Matrixx Enhanced Models
Matrixx Standard Models
Current rating limits – In most cases the coaxial connector will set the model’s current limit value. Common connector types including; BNC, N and, HN all have small center conductors that are required to pass the RF and/or DC current to the plasma load. Type 7/16 DIN and UHF type connectors have a larger center conductor that enables higher currents to safely pass.
Vacuum relay current ratings – All relay types are specified to handle higher DC/Pulsed DC/AC currents (than 13MHz RF currents) as the RF current only flows on the conductor surfaces and not through the conductor’s cross section. For example, a 10kW 350KHz pulsing DC power supply has a maximum current output of 30.8 amps. A 20kW model would have twice that rating or 61.6 amps. The typical vacuum relay we use is specified at 50 amps DC/60Hz AC and de-rates downward as the frequency of operation goes up. At 2.5MHz the maximum current rating is now 30 amps and even less at 13.56 MHz, 17 amps. To accommodate many different applications, power levels and, frequencies we will use these relays in series and parallel configurations.
The real (specification) story here is that switch modules (as well as impedance matching networks) should be rated in “RF or DC Amps” and not “Watts”.
Power loss – Based on the model complexity and application, there will be some small amount of input power lost (as resistive/reactive heating of the conductors and components) as the power travels through the switch module. High conductivity, low impedance and, plated conductors are employed to minimize these losses. Proper RF design is applied to each model to ensure high reliability, functionality and low throughput losses.
Use of dual (parallel) coaxial cables
Some OEM system and magnetron cathode manufacturers have products that utilize dual (parallel connected) coaxial cables designed to handle high RF currents. Parallel connected cables will equally share the plasma’s RF current load while keeping the currents and the cable and connector’s operating temperatures within specifications. The only consideration is that the impedance matching network will need to be properly configured to accommodate the additional output capacitance that the second cable adds. This is done by adding additional and fixed shunt capacitance on the 50 ohm side of the match. Manitou Systems supplies both switch modules and parallel coaxial cable modules equipped for this purpose.
Heating of coaxial cables
All coaxial cables will heat up above the room temperature when used at 50 to 100% of their rated current/power specifications. Cables used to transfer RF power between devices are typically more prone to heating, especially when operated at high frequencies or when operated outside of the 50 ohm environment. In most 50 ohm applications (connecting an RF generator to a matching network) you can use either a plastic or Teflon insulated cable with excellent performance and reliability. Always consult the cable manufacturer for the typical operating specifications. Reliability problems and failures typically occur when the cable is used to connect the impedance matching network output to the magnetron cathode. In all cases DO NOT USE a poly-ethylene insulated cable – do use a Teflon insulated cable as there will be heating in the cable based on the RF circulating currents. The failure mode in all cases is melting of the insulator and migration of the center conductor. Some failures occur from loose coaxial connector connections – always tighten the connectors based on the connector manufacturer’s suggested technique and specifications.
Contacting Manitou Systems
In preparation to discuss your switching application, we suggest that you have the following information ready and available: