The Need for Selective Welding of Rigid PCB Board
Today and we explain about the Rigid PCB circuit board selective welding of a necessary performance, we all know Rigid PCB circuit board selective welding technology is a relatively complex part of the circuit board module, from the characteristics to the process are very difficult to understand Knowledge, for everyone to be able to play the basic foundation, I am here for the Rigid PCB circuit board selective welding technology to do a full range of interpretation, I hope you can learn to help.
First, Rigid PCB circuit board selective welding technology of the process characteristics
Can be compared with the wave soldering to understand the characteristics of selective welding process. The most obvious difference between the two is that the lower part of the Rigid PCB circuit board is completely immersed in the liquid solder in the wave soldering, and in the selective welding, only some specific areas are in contact with the solder wave. Since the Rigid PCB circuit board itself is an undesirable heat transfer medium, it does not heat and melt the solder joints of adjacent components and Rigid PCB areas during soldering. The flux must also be pre-applied before welding. Compared with the wave soldering, the flux is only applied to the lower part of the Rigid PCB to be welded, rather than the entire Rigid PCB. In addition, selective welding is only applicable to the welding of the cartridge. Selective soldering is a completely new way to thoroughly understand the need for selective soldering processes and equipment for successful soldering.
Second, Rigid PCB circuit board selective welding technology
Typical circuit board selective welding technology processes include: flux coating, Rigid PCB preheating, dip welding and drag welding
(1) flux coating process
In selective soldering, the flux coating process plays an important role. At the end of the welding and welding, the flux should have sufficient activity to prevent the generation of the bridge and prevent the Rigid PCB from being oxidized. Flux Spray is carried by the X / Y robot to carry the Rigid PCB single-sided circuit board through the flux nozzle above, and the flux is sprayed onto the Rigid PCB to be soldered. Flux has a single nozzle spray, microporous jet, synchronous multi-point / graphics spray a variety of ways. Reflow soldering process after the microwave peak selection welding, the most important thing is the flux spray. Microporous jet type will never smear the area outside the solder joint. Micro-point spray the smallest flux point diameter greater than 2mm, so the spray deposited on the Rigid PCB flux position accuracy of ± 0.5mm, in order to ensure that the flux is always covered in the welded parts above the spray flux tolerance provided by the supplier, the technical instructions should Specified flux usage, usually recommended 100% of the safety tolerance range.
(2) preheating process
The main purpose of the preheating in the Rigid PCB soldering process is to reduce the thermal stress, but to remove the solvent pre-drying flux, before entering the solder wave, so that the flux has the correct viscosity. In welding, the effect of preheating on the quality of the welding is not a critical factor, Rigid PCB material thickness, device package size and flux type determine the preheat temperature setting. In selective welding, there are different theoretical explanations for preheating: some process engineers believe that the Rigid PCB should be preheated before the flux is sprayed; another view is that welding is required without preheating. The user may arrange the selective welding process according to the specific situation.
Third, Rigid PCB circuit board selective welding technology There are two different processes: drag welding process and dip welding process.
The selective trapping process is done on a single small tip solder wave. The trapping process is suitable for welding on a very tight space on the Rigid PCB. For example: individual solder joints or pins, single row of leads can be trailer welding process. The Rigid PCB moves at different speeds and angles on the solder wave of the tip to achieve optimum welding quality. To ensure the stability of the welding process, the inner diameter of the nozzle is less than 6mm. After the flow of the solder solution is determined, the welds are installed and optimized in different orientations for different welding needs. The manipulator can approach the solder wave from different angles, that is, 0 ° ~ 12 °, so that the user can weld the various components on the electronic components. For most devices, the recommended inclination angle is 10 °.
Compared with the dip welding process, the welding process of the solder solution and Rigid PCB board movement, making the welding heat conversion efficiency than the dip welding process. However, the heat required to form the weld connection is transmitted by the solder wave, but the soldering wave of the single tip has a low mass and only the temperature of the solder wave is relatively high to meet the requirements of the trailing process. Example: Soldering temperature is 275 ℃ ~ 300 ℃, dragging speed of 10mm / s ~ 25mm / s is usually acceptable. In the welding area for the supply of nitrogen to prevent the oxidation of solder waves, solder wave to eliminate the oxidation, making the trapping process to avoid the formation of bridge defects, the advantages of increased drag welding process stability and reliability.