Single-blade drill for printed circuit boards

Abstract

The present invention provides a single-blade drill for printed circuit boards that can minimize the residue of burrs even when wear remains on the corners of the cutting edge. [Solution] A single-blade drill for printed circuit boards, wherein in the margin portion 9, between a first position P1 which is the position closest to the tip of the drill body and does not include both the relief surface 10 on the first land portion 7 side and the relief surface 10' on the second land portion 8 side, and a second position in the margin portion 9 which is located 0.25 mm away from the base end of the drill body of the margin portion 9 toward the tip of the drill body, the angle θ formed by the line connecting the first leading edge X and the drill rotation center axis O on a flat cross section perpendicular to the drill rotation center axis O and the line connecting the second leading edge Y and the drill rotation center axis O is configured to gradually increase from the first position P1 to the second position P2.

Description

Technical Field

[0001] The present invention relates to a single-edge drill for printed wiring boards.

Background Art

[0002] Many of the electronic components used in consumer electronic devices such as smartphones and notebook computers are produced using substrates (hereinafter referred to as "HDI substrates") manufactured by the build-up method.

[0003] In this HDI substrate, due to the high performance and miniaturization of the electronic devices, the density of the mounted components and circuits has increased. Along with this, improvements in performance such as the heat resistance of the substrate material and the stability of electrical signals are required. As a result, many of the substrate materials are required to have characteristics such as low CTE (coefficient of thermal expansion), low Dk (relative permittivity), and low Df (dissipation factor). In order to achieve these characteristics, the application of high-elasticity and low-thermal-expansion glass and high filling of inorganic fillers are carried out on the substrate, increasing the cutting load on the drill and making the wear of the drill progress easily, and the difficulty of drilling has become high.

[0004] Under such circumstances, in the processing of HDI substrates, single-edge drills with characteristics of high rigidity and long processing life and excellent workability are often used.

[0005] With regard to this single-flute drill, the applicant has proposed the drill disclosed in Patent Document 1. This drill has two helical chip evacuation grooves (a first helical chip evacuation groove and a second helical chip evacuation groove), the first and second chip evacuation grooves are positioned asymmetrically with respect to the drill's rotation center, the land portion behind the first chip evacuation groove is set to be larger than the land portion behind the second chip evacuation groove, and the edge of the wall surface of the second chip evacuation groove facing the drill's rotation direction is set to be embedded with the cutting edge. As a result, thickness (rigidity) is ensured while suppressing deterioration of chip evacuation performance, the land portion behind the second chip evacuation groove does not directly receive cutting resistance, and hole position accuracy (the amount of deviation between the target hole machining position in the program and the actual machined position) is improved compared to conventional two-flute drills. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2006-150553 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] In the processing of HDI boards, it is common practice to place an aluminum plate or a resin-coated aluminum plate on top of multiple stacked boards (printed circuit boards) as a backing plate to improve the centering of the drill before drilling.

[0008] Incidentally, when a single-blade drill cuts in a spiral pattern with only one cutting edge, elongated chips are generated on the upper surface of the backing plate 30 shown in Figure 8, connecting to the edge of the hole being machined. In particular, if the corner of the cutting edge 22 shown in Figure 10 is worn, as shown in Figure 8, elongated whisker-like (thread-like) chips tend to remain on the upper surface of the backing plate 30, connected to the edge of the hole even after the drilling process is complete. If these remaining chips (hereinafter referred to as whisker burrs 40) are located at a drilling position to be drilled thereafter, the drill may run over these whisker burrs 40 (by stepping on the whisker burrs 40), potentially causing sudden abnormalities in hole position accuracy or even drill breakage.

[0009] When the drill is new or nearly new, as shown in Figure 9, the trajectory a drawn during drilling at point A forming the outer circumference of the drill on the leading edge (the ridge formed by the first land 21 and the first chip evacuation groove 20, hereinafter referred to as the "first leading edge") of the land behind the first chip evacuation groove 20 (hereinafter referred to as the "first land 21") relative to the direction of drill rotation (direction of the arrow with the symbol T) is approximately equal to the trajectory b drawn during drilling at corner B of the cutting edge 22 in the part where wear has not progressed. Therefore, it is thought that the chips generated at the edge of the hole are thin and removed by the leading edge (the ridge formed by the second land 24 and the second chip evacuation groove 23, hereinafter referred to as the "second leading edge") of the land behind the second chip evacuation groove 23 (hereinafter referred to as the "second land 24") relative to the direction of drill rotation. Traditionally, before wear reduced the cutting function and made it impossible to meet the required quality standards for machined holes, such as hole position accuracy, the drill bit was thoroughly ground down and regrinded to a near-new condition, making it less likely for hole position accuracy abnormalities to occur. Therefore, the retention of burrs 40 as described above was not frequent. Regrinding involves applying a grinding wheel to the tip of a used drill so that the tip angle and relief angle are the same as those of a new drill, and the overall length of the drill is shortened by a predetermined distance (amount of grinding) in the axial direction of the drill.

[0010] However, this regrinding process requires a large amount of grinding per pass if the goal is to completely remove the worn portion of the cutting edge 22 and the first land 21. As a result, it can only be performed once or twice on a single drill. Moreover, as mentioned above, in recent years, there has been an increase in workpiece materials that cause drill wear to progress rapidly. Consequently, the number of holes drilled per drill has decreased, the number of drills required for drilling has increased, and costs have risen.

[0011] Against this backdrop, some manufacturers are attempting to reduce costs by decreasing the amount of material removed per regrinding cycle, increasing the number of regrinding cycles per drill, and enabling more drilling operations with a single drill.

[0012] However, if the amount of grinding is reduced, wear is more likely to remain on the corners of the cutting edge 22. When drilling is performed with wear remaining on the corners of the cutting edge 22, as shown in Figure 10, the boundary B' between the area of ​​the cutting edge 22 where wear has been removed by regrinding and the area where wear remains is located further inward (in the direction of the intersection of the cutting edge 22 and the chisel edge) compared to a new or near-new state. As a result, the gap between the trajectory a' drawn when drilling at point A', which forms the outer diameter of the drill at the very tip of the drill body 1 on the first leading edge, and the trajectory b' drawn when drilling at the boundary B' between the area of ​​the cutting edge 22 where wear has been removed by regrinding and the area where wear remains, widens. Insufficient cutting power is at work in the area between trajectories a' and b', so the chips generated at the edge of the hole become thicker, and as they undergo plastic deformation to be pushed outwards towards the outer circumference of the drill, work hardening occurs, making it impossible to remove them with the second leading edge, resulting in significant residue of burrs 40.

[0013] Thus, it is difficult to achieve both suppressing the residue of burrs 40 and reducing costs by decreasing the amount of material removed per regrinding pass and increasing the number of regrinding passes for a single drill. In the end, in order to suppress the residue of burrs 40, a sufficient amount of material must be removed per regrinding pass to restore the drill to a like-new condition. Therefore, currently, a single drill can only be regrinded once or twice at most.

[0014] This invention has been made in view of the current situation, and aims to provide a single-blade drill for printed circuit boards that can suppress the residue of burrs as much as possible, even when wear remains on the corners of the cutting edge. [Means for solving the problem]

[0015] The gist of the present invention will be explained with reference to the attached drawings.

[0016] A chisel edge 2 is provided at the tip of the drill body 1, and in view of the drill tip, a spiral first chip evacuation groove 3 and a spiral second chip evacuation groove 4 are provided on the outer circumference, asymmetrical with respect to the drill rotation axis O, and a cutting edge 6 is provided on the edge of the rake face 5a of the first chip evacuation groove 3, and a first land portion 7 is provided behind the first chip evacuation groove 3 in the direction of drill rotation, and a second land portion 8 is provided behind the second chip evacuation groove 4 in the direction of drill rotation, with a land width narrower than the first land portion 7, and a first leading edge X is provided at the intersection of the first chip evacuation groove 3 and the first land portion 7, and the intersection of the second chip evacuation groove 4 and the second land portion 8 This invention relates to a single-blade drill for printed circuit boards, wherein a second leading edge Y is provided on the ridge line, and a margin portion 9 is provided at the tip of the drill body 1, and further, between a first position P1 defined in 1 below and a second position P2 defined in 2 below, the angle θ formed by the line connecting the first leading edge X and the drill rotation center axis O on a planar cross section perpendicular to the drill rotation center axis O, and the line connecting the second leading edge Y and the drill rotation center axis O, is configured to gradually increase from the first position P1 to the second position P2. Note 1 The first position P1 is the position in the margin portion 9 that is closest to the tip of the drill body and does not include either the relief surface 10 on the first land portion 7 side or the relief surface 10' on the second land portion 8 side. Note 2 The second position P2 is a position in the margin portion 9 that is 0.25 mm away from the base end of the drill body towards the tip of the drill body.

[0017] Furthermore, the present invention relates to a single-blade drill for printed circuit boards according to claim 1, characterized in that the angle θ at the first position P1 is defined as angle θ1, the angle θ at the second position P2 is defined as angle θ2, and the relationship between angle θ1 and angle θ2 is 10° ≤ θ2 - θ1 ≤ 40°.

[0018] Also, in the single-edge drill for printed wiring boards according to claim 2, the angle θ1 is 130° or more and 150° or less, and the angle θ2 is 140° or more and 170° or less. It relates to a single-edge drill for printed wiring boards characterized by this.

[0019] Also, in the single-edge drill for printed wiring boards according to any one of claims 1 to 3, the twist angle β of the second chip discharge groove 4 is set to a twist angle smaller than the twist angle α of the first chip discharge groove 3. It relates to a single-edge drill for printed wiring boards characterized by this.

[0020] Also, in the single-edge drill for printed wiring boards according to any one of claims 1 to 3, the land width of the second land portion 8 at the second position P2 is 2 times or more the land width at the first position P1. It relates to a single-edge drill for printed wiring boards characterized by this.

[0021] Also, in the single-edge drill for printed wiring boards according to claim 4, the land width of the second land portion 8 at the second position P2 is 2 times or more the land width at the first position P1. It relates to a single-edge drill for printed wiring boards characterized by this.

Effect of the Invention

[0022] Since the present invention is configured as described above, even when drilling is performed with wear remaining at the corner of the cutting edge, the remaining burrs are suppressed as much as possible. As a result, the amount of polishing per re-polishing process can be reduced, and it is also possible to increase the number of re-polishing times for a single drill to reduce costs. It becomes a revolutionary single-edge drill for printed wiring boards.

Brief Description of the Drawings

[0023] [Figure 1] It is a front view showing the tip of the drill body of this embodiment. [Figure 2] It is a front view of the tip of the drill body of this embodiment. [Figure 3]This is an explanatory diagram defining the helix angles of the first chip discharge groove (a) and the second chip discharge groove (b) in this embodiment. [Figure 4] This is an explanatory diagram defining angles θ1 and θ2 in this embodiment. [Figure 5] This graph shows the results of the hair follicle retention rate in Experiment 1. [Figure 6] These are photographs showing the observation results of the condition of the drill tip surface before and after drilling in Conventional Example 1 and Example 1, both of which underwent four regrinding processes in Experiment 1. [Figure 7] This graph shows the evaluation results of hole position accuracy in Experiment 2. [Figure 8] This photograph shows the amount of burrs remaining after drilling. [Figure 9] This is an explanatory diagram showing the mechanism of burr formation in a drill that is new or in near-new condition. [Figure 10] This is an explanatory diagram illustrating the mechanism of burr formation in a drill with remaining wear on the corners of the cutting edge. [Figure 11] These are a front view (a) and a front view (b) showing the tip of the drill body in another example 1 of this embodiment. [Figure 12] These are a front view (a) and a front view (b) showing the tip of the drill body in another example 2 of this embodiment. [Figure 13] Figure 11 is an explanatory diagram showing the land width and margin width in another example 1 of this embodiment. [Figure 14] Figure 12 is an explanatory diagram showing the land width and margin width in another example 2 of this embodiment. [Figure 15] This is an explanatory diagram illustrating the effects and benefits of the present invention. [Modes for carrying out the invention]

[0024] A preferred embodiment of the present invention will be briefly described with reference to the drawings, illustrating the operation of the present invention.

[0025] In the present invention, in the margin portion 9, between the first position P1 closest to the tip of the drill body, which does not include both the relief surface 10 on the first land portion 7 side and the relief surface 10' on the second land portion 8 side, and the second position P2, which is 0.25 mm away from the base end of the drill body towards the tip of the drill body, the angle θ formed by the line connecting the first leading edge X and the drill rotation center axis O on a planar cross section perpendicular to the drill rotation center axis O, and the line connecting the second leading edge Y and the drill rotation center axis O, is such that the angle θ is such that the first position P1 does not include both the relief surface 10 on the first land portion 7 side and the relief surface 10' on the second land portion 8 side. Because it is configured to gradually increase toward P2, when the drill body 1 is resharpened, the second leading edge Y is positioned closer to the first leading edge X located forward in the direction of drill rotation at the tip of the drill body 1. As a result, the second leading edge Y is able to make early contact with the chips generated at the edge of the hole at the tip of the drill body 1. Even if some wear remains on the corners of the cutting edge 6 during the resharpening process, the chips generated at the edge of the machined hole are removed, and the residue of burrs 40 is suppressed as much as possible.

[0026] This makes it possible to reduce the amount of material removed per regrinding cycle, and to increase the number of regrinding cycles for a single drill, thereby reducing costs. This is a groundbreaking single-blade drill for printed circuit boards. [Examples]

[0027] Specific embodiments of the present invention will be described with reference to the drawings.

[0028] In this embodiment, a chisel edge 2 is provided at the tip of the drill body 1, and in view of the drill tip, a spiral first chip evacuation groove 3 and a spiral second chip evacuation groove 4 are provided on the outer circumference, which are asymmetrical with respect to the drill rotation axis O. Furthermore, a cutting edge 6 is provided on the edge of the rake face 5a of the first chip evacuation groove 3 (specifically, the ridge line between the rake face 5a of the first chip evacuation groove 3 and the relief face 10 on the first chip evacuation groove 3 side is formed as the cutting edge 6). In addition, a first land portion 7 is provided behind the first chip evacuation groove 3 in the direction of drill rotation, and the second chip evacuation groove 4 has a land width (lead- This is a single-blade drill for printed circuit boards, in which a second land section 8 is provided, having a narrow distance (on a cross section perpendicular to the axis) from the leading edge to the land section or secondary beveling surface and the adjacent chip evacuation groove located behind it in the direction of drill rotation; a first leading edge X is provided at the intersection of the first chip evacuation groove 3 and the first land section 7; and a second leading edge Y is provided at the intersection of the second chip evacuation groove 4 and the second land section 8 (hereinafter, the land width of the first land section 7 will be referred to as "first land width W1", and the land width of the second land section 8 will be referred to as "second land width W2" (see Figures 4(b) and 4(c))).

[0029] The drawings illustrating this embodiment show a right-hand cutting, right-handed twist type drill in which the drill body 1 is moved toward the drill tip while rotating counterclockwise when viewed from the tip side of the drill body 1 to cut the workpiece and chips are discharged from the base end side of the drill body. However, this embodiment can also be applied to a left-hand cutting, left-handed twist type drill.

[0030] The components of this embodiment will be described in detail below.

[0031] As shown in Figure 1, the drill body 1 is configured as an undercut type with a margin portion 9 provided in a predetermined range on the tip side. This embodiment is not limited to the configuration in which no clearance is provided on the outer circumference of the drill as shown in Figure 1. For example, as shown in Figure 11, a clearance 12 may be provided at the rear edge in the direction of drill rotation of the outer circumference of the first land portion 7 and the second land portion 8 to reduce the contact area with the inner wall of the machined hole, reduce cutting resistance, and prevent roughening of the wall surface (Another Example 1). Alternatively, as shown in Figure 12, a clearance 12 may be provided in the center of the outer circumference of the first land portion 7 to form a so-called double margin shape (Another Example 2). Furthermore, a configuration in which clearance is provided in only one of the first land portion 7 or the second land portion 8 (not shown) is also possible. Here, the depth of the clearance 12 (the depth from the outer circumference of the drill body 1 to the secondary fringing surface 13) is generally set to 15% ± 10% of the diameter of the drill body 1, taking into consideration the effects of insufficient rigidity of the drill body 1, such as a decrease in fracture resistance if it is too deep, and the risk that the clearance 12 may disappear if the outer circumference of the drill body 1 wears down if it is too shallow. Furthermore, as shown in the alternative example 1 in Figure 11, if clearance 12 is provided at the rear edge in the direction of drill rotation of the outer circumference of the first land portion 7 and the second land portion 8, then, as shown in Figure 13(a), the distance on a cross section perpendicular to the axis from the first leading edge X to the intersection of the second beveling surface 13 formed by providing clearance 12 to the first land portion 7 and the second chip discharge groove 4 is defined as the first land width W1, and the distance on a cross section perpendicular to the axis from the second leading edge Y to the intersection of the second beveling surface 13 formed by providing clearance 12 to the second land portion 8 and the first chip discharge groove 3 is defined as the second land width W2.

[0032] Furthermore, in the above configuration, the margin width W3 on the first land section 7 side and the margin width W4 on the second land section 8 side are as shown in Figure 13(b).

[0033] Furthermore, as shown in the alternative example 2 in Figure 12, when a clearance 12 is provided in the center of the outer periphery of the first land portion 7, the distance on the cross section perpendicular to the axis from the first leading edge X to the intersecting ridge line between the outer periphery of the first land portion 7 and the second chip discharge groove 4 is defined as the first land width W1, as shown in Figure 14(a). In this configuration, the margin widths W3 and W3' on the first land portion 7 side and the margin width W4 on the second land portion 8 side are as shown in Figure 14(b).

[0034] Furthermore, as shown in Figure 2, relief surfaces 10 and 10' are formed on the side of the first chip evacuation groove 3 and the side of the second chip evacuation groove 4, respectively, so that a chisel edge 2 is formed at the tip of the drill body 1. In the figure, arrows with the symbol T indicate the direction of drill rotation.

[0035] Specifically, so that a pointed tip (chisel point) is formed at the tip of the drill body 1, the relief surfaces 10, 10' on the side of the first chip evacuation groove 3 and the side of the second chip evacuation groove 4 are composed of a first relief surface 10a, 10a' set at a predetermined relief angle with respect to the cutting edge 6, and a second relief surface 10b, 10b' which is connected to the first relief surface 10a, 10a' and is set at a larger relief angle than the first relief surface 10a, 10a'. Note that the relief surfaces 10, 10' are not limited to the above configuration and can be modified as appropriate, for example, by being composed of only the first relief surface.

[0036] Furthermore, the drill body 1 is configured such that its core thickness gradually increases (becomes thicker) from the tip end to the base end in order to improve the drill's rigidity. Accordingly, the groove depths of the first chip discharge groove 3 and the second chip discharge groove 4 are also configured to gradually become shallower from the tip end to the base end.

[0037] Furthermore, the first chip discharge groove 3 and the second chip discharge groove 4 are set to different helix angles.

[0038] Specifically, the helix angle β of the second chip evacuation groove 4 (see Figure 3(b)) is set to be smaller than the helix angle α of the first chip evacuation groove 3 (see Figure 3(a)). More specifically, the helix angle α of the first chip evacuation groove 3 is set to 40° to 45°, and the helix angle β of the second chip evacuation groove 4 is set to be 2° to 10° smaller than the helix angle α of the first chip evacuation groove 3. Furthermore, the second chip evacuation groove 4 is configured to connect (converge) with the first chip evacuation groove 3 on the base end side of the drill body 1 from the base end of the margin portion 9.

[0039] In this embodiment, in the margin portion 9, between the first position P1, which is the closest to the tip of the drill body and does not include either the relief surface 10 on the first land portion 7 side or the relief surface 10' on the second land portion 8 side (in this embodiment, as shown in Figure 4(a), the position of the relief surface 10' on the second land portion 8 side closest to the drill base end), and the second position P2 (see Figure 4(a)), which is 0.25 mm away from the base end of the drill body towards the tip of the drill body, the first leading edge X on a flat cross section perpendicular to the drill rotation center axis O and The angle θ formed by the line connecting the drill's rotational axis O and the line connecting the second leading edge Y and the drill's rotational axis O gradually increases from the first position P1 to the second position P2. As a result, when regrinding is performed, the second leading edge Y is positioned on the tip side of the drill body of the margin section 9 so as to approach the first leading edge X in the rotational direction of the drill body 1. This shape allows the second leading edge Y to quickly remove chips generated at the edge of the hole that have separated from the corner of the cutting edge 6. Therefore, in this embodiment, it is assumed that a certain amount of chips generated at the edge of the removed hole and chips generated when the chisel edge 2 etc. come into contact with the workpiece will flow into the second chip discharge groove 4. To avoid poor discharge at this time, the twist angle of the first chip discharge groove 3 is increased from the base end side of the drill body of the margin section 9, connecting the second chip discharge groove 4 to the first chip discharge groove 3 and securing a path for the chips.

[0040] As described above, in this embodiment, the groove depths of the first chip discharge groove 3 and the second chip discharge groove 4 are configured to gradually become shallower from the tip side to the base side, and the twist angle β of the second chip discharge groove 4 is set to a twist angle smaller than the twist angle α of the first chip discharge groove 3. As a result, at least between the first position P1 and the second position P2 in the margin portion 9, the angle θ formed by the line connecting the first leading edge X and the drill rotation center axis O on a planar cross section perpendicular to the drill rotation center axis O and the line connecting the second leading edge Y and the drill rotation center axis O gradually increases from the first position P1 to the second position P2, and the first land width W1 gradually narrows from the tip side to the base side, and the second land width W2 gradually widens from the tip side to the base side.

[0041] Generally, when drilling holes, the wider the land width and the larger the contact area between the inner wall of the drilled hole and the outer circumference of the drill, the less wear occurs on the outer circumference of the drill. Therefore, by configuring it as described above, it is considered that the effect of reducing outer circumference wear in the second land portion 8 can be obtained. In this embodiment, the second land width W2 at the second position P2 is configured to be at least twice the second land width W2 at the first position P1.

[0042] As described above, widening the second land width W2 is expected to reduce outer wear. However, if the focus is on reducing inner wall roughness during hole machining, a clearance 12 may be appropriately provided in the first land portion 7 and the second land portion 8 to reduce the contact area between the inner wall of the machined hole and the outer circumference of the drill. In this case, the clearance 12 may be provided in the first land portion 7 and the second land portion 8 so that the width of the outer circumference of the drill in the cross section perpendicular to the axis that contacts the inner wall of the machined hole (the so-called margin width) is constant from the tip side to the base side of the drill body 1. Alternatively, to prevent the margin width W4 of the second land portion 8 from becoming too wide, the clearance 12 may be provided from a position a predetermined distance away from the tip of the margin portion 9.

[0043] Furthermore, in the margin section 9, the first land section 7 and the second land section 8 have a first position P1 which is the closest to the tip of the drill body and does not include either the relief surface 10 on the first land section 7 side or the relief surface 10' on the second land section 8 side, and a second position P2 which is the tip-side position 0.25 mm away from the base end of the drill body 1 of the margin section 9, between which is the line connecting the first leading edge X and the drill rotation center axis O on a flat cross section perpendicular to the drill rotation center axis O, and the second leading edge Y The angle θ formed by the line connecting the drill's rotational axis O gradually increases from the first position P1 to the second position P2 (more preferably, the angle θ1 at the first position P1 and the angle θ2 at the second position P2 are 10°≦θ2-θ1≦40°, and even more preferably 130°≦θ1≦150° and 140°≦θ2≦170°). (Note that in the conventional example, the angle θ1 at the first position and the angle θ2 at the second position are θ1=θ2, i.e., the angle θ is constant.)

[0044] Here, the second position P2 is defined as a flat cross-section perpendicular to the drill's rotational axis O at a tip-side position 0.25 mm away from the base end face of the drill body of the margin portion 9. This is because if the axial length (margin length) of the margin portion 9 falls below 0.25 mm after the drill has been resharpened and used, there is a risk that the drill may not be able to fully perform its function, such as in terms of hole position accuracy.

[0045] In contrast to the conventional example where the angle θ is constant, in this embodiment, the angle θ is configured to gradually increase from the first position P1 to the second position P2 between the first position P1 and the second position P2. This ensures that the second leading edge Y at the tip of the drill body 1 approaches the first leading edge X, which is located forward in the direction of drill rotation. This removes chips that have detached from the cutting edge 6 and formed on the edge of the hole, and suppresses the retention of burrs 40. Furthermore, by positioning the second leading edge Y on the tip side of the drill body 1 closer to the first leading edge X located forward in the direction of drill rotation, in this embodiment, the position of the second leading edge Y on the tip side of the drill body 1 after the resharpening treatment shown in Figure 15(b) is closer to the corner (point A) of the cutting edge 6 than the position of the second leading edge Y on the tip side of the drill body 1 when new (point C) shown in Figure 15(a) (the distance between A and C shown as L1 in Figure 15(a) becomes shorter to the distance between A and C shown as L2 in Figure 15(b)). This also makes it easier for the second leading edge Y to come into contact with the chips that have separated from the cutting edge 6 and formed on the edge of the hole earlier, thereby suppressing the retention of burrs 40. Furthermore, setting the angle to 10°≦θ2-θ1≦40° further enhances the effect of suppressing the residue of burrs 40, and setting it to 130°≦θ1≦150° and 140°≦θ2≦170° enables drilling with suppression of burr residue 40, good chip evacuation, and hole position accuracy.

[0046] The reason for setting the angle θ1 at the first position P1 to 130° or more is that if the angle θ1 is less than 130°, sufficient groove width cannot be secured in the first chip evacuation groove 3 where the cutting edge 6 is located, making it impossible to smoothly discharge chips and potentially causing the drill to break.

[0047] Furthermore, the reason for setting the angle θ2 at the second position P2 to 170° or less is that if the angle θ2 is greater than 170°, the backup amount of the cutting edge 6 (first land width W1) may not be sufficient, and there is a risk that the drill rigidity and hole position accuracy required for a single-blade drill for printed circuit boards may not be met.

[0048] Furthermore, in a configuration where the angle θ formed by the line connecting the first leading edge X and the drill rotation center axis O on a planar cross section perpendicular to the drill rotation center axis O, and the line connecting the second leading edge Y and the drill rotation center axis O, gradually increases from the first position P1 to the second position P2, it is desirable that the twist angle α of the first chip evacuation groove 3 and the twist angle β of the second chip evacuation groove 4 are α > β. In this embodiment, α > β is set, and furthermore, the groove depth of both the first chip evacuation groove 3 and the second chip evacuation groove 4 is set to gradually become shallower at the same rate of change (= change in groove depth / axial distance) from the tip side to the base side of the drill body 1.

[0049] Alternatively, the twist angle β of the second chip evacuation groove 4 may be set to a smaller twist angle α than that of the first chip evacuation groove 3, and the groove may be made shallower from the tip side to the base side of the drill body 1 so that the rate of change in groove depth of the second chip evacuation groove 4 is greater than that of the first chip evacuation groove 3.

[0050] Furthermore, if the diameter of the drill body is smaller than 0.05 mm, the risk of the drill body breaking during drilling or regrinding is high due to the diameter becoming too small, and it is only used as new and not regrinded. When the diameter of the drill body 1 is 0.05 mm or more, the angle θ is configured to gradually increase from the first position P1 to the second position P2, so that the second leading edge Y can easily contact the chips generated at the edge of the hole when regrinding is performed, thereby suppressing the retention of burrs 40 in the regrinded drill. Therefore, the diameter of the drill body 1 that achieves the effect of suppressing the retention of burrs 40 as much as possible according to this embodiment is 0.05 mm or more.

[0051] As this embodiment is configured, by performing the regrinding process, the second leading edge Y at the tip of the drill body 1 is positioned closer to the first leading edge X in the direction of drill rotation. This results in a shape that makes it easier for the second leading edge Y to contact the chips generated at the edge of the hole, and even if drilling is performed with some wear remaining on the corners of the cutting edge 6, the retention of burrs 40 is suppressed as much as possible.

[0052] Therefore, this is a groundbreaking single-blade drill for printed circuit boards that can reduce the amount of material removed per regrinding cycle, and increase the number of regrinding cycles for a single drill, thereby reducing costs.

[0053] The following is an experiment that supports the effectiveness of this embodiment.

[0054] <Experiment 1> In Experiment 1, the residual status of burrs 40 was confirmed when regrinding and drilling were repeatedly performed on the conventional example (Conventional Example 1) and the present example (Example 1, Example 2).

[0055] Specifically, using a drill with a diameter of 0.2 mm, a groove length of 4 mm, and a margin length of 0.65 mm, the angle θ1 formed by the line connecting the first leading edge X1 and the drill rotation axis O on a flat cross section perpendicular to the drill rotation axis O at the first position P1 shown in Figure 4(b), and the line connecting the second leading edge Y1 and the drill rotation axis O, and the angle θ2 formed by the line connecting the first leading edge X2 and the drill rotation axis O on a flat cross section perpendicular to the drill rotation axis O at the second position P2 shown in Figure 4(c), were set as shown in Table 1, and the cutting conditions were set to a spindle speed of 180,000 min⁻¹. -1The number of remaining burrs (number of remaining holes) was checked (counted) when 1,500 holes were drilled on a workpiece consisting of three 0.81 mm thick printed circuit boards stacked together and a 0.19 mm thick resin-coated aluminum backing plate, with a feed rate of 1.8 m / min, for both new tools and tools that had undergone 1 to 4 resharpening treatments (amount polished per treatment: 0.07 mm).

[0056] In addition, in Conventional Example 1, Example 1, and Example 2, the groove depth of the first chip discharge groove 3 and the second chip discharge groove 4 is configured to gradually become shallower from the tip side to the base side (a configuration in which a web taper with a larger core thickness is set).

[0057] Furthermore, in Conventional Example 1, the twist angle α of the first chip discharge groove 3 and the twist angle β of the second chip discharge groove 4 are both set to 40°, and the configuration is such that angles θ1 and θ2 are both 140°. In Example 1, the twist angle α of the first chip discharge groove 3 is set to 40°, and the twist angle β of the second chip discharge groove 4 is set to 36°, and the configuration is such that θ1 = 145° and θ2 = 168°. In Example 2, the twist angle α of the first chip discharge groove 3 is set to 40°, and the twist angle β of the second chip discharge groove is set to 38°, and the configuration is such that θ1 = 144° and θ2 = 156° (see Table 1).

[0058] Furthermore, in Conventional Example 1, Example 1, and Example 2, the first chip discharge groove 3 and the second chip discharge groove 4 are connected by increasing the helix angle of the first chip discharge groove 3 from 40° to 50° on the drill body base end side of the margin portion 9. The axial distance from the tip of the drill body 1 to the position where the two chip discharge grooves are connected (the intersection of the outer peripheral end of the wall surface 5 of the first chip discharge groove 3 facing forward in the drill rotation direction and the outer peripheral end of the wall surface 11 of the second chip discharge groove 4 facing forward in the drill rotation direction) is configured to be 1.2 mm.

[0059] [Table 1]

[0060] Furthermore, Table 2 shows the first land width W1, the second land width W2, and the ratio of the second land width W2 at the first position P1 and the second position P2 (land width ratio) for Conventional Example 1, Example 1, and Example 2, respectively.

[0061] [Table 2]

[0062] Figure 5 shows the experimental results (the number of holes on the upper surface of the backing plate after drilling in which burrs 40 remained, and the ratio of this number to the total number of holes drilled (1,500) = burr retention rate). The criteria for counting the burrs 40 were not considered in terms of their size; any hole in which burr-like chips were observed remaining around the drilled hole was counted as "1".

[0063] As shown in Figure 5, in Conventional Example 1, Example 1, and Example 2, the amount of remaining hair burrs increased with each repolishing treatment. However, it was confirmed that the amount of remaining hair burrs was suppressed more in Examples 1 and 2 than in Conventional Example 1 (it was confirmed that in both Examples 1 and 2, the amount was approximately half or less of that in Conventional Example 1).

[0064] In particular, in Example 1, where the twist angle β of the second chip discharge groove 4 was made smaller relative to the twist angle α of the first chip discharge groove 3 (with a difference of 4° in the twist angle), and the angle θ was gradually increased from the first position P1 to the second position P2, the rate of burr residue was significantly reduced even after drilling four times of regrinding, confirming that the effect of removing chips generated at the edge of the hole and suppressing the residue of burrs was fully demonstrated.

[0065] In Experiment 1, the condition of the drill tip surface before and after drilling was observed for both Conventional Example 1 and Example 1, which underwent four resharpening processes.

[0066] As a result, as shown in Figure 6, it was confirmed that in Example 1 after drilling, wear was observed near the corner on the second land portion 8 side (indicated by the arrow in the figure). This indicates that the corner on the second land portion 8 side is in contact with the workpiece containing chips generated at the edge of the machined hole, and that the second leading edge Y following the corner on the second land portion 8 side is also more likely to come into contact with the workpiece containing chips generated at the edge of the machined hole compared to Conventional Example 1. From this point of view, it was confirmed that Example 1 exhibits the effect of removing chips generated at the edge of the hole and suppressing the residue of burrs. Furthermore, it was confirmed that a similar effect was exhibited in Example 2 after four regrinding cycles.

[0067] Furthermore, as shown in Table 2, in the second land portion 8, the ratio of the land width at the second position P2 to the land width at the first position P1 was 1.6 times in Conventional Example 1, but 2.2 times in Example 2 and 2.8 times in Example 1. As mentioned above, the wider the land width and the larger the contact area between the inner wall of the machined hole and the outer circumference of the drill during drilling, the less wear occurs on the outer circumference of the drill. Therefore, with this configuration, even if the number of regrinding cycles increases and the number of contact cycles between the inner wall of the machined hole and the outer circumference of the drill increases, the degree of wear on the outer circumference of the second land portion 8 is reduced in Examples 1 and 2, which is thought to prevent a decrease in the ability to remove chips generated at the edge of the hole.

[0068] <Experiment 2> In Experiment 2, we further investigated the effects of different combinations of angles θ1 and θ2 on hole position accuracy and reducing the amount of burr residue.

[0069] Specifically, the diameter is 0.2 mm, the groove length is 4 mm, the margin length is 0.65 mm, and the twist angle of the first chip evacuation groove 3 is increased from 40° to 50° on the drill body base side of the margin portion 9, thereby connecting the first chip evacuation groove 3 and the second chip evacuation groove 4, and the axial distance from the tip of the drill body 1 to the position where the two chip evacuation grooves are connected (the intersection of the outer peripheral end of the wall surface 5 of the first chip evacuation groove 3 facing forward in the drill rotation direction and the outer peripheral end of the wall surface 11 of the second chip evacuation groove 4 facing forward in the drill rotation direction) In a single-blade drill for printed circuit boards with a diameter of 1.0 mm, experimental examples were created by adjusting the groove division angle of the first chip evacuation groove 3 and the second chip evacuation groove 4, and the helix angle α of the second chip evacuation groove 3 and the helix angle β of the second chip evacuation groove 4, so that angle θ1 is 120°, 130°, 140°, 150°, 160° and angle θ2 is 120°, 130°, 140°, 150°, 160°, 170°, with θ1 ≤ θ2 (the case where θ1 = θ2 is a conventional example), and the cutting conditions were set to a spindle rotation speed of 180,000 min⁻¹. -1 The hole position accuracy and the number of burr-filled holes were evaluated when drilling 2,000 holes in a workpiece consisting of three 0.81 mm thick printed circuit boards stacked on top of a 0.19 mm thick resin-coated aluminum backing plate, with a feed rate of 1.8 m / min.

[0070] Figure 7 shows the evaluation results for hole position accuracy when the drill was new, and Table 3 shows the evaluation results for the number of burr-retaining holes in a drill that underwent four regrinding processes with a polishing amount of 0.07 mm per regrinding process. Here, hole position accuracy was evaluated as the amount of deviation between the target position in the program and the position of the processed hole on the back side of the bottommost substrate in a three-layer stack.

[0071] Furthermore, the drill used to evaluate the hole position accuracy when new (Figure 7) was one of the drills from the aforementioned experimental examples where angle θ2 was 10° greater than angle θ1, and the hole position accuracy was good when angle θ1 was 130° ≤ θ1 ≤ 150°. In addition, when θ1 < θ2, it was confirmed that the hole position accuracy is equivalent to the conventional example where θ1 = θ2 regardless of angle θ2 (not limited to θ2 - θ1 = 10°) if angle θ1 is the same.

[0072] In the evaluation of the number of residual holes due to burrs (Table 3), drilling was performed using a drill with a 130°≦θ1≦150° angle, which showed good hole position accuracy when new, as shown in the experimental example above in Figure 7.

[0073] In this embodiment, the groove depth is configured to decrease from the tip side to the base side of the drill, with the degree of decrease being equal for the first chip evacuation groove 3 and the second chip evacuation groove 4. By setting the helix angle α of the first chip evacuation groove 3 and the helix angle β of the second chip evacuation groove 4 to α > β, the angle θ is configured to gradually increase toward the base side of the drill. For example, in a drill with θ1 = 140° and θ2 = 150°, the helix angle β of the second chip evacuation groove 4 is configured to be 2° smaller than the helix angle α of the first chip evacuation groove 3, and in a drill with θ1 = 130° and θ2 = 170°, the helix angle β of the second chip evacuation groove 4 is configured to be 10° smaller than the helix angle α of the first chip evacuation groove 3. Thus, the larger the angle difference between the helix angle α of the first chip evacuation groove 3 and the helix angle β of the second chip evacuation groove 4, the larger the angle difference between angle θ1 and angle θ2.

[0074] Regarding Table 3, for the number of remaining hair follicle holes, a decrease in the number of remaining hair follicle holes compared to the conventional example (θ1=θ2) is indicated with ○, and among those, a decrease in the hair follicle retention rate to 5% or less is indicated with ◎.

[0075] [Table 3]

[0076] As shown in Figure 7, the configuration that yielded good hole position accuracy when new was 130°≦θ1≦150°, while θ1=160° yielded inferior results. Furthermore, even for combinations of angles θ1 and θ2 other than those evaluated in Figure 7 (θ2=θ1+10°), the hole position accuracy was similarly good when 130°≦θ1≦150°.

[0077] Furthermore, at θ1 = 120°, even when θ2 > θ1 + 10°, breakage of the drill body 1 occurred, which is thought to be due to poor chip evacuation.

[0078] Furthermore, from the results of the above-mentioned examples, it was found that when a drill is repeatedly reground with an insufficient amount of grinding, a drill with an angle θ2 that is 10° or more greater than the angle θ1 has a reduced number of holes with residual burrs compared to the conventional example. In particular, it was found that the burr retention rate can be further improved when θ2 ≥ 160°. As mentioned above, when the drill is new, the hole position accuracy at θ1 = 160° is inferior to that at 130° ≤ θ1 ≤ 150°, but at 160° ≤ θ2 ≤ 170°, the retention of burrs 40 after reground treatment can be suppressed, thus confirming that the deterioration of hole position accuracy due to the drill riding on burrs 40 is suppressed.

[0079] It should be noted that the present invention is not limited to this embodiment, and the specific configuration of each constituent element can be designed as appropriate. [Explanation of Symbols]

[0080] 1. Drill body 2 Chisel Edges 3 First waste drainage groove 4 Second chip discharge groove 5a Scoop face 6 cutting edges 7. First Land Section 8. Second Land Division 9. Margin section 10,10' Escape face O Drill rotation center axis P1 First position P2 Second position X First Leading Edge Y Second Leading Edge α The twist angle of the first waste discharge groove β Helix angle of the second chip evacuation groove

Claims

1. A chisel edge is provided at the tip of the drill body, and in view of the drill tip, a spiral first chip evacuation groove and a spiral second chip evacuation groove are provided on the outer circumference, asymmetrical with respect to the drill's rotation axis, and a cutting edge is provided on the edge of the rake face of the first chip evacuation groove, and a first land portion is provided behind the first chip evacuation groove in the direction of drill rotation, and a second land portion is provided behind the second chip evacuation groove in the direction of drill rotation, with a land width narrower than the first land portion, and a first leading edge is provided at the intersecting ridge of the first chip evacuation groove and the first land portion, and the second chip evacuation groove and the second land portion A single-blade drill for printed circuit boards, wherein a second leading edge is provided on the intersecting ridge line, the tip of the drill body is provided with a margin, and furthermore, the angle θ formed by the line connecting the first leading edge and the drill rotation center axis on a planar cross section perpendicular to the drill rotation center axis, and the line connecting the second leading edge and the drill rotation center axis, is configured to gradually increase from the first position to the second position, between the first position defined in 1 below and the second position defined in 2 below. Note 1 The first position is the position in the margin portion that does not include either the relief surface on the first land portion side or the relief surface on the second land portion side, and is closest to the tip of the drill body. Note 2 The second position is a position in the margin portion that is 0.25 mm away from the base end of the drill body towards the tip of the drill body.

2. A single-blade drill for printed circuit boards according to claim 1, characterized in that the angle θ at the first position is angle θ1, the angle θ at the second position is angle θ2, and the relationship between angle θ1 and angle θ2 is 10° ≤ θ2 - θ1 ≤ 40°.

3. A single-blade drill for printed circuit boards according to claim 2, characterized in that the angle θ1 is 130° or more and 150° or less, and the angle θ2 is 140° or more and 170° or less.

4. A single-blade drill for printed circuit boards according to any one of claims 1 to 3, characterized in that the twist angle of the second chip discharge groove is set to be smaller than the twist angle of the first chip discharge groove.

5. A single-blade drill for printed circuit boards according to any one of claims 1 to 3, characterized in that the land width of the second land portion at the second position is twice or more the land width at the first position.

6. A single-blade drill for printed circuit boards according to claim 4, characterized in that the land width of the second land portion at the second position is at least twice the land width at the first position.

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