PCBA processing is completed by a variety of processes, such as solder paste printing, pick and place machine, SMT SPI detection, AOI detection, reflow oven welding and so on, each process step has a different purpose, if the process step out of the batch problem, will cause the whole piece of bad output. Today we briefly analyze which factors affect the effect and quality of reflow oven welding.
Solder paste is a mixture of solder powder and flux. Its main function at the patch end is to stick the electronic components, so as to prevent the electronic components from falling off during mounting or flow. In high-temperature melting of reflow soldering terminal is secure electronic components in the specified solder, flux of rosin, viscous agent, surfactant, such as various elements, so the flux is one of the important factors affect tin penetration in the PCBA processing, the flux of the main role is to get rid of the surface oxide, PCB and components and to prevent the reoxidation in the process of welding.
On the premise that PCB design is correct and the quality of components is guaranteed, solder paste printing is responsible for more than 70% of the quality problems in PCBA SMT processing. Whether the printing position is correct or not, the amount and uniformity of printing directly affect the quality of reflow welding. Generally, empty welding is due to less solder paste printing, coupling bridge is due to too much solder paste printing offset, monument is due to uneven printing uniformity and so on. Therefore, SPI machine should be added to detect the factor quality of solder paste after solder paste printing to reduce the influence ratio of solder paste printing on reflow welding.
The electronic components mounted by the lamination machine, the accuracy of the position of the component mounted, the pressure of the component mounted and so on will cause quality problems in welding. If the accuracy is too low, it will cause welding short circuit and empty welding, etc.
Reflow furnace temperature curve is a key link affecting welding. Reflow welding generally has four temperature zones, namely preheating, heat absorption, reflow and cold zone. The temperature of different temperature zones are different, so it is necessary to set the temperature curve in line with the product to generate high quality and good quality welding quality.
The thermal compensation effect of reflow welding (related to the insulation effect of reflow welding) and the anti-collapse effect of guide rail (the deformation of guide rail caused by long-term heat absorption affects the accuracy of guide rail and leads to uneven heating of PCB or components)
In PCBA processing, different boards and products have different electronic components, and even similar electronic components products have different brands, resulting in the quality of electronic components themselves are uneven, so the choice of good brand, good reputation of electronic components is conducive to the rate of good after welding.
