![]() This design incorporates the encapsulating cap. The plated-through holes located under the termination provide a thermal path to the bottom sink. The model on the left has the termination attached to the PCB at the location of the third port. The two basic models of isolators intended for low power applications, where the reverse power does not exceed 5 W, are shown in Figure 1. The units are also available in tape and reel format. ![]() ![]() The SM circulators have a flat top allowing the use of pick-and-place techniques such as vacuum suction or magnetic attraction. The usage of a PCB as a base for the ports makes them rigid and inherently coplanar. The SM circulators and isolators are designed to sustain a temperature rise of 475☏ (~245☌) for 10 seconds allowing the utilization of standard reflow procedures during assembly. After assembling on the user's PCB, the unit becomes environmentally sealed and aqua-washable. The cap is made from an epoxy mold and is sealed to the PCB with a silicone rubber adhesive. A rigid cap protects the circulator/isolator housing. Under forced cooling conditions, the SM devices are capable of handling up to 175 W of CW power. With a typical room temperature insertion loss maintained below 0.25 dB, and less than 0.35 dB over the specified temperature range, the units are rated to 100 W CW forward power. The completed vias, having a total thermal impedance of 1° to 2☌/W, provide an additional thermal path to the ground. These via holes become filled with solder when the housing is assembled on a PCB. The 18 plated-through holes located in the central area carry electrical ground to the housing of the circulator. The configuration of all three ports is consistent with standard footprint patterns established in the microwave industry for this class of ferrite devices. The 50 Ω lines and half-moon plated-through holes at the PCB's periphery provide the required transition of contact ports from the top to the bottom face of the PCB. The circulator housing is mounted on top of the PCB. Coplanarity of ± 0.004" in this new series of ferrite devices was achieved by using a 0.031" thick PCB as a circulator base and by docking all output ports along with the ground on the bottom face of the PCB. ![]() The product photograph above shows the basic design of a high power coplanar surface-mount circulator. Another important feature of a truly surface-mountable device is the ability to sustain an aqua-wash after the unit is assembled on a board. The term surface-mountable usually refers to the electronic components having coplanar ports, so that the unit could be directly mounted on the user's PCB. Mechanical Design and Thermal Considerations ![]()
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