Because the wetting characteristics of lead free solder, using good flux chemistry is critical. Additionally, the higher temperatures needed for lead-free soldering require a flux chemistry that can withstand preheat temperatures up to 130'C and liquid temperatures as high as 280'C for up to 3 seconds. VOC-free, water-based flux is generally recommended since they meet these higher temperature requirements.



Often an existing wave solder machine may need upgrading with a newer spray fluxer to be suitable for processing VOC, water-based fluxes. An ultrasonic or nozzle type spray fluxer works best since the flux droplet size can be controlled and a continuous and uniform spray pattern can be applied across the entire PCB. This is essential since it is important to achieve the smallest possible droplet size with VOC-free fluxes to obtain good through hole penetration. More preheating is generally required because of the higher melting point of lead-free alloys. A longer preheating section is often needed to reach these higher temperatures and avoid thermal shocking of the PCB when entering the chip wave. Achieving proper preheat temperatures on the top of the PCB has the greatest single effect in reducing solder defects such as bridging and insufficient topside fillets. Optimum preheating of a PCB can best be achieved with a combination of infrared heating from the bottom and convection heating from the top.

Preheating for lead-free can require a heating length of up to 1.8 meters for conveyor speeds as high as 120 mm/minute and as long as 2.4 meters for conveyor speeds greater than 180 mm/minute. An effective upgrade strategy is to replace an existing spray fluxer with an external spray fluxer. This not only improves the quality of flux application but frees up space inside the wave solder machine that can be used to extend the preheat capacity. The operating temperature of the solder pot will generally increase depending on the lead-free solder alloy. For tin-silver copper alloys (Sn, Ag, and Cu) with a melting point of 217'C, the solder pot temperature may be between 260-270'C. For high melting point alloys such as tin-copper (Sn, Cu), the solder temperature may be as high as 270-280'C should be used.

The parameters discussed above plays key role in determing the performance of the wave solder process. Also these facts determine the quality of the product manufactured by the wave solder process. So all the wave solder parameters must be watched and monitored pretty carefully so that the performance of the wave solder machine and the performance of the wav solder process could be enhanced. The wave solder process parameters have a great impact on the product quality and if monitored well we could easily achieve a great product quality for our process and on a consistent basis.