The present situation and future of wave soldering technology
Production process
Avoid defects
Inert weld
Productivity problem
What kind of wave soldering method is used?
Wind knife to bridge technology
Machine selection
In most do not require the miniaturization of products still in use perforation (th) or mixed technology circuit boards, such as TV, home audio-visual equipment and the upcoming digital set-top boxes and other still remains in perforated elements. Therefore, it is necessary use wave soldering. From a technical point of view, wave soldering machine can only provide a little bit of the most basic equipment to adjust the operating parameters.
Production process
Circuit board through the conveyor belt into a wave soldering machine, through a form of flux coating device, here flux using crest, foaming or spray coating method to the circuit board. Because most of the flux on welding must be to achieve and maintain a activation temperature to ensure the welding of complete wetting, so circuit board before entering the crest trough to go through a preheating zone.
Flux coating after preheating can gradually increase the temperature of the PCB and the flux activation. This process is also reduced group packages into the wave generated during thermal shock. It can also be used for all possible absorption of moisture or diluted flux carrier solvent to evaporate, if these things are not removed, they will peak in boiling and caused solder sputtering, or produce steam in the solder formed inside hollow solder joint or trachoma.
Wave soldering machine preheating section length by yield and conveyor speed to decide, the higher the yield, the Board reached the temperature required for the infiltration of the longer. In addition, due to the heat capacity of double-sided and multilayer large, so they need more than a single panel preheating temperature high.
The current wave soldering machine basically adopts the heat radiation of preheating, wave soldering preheating method are the most commonly used hot air convection, forced convection, electric heating plate electric bar heating and infrared heating etc.. In these methods, forced convection is often considered the most in the process of wave soldering machine most effective heat transfer method.
In the warm-up, circuit board using single wavelength (lambda wave) or double waves (disturbance waves and Bo) for welding. The perforated element in terms of single wave is enough, the circuit board into the wave when the direction of the flow direction and board solder instead, can produce eddy current in the element around the pin. Like this is a wash, above all flux and oxidation residue removal in solder joints reach infiltration temperature formed when infiltration.
The general assembly for hybrid technology, is used in a disturbing wave front. This wave is relatively narrow, vertical pressure disturbance with high, can make the solder well into the placement of pins and surface mounted components compact (SMD) between the pads, and solder joint forming with the completion of a wave.
Before making any assessment of the equipment and the supplier in the future, need to identify all the technical specifications for welding board with the crest, because these can determine the performance of machines needed.
To avoid the defects
With the current components become smaller and PCB more and more dense, and the possibility of occurrence of bridge circuit also result in an increase in the solder joints between. But there are some effective methods to solve this problem, one method is the use of air knife technology. This is in the PCB away from the crest used a knife to the melting of the solder joint blow out a bunch of hot air or nitrogen, air knife of the PCB width can be on the PCB width of complete quality inspection, eliminate bridge or even short-circuit and reduce operating costs.
And possible other defects including weld or leak welding, also known as open circuit, if the flux is not painted on the PCB will be formed. If the flux is not enough or not running correctly the preheating stage will cause poor wetting the top surface.
In spite of welding in bridged or short circuit can be found in the test after welding, but to know weld will in the quality inspection, after welding, testing qualified, and later in the use of problems. Use problems will seriously influence the formulation of the lowest profit targets, not only because field replacement will produce cost, and due to the customer to find the quality problem and the future sales will affect.
In the peak phase of the welding, PCB must be immersed in wave solder coating in the solder joints, so the wave height control is a very important parameter. Can be in crest added a closed-loop control so that the crest height remains unchanged, a sensor installation on the crest above the conveyor chain guide rail, a highly measuring peak with respect to the PCB, and then use the tin pump speed up or slow to keep correct immersion tin height.
The accumulation of tin slag on wave soldering is harmful. If in the tin trough together with tin slag, then tin slag will increase the possibility of entering the peak. To avoid this problem by designing the pump system, extraction from the top tin tin bath bottom instead of tin slag aggregate. Can also reduce tin slag and save expenses by inert gas.
Inertia welding
Nitrogen welding can reduce tin slag to save cost, but the user must bear the initial investment cost and nitrogen delivery system. Usually consider the above two factors, so be sure to reduce maintenance and thus better because solder wetting defect rate, reduce the cost savings. Also can use the low residue process at this time will some flux residues remain in the board, and according to the requirements of customers of the product or the residual is acceptable.