Implementing methods to monitor contamination and installing cleaning processes to achieve the required cleanliness levels are major challenges in disk drive manufacturing. Survey of Cleaning and Cleanliness Measurement in Disk Drive Manufacture BY R. NAGARAJAN

he hard disk drive industry has made significant 1. Incoming components 2. Assembly process. advances in read/write technology, but at the cost of Typical surface defects on components are listed by Hill T increased exposure to contamination-related failures. (1990). They include roughness and wear, flaking, porosity, Defining the acceptable cleanliness levels of technology com- loose debris, nonvolatile residue, flash, bloom and inclusions ponents. and of mechanical components is becoming a critical on plastics, burrs and rust on metals, lubricant leakage in ball need. Implementing methods to monitor contamination to bearings, packaging debris and uncured adhesives. these levels and installing cleaning processes to achieve the Assembly process sources are discussed by Ackerman and required cleanliness levels are the major challenges in disk Ayala (1990) and Lutz (1995). They include facilities, air and drive manufacturing. This paper will survey published and chemicals, tools and workstations, transport mechanisms, publicly-presented literature to identify current industry prac- consumables, garments, people, process, and rework/tear- tices in these areas and will attempt to establish relationships down procedures. between common failure mechanisms and product-level con- The contaminants emanating from these sources affect tamination levels. Current knowledge of particle generation product quality in several ways. The read/write heads and the and transport phenomena in disk drives will be outlined. disks are separated by a thin layer of air, 5 microinches or less, Particulate contamination can cause disk damage, disk with the disk pack rotating at high speeds below the heads. scratching and head crashes: magnetic contamination can Particles in that size range can therefore cause the head to result in unrecoverable data erasure: organic contamination crash, damaging both the head and the magnetic medium can cause stiction fails, where the motor current is not suffi- (Mallinson, 1987). The role high-energy magnetic particles cient to lift a head stuck to the disk upon landing; and ionic such as samarium cobalt (SM-Co) and neodymium-iron-boron contaminants can cause corrosion of the head and/or disk. (Nd-Fe-B) play in causing data loss has been detailed by These defects may be detected at the manufacturing line or may Peterson (1993). Particle detachment from disk surfaces in escape to the field, thereby impacting customers. While there disk drives has been studied by Tsai et al. (1991), among oth are many contributors to the total contamination inventory in ers. They found that detachment of sub-micron particles from disk drives, the component parts, including heads and disks, the disk surface by a slider air-bearing is possible. They have are certainly one of the major sources. With increased leverag- also calculated the critical speed for detachment of particles of ing of low-cost manufacturing into high-capacity, high- various sizes and compositions. Transport and deposition of performance products, contamination issues have recently wear particles generated in disk drives due to head-disk con- come to the forefront industry-wide. Increasingly, drive manu- tact was later investigated by Tsai et al. (1992). Here. they facturers are expecting component suppliers, external and found that wear particles do indeed fly close to and deposit on internal. to characterize the cleanliness of their parts, and to disk surfaces; cooling air flow from the hub can help keep the achieve optimal cleanliness levels on these components. With wear particles entrained. the simultaneous environmental regulatory pressure to elim- Ananth (1988) and Fardi and Liu (1990) have studied the nate use of certain solvents, the industry and its vendor base deposition of particles on spinning computer disks. Dominant have been forced to be creative in developing methods for clean deposition mechanisms for particles below 0.1 um and larger ing and for cleanliness-measurement that are both cost-effec- than 1.0 um in diameter were found to be Brownian diffusion rive and functionally satisfactory. This survey paper is a salute and sedimentation, respectively. Deposition of particles > 0.5 to the many contamination-control practitioners who have been urn on the disk bottom surface was found to be negligible. In instrumental in channelling this groundswell of innovation. addition, inertial forces were found to play no role in deposit&m of sub-micron particles. Tseng (1994) found that the charac- SOURCES AND EFFECTS teristics of particle deposition on disks were dominated by the Source detection methodologies are delineated by Hanke airflow features of the bulk flow outside the boundary layers of (1995). Contamination sources may be broadly divided into the rotating disks; typically, particle deposition rates were two categories: found to have increased with radius on all disk surfaces. The

February, 1997 13 non-uniformity of the flow field in disk under an applied load. In the presence early in the product development cycle. drives has to be understood in order to of a thin liquid ftim, caused by conden- Drive-level contamination control achieve optimal contamination control. sation of water vapor or volatile organic using particulate and chemical filters The role of sulfur contaminants in ini- vapors (or by the transport and deposi- (O’Brien et al.. 1994: Smith, 1995) is tiating disk corrosion has been dis- tion of aerosolized droplets), capillary necessary, but not sufficient to keep the cussed by Toxen (1995). Ross (1990) adhesion can occur at the slider/disk head/disk interface clean during prod- reports a corrosion problem that led to contact points. When the disk drive is uct life. The initial cleanliness of the $250,000 per year in scrap and rework started under these conditions, the assembly is a key factor in determining costs. In this case, corrosion was occur- adhesive force can damage the disk the longevity of the drive. How this is ring on 400-series ‘stainless’ steel parts. media, the slider or the slider suspen- achieved, measured and controlled in Corrosion of cobalt alloy magnetic disks sion. The drive may even be rendered the hard disk drive industry will be dis- due to ionic contaminants from chro- inoperative. Any outgassing (e.g., adhe- cussed in the next two sections. mate-conversion coated and electroless- sives) or aerosoling (e.g., motor) compo- nickel plated components is discussed nent in the drive can be a contributor in CLEANING METHODS by Godson and Cormia (1992). Here, this failure mode. Yang et al. (1991) Mechanical Components the primary mechanism is gas-phase report that adsorption of contaminants Cleaning of the mechanical compo- transfer of volatile inorganic species. on the surface of the disk from the nents of a hard disk drive is typically The reduced distance of separation atmosphere could lower the surface accomplished in two stages: the compo- between disks and components in small energy and thereby modify the tribology nent supplier performs a rough-clean, form-factor files (3.5”, 2.5”) has height- of the lubricant. Rougher disk textures and the drive manufacturer then does a ened disk sensitivity, particularly to are typically more resistant to stiction. final-clean prior to introducing the parts line-of-site contaminants. Another dele- Micro-textures surfaces are also very into a Class 100 (or better) cleanroom terious factor is increased use of susceptible to surface impurities that assembly environment. Recently, the high-end disk drives in uncontrolled are not effectively removed by cleaning trend has been towards outsourcing temperature/humidity environments. (Jiaa et al., 1994). Delamination due to many assembly steps that used to be Strohmeier et al. (1993) have studied micro-asperities is frequently encoun- done at the drive manufacturing facility. the effect of trace contaminants on the tered in smooth disk applications. As a result, more sub-assemblies, that durability of zincated aluminum alloy Slider design could be a key variable are inherently uncleanable, are now memory-disk substrates. Atmospheric in the contamination sensitivity of a being procured for direct entry Into the corrosion of thin-film cobalt-based mag- drive. Hardie et al. (1994) proposed a drive assembly area. This has shifted netic recording media has been studied design that uses a positive-pressure the emphasis on component cleaning by Inoue and Tanaka (199 1). They con- shaped rail in combination with a nega- out to the supplier. The generic, all-pur- clude that thin-film corrosion is related tive pressure cavity. Contamination pose cleaning equipment favored in the to the quantity and size of dust particles effects were studied via drive-level eval- past by drive manufacturers for in- in the drive environment, in addition to uations including continuous start-stop house cleaning of multiple parts is being the amount of condensible vapors. testing at elevated temperatures. The supplanted by more customized clear- While a carbon overcoat on the disk key parametrics were contamination ers at supplier locations offering a wider (and head) can reduce its susceptibility buildup in the negative pressure cavity, variety of chemistries and mechanisms. to corrosion, it will by no means elimi- and accumulation of particulate and In the late 80s and early 90s. many nate the problem (Sides, 1992): micro- organic material on leading edge tapers. disk drive manufacturers made the gaps in the carbon layer cannot be Several source materials, including major change away from using chloro- avoided. The effect of particulate and hydrocarbon greases, silicon-based oils,. fluorocarbons (CFCs) in cleaning to hydrocarbon contamination on the silicone and RTV-sealants and di-octyl using water-based systems. Phillips growth and morphology of permalloy phthalate, were investigated in this (1991) describes the challenges of mak- film used in read/write heads was study. Of these, hydrocarbons and sili- ing this transition. He lists steps in the investigated by Narayan and Herrera con oils were found to be the most evaluation process that remain relevant (1992). benign. any time a cleaning process change is Jabbar et al. (1992) describe contan- Tomiyasu et al. (1991) have evaluat- being considered: ination consequences for disk drive ed the head/disk interface of a nega- l Review process steps where cleaning spindle motors. Outgassing-related and tive-pressure slider, and concluded occurs. lubricant migration problems typically that controlling the cleanliness of the l Eliminate any unnecessary cleaning worsen at high speeds of revolution (the disk surface strongly influences the steps. Industry trend). Spindle motors are typ mean time to failure. Clearly, contami- l Identify constraints. ically sealed with magnetic fluid at both nation levels in drives affect slider l Define cleanliness requirements. ends to isolate the bearings and lubri- design: conversely, the head/disk l Select and implement alternative cant from the rest of the drive assembly. interface design will influence allow- process. Stiction or liquid-mediated adhesion able contamination levels. The more Vosper et al. (1992) describe a high- at the disk/slider interface has received robust the Interface, the less is the volume precision aqueous cleaning sys- extensive investigation (Best, 1991; need for stringent contamination con- tems installed at Digital Equipment Smallen et al., 1990; Bhushan and trol measures that can add cost. Disk Corporation to clean hard disk electron- Koinkar, 1994). During periods when contamination effects on the head/disk mechanical components. After evaluat- rigid disk magnetic storage devices are interface have been illustrated by ing several alternatives, including not powered, the head is typically in Nadimpalli (1995), who also presents a hydrocarbon solvents, alcohol, terpenes, direct contact with the disk surface framework for testing for such effects HFCs and HCFCs (hydrofluorocarbons Continued on page 16 Continued from page 14 and hydrochlorofluorocarbons), they Development teams to ensure that parts necessary for effective cleaning. settle on water as the best long-term were designed for solvent-free cleaning cleaning is shown not to be nece cleaning medium. The aqueous cleaning (Nagarajan, 1991). Parts design for for effective cleaning. It offers the project was then completed In three aqueous cleaning has also been dis- siderable benefit of area-select phases - process and chemistry defini- cussed by Sipitkowski (1993). cleaning at contaminated sites. tion, prototype and process develop- Specialized aqueous cleaners have been cleaning of wetted surfaces with ment, and production implementation. installed at critical parts suppliers to micron-thick liquid film, also known as Its eight-station system contains a hold- ensure, in some cases, state-of-the-art ‘steam laser cleaning’, is report ing stage, Immersion ultrasonic wash, cleanliness levels, and in all cases, to enhance cleaning efficiency for parti- rough spray rinse, Immersion ultrason- achieve functionally-required levels cles and organics (Zapka et al., ic rinse, final spray rinse, clean air blow- (Nagarajan and Welker, 1992: Nagarajan Another dry cleaning method that off, infrared radiation heating and exit et al., 1990; Nagarajan, 1992). frequently finds a use in head/disk manu- staging. A high-purity water production Non-aqueous methods in use include facturing is carbon dioxide (CO2) and reclamation system is Integrated isopropyl alcohol (IPA) rinsing and drying cleaning (Sloan, 1993). Also known as within the cleaner. This configuration is (Walter, 1991). A totally-enclosed, zero- dry ice cleaning, this method has fairly representative of most aqueous emission systems for this purpose has used successfully to remove sub-m cleaners used in the disk drive industry, been designed by CFM Technologies. particles from drive heads and magnetic though final drying is more frequently Here, while IPA vapor is brought to the media. Here again, the actual prevents accomplished by convective air drying or top of the chamber, a pump slowly mechanism is hard to define, involving vacuum drying. drains the fluid out through the bottom. aspects of sublimation, kinetic e: Johnson (199 1) has presented Conner The IPAvapor condenses on the receding transfer and mass diffusion. BL Peripheral’s approach to disk drive parts cooler liquid, forming a floating layer of effectiveness, and associated prot cleaning in a CFC-free world. Gibbons IPA. As the IPA layer moves downwards, - thermal shock, moisture cond- (1987) discusses the then state-of-the- particles are stripped by interfacial sur- tion, static discharge, contamination design art in parts cleaning technology face tension forces. Rinsing and drying persion, high pressure Impact - throughout IBM. Among the forms of occur simultaneously. This technique well known, and must be considered cleaners detailed are vapor degreasers, has been trademarked under the name a case-by-case basis. ultrasonic cleaners and non-immersion Direct-Displace IPA vapor drying. This A precision aqueous cleaning system cleaners such as high pressure spray method has demonstrated good success for fully-assembled head-stack asem- washers and atmospheric-pressure in ionic and particle removal from stain- blies (HSAs) is described by Manch atomizer sprayers. Solvent and aqueous less steel screws, electromechanical coils (1994). This system, in use at D cleaning media are contrasted. Drying and actuator assemblies. Equipment Corporation, contains methods, filtration needs, cleanliness Cleaning using supercritical fluids separate process modules: an measurements and automation trends such as carbon dioxide is receiving sonic cleaning tank, a Quick L are reviewed as well. increasing attention as a possible niche Rinse (QDR), an air-knife water IBM’s disk drive manufacturing facili- application In parts cleaning, particu- module, and two vacuum drying ties in San Jose, CA, Rochester, MN and larly where the emphasis is on select- conditions. Sonic energy distribution, Havant, UK have published extensive ive removal of organic contaminants degassing. recirculation and filtration accounts of their efforts to implement (Pm-tell and Rothman, 1993). rinsing effectiveness, water dropler CFC-free cleaning in-house and at sup- placement and vacuum pump d pliers. Typical CFC-based cleaning sys- Technology Components are stated to be critical process par tems are described by Phillips et al. Hosokawa et al. (1991) describe an ters to control. A similar system (1984). Although predominantly driven automated tape head cleaning tech- at IBM San Jose has been present at by environmental considerations (Young nique for use in automated mass stor- Nagarajan and Carroll (1993). and Anderson, 1994). water cleaning age systems based on VHS videocas- CFC-free lubrication of thin has also, in general, resulted in cleaner settes. Lu et al. (1994) and Lu and magnetic recording disks was a parts and higher product yields Aoyagi (1994) describe a dry cleaning thrust in the industry in the (Nusbaum, 1991) - clearly a situation process for magnetic head sliders that 1990s (Steiber, 1993). Agarwal (- where environmental and manufactur- involves laser irradiation in ambient air describes a Fluorinert (FC-72)-l ing objectives were not mutually exclu- with pulse output and short wave- lubing process Introduced in He sive. In San Jose, an aqueous cleaner length. Contaminants on sliders are Packard in 1991. HFCs and with ultrasonics for disk drive parts was classified Into three major categories: recently hydofluoroethers (HFEs) first implemented in 1989 (Ko, 1989). irremovable organic glue such as epoxy emerged as leading alternatives to Larger, more aggressive aqueous ultra- resin, radius residue generated in the fluorocarbons such as FC-72. PFC sonic cleaners for the same purpose milling process which consists of sili- considered ‘greenhouse’ gases and went on-line in July 1992 (Nagarajan et con particles and organic grease, and restricted in their use. Solvent al., 1992) the date when IBM San Jose embedded metallic contaminants lubrication is also being investigate ceased to use CFCs in cleaning - 2.5 which are usually tin particles. many disk manufacturers. years ahead of the EPA mandate and 1.5 Cleaning mechanisms involved here An aqueous washing system for years ahead of the Corporate directive. include laser photodecomposition, substrates prior to application of a In addition, IBM San Jose has worked laser ablation and surface vibration magnetic coating is described by Nusb extensively with their supplier base to due to the impact of the laser pulse. (1991). This cleaner, in use at IBM ensure that manufacturing processes The precise mechanism is still not fully Jose, uses hot DI water spray, followed were compatible with water-based understood. Short wavelength and by evaporative heating. Water quality cleaning, and with their own Design and short pulse duration are stated to be requirements for this application defined in this paper. Use of high pres- and contamination/handling damage. characterization. Other techniques. par- surewater spray and high pressure per- Mandle (1990) describes the use of opti- ticularly useful in detecting chemical fluorocarbon spray for substrate clean- cally stimulated electron emission residues on surfaces, are presented by ing are also common practice. (OSEE) to measure the effectiveness of Greene et al. (1991). Detection of magnetic disk cleaning processes. In silicone contamination by X-ray Photo- CLEANLINESS MEASUREMENT this method, the cleaned surface is irra- electron Spectroscopy (XPS) and proton PROCEDURES diated in air with short wavelength nuclear magnetic resonance (NMR), in Determining ‘how clean is clean’ for ultraviolet energy: electrons are collect- addition to FTIR and AES, has been disk drive components has always been ed across an air gap and measured. investigated by Hanke (1995). Newer a difficult issue (Brand and Hoffman, Most recently, scanning tunneling methods such as supercritical fluid 1993; Nagarajan, 1990, 1993); however, microscopy is finding increasing use in chromatography and capillary elec- it remains a self-evident truth that ‘you magnetic storage device manufacturing trophoresis have been introduced by cannot control what you do not mea- (Strecker and Persch, 1991). with par- Lopez-Avila (1995). sure:. Thus, many cleanliness measure- ticular applicability to disk smoothness ment methods proliferate in the disk drive Industry. A complete treatment of cleanliness measurement techniques may be found in two tutorial presenta- tions by Phillips (1989) and by Welker and Nagarajan (1991). The latter tutori- al, parts of which are excerpted In Welker (1995), contain a description of the methodology to use to ascertain the gage capability (repeatability and repro- ducibility) of such techniques. Methods for measuring surface cleanliness may be broadly classified into two categories: l Direct, where the surface is directly inspected for contaminants, and l Indirect, where the contaminants to be measured and/or analyzed are extracted into a fluid medium for sub- sequent processing. Measurement methods may also be classified as those that characterize gross cleanliness (subjective), and those that characterize precision cleanliness (quantitative). But this section will clas- sify and deal with methods based on whether they are direct or indirect.

Direct Methods Visual observation of surfaces in room light is the simplest and most direct of tests (Phillips, 1991). It is, however, surprisingly effective for detecting a wide variety of contami- nants. Using enhanced illumination, bright light or UV light, can significant- ly enhance detection capabilities. Use of dental probes, tweezers and cleanroom swabs is advocated by Hill (1991). At the other end of the analyti- cal spectrum, ellipsometry, Electron Spectroscopy for Chemical Analysis (ESCA) (Finney 1995). and Secondary Ion Mass Spectroscopy (SIMS) are frequently used to study disk tribology and contamination (Viswanathan, 1989; Viswanathan and Wadkins, 1991). Integrating surface analysis and infraspectrometry for disk defect char acterization are introduced by Hepplewhite and Stoneham (1995). Other disk monitoring methods such as Auger Electron Spectroscopy (AES) and depth profiling are described by Brar and Narayan (1989). These methods, when applied appropriately, can detect substrate defects, processing defects Indirect Methods (GC/MS), which can also determine the graph estimates total ionics by means Tape testing (Phillips, 1991) is possibly composition of the outgassing substance. of conductivity measurements: the the simplest indirect method for assess- Magnetic particles are typically meas- Hydrocarbon Residue Analyzer (HRAI ing surface cleanliness, particularly for ured using indirect techniques such as uses thermal elctraction to volatilize and transferable films. Tape can also lift par- tape-pull or solvent extraction. followed collect organic vapors: and a semicon- ticle% off surfaces. but the particles have by SEM/EDX analysis to identity and ductor detector quantifies the amount of to be concentrated in small areas for the quantity (Peterson, 1993: Roberts, evolved organics. method to be sensitive. The tape can 1991). In terms of general particulate then be examined visually under a light contamination, ASTM Test Method F24 Assembly and Drive-Level microscope by placing on a glass slide. documents a procedure for extracting Contamination Measurement Use of a densitometer (Welker, 1995) parts and measuring the extract solution Collection and analysis of particulate provides a measurement of the amount by filtration and microscopic counting. contaminants associated with the of material lifted by the tape. Nonvolatile Use of turbidity and liquid-borne particle assembly process is discussed by residue analysis (NVR) involves remov- counting (LPC) as alternatives to the Ackerman and Ayala N (1990). Methods ing organics and particles from surfaces laborious microscopic-count procedure of sample collection from various with a solvent. then driving the solvent was introduced by IBM in the mid- 1980s sources. sample preparation, analytical off for weight change determination, (Brand et al., 1992; Roberts, 1991; techniques and data interpretation are Fourier Transform Infrared Spectro- Nagarajan. 1990). These instruments dealt with. Typical collection methods scopy (FTIR) or other analyses (Hill, have now found widespread acceptance include application of a carbon planchet 1991). Outgassing and thermogravime- across the disk drive industry. LPC lower with a strip of double-sided tape to cap- try, where the sample is heated to mea- detection limits are typically set at 2-5 ture airborne dust and surface particu- sure weight loss. is a popular monitoring um. Turbidimetry is usually adequate for lates. The stub may then be analyzed technique for volatile residue (Ni et al., less critical components. and for more with a SEM/EDX (Scanning Electron 1989). rugged drives. Brand et al. (19921 also Microscope/Energy Dispersive X-Ray) Another leading technique for mater- describe three simple instruments for set-up. Use of witness plates for collect- ial outgassing characterization is quantifying ionic and organic contami- ing organic and ionic contaminants is gas chromatography/mass spectrometry nation on component parts. The lono- discussed by Roberts (1991). While

For Information Circle No. 50 organics are usually measured by using where it is at with respect to satisfying Investigations of Particulate Contamination in techniques listed earlier (such as gravi- these needs. q Disk Drives, ” Ph. D. Thesis, Mechanical metric NVR], ionic species are normally Engineering Department, U. Minnesota. characterized using ion chromatogra- REFERENCES Minneapolis, MN. 1988. 4. Bhushan. B. and Koinkar phy, which can differentiate between 1. Ackerman, E.R. and Ayala IV, S.. V.N., “Particulate Contamination Associated with ‘Tribological Studies of Silicon .for Magnetic individual anions and cations. Airborne Recording Applications,” J. Appl. Phys.. 75, particle counters are usually employed Disk Drive Assembly,” Proc. Microcontamin- ation 90, Santa Clara, CA, Oct 31 - Nov 2. (10). 15 May 1994, pp. 5741-5746. in continuous or audit mode to ensure 1990, pp, 185-195. 5. Best, G.L.. “Precise Stiction Mapping,” IEEE that the cleanroom facility meets the 2. Agarial. A., “Development and Imple-men- Transaction on Magnetics. Vol. 27, No. 6, appropriate cleanliness levels. tation of a CFC-Free Lubrication Process for November 1991. pp. 5169-5171. Drive-level cleanliness measurements Thin-Film Magnetic Recoding Disks,’ present- 6. Brand, J.L.. Blumentritt, B.F: and Hoffman, are more difficult to perform than com- ed at Tribology of the Head-Medium Interface R.J., “Measurement of Contamination on Disk ponent-level tests. Drive-level particle CMRR, UC San Diego, March 2, 1992. Drive Components, ” Proc. Microcontamination 92, Santa Clara CA, October 27-30, 1992, pp. counting is used by nearly all manufac- 3. Ananth, GP., “Experimental and Numerical turers as an indication of start-up cleanliness. Conventionally. air from the interior of the disk drive is sucked out via a particle-count port, and a laser particle counter is used to count parti- cles larger than 0.1 um in diameter. The incorporation of a condensation nuclei counter (CNC) can extend the lower detection limit to 0.01 um (Sommer and Futrell, 1991). In this test, the sensor is placed within the head/disk assembly (HDA) enclosure. Particle counts may be obtained during disk spin-up, full speed operation and spin-down. Air flow spin- ning off the disk is monitored in this test, which is therefore more represent- ative of real-life operation. Tear-down and analysis of the head- disk interface is frequently done on an audit basis to determine debris build-up with time. Stiction force measurements in a simulated drive environment (Best, 1991) are performed less frequently to assess drive susceptibility to slider/disk adhesion. A test system that closely mimics the chemical environment of a disk drive has been presented by Koka (1993). This system is designed specifi- cally to study the effect of organic contaminants in a well-controlled, chemically-stressed environment. In the tester, heads and disks are subjected to several thousand contact start/stops, and friction/stiction forces at the head/disk interface are continuously monitored. Key elements of the tester are the spin-stand and controller, the data acquisition and control unit and the contaminant introduction system. Cleaning the system prior to a new test is a critical procedure.

CONCLUSION An effort has been made in this paper to survey the literature for cleaning methods and cleanliness measurement methods prevalent in the hard disk drive industry. Though by no means com- plete, this survey nevertheless captures many key aspects of many technologies. Emerging trends are glimpsed by means of a critical appraisal of current and future cleaning and measuring needs. It is intended that this paper sense as the spring-board for the industry to assess