Basic knowledge of lead-free solder

Basic knowledge of lead-free solder

1. The basis of welding operation
① The purpose of welding operation:
(i) Mechanical connection: connect two metals and fix them.
(ii) Electrical connection: connect two metals and make them electrically conductive. This electrical connection is the characteristic of welding operation, which cannot be achieved by adhesives.
② Characteristics of welding operation:
The characteristic of welding operation is that a large amount of welding can be completed at one time, such as welding using a jet flow tank and welding using viscous solder; another characteristic is that it can be easily corrected.
③ Definition of solder:
Generally speaking, solder is an alloy composed of tin (melting point 232 degrees) and lead (melting point 327 degrees). Among them, solder composed of 63% tin and 37% lead is called eutectic solder, and the melting point of this solder is 183 degrees. The wire solder used in standard welding operation is called rosin solder or wire solder. As shown in the figure, flux is added to the solder. This flux is composed of rosin and a small amount of activator.
④ Setting temperature of welding operation
The temperature setting during welding operation is very important. The most suitable temperature for soldering is the melting point of the solder used + 50 degrees. The set temperature of the soldering iron tip should be increased by 100 degrees on the basis of the above temperature due to the size of the soldering part, the power and performance of the electric soldering iron, the type and line of the solder.
2. Harmfulness of lead
The solder used in the latest machines actually has a very long history. It has been used 5,000 years ago. Since the solder contains lead that is harmful to the environment, it may have an impact on the environment, so the composition of the solder is also changing.
3. Background of the actual use of lead-free solder

4. Lead-free solder and its problems

Table 1, rosin into lead-free solder

① Poor tinning ability
Lead-free solder has poor solder diffusion, and the diffusion area is about 1/3 of eutectic solder.
② High melting point
The melting point of lead-free solder is about 34~44 degrees higher than that of ordinary Sn-Pb eutectic solder, so the temperature setting of the soldering iron tip should also be relatively high.

③ Shortened service life of the soldering iron tip
④ Oxidation of the soldering iron tip
When using lead-free solder, the surface of the soldering iron tip may sometimes turn black, lose the ability to tin, and cause the soldering operation to be terminated.
◆ When the soldering iron tip temperature is set at 400 degrees
◆ When there is no soldering operation, the electric soldering iron is left on for a long time.
◆ The soldering iron tip is not cleaned.
When, etc., oxidation is more likely to occur.
5. Points to note when using lead-free solder
① Temperature management of the soldering iron tip is very important
For electric soldering irons with temperature adjustment, it is very important to choose the most appropriate soldering iron tip temperature setting according to the solder used.
Before working, it is important to measure the temperature of the soldering iron tip with a soldering iron tip thermometer.
② Use authentic soldering iron tips that match the manufacturer (e.g. Baiguang Tools)
Counterfeit soldering iron tips have different apertures (for inserting the heating core) and different thicknesses of the sleeves. These all cause the performance of the electric soldering iron to not be fully utilized, and sometimes cause the cause of the electric soldering iron failure.
③ Use a soldering iron with good thermal properties such as thermal recovery.
When using lead-free solder for soldering, the set temperature of the soldering iron tip is generally expected to be below 350-370 degrees due to the heat resistance of the parts and safety considerations.
A soldering iron with good thermal recovery, such as the HAKKO942, integrates the heater/sensor/soldering iron tip, making the thermal recovery very good.

④ It is necessary to select the most suitable soldering tip
It is important to select the most suitable soldering tip according to the different welding operations of the electric soldering iron.
The appropriate soldering tip can reduce the temperature of the soldering tip and increase the efficiency of the operation.
⑤ The maintenance of the soldering tip is also very important.
◆Unlike ordinary sponges containing water, metal wires soaked in additives are required, which can not only play a cleaning role without reducing the temperature of the soldering tip, but also remove the oxide on the surface of the soldering tip.
◆Set the temperature of the soldering tip as low as possible.
◆When the electric soldering iron is not used for more than 10 minutes, the power supply should be turned off.
◆When the soldering iron tip is oxidized and blackened, first use the solder with flux to remove the oxide. If it cannot be removed, first use a metal wire cleaner soaked in additives to remove the oxide on the surface, and then apply new solder.

■ After all work is completed, new solder should be applied to the soldering iron tip and stored at the soldering station.

⑥ Improved tinning ability
With the use of lead-free solder, the tinning ability/solder diffusion will be improved.

In summary, the method of using lead-free solder is to "perform soldering operations at low temperatures as much as possible" and "thoroughly maintain the soldering iron tip", which is actually the basis of soldering operations.
These are not completely professional techniques for lead-free soldering, but are just a comparison of the techniques used in traditional lead eutectic soldering.