Pcb circuit board industry technology development process, a clear trend reflow technology. Cartridge principle of traditional reflow process can also be used , which is commonly referred to through-hole reflow soldering. Its advantage is that it is possible to complete all of the joints at the same time , so that production costs to a minimum . However, it limits the temperature-sensitive element reflow soldering applications , either Cartridge or SMD. Then people turn to select welding. Most applications can be adopted after reflow soldering choice . This will become an economic and efficient completion of welding residual Cartridge , and is fully compatible with future lead-free soldering . Selective soldering process characteristics can be compared with the wave soldering process to understand the characteristics of selective soldering . The most obvious difference between the two lies in the lower part of the wave soldering PCB is completely immersed in the liquid solder , and in selective soldering , only part of the specific area in contact with the solder wave . Since the PCB itself is a poor heat conduction medium , so it does not heat to melt the welding of components and PCB area adjacent solder joints . Before welding must also be pre- coated with flux. Compared with the soldering flux is coated on only the lower portion of the PCB to be welded, rather than the entire PCB. Also applies only selective soldering soldering cartridge components.
Selective soldering is a new approach , a thorough understanding of the selective soldering process and equipment are required for successful welding . Selective soldering processes typical selective soldering process include : the flux coating , PCB preheating, dip soldering and drag soldering . In selective soldering flux coating process , the flux coating process plays an important role . At the end of the heating and welding welding , flux activity should be sufficient to prevent the generation of the bridge and prevent PCB oxidation . Fluxing by the X / Y robot carrying PCB flux through the top of the nozzle , spray flux to be soldered to the PCB position . Flux has a single mouth spray , micro -jet , synchronized multi-point / graphics spray a variety of ways . Microwave peak reflow soldering process after the election , the most important is accurate spray flux .
Microporous jet never soiled area outside the joints . Lightly spray dot pattern diameter greater than the minimum flux 2mm, so the spray deposition flux on the PCB position accuracy of ± 0.5mm, in order to ensure the flux is always covered in welded parts of the above , spray welding dose tolerance provided by the supplier , technical specifications should prescribed amount of flux is generally recommended 100% safe tolerances. The main purpose of the preheating process in the preheating process is not selective soldering reduce thermal stress , but the pre- dried to remove the solvent flux , prior to entering the solder wave , such that the flux has the correct viscosity. When welding , preheating is not critical influence of heat brought to the welding quality , PCB material thickness , the device determines the type of package specifications and flux preheat temperature setting. In selective soldering , there are different theories to explain the warm-up : Some process engineers think PCB should be conducted before fluxing , preheating ; another point of view does not require preheating and soldering directly . Users can be arranged according to the specific circumstances of the selective soldering process . Welding process selective soldering process , there are two different processes : drag soldering process and dip soldering processes. Selective soldering process is dragging on a single small tip solder wave completed . Drag soldering process is applicable on the PCB very close to the welding space . For example: an individual solder joints or pins , single-row pin can be dragged welding process .
PCB with different speed and angle of movement of the tip of the solder wave on the optimum weld quality. To ensure the stability of the welding process, the inner diameter of the tip is less than 6mm. After flowing the solder bath is determined, the need for different welding , and optimizing the tip installed in different directions . Robot from different directions , namely 0 ° ~ 12 ° angle close to the solder wave different , so the user can weld a variety of devices in the electronic components, for most devices , it is recommended tilt angle of 10 °. Compared with the dip soldering process, the welding process dragging motion solder and PCB board solution , making thermal conversion efficiency during welding better than the dip soldering process . However, the formation of the weld joint by the heat required for the solder wave to pass , but the tip of the solder Studio wave quality , only the relatively high temperature of the solder wave , in order to achieve drag welding process requirements. Example : Solder temperature of 275 ℃ ~ 300 ℃, drag speed 10mm / s ~ 25mm / s is generally acceptable. Nitrogen in the weld region , in order to prevent oxidation of the solder wave , to eliminate oxidation of the solder wave , so that the welding process to avoid dragging bridging defects , and this advantage increases the drag stability and reliability of the welding process . Machine has the characteristics of high precision and high flexibility , modular design of the system can be fully in accordance with the customer to customize the special production requirements , and can be upgraded to meet the needs of future production growth. Robot motion can cover a radius of flux nozzle , preheat and solder nozzle , thus the same device can perform different welding processes. Machine-specific synchronization process can greatly shorten the process cycle veneer .
Robot with the ability to make this choice has the characteristics of high precision and high quality welding welding . First, the robot highly stable precision positioning capability (± 0.05mm), to ensure that the parameters of each plate produced highly repetitive consistent ; followed by 5 -dimensional motion manipulator makes the PCB can be any optimization of the angle and orientation of the contact tin surface , to get the most good welding quality. Plywood installed on the robotic device solder wave height stylus , made of titanium , tin wave height can be measured regularly under program control , by adjusting the pump speed to control the tin solder wave height to ensure process stability . Despite these advantages are so many single mouth solder wave soldering process can also drag shortcomings : the time is in flux spray welding , preheating and soldering processes three longest . And because a solder joint is a drag soldering , welding points with increasing welding time will increase significantly in the welding efficiency can not be compared with the traditional wave soldering process . But the situation is undergoing change , multi- tip design to maximize yield, for example , dual welding nozzles can yield double the flux also can be designed for dual nozzles. Immersed in selective soldering system has multiple solder mouth, and with the PCB solder joint is one to be designed , although less flexibility manipulator type, but production was equivalent to the traditional wave soldering equipment, equipment cost is low relative to the robot type .
According to the size of the PCB , the board or panel may be transmitted in parallel , all the joints are to be completed in parallel, fluxing , preheating and soldering at the same time . However, due to the different distribution of different PCB solder joint , thus making the need for different PCB solder dedicated mouth. Tip sizes as large as possible , to ensure the stability of the welding process , does not affect the surrounding adjacent devices on the PCB , it is important for design engineers to speak , and it is difficult because of the stability of the process may depend on it. Selective soldering process using immersion , welding joints 0.7mm ~ 10mm , the short pin and the welding process is more stable small pads , but also the possibility of a small bridge , between the adjacent edges of joints , the tip of the device and the distance should be greater than 5mm.
