A supplier of fluid, chemical, and gas delivery systems claims its new method of securing heater cartridges eliminates an annoying problem that can stall wafer processing.

Kim Vu, chief engineer of California-based Celerity, says the low-cost method he has invented prevents heater cartridges from slipping out of a gas delivery system substrate. The hold is secure enough that an engineer could pick up several delivery units just by holding one end of the heater cartridge. Even though the cartridge will not slip out or shift when tugged at, it can be removed easily with a steady pull, Vu says.

The chief engineer points out that a heater cartridge slips out of a delivery substrate when a setscrew is loose or an external retaining clip becomes dislodged. "The unenclosed portion of the heater cartridge becomes a hot spot and will destroy itself when the power is applied. It slows everything down. It's counterproductive."

The key to the effectiveness of Vu's invention is a short length of coil spring that has been counter-bored inside a modular substrate block. A heater cartridge inserted through the pathway and the coil-spring retainer is locked in place by the "friction hold" of the retainer, according to the engineer.

The retainer measures 5/32 in. long. It has an overall diameter of 5/32 in. and a spring wire diameter of 18/100 in. The heater cartridge measures 5 to 12 in. long and has a diameter of 1/8 in.

Vu cites other advantages. The retainer's simple design expedites installation. In addition, because the retainers are completely enclosed in the substrate, they fit into compact delivery systems with only a few external components required. Furthermore, the coil-spring retainer is small enough to fit in delivery blocks tightly packed with internal tubing and cross-connections.

Setscrews that are fastened too tightly can crimp the cartridge jacket so much that a damaged heater core inside causes an electrical short,Vu adds. "My coil-spring retainer is simple in concept, but it holds a heater cartridge in place with 100% certainty," the chief engineer boasts.