Vacuum Metallizing-Quality and Productivity Enhancements Through In-Line Technology by John H

Vacuum Metallizing-Quality and Productivity Enhancements Through In-Line Technology by John H. Durant, Durant, I.H. 1995. Yonrum Uelallizing: Quliry and Pmducfiviv Mill Lane Engineering Co. Inc., Lowell, Mass. Enhoncemnfs ntrough In-Line techno log^ Metal Finishing 9313). 27- 29. Reprinted with permission f”Elsevier Science Inc. .- acuum mating. frequently des- ically. The basecoating of lacquer fills together with virtually total exclusion ignated physical vapor deposi- in minor imperfections, which would of dust and other contaminants-for Vtion or PVD. offers an intriguing otherwise require buffing and polishing. example, for semiconductor wafer variety of solutions to application prob- The vacuum-deposited film of alumi- processing-in quantities that in- lems as well as relief from the increas- num (aluminized) may receive a trans- creased to undreamed-of levels. ingly astly business of handling, trans- parent topcoating for additional protec- Although the two applications cited porting. and disposing of the toxic and tion or perhaps color tinting. if requircd. are as diverse as one could select, they hszprdour wastes associated with vari- The use of an organic basecoat on a share in-line technology. As part sizes ws chemical plating processes. metal part, in effect, presents a surface increase or as requirements for ex- Production vacuum evaporation was that is quite similar to that of a molded tremely close process control and for a first employed by the optical industry or extruded plastic part. Thus, a mer- clean. uniform process environment in the 1930s for depositing thin magne- chant metallizer has the opportunity to tighten, the technical limitations of sium fluoride glare-resistant films on serve a wider market than would be batch systems become apparent. lenses with dramatic improvement in possible if the customers were solely metal-parts oriented. light transmission and image clarity. MATERIALS HANDLING Evaporated aluminum coatings pro- Parts of moderate size and weight, duced superior reflective performance BATCH VERSUS CONTINUOUS which allow convenient manual han- at a fraction of the cost of chemical PROCESSING silvering. Production vacuum sputter- dling, were customarily racked in jigs ing, which characteristically deposits The emergence of evaporation and and fixtures that could be loaded into at a much slower rate, was first used for sputtering PVD processes as viable batch vacuum chambers for metal- lowcost thin films of precious metals. industrial finishing methods owes lizing-usually by evaporation. An early application was the manufac- equal credit to equipment manufactur- When the finish-coated load is re- ture of metal dies used to stamp ers who were looking for new markets, moved, another is ready for immediate phonograph records. The wax master and to entrepreneurs who were seeking insertion. thus keeping the system on was coated with a sputtered film of new opportunities in providing low- line until the buildup of evaporant gold to obtain an electncally conduc- cost, brilliant, decorative metallic fin- inside the chamber requires a sched- tive surface, which could be subse- ishes on metal and polymer parts. uled shutdown to replace the evaporant quently built up by electroplating. The Metallizers are largely merchant manu- shields and remove unwanred deposits microgrooves were thus transferred to ,, facturen who serve their customers by from other parts of the interior. Failure the die face and transformed into a providing specialized equipment and to practice such scheduled mainte- durable working surface capable of technology at very competitive prices. nance results in excessively long reproducing the master many thou- Flexibility to handle a variety of part pump-down cycles, poor quality coat- sands of times. configurations in large or small volume ings, and, in extreme cases, spontane- favored the use of batch equipment. ous ignition of deposits of metal, Technology was relatively simple, cap- which may become pyrophoric when NEW APPLICATIONS AND excessive amounts are permitted to MARKETS ital investment was modest, and haz- ardous waste disposal problems were accumulate. PVD technology has expanded rap- minimal. In common with other prod- A typical panel of architectural glass idly in both functional and decorative uct-finishing operations, the labor that weights 500 Ib is, of necessity, an applications. Glass bell jars have been force could be largely unskilled. item for conveyorized delivery to the largely supplanted in industrial plants In addition, certain captive metal- coater via a vacuum load lock into the by larger metal chambers capable of lizing operations merged, typically in coating process chamber, which runs handling small objects by the thousand situations where: (1) tremendous in- continuously without exposure to am- and large objects with dimensions vestments in very specialized equip- bient atmosphere. The load lock cham- govemed only by materials handling ment were required for large part-for ber provides conditions to clean the limitations. example, architectural glass panels, surface by heat, plasma, or both prior to In mtal fmishing, vacuum coating or 12-ft long x 7-ft wide, with sputtered transfer into the coating chamber. The mtalliig is frequently employed in coatings for heat insulatiorand light exit lock may be used to control the Conjunction with an organic basecoat- transmission control; and (2) compaa- conditions of venting up to ambient in& which together can produce a ble heavy capital commitments to pressure by employing filtered, dust- brilliant decorative finish most econom- achieve supercritical process control free air or a controlled gas composition. esses employing high vacuums h been slower to gain acceptance. technical barrier was the developn of reliable locks for moving the wi piece@) in and out of the continuo1 operating process chamber. Systi employing locks are, in effect, sc continuous where workpiece introc lion and removal are conducted in, mentally. Vacuum gates capable hundreds of thousands of cycles, c trolled by solid-state circuitry, demonstrating high levels of depei bility and longevity in numerous c cal manufacturing operations. Well-established in-line vaci equipment technology, which der1 from handling massive glass pal with optical quality pin-hole-free ci Figure 1. In-line melallizer lor automotive bim combines widely accepted leatures found in ings, together wiih semiconductor j batch and continLous systems. Work is held in spindles, which are rotated around the center duction equipment that provides h axis 01 the fixture while in the processing chamber. Loading and unloading are done yields of wafers where submicrosci automatically by means 01 poweredconveyors, which serve the entrance and exit load locks. particular contamination must be tally excluded, have arrived fo sc Quality Considerations inch or less are common, if it,were the merchant metallizers and the c In a wafer processing line, multiple necessary to move the workpiece out live shops. These shops handle a u PVD deposited layers employing evap- of one batch machine into the next. range of applications with brilli oration andlor sputtering may be con- functional, and durable decora, ducted in separate stations. possibly in coatings on metal or plastic parts v TRICKLE-DOWN TECHNOLOGY demonstrable advantages (see Fig. conjunction with a chemical vapor AVAILABLE TO THE deposition (CVD) step. The possibility METALLIZER of multiple processing stations is par- Productivity ticularly useful when one considers the Although the advantages of continu- The coating source runs conti daunting task of protecting the work- ous processing over batch are well ously, providing long life by elimii pieces from minute contamination, established in chemical, metallurgical. ing repeated thermal shock and ex - sure to ambient atmosphere, but v petroleum, food, paper packaging, and which could destroy the function of a the consequence of shortened life circuit where line widths of 1 micro- fiber and film manufacturing, proc- oxidation. The initial pumpdown, which complishes outgassing and substi cleaning of the next load, is d, simultaneously while another loai being coated. Lot size of the in-line load relatively small, best suited to smoc uniform materials flow in the facti In contrast, the lot size of the ba equipment is large, producing eithc glut or a shortage of parts at upstre: downstream stations. Quality The separate outgassing/cleaning trance lock ensures that conlamina removed will not enter the proc chamber where they might otherw be regurgitated when exposed to pr I Figure 2. In-line spunering system (interior view) produces uniform coatings on both sides 01 essing temperatures that could aff an infrared optical element one at a time for optimum unilormity and reproducibility. This the coating. equipment operates in clean room environments and is adaptable to conveyorized or cassene The separate ventingkxit lock p product transler systems. tects the process chamber from 28 METAL FINISHING - MARCH 1C Summary of Metallizing Equipment Considerations IC Batch frrline G-sileMgm Sum of length + girvl SZO3 in: weigh1 to 25 Ib based M Sm ol length + girvl a4w in.: weigh1 lo 500 Ib maMlal lilliwj M more Large baweS, inegdar (low Small. ‘ocremental. even now LMls Shorr Evaporatii batch Evaparalim. moliouous Spmm. batch Sputlerirg. conlimus I ~-0P~Cyde Tine required ir added lo lhe cycle Simullaneous wilh matkg in a separate chamber I. in-rush of air. which contaminates the ing affords

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