1. The Wave Soldering Process
A standard wave soldering machine consists of 3 main process zones, Fluxing, Preheating and Soldering.
Fluxing is used to improve the soldering characteristics of the PCB. The flux used achieves this by removing oxidation from the surfaces to be soldered, preventing further oxidation and by improving the wettability of the solder. The preheat section gently heats the PCB, which in turn activates the flux and removes flux carrier solvents. This even heating of the PCB helps to prevent thermal shock as the board enters the soldering zone.
Wave soldering is done by pumping molten solder through specially designed nozzles which creates a flow of solder, over which the PCB is passed. Surface tension leaves the solder joint in tact as the board exits this flow of solder. Nitrogen (N2) is sometimes used to envelop the solder pot area to improve the soldering and to minimise dross formation as the molten solder oxidises.
The 3 process zones in a wave soldering machine are closely linked and must be tightly controlled to achieve the best results.
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2. Wave Soldering Applications
Wave soldering equipment is used for both conventional through hole printed circuit assemblies and surface mount PCB's. In surface mount applications the components must be glued in position prior to being wave soldered.
Although many traditional through hole wave solder applications have now transferred to SMT and are now soldered using reflow, many applications still require or benefit from the wave solder technique. These applications include large power devices, high pin count connectors, industrial lighting and white goods.
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3. Wave Soldering Machine Types
Wave soldering machines come in many different sizes offering various levels of capability, from small desktop systems to large fully automatic multi zone machines.
The type of machine you require is dependant on a number of factors; your PCB size, type of flux you wish to use, solder type, component density, thermal mass and volume requirements. The answers to these questions will determine machine configuration.
Flux type will specify whether your machine will need a foam fluxer or a spray fluxer. Volume requirements, size and thermal characteristics of your PCB's will determine what length of preheat you may require and also whether there is a need for topside heating also. While solder type will decide what nozzle configurations you may need and also whether N2 is necessary.
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4. Troubleshooting Wave Soldering Problems
Wave soldering is a process which requires a good process knowledge to achieve good results. However a number of common problems are described below:
Poor Barrel Fill..
There are 3 main reasons for this symptom, insufficent flux, insufficient preheat and insufficient solder time. Thus you must ensure that you are applying enough flux to the joints in question. Check board temperatures top and bottom to confirm that you are applying enough preheat and finally ensure that you are allowing enough contact time in the solder to enable flow through. This advise is more critical when using Pb free solder due to the higher molten temperatures.
Icicles and Shorts..
This phenomenum is usually associaed with poor flux stability at the point of soldering, poor wettability, board to wave levelling or speeds. Therefore you must check that your flux application is even, preheats are not exhausting the flux before it reaches the pot, check components for wettability and ensure that your pot is level to the PCB. Also check for excess dross formation.
Cold/Disturbed Joints..
Recognised by rough or dull finish on joints, this is normally associated with excess solder pot temperature or mechanical impact whilst joint is solidifying.Therefore you must ensure that your pot temperature is at the specified setting and that your conveyor system is properly lubricated and allows smooth PCB transport.
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5. Expert Advice..
Please visit individual supplier websites for further detailed information.Browse manufacturers wave soldering equipment here
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