In the single wave soldering process of surface mount technology (SMT) and surface component (SMC) circuit boards, wave soldering technology and equipment of liquid solder are needed.
At present, the domestic wave soldering technology is mechanical pump wave soldering machine, and only one company has developed single-phase induction electromagnetic pump wave soldering machine. Wave soldering machine abroad is mainly mechanical pump wave soldering machine. In the late 1980s, Switzerland, the United States and other countries produced a wave soldering machine with conductive electromagnetic pump (patent US-3.797.724), which was discontinued due to unstable performance.
In 1990s, China developed the first generation of single-phase induction electromagnetic pump wave soldering machine (patent CN9 1058 162a. CN.93246899.3)。 Since then, China's wave soldering machine technology has been at the forefront of the world, followed by the successful development of the second generation induction electromagnetic pump-three-phase asynchronous induction pump based on the military technology electromagnetic gun (patent CN966). Single/double wave crest automatic welding machine using three-phase asynchronous induction pump as wave crest generator has also entered mass production.
Second, the necessity of developing three-phase asynchronous induction pump
At present, wave soldering machines used in electronic assembly production are mostly mechanical pump wave soldering machines. Because the mechanical pump blades rotate at high temperature (about 250℃), they wear quickly, which pollutes the solder on the one hand; On the other hand, it needs regular maintenance and replacement of worn blades and worn parts, which brings inconvenience to users. Moreover, due to the rotating motion of the mechanical pump, the tin surface is disturbed, which leads to intensified oxidation and a large amount of tin slag.
In order to solve the above problems, a wave soldering machine with conductive electromagnetic pump was developed abroad, which eliminated the mechanical pump, no rotating parts, no wear and maintenance, and the output of tin oxide slag decreased, which partially solved the problem of wave soldering with mechanical pump. However, the conductive electromagnetic pump can not meet the requirements of production process because of its inherent instability and high and low peaks.
In 1990s, domestic related units developed single-phase induction electromagnetic pump wave soldering machine to solve the above problems, which solved the problems of unstable wave crest, no rotating parts and no maintenance, and basically solved the problems existing in mechanical pump wave soldering machine. However, this machine is insufficient in making wide wave crest (300 mm ~ 400 mm wave crest width) and ultra-high wave crest (40mm height).
In order to solve the above problems, China has developed a three-phase asynchronous induction pump based on the electromagnetic gun theory, which has the advantages of no rotating parts, no wear, no maintenance, smooth peak, stable tin surface on the tin bath, no rotating disturbance of tin material on the peak, and obvious reduction of oxide slag formation. Because of its high efficiency, wave soldering machines with wide wave crest (400mm) and ultra-high wave crest (40mm) can be prepared, which basically meets the needs of wave soldering machines.
Third, the technical principle
1, principle of mechanical pump wave soldering machine
Schematic diagram of mechanical pump
As shown in the figure, the liquid tin material pumped by the mechanical pump has a rotating component, which leads to unstable wave crest, and it can only be used after several times of pressure equalization and steady flow. Moreover, due to the rotation, the tin surface is unstable, and a large amount of tin oxide slag is formed, which increases the welding cost. Rotating at high temperature leads to the wear and failure of blades and seals. Therefore, production and maintenance must be stopped regularly.
2. Principle of conductive electromagnetic pump
Principle of conductive electromagnetic pump
As shown in the figure, the principle of the conductive electromagnetic pump is that when the conductor in the magnetic field passes through the current, the conductor will be pushed by the magnetic field. The three directions are perpendicular to each other, and the thrust is f = I× B.
The conductive electromagnetic pump has no rotating parts, which solves the wear problem of mechanical pump and forms a maintenance-free welding machine. However, in the process of conducting current from a large current electrode in contact with liquid metal, the peak value is unstable or even fluctuating due to the adhesion and shielding of oxide slag on the electrode, which makes it impossible to produce stably. Nearly 50 models imported from Switzerland by China were basically stopped.
3. Principle of induction electromagnetic pump
The principle it adopts is to use a single-phase C-shaped open-ended electromagnet to generate the phase difference of the inner and outer magnetic fields due to the magnetic circuit difference, and then form the forward magnetic field component, that is, the forward magnetic field component from the leading phase to the lagging phase. The liquid metal solder in the advancing magnetic field component cuts the magnetic field lines, so it is subjected to a positive induction force to achieve the purpose of pumping the liquid metal solder.
Because the phase difference is generated by the magnetic circuit difference, the forward magnetic field component is very limited, and most of them are pulsating magnetic fields that do not generate forward thrust, so it is very difficult to manufacture wide peaks (300 mm to 400 mm in width) and ultra-high peaks (40mm in height) as shown in the figure.
4. Principle of three-phase asynchronous induction pump
This is another patented technology of wave soldering machine in China. It not only solves the problem that the conductive current electrode of the conductive electromagnetic pump is unstable due to the shielding of oxide slag, but also has no rotating parts, no converter, no maintenance, no wear, high efficiency, large and strong peak value and wide peak value.
The principle of three-phase asynchronous induction pump is to use the phase difference of three-phase power supply 120 to form their own magnetic fields in space, and its synthetic magnetic field is a positive magnetic field to cut magnetic lines, induce current and form a positive electromagnetic force.
Because the inherent phase difference of the three-phase power supply is directly used, the synthetic magnetic field basically has no pulsating magnetic field component, and it is a synthetic magnetic field that generates positive force, which is exactly the same as the principle of the electromagnetic gun, so the efficiency can reach more than 70%. Wave soldering machine composed of three-phase asynchronous induction electric pump has all the advantages of induction electromagnetic pump, such as superposition of audio disturbance vibration waves, enhanced welding ability and climbing ability, no rotating parts, no wear, no maintenance and simple structure.
Because the asynchronous induction pump produces linear thrust, the liquid metal tin material does not rotate, the tin bath is calm, and the generated oxide slag is greatly reduced. The oxide slag is reduced by about 4KG per shift, and the investment can be recovered only by saving the solder value for one year, which is nearly 654.38+10,000 yuan.
Four. Comparison of application effects
The single/double wave crest automatic welding machine developed by using three-phase asynchronous induction pump, after comparison, we get the following results:
Due to the unique superposition of disturbance vibration waves, the gas in the shielded soldering area generated by the thermal decomposition of flux and adhesive in SMT soldering can be effectively removed, and the jump welding and shadow area of SMC and SMD can be eliminated, which meets the requirements of SMT soldering. At the same time, due to the superposition of disturbance waves, the hole climbing ability of wave soldering is not obviously enhanced, and the welding reliability and yield are improved.
The peak is smooth and there is no rotation component. Because the three-phase asynchronous induction electromagnetic pump produces linear thrust instead of rotating thrust of mechanical pump blades, the wave crest is smooth, the disturbance of tin bath liquid level is small and the oxidation is slight.
The peak is stable. Because of the induction pump technology and the principle of voltage stabilization, when the grid voltage fluctuates 10%, the voltage on the induction pump fluctuates by nearly 3%, so the peak value is stable.
High efficiency. Because there is no pulsating magnetic field component, the efficiency of three-phase asynchronous induction electromagnetic pump is greatly improved. The prototype shows that the peak width is 400mm and the peak height is 40 mm, but the magnetization current of the three-phase induction pump is only about 5A, which ensures that the three-phase asynchronous induction pump works in a low-heat and low-current load state and ensures long-term life reliability.
No rotating parts, no wear, truly realize the maintenance-free, eliminating the regular maintenance link.
From the comparison of the above principles and the application results of the prototype, we draw the conclusion that the three-phase asynchronous induction pump used in the wave soldering machine has solved most of the problems that need to be solved in the current process, realized maintenance-free, saved solder, reduced the generation of oxide slag, and conveniently obtained various requirements such as wide wave crest and ultra-high wave crest. With the deepening of application, the three-phase asynchronous induction electromagnetic pump used in wave soldering machine is the future development trend, which will promote the development of electronic assembly technology, especially SMT mixed assembly.
Ps: I think it's a machine for welding circuit boards!