Wave Soldering vs. Reflow Soldering

The difference between wave soldering and reflow soldering can never be ignored since many users have no idea which one to select when purchasing PCB assembly services. A modification in terms of soldering tends to cause changes in the entire assembly manufacturing process. These changes include manufacturing efficiency, cost, time to market, gains, etc.

Figure 4 illustrates the difference between soldering process steps. The essential difference between wave soldering and reflow soldering lies in flux spraying — wave soldering contains this step, while reflow soldering does not. Flux enables dioxide elimination and surface tension reduction in the material to be soldered. Flux works only when it's activated, which requires rigorous adherence to temperature and time control. Since flux is contained in solder paste in reflow soldering, flux content has to be appropriately arranged and achieved.

Figure 4. The differences between wave soldering and reflow soldering process steps.

Soldering defects seem unavoidable. It is impossible to determine which soldering technology creates more defects than the other, since the process differs each time. In spite of the inevitability of soldering defects occurring, their frequency can be reduced when assemblers conform to professional assembly manufacturing regulations, and are fully aware of the characteristics and performance of all equipment along the manufacturing line. In addition, engineering staff should be qualified and regularly trained in order to keep pace with the progress of modern technologies.

Generally speaking, reflow soldering works best for SMT assembly, while wave works best for THT or DIP assembly. Nevertheless, a circuit board almost never contains pure SMDs (surface mount devices) or through-hole components. In terms of mixed assembly, SMT is normally first carried out and then THT or DIP is performed, since the temperature required for reflow soldering is much higher than that required for wave soldering. If the sequence of two assemblies is inverted, solid solder paste will possibly be melted again, with well-soldered components suffering from defects or even falling from the board.

This article was written by Dora Yang, Technical Engineer at PCBCart, Hangzhou, China. For more information, Click Here.