Processing silicon wafers and chips involves the use of some highly reactive materials; hydrofluoric acid in particular. California water discharge and solid waste requirements have shaped neutralizing system designs, which are now being applied in other industries; and are being marketed worldwide.
In 1983, Harry Roennmann was a facilities engineer for InterDesign; a Silicon Valley supplier of monochips. InterDesign moved to larger quarters and the new tenent asked Harry to help modify some old special equipment used in silicon etching. Harry did this as a spare-time favor. Shortly thereafter, the new tenant was stymied by a city-denied permit plus the owner's refusal to allow extensive building and parking lot renovations needed for a new processing lab.
The new tenant again contacted Harry and, after some study, he agreed to design and build a compact, acceptable system located within the lab space. News spread among the local wafer processors and Harry soon had all his free time and garage consumed with acid neutralization systems.
Son Glenn was in college at the time and became the hands-on fabricator of the systems. They soon outgrew their garage operations; formed Neutralization Technology, Inc (NTI); and, in today's parlance; "the rest is history".
Safely Handling Corrosive Liquids
Harry points out that building approved neutralization systems in Silicon Valley is akin to Sinatra's famous New York song--If you can make it there, you can make it anywhere. NTI now has a number of system packages capable of waste hydrofluoric acid destruction in either batch or continuous flow modes. Standard continuous flow units can handle rates from 10 to 100 gpm.
The primary neutralizing reagent is NaOH along with other chemicals used to enhance precipitation and separation. Package designs also include safe and reliable reagent tanks and flow components. Formed sludge is separated automatically and qualifies as a solid waste suitable for industrial landfills.
Containment vessels are usually double-walled 1/2-inch polypropylene. NTI also supplies fiberglass or stainless steel tanks and reactor vessels. Steel bracing needed to maintain tank integrity is embedded in polypropylene for corrosion protection. Bracing can be located either outside or within the vessels. Viewable control panels are usually mounted directly on the tanks inside NEMA 4X vapor-proof enclosures Cart-mounted small quantity units are available to accommodate pilot-sized, multiple work stations.
Components & Controls
Selection of chemically resistant components such as pumps, valves, flowmeters, level controls and various sensors is basic to system performance. Self-priming centrifugal pumps are used for corrosive material transfer and double diaphragm pumps for reagent delivery. Both types of pumps provide variable flow rates automatically adjusted by the integral PLC-based control unit. ORP and/or pH sensors are the primary analytical signal inputs for controlling the reactions.
Sensor signals are fed to a PLC equipped to accept digital or analog signals, or pulses from turbine flowmeters. The standard PLCs are models manufactured by International Parallel Machines Inc (IPMI) and have proven to be robust and cost effective. Several networking protocols are standard with the IPMI units so that interfacing with PCs is easily accomplished. PID type control is often included with pH or ORP units and these also can be easily interfaced with the PLC analog ports.
Two basic models are widely used; the first is IPMI's 1612 which offers a variety of options among the unit's 16 inputs and 12 outputs. Inputs can be 115 or 220 vac; 5-to24 vdc; or analog signals or pulses. Outputs can be up to 220 vac and up to 8 amps to directly drive motors or actuating devices; or up to 48 vdc and 8 amps. Analog outputs can be in dc volts or the traditional 4-20 mA. A larger model, IPMI's 3416--shown in Figure 3--offers an array of 34 input and 16 output options with more computational, communication, and interfacing features.
Outside the HF Destruction Box
Along with the line of engineered neutralization packages, NTI has developed transfer systems to safely move hazardous liquids from chemical sinks or other remote locations to and from treatment or bulk storage units. The key feature of these systems is that the material is moved by a venturi induced vacuum so that any developed leaks simply pull building air into the system.
Corrosive or hazardous materials pump stations and wet chemical process stations are also provided. Beyond HF destruction systems, packaged units are provided for industrial acid or caustic wastewater treatment. NTI has built systems for cyanide destruction and removal of heavy metals in solution. Cyanide is converted to a bicarbonate and nitrogen in a 2-stage process.
A 2-stage process is also used to handle the special case of chromium in plating operations waste. A first stage converts the highly soluble hexavalent chrome ion to a trivalent form, and the second stage meters in caustic to raise the pH and precipitate the formed chromium hydroxide.
Additional information or problem consultation is available from Glenn Roennmann, NTI president. Phone 408/945-6445 or visit the web site: www.Neutralizationtech.com.
Machines PLCs, contact IPMI President Dr Robin Chang at 877-476-4752; or visit the web site: www.ipmiplc.com.
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