In the PCBA processing orders, many people will hear the terms lead and lead-free processes. Everyone should have a basic understanding of these two concepts. That is, lead will harm the environment, and lead-free is in line with the current Environmental protection requirements, do you know the specific difference?
1. Alloy composition
The common tin-lead composition in PCBA processing is 63/37, while the lead-free alloy composition is SAC 305, ie Sn: 96.5%, Ag: 3%, Cu: 0.5%. Although the lead-free process is not to say that there is no lead at all, the content is generally very low.
2. Melting point
The melting point of leaded tin is 180~185℃, and the working temperature is about 240~250℃. The melting point of lead-free tin is 210~235°C, and the working temperature is 245°~280°.
3. Cost
Everyone knows that the price of tin is more expensive than lead, so the cost of solder will be higher after replacing the lead in the solder with tin. This is the main reason why the lead-free process in the PCBA factory is more expensive than the lead process when calculating the cost. One.
4. Craftsmanship
This can be seen from the name of the lead process and lead-free process. However, as far as the process is concerned, the solder, components and equipment used, such as wave soldering furnaces, solder paste printers, and soldering irons for manual soldering, are different.
2. Wave soldering process
PCBA poor tin penetration naturally has a direct relationship with the wave soldering process. Re-optimize the soldering parameters of poor tin penetration, such as wave height, temperature, welding time or moving speed. First, the orbital angle is appropriately lowered, and the height of the wave peak is increased to increase the contact between the liquid tin and the solder tip; then, the temperature of the wave soldering is increased. Generally speaking, the higher the temperature, the stronger the tin permeability, but this must be considered The withstand temperature of the components; Finally, the speed of the conveyor belt can be reduced, the preheating and welding time can be increased, so that the flux can fully remove oxides, infiltrate the solder end, and increase the amount of tin eaten.
3. Flux
Flux is also an important factor that affects PCBA's poor tin penetration. Flux mainly removes the surface oxides of PCB and components and prevents reoxidation during the welding process. The type of flux is not good, the coating is uneven, and the amount is too small. All will lead to poor tin penetration. You can use well-known brands of flux, the activation and wetting effect will be higher, which can effectively remove the oxides that are difficult to remove; check the flux nozzle, damaged nozzles need to be replaced in time to ensure that the PCB board is coated with an appropriate amount of flux, Give full play to the fluxing effect of flux.
4. Manual welding
In the actual plug-in welding quality inspection, a considerable part of the weldment has only a surface solder that forms a cone, and there is no tin penetration in the via. The functional test confirms that there are many parts of this part that are virtual soldering. In soldering, the reason is that the temperature of the soldering iron is inappropriate and the soldering time is too short. Poor PCBA tin penetration can easily lead to virtual soldering problems and increase the cost of rework. If the requirements for PCBA through tin are relatively high, and the welding quality requirements are relatively strict, selective wave soldering can be used, which can effectively reduce the problem of poor PCBA through tin.
This can be seen from the name of the lead process and lead-free process. However, as far as the process is concerned, the solder, components and equipment used, such as wave soldering furnaces, solder paste printers, and soldering irons for manual soldering, are different.
2. Wave soldering process
PCBA poor tin penetration naturally has a direct relationship with the wave soldering process. Re-optimize the soldering parameters of poor tin penetration, such as wave height, temperature, welding time or moving speed. First, the orbital angle is appropriately lowered, and the height of the wave peak is increased to increase the contact between the liquid tin and the solder tip; then, the temperature of the wave soldering is increased. Generally speaking, the higher the temperature, the stronger the tin permeability, but this must be considered The withstand temperature of the components; Finally, the speed of the conveyor belt can be reduced, the preheating and welding time can be increased, so that the flux can fully remove oxides, infiltrate the solder end, and increase the amount of tin eaten.
3. Flux
Flux is also an important factor that affects PCBA's poor tin penetration. Flux mainly removes the surface oxides of PCB and components and prevents reoxidation during the welding process. The type of flux is not good, the coating is uneven, and the amount is too small. All will lead to poor tin penetration. You can use well-known brands of flux, the activation and wetting effect will be higher, which can effectively remove the oxides that are difficult to remove; check the flux nozzle, damaged nozzles need to be replaced in time to ensure that the PCB board is coated with an appropriate amount of flux, Give full play to the fluxing effect of flux.
4. Manual welding
In the actual plug-in welding quality inspection, a considerable part of the weldment has only a surface solder that forms a cone, and there is no tin penetration in the via. The functional test confirms that there are many parts of this part that are virtual soldering. In soldering, the reason is that the temperature of the soldering iron is inappropriate and the soldering time is too short. Poor PCBA tin penetration can easily lead to virtual soldering problems and increase the cost of rework. If the requirements for PCBA through tin are relatively high, and the welding quality requirements are relatively strict, selective wave soldering can be used, which can effectively reduce the problem of poor PCBA through tin.
