In the PCBA patch processing factory, in order to make the cleaning of the printed circuit components smoothly and achieve good results, in addition to understanding the cleaning mechanism, cleaning agents and cleaning methods, it is also necessary to understand the main factors affecting the cleaning effect, such as yuan. The type and arrangement of the device, the design of the PCB, the type of flux, the process parameters of the solder, the residence time after soldering, and the parameters of the solvent spray.
PCB layout should avoid placing plated through holes under the components. In the case of wave soldering, the flux flows through the plated through holes provided under the component to the upper surface of the SMA or the SMD on the upper surface of the SMA, which makes cleaning difficult. The thickness and width of the PCB should match each other and the thickness should be close. In the case of wave soldering, the thinner substrate must be stiffened or stiffened to increase the resistance to deformation, and this reinforcing structure intercepts the flux and is difficult to remove during cleaning.
With the development of miniaturization and thinning of components, the distance between components and PCBs is getting smaller and smaller, which makes it more and more difficult to remove the residue from the SMA. For example, complex components such as SOIC, OFP, and PLCC, when cleaning after soldering, block the penetration and replacement of the cleaning solvent. When the surface area of the SMD is increased and the center-to-center spacing of the leads is reduced, especially when there are leads on all four sides of the SMD, post-weld cleaning operations are made more difficult. The component arrangement affects the SMA's cleanability in both the component lead extension direction and the component orientation. They have a large influence on the flow rate, uniformity and flow of the cleaning solvent passing under the component.
The type of flux is a major factor affecting post-weld cleaning of SMA. As the percentage of solids in the flux and the activity of the flux increase, it is more difficult to clean the remainder of the flux. For the specific SMA, which type of flux should be selected for welding, it must be considered in combination with the cleanliness level required by the component and its cleaning process that can satisfy this level.
The effect of reflow soldering process on cleaning is mainly reflected in the temperature of preheating and reflow heating and its residence time, which is the rationality of the reflow heating curve. If the reflow heating curve is unreasonable, the SMA will overheat, which will cause the flux to deteriorate and deteriorate, and the deteriorated flux cleaning is difficult. The post-weld dwell time refers to the dwell time before the component enters the cleaning process after welding, that is, the process dwell time. During this time, the flux residue will gradually harden so that it cannot be cleaned. Therefore, the post-weld dwell time should be as short as possible. For a specific SMA, the maximum allowable dwell time must be determined based on the manufacturing process and the type of flux.
In order to improve the cleaning efficiency and cleaning quality, spray cleaning is mostly used on the basis of static solvent or steam cleaning. The use of high-density solvents and high-speed spraying allows contaminant particles to be easily removed by large forces. However, when the solvent is selected, the density of the solvent is no longer a parameter that can be rounded, and the only adjustable parameter is the spray rate of the solvent.