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Metcut symposium proceedings
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Grinding brittle materials Faster finishing of the back surfaces of silicon wafers than with the normal processes, such as lapping, has been achieved by grinding. According to Cone-Blanchard, the process is equally applicable to optical glass, ferrite, quartz, sapphire and germanium. In the process a diamond cup wheel is mounted on a precisely balanced, vertical spindle. The work pieces, typically silicon wafers, are placed on a horizontal, rotating worktable, which traverses to take them below the grinding wheel. Down feed of the grinding wheel is infinitely variable from 0.0025 to 0.25 mm/min: grinding wheel and worktable rotate in opposite directions. Cone-Blanchard claim that flatness, parallelism, and size of product are consistently within 15/.Lm and surface finish is 0.2#m cla or better. In a typical operation, claimed to demonstrate the high productivity of the process, the back surfaces of 3 in (76,2 mm) diameter silicon wafers were ground. Capacity of the 508 mm diameter worktable was 25 wafers of this size; floor-to-floor time was less than one minute per wafer. Crucial to the success of wafer grinding is the special chuck, which is
a vacuum device. A set of porous ceramic workholding stations, one for each wafer is installed on the worktable. To protect the front face of the wafer, a piece of porous paper is placed between wafer and workholder. With air evacuated from the worktable, the wafers are held firmly in place during the grinding process. Flat thin objects are, of course, extremely difficult to pick up. To aid the operator, the vacuum pump unit can be reversed so that air flows into the worktable. Each wafer now hovers on a cushion of air, and is easily removed by the operator. Cone-Blanchard Machine Company Ltd, Northgate, Aldridge, Walsall, UK, WS9 8TY
Accurate stress measurement Presentation of data in an easily assimiable form in a fraction of the time required for traditional techniques are among the benefits claimed for Stress Patern Analysis by Thermal Emission. Embodied in hardware as SPATE 8000, the technique provides continuous colour maps of stresses over a wide range of dynamic loads. SPATE 8000 is said to have been designed specifically to meet the needs of stress and design engineers in advanced aerospace, defence and
engineering technologies for a highly flexible instrument in the critical analysis of stress problems. The principle of the technique is based on the measurement of the thermoelastic effect in materials when the imposition of stress by dynamic loading produces minute temperature changes. Temperature changes of 0.001 °C are recorded; thus stress changes of 1 N/mm 2 (145 p.s.i) in steel or 0.4 N/mm 2 (58 p.s.i.) in aluminium are detected. The data derived from the changes in temperature on the surface of the component are processed electronically to give high resolution, accurate, quantitative colour maps representing the stress patterns with the different stress levels represented by up to 16 different colours, arranged as a linear scale. Stresses are measured on a thousand point scale and different areas of the object less than a millimetre apart can be analysed. The equipment can be calibrated for a wide range of materials including plastics and metals. The operator can choose from a range of display resolutions and scan times which may be used to speed up the assessment of an unfamiliar component. Key stress points are identified on a low resolution scan and then a zoom capability may be used to obtain a high resolution of detailed analysis of the stress points. SPATE 8000 is being marketed internationally by Ometron Ltd, Park Road, Chislehurst, Kent, UK, 8R7 5AY
Metcut symposium proceedings
Vacuum chucking o f silicon wafers; reversing of the vacuum pump causes wafers to hover, for easy unloading.
28
Proceedings of an International Manufacturing Engineering Symposium, held on June 19, 1982, in Cincinnati, to mark the retirement of Dr Michael Field, are now available. Seventeen of Dr Field's many colleagues and friends prepared technical papers for the symposium. Copies of the 360-page Proceedings price $35.00 plus $15.00 for airmail delivery outside the USA, are available from Machinability Data Center, Metcut Research Associates Inc., 3980 Rosslyn Drive, Cincinnati, OH 45209, USA
J A N 1983 V O L 5 NO 1
Grinding brittle materials Faster finishing of the back surfaces of silicon wafers than with the normal processes, such as lapping, has been achieved by grinding. According to Cone-Blanchard, the process is equally applicable to optical glass, ferrite, quartz, sapphire and germanium. In the process a diamond cup wheel is mounted on a precisely balanced, vertical spindle. The work pieces, typically silicon wafers, are placed on a horizontal, rotating worktable, which traverses to take them below the grinding wheel. Down feed of the grinding wheel is infinitely variable from 0.0025 to 0.25 mm/min: grinding wheel and worktable rotate in opposite directions. Cone-Blanchard claim that flatness, parallelism, and size of product are consistently within 15/.Lm and surface finish is 0.2#m cla or better. In a typical operation, claimed to demonstrate the high productivity of the process, the back surfaces of 3 in (76,2 mm) diameter silicon wafers were ground. Capacity of the 508 mm diameter worktable was 25 wafers of this size; floor-to-floor time was less than one minute per wafer. Crucial to the success of wafer grinding is the special chuck, which is
a vacuum device. A set of porous ceramic workholding stations, one for each wafer is installed on the worktable. To protect the front face of the wafer, a piece of porous paper is placed between wafer and workholder. With air evacuated from the worktable, the wafers are held firmly in place during the grinding process. Flat thin objects are, of course, extremely difficult to pick up. To aid the operator, the vacuum pump unit can be reversed so that air flows into the worktable. Each wafer now hovers on a cushion of air, and is easily removed by the operator. Cone-Blanchard Machine Company Ltd, Northgate, Aldridge, Walsall, UK, WS9 8TY
Accurate stress measurement Presentation of data in an easily assimiable form in a fraction of the time required for traditional techniques are among the benefits claimed for Stress Patern Analysis by Thermal Emission. Embodied in hardware as SPATE 8000, the technique provides continuous colour maps of stresses over a wide range of dynamic loads. SPATE 8000 is said to have been designed specifically to meet the needs of stress and design engineers in advanced aerospace, defence and
engineering technologies for a highly flexible instrument in the critical analysis of stress problems. The principle of the technique is based on the measurement of the thermoelastic effect in materials when the imposition of stress by dynamic loading produces minute temperature changes. Temperature changes of 0.001 °C are recorded; thus stress changes of 1 N/mm 2 (145 p.s.i) in steel or 0.4 N/mm 2 (58 p.s.i.) in aluminium are detected. The data derived from the changes in temperature on the surface of the component are processed electronically to give high resolution, accurate, quantitative colour maps representing the stress patterns with the different stress levels represented by up to 16 different colours, arranged as a linear scale. Stresses are measured on a thousand point scale and different areas of the object less than a millimetre apart can be analysed. The equipment can be calibrated for a wide range of materials including plastics and metals. The operator can choose from a range of display resolutions and scan times which may be used to speed up the assessment of an unfamiliar component. Key stress points are identified on a low resolution scan and then a zoom capability may be used to obtain a high resolution of detailed analysis of the stress points. SPATE 8000 is being marketed internationally by Ometron Ltd, Park Road, Chislehurst, Kent, UK, 8R7 5AY
Metcut symposium proceedings
Vacuum chucking o f silicon wafers; reversing of the vacuum pump causes wafers to hover, for easy unloading.
28
Proceedings of an International Manufacturing Engineering Symposium, held on June 19, 1982, in Cincinnati, to mark the retirement of Dr Michael Field, are now available. Seventeen of Dr Field's many colleagues and friends prepared technical papers for the symposium. Copies of the 360-page Proceedings price $35.00 plus $15.00 for airmail delivery outside the USA, are available from Machinability Data Center, Metcut Research Associates Inc., 3980 Rosslyn Drive, Cincinnati, OH 45209, USA
J A N 1983 V O L 5 NO 1