GB2362653A

GB2362653A - Laminated diamond saw blade

Info

Publication number: GB2362653A
Application number: GB0112667A
Authority: GB
Inventors: Robert Carrol Runyon; David Walter Smith
Original assignee: KETECA USA Inc
Current assignee: KETECA USA Inc
Priority date: 2000-05-26
Filing date: 2001-05-24
Publication date: 2001-11-28
Also published as: GB0112667D0

Abstract

A laminated diamond saw blade for minimizing the chipping of a semiconductor wafer or substrate has at least two outside layers of similar electro deposited metal including nickel, and which has had encapsulated diamond particles covered by the nickel. The centre layer of the electrodeposited nickel saw blade encapsulates diamonds that are bonded between the two outside layers and the centre layer is thicker than the outside layers, whereby the centre layer wears faster than the outside layer, so that the face of the saw blade remains substantially square, or slightly concave during the sawing operation so as to minimize chipping. In a modification a self cleaning diamond blade includes a centre layer of electrodeposited nickel containing a homogeneous mixture of diamond particles of a size greater than six microns and a homogeneous mixture of soft particles dispersed throughout the diamond saw blade adapted t break free and form self cleaning pockets in the diamond saw blade.

Description

2362653 1 LAMINATED DIAMOND SAW BLADE AND METHOD OF MANUFACTURE The

present invention relates to a laminated saw blade and its manner of manufacture, and is related to a co-pending application filed by the applicants on the same date and entitled "Diamond saw blade and method of manufacture". Such blades are suitable for dicing semiconductor wafers and substrates of different materials and are sometimes referred to as. dicing blades which are used in saws known as dicing saws. Wafers and substrates of different materials require different dicing saw blades. Saw blades and a method of making saw blades for sawing semiconductors with a minimum of chipping, cracking, and clogging of the saw blades will be described below, by way of example, in the belief that it will enable the invention to be better understood.

In the early years of separating an individual die from a wafer, the wafer was scribed with a v-shaped diamond pointed tool or tools. The wafer was then subsequently broken or cracked along the vee groove, or a scribed line on top of the wafer. This method was abandoned and replaced with diamond saws using diamonds encapsulated in nickel dicing saw blades. The dicing saw blades cut streets or pathways completely through the semiconductor substrates or wafers and theoretically left square sides on each die sawn from the wafer. However, in actual practice dicing saw blades produce very small chips in the top of the wafer and even larger chips at the bottom of the wafer caused by the protruding diamond and the forces exerted by the saw blade, as will be explained hereinafter. The cutting saw blade extends through the thickness of the wafer and produces shear forces in the lower half of the wafer which tear small chips from the wafer as the blade exits. While there is considered to be an optimum cutting speed for each diamond saw blade, 2 dependent on the concentration and the size of diamonds encapsulated in the nickel blade, the larger the diamond the less loading or filling of the blade occurs and, theoretically, the cleaner the blade the faster the cut. The trade off is that larger diamonds create larger destructive forces acting on the wafer and larger chips will occur at the bottom surface than at the top surface of the wafer being cut. Every manufacturer of dicing and saw blades makes blades in different thickness or widths having a range of sizes of different diamond particles. Diamond particle sizes are adjusted for the thickness in the saw blade and the substrate material being cut.

When substrates and wafers are made using plastics, gold, copper and other materials, the heat generated at the cuffing edge of the saw blades melts the soft materials that mix with and form an alloy of wafer dust and the sawn powder of waste material that builds up at the tip and sides of a saw blade. As the blade clogs up it will not cut as fast as a clean saw blade. If the cuffing speed is maintained, the aforementioned compressive forces and shear forces will increase and will destroy the die being sawn or the dicing saw blade.

Diamonds impregnated nickel saw blades are only a few thousandths of an inch thick and are bendable, or flexible. When the diamond saw blades load up with soft materials, globs may form on the side surfaces which, in turn, cause bending forces in the flexible blade that are capable of destroying the saw blade.

It is important from the stand point of production efficiency, as well as for the yield of good die from a wafer to have a diamond saw blade that cuts true and clean until it wears out completely, rather than one that requires replacement due to loading or clogging during operations. Part of the requirement for wearing true and cutting clean is the need for maintaining a square working face, rather than one that becomes bullet nosed in shape at the working face, which causes excessive bottom chipping as the blade leaves the 3 wafer being cut. Accordingly, it would be desirable to provide a dicing saw blade which minimises the effect of the problems described hereinbefore.

Features of a composite diamond dicing saw blade to be described below, by way of example, in the belief that it will enable the invention to be better understood are that it is laminated, that it has different sized diamonds in different layers of the laminations, that it is self cleaning, and that it has diamonds and a fitter of softer particles that break away leaving porous self cleaning pockets in the saw blade.

Other features of a diamond dicing saw blade to be described below, by way of example in the belief that the invention may be better understood, are that it has managed wear which enables a substantially square saw face to be maintained on the diamond dicing saw blade, that the blade wears faster in the centre than at the sides, that the blade is harder at the edges and wears slower at the edges than at the centre face, that the blade has different wear characteristics across the face of the saw blade, and that a novel wear characteristic is provided on the face of a diamond dicing saw blade that enables the shear forces to be changed and minimizes the occurrence of bottom chipping.

A particular laminated saw blade to be described below, by way of example, in the belief that it will enable the present invention to be better understood, has a centre portion that wears faster than the side portions, thus maintaining a square or substantially square cutting face, or a concave face that cuts clean by and reduces bottom chipping.

A previously proposed arrangement will now be described with reference to Fig. 1 of the accompanying drawings, and arrangements which it is believed will enable the invention to be better understood will now be described with reference to Figs. 2 to 9 of the accompanying drawings.

4 In the drawings:- Figure 1 is an enlarged section, in elevation, of the cutting edge of a previously proposed hub type mounted diamond dicing saw blade as it cuts through the bottom edge of a semiconductor wafer, Figure 2 is an enlarged section, in elevation, of a dicing saw blade before any wear has occurred at the working face edge, Figure 3 is an enlarged section, in elevation, of a saw blade shortly before it reaches the bottom edge of a semiconductor wafer, Figure 4 is an enlarged section, in elevation, of the saw blade of Figure 3 as it passes through the bottom edge of the semiconductor wafer and cleans and smooths the bottom edges of the wafer with minimum chipping, Figure 5 is a detailed enlarged section, in elevation, of a cutting edge of a laminated diamond dicing saw blade having controlled wear of the working face before a first cut, Figure 6 is a detailed enlarged section, in elevation, of the diamond dicing saw blade shown in Figure 5 after burn in, Figure 7 is a detailed enlarged section, in elevation, of another exemplary arrangement having self cleaning and controlled wear characteristics which are useful for cutting plastic and soft metals known to cause loading and clogging, Figure 8 is a side view of a diamond dicing saw blade cutting through a semiconductor wafer showing relative movement of the blade relative to the wafer, and Figure 9 is a greatly enlarged section, in elevation, of the cutting face of a diamond dicing saw blade as it reaches the bottom face of a wafer showing the novel chip or chips that break out due to the cutting forces acting on the face of the saw blade.

Refer now to Figure 1, which shows an enlarged section, in elevation, of the cutting edge or tip of a diamond dicing saw blade (10) as it passes through the thickness of a wafer, or a semiconductor carrier (11), causing chips to occur at both the top surface (12) and the bottom surface (13). The bullet nose (14) formed on the dicing saw blade (10) is a natural and known occurrence in which forces cause the break-out of large chips (15) from the bottom surface (13).

The saw blade causes small chipping proportional to the size of the diamonds in the cutting blade (10) at the surface edge (16).

Refer now to Figure 2, which shows an enlarged section, in elevation, of the diamond dicing saw blade (10) before it has been burned in to form the bullet nose (14) described with reference to Figure 1. The dicing saw blade (10) when first produced has a substantially square working face (1 4A) With small rounded fillets at the side edges. As the blade passes through the wafer (11) and reaches the bottom surface (13), cracks, formed by force on the fillets, cause chips to occur which are larger than the path or street being cut by the diamond dicing saw blade (10). When the blade is first used, these chips are smaller than the aforementioned chips (15) shown with reference to the previously proposed arrangement of Figure 1. However, shortly after burning in the diamond dicing saw blade (10), it becomes bullet nosed and continues to be bullet nosed until it is worn out or destroyed.

Referring now to Figure 3, there is shown an enlarged section, in elevation, of a diamond dicing saw blade (30) shortly before it reaches the bottom edge (13) of a semiconductor wafer (11). The novel saw blade (30) is made and formed in a manner that produces a controlled wear face (17), which 6 appears, in Figure 3, as a concave working face, or a dog boned shape to be described in detail hereinafter. The novel working face (17) causes the chips (18) to be controlled in shape so that the chipping occurs underneath the diamond dicing saw blade, and not at the outside edges thereof.

Refer now to Figure 4, which shows an enlarged section, in elevation, of the novel saw blade (10) after it has passed through the bottom edge (13) of the semiconductor wafer (11), showing how it cleans out the edges left by the chipping shown in Figure 3, so as to provide minimum chipping or diamond scratch marks at both the bottom surface (13) and the top surface (12) Refer now to Figure 5, which shows a detailed enlarged section, in elevation, of the cutting edge of one preferred arrangement of the laminated diamond dicing saw blade having controlled wear of the working face (1 7A) before a first cut is made. The novel saw blade (30) has a laminate with a first layer (21), on which is deposited a second layer (22) on which a third layer (23) is deposited to form a novel laminated diamond dicing saw blade in which the sizes of the diamonds in the two outside layers (21 and 23) are preferably maintained substantially identical for purposes to be explained in greater detail hereinafter. In contrast thereto the centre section (22) is preferably made from diamonds having a size and concentration that may be varied to suit the task of cutting a particular piece of material. For example, larger diamonds may be used in the centre layer (22) to control the speed of cutting. Smaller diamonds may be used in the outside layers (21 and 23) to control the scratching or minimal cracking that occurs at the top and bottom surfaces of the wafer. Further, the diamond composition in the centre layer (22) may be made self cleaning by adding softer particles which break away and cause porous like pockets that enhance self cleaning. When the preferred arrangement does employ softer particles, they preferably have the same size as the selected size diamond particles in the centre layer (22) and replace a percentage of the diamonds so as provide a compbsition by volume of the original consistency of 7 diamonds. It was observed that the softer glass like particles broke away and caused a clean controlled weadng at the working face (1 7A) The controlled wear maintains a square working face as will now be explained.

Refer now to Figure 6 showing the novel laminated diamond dicing saw blade (30) after burn in. It will be noted that the three layers (21, 22 & 23) maintain very sharp square edges and the working face (17) has a slight concave portion (25), as the edges (24) remain substantially square. This is a result of having the correct composition and mixture of diamonds and soft particles in the centre (22). While a frit or glass includes a preferred soft particle, it is possible to use particles of synthetic gem stones, such as sapphires andlor particles containing fullerene, which is a known hard form of carbon.

Refer now to Figure 7, which shows a section, in elevation, of another preferred arrangement of a diamond dicing saw blade (40). Before describing the saw blade (40) in detail it will be understood that some of the newer types of semiconductor die are either encapsulated in layers of plastics, or produced as semiconductor packages in plastics that include a plurality of die that must be separated one from another. In order to cut the die one from another, it is necessary to cut through multiple layers of plastics, some of which are moulded and others in laminated form. The diamond impregnated saw blades previously available are not capable of cutting any plastics without clogging and filling long before the blade shows wear, even to a slight degree. This is to say that the diamond blade really does not wear out cutting the plastics, but it must be recycled and cleaned if it is to be used again as an effective saw blade. The blade is removed from the saw to remove the build up of plastics particles, which effectively reduces the saw blade to a smooth cutting wheel. The particular preferred saw blade (40) is a controlled wear saw blade in which there are diamond particles (DIP) and soft particles (SP) formed as a mass of homogeneous particles (HP) in a single saw blade encapsulated in an electro- 8 deposited matrix of nickel. The same technology, which is used to deposit diamonds and nickel simultaneously, is used to deposit both sp and dp particles simultaneously in the same continuous process, until a thick blade (40) is built up which is capable of cutting plastics with a controlled wear. The new semiconductor devices referred to as ball grid array (BGA), wafer scale array (WSA) and chip scale (CS) with copper on lead frames all present problems which result in filling and clogging. When the novel blade shown at 40 in Figure 7 is of the proper composition and percentage of SP particles and DP particles, it is possible to load up the working face of the blade 40 while it is cutting through the plastics portion of the semiconductor device, and, as it cuts through the hard portions, such as the metal lead frames and the silicon wafer portion, the blade wears and self cleans itself in the same continuous operation.

Refer now to Figure 8, which shows a side view of a hubless diamond dicing saw blade cutting through a sem iconductor wafer, and which shows the relative movement of the blade (26) and the wafer (11). It will be noted that the direction of the blade and the wafer causes maximum chipping at the bottom surface (13) of wafer (11) at the chip point (15). In the illustration shown in Figure 8 the hubless blade (26) is an annular disk that is clamped in a hub type chuck. A hub type diamond saw blade is electro-deposited directly onto a flange of a disposable hub.

Refer now to Figure 9, which shows a greatly enlarged section, in elevation, of the cutting face of yet another preferred diamond disk saw blade as it is reaches the bottom face (13) of a wafer (11), and which shows the chip or chips (18) as they break out from the wafer (11). In the drawings, there has been added to the working face (17) of the blade (30) a parallel array of arrows indicating the forces and the direction of the forces exerted by the saw blade (30) as it moves through the wafer (11). It will be noted that the arrows which are directly under the outside layers (21 & 23) form a concentrated force which cause fraction lines (F1 & F2) to break vertically under the blade (30), but which 9 do not fracture in a line which exceeds the width of the blade (30). Thus after breaking out the chips or chip (18), the blade continues downwardly and cleans up the jagged working face of the fracture lines (F1 & F2) leaving the smooth surface described hereinbefore with reference to the saw blade in Figure 4.

Having explained preferred dicing saw blades of the type which is both self cleaning and having controlled wear, so as to maintain a desired working face profile, it will be understood that the size of the diamonds in the outside layers (21 & 23) will determine the smoothness of the side wall cut. If they are smaller than the fast cutting diamonds embodied in the centre layer (22) a smooth cut results. The composition of the diamonds and the soft particles in the centre layer (22) may be controlled so that they break away continuously and expose new diamonds and a clean working surface. The hardness and the composition of the material or materials that are being cut by the diamond saw blade will determine the composition of particles required in centre layer (22) - For example, hereinbefore it was impossible to cut the plastics impregnated ball grid array stripes to separate the dies one from another without loading up the saw blade before any wear to the blade was apparent. Thus the blade had to be removed and reworked in order to be used again, or thrown away if it was beyond repair. Some manufacturers cutting ball grid arrays encapsulated in plastics layers would use a saw blade of the previously proposed type until it was loaded with plastics and other material, they would then stop the manufacturing operation and use some form of dressing tool to remove the filled or clogged working face of the dicing blade, thus losing manufacturing time as well as destroying the working life of the dicing blade in the process. Having described a preferred laminated multi-layered diamond dicing saw blade (30) it will be understood the techniques used in the above mentioned co-. pending application may be used to equalize the outside cutting faces of the outside layers (21 & 23). For example if layer 21 is laid down on the base electrode and layer 22 is deposited thereon, and layer 23 is deposited on layer 22, then the outside working face of layer 21 is smooth and the outside working face of layer 23 has exposed diamonds not fully encapsulated in the nickel. In our copending application, it is explained that an additional layer of nickel may be applied on top of the diamonds at the outside surface of layer 23 and both outside layers etched or simultaneously polished to equalize and expose diamonds on the outside surfaces (21 & 23). The same technique may be applied to the novel diamond dicing saw blade (40) described above in which the outside surfaces (27 & 28) are post treated to equalize the diamond exposure on those surfaces.

It will be understood that, although particular arrangements have been described, by way of example, in order to enable the invention to be better understood, variations and modifications thereof, as well as other arrangements may be conceived within the scope of the appended claims. For example, in one arrangement the first, second and third layers are deposited as an annular ring on the outer perimeter of a prefabricated hub base, the second layer is thicker than the first and third layers, the diamond concentration in the first and third layers is 30 to 45 per cent by volume, and the diamond concentration in the second layer is up to 10 per cent less than the concentration in the first and third layers 11

Claims

1. A method for controlling the wear of the face of a diamond saw blade, including the steps of masking a mandrel or base for receiving electro-deposited nickel in the shape of a saw blade, depositing a first outside layer of nickel with diamonds of a first size or concentration, depositing a second layer of nickel on top of the first layer with diamonds of a second size or concentration, and depositing a third layer of nickel on top of the second layer with diamonds substantially identical to those in the first layer, the second layer having faster wear characteristics than the first and the third layers, so that the laminated diamond saw blade does not form a rounded or bullet nose during sawing operations.

2. A method as claimed in claim 1 wherein the diamond saw blade is a hubless saw blade, the step of depositing a first outside layer includes depositing nickel with encapsulated diamonds on a flat sheet of conductive metal, and wherein nickel is removed from the first and third layers to expose an equal amount of diamonds on the sides of the saw blade.

3. A method as claimed in claim 1 wherein the step of depositing a second layer includes depositing a lesser concentration of diamonds than in the'first and third layers.

4. A method as claimed in claim 1 wherein the step of depositing the first 30 second and third layers includes depositing particles of the same concentration and size, and the step of depositing the second layer includes depositing a 12 small percentage of particles softer than diamonds to complete the concentration in the second layer.

5. A method as claimed in claim 1 which includes plating a covering layer of nickel on top of any exposed diamonds on top of the third layer to equalize the exposed diamonds on the outside of the first and the third layers.

6. A method as claimed in claim 5 which includes etching one or more outside layers to equalize better the exposed diamonds in the outside of the first and the third layers.

7. A method as claimed in claim 1 wherein the step of depositing the first and third layers includes depositing smaller diamonds than those deposited in the second layer, so that the edges of the object being cut are smooth, while maintaining a faster cutting speed with a substantially square edge saw blade.

8. A method as claimed in claim 1 wherein the steps of depositing the first and third layers of nickel includes depositing harder nickel layers than the nickel deposited in the second nickel layer, so that the second layer wears faster than the first and third layers.

9. A method as claimed in claim 1 wherein the first, second and third layers are deposited as an annular ring on the outer perimeter of a prefabricated hub base.

10. A method as claimed in claim 1 wherein the second layer of nickel includes particles of an encapsulated material softer than diamonds, and the method includes the step of removing the softer particles during a sawing operation to provide a self cleaning diamond saw blade.

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11. A laminated diamond saw blade for minimizing the chipping of semiconductor substrates, including at least two outside layers of similar electro-deposited metal including nickel having encapsulated diamond particles covered by the nickel, 5 a centre layer of electro- deposited nickel and encapsulated diamonds bonded between the two outside layers, wherein the centre layer is thicker than the outside layers, in which the centre layer wears faster than the outside layers so that the face of the saw blade remains substantially square or slightly concave during a sawing operation in order to minimize chipping.

12. A laminated diamond saw blade as claimed in claim 11 wherein the diamond concentration in the centre layer is lesser than the concentration in the outside layers.

13. A laminated diamond saw blade as claimed in claim 12 wherein the centre layer includes particles of similar size material to the encapsulated diamonds but which are soft enough to break loose, leaving porous pockets during a cutting operation.

14. A laminated diamond saw blade as claimed in claim 12 wherein the diamond concentration in the outside layers is 30 to 45 percent by volume.

15. A laminated diamond saw blade as claimed in claim 14 wherein the diamond concentration in the centre layer is up to 10 percent less than the concentration in the outside layers.

16. A laminated diamond saw blade as claimed in claim 11 wherein the size of the diamond particles entrapped in the outside layers is greater in size than the diamonds in the centre layer.

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17. A laminated diamond saw blade as claimed in claim 11 wherein, the size of diamond particles entrapped in the outside layers is smaller in size than the diamonds in the centre layer.

18. A self cleaning diamond saw blade, including a centre layer of electrodeposited nickel containing a homogeneous mixture of diamond particles of a size greater than six microns, and a homogeneous mixture of soft particles dispersed throughout the diamond saw blade adapted to break free and form self cleaning pockets in the diamond saw blade, the outside surfaces of the centre layer being processed to provide an equal exposure of diamond particles.

19. A self cleaning diamond saw blade as claimed in claim 18 including diamond particles and break-away particles, the ratio by volume of breakaway particles replacing up to thirty percent by volume of diamonds, the same volume of electro-deposited nickel remaining substantially unchanged and the blade strength remaining substantially unchanged with the enhanced self cleaning ability.

20. A method of controlling the wear of the face of a diamond saw blade as claimed in claim 1 substantially as described here with reference to Figs. 2 to 6, 2 to 4 and 7, and 2 to 4 and 8 and 2 to 4 and 9 of the accompanying drawings.

21. A laminated diamond saw blade as claimed in claim 11 including an arrangement substantially as described herein with reference to any one of Figs. 2 to 9 of the accompanying drawings.

22. A self cleaning diamond saw blade as claimed in claim 18 including an arrangement substantially as described herein with reference to any one of Figs. 2 to 9 of the accompanying drawings.