PCB Fabrication

Related matters that need to be understood when designing the PCB version of the mobile phone

by:A-TECH      2021-03-26
With the development of mobile phones and the continuous expansion of demand, the demand for mobile phone PCB boards is also increasing day by day, so what should be paid attention to when designing mobile phone PCB boards, let's discuss this topic together. 1 The common ground processing of digital circuit and analog circuit. Many PCBs are now composed of a mixture of digital and analog circuits, instead of a single functional circuit (digital or analog circuit). Therefore, it is necessary to consider each other when wiring. Interference problems, especially noise interference on the ground wire. The frequency of the digital circuit is high, and the sensitivity of the analog circuit is strong. For the signal line, the high-frequency signal line should be as far away as possible from the sensitive analog circuit device. For the ground line, the whole PCB has only one node to the outside world, so The problem of digital and analog common ground must be dealt with inside the PCB, and the digital ground and analog ground inside the board are actually separated and they are not connected to each other, but at the interface (such as plugs, etc.) connecting the PCB to the outside world. There is a short connection between the digital ground and the analog ground. Please note that there is only one connection point. There are also non-common grounds on the PCB, which is determined by the system design. 2 When the signal line is laid on the electrical (ground) layer and the multilayer printed board is routed, there are not many wires left in the signal line layer that are not laid out. Adding more layers will cause waste and increase production. The workload and cost have also increased accordingly. To solve this contradiction, you can consider wiring on the electrical (ground) layer. The power layer should be considered first, and the ground layer second. Because it is best to preserve the integrity of the formation. 3 The processing of the power supply and the ground wire makes the wiring in the entire PCB board very good, but the interference caused by the improper consideration of the power supply and the ground wire will reduce the performance of the product, and sometimes even affect the product. Success rate. Therefore, the wiring of the electric and ground wires must be taken seriously, and the noise interference generated by the electric and ground wires should be minimized to ensure the quality of the product. Every engineer engaged in the design of electronic products understands the cause of the noise between the ground wire and the power wire, and now only the reduced noise suppression is expressed:    (1). It is well known that the noise between the ground wire and the ground wire Add decoupling capacitors between. (2) Widen the width of the power and ground wires as much as possible, preferably the ground wire is wider than the power wire, their relationship is: ground wire>power wire>signal wire, usually the signal wire width is: 0.2~0.3mm, the most The slender width can reach 0.05~0.07mm, and the power cord is 1.2~2.5 mm. For the PCB of the digital circuit, a wide ground wire can be used to form a loop, that is, to form a ground net to use (the ground of the analog circuit cannot be used in this way)    (3), use a large area of u200bu200bcopper as the ground wire, and use it on the printed board. The unused places are connected to the ground as a ground wire. Or it can be made into a multilayer board, and the power supply and ground wires occupy one layer each.  4 The role of the network system in wiring   In many CAD systems, the wiring is determined based on the network system. The grid is too dense and the path has increased, but the step is too small, and the amount of data in the field is too large. This will inevitably have higher requirements for the storage space of the device, and also the computing speed of the computer-based electronic products. Great influence. Some paths are invalid, such as those occupied by the pads of the component legs, or by mounting holes and fixed holes. Too sparse grids and too few channels have a great impact on the distribution rate. Therefore, there must be a well-spaced and reasonable grid system to support the wiring. The distance between the legs of standard components is 0.1 inches (2.54 mm), so the basis of the grid system is generally set to 0.1 inches (2.54 mm) or an integral multiple of less than 0.1 inches, such as: 0.05 inches, 0.025 inches, 0.02 Inches etc. 5. Treatment of connecting legs in large-area conductors. In large-area grounding (electricity), the legs of common components are connected to it. The treatment of connecting legs needs to be considered comprehensively. In terms of electrical performance, the pads of component legs It is better to be fully connected to the copper surface, but there are some undesirable hidden dangers in the welding and assembly of the components, such as: ① Welding requires a high-power heater. ②It is easy to cause virtual solder joints. Therefore, both electrical performance and process requirements are made into cross-patterned pads, called heat shields, commonly known as thermal pads (Thermal), so that virtual solder joints may be generated due to excessive cross-section heat during soldering. Sex is greatly reduced. The processing of the power (ground) leg of the multilayer board is the same.
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