The difference between selective soldering and wave soldering - advantages and differences
And what the automatic THT assembly for LEDs in an Airbus galley has to do with it
As an EMS (Electronic Manufacturing Service) manufacturer, we use different soldering processes for THT and SMD assembly. In addition to the original time-consuming manual soldering, we work with automated wave soldering systems and selective soldering systems. In this article, you will discover the difference between the two soldering processes and the advantages they offer our customers - with an example from our customer Airbus.
What is selective soldering?
Put simply, selective soldering replaces manual soldering in assembly production. It is an automated 3D soldering process that is controlled by software. X, Y and Z coordinates are defined on the circuit board. The coordinates indicate where the hot solder is deposited on the circuit board in order to solder specific components. A cone-shaped nozzle approaches the circuit board from below and sets the soldering point at specific points. The selective soldering process is recorded on video.
The advantages of selective soldering
Most SMD boards are fitted with components on both sides. If THT parts are also arranged in such a complex way that they cannot be soldered in any other way, the selective soldering process is used. Here we can selectively choose the soldering points using X, Y and Z coordinates without affecting other components.
At A+B Electronic, the processes are optimized in such a way that serial productions run much more efficiently through the manufacturing process and are therefore delivered to the customer faster. The selective soldering process plays an important role here. This technology is the most economical, especially when only a few components need to be soldered on a circuit board. In contrast to soldering by hand, selective soldering produces a clean and uniform soldering pattern and therefore increases the quality of each individual circuit board.
These selective soldering systems are in use at A+B Electronic
- ERSA Versaflow 4/55 (2 single pots) lead-free
- ERSA Versaflow 3/45 (2 single pots) lead-free
- ERSA Versaflow 40/50 (1 single pot) lead-free
With our selective soldering systems, we can create individual programs for each PCB and respond flexibly to customer requirements.
What is wave soldering or wave bath soldering?
Wave soldering is an integrated, automated soldering process in which a conveyor belt guides a THT-equipped circuit board through a solder bath. A literal wave of solder wets the entire underside of the PCB, including the plated-through components. Wave soldering therefore only works on one side of the board and over the entire surface.
After the entire board has been wetted with flux, it is heated over several preheating stages so that the solder bonds with all the through-hole wires. This is followed by a controlled cooling process in which the solder hardens. The circuit board then travels back to the assembly station on a conveyor belt.
Wörthmann wave - our standard process
With this nozzle, the solder wave is created through small holes in a perforated plate. The advantage of the Wörthmann wave is better access to the components. This process also results in fewer solder bridges that can cause short circuits, which is also a quality feature.
These wave soldering systems are in use at A+B Electronic
- ERSA Powerflow N² lead-free
- ERSA N-WAVE 330 leaded
We can process different orders with our systems. The system recognizes the requirements of the respective circuit board via individually written transponders on the solder frame. This means that the same frame can be programmed for a different project tomorrow and use the data from the first project again in three weeks' time.
The advantages of wave soldering
We use wave soldering when a large number of THT components need to be soldered. Soldering over the solder wave is a time and cost-saving process, especially for series production.
Process optimization brings further time benefits
The aim is to integrate the inspection of soldered PCBs directly into the production line. Our employees who receive the PCB back from the press can immediately carry out the revision service on the line. From there, the PCB goes directly to further processing.
What exactly is the difference between selective and wave soldering?
The biggest difference is that with wave soldering, the entire underside of the PCB, including all components, is continuously wetted with solder. With selective soldering, we only solder the areas that we have previously defined. You can imagine this as being analogous to selective conformal coating: precise selection of the application areas instead of full coating.
We use wave soldering for THT series production. The process is fast and economical. However, wave soldering is not always feasible for double-sided, SMD-equipped PCBs with THT components. In these cases, selective soldering has established itself. It requires more time, but is more precise and designed for customized assemblies.
The processes also differ in terms of the nitrogen supply. In wave soldering, the PCB passes through a nitrogen tunnel. In selective soldering, we wet the nozzle, which sits on top of the crucible, with nitrogen. The aim of both processes is to remove the remaining oxygen content from the solder joints.
Best practice: Process optimization for automatic THT assembly for Airbus galley LEDs
As an EMS manufacturer for Airbus, we have many years of experience with standardized processes and process optimization. Firstly, because we are certified ourselves. And secondly, because production processes for Airbus are also standardized. When we received the order to manufacture LEDs for Airbus galleys several years ago, the requirements were clear and we asked ourselves: How can we implement these requirements as efficiently as possible?
The solution: We converted an automatic placement machine from SMD production to be able to assemble THT LEDs. This enabled us to automate a standardized manual process in-house and make it many times more efficient.
