Professional terminal design needs to know these terms
Design of terminal block, including terminal block, terminal block and terminal block. There are three kinds of contact modes: surface, line and point. Point contact is the most reliable. In order to ensure the contact reliability of mobile phone connector, convex hull is used at the contact part of terminal. In addition, attention should be paid to the selection of appropriate bending radius in the contact area. The smaller the bending radius is, the easier it is to cause cracks. In addition, the contact area of the terminal shall not have burr, so as not to affect the contact reliability with the connected device.
Structural design of terminal spring wall: pay attention to positive force, permanent deformation, friction force and insertion and extraction force
Positive side of terminal: F = w width e elastic coefficient b reduction H ^ 3 thickness cubic / 4L ^ 3 length cubic
Permanent deformation: 6F positive force l wall length / W width H ^ 2 Thickness square
The calculation formula of friction force is fi (max) = FN (max) [(sin α + μ cos α) / (COS α - μ sin α)]. According to the relationship between material stress and strain, the relationship between terminal stress and yield strength determines the size of permanent deformation. When the maximum stress is less than or equal to the yield strength, there is no permanent deformation; when the maximum stress is greater than the yield strength, there will be permanent deformation. The design of barbed structure includes pre inserted section, barbed section and tail section
Pre insertion: when the terminal is assembled into the plastic, the terminal is initially fixed in the plastic, waiting for deep pressing. If it is too short, it will cause a high defect rate in the process.
Barbed: provide the retention force of the terminal in the plastic to ensure that the terminal and the plastic do not separate in normal use. According to the actual application of the product, the selection of retention force is also different. The area of the straight line segment that affects the retention force except the interference size and the interference size. It also has an effect on the size of the undercut to the plastic surface.
terminal block leg design: the requirement of eliminating seesaw phenomenon and ensuring coplanarity of terminals shall be considered. The exposed plastic bottom surface of all terminal block pins is generally 0.05mm. The gap between terminal block pins and surrounding plastic shall be reserved to prevent short circuit caused by tin creeping. The strip design should mainly consider the impact on stamping, electroplating, assembly, cost and so on. Therefore, opinions on stamping, electroplating and assembly should be consulted, or the stamping engineer should decide the strip layout on the premise of meeting the requirements of electroplating and assembly. The selection of belt hole diameter should consider the standardization of assembly and cutting or automatic assembly. In the case that the terminal is easy to deform under pressure during packaging, the protective foot shall be added to prevent the terminal from deformation. In order to meet the requirements of strip removal in production, the connection between terminal and strip is often pre broken.
Plastic design: the function of plastic is to fix terminals and keep insulation between terminals. Due to the limitation of filling performance of plastic raw materials, when the thickness of plastic wall is less than 0.2mm, it will be difficult to fill. The larger the thickness, the more likely it will be that the mold will not be full. The insulation impedance and withstand voltage performance of the connector are mainly determined by the thickness of the plastic material between the terminals. If there is insufficient mold between the terminals, the terminals will be likely to open circuit (serious quality problems). The thickness of the plastic wall between the terminals should be more than 0.25 mm as far as possible, and the length of the thin-walled section should be reduced as far as possible. In the structural design of plastic parts, attention should be paid to reducing the use of unnecessary sliding blocks as far as possible. The rationality of the structure can be evaluated by consulting the molding engineer. As for the thin wall (less than 0.3mm) often appears on both sides of plastic parts due to size limitation, it is necessary to find a way to thicken it, otherwise it is easy to cause damage in injection molding, packaging and turnover due to insufficient mold filling or too low strength. For the plastic of the connector that needs SMT patch, there should be a position for vacuum nozzle to absorb on the top surface of the connector under the actual application state, and the surface quality of the area must ensure that there will be no vacuum leakage.
Dimensioning: how to size and how much the tolerance value is appropriate has the final say of the designer or the size of the person, and is determined by the product requirements (function, process requirements, process capability). For finished products, key dimensions are usually more important for customers to use, such as terminal contact height, card height, coplanarity, or other dimensions specifically required by customers; there are also some more important dimensions in production control, such as terminal indentation depth. At the same time, the factors such as assembly, electroplating and automatic machine production should be considered in the design.
