What Are Reflow and Wave Soldering?

By: Jack Vanden Broek

3 Min Read

1 Aug, 2021

At LAVA, we are committed to ensuring that our products meet the highest quality standards demanded both internally and by our customers. To accomplish this, we perform the majority of manufacturing, including soldering components onto PCBs, at our production facility in Toronto, Canada. Soldering is an essential part of our manufacturing process, and in order to build our products we use two standard soldering processes: reflow soldering and wave soldering. This article will shed light on what these processes are, the differences between them, and the purposes they serve in the manufacturing of LAVA’s adapters.

Soldering is a metal joining technique that does not change the state or composition of the base materials, but instead uses a liquefied filler metal (melting point lower than that of base metals), known as solder, to create a bond or joint. This process differs from traditional welding, where the base metals are melted and then cooled to form a mechanical bond. At LAVA, soldering is used to add components onto unpopulated PCBs, without interfering with the board’s Copper Clad Laminate (CCL) base.

Reflow soldering is the first method used in LAVA’s manufacturing process, since it is the most effective way to solder surface mounted components such as resistors and capacitors. Unpopulated PCBs arrive at our facility with our layouts already imprinted on them, to serve as blueprints for our soldering machines. The boards are first placed in our pasting machine and covered by a solder screen, featuring the same blueprint as the PCB’s CCL base with cut outs that match where the components are to be surface mounted. The solder paste (a mixture of flux and powdered solder) is wiped across the solder screen, filling the cut outs and acting as glue for the components. Next, the boards are placed in Surface-Mount Technology (SMT) machines, where the components are placed onto the exposed solder paste and PCB underneath. The machines are also programmed with the CCL base blueprint, for efficient automated surface mounting. Finally, the populated PCBs pass through a solder oven to ensure the paste is melted and cooled properly, and the components are securely attached. For a breakdown of LAVA’s reflow soldering process with visual guides, click here.

Wave soldering is the second step in PCB soldering because it is used for through-hole technology (THT) joining. Rather than attaching components to the surface of the board, some components (such as pins) pass through small holes in the board to be featured on both the top and the bottom of the PCB. The pins are inserted into the small holes in the PCB, and sprayed with a flux solution to reduce the surface tension and eliminate oxides, allowing for a cleaner and more effective joint to be made. Note that applying the flux is a separate stage in wave soldering, whereas it is built into the paste in reflow soldering. Next, the boards are transported via conveyor belt through the molten solder “wave” – the solder washes over the underside of each PCB to secure the THT component’s position and ensure each pin is covered with a layer of solder. The final step is to cool and clean the now completed adapter, before the final testing stages and installing them within casings. For a breakdown of LAVA’s wave soldering process with visual guides, click here.

LAVA uses the combination of reflow and wave soldering sequentially because they fulfil specific requirements in the process of adapter assembly. Reflow soldering is completed first because the application of the solder screen and solder paste would interfere with the THT components. Wave soldering is completed second to account for the stronger solder required for THT components, since the components pass through the entire PCB base rather than being applied to the surface. This chronological order allows us to take a bare PCB, populate it, and transform it into a finished LAVA adapter. For further insight into LAVA’s production and manufacturing strategies, you can read previous articles on techniques such as Just in Time Production, Batch Production, and more.