The goal of core board design is to be smaller, faster, and less costly. Since the interconnection point is the weakest link in the circuit chain, in the RF design, the electromagnetic properties at the interconnection point are the main problems faced by the engineering design. It is necessary to examine each interconnection point and solve the existing problems. The interconnection of the board system includes three types of interconnections, such as chip-to-board, interconnection within the core board, and signal input/output between the core board and an external device.
In the design of the core board, the interconnection of the chip and the core board is important for the design. However, the main problem of interconnecting the chip and the core board is that the interconnect density is too high, which causes the basic structure of the core board material to limit the interconnect density. the elements of. This article shares practical tips for high frequency core board design. For high-frequency applications, the techniques for interconnecting high-frequency core boards in the core board are:
1. The corner of the transmission line should adopt a 45° angle to reduce the return loss;
2. A high-performance dielectric circuit board with a dielectric constant value strictly controlled by the number of layers is used. This method is beneficial for the effective simulation calculation of the electromagnetic field between the insulating material and the adjacent wiring.
3. Design specifications for core boards for high-precision etching. Consider the total line width error of +/- 0.0007 inches, manage the undercut and cross section of the wiring shape, and specify the wiring sidewall plating conditions. Overall management of the routing geometry and coating surface is important to address the skin effect issues associated with microwave frequencies and to implement these specifications.
4. There are tapping inductance and parasitic effects in the protruding pin leads, and the use of leaded components should be avoided. In high frequency environments, surface mount SMD components are preferred.
5. For signal vias, avoid using via processing on sensitive boards because this process can cause lead inductance at the vias. For example, when a through hole on a 20-layer board is used to connect 1 to 3 layers, there are 4 to 19 layers of lead inductance, and a blind hole or a back drill is used.
6. To provide a rich grounding layer. These ground planes are connected using molded holes to prevent the effects of 3-dimensional electromagnetic fields on the board.
7. To choose electroless nickel plating or immersion gold plating, do not use HASL method for electroplating. This plated surface provides a better skin effect for high frequency currents. In addition, this high solderable coating requires fewer leads and helps reduce environmental pollution.
8. The solder mask prevents the flow of solder paste. However, due to the uncertainty of thickness and the unknown dielectric constant properties, covering the entire surface of the board with the solder mask material will result in changes in circuit performance in the microstrip design. A solder dam is generally used as a solder mask.