The printed circuit board is often referred to as PCB. PCB component is called PCB assembly service. Components on board can be SMT (surface mount) components, plug-in components, pressure components, or assembly parts. Today, take a common motherboard as an example to share the assembly process and common problems of the PCBA factory. After the ICT test station, it needs to go through an assembly station to install the button battery, radiator, CPU base bracket, CPU backplane, handle, some isolating Mylar, the plastic column for limit, screw, etc. Figure 1 shows the server motherboard with assembly. When assembling parts, some external forces should be applied to PCBA, so PCBA should be fixed and supported on the assembly fixture before assembly. Some PCBA need to assemble the bottom surface of the PCBA board, so two supporting fixtures need to be made. The support fixture also needs to pass electrostatic protection and stress test before delivery to the production line. The standard of electrostatic protection can refer to ANSI / ESD s20.20. Refer to IPC-JEDEC-9704a (L) for the stress test. The following describes the process and common problems of PCB assembly service according to the type of components.
Battery There are two types of batteries on this motherboard: discrete type and horizontal type, as shown in Figure 2. Button batteries should be placed horizontally and can not be stacked or taken with bare hands. The battery stack and the bare hand take may cause low power due to the discharge, reduce its service life. The battery needs to be stored in the original disk, as shown in Figure 3. The original battery tray is made of plastic material, which is easy to generate static electricity. It needs to use an ion blower to dissipate static electricity. Ion fan can produce a large number of positive and negative charge airflow, and neutralize the charge on the charged object. The plastic comb we use in our life is easy to generate static electricity, especially when it is very dry in winter, the hair will fly up. When we have static electricity on our bodies and just touch the metal doorknob, our hands will feel an electric shock. In the same way, static electricity will do great harm to the static sensitive devices such as IC on PCBA, and the process test may not be able to completely screen out. As shown in Figure 4 is a hanging ion fan, which covers a large area and does not occupy desktop space. When taking the battery, you can use a finger cover to avoid discharge and dirt. In addition, the battery has a polarity, and the positive and negative poles of the battery should be checked during installation.
Radiator There are several types of radiators, as shown in Figure 5. Some radiators are supplied with a layer of transparent plastic, which needs to be torn off before assembly. Otherwise, there is a layer of plastic between the components and the radiator, which will affect the conduction and release of heat. After assembling the radiator, it is necessary to ensure that the radiator is flatly attached to the BGA body, and the radiator buckle or spring piece has been opened to clamp the PCB or hook. Some radiators are directional, and failure to install such radiators in the direction will affect the heat release, which may lead to abnormal temperature test of the product or damage the components. In order to avoid such assembly errors, the design engineer can be asked to change the materials in the trial production stage. In addition, industrial engineers can also design some pressure bar fixture to assist in the installation of the radiator to reduce the difficulty of operation.
Screw Use an electric screwdriver to assemble the screws. Different screw heads have different electric drivers, and the torque may be different, as shown in Figure 6. Before use, the electric screwdriver needs to calibrate the torque, which is consistent with the screw manufacturer’s recommendation. With the same torque, the different electric heads can be replaced to complete the assembly of different screws. The operation method of the electric screwdriver is vertical downward. The tilted electric driver may cause the screw to slip and not fully lock into the screw hole. The screw will float high and may hit the components around the screw hole. PCBA assembly service factory can make fixtures for the working position of the electric batch, as shown in Fig. 7. The PCBA is protected and only the screw hole position is exposed to prevent the electric batch from hitting PCB copper foil or peripheral components.
Myra Nonmetallic Mylar is plastic, as shown in Figure 8, which also requires an assembly station equipped with an ion blower. In addition to the hanging ion fan in Fig. 4, the desktop ion fan in Fig. 9 is also widely used in PCBA plants. However, the ion airflow produced by the suspended ion fan covers a large area, and the wind power regulation range is wide. Of course, the price is higher.