SMT Stencil Printer Pick and Place Machine and Its Ambient Factors Analysis
Surface mount technology (SMT) stencil printer pick and place machines (SPPPMs) are divided into different types based on the technology used, including pick-and-place machines, screen-printing machines, and reflow ovens. Each of these types is used in different stages of an SMT assembly process. Usually, in SPPPM, there are sometimes difficulties during production, such as misalignment of components, stuck components, and feeder off errors. The main purpose of this paper is to analyze pick-and-place process and its ambient factors with respect to SPPPM.
Firstly, pick-and-place process includes three main steps: pick, place, and post-processing. In the pick process, the nozzle fixture is driven by a stepper motor and guided by vision systems, which allow the nozzle to locate and pick parts from a feeder. The pick process should always be done precisely, as it is the most critical part in SPPPM. After the pick process, the place process follows. In this stage, the nozzle is driven to the precise position of each component, and the part is then placed on the substrate by the nozzle. In the post-processing stage, components often require additional assembly solutions like cleaning and trimming. Every step of the pick-and-place process should have the right ambient conditions like temperature, humidity, and light, since it is essential to the reliability and quality of the finished product. To maintain the appropriate ambient conditions, thorough temperature and humidity control in the workshop, including controlling temperatures in the equipment and other factors, is of great importance.
Temperature is especially critical during SPPPM. The main reason to control the temperatures is that it affects the curing of the solder paste on the PCB, which is in direct contact with the Teflon nozzle on the pick-and-place machine. Due to a mismatch of temperatures, gaps will form between the parts and the nozzle and thus cause misalignment of the components. In the place process, temperature also determines the “tack-time” of the components. This is the time it takes for the solder paste or adhesive to set into the correct position and stay stuck in the correct position. Temperature also plays a vital role in the post-processing stage of SPPPM, as the solvent used for cleaning the components can also set in too quickly or too slowly depending on the temperature of the workspace.
Humidity is also closely related to SPPPM. Excessive humidity can cause defects of components, such as blurring of components, and it can also cause rust on the parts. High humidity can also affect the electrical components, which can lead to overheating problems. On the other hand, too low humidity will increase dust in the air, making components difficult to stick. Poor insulation between the parts and substrate may occur due to too low humidity, causing short circuits to make the entire assembly process invalid. Thus, the working environment must be strictly controlled to keep the humidity at an underlying level.
Light control also plays a part in SPPPM, as the components must be subjected to the same light intensity conditions during pick-and-place. It is very important to ensure that the parts are not subjected to light at different times because it will affect their uniform contact with the paste/adhesive. Furthermore, too much light may expose parts to ultraviolet radiation, which can cause discoloration, deformations, and other issues that can damage some of the components. The illumination should also be consistent when printing the solder paste onto the board for pick and place process.
In conclusion, ambient factors play a crucial role in the efficiency and success rate of the SMT stencil printer pick and place process. Temperature and humidity need to be controlled to their appropriate levels, while illumination should also be consistently monitored. If it is not done, it may lead to misalignment of components, stuck components, and feeder off errors. Therefore, a good working environment and diligent monitoring should be in place for successful SMT stencil printer pick and place operations.
