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Wave Soldering and Reflow Soldering +MORE

Wave-soldering and reflow-soldering are two different technologies for PCB boards assembly (PCBA). Solder-reflow services for surface mounted technology (SMT), and wave-soldering is used for dual in-line package (DIP) components. Usually we will assemble the SMT components first, and then assemble DIP parts.

Normal procedures for PCB SMT are: soldering paste application - components mounting - reflow soldering - QC.

1. Soldering paste application: Its goal is applying the soldering paste on the PCB pads uniformly, to guarantee the good electrical connections of the components and the corresponding pcb pads during the reflow soldering. Soldering paste is mixed by alloy powder, paste flux and some additives, with good viscosity and touching characteristics. At room temperature, the components can be located on the pads rely to the paste’s viscosity, and they would not move in the condition of no collision force. Then the alloy in the paste will melt and the liquid solder will soakage into the welding end of components and the pads, and the welding spot for electrics and mechanical connecting will form after cooling down.

2. Components mounting: This process is placing the components to its corresponding position on the pcb surface which has been applied the soldering paste. It can be finished by hand or mounting machine.

3. Reflow soldering: This is working as re-melting the soldering paste which has been applied to the pads, to fulfill the electrics and mechanical connection of SMT components’ welding end or pins and the pcb pads.

Normal procedures for PCB DIP components are: insert the components into corresponding holes - soldering flux pre-coating - preliminary drying (temperature 90-100 degree, length 0.8-2.0m) - wave soldering (temperature 220-240 degree) - cut exceeding pins - QC

Some factors that will influence the quality of wave soldering: Is the temperature high enough to melt the flux? The PCB board and components have to be heated enough to make sure flux and metal on PCB board will develop to alloy. Flux must be heated to a certain temperature to make sure its activity and response ability, as well as its ability to resolve the oxides and dirt on the welded metal surface. Workers must control the temperature of wave, speed of band carrier, preheat temperature, crest contact time and joint density strictly, or there would lead to cold solder or other problems.

Differences between reflow soldering and wave soldering:

Reflow soldering: SMT components are soldered by the reflow formed by hot air; and the welding flux is ok before move to the machine, and paste will be melted and form weld point in the machine. 

Wave soldering: PTH/DIP components are soldered by the wave crest formed by melted solder.