Wave Soldering vs. Reflow Soldering

This Gold Phoenix PCB Knowledge Center article compares wave soldering and reflow soldering for printed circuit boards.

Soldering is a huge part of the printed circuit board design process. The only reliable way to get your circuits to stick to your board and stay there is by soldering them on. Without soldering, there are no printed circuit boards. But not all types of soldering are created equal, and it can be important to differentiate between the different types for PCBs.

There are two main types of soldering for PCBs: wave soldering and reflow soldering. What is the difference between the two, and how do you know which type of soldering to use in which circumstances?

What Is Wave Soldering?

Wave soldering is a bulk soldering process that enables one to manufacture many circuit boards in a very short amount of time. It works by passing each circuit board over a pan of molten solder. A pump in the pan creates a “wave” of solder that washes over the board, soldering the components to the board. The PCB then receives a water spray or air blowing to safely cool it and fix the parts in place.

Proper temperatures are very important during the wave soldering process. Failing to sufficiently control for temperature can put mechanical stress on the board, which can lead to cracks and loss of conductivity. Insufficient preheating can cause cavities, which can compromise both board strength and conductivity. The wrong solder temperature can result in failure to obtain the proper solder thickness, which could make the board more susceptible to stress.

What Is Reflow Soldering?

The reflow soldering process is a little bit different than wave soldering, but it is the most common way to attach surface mount components to a circuit board. Wave soldering is more frequently used for soldering through-hole components. Although it is possible to use reflow soldering for this purpose, it rarely is since wave soldering is more cost effective.

In reflow soldering, a solder paste is made out of powdered solder and flux, then that paste is used to attach components to contact pads. The entire assembly is then heated in a reflow oven or under an infrared lamp to melt the solder and connect the joint. Individual joints can be soldered with a hot air pencil if necessary.

Wave Soldering vs. Reflow Soldering

So, how do you know which type of soldering to use and when? It may depend on a variety of factors, such as pad shapes, the amount of time you have, component orientations, type of printed circuit board and more. In some ways, wave soldering is more complex. Issues like board temperature and time the board spends in the solder wave need careful monitoring. Failure to create the right wave soldering environment is much more likely to lead to board defects.

You do not need to be nearly as concerned about controlling the environment when utilizing reflow soldering to fabricate printed circuit boards. However, even with that being the case, wave soldering tends to be faster and cheaper than reflow soldering. In more than a few cases, it is the only practical way to solder a board. Reflow soldering is typically used in smaller scale manufacturing products that do not require a method amenable to fast, cheap mass production.

Keep in mind that both reflow soldering and wave soldering may be used for certain situations. You might reflow solder parts on one side and then wave solder them on the other. Also, manual or hand soldering of PCB components is always possible, but this will rarely be a good approach if access to one of the mechanical methods of soldering is available. Manual soldering would only be an alternative to reflow soldering, but reflow soldering is still far superior.