Design of connectors between PCB boards
Design and mechanical and electrical properties of connectors between PCB boards
First generation inter PCB connector
At present, the gradually promoted board to board RF solution, the traditional small RF "board to board" coaxial connector, such as MCX, does not allow any tolerance, especially the tolerance of board to board axial distance. In SMB series, a pair of male and female connectors cooperate to realize the axial and radial offset through the elastic change of the slotted parts of the female connector. However, due to the limit of the elastic change of the elastic parts, the allowable axial and radial offset is very small, so that the connectors installed on the same circuit board will not exceed three pairs.
Second generation inter PCB connector
It is mainly a three-stage coaxial connector. The solution is based on the principle of coaxial transmission line. The position deviation between PCBs is overcome by different inclination angles of the intermediate adapter rod and the gap of the interface. This kind of connector application can be called three-stage hard connection scheme. Advantages: compact structure, short transmission distance, high placement density, blind insertion can be realized, simple disassembly and assembly, high test efficiency, better performance than cable, which is conducive to the modular design of products. For example, mmbx and SMP series, by adding an adapter as the intermediate connector and adopting the method of three piece set, the adapter as the intermediate connector can rotate slightly relative to the socket fixed on the circuit board, so as to allow a certain large radial offset. Third generation inter PCB connector
With the development of the third generation equipment, there are more and more connectors on the same circuit board, and the requirements for the axial and radial floating amount of connectors are also higher and higher (the interconnection diagram of the third generation inter board connectors is shown in Figure 4). Therefore, a new generation of board to board schemes are born: such as PSMP, smp-max, MBX, etc. (as shown in Figure 5). Such applications are usually used below 10GHz, The axial and radial tolerances are basically + / - 1mm.
Smp-max is a new inter board connection scheme. The sockets at both ends are tight fitting end and loose fitting end respectively, and the two middle adapters are symmetrical. During application, the intermediate adapter is manually matched with the tight fitting end, and the tight fitting end is designed with a clamping slot to ensure a large pull-out force after the adapter is matched with it. At the same time, a large bell mouth is set at the loose fitting end for blind insertion guidance, which is convenient for the operator to lead in smoothly when closing the upper and lower modules (of course, a guide column is set on the upper and lower modules to help the introduction of the connector and prevent the damage of the petal groove). After matching, the adapter can float freely at the loose end, which is determined according to the actual working distance of the upper and lower modules.
Smp-max is a board to board connector with super tolerance. The radial deflection angle of smp-max is 3 degrees, and the axial floating amount is + / - 1mm, even up to + / - 1.2mm. The connection interface adopts a unique patented impedance matching technology. Even if the plate to plate axial tolerance reaches the maximum, when there is a gap as large as 2mm (0.78 ") between connectors, it can still achieve good impedance matching, so as to ensure that the performance of all electrical appliances meets the standard. The maximum axial tolerance is even 4 times that of SMP. The radial tolerance also has good performance. It can reach a maximum inclination of 3 ° in the DC-6 GHz range of the whole working frequency band. At the same time, it can achieve VSWR better than 1.2 and maximum power of 165 watts in 3GHz.
RF interconnection design between PCB and module
In RRH, the RF interconnection between PCB, filter, antenna and other modules in active wires can be realized not only by the above three-stage connector between boards, but also by hard connection, so as to reduce cost and improve flexibility.
RF interconnection design between coplanar PCB boards
In the application of three-stage type, the reed is used to transmit RF signal. At the same time, it has certain tolerance ability, and the cost is 2 / 3 less than that of three-stage type. In the low-cost mode, the same connector can be used to transmit RF, digital and power supply. To a certain extent, it can be said that it is a general connector.
With the extensive deployment of 5g base stations and the application of small active antennas, small base stations and other equipment in recent years, the market requires wireless base station modules such as RRH to be smaller and more compact. Therefore, the application of inter board connectors with reliable performance, small volume, large tolerance and high cost performance has become the consensus of R & D engineers of communication equipment manufacturers. According to the specific design requirements of the equipment, the layout form of PCB board and the transmission requirements of RF signal, select the appropriate parallel board to board connector and bridge connector between common boards, which is very helpful to the research and development of wireless equipment. In the design of RRH, active antenna and small base station, the following methods can be selected:
(1) The product has small volume, small PCB board spacing and low tolerance requirements. Mmbx series and other similar connectors can be selected, and the minimum board spacing is 6.7mm.
(2) The size of the product is large, the spacing between PCB boards is greater than about 13mm, and the tolerance requirements are high. PSMP, smp-max, MBX and other series connectors can be selected.
(3) For common panel, bridge connector and new reed connector can be selected, which can transmit RF, power supply and digital signals at the same time.
(4) For the RF connection from PCB to filter, antenna and other modules, in addition to the above 1 and 2 connectors, the hard connection form can also be selected according to the actual design to reduce the cost and improve the flexibility.