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PCBA: what are the factors that affect the quality of wave welding

325 Published by FASTPCBA 7月 23,2018

What is wave welding?(wave welding)
Wave soldering is to make the welding surface of the plug-in plate contact with the high temperature liquid tin directly to achieve the welding purpose. The high temperature liquid tin maintains an inclined surface, and a special device makes the liquid tin form a phenomenon similar to waves, so it is called “wave soldering”.Simple speak it refers to the soft soldering material will melt tin alloy (lead), electric pump or electromagnetic pump flow into the design requirements of the solder wave, can be formed by the injection of nitrogen to solder pool, take the PCB with components in advance through the solder wave, components and PCB solder welding end or pin of mechanical and electrical connections between soft soldering.
Wave soldering process
Insert the element into the corresponding hole of the element – precoated flux – prebaked (temperature 90-1000c, length 1-1.2m), wave soldering (220-2400c), removing the excess pin – inspection.
In the process of welding, there are many factors that affect the welding quality. The parameters that need to be paid attention to include welding temperature, transmission speed, track Angle, peak height and so on.
1. Welding temperature
When the welding temperature is too low, the expansion rate and wettability of the welding material will be poor, so that the welding end of the welding plate or component cannot be sufficiently wetted, resulting in defects such as virtual welding, drawing tip and bridge connection.When the welding temperature is too high, it speeds up the oxidation of the welding disc, the pin of the components and the solder, which is easy to produce virtual welding.
2. Transmission speed
The tin wave should be as smooth as possible, so the speed of the conveyor belt should not be too high.
3. Orbital Angle
Adjusting the Angle of the orbit can control the contact time between PCB and wave peak, and the proper inclination Angle can help the liquid solder separate from PCB more quickly.When the inclination Angle is too small, bridge is more likely to occur.However, if the inclination Angle is too large, it is beneficial to eliminate bridge joints, but the solder joints eat too little tin, so it is easy to produce virtual soldering.Orbital tilt Angle should be controlled between 5 ° ~ 7 °.
4. Peak height
Wave peak height refers to the height of PCB tin feeding during wave peak welding, which is usually controlled at 1/2~2/3 of the thickness of PCB board.The wave height is too high to cause the molten solder to flow to the surface of the PCB, forming a “tin connection”.The height of the wave peak will change as the working time of welding goes on.The commonly used tool for measuring peak height is depth gauge or high temperature glass.
5, solder
In wave soldering, the impurities of solder mainly come from the copper leaching on the PCB solder plate. Excessive copper will lead to the increase of welding defects.
Tin-lead solder at high temperature (250 ℃) oxide, tin – lead solder in the solder pot tin content is declining, deviating from the eutectic point, leading to poor liquidity, appear even the welding, and virtual welding, solder joint strength is not quality problem.The following solutions can be adopted to solve this problem:
Oxidizing reducing agent was added to reduce oxidized SnO to Sn and reduce the production of tin slag
The cinder is continuously removed
Add a certain amount of tin before each welding (the above measures need to be carried out regularly according to the operation specification)
The welding material containing phosphorous oxide is adopted
Transaction nitrogen protection (oxygen content should be monitored)
All parameters in the wave soldering process need to coordinate with each other and repeatedly adjust according to the actual welding effect.
Maybe for many colleagues who have just entered the electronic processing industry, the name of the complex equipment on the production line is enough to know for a long time.So let’s look at that by the way
What is the difference between wave soldering and reflow soldering?
Difference between wave soldering and reflow soldering (1)
The reflow soldering process is to remelt the paste solder pre-allocated to the plate soldering plate to realize the soft soldering of mechanical and electrical connection between the welding end of the surface assembly components or the pin and the plate welding plate.
Wave soldering has a new welding technology with the enhancement of people’s awareness of environmental protection.In the past, tin-lead alloys were used, but lead is a heavy metal that does great harm to people.So now we have lead technology.It USES tin silver copper alloy and special soldering flux and requires higher preheating temperature for welding joints. Also, a cooling zone workstation should be set up after PCB plates pass through the welding zone. This aspect is to prevent thermal shock.
Wave soldering can be basically solved by soldering the tin to the larger and smaller components, which is different from the reflow soldering, and the reflow soldering heats the plates and components, in fact, the solder paste that was originally painted is liquefied to achieve the goal of connecting the components to the plates.(wave welding)
1. Reflow welding goes through preheating zone, reflow zone and cooling zone.In addition, wave soldering is applicable to manual insert plate and glue plate, and all components are required to be heat resistant. There can be no SMT solder paste components on the wave surface, and SMT solder paste boards can only be re-weldable, not wave soldering.
2. Wave soldering is to dissolve the tin rod into liquid through the tin groove. The motor is used to agitate the tin rod to form waves so that the PCB can be welded with some products. Generally, the welding of the hand plug-in and the glue board of SMT are used.Reflow soldering is mainly used in the SMT industry, which melts the solder paste printed on PCB and welds parts through hot air or other heat radiation transmission.
3. Different process: spray flux first, then preheat, weld and cool zone.
Difference between wave soldering and reflow soldering (ii)
Wave soldering is mainly used for welding plug-in.Reflow soldering is mainly used to weld laminated components
1. Wave soldering is to dissolve the tin rod into liquid through the tin groove. The motor is used to agitate the tin rod to form waves so that the PCB can be welded with some products.Reflow soldering is mainly used in the SMT industry, where soldering solder paste printed on PCB is fused with parts of products through hot air or other heat radiation transmission.(wave welding)
2. Different process: spray flux first for wave soldering, then preheat, welding and cooling zone.Reflow soldering goes through preheating zone, reflow zone, cooling zone.In addition, wave soldering is applicable to manual insert plate and glue plate, and all components are required to be heat resistant. There can be no SMT solder paste components on the wave surface, and SMT solder paste boards can only be reflow soldered, not wave soldering.(wave welding)

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