In manufacturing electronic circuits, PCB assembly is a very important stage. Assembling a printed circuit board can be done manually by using skilled workers. In the modern era of electronics manufacturing, though, large PCB fabrication companies rely on automated assembly lines to deal with these procedures. One automated procedure electronic devices should undergo is the soldering process. This article will discuss a soldering procedure and technique called wave soldering. It is a very important technique, especially if one would want to start a simple, but automated way of soldering PCBs.
For starters, soldering is used to attach the component pins, or lead, to the board. PCB assembly cannot be completed, if there are no means of “gluing” the board and components together. “Gluing” can either be done by using one of these technologies:
•surface mount technology (SMT)
•through-hole mounting (THM)
SMT allows the components to just set foot onto the circuit. Through-hole mounting, on the other hand, places the components pins on drilled holes. These technologies have specific methods to permanently fix the component pins through solder.
Soldering can also be performed manually. It, however, takes a lot of time and skill to even complete one circuit. There are two popularly used automated-techniques in the industry:
Wave soldering is an inexpensive soldering technique. This technique is still popular to standard circuit board fabricators. It can be used on both SMT- and THM-reliant circuits.
So what is wave soldering? As its name suggests, it literally passes a “wave” of liquefied solder to a pre-heated printed circuit board. A wave soldering machine is used to melt the solder, and to hold and move the board into different “zones”. It also must have a mechanism to create that “wave”, and another one to let the PCB “surf” through the waves. These zones are:
•fluxing –the components and copper surface to be soldered are first cleaned using a flux agent.
•preheating –the board is heated to a specific temperature to activate the flux, and remove any unnecessary contamination from the board and connections
•soldering – the board is then moved via a conveyor belt into a tank of molten solder
•cleaning – all the leftover solder will be washed away with chemical solvents.
The procedures above, or zones, make up the wave soldering process. But, why do PCB fabrication and assembly companies use this technique? First of all, it is economical and practical to use, as compared to manual soldering techniques. For a startup company, it also is the cheapest and simplest among the automated machines. A basic wave-soldering machine consists of just these parts:
•conveyor that moves the PCB through the different zones
•the solder tank, or a container that contains the molten solder, used in the soldering process
•pump that produces the actual wave
•sprayer for the flux and the preheating pad
•a heating tool or equipment, and a thermometer
If you think about it, the machine can even be a DIY project. The wave process may also be semi-automated. Practicality and cost-effectiveness are the reasons why this method is still used today.
Wave soldering has also some disadvantages, as well. Wave soldering is a demanding process. Its equipment and setup may be simple, but the conditions and procedures it contains are tasking. When using this technique, some of the important factors that affect the PCB assembly include:
•heating profile and cooling profiles
•solder temperature and flow rate
•time in solder
The pad shapes and component orientations must also be checked first before transporting the board to the molten solder. Component pins must also be cleared first of any obstacles. The conditions in this procedure, therefore, must first be understood thoroughly to not damage the PCB and components to be soldered.
There is also another automated soldering technique. It is also the latest. It is called the soldering reflow. It boasts of the benefits that are not found in the wave process. It actually replaced wave soldering as the king of the automated soldering. Reflow, however, works only in SMT devices, or SMDs. Wave soldering can also be used for SMT, and some instances in PCB assembly were both SMT and THM are used in a board. Reflow cannot also be used on large power devices.
Soldering reflow is the latest technique. In contrast to wave soldering, reflow requires expensive equipment and complicated setup when starting up an electronics business.
Wave soldering may be an old PCB assembly technique, but is still a widely-used one, because of its practicality and cost-effectiveness. Startup businesses may choose this technique to automate the workplace.