7 Tips in Designing PCB

1. Flexible application of via design

For high-voltage, high-current, high-power, and high-heat components, the layout of components should be as loose as possible when designing printed boards. The size of the component pads and the pad spacing of each solder pin can also be designed bigger. If the number of circuit components and the size of the printed board allow, you can also design some vias in the space between the pads of the components and the copper foil of the printed board according to needs, that is, remove excess printed circuit board substrates, leave some space. Doing so not only helps the components to dissipate heat to each other, but also helps to improve the insulation performance between the components and the copper foil of the printed board, which can prevent leakage between the printed circuit board copper foil and the printed board pads, burr discharge, breakdown short circuit, etc. The size and shape of the openings can be determined according to needs. The positions of the openings can be selected, for example, between the welding pins of the power input socket, between the rectifier bridge welding pins, between the optocoupler input / output welding pins, between high-power triodes, between the welding feet, between the welding feet of the tube base of the tail tube of the picture tube, between the copper foil of some printed boards, and other required places.

2. Copper foil traces should be smooth

When designing the copper foil traces for printed boards, the shape of the copper foil of the printed board should be as small as possible to avoid sharp corners, burrs, and the ends and corners of the copper foil should be designed as rounded, chamfered, and copper foil edges as possible. It should be designed to be neat and smooth with smooth lines. This is because sharp corners, burrs and other dust, moisture, etc. often form sparks and discharges, causing faults such as leakage and short circuit. In addition, in the design of radio frequency (RF) circuits, the copper foil traces of printed boards should use 45 ° wires as much as possible, and do not use 90 ° folded wires to reduce the emission of high-frequency signals.

3. The ground and power cables must be thick and strong

The key copper foil wires such as the copper foil ground wire and power cord of the printed board should be designed as thick and sturdy as possible when conditions permit. There are two main reasons: One is that the thick ground wire is conducive to reducing the impedance of the ground wire and improving the anti-interference ability. In addition, the printed circuit board ground wire is often connected with large pieces such as a grounded radiator and a metal shield plate, and large soldering is also required. The disk is firmly fixed; The second is to thicken the power cord, which is conducive to improving power efficiency. It should be noted that a thin layer of tin is added to the surface of the copper foil in some places, which can further reduce the internal resistance of the circuit, enhance the ability to resist current shock, and increase the strength of printed boards and copper foil circuits To a certain extent, the thin tin on the surface of the copper foil can also increase the heat dissipation area and act as a heat sink. In addition, the open area of the printed board is reasonably filled with copper skin, and network-shaped, strip-shaped ground wires are added and thin tin plating is added, which will also play a role in shielding interference.

4. Use IC sockets carefully

When designing printed boards, integrated circuit plugs (IC sockets) should be used with caution or not. IC sockets are usually used for circuit design and debugging. At the beginning of the experiment, in finished circuits, IC sockets should be avoided (except for special circuit boards with special requirements). IC can be directly soldered on printed boards. Because the use of IC sockets has certain limitations, it is true that the use of IC sockets on printed boards makes it easier to install, remove, and replace IC, but it also brings certain disadvantages at the same time. On the one hand, the IC pins and IC The socket is prone to poor contact, which reduces the reliability of the circuit. At the same time, the IC socket will also bring large distributed capacitance, causing unnecessary interference. Especially in the design of radio frequency (RF) circuits, the IC socket should not be used as much as possible. .

5. Partition Design when design printed circuit

When designing a printed circuit, each part of the circuit can be divided into sections and blocks according to its function. Under the premise of not affecting the performance of the circuit, according to the principle of the circuit and the circuit structure, the parts of the circuit can be divided into areas according to their functions. The layout makes each part of the circuit components relatively close together, which not only helps reduce mutual interference, but also makes the distribution of the parts of the circuit appear neat and orderly, and also facilitates future fault inspection, maintenance and elimination.

6. Seismic / shock absorption of component is the key

When designing a printed board, the component mounting method is very important, and the seismic and shock absorption performance of component mounting is particularly critical. In the installation of large components, circuit module components, high-power radiators, etc., in addition to their layout, heat dissipation conditions, and interference, etc., they must also fully take into account the ability to resist vibration and impact. When designing, you can increase the firmness according to the characteristics of the component installation structure. If necessary, you can design additional fasteners to fix the assembly reasonably and reliably. This can effectively enhance the seismic performance and improve the reliability and stability of the circuit. Such as power switches, high-power resistors, large radiators, line output transformers, etc. using rivet welding technology; computer power supply DC output leads mostly use special welding head welding. After the line output transformer is installed, it is fixed to the motherboard. The input and output terminal boards of color TVs are often fixed to the motherboard and the chassis. In addition, for some key components and parts that are afraid of vibration, special insulation glue can be used to attach the shell to the printed board during assembly, such as capacitors, wire sockets, etc. For some components with high seismic performance requirements, such as the crystal oscillator of radio frequency (RF) circuits, it can be installed overhead with a rubber or foam soft bracket or measures such as adding damping pads between the components and the printed board. It plays the role of releasing vibration buffer energy and enhancing heat dissipation, thereby further reducing the adverse consequences caused by vibration.

7. Pay attention to ground pad design

When designing the printed circuit board ground pad, in order to ensure the reliable contact between the ground pad and the ground chassis or solder pads, a thin tin or a protective layer around the ground pad (rust prevention Insulation protective paint) design a circle of small round or strip solder joints and add solder plating (can fix the screw hole around the pad, design a circle of auxiliary small solder joints around the pad). In addition, when fixing the ground pad screw, a lace washer can be added to form a good contact. The function of tinning the pads here is: first, to prevent the exposed copper foil from oxidizing and rusting; The second is that the tin-plated pad has better conductivity, and the height of the tin-plated plate is significantly higher than the plane of the printed board, so that it can form a sufficient and effective contact with the object after fixing by screws, then to achieve the best connectivity.