There are two main methods of soldering commercially – reflow and wave soldering.
Wave soldering involves passing solder along a preheated board. Board temperature, heating and cooling profiles (non-linear), soldering temperature, waveform (uniform), solder time, flow rate, board velocity, etc. are all important factors that affect soldering results. All aspects of board design, layout, pad shape and size, heat dissipation, etc. need to be carefully considered for good soldering results.
It’s clear that wave soldering is an aggressive and demanding process – so why use this technique at all?
It is used because it is the best and cheapest method available, and in some cases the only practical method. Where through-hole components are used, wave soldering is usually the method of choice.
Reflow soldering refers to the use of solder paste (a mixture of solder and flux) to connect one or more electronic components to the contact pads, and to melt the solder through controlled heating to achieve permanent bonding. Reflow ovens can be used , infrared heating lamps or heat guns and other heating methods for welding. Reflow soldering has less requirements on pad shape, shading, board orientation, temperature profile (still very important), etc. For surface mount components, it’s usually a very good choice – the solder and flux mixture is pre-applied by a stencil or other automated process, and the components are placed in place and usually held in place by the solder paste. Adhesives can be used in demanding situations, but are not suitable with through-hole parts – usually reflow is not the method of choice for through-hole parts. Composite or high-density boards can use a mix of reflow and wave soldering, with only the leaded parts mounted on one side of the PCB (called side A), so they can be wave soldered on side B. Where the TH part is to be inserted before the through-hole part is inserted, the component can be reflowed on the A side. Additional SMD parts can then be added to the B side to be wave soldered with the TH parts. Those keen on high wire soldering can try complex mixtures of different melting point solders, allowing side B reflow before or after wave soldering, but this is very rare.
Reflow soldering technology is used for surface mount parts. While most surface mount circuit boards can be assembled by hand using a soldering iron and solder wire, the process is slow and the resulting board can be unreliable. Modern PCB assembly equipment uses reflow soldering specifically for mass production, where pick-and-place machines place components on boards, which are coated with solder paste, and the entire process is automated.
Post time: Jun-05-2023