Precision PCB Fabrication, High-Frequency PCB, High-Speed PCB, Standard PCB, Multilayer PCB and PCB Assembly.
The most reliable PCB & PCBA custom service factory.
Because PCB single-sided boards are low-cost and easy to manufacture, they are widely used in switching power supply circuits. Because they have only one side of copper bound, the electrical connections and mechanical fixation of devices must rely on that layer of copper, and care must be taken when handling.
In order to ensure good PCB welding mechanical structure performance, the single-sided PCB pad should be slightly larger to ensure a good binding force between the copper skin and the substrate, and the copper skin will not peel off or break off when subjected to vibration. Generally, the width of the welding ring should be greater than 0.3mm. The diameter of the pad hole should be slightly larger than the diameter of the device pin, but it should not be too large. Ensure that the solder connection distance between the pin and the pad is the shortest. The diameter of the feet is 0.1-0.2mm. Multi-pin devices can be larger to ensure smooth inspection.
The electrical connection should be as wide as possible, and in principle, the width should be greater than the diameter of the pad. In special cases, the wire must be widened when the connection meets the pad (commonly known as teardrop generation) to avoid breaking the wire and the pad under certain conditions. In principle, the minimum line width should be greater than 0.5mm.
The components on the single panel should be close to the circuit board. For devices that require overhead heat dissipation, a sleeve should be added to the pins between the device and the circuit board, which can support the device and increase insulation. It is necessary to minimize or avoid external impact on the pad and the pin connection. The impact caused by the strengthening of the firmness of the welding. The heavier components on the circuit board can increase the supporting connection points, which can strengthen the connection strength with the circuit board, such as transformers and power device radiators.
The PCB single-sided soldering surface pins can be kept longer without affecting the distance between the PCB and the shell. The advantage is that it can increase the strength of the soldering part, increase the soldering area, and the phenomenon of virtual soldering can be found immediately. When the pin is long and cuts the leg, the welding part receives less force. In Taiwan and Japan, the process of bending the device pins at a 45-degree angle with the circuit board on the soldering surface and then soldering is often used, and the reason is the same as above. Today, I will talk about some matters in the design of double-sided boards. In some applications with higher requirements or higher wiring density, double-sided printed boards are used. Its performance and various indicators are much better than single-sided boards.
PCB double-sided board pads have higher strength due to the metalization of the holes, the solder ring can be smaller than the single-sided board, and the diameter of the pad hole can be slightly larger than the pin diameter, because it is beneficial for the solder solution to penetrate through the solder hole during the soldering process. Top layer pads to increase soldering reliability. But there is a drawback. If the hole is too large, part of the device may float up under the impact of the jet tin during wave soldering, resulting in some defects.
For the treatment of large current traces, the line width can be processed according to the previous post. If the width is not enough, it can generally be solved by tinning the traces to increase the thickness. There are many methods.
1. Set the trace to the pad property, so that the trace will not be covered by the solder resist when the circuit board is manufactured, and it will be tinned during the hot air leveling.
2. Place a pad on the PCB wiring, set the pad to the shape that needs to be routed, and pay attention to setting the pad hole to zero.
3. Place the wire on the solder mask. This method is the most flexible, but not all circuit board manufacturers will understand your intentions, and you need to use text to explain. No solder resist will be applied to the solder mask where the wire is placed.
Several methods of tinning the circuit are as above. It should be noted that if the very wide traces are all tinned, a large amount of solder will be bonded after soldering, and the distribution will be very uneven, which will affect the appearance. Generally, a slender strip of tin-plated width is 1~1.5mm, and the length can be determined according to the circuit. The tin-plated part is separated by 0.5~1mm. The double-sided circuit board provides great selectivity for layout and wiring, which can make the wiring more Tends to be reasonable. Regarding grounding, the power ground and the signal ground must be separated. The two grounds can be merged at the filter capacitor to avoid accidental factors of instability caused by large pulse currents passing through the signal ground connection. The signal control loop should be grounded as far as possible. There is a trick, try to put non-grounded traces on the same wiring layer, and finally lay ground wires on another layer. The output line generally passes through the filter capacitor first, and then to the load. The input line must also pass through the capacitor first, and then to the transformer. The theoretical basis is to let the ripple current pass through the filter capacitor.
Voltage feedback sampling, in order to avoid the influence of large current passing through the wiring, the sampling point of the feedback voltage must be placed at the end of the power supply output to improve the load effect index of the whole machine.
The wiring change from one wiring layer to another wiring layer is generally connected by via holes, and it is not suitable to realize through the device pin pads, because this connection relationship may be destroyed when the device is inserted, and when every 1A current passes through, There should be at least 2 vias, and the diameter of vias should be greater than 0.5mm in principle. Generally 0.8mm can ensure processing reliability.
Device heat dissipation. In some low-power power supplies, the circuit board traces can also serve as heat dissipation. Its characteristic is that the traces are as wide as possible to increase the heat dissipation area. No solder resist is applied. If possible, the vias can be evenly placed to enhance the thermal conductivity.
