WO2008003973A1

WO2008003973A1 - A method and apparatus for the formation of coatings on drills

Info

Publication number: WO2008003973A1
Application number: PCT/GB2007/002515
Authority: WO
Inventors: Dennis Teer
Original assignee: Teer Coatings Limited
Priority date: 2006-07-07
Filing date: 2007-07-05
Publication date: 2008-01-10
Also published as: GB0613510D0

Abstract

The invention relates to a method and apparatus for the application of, typically multilayered, coatings onto a batch of drill bits which are mounted on a carrier which is rotatable within a coating chamber. The apparatus and method is of particular use in relation to the coating of micro drills which are drills of a relatively small diameter and the coating apparatus can be provided in a closed field configuration.

Description

A Method and Apparatus for the Formation of Coatings on Drills

The invention which is the subject of this application relates to a method and apparatus for the formation of coatings on at least the working function portion of a drill bit and in particular, although not necessarily exclusively, on the formation of effective coatings on the working function portions of drills which are known as micro drills and which are typically of a. relatively small diameter such as, for example, of diameters down to a size of typically 0.1 mm, or less .

Drill bits typically comprise a first end portion which is provided to be substantially circular in cross section and which portion is used to clamp or grip the drill bit by the apparatus provided to rotate the same to perform the drilling operation. At the opposing end from said portion are a series of flutes, typically of a helical formation, and which flutes define the working function portion which leads to a point at the opposing end and which, when the drill bit is rotated, the flutes edges cause the drilling of a hole to be achieved. Each of the flutes is provides with a cutting edge and for the drill bit to be effective in forming the drilling operation, it is important that the cutting edge, as well as the remainder of the dimensions of the flutes and working portion, are formed of appropriate material and are formed in appropriate shape characteristics.

One type of drill which is increasingly used is a type referred to as a micro drill. A micro drill is a relatively small diameter drill which s used for many different functions but typically, is used to perform a drilling operation on items such as printed circuit boards (PCB's) . PCB's are, by their nature, required to be manufactured to relatively small tolerances and hence it is critical for the drilling operations which are performed on the same, to be done accurately.

Typically, the material from which the drill bit is itself manufactured, while suitable to allow the manufacture of the bit, is not the most suitable material to be used in contact with the item which is to be drilled. For this reason, it is known to coat drill bits with further materials or a combination of materials to provide a drill bit with the required external surface formed of the material to allow a desired drilling operation to occur. Most conventional coating operations are satisfactory for use with larger drill bits where there are larger acceptable tolerances. However, with micro drill, where tolerances are small, the conventional coating techniques which are used, are found to be problematic.

It is known that the coating of micro drills has been performed using arc coating techniques and apparatus . However, in practise, the arc coating technique produce relatively rough coatings on the drill bits and, therefore provide problems in the use of micro drills as rough coatings should be avoided because the roughness of the coating, when in contact with the item to be drilled, during the drilling operation, means that relatively uneven, rough edged holes are formed which fall outside the required tolerances for the drilled holes.

A further problem is that roughness of the coating drills can cause dragging or joining of the copper layers of the PCB which can cause shorting to occur between the layers and modification of the PCB .

Thus, although it is known to coat micro drills with layers of material, using arc techniques, the resultant drill bit which is formed, is often unsatisfactory and, in certain instances, may be unusable for the specific purposes required, such as for example, drilling holes in a PCB.

The aim of the present invention is to provide a coating method and finished drill which allows the method and apparatus to be used for the coating of micro drills and to provide coatings on the same which are relatively smooth and thereby meet the tolerance requirements for the holes which are formed using said drills .

In a first aspect of the invention, there is provided a method for applying a coating of at least one layer of material onto at least one drill bit, said method comprising the steps of placing the at least one drill bit into a coating chamber, forming a substantial vacuum in said chamber, and selectively operating a plurality of magnetrons in said chamber, at least one of said magnetrons including a target of a material to be deposited from the magnetron onto the at least one drill bit to form at least one layer on at least the working portion of said drill bit.

In one embodiment, the material is applied to form a coating over substantially all of the drill bit.

In one embodiment, at least one of the magnetrons provided in the coating chamber is an unbalanced magnetron. Typically, all of the magnetrons are unbalanced magnetrons .

In one embodiment, one or more of the magnetrons includes a target of Cr and a further magnetron includes a further metal target.

Typically, a plurality of layers of coating material are applied, the composition of each of said layers at least partially defined by the selective operation of one or more of the magnetrons during the formation of said layer.

In one embodiment, different sequences of operation of magnetrons and/or different periods of time of operation of magnetrons are selected to form a series of layers .

In one embodiment, the coating is in the form of a series of iianocomposite layers.

Typically the magnetrons are arranged at spaced intervals around the external wall of the coating chamber and facing inwardly of said chamber such that the at least one drill bit provided in the chamber is effectively surrounded by magnetrons.

In one embodiment, batches of drills are coated at a time, each batch provided to be located in the coating chamber.

In one embodiment, each batch of drills is mounted on a rotatable carrier such that the drills rotate about the rotational axis of the carrier. This therefore avoids the need for each of the drills to be rotated about its own axis as is conventionally the case with conventional drill bits.

In one embodiment, each of the drill bits in the batch is a micro drill.

In one embodiment, the method utilises a closed field unbalanced magnetron sputter ion plating technique.

In one embodiment, the method is used to sputter deposit material to form a multi-layered coating of between 0.5 and 6 microns thickness. In a preferred embodiment, the thickness of the multilayered coating applied is between 1.5 and 2.5 microns thickness.

In one embodiment the coating which is applied has a relatively" smooth external surface thereby providing a low friction value between the drill bit and the workpiece in which a hole is to be drilled.

In one embodiment, the outer layer o f the coating is formed as a diamond like carbon (DLC) coating to further reduce the friction value between the drill bit and the workpiece.

In one embodiment, the method incorporates the step, once the coating has been applied, of regrinding the drill bit to form the finished working portion.

Typically, the provision of the batch of drills in the coating chamber, surrounded by said magnetrons, means that a uniform coating flux is created within the coating chamber and as a result, uniform coatings are applied to each of the drill bits in the batch. This therefore means that the impracticality of rotating each of the drill bits about its own axis, is not a problem as the uniform coating can be applied without the need to rotate the drill bits individually.

In one embodiment, the coating applied is chemically insoluble in copper.

In one embodiment, the coating applied is a complex multilayer coating based on CrN.

In one embodiment, the drill bits which are coated using this method have a diameter of down to 0.1 mm, but smaller diameter drill bits can also be coated. In one embodiment, the method includes the step of depositing a layer of material onto the drill bit as a first layer, which layer acts as an adhesion layer to encourage the subsequently deposited material to adhere to the drill bit.

In a further aspect of the invention there is provided a drill bit with a coating applied thereto using the method as herein described.

In a further aspect of the invention there is provided apparatus for the formation of a multilayered coating on a batch of drill bits, said apparatus comprising a coating chamber, means for drawing a vacuum in the coating chamber, a plurality of magnetrons, each of said magnetrons including a target of a material to be selectively applied into the coating chamber, and a means for introducing one or more gases into the coating chamber, control means for allowing the selective operation of said magnetrons to allow selected coating compositions to be applied as layers to form the multilayered coating on a plurality of drill bits, said drill bits held on a holder located within the said chamber and towards which said magnetrons deposit material.

Typically the magnetrons are arranged in a closed field manner in the coating chamber.

In one embodiment, the magnetrons are unbalanced magnetrons .

In one embodiment, one or more magnet arrays are located intermediate said magnetrons so as to provide a closed field configuration and allow a substantially uniform coating flux to be created in the coating chamber at least in the area in which the holder or carrier is located. In one embodiment, the earner is rotatable about a rotational axis and the drills are held in a stationary position on said carrier.

Specific embodiments of the invention will now be described with reference with the accompanying drawings, wherein:-

Figure 1 illustrates a micro drill bit of a type to be coated in accordance with the invention;

Figures 2a and b illustrate photographs of holes cut by a drill coated in accordance with the current invention; and

Figures 3a and b illustrate two closed field coating apparatus configurations which can be used to apply the coating in accordance with one embodiment o f the invention.

Referring firstly to Figure 1 , there is illustrated a micro drill bit 2 of the type to be coated in accordance with the invention. The micro drill bit incorporates a first portion 4 which is utilised to grip the drill bit to perform the drilling operation. At the opposing end, a working portion 6 is provided which has a series of flutes 8 formed in and leading to a point 10. In use, the edges of the flutes, perform the cutting and drilling operation and, when one considers that the diameter of the micro drill bit can go down to approximately 0.1 mm and perhaps smaller, it will be appreciated that the edges of the flutes are of necessity very fine and it is imperative, in order to perform the cutting operation, that the same be retained during the subsequent coating of the drill bit.

It has been found that using the conventional arc coating technique the coating which is applied is relatively rough and, as a result, the holes which are formed by the edges of the flutes, when using the drill bit, are themselves relatively rough. The roughness of the drilling operation, can cause dragging of the various copper layers of a printed circuit board and the dragging has the effect of causing contact between the respective layer which in turn, can cause short circuiting of the printed circuit board in use. It will therefore be appreciated that smooth holes are required to be formed using these micro drills.

Apparatus which can be used in accordance with the invention is illustrated in plan in Figures 3a and b with the top portion of the coating chamber removed so as to allow the components to be illustrated.

In both Figures 3a and b, there is shown a coating chamber 12 with an external wall 14 which defines the side of the chamber. Mounted at spaced locations around the wall, are a series of magnetrons 16, each having a target of material 18 of a type which is selectively applied by sputter deposition from the targets by selective operation o f the magnetrons. The magnetrons 16 are provided in a closed field configuration which means that the magnetic polarity of the magnetrons is arranged such that adjacent magnetrons have reverse magnetic polarity as is illustrated in Figure 3a. Alternatively, and as shown in Figure 3b magnet arrays 17 can be provided between the magnetrons and in this case, it is the magnet array and adjacent magnetrons which have the respective reverse polarities so as to form a closed field configuration.

The use of sputtering apparatus with the magnetrons held in a closed field configuration allows the generation of a uniform coating flux within the coating chamber which is found to be particularly effective in allowing a uniform application of the coating material onto the articles which are to be coated, in this case, drill bits 20.

In this case, the drill bits 20 are mounted on a carrier 22 located substantially centrally of the coating chamber 12. The carrier 22 is provided to be rotatable about an axis 24 as shown as the material is sputter deposited from these magnetrons which selectively operated. As the drill bits can be held in a fixed position on the rotating carrier 22, there is no need for the drill bits themselves to be rotated about their own axis as it is found in accordance with the invention, that the uniform coating flux which is created throughout the chamber, and in which the drill bits are positioned, ensures that the uniform coating of the drill bits can be achieved.

The material which is applied to form the coating on the drill bits, can be chosen to suit particular subsequent uses of the drill bits . For example, if the drill bits are to be used to drill holes in PCB's, which include copper layers, the material applied to coat the drill bit, is required to be chemically insoluble with regard to copper.

In certain instances, the coating layers which are formed, include a first layer which acts as an adhesion layer to ensure that the subsequent coating layers adhere to the drill bit, followed by one or more layers of required material such as CrN and in turn, followed by an external layer of diamond-like carbon (DLC) to provide a particularly smooth, low friction external coating surface which, in turn, means that the holes which are formed in the PCB or other workpiece, are particularly smooth. The selective operation of the magnetrons and use of the same for sputter deposition of the material, allows the formation of nano composite layers and which are found to have a relatively low friction, be smooth and be relatively hard.

It is preferred that the apparatus used to apply the coating is provided in a Closed Field configuration as shown in Figures 3a and b in contrast to other coating systems as it is found that in the other systems the necessary level of adhesion of the coating material to the drill is difficult to achieve. Other systems can obtain good adhesion by using an arc source to produce metal ions which are used to ion clean the substrates prior to deposition by a magnetron technique, but metal droplets are produced and deposited during this cleaning operation and produce a rough coating.

The use of a closed filed unbalanced magnetron sputter ion plating configuration of the type illustrated in Figures 3a and b allows the production and application of a coating to the drill which has good adhesion, no droplets and therefore a smooth coating is achieved. For very fine drills, down to 0.1mm diameter for example, the sharp cutting edges really do make severe demands on the adhesion but it is found that the adhesion obtained in accordance with the invention is sufficient to withstand those demands.

In addition to good adhesion, the coating applied has to be relatively hard and by using 4 magnetrons in the Closed Field configuration nanoscale multi layer coatings can be effectively applied with a hardness value in excess of 3500HV.

In one embodiment the coating which is applied is CrAlTiN or CrAlMoN but many others are possible.

The micro drills, themselves are typically 0.1 to 0.4mm diameter and formed of WC-Co material. Drilling conditions are typically 120,000 to 130,000rpm with a feed rate of over 1800mm per minute. Uncoated drills of this type have a life of between 1200 and 3500 holes. The coated drills have a life of at least 7000 to 8000 holes but we have achieved over 10,000 holes in some cases. Referring to Figure 2 there are shown two photographs of holes drilled in a 5Cu flexible foil using an ST 0.25mm drill in accordance with the invention and using a Hitachi-mk30d drilling machine. Figure 2a shows a cross section through a hole which has been drilled when the drill has been used to drill 5000 holes and Figure 2b shows a cross section through a hole cut using the drill after the same has been used to cut 10000 holes . Although the smoothness of cut in Figure 2b is less than that in Figure 2a, the same is still acceptable and the lifetime of the drills which is obtained far outlasts conventional drills of this type and avoids the "dragging" of the copper layers.

Thus, in conclusion, there is provided apparatus and a method which allows the formation o f a nanocomposite multilayer coating on relatively small drills such as micro drills . The coating which is applied is found to be controllable and therefore allow an effective smooth, low friction and hard wearing coating to be formed on drills of a size which would not be possible using the conventional arc coating techniques.

Claims

1. A method for applying a coating of at least one layer of material onto at least one drill bit, said method comprising the steps of placing the at least one drill bit into a coating chamber, forming a substantial vacuum in said chamber, and selectively operating a plurality of magnetrons in said chamber, at least one of said magnetrons including a target of material to be deposited from the magnetron onto the at least one drill bit to form at least one layer on at least the working portion of said drill bit.

2. A method according to claim 1 wherein the material is applied to form a coating over substantially all of the external surface of the drill bit.

3. A method according to claim 1 wherein at least one of the magnetrons provided in the coating chamber is an unbalanced magnetron.

4. A method according to claim 3 wherein all of the magnetrons are unbalanced magnetrons .

5. A method according to claim 1 wherein one or more of the magnetrons include a target of Cr and a further magnetron includes a further metal target.

6. A method according to claim 1 wherein a plurality of layers of coating material are applied, the composition of each of said layers at least partially defined by the selective operation of one or more of the magnetrons during the formation of said layer.

7. A method according to claim 6 wherein different sequences of operation of magnetrons and/or different periods of time of operation of the magnetron are selected to form a series of layers in a previously defined form.

8. A method according to claim 6 wherein the coating is in the form of a series of nano-composite layers.

9. A method according to claim 1 wherein the magnetrons are arranged at spaced intervals around the external wall of the coating chamber and facing inwardly of said chamber such that the at least one drill bit provided in the chamber is effectively surrounded by magnetrons .

10. A method according to claim 1 wherein batches of drill bits are coated at a time.

1 1. A method according to claim 10 wherein each batch of drill bits is mounted on a rotatable carrier such that the same rotate about the rotational axis of the carrier.

12. A method according to claim 1 wherein each of the drill bits in the batch is a micro drill.

13. A method according to claim 1 wherein the method utilises a closed field unbalanced magnetron sputter ion plating technique.

14. A method according to claim 13 wherein the method is used to sputter deposited material to form a multilayered coating of between 0.5 and 6 microns in thickness.

15. A method according to claim 14 wherein the thickness of the multilayered coating applied is between 1.5 and 2.5 microns in thickness .

16. A method according to claim 1 wherein the coating which is applied has a low friction value between the drill bit and the workpiece in which a hole is to be drilled using the drill bit.

17. A method according to claim 1 wherein the outer layer of the coating is formed as a diamond-like carbon (DLC) coating.

18. A method according to claim 1 wherein, once the coating has been applied a regrinding of the drill bit is performed to provide a working portion of the drill bit.

19. A method according to claim 1 wherein the at least one drill bit which is to be coated, is surrounded by a uniform coating flux within the coating chamber.

20. A method according to claim 1 wherein the coating applied is chemically insoluble in copper.

21. A method according to claim 1 wherein the coating which is applied is a complex multilayer coating based on CrN.

22. A method according to claim 1 wherein the method includes a step of deposition a layer of material onto the drill bit as a first layer, which layer acts as an adhesion layer to encourage the subsequently deposited material to adhere to the drill bit.

23. A drill bit with a coating applied thereto using the method as herein described with reference to claims 1 to 22.

24. Apparatus for the formation of a multilayer coating on a batch of drill bits, said apparatus comprising a coating chamber, means for creating a vacuum in the coating chamber, a plurality of magnetrons, each of said magnetrons including a target of a material to be selectively applied into the coating chamber, and a means for introducing one or more gases into the coating chamber, control means for allowing the selective operation of said magnetrons to allow selective coating compositions to be applied as layers to form the multilayered coating on a plurality of drill bits, said drill bits held in a holder located within said chamber and towards which said magnetrons deposit material.

25. Apparatus according to claim 24 wherein the magnetrons are arranged in a closed field manner in the coating chamber.

26. Apparatus according to claim 24 wherein the magnetrons are unbalanced magnetrons .

27. Apparatus according to claim 24 wherein one or more magnet arrays are located intermediate said magnetrons so as to provide a closed field configuration and allow a substantially uniform coating flux to be created in the coating chamber at least in the area in which the holder or carrier is located.

28. Apparatus according to claim 24 wherein the carrier is rotatable about a rotational axis and the drills are held in a stationary position on said carrier.