Every soldering process, such as selective soldering, wave soldering or reflow, has benefits and drawbacks. In certain instances, selective soldering is clearly the appropriate soldering method and wave soldering is clearly the better soldering process in others. In order to choose which to employ, one has to consider the intended application for which the wave or selective soldering machine will be used.
Though other soldering methods certainly have their place, wave soldering is the best method for certain applications. Specifically, the best application for wave soldering is mounting a large number of components to a printed circuit board that require surface mounting or in certain instances, where through-hole soldering is required.
Prior to wave soldering, the PCB and components must be subjected to a wash of flux and also preheating, to clean the components to be soldered and also to prevent thermal shock that can be caused by the soldering process.
Wave soldering works by means of a pump, which creates a wave in a pan of molten solder. PCB's pass over the pan and the waves solder components that are pre-attached to the board, but merely require soldering to establish the connection.
After the soldering, the PCBs may require - depending on the type of flux and solder used - a cleaning stage, usually with deionized water or solvents. After the cleaning and the solder cools, the soldered board goes to the next stage of the production cycle.
Wave soldering is best used in applications where a large amount of soldering has to be done at one time in a small area, either due to a large number of components being attached to the board, connectors with a high number of pins, or components that are subjected to generous amounts of power.
Selective soldering, on the other hand, is better suited for applications requiring precision soldering. Typical applications for selective soldering are when soldering a component to a PCB is necessary but wave soldering or other methods pose too much risk of damaging the rest of the board and other components due to heat, such as any components soldered after the majority of components have already been soldered to the board via reflow oven or wave soldering.
There are many methods of selective soldering, such as selective aperture tooling over wave solder, mass selective dip solder fountain, miniature wave selective solder fountain and laser selective solder systems. Each has their own mechanism; selective aperture tooling, for instance, blocks off sensitive areas so a PCB can through a second round of wave soldering to install additional components, and laser systems solder components by virtue of a pinpointed laser, controlled by CAD software for ultra-precise soldering.
Selective soldering, therefore, is best-suited to more sensitive and specific applications.
The method one should employ - be it selective solder or wave solder - depends on precisely what one is soldering. By way of analogy, some woodworking requires merely a table saw. Some tasks, though, require a planer/jointer, a bandsaw or a Dremel tool. Hunting an animal, likewise, can require use of a rifle or a shotgun, depending on one's quarry.
A printed circuit board with a large number of surface-mounted components would be easily assembled by wave soldering, though this application has fallen out of favor in recent years in favor of reflow ovens, which heat a solder paste to the point where it fuses components in an oven. If specific components in specific and sensitive locations on a PCB need to be soldered instead of a large number of components in one fell swoop, then selective soldering is the better process. If intersted in learning more we also disucssed hand soldering vs. selective soldering.
Wave soldering machines and selective soldering machines are tools. As with anything else, one has to pick the right tool for the task. If you need a professional opinion about which method is best for your current proejct give us a call at 509.891.1680 x253 or use our contact form to get in touch.