In the field of electronic manufacturing, two primary automated soldering techniques are commonly employed for assembling printed circuit boards: reflow soldering and wave soldering. These two techniques have significant differences in principles and applications, and their practical use cases vary. In this article, we will provide a brief overview of these two techniques, explore their similarities and differences, and discuss how the electronics industry determines which soldering technique to use in different scenarios.
Reflow soldering refers to the process of melting pre-applied solder paste on solder pads, allowing the pins or leads of electronic components pre-mounted on the solder pads to establish electrical connections on the PCB, ultimately soldering the electronic components onto the PCB. Reflow soldering relies on the action of hot air flow on the solder joints, the solder paste undergoes a physical reaction under a specific high-temperature airflow to achieve SMD soldering, hence the name "reflow soldering." Since gases circulate within the soldering machine to generate high temperatures for soldering, reflow soldering typically consists of preheating, heating, and cooling zones.
Reflow soldering process
It needs to place accurately the solder material on the board by using the solder paste stencil. Then placing the components on the pad with using a specialized pencil by the name“pick and place”. the reflow soldering process is as follows.
Preheating: preheating is compliance with thermal profile and do well in removing the volatile solvent that may include the solder paste.
Thermal soak: after the board is rising in temperature, it will go into the thermal soak area. There are two reasons why the card us maintained at temperature, one is to make sure any areas that are not fully heated due to shadowing effects come up to the necessary temperature. The other is to active the flux and remove the solder paste solvents or volatiles.
Reflow soldering: the area of reflow is the area where get to the highest temperatures in the soldering process. The solder is melting here and create the necessary solder joints. And the practical reflow process refers to the flux to reduce the surface tension at the metal joint so that achieve metallurgical bonding, allow the individual solder powder spheres to combine and melt.
Cooling: it needs to be done in a way without any stress to the components for the cooling boards after reflow. Appropriate cooling can restrain redundant intermetallic compound formation or thermal shock to the components. The range of typical temperatures in the cooling zone is 30-100℃ ( 86-212°F ), where is creating the relatively quick cooling rate for the temperature, and it can be a great grain structure in the solder with this method so that offer the most mechanically sound joint.
Wave soldering is a soldering process in which molten solder (usually a lead-tin alloy) is pumped or jetted into a desired solder wave shape. Printed circuit boards, pre-fitted with electronic components, pass through this solder wave to achieve both mechanical and electrical connections between the component leads or pins and the PCB solder pads through soft soldering. A wave soldering machine typically comprises a conveyor belt, flux application zone, preheating zone, and wave solder bath. The primary material used in this process is solder bars.
Wave soldering process
There are four major steps of wave soldering process as following.
Flux spry: the solder flux is mainly in removing the oxides from the board. And the application of flux offers the lower surface tension, heat transmittance, as well as a smoother soldering process.
Preheating: the board is heating on the tunnel after passing through a tunnel. And preheating creates the activation of flux, as well as the chain that is used for resembles a conveyor belt.
Wave soldering: the solder paste will be a liquid due to high degrees of temperature attained. What’s more, a wave is formed and the components are bonded with the boards.
Cooling: it will be subsequently lowered after the temperature achieves its highest degree or peak value. Once the solder components and the board are cooled adequately, it will start the assembly process.
There are some factors as important as mentioned above. Such as temperature, wave contact duration, the speed of band carrier and so on. So it should be taken into consideration during the wave soldering process.
