Tin bead phenomenon is one of the main defects in SMT processing. Due to its occurrence of more reasons, it is not easy to control, so it often plagues SMT SMD plus engineers and technicians. Next, we will introduce the reasons for SMT processing to produce tin beads.
一、The tin bead mainly appears in the chip resistor and capacitor components on the side of the tin bead mainly appears in the chip resistor and capacitor components on the side of the tin bead, and sometimes appear in the patch near the IC pins. Tin beads not only affect the appearance of board-level products, more importantly, due to the high density of components on the PCBA board, there is a risk of short-circuit during use, thus affecting the quality of electronic products. There are many reasons for the generation of tin beads, usually caused by one or more factors, so it is necessary to do a good job of prevention and improvement measures to control tin beads.
二、 The tin paste may be due to various reasons, such as collapse, extrusion beyond the printed solder paste tin beads are some of the large tin balls in the solder paste before soldering, the tin paste may be due to various reasons, such as collapse, extrusion beyond the printed solder paste in the soldering process, beyond the solder paste failed to soldering and the soldering process of the solder paste board melted and independent of each other, formed in the component body or near the pads.
三、 The pad will be designed as a square chip components, if the presence of more solder paste, it is easy to produce solder beads most of the solder beads appear on both sides of the chip components, for example, the pad will be designed as a square chip components, after printing the solder paste, if the presence of more solder paste, it is easy to produce solder beads. Solder paste that is partially fused to the solder pad does not form solder beads.
But when the amount of solder increases, the element exerts pressure on the solder paste in the component below the body, and thermal fusion occurs during reflow soldering because the surface energy melts the solder paste into a globule, which has a tendency for the component to rise, but this tiny force is formed during the cooling of the solder bead, and there is a gravitational force between the individual components on both sides and separates the solder pads. If the component gravity is high and more solder paste is extruded, it may even form multiple solder beads.
四、According to the reasons for the formation of tin beads, the main factors affecting the production of tin beads in the SMT SMD production process are:
- The design of the SMT stencil and pads.
- The impact of printing parameters.
- Repeatability of the SMT mounter and the height of the pressure-related settings.
- Reflow oven temperature profile is reasonable.
- whether there is a need to optimise the solder paste control process.
- Whether the electronic components are affected by moisture.