Patent Publication Number: US-6659843-B2

Title: Substrate dicing method

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is a continuation of co-pending U.S. Ser. No. 09/645,917 filed on Aug. 25, 2000, now U.S. Pat. No. 6,354,909 which is a continuation of U.S. Ser. No. 09/358,046 filed on Jul. 21, 1999 and now issued as U.S. Pat. No. 6,152,803, which is a continuation-in-part of U.S. Ser. No. 09/022,619 filed on Feb. 12, 1998 and now issued as U.S. Pat. No. 5,934,973, the disclosures of which are hereby incorporated by reference in their entirety. 
     Application Ser. No. 09/022,619 filed Feb. 12, 1998 for a “Semiconductor Wafer Dicing Saw,” which itself is a divisional application of U.S. patent application Ser. No. 08/546,216 filed Oct. 20, 1995 for a “Semiconductor Wafer Dicing Method,” now U.S. Pat. No. 5,718,615, and incorporates by reference and claims priority to provisional Application No. 60/126,174 filed Mar. 25, 1999 for an “Alignment System And Method For A Programmable Dicing Saw,” commonly owned with the present application. 
    
    
     BACKGROUND OF INVENTION 
     1. Field of Invention 
     The invention relates generally to the dicing of semiconductor wafers and, more particularly to the monitoring of blade location and flange clearance for safely cutting a semiconductor wafer. 
     2. Background Art 
     Die separation, or dicing, by sawing is the process of cutting a microelectronic substrate into its individual circuit die with a rotating circular abrasive saw blade. This process has proven to be the most efficient and economical method in use today. It provides versatility in selection of depth and width (kerf) of cut, as well as selection of surface finish, and can be used to saw either partially or completely through a wafer or substrate. 
     Wafer dicing technology has progressed rapidly, and dicing is now a mandatory procedure in most front-end semiconductor packaging operations. It is used extensively for separation of die on silicon integrated circuit wafers. Increasing use of microelectronic technology in microwave and hybrid circuits, memories, computers, defense and medical electronics has created an array of new and difficult problems for the industry. More expensive and exotic materials, such as sapphire, garnet, alumina, ceramic, glass, quartz, ferrite, and other hard, brittle substrates, are being used. They are often combined to produce multiple layers of dissimilar materials, thus adding further to the dicing problems. The high cost of these substrates, together with the value of the circuits fabricated on them, makes it difficult to accept anything less than high yield at the die-separation phase. 
     Dicing semiconductor wafers by sawing is an abrasive machining process similar to grinding and cutoff operations that have been in use for decades. However, the size of the dicing blades used for die separation makes the process unique. Typically, the blade thickness ranges from 0.6 mils to 500 mils, and diamond particles (the hardest well known material) are used as the abrasive material ingredient. Because of the diamond dicing blade&#39;s extreme fineness, compliance with a strict set of parameters is imperative, and even the slightest deviation from the norm could result in complete failure. 
     The diamond blade is a cutting tool in which each exposed diamond particle comprises a small cutting edge. Various dicing blades are available commercially. By way of example, a sintered diamond blade includes diamond particles which are fused into a soft metal such as brass or copper, or incorporated by means of a powdered metallurgical process; a plated diamond blade includes diamond particles which are held in a nickel bond produced by an electroplating process; and a resinoid diamond blade is one in which diamond particles are typically held in a resin bond to create a homogeneous matrix. Silicon wafer dicing typically uses the plated diamond blade, which has proven to be most successful for this application. 
     Because most state-of-the-art dicing equipment has been designed specifically to dice silicon wafers, problems arise when it is necessary to cut harder and/or more brittle materials. Blade speed and torque, depth of cut, feed rate, and other performance parameters have been optimized for silicon. However, hard and brittle materials require different blades and equipment operating parameters, the proper selection of which is a key to success for high-yield dicing. In any cutting operation, tool sharpness is of primary importance. More exactly, it is necessary that the cutting tool maintain its sharpness throughout the cutting operation. When cutting hard material such as sapphire or garnet, the cutting edges become dull quite rapidly. Because the dulled cutting edges cannot be re-sharpened in the usual manner, it is desirable that they be pulled loose from the blade, or else be fractured to expose new sharp cutting edges. 
     An important characteristic of the resinoid diamond blade that promotes effective cutting is its self-sharpening ability. The blade requires no dressing at all, in contrast to most metal-bonded (sintered or electroplated) diamond blades. Sharpening is accomplished automatically by the cutting process. As a cutting edge becomes dull, it experiences increased cutting forces that eventually either pull the diamond particle loose from the blade or else fracture it to produce a new sharp cutting edge. A diamond blade that does not exhibit this property cannot properly cut hard materials, nor can it perform properly if saw operating parameters interfere with the self-sharpening mechanism. 
     By way of example, U.S. Pat. No. 4,219,004 addresses a problem in the art of getting the blade cutting surface perpendicular to the substrate being cut and discloses blade mounting means comprising a pair of generally flat round collars, flanges, having a round central opening for receipt by the saw spindle. Further, the outer diameters of the collars are less than the blade diameter for providing an exposure of approximately 15 mils. A blade exposure not greater than 20 to 25 times the blade thickness is recommended. Replacing the collars with those having smaller diameter are disclosed for providing desired exposure and for replacing collars as the blade wears and exposure is reduced. Methods for monitoring or measuring the exposure during the dicing of the substrate is not addressed. U.S. Pat. No. 4,787,362 discloses an abrasive cutting blade having very high rigidity useful dicing silicon wafers and hard materials. The use of the flange or spacer for maintaining blade rigidity and providing blade exposure sufficient for completely penetrating the work piece and cutting partially into the intermediate carrier typically used is disclosed. Wobble or run-out is of concern and is inversely proportional to the blade exposure. As a result, blade exposure is held to tight and typically minimal dimensions. A rigid blade core is described for preventing run-out from causing the core to make contact with the workpiece and causing widening of the cut and a less than even cut. Making the flange larger for providing less exposure is not addressed. However, less exposure means greater chance for inadequate cooling and greater chance of the flange hitting the work piece. There remains a need to effectively and economically resolve these problems. U.S. Pat. No. 3,987,670 discloses a displacement transducer manually applied to a diamond blade cutting surface for measuring a distance from the blade cutting edge to a fixed reference distance on the blade. The transducer is mounted on a portable fixture. Blade wear of diamond blades generally in the range of 18 to 36 inches are addressed and the problems associated with measuring blade wear of these blades are identified. The transducer is provided with suitable readout devices to determine blade wear. Although blade wear is addressed, it is for relatively large, easily visible blade sizes, and measured while the blade is held motionless. Further, the issues associated with exposure and depth of cut into a substrate is not addressed. Flange clearance is not a major concern for 18″ to 36″ blades. 
     There is a need to monitor blade exposure, the amount of blade extending from the flanges holding the blade therebetween, during a wafer or substrate dicing for maintaining sufficient clearance between the flange edges and the substrate to provide adequate cooling, and further for preventing the flanges from contacting the substrate, often containing electronic chips valued in the many thousands of dollars. There is further a need to monitor and control the location of the cutting blade with respect to the location of the wafer to be cut and to efficiently and effectively control positions prior to a first cut and during movement of the wafer on its table for subsequent cuts. By way of example, a dicing machine user will typically try to mount the wafer at the center of the table or chuck holding the wafer during the cutting operation. In the alternative, computer aided chuck and saw movement will determine measured cuts from the table center and move the dicing saw relative to the center coordinates, sometimes actually moving the table to the center prior to moving it to the appropriate cutting location. This adds expensive operating time, especially when one considers that thousands of cuts may be required within one wafer dicing project. When a cut is to be made close to an edge of the wafer, and the blade is allowed to make a cut close to the wafer edge, the blade may ripe off a section of the wafer, which can require disposal of the entire wafer, or extensive attempts and time for salvaging what is typically a very expensive wafer including multiple electronic elements. 
     Various approaches have been used to identify a locations of a workpiece in computer aided machines. By way of example, U.S. Pat. No. 4,233,625 to Altman discloses the use of television monitoring for aligning successive configurations of semiconductors. U.S. Pat. No. 5,422,579 to Yamaguchi discloses the use of a camera for identifying probe positions on a card and recognizing reference probes for providing a corrective movement to a work table. U.S. Pat. No. 4,819,167 to Cheng et al. discloses a system and method for determining the location of a semiconductor wafer relative to its destination position using an array of optical sensors positioned along an axis transverse the path of movement of the wafer. Trigger points provided by the sensor array as the wafer is moved, provide locus information data to a processor for calculating the center of the wafer. U.S. Pat. No. 3,670,153 to Rempert et al. discloses the use of a light sensing element and scanning of the object for detecting dark and light regions in determining edges of the object to be measured. In spite of the many computerized optical devices and configurations, there still remains a need to economically provide a method for effectively and efficiently locating the position of the wafer on the work table for optimizing movement of the table or workpiece during sawing operations and for providing a safe location at which the saw can operate without damage to the wafer and saw, or hazard to the saw and operator. 
     SUMMARY OF THE INVENTION 
     In view of the foregoing background, it is therefore an object of the present invention to provide a method for safely and efficiently dicing a semiconductor wafer or substrate by moving the table relative to the saw based of a location of the wafer, while preventing the blade flange from contacting the substrate. It is further an object of the invention to prevent the cutting of a substrate so close to its edge that it may shatter the substrate or damage the blade. It is yet another object of the invention to monitor flange clearance during the cutting of the wafer for cutting the wafer without having the flange contact the wafer as a result of blade wear. It is yet another object of the invention to provide automation to the traditionally manual and semiautomatic monitoring of the wafer dicing process. 
     These and other objects, features, and advantages of the invention, are provided by a method for dicing a substrate using a programmable dicing saw. The dicing saw includes a processor operable for movement of a spindle carrying a dicing blade and a work surface upon which the substrate is removably secured. Movement of the dicing blade toward and away from the work surface is controlled by movements within an orthogonal coordinate system having its center at a center location of the work surface. The dicing blade is mounted onto the dicing saw spindle juxtaposed between a flange pair for rotation of the dicing blade about a spindle axis. The dicing blade has an outer diameter defining a cutting edge and is greater than each flange diameter of the flange pair for providing a blade exposure for cutting into a substrate. Preferably, the substrate to be cut is removably securing onto the work surface and within a blade path of the dicing blade. 
     Locating the center of the substrate provides for an efficient movement of the blade relative to the center and save time when compared to attempts to manually center the substrate and move the blade during the cutting process relative to the center of the work surface rather than the center of the substrate. A preferred method of locating the center of the blade includes the steps of aligning the dicing blade with a first edge of the substrate for determining a substrate first edge location on the work surface, aligning the dicing blade with a second edge of the substrate for determining a substrate second edge location on the work surface, wherein the first edge laterally opposes the second edge and the rotational axis of the dicing blade is perpendicular to the blade paths along the first and second edges, rotating the substrate ninety degrees about an axis perpendicular thereto, aligning the dicing blade with a third edge of the rotated substrate for determining a substrate third edge location on the work surface, wherein the blade path along the third edge is perpendicular to the blade path along the first edge, and aligning the dicing blade with a fourth edge of the substrate for determining a substrate fourth edge location on the work surface, wherein the third edge laterally opposes the fourth edge. Edge data representative of the measured substrate first, second, third, and fourth edge locations is entered into the processor operable with the dicing saw for determining the center of the substrate and calculating a distance between the center of the substrate and the center of the work surface for providing a compensating command to the programmable dicing saw. Movement of the substrate is then made relative to the center of the substrate. If desired, the dicing saw is located over the center of the substrate when initiating blade and work surface movement. The spindle and work surface are moved relative to the center of the substrate for positioning the dicing blade based on the compensating command. 
     In a preferred operation of the dicing saw when cutting a substrate includes aligning the dicing blade for making a cut into the substrate along a first blade path, dicing the substrate along the first blade path, and subsequent blade paths as desired. The blade outer diameter reduces with each cut into the substrate, thus reducing the blade exposure, and further reducing a clearance between the flange pair and a substrate top surface for each subsequent cut. Therefore, the flange clearance is determined and monitored by measuring the blade exposure after a preselected number of cuts during the substrate dicing. 
     In one preferred method when aligning the blade for dicing along an edge of the substrate, the dicing blade is first aligned for travel parallel to and proximate the first edge of the substrate. An offset command is provided to the programmable dicing saw for laterally moving the blade toward the center of the substrate prior to making a cut into the substrate. The offset command is representative of a preselected offsetting displacement of the blade from the edge to avoid damage to the blade and substrate that typically results when the blade slides along the substrate edge rather than cutting into the substrate. 
     The present invention provides for accurately making arcuate cuts into the substrate. With such a method, the dicing blade aligning comprises first aligning the dicing blade for travel along a first blade path at a preselected distance from the center of the substrate for the dicing thereof. A desired cut is made into the substrate. Then the dicing blade is aligned for travel along a second blade path at the preselected distance from the center of the substrate for the dicing thereof, wherein the second blade path radially opposes the first blade path. A desired cut is then made. The substrate is rotated by a preselected arc and the aligning and dicing steps are repeated for providing multiple cuts within the substrate. The substrate rotating comprises incrementally rotating of the substrate a multiplicity of times sufficient for providing an arcuate cut to the substrate. With such a method, a circular shape can result. 
     To guard against damage to the substrate, the dicing method further comprises the step of automatically stopping the dicing of the substrate when the flange clearance is reduced to less than a preselected minimum clearance. A separation distance between the work surface and the blade cutting edge is calculated using the processor, and blade movement into the substrate is automatically stopped when the blade cutting edge is greater than a preselected separation distance. In one embodiment, the flange clearance is calculated by sensing the blade cutting edge during blade rotation and prior to the substrate cutting step for setting a reference position for the blade edge and spindle axis, and sensing the blade cutting edge after the preselected number of cuts for determining an axis position difference for the worn blade. The difference is used to update data input to the processor regarding the reduction in blade diameter, the blade exposure, and thus the step of determining the flange clearance. The blade exposure measurement is made at preselected intervals throughout the substrate dicing steps. The flange clearance is automatically calculated at preselected intervals throughout the substrate cutting. A minimum flange clearance is preselected for continuing the dicing. The minimum flange clearance should provide effective coolant flow to the blade, adequate blade rigidity and thus a squareness of cut, and an acceptable blade chipping. Calculating blade exposure includes measuring blade wear after a preselected number of cuts for automatically monitoring the exposure during the dicing step and providing a first stop movement signal to the processor when a minimum exposure results in a minimum flange clearance for the dicing steps. Calculating a separation distance between the work surface and the blade cutting edge is made and provides a second stop movement signal to the processor when a preselected maximum separation distance is measured, thus indicating blade wear. Movement of the dicing blade toward the work surface is automatically stopped when any stop movement signal is received. The exposure calculating step comprises the sensing of the blade edge during blade rotation prior to the dicing of the substrate for setting a reference position for the blade edge and spindle axis, and sensing the blade edge after the preselected number of cuts for determining an axis position difference for the worn blade. The exposure calculating step is made by the processor using the axis position difference and the flange diameter. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     A preferred embodiment of the invention as well as alternate embodiments are described by way of example with reference to the accompanying drawings in which: 
     FIG. 1 is a partial diagrammatic side view of a dicing saw embodiment of the present invention; 
     FIG. 2 is a partial end view of a dicing blade held onto a spindle within flanges; 
     FIGS. 3 a  and  3   b  are plan and end views, respectively, of a dicing saw blade; 
     FIG. 4 is a partial diagrammatical elevation view of a wafer cutting arrangement; 
     FIG. 5 is a functional block diagram of the system control used in one preferred embodiment of the present invention; 
     FIG. 6 is a partial cross-sectional view of a height sensor; 
     FIG. 7 is a flow diagram illustrating a logic of the dicing saw system of the present invention; 
     FIGS. 8 a ,  8   b , and  8   c  are diagrammatical plan views of a substrate illustrating aligning and dicing thereof; 
     FIG. 9 is a perspective view of one preferred embodiment of a dicing saw operable with the present invention; 
     FIG. 10 is a partial diagrammatical plan view illustrating an offset blade path; and 
     FIG. 11 is a diagrammatical plan view illustrating a circular cutting of a substrate in accordance with the present invention. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENT 
     The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout. 
     The preferred embodiment of the present invention is described with reference to the drawings, wherein a method and system  10  for automatically dicing a semiconductor wafer or a substrate  12 , herein described by way of example, provides a safe clearance  14  between a dicing blade flange  16  and the substrate  12 , as illustrated with reference to FIG.  1 . By way of example, a resin-bonded dicing blade  18  will wear or reduce in diameter  20  as it is used to cut various substrate materials. The blade  18  is mounted on a spindle  22 , as illustrated with reference to FIG. 2, for rotation about a spindle axis  24 . The flange  16  is typically a flange pair  17  holding the blade  18  between the flange pair  17 . The dicing blade  18  has its diameter  20 , an outer diameter, defining a cutting edge  26 . The blade outer diameter  20  is greater than the diameter of each flange  16  thus providing a blade portion  28  extending radially outward from the flange pair  17  for providing this portion  28  as the blade exposure. 
     Depending on the hardness, density and abrasiveness of the blade material, as well as the cutting rates, spindle rotation speeds, and ability to cool the blade  18  while it is cutting, varying amounts of blade wear will be realized, thus reducing the blade exposure  28 . The blade wear is further complicated by the type or make-up of the diamond blade  18  itself. Fine abrasive blades are more difficult to cool than blades having larger abrasives. A typical dicing blade  18  is further illustrated with reference to FIGS. 3 a  and  3   b  identifying a blade width  30  and blade inner diameter  32  as well as the outer diameter  20  defining the blade cutting edge  26 . 
     Dicing blades  18  are typically fragile. They may be metal or resin in make-up, and are typically have widths  30  ranging from as thin as 0.00012″ to 0.500″. Outer diameters  20  vary from as little as 1″ to 6″. Due to the fragile nature of the dicing blade  18 , they require stiff flanges  16  for mounting them onto the rotating spindle  22 . Flanges  16  are typically made from metals such as aluminum, stainless steel or titanium. Flanges  16  for holding the dicing blade  18  come in an infinite range of diameters, each smaller to some degree than the dicing blade  18  as earlier described. The difference between the flange radius and blade radius is the blade exposure  28 . It is the flange pair  17  and small blade exposure  28  extending therefrom, that gives the extremely thin dicing blade  18  a stiffness sufficient for cutting into the substrate  12 . 
     With reference again to FIG. 1, the substrate  12  having a substrate thickness  34  is held onto a work surface  36  of the dicing saw. Typical work surfaces or dicing saw chucks, as they are also known, hold a workpiece, such as the substrate  12 , using a vacuum. In many arrangements, as illustrated by way of example, with reference to FIG. 1, a carrier  38  is placed on the work surface  36  for receiving the substrate  12 . Such an arrangement permits the blade  18  to cut completely through the substrate  12  without cutting into the work surface  36 . 
     By way of further example, and with reference to FIG. 4, it is preferred that the blade exposure  28  be about ten times the blade width  30 . For example, a 0.002″ thick blade would be exposed 0.020″ as a rule of thumb. Application know-how by those skilled in the art will allow flexibility of adherence to this rule. In addition, there is a minimum or safe flange clearance  14  between a flange edge  40  and a substrate top surface  42 . The flange clearance  14  must be sufficient for permitting coolant from a coolant nozzle  44 , as illustrated with reference again to FIG. 1, to provide adequate cooling during the dicing process. Further, the flange clearance  14  must be monitored and a minimum clearance not exceeded in order to avoid contact between the flange edge  40  and the substrate top surface  42  which will result in damage to a typically expensive semiconductor wafer or substrate  12 . With reference again to FIG. 4, and continuing with a dimensional example, cutting the substrate  12  having a thickness of 0.010″ and wanting to cut through the substrate and beyond by 0.002″, the depth of cut  46  would be 0.012″. This would result in a flange clearance  14  of 0.008″. As the dicing blade  18  wears, reducing the length of its outer diameter  20 , and the dicing saw is programmed to automatically maintain the depth of cut  46 , or a dicing saw operator manually lowers the blade  18 , the flange clearance  14  is reduced. If such lowering continues, the flange  16  will collide with the substrate  12  resulting in damage to the substrate  12 , the blade  18 , and possibly cause injury to the operator. As a result, tracking the flange clearance  14  is an essential step for providing operator and product safety. 
     If one considers the flange clearance  14  at a dimension as small as 0.008″, by way of example, and the that the operator cannot distinguish between clearances  14  of 0.008″ and 0.000″, it is apparent that the need exists to track such minute clearances automatically. Typically, a 5 mil flange clearance  14  is desired. An operator would have to see 3 mils of wear. When one adds coolant and blade shields (not shown) to protect the operator, the extreme difficulty in seeing the flange clearance  14  is further realized. Manually tracking blade wear and calculating any resulting reduction in flange clearance  14  becomes an impractical and inadequate method resulting in an untrustworthy operation for the dicing of expensive semiconductor substrates  12 . 
     With reference again to FIG. 4, it is clear that in addition to monitoring the flange clearance  14  and depth of cut  46 , a separation distance  48  between the blade cutting edge  26  and work surface  36  can also be determined. Further, a depth of cut  50  into the carrier  38  can also be monitored. 
     With reference again to FIG. 1, in one preferred embodiment of the present invention, a height sensor  52  is rigidly affixed to the dicing saw  54  with the work surface  36  and are moveable together. In this way, a sensing surface  56  of the height sensor  52  provides an accurate reference position  58 . With such a reference position  58  for the sensing surface  56 , the height positions of the work surface  36 , the blade cutting edge  26 , the substrate top surface  42 , a carrier top surface  60  are measurable and their relative elevations located. The position of the spindle axis  24  is controllable for movement of the axis  24  for causing the cutting edge  26  of the blade  18  to make contact with the sensing surface  56  wherein the height sensor  52  provides a signal representative of the position of the blade cutting edge  26 , relative to an initial position established prior to the cutting process. In one embodiment of the saw  54 , the work surface  36  and sensor  52  move to position the sensor  52  and substrate  12  for the operation of the saw  54 . As schematically illustrated with reference to FIG. 5, a sensing signal  62  is delivered to a processor  64  for calculating blade wear, the blade exposure  28 , and thus the flange clearance  14  having data representative of the substrate thickness  34 , carrier thickness  64  and surface locations as earlier described. The processor  64  calculates the flange clearance  14  by measuring the blade wear after a preselected number of cuts into the substrate  12  for automatically monitoring the exposure  28  and thus the flange clearance  14  during the dicing of the substrate  12 . In typical operation, the dicing blade  18  makes multiple cuts through the substrate  12  for separating the substrate into individual chips or die (not shown), makes cuts into a blank substrate, or shapes a substrate as desired. By repeating the sensing of the blade cutting edge  26  through the movement of the spindle axis  24  toward the sensing surface  56  for contacting the sensing surface  56  with the blade cutting edge  26 , the flange clearance  14 , which is reduced as the blade  18  wears, is monitored during dicing or cutting of the substrate  12 . The flange clearance  14  is calculated by the processor  64  using updated blade exposure  28 , position of blade edge  26  above the work surface  36 , the substrate thickness  34  and a diameter for the flange  16  selected. The processor  64  is programmable for controlling spindle movement  66  and for storing  68  and displaying  70  the input and monitored data. 
     With the data storage  68 , a blade history is automatically tracked; with such history, displays blade wear information to the operator as well as total wear of the blade  18  using display  70 . Such history is then used for determining the control of the spindle axis  24  for making height sensing movements. Efficiency is thus increased by making such height sensing movements when necessary based on the blade history for the blade  18  having a known composition. Empirical data rather than judgment is then relied upon for setting the control parameters for the dicing saw. 
     As illustrated by way of example with reference to FIG. 6, the height sensor  52  used in the embodiment herein described, comprises a sensor provided by European Semiconductor Equipment Center (ESEC), employing a flexible membrane  72  moveable when the sensing surface  56  is contacted. A ceramic member  74  is attached between the flexible membrane  72  and a piezo-electric crystal  76 . Movement of the crystal  76  causes the signal  62 , representative of the movement. The blade  18  makes contact with the sensing surface  56  while rotating and thus causes wear or cutting of the sensing surface  56 . Such cutting or wear causes excessive vibration and damage to the piezo-electric crystal  76 . Replacement of the height sensor  52  or components such as the flexible membrane  72  are impractical and often times expensive. An improvement to the height sensor is made by attaching a disk  78  to the sensing surface  56 . The disk  78  is replaceable and protects the sensing surface  56 . The disk  78  is preferably made of a hard material that will resist cutting by the dicing blade  18 , or if damaged, easily and inexpensively replaced. In a preferred embodiment of the present invention, the disk  78  is magnetically attached to the sensing surface  56 . Alternate adhesion methods, such as gluing, are acceptable. In one embodiment, the disk  78  is made from carbon steel. The carbon steel disk  78  is first nickel-coated for preventing the steel from rusting due to exposure from the coolant, and provided with a second coating of diamonds and chrome for providing hardness and resisting damage by the rotating blade  18 . In an alternate embodiment, the disk  78  comprises a magnetic ceramic material. 
     In operation, and as illustrated with reference again to FIGS. 1 and 2, the blade  18  is mounted on the spindle  22  between the flange pair  17  for providing the blade exposure  28 . The substrate  12  to be cut is mounted on the work surface  36  as earlier described, and as illustrated in the flow diagram of FIG. 7 as numeral  80 . The blade  18  is rotated about the spindle axis  24  as is typical for dicing saws, and the substrate  12  is cut or diced as desired. The substrate dicing  82  continues for a preselected number of cuts. When the number of cuts reaches the preselected number, or exceeds a maximum specified  84 , the blade edge  26  is delivered to the sensing surface  56  for making a height measurement  86 . Blade exposure is calculated for determining the flange clearance  14  and the separation distance  48 , as earlier described, is also calculated  88 . The calculated flange clearance is compared to a minimum allowable clearance  90 , and the separation distance  48  is compared  92  to a preselected distance. If the flange clearance  14  or the separation distance  48  do not meet that required, dicing saw operation is stopped  94  until corrective action is taken. If the dicing saw is operating within the standards set for flange clearance and separation, substrate dicing continues  96 . 
     With reference now to FIG. 8 a , it is typical for an operator of the dicing saw to attempt to mount the substrate  12  at the center  100  of the dicing saw chuck or work surface  36 , as has been herein described, by way of example. However, there have always been errors in attempting a precise placement of the substrate  12 . The present invention provides for the automatic transfer of a “home position” at the center  100  of the work surface  36  to the center  102  of the substrate  12 , and uses the dicing saw processor  64  to compensate for placement of the substrate at other than work surface center  100 . The present invention provides for the determination of the center  102  of the substrate  12  and its distance away from the center  100  of the work surface  36  by aligning of the dicing blade  18  at edges of the substrate  12  and entry of the edge locations into the processor  64 . 
     As illustrated with reference again to FIG. 8 a , determining the center  100  of the substrate  12  preferably comprises the step of first aligning the dicing blade  18   t  with a top edge  104  of the substrate  12  for determining a substrate top edge coordinate location  106  on the work surface  36  relative to the center  100  of the work surface. The location is entered into the processor  64 . By way of example, reference is made to top and bottom edges as the edges would typically appear to the operator as the operator faces the work surface from in front of the dicing saw  54 . Likewise, relative terms as first, second, and the like can also be used. Next, the dicing blade  18   b  is aligned with the bottom edge  108  of the substrate  12  for determining a substrate bottom edge location  110  on the work surface  36 . The top edge  104  laterally opposes the bottom edge  110  and the rotational axis  24  of the dicing blade  18  is perpendicular to the blade paths  112 ,  114  respectively, along the top and bottom edges. Also, it is preferred that the same edge of the blade  18  be used when aligning the blade with the edges, the top edge of the blade  18  is illustrated herein by way of example. Further, the substrate  12  herein described by way of example has a rectangular shape. The present process is applicable to arcuate shaped substrates as well, in which case the blade  18  would be aligned generally tangent to the arcuate edge. Likewise, and as illustrated with reference to FIG. 8 c , the substrate  12  may be placed on the work surface  36  at other than parallel to the blade path  112 . In such a case, the blade would be preferably aligned with edges closest to the center of the substrate. 
     After alignment and data entry of the top and bottom edges  104 ,  108 , the substrate is rotated by rotating the work surface ninety degrees, as illustrated with reference to FIG. 8 b . The dicing blade  18   t  is aligned with a third edge, now viewed as a rotated top edge  116  of the rotated substrate  12  for determining a substrate rotated top edge location  120  on the work surface  36 , wherein the blade path  112  along the rotated top edge  116  is perpendicular to the blade path along the earlier measured top edge  104 . The dicing blade  18   b  is then aligned with the rotated bottom edge  118  for determining a substrate rotated bottom edge location  122  on the work surface, wherein the rotated top edge laterally opposes the rotated bottom edge. Rotated top and bottom edge locations  120 ,  122  are entered into the processor  64  for calculation of the center  102  of the substrate  12  and its location relative to the center  100  of the work surface  36 . By determining a distance between the center of the substrate and the center of the work surface for providing a compensating command  124  to the processor  64 , as illustrated with reference again to FIG. 5, for movement of the work surface by a controller  126 . The controller  126  is manually directed during the aligning steps through a control panel input  128 . 
     As illustrated with reference to FIG. 9, such alignment preferably includes the use of a camera  130  focused onto the substrate  12  and a video monitor  132  for viewing the substrate image  134  and blade path images which is indicated by cross hairs  136  provided for viewing by the video monitor  132 . A data monitor  138 , a keyboard  140 , and joysticks  142  are provided for data input and processor output viewing. The process of lining up the top edge the blade  18  with the substrate  12  far edges preferably includes using the joystick and optics illustrated with reference to FIG. As described, the video monitor  132  displays the blade path as well as the substrate, and thus allows the operator to match up the entities by moving the joysticks  142  on the control panel  128 . In a preferred operation, the work surface is at a rotation angle of zero degrees within an X-Y plane of the work surface. This zero degree rotation angle is approximate and should be fairly close for a rectangle substrate, but is not critical for a round or circular substrate. In one preferred embodiment of the system  10 , a dialog box  144  on the data monitor  138  is viewed by the operator. Commands for the processor are viewed and the operator enters and views the particular commands such as the aligning steps earlier described. Further, and by way of example, in one programmed process, the work surface is automatically rotated after entry of the second alignment step. The workpiece is rotated 90 degrees and shown in its new orientation within the dialog box  144  on the data monitor  138 . 
     Generally, the operator completes the alignment steps and with each step provides a data entry to the processor. For each step, the operator is guided by the processor through the dialog box display which will include a status as well as instructions for the process being completed. After sufficient data has been entered for a particular calculation, such as the determination of substrate center, the processor displays the substrate center coordinates, which coordinates are used to efficiently move the work surface during operation of the dicing saw for making multiple cuts into the substrate, as earlier described. 
     It is often desirable to make cuts in a blank substrate for reshaping the substrate or providing special cuts, whether rectangular or arcuate in shape. To avoid making a cut so close to the edge, top edge  104  by way of example with reference to FIG. 10, of the substrate  12  so as to damage the blade having blade width  30  or break apart the substrate, an offset command  146  is entered into the processor  64 , as illustrated with reference again to FIG. 5, to allow the processor to automatically relocate the blade path  112  prior to cutting the blank substrate  12 . The offset alignment process allows the operator to make a multiple offsets, and with the aid of the optics and joysticks earlier described, can adjust and select the applicable blade path  112  for the particular cut of interest. 
     Generally, the offset alignment will be made for all desirable sides of the substrate before the dicing begins. The automatic adjustment or offset alignment for the preselected edges are made just before the side is cut. An offset dimension will generally range from zero to a few millimeters. An offset will also be used when a blank substrate or wafer having a circuit pattern removed from its edges is to be cut. In other words there are no streets with discrete die formations on the substrate, by way of example. 
     As illustrated, by way of example, with reference again to FIG. 10, the operator lines up the top edge  104  of the substrate  12  for displacement  148  of the cut at a distance into the substrate toward the center  102  of the substrate. An offset dimension representative of the displacement  148  is entered into the processor, and will typically only be activated on the first cut line for a given side. To initiate the offset process, the operator will align the cross hairs  136 , earlier described with reference to FIG. 9, using the optics joysticks  142  to set the edge location  106  of the substrate. The offset will be calculated from this aligned location  106 . When desired, a flange alignment is also implemented with respect to the center of the substrate. 
     By way of further example of the unique capability provided to the dicing saw by the present inventive methods, the blank substrate  12  is cut into a circular shape substrate  150  or a circle may be cut therein, as illustrated with reference to FIG.  11 . As earlier described with reference to FIGS. 8 a  and  8   b , the present invention provides for accurately locating the center  102  of the substrate. As a result, an arcuate cut can be made into the substrate by making a multiplicity of straight dicing styled cuts  152 . In a preferred method, the dicing blade aligning comprises first aligning the dicing blade for travel along a first blade path  154  at a preselected distance  155  from the center  102  of the substrate  12  for the dicing thereof. A desired cut is made into the substrate. Then the dicing blade is aligned for travel along a second blade path  156  at the preselected distance  155  from the center  102  of the substrate  12  for the dicing thereof, wherein the second blade path radially opposes the first blade path. A desired cut is then made. The substrate is rotated by a preselected arc  158  and the aligning and dicing steps are repeated for providing the multiple cuts  152  within the substrate. The substrate rotating comprises incrementally rotating of the substrate a multiplicity of times sufficient for providing an arcuate cut to the substrate. With such a method, the circular shaped substrate  150  can result. The accuracy or tolerance within which a circle can be cut will depend on the preselected number of multiple straight cuts  152 , generally governed by the specific use of the substrate an the practicality of making a large number of cuts. One measurement of tolerance includes the difference in the length of a radius  160  for a circle  162  inscribed tangent to and excluding the multi-sided arcuate shape  150  and a radius  164  of a circle  166  inscribed tangent to and including the multi-sided shape. This tolerance is illustrated with numeral  168  in FIG. 11, by way of example. 
     Some important guidelines that should be considered in the selection of equipment intended for dicing hard, brittle materials include those related to feed rate or work surface movement, spindle rotational speed, blade use, and depth of cut. The range of feed rates available is important, and should be compatible with the intended applications. Beware of machines that cannot achieve the low range of feed rates, and those that produce uneven table movement when set to low feed rates. The spindle rotational speed (rpm) is preferably variable, and preferably from about 5,000 to 40,000 rpm for a nominal two through five inch diameter blade. The method of accomplishing spindle speed changes is important, and the machine should provide operator indication of the selected spindle speed. The dicing saw should be capable of accepting hub-type or free-standing diamond blades in conjunction with adjustable coolant nozzles  44  and microscope alignment to accommodate any design differences. A machine that limits the user to a single type or source of diamond blade  12  should not even be considered. When considering the selection of a dicing saw, the maximum attainable depth of cut  46  should be ascertained, so that optimum blade utilization can be realized. This is a particularly important consideration for cutting thick substrates or substrates  12  as described herein. 
     We would all like to think that any cutting task could be successfully achieved by simply acquiring any machine and blade  18  combination, producing parts with virtually no loss of the substrate  12  or material being processed, and experiencing no edge damage to the finished parts or diced substrate. However, it has been shown that careful planning and control over the numerous variables is necessary in order to create such an efficient sawing system. Material type, depth of cut, desired throughput, feed rates, spindle speed, cooling nozzle design, mounting, kerf, blade exposure, diamond particle size, available power, and blade flange design, are but a partial list of the variable components affecting the sawing process. There are three critical laws or constraints for dicing and diamond grinding technology that should be followed. Applying these laws properly is critical in the proper selection of process components. 
     The parameters of rigidity, power, and cooling must be considered for each system component selection. It must also be understood that each component involved in the dicing or cutting process cannot create sawing efficiency alone, but rather all of the components as an interactive system must be compatible in meeting standards. If just one component is in error, it could render all other properly selected components ineffective due to its dominance in the sawing process. Whether dicing thin silicon materials at inch-per-second feed rates, or cutting into heavy cross-sections of ceramic-based materially, system rigidity plays a major role in sawing efficiency. It is most important to note that rigidity not only pertains to the equipment being used, but also to the diamond blade  18  and workpiece or substrate  12  mounting methods, as well as to operating parameters. A rigidly mounted spindle  22  with virtually no end play or vibration is mandatory for dicing and diamond grinding. Additionally, the perpendicularity of the spindle axis  24  to the spindle direction of movement toward the work surface  36  is essential for the diamond blade  18  to run true. Presently, air-bearing spindles are the most commonly used because of their exceptionally smooth operation and extended working life. 
     While most end users will take considerable steps in assuring the rigidity of the machine they purchase, they will most often overlook the critical mounting requirements necessary for the diamond blade. No matter how well the diamond blade  18  was manufactured to run true, it can only run as accurately as the surfaces with which it comes into contact. The bearing surfaces of the flanges  16  or spacers (not shown) must be flat, clean, and parallel. Spacers used in gang cutting operations are generally made from aluminum or titanium carbide, depending on the application. As described, the flanges  16  for single blade mounting are usually made from stainless steel. The flanges  16  will incorporate an undercut to reduce the bearing surface area in order to enhance intimate contact with the diamond blade. These surfaces, as well as the diamond blade surfaces, must be clean, with no loose particles present prior to assembly. This insures proper fitting of the mating surfaces. All flanges and spacers must be supplied with torque specifications to aid the user in preventing distortion and separation of the bearing surfaces from the diamond blade. The most frequent cause of blade breakage and oversize cut widths, with relation to blade thickness  30 , is an improper flange torque or poor flange quality. Flanges  16  and spacers must be of high integrity in order not to induce vibration at operating spindle speeds. 
     The blade exposure  28  is a critical component within the variables affecting the overall rigidity of the sawing system. Over-exposure may cause wider than desired kerf, excessive edge chipping, non-squareness of cut, and blade breakage, while too little blade exposure can divert the critical coolant supply from the blade/material interface. The best results will be attained by adjusting the “ten times blade thickness” guideline or rule, earlier described, in accordance with a prerequisite that at least ⅓ to ½ of the diamond blade&#39;s exposure be buried into the cut. This prerequisite is the dominant variable in establishing proper blade exposure  28 . This approach offers improved stability at start, and depending upon material hardness and feed rates, can be fine-tuned with only minor adjustments. The tendency should be to expose the diamond blade  18  at a minimum to attain maximum blade rigidity, with caution given in regard to a possible coolant cut-off or a collision of the flange with the workpiece. The alternative is to run a maximum exposure within the guidelines, to reduce the amount of flange changes required in order to consume the entire working range of the self-sharpening diamond blade. 
     Equally important to rigid blade mounting procedures are the substrate mounting techniques. These two variables of the sawing system are the closest in proximity to the desired finished parts, and warrant proper attention. As earlier described, the substrate  12  is normally mounted on an intermediate carrier  38 , which is then mounted onto the work surface by vacuum or mechanical means. This enables the user to cut completely through the substrate without causing damage to the work surface  36 . Vacuum work surface chuck systems require a vacuum gauge to indicate holding stability and assure operating safety. The two most common intermediate carriers  38  are tape and glass. The substrate  12  is held to the “tacky” side of the tape, while wax is used as the holding medium for mounting on glass. 
     Effective cooling of the diamond blade at the point of contact with the material being processed is a basic essential for any diamond grinding application. The starting point for an efficient cooling system is the supply nozzle configuration  44  which directs the coolant medium. Dual nozzle  44  arrangements, illustrated with reference again to FIG. 2, are superior to single nozzle design in supplying coolant to the critical areas of the diamond blade during the cutting operation. Coolant must be directed at the blade/material interface as well as the leading edge of the blade. The coolant, after leaving this initial contact point, should follow along both sides and the extreme outside edge of the blade in such a manner that it will create intimate contact with these blade surfaces. A single nozzle will satisfy the directional requirement, but will fail to create intimate contact with the blade along its sides. The single stream of coolant, directed at the cutting interface, is split by the diamond blade into two separate streams and deflected away from the sides of the blade. The resulting decrease in cooling efficiency is noted by higher edge chipping damage when processing brittle materials, lower blade life, and erosion on the sides of the diamond blade, which will cause uneven cuts. Dual Nozzles provide two separate streams of coolant to the cutting interface, and at an angle to the cutting edge of the blade, so that each stream will favor one side of the diamond blade after providing the necessary coolant to the leading edge. This complement provides the necessary coolant to all of the critical areas of the cutting blade, with no loss of direction required for removing the debris generated during cutting. Coolant nozzles  44  must provide a full and airless flow of coolant. Additionally, the nozzles should be installed in close proximity to the blade in order to prevent excessive pressure drop of the supply, and to insure that no air will become entrapped in the coolant stream prior to contact with the blade/material interface. Recirculating coolant systems require efficient filtering to remove the particles generated during cutting. Coolant temperatures have a pronounced effect on blade life and cut quality in diamond grinding technology. Test results indicate that coolant temperatures above 80 degrees Fahrenheit should be avoided, while temperatures of 50 degrees or less dramatically improve cutting performance. Refrigeration of the coolant medium is easily adapted to most recirculating systems, and is highly recommended. 
     While a specific embodiments of the invention have been described in detail herein above, it is to be understood that various modifications may be made from the specific details described herein without departing from the spirit and scope of the invention as set forth in the appended claims. Having now described the invention, the construction, the operation and use of preferred embodiments thereof, and the advantageous new and useful results obtained thereby, the new and useful constructions, methods of use and reasonable mechanical equivalents thereof obvious to those skilled in the art, are set forth in the appended claims.