In SMT chip processing, chip inductors mainly play the role of choking, decoupling, filtering and tuning. There are two types of chip inductors, winding type and laminated type. How to choose suitable chip inductors? How should the performance and appearance quality of SMT components be tested?
SMD inductor selection:
1. The net width of the SMD inductor should be smaller than the net width of the inductor to prevent excessive solder from causing excessive tensile stress to change the inductance value during cooling.
2. Most of the chip inductors available on the market have a precision of ±10%. If you want the precision to be higher than ±5%, you need to order in advance.
3. Many chip inductors can be soldered by reflow soldering and wave soldering, but some chip inductors cannot be soldered by wave soldering.
4. When repairing, it is not possible to exchange chip inductors only by inductance. It is also necessary to know the task frequency band of the chip inductor to ensure the task function.
5. The shape and size of the chip inductors are basically similar, and there is no clear mark on the shape. When hand soldering or hand patching, don’t get the wrong position or take the wrong parts.
6. There are three rare chip inductors at present: 1. High-frequency inductors for microwaves. Suitable for use in frequency bands above 1GHz. 2. High-frequency chip inductors. It is suitable for resonant circuit and frequency selective circuit. 3. Universal inductance. Generally applicable to circuits of tens of megahertz.
7. Different products have different coil diameters, opposite inductances, and different DC resistances. In the high-frequency circuit, the DC resistance has a great influence on the Q value, so you should pay attention to it when designing.
8. It is also a goal of chip inductors to allow large currents to pass. When the circuit needs to bear large currents, it is necessary to think about this goal of the capacitor.
9. When a power inductor is used in a DC/DC converter, its inductance indirectly affects the task form of the circuit. In theory, it is often possible to change the inductance by increasing or decreasing the coil to achieve good results.
10. Wire-wound inductors are commonly used in communication equipment operating in the 150~900MHz frequency band. In circuits with frequencies above 1GHz, microwave high-frequency inductors must be selected.
The above are the top ten considerations when selecting chip inductors in SMT chip processing. Better use of chip inductors can better ensure the quality of SMT chip processing.
smt appearance inspection:
The solderability of component pins (electrode terminals) is the main factor affecting the reliability of SMA welding. The main cause of solderability problems is the oxidation of component pins. Since oxidation is prone to occur, in order to ensure welding reliability, on the one hand, measures must be taken to prevent components from being exposed to the air for a long time before welding, and to avoid long-term storage; on the other hand, they must be weldable before welding. The most primitive method of solderability testing is visual evaluation. The basic test procedure is: immerse the sample in the flux, take out and remove the excess flux, and then immerse it in the molten solder tank. When the immersion time reaches about twice the actual production welding time, take it out for visual evaluation. This kind of test experiment is usually carried out with an immersion tester, which can accurately control the immersion depth, speed and immersion residence time of the sample according to regulations.
Electronic component inspection
smt component inspection:
Surface assembly technology is to mount components on the PCB surface. For this reason, there are strict requirements for the coplanarity of component pins. Generally, it must be within a tolerance of 0.1mm. This tolerance zone consists of two planes, one is the PCB soldering area plane, and the other is the plane where the component pins are located. If the plane of the three lowest points of all the pins of the component is parallel to the plane of the soldering area of the PCB, and the distance error between each pin and the plane does not exceed the tolerance range, the mounting and soldering can be carried out reliably, otherwise it may lead to Welding faults such as false or missing feet.
There are many ways to detect component pin coplanarity. The simplest method is to place the component on the optical plane and use a microscope to measure the distance between the non-coplanar pin and the optical plane.
At present, the high-precision placement systems used generally have their own machine vision system, which can automatically detect the coplanarity of the component pins before placement, and eliminate the components that do not meet the requirements.