solder, so that the soldering iron can be operated at the operating temperature.
The range of variation is significantly reduced. This not only brings difficulties to the process, but also jeopardizes the performance of the substrate and components due to over-temperature, and the poor wetness of the solder of the error-free solder increases the difficulty of soldering lead-free soldering iron.
In order to meet the needs of lead-free soldering iron welding, the current main countermeasures are as follows:
1. Technical training for the operating staff, first understand the characteristics of lead-free soldering iron welding in theory, and be fully prepared for consciousness.
2. Use PID temperature-controlled soldering iron to ensure the temperature of the soldering iron is stable and correct.
3. Select the solder wire. Preferably, the Sn-Ag-Cu solder wire has a content of Ag of 1%, not necessarily 3% to 4%, and the diameter of the solder wire can be coarse and coarse, and if necessary, Sn-Ag-Cu-In-X can be used. Solder wire.
4. Practice the operation skills. When welding, add a certain amount of preheating time (usually no more than 3s) to the base material. Be careful when working, be careful.