Although you’ve seen it on TV, there is no comparison to actually being part of a “wave” at a sporting event. Not only does the wave look really impressive as it makes its way around the stadium towards you, but you also end up feeling like you’ve contributed in a small way to a greater whole. And who knows, you may even find yourself on some highlight videos during the next local news broadcast.
Wave soldering a printed circuit board may only go in one direction, but like a stadium wave, it is designed to touch as many participants as possible. In this case, though, the participants are the components on your circuit board instead of the spectators in the arena. Wave soldering is the oldest form of soldering used in the mass-production of circuit boards, and it is still used to a great extent. Let’s take a look here at this process, and find out a little more about how component orientation for wave soldering can make a big difference in the manufacturability of your circuit board.
Everything You’ve Always Wanted to Know About Wave Soldering, but Have Never Asked
In the late 1940s, after the war, electronic devices became increasingly popular. It soon became apparent that soldering each lead and wire individually of these products was not practical for mass-production, and for a while, the dip method of soldering was used. But dipping the board into liquid flux and then into molten solder was slow and problematic, and a new method of automatically applying fresh solder alloy was needed. In the mid-1950s, the precursor to the modern wave soldering system was invented by pumping molten solder through a nozzle to create a wave for the solder joints to pass through.
Although wave soldering has been around for a long time now, it is still very important to the circuit board assembly process. Thru-hole parts need to be wave soldered and some surface mount parts can be too. The circuit board is moved through the wave machine on a conveyor belt where it passes over the molten wave of solder. The wave action forces the solder up through the holes of the board and around the pins in the holes to create a good solid solder joint. Wave soldering is still highly favored because it can solder a lot of boards quickly with less setup time than other methods.
To prepare for wave soldering, the board will be checked for fit and set up with spacers for heat dissipation and the height of components on the board. These spacers will later dissolve in the wash tanks. The board will also have areas masked off where solder is not desired, and it may also be fitted with a fixture to protect bottom-side components if needed. The wave solder machine meanwhile will have its conveyor adjusted for speed and wave height to match the parameters of the board. The solder chemistry will be heated to 500 Fahrenheit while the actual soldering times and temperatures will be controlled by the speed of the conveyor.
At this point, the boards are ready to be soldered, but the success of the soldering will ultimately be dependent on how the parts are arranged on the board.
The Importance of Component Orientation for Wave Soldering
The success rate of wave soldering circuit boards depends on how well the part placement is optimized for the process. The location and orientation of the parts can make a huge difference in how well the board is soldered. Here are some important points to keep in mind during component placement:
- Surface mount components placed on the back-side of the board will be a problem if they are too close to thru-hole pins. The location of the SMT parts may make it difficult to fashion the fixture correctly which could block the thru-hole pins from the full force of the solder wave. This will result in poor solder connections on those thru-hole pins.
- Large thru-hole connectors with multiple pins need to be placed so that they travel perpendicular to the wave. The more closely placed pins there are in a line that goes through the wave, the more likely that the trailing pins will not be soldered as well.
- Small individual discrete surface mount components should also travel through the wave perpendicular so that both pins get soldered at the same time. This requires that the designer knows which direction the board will be traveling through the wave before the layout begins.
- When placing surface mount components to be wave soldered, avoid placing smaller components behind larger ones in the direction of the wave. This could result in the larger components shadowing the smaller ones and creating a poor solder joint.
- Multi-pin SMT parts such as ICs can be wave soldered, but they should be placed in line with the direction of the wave to avoid shadowing the trailing pins.
- Be careful to not create land pattern pad shapes too large as this could cause solder bridging between them. It is always best to follow IPC specifications when creating your PCB footprints.
- Remember that the height of the wave has its limits, so taller components may not allow for that side of the board to go through wave solder.
With the component placement optimized for wave soldering, your board can be assembled faster, and with fewer problems that have to be touched-up. This will result in higher yields and lower costs for you, and possibly longer-term reliability for the board. The next step is to partner with someone that can help you with this placement optimization.
A wave soldering machine ready to solder a run of circuit boards
How Your Contract Manufacturer Can Help You Layout Your PCB for the Wave
Wave soldering is typically faster in both setup and soldering, making it the “go-to” process whenever possible. Wave soldering also gives better consistency over hand soldering. Even SMT boards will often still go through the wave in order to get a more robust installation of their connectors and other thru-hole parts. It is obvious that wave soldering is here to stay, the key is to get the best results from it.
Here is where the help of your PCB contract manufacturer can be of great assistance to you. At VSE we have worked with many customers just like you who need the highest yields and quality in their circuit board manufacturing. Our wave soldering processes are fine-tuned to give you the results that you need, and our technical teams are ready to help you with any questions.