Wave Soldering and Reflow Soldering in PCB assembly process

Wave Soldering and Reflow Soldering in the PCB assembly process

One of the most important steps in the life-cycle of a PCBA is Wave Soldering and Reflow Soldering. These steps ensure that your components are attached to your PCB thus allowing the intended electrical connections to be completed. Understanding the differences and understand which one your project needs is crucial to ensuring a reliable product. These two are the most popular forms of bulk soldering, however there is also selective, robotic, and hand soldering techniques.

Wave Soldering Process

Wave soldering requires the use of a wave solder machine. These come in all shapes and sizes but at the root of them all, a fully stuffed (populated) board is placed onto a conveyor which runs the PCB through the different zones. As the board travels along the conveyor, flux is sprayed on the underside of the board. Flux is used to clean off the components and specifically, any oxide layers that may have formed. The board will then continue along the conveyor and get pre-heated before it goes across the wave. The “wave” name comes from the wave of molten solder that the board runs across for all the components to get soldered on. This final step of the wave solder machine is crucial and requires years of experience to accomplish perfectly. Many variables can be adjusted such as angle, speed, temp, and others in order to minimize rework.

Reflow Soldering Process

Reflow soldering on the other hand is a less complex process. After the stencil printing and pick and place steps, the operator will place the boards on the conveyor of a reflow oven. These ovens have specific temperature profiles and sections according to the specified solder paste being used. This profile dictates which sections of the oven are which temperatures. This pre-heats the board, melts the solder paste and then allows it to solidify creating a solder joint for your component.

Which One is Right for your Project?

Generally, reflow will be used for SMT boards and wave soldering will be used for through hole boards. If your board is mixed technology, generally the reflow phase will happen first and then the wave. Although wave soldering is more finnicky, it is a faster process than reflow. Regardless of the process and how experienced the technician is, usually there will be some sort of touch ups required to get some of the boards to IPC-610 standards. This will be done by a technician using a hand solder.