Today, wave soldering is the most common and most efficient form of through hole soldering available. It involves a solder pot large enough to handle the width of the largest boards you expect to process. By pumping hot solder through a nozzle in a way that the bottom of the board surface encounters the wave caused by the nozzle, the resultant hot solder waterfall creates a single point of contact across all the connection joints on the board, eliminating any potential bridging. The system usually integrates a fluxing station, a pre-heat station, and a wave station in a conveyorized system, using fingers or pallet-type board mounts.
The process consists of two phases: cleaning all of the metallic surfaces that have been designated for soldering and bringing these surfaces to the proper temperature to accept solder. Cleaning is generally accomplished by chemically etching the surface with an acidic compound such as flux. This step removes any oxidation or dirt that may have collected on the board prior to the wave soldering process.
The next phase in surface preparation heats the board. Heating accomplishes two tasks: flux activation and a reduction in temperature between the printed circuit assembly and the solder wave. Most fluxes require heat for thermal activation to break down the oxides. Manufacturers’ directions specify the amount of heat and time needed for activation. The second role in preheating the board and components is that of bringing the PCA temperature to near solder temperature.
The important factor in selecting a Wave system is to identify the largest board size the machine will be expected to process. This will determine the machine size and, just as importantly, its cost, from a bench top unit handling boards, up to free-standing machines with capacities up to 24” using a very large solder pot. The larger sizes will also accommodate much more solder, which also contributes to the cost of ownership. Generally, there are two types of wave in wave soldering process which possesses good feature.
- Laminar wave produces a very smooth laminar flow of solder much like a waterfall. This is the most widely used type.
- Turbulent wave sends solder up into the board with a highly turbulent wave used for thru-hole components such as pins with long legs that are fairly closely positioned, and for denser components. The turbulent wave helps to wick off excess solder to reduce icicles or bridging.
This process of soldering process utilizes a whole container of tin for performing welding. Tin goes through high temperatures, which melt its bar and molten tin is formed. The liquefied tin is taken as “lake water.” It is called “leveling wave” when the lake is static and horizontal. And, It is called “spoiler wave” when there are waves in the lake.
Wave Soldering Process
This process is purely based on the factors such as temperature and the machinery used with correct work force. Let us go through the processes and steps involved in the wave soldering process:
Fluxing
Flux mainly removes dirt and oxides on the surface of the metal. Further, it also creates a film to stop the air from reacting with the metal surface during high-temperature setup. Thus, solder cannot get oxidized easily. Nonetheless, one should use the liquefied tin for soldering during the wave soldering process. The flux is sprayed through the nozzle as the circuit board passes. The drawback of this method is that the flux can be easily passed through the board gaps. And, flux can also directly pollute the electronic components of the circuit board’s front.
Preheating
Preheating before the main wave welding process begins. It can increase the upper plate’s temperature to between 65 and 121°C with heating rate lying between 2 °C /s and 40 °C /s. It will not be able to get the best soldering results if preheating is insufficient. It is because flux may not be able to reach every part of the PCB. On the other hand, if a very high temperature for preheating is concerned, no-clean flux can suffer.
Cleaning
The cleaning process washes a PCB with deionized water or with solvents to get rid of flux remains. However, there exists a kind of flux which doesn’t need cleaning. But, it is needed to be careful; there are some applications which do not want “no-clean” fluxes. It is simply because “no-clean” fluxes can be very sensitive to the conditions of the process. Now that you know all about the wave soldering process. The coming chapter will relate wave soldering with other types of soldering.
Methods in wave soldering system
Automated In-Line System
This arrangement is usually tied in to a total PC board assembly line, where the conveyor simply moves assembled boards from the assembly stage through the Wave Solder machine and on to cleaning, finishing and other secondary operations. There is no manual interference at the solder machine; it’s a totally hands-off operation from beginning to end. Wave machines that run this way are usually very expensive and are used in high-volume repetitive operations. SMEMA (Surface Mount Equipment Manufacturers Association) defines uniform specifications for in-line systems to assure that all the operations in an assembly environment transfer boards seamlessly from one machine to another, regardless of the manufacturer, machine model, etc.
Palletized System
A palletized carrier is used to hold the circuit boards (which may include multiple boards) and the entire pallet is loaded onto the Wave solder machine. This is a batch process rather than an in-line system. The pallets are usually a fixed size according to the wave capacity (width and length). Good support for odd-shaped boards or thin boards that could warp otherwise; can be customized to hold unusually shaped boards, or multiple boards; very easy to maintain pallets and fingers because everything can be done outside the machine; pallets don’t rely on a set of fingers internal to the machine that would require shutting it down for maintenance.
Conclusion
While manual soldering is still done today, it is usually not found in a production environment because it involves highly skilled and labor intensive work producing very low numbers of boards. Dip and Drag were introduced many years ago as lower cost alternatives to Wave soldering, but have become outdated forms with the advent of more affordable and highly accurate Wave systems. Wave soldering is a clear player in heavy and high end manufacturing process and is the need of today’s industry thereby making the PCB manufacturing process more stable and fast.
By Mannu Mathew | Sub Editor | ELE Times
