Circuit board fly wire

Common PCB circuit board faults are mainly concentrated on the components, such as capacitance, resistance, inductance, diode, audion, field effect, etc., the obvious damage of integrated chips and crystal oscillators, and the more intuitive way to judge the faults of these components can be observed by eyes. The surface of the electronic components with obvious damage has obvious cautery marks. Such faults can be solved directly by replacing the faulty component with a new one.

Suspected damaged component? It's not the component that's broken

Of course, not all the damage of electronic components can be observed with the naked eye, such as the above mentioned resistance, capacitor, audion, etc., in some cases the damage is not visible from the surface, need to use the most inspection tools for maintenance, commonly used inspection with: For multimeters and capacitance meters, if the voltage or current of an electronic component is detected outside the normal range, it indicates that there is a problem with the component or * component. Directly replace the component and check whether it is normal.

A circuit board that is not damaged in appearance and cannot be detected

If a component is broken, it can be detected no matter by eye observation or instrument detection. However, sometimes when we put components on PCB board, there will be no problem detected, but the circuit board cannot work normally. A lot of novices have no idea what to do with this kind of problem, so you have to either build a new board or buy one. In fact, in many cases, components in the installation process, because of the coordination of each component, there may be unstable performance.

According to the number of layers of the conductor pattern, the circuit board can be divided into single sided, double sided and multilayer printed boards. The basic manufacturing process of single panel is as follows

Foil-covered plate --> Cutting material --> Drying board (prevent deformation) -> Mold making --> Wash and dry --> Film (or screen printing) - > Exposure development (or corrosion resistant ink) -> Etching --> Remove film --> Electrical on-off detection -> Cleaning treatment -> Screen welding resistance graphics (printing green oil) -> Curing --> Screen marking symbol -> Curing --> Drilling -> Shape processing -> Cleaning and drying --> Inspection --> Packaging --> The finished product.

The basic manufacturing process of the double panel is as follows:

Graphic plating process flow

Foil-covered plate --> Cutting material --> Punching reference hole --> CNC drilling --> Inspection --> Deburring --> Electroless copper plating -> Electroplated copper -> Inspection --> Brush board --> Film (or screen printing)- > Exposure development (or curing)- > Inspection repair plate ----> Graphic plating (Cn 10 Sn/Pb)--> Removing film --> Etching --> Inspection repair plate -> Nickel plated plug -> Hot melt cleaning -> Electrical on-off detection -> Cleaning treatment -> Screen welding resistance graphics -> Curing --> Screen marking symbol -> Curing --> Shape processing -> Cleaning and drying --> Inspection --> Packaging --> The finished product.

The main advantage of SMOBC process is that it solves the short circuit phenomenon of solder bridging between thin lines. At the same time, because the ratio of lead to tin is constant, it has the best weldability and storability than hot melt plate. The SMOBC process for reremoving lead tin is similar to the process for graphic plating. It only changes after etching. Double clad copper foil -> According to the graphic electroplating process to the etching process -> Leaded tin -> Check ----> Cleaning --> Welding resistance graphics -> Nickel plated plug -> Plug tape -> Hot air leveling ----> Cleaning --> Screen mark --> Shape processing --> Wash and dry --> Inspection of finished products -> Packaging --> The finished product.

First, to clear the design objectives

When you receive a design task, you should make it clear whether it is an ordinary PCB board, a high frequency PCB board, a small signal processing PCB board or a high frequency and small signal processing PCB board. If it is an ordinary PCB board, as long as the layout and wiring is reasonable and neat, the mechanical size can be accurate, such as a medium load line and long line, it is necessary to use certain means for processing, reduce the load, long line to strengthen the drive, the best is to prevent long line reflection. When there are more than 40MHz signal lines on the board, special consideration should be given to these signal lines, such as cross-talk between the lines and other issues. If the frequency is higher, there will be a strict limit on the length of the wiring. According to the network theory of distributed parameters, the interaction between the high-speed circuit and its wire is the decisive factor, which cannot be ignored in the system design. With the increase of the gate transmission speed, the opposition on the signal line will increase correspondingly, and the crosstalk between adjacent signal lines will increase in direct proportion. Usually, the power consumption and heat dissipation of high-speed circuits are also large, so sufficient attention should be paid to the high-speed PCB.

When there is a weak signal of millivolt level or even microvolt level on the board, special attention is needed for these signal lines. Small signals are too weak and very susceptible to interference from other strong signals. Shielding measures are often necessary, otherwise the signal-to-noise ratio will be greatly reduced. So that useful signals are drowned out by noise and cannot be effectively extracted.

The commissioning of the board should also be considered in the design phase, the physical location of the test point, the isolation of the test point and other factors can not be ignored, because some small signals and high frequency signals can not be directly added to the probe to measure.

In addition, some other relevant factors should be considered, such as the number of layers of the board, the packaging shape of the components used, the mechanical strength of the board, etc. Before doing PCB board, to make the design of the design goal in mind.