History of Wave Soldering: Developing the Wave Soldering Process

Created: March 6, 2018
Updated: September 25, 2020

Mixed horizon

It is often said that the sun rises in the east and sets in the west. Of course, Copernicus long ago dispelled this misinterpretation. Even so, when I am on the road early in the day and the horizon is continually getting brighter I always get a sense of excitement coupled with uncertainty as to what the day will bring.

With the speed at which technology changes today, what the future will bring is a constant concern for engineers and designers, software developers, and manufacturers who create and build PCBs. This is especially true of the wave soldering process. Wave soldering has been around for decades and as the primary method for soldering components has played a major role in the growth of the utilization of PCBs.

There is a tremendous thrust to make electronics products smaller with more functionality and PCBs, the heart of these devices, has made this possible. This trend has also spawned new soldering processes as an alternative to wave soldering. It is clear that PCBs will continue to be a predominant element of technology advancements; however, what role wave soldering will play is not certain.

Before Wave Soldering: PCB Assembly History

Soldering as a process of joining metallic components is thought to have originated soon after the discovery of tin, which remains a major element of solder paste today. The first PCB, on the other hand, came along in the 20th century.

Albert Hanson, a German inventor, came up with the idea for a flat with multiple layers; including an insulation layer and foil conductor. He also described using holes in the device, which is basically the same method used for through-hole component mounting today.

During the second world war, the development of electrical and electronic devices took off as countries sought to improve the capability and precision of communications and accuracy or ordinances.

Paul Eisler, the inventor of the modern PCB, developed a process of attaching copper foil to a glass insulating base in 1936. He later demonstrated how a radio could be assembled on his device. Although his board used wiring to connect the components, which was a slow process, it sufficed at the time as large-scale production of manufacturing of PCBs was not in demand.

old type writer and parchment, vintage technology
While there’s a joy to the older technology, it would take ages to do modern designs with them.

Wave Soldering History: Wave Solder to the Rescue

In 1947, the transistor was invented by William Shockley, John Bardeen and Walter Brattain at Bell Laboratories in Murray Hill, NJ. This lead to the reduction in the size of electronic components and with later developments in etching and lamination paved the way for a production level wave solder technique.

As electronic components continued to be through-hole it was easiest to supply solder paste to the entire board at once, instead of soldering them individually using a soldering iron. Thus, wave soldering was born where the entire board is run over a “wave” of solder.

Today, wave soldering is performed by a wave solder machine. The process consists of the following steps:

  1. Melt - the solder is heated to approximately 200° C so it will flow easily.
  2. Flux - the cleaning of the components to ensure there are no obstructions. Wave soldering fluxes ensure these obstructions don't prevent the adhesion of the wave solder.
  3. Placement - PCB is properly placed to ensure solder paste reaches all of board.
  4. Application - solder is applied to the board and allowed to flow to all areas.
  5. Cleaning - Solvents are used to thoroughly wash and clean the board.
 PCBs on the way to be wave soldered
PCBs on the way to be wave soldered

The Future of Wave Soldering

Wave soldering once was the most applied soldering technique. This was due to its speed advantage over manual soldering that enabled the automation of PCB assembly. The process is especially adept at soldering through-hole components that are well-spaced very quickly. As the demand for smaller PCBs led to the use of multilayer boards and surface mount devices (SMDs) the need for more precise soldering techniques developed.

This led to selective soldering methods where connections are soldered individually, as in manual soldering. Advancements in robotics, that are faster and more precise than manual soldering enable the automation of this method.

Wave soldering has remained a well-implemented technique due to its speed and its adaptation to the newer PCB design requirements that favor the use of SMDs. One advancement known as selective wave soldering has emerged that uses a spray jet that allows the application of solder paste to be controlled and directed only to select areas.

Through-hole components are still in use and wave soldering is undoubtedly the fastest technique to solder a large number of components quickly and may be the best method depending on your design.

Although, the application of other soldering methods, such as selective soldering, are steadily increasing there are advantages to wave soldering that continue to make it a viable option for PCB assembly. With an advanced PCB design software package, such as Altium Designer® with its PDNA you have the ability to design your boards to favor the use of wave soldering or other techniques.

For more information about wave or other soldering methods and how to design your PCB for them, contact an Altium Designer PCB design expert.

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