1. Adopt shielding measures
It is an effective way to deal with the crosstalk problem that the circuit board provides packet ground for high-speed signals. But. It makes the limited wiring area more congested. In addition, in order to achieve the desired purpose of ground wire shielding, the distance between ground points on the ground wire is very important, which is usually less than twice the length of signal variation. At the same time, the ground wire will also increase the spread capacitance of the signal, increase the impedance of the transmission line, and slow down the signal along the transmission line
2. The possible condition is to reduce the conversion rate of the low signal edge
While meeting the design standards, slow devices should be selected as much as possible, usually in the time of device selection. And to prevent the mixed use of different kinds of signals, because the fast transform signal has potential crosstalk risk to the slow transform signal.
3. Set up different wiring layers
The plane layer is set reasonably, and different wiring layers are set for different speed signals. It’s also a good way to deal with crosstalk.
4. Reasonable arrangement of layers and wiring
The length of parallel signal is reduced, and the routing layer and spacing are set reasonably. Reducing the distance between the signal layer and the plane layer, increasing the distance between the signal lines, and reducing the length of the parallel signal lines (within the critical length range) can effectively reduce the crosstalk.
5. Impedance matching
It can also greatly reduce the amplitude of crosstalk. If the impedance of the near or far end of the transmission line matches the impedance of the transmission line.
In the process of using circuit board, the pad often falls off, especially when the circuit board is repaired. When using electric soldering iron, it is very easy to see the phenomenon of pad falling off. In this paper, the circuit board factory analyzes the causes of pad falling off, and also takes corresponding countermeasures.
Analysis of the reason why the pad is easy to fall off during PCB welding
1. The influence of PCB storage conditions. Affected by the weather or stored in a wet place for a long time, the moisture content of the circuit board is too high. In order to achieve the ideal welding effect, the chip welding should compensate for the heat taken away by moisture volatilization, and the welding temperature and time should be extended. Such welding conditions are easy to cause delamination between copper foil and epoxy resin.
2. Plate quality problems. Due to the poor adhesion between the copper foil and epoxy resin, even if the copper foil of the circuit board with large area is slightly heated or under external mechanical force, it is very easy for the copper foil to separate from the epoxy resin, resulting in pad shedding and copper foil shedding.
3. Generally, the adhesion of the circuit board can meet the requirements of ordinary welding, and the pad will not fall off. However, the electronic products are likely to be repaired. Generally, the repair is done by soldering with electric iron. Because the local high temperature of the electric iron often reaches 300-400 degrees, the local instantaneous temperature of the pad is too high, and the resin adhesive under the copper foil of the pad falls off due to the high temperature, The pad has fallen off. When the electric iron is disassembled, it is easy to attach the physical force of the electric iron head on the pad, which is also the cause of the pad falling off.
In view of the fact that the pad is easy to fall off under the condition of use, the PCB Factory takes the following measures to improve the resistance welding times of the pad as much as possible to meet the needs of customers.
1: Before delivery, the circuit board factory should use vacuum packaging and place desiccant to keep the circuit board in a dry state. In order to reduce the false welding and improve the weldability.
2: In view of the thermal impact on the pad when the electric iron is repaired, we try to increase the thickness of the copper foil of the pad by electroplating. When the electric iron heats the pad, the thermal conductivity of the thick copper foil pad is significantly enhanced, which effectively reduces the local high temperature of the pad. At the same time, the rapid thermal conductivity makes the pad easier to disassemble. The solder resistance of the pad is achieved.
3: Copper clad laminate is made of genuine and quality guaranteed substrate. The material selection and pressing process of the glass fiber cloth of the general authentic CCL can ensure that the solderability of the circuit board manufactured meets the requirements of customers.
