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Wave Soldering Cheat Sheet by

Wave Soldering
circuit     manufacturing     soldering     wave     boards

Introd­uction

As its name implies, wave soldering is used to combine PCBs and parts through a liquid “wave” formed as the result of motor agitation. The liquid is actually dissolved tin. It is carried out in a wave soldering machine (Figure 2).

The wave soldering process is composed of four steps: flux spraying, prehea­ting, wave soldering, and cooling.

1. Flux Spraying

Cleanl­iness of metal surfaces is the basic element ensuring soldering perfor­mance, depending on functions of solder flux. Solder flux plays a crucial role in smooth implem­ent­ation of soldering. Primary functions of solder flux include elimin­ating oxide from the metal surface of boards and component pins; protecting circuit boards from secondary oxidation during the thermal process; reducing surface tension of solder paste; and transm­itting heat.

2. Pre-He­ating

In a pallet along a chain similar to a conveyor belt, circuit boards travel through a heat tunnel to carry out preheating and activate flux.

3. Wave Soldering

As temper­ature constantly rises, solder paste becomes liquid with a wave formed from the edge boards that travel above. Components can be solidly bonded on boards.

4. Cooling. Wave

Cooling. Wave soldering profile conforms to a temper­ature curve. As temper­ature reaches the peak in the wave soldering stage, it is reduced, which is called a cooling zone. After being cooled to room temper­ature, the board will be succes­sfully assembled.
 

Wave flow Soldering

Process

As circuit boards are placed on a pallet ready to go through wave soldering, time and temper­ature are closely associated with soldering perfor­mance. As far as time and temper­ature are concerned, a profes­sional wave soldering machine is necessary, while the PCB assemb­ler's expertise and experience are seldom easy to obtain since they depend on applic­ation of up-to-date techno­logies and business focus.

If temper­ature is set too low, flux won't be melted properly, reducing the ability to react and dissolve oxide and dirt on the surface of the metal. In addition, the alloy won't be generated by flux and metal if the temper­ature is not suffic­iently high. Other factors such as speed of the band carrier, wave contact time, etc. should be taken into consid­era­tion.

Generally speaking, even though the same wave soldering equipment is used, different assemblers offer differing manufa­cturing efficiency due to operation methods and the extent of knowledge about how to operate the machine.

Reflow vs Soldering

Figure illust­rates the difference between soldering process steps. The essential difference between wave soldering and reflow soldering lies in flux spraying — wave soldering contains this step, while reflow soldering does not. Flux enables dioxide elimin­ation and surface tension reduction in the material to be soldered. Flux works only when it's activated, which requires rigorous adherence to temper­ature and time control. Since flux is contained in solder paste in reflow soldering, flux content has to be approp­riately arranged and achieved.

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