JPH06344212A - Drill of super-small diameter for printed circuit board - Google Patents

Abstract

PURPOSE:To improve the chipping resistance and prevent accidents of the drill breakage in drilling operation by interposing a buffer part of intermediate strength consisting of a cylindrical part of a diameter smaller than the shank diameter or a tapered part between a drill body and a shank. CONSTITUTION:An outer circumferential cutting edge 4 is formed by a margin 6 at the tip part in the axial direction of a drill body 2 and a crossing side of a torsional groove 5. This margin 6 is left because an undercut part 7 and an outer circumferential flank 8 are machined. This drill body 2 is integrated with a shank 9, and a strength buffer part 10 is interposed between the drill body 2 and the shank 9. This strength buffer part 10 consists of a cylindrical part of a diameter smaller than that of the shank 9. The diameter of the tip of the drill body 2 is small, and the rigidity of the strength buffer part 10 can be reduced, and the resistance against the bending of the drill body 2 can be improved thereby.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a very small diameter drill for a printed wiring board, and more particularly to a breakage resistance which is improved.

[0002]

2. Description of the Related Art Conventionally, drills for printed wiring boards are
For example, as disclosed in Japanese Examined Patent Publication (Kokoku) No. 3-167, a chamfered conical portion is interposed between a tool main body portion having a spiral groove and a shank portion having a diameter larger than this. It is a thing. And, in terms of the cutting edge diameter, the mainstream of this drill is about φ0.15 to φ0.25 mm.

[0003]

However, in drilling a printed wiring board of this type, breakage of the drill that occurs during drilling, hole position accuracy due to improper drill shape, roughness of the machined hole inner wall, and smear. Occurrence has become a problem, and breakage of the drill is particularly important.

Then, in order to solve the breakage of the drill, the drilling by the step processing and the reduction of the feed rate are dealt with, but the fundamental problem has not been solved.

In view of the above, the present invention has been improved in terms of shape so as to reduce breakage of the drill.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and a strength buffering portion is interposed between a drill body having a spiral groove and a shank, and
The outer peripheral cutting edge ridge is formed by the intersecting ridge of the margin and the twist groove provided in the axial tip portion of the drill body. In this case, the margin is left in the axial tip portion of the drill body by processing the undercut portion and the outer peripheral flank.

[0007]

In the extremely small diameter drill for printed wiring boards of the present invention, since the outer peripheral cutting edge is present in the margin provided at the tip of the drill body in the axial direction, the contact with the hole wall is shortened. A reduction in frictional resistance is observed, which prevents breakage of the drill.

Further, since the strength buffering portion is interposed between the drill body and the shank in accordance with the structure of the margin and the outer peripheral cutting edge, the breakage of the drill is also prevented by this. This is because the diameter of the drill main body is small, so that the rigidity of the connecting portion with respect to the shank is lowered and the cause of breakage due to bending is reduced.

[0009]

EXAMPLE An example of an extremely small diameter drill for a printed wiring board according to the present invention will be described below with reference to the drawings.

1 to 3, reference numeral 1 is a very small diameter drill for a printed wiring board according to the present invention. The drill body 2 has a pair of tip cutting edge ridges 3 and outer peripheral cutting edge ridges 4. , And the twist groove 5 is formed. In this case, the outer peripheral cutting edge ridge 4 is formed by the intersecting ridge of the margin 6 and the spiral groove 5 at the tip of the drill body 2 in the axial direction. This margin 6 is shown in FIG.
As is clearly indicated by, the undercut portion 7 and the outer peripheral flank 8 are processed and thus remain. In this case, the neck diameter of the undercut portion 7 is applied in the range of 0.75 to 0.99 times the blade edge diameter D. This is because if it is less than 0.75, the drill strength is lowered and it becomes a problem.

Further, the margin 6 is set such that its width W is set within a range of 40 to 60% of the core thickness d, and the outer peripheral relief depth δ is set within a range of 5 to 15% of the cutting edge diameter D. It
These are set based on hole wall roughness, hole position accuracy, drill strength, and the like. The core thickness d is 2 of the cutting edge diameter D.
It is set within the range of 0 to 40%.

Further, the drill body 2 is integrally connected to the shank 9, but a strength buffer portion 10 is interposed between the drill body 2 and the shank 9. The strength buffering portion 10 is constituted by a cylindrical portion having a diameter smaller than that of the shank 9 in FIG. 1, but may be constituted by a tapered portion as seen in FIG. This is because the diameter of the cutting edge of the drill body 2 is small,
The rigidity of the strength buffering portion 10 is reduced to increase the resistance of the drill body 2 to bending. That is, when the rigidity of the strength buffering portion 10 is high, the strength of the drill body 2 side is relatively weakened, and the drill body 2 is broken due to a notch effect or the like.

The extremely small diameter drill 1 for a printed wiring board according to the present embodiment can be applied to a cutting edge diameter of about φ0.1 to 0.3 mm due to the above-mentioned measures against breakage. . As the main shape of the drill of the present invention,
When the blade diameter is 0.2 mm, the tip angle is 130 °,
Twist angle; 30 °, core thickness; 0.065, core thickness taper;
0.025 / 1, margin width; 0.030 mm, groove width ratio; 1.60, groove length; 3.0 mm. However, regarding the shape of the drill, for example, the tip angle is 110 ° to 151 ° and the helix angle is 20 ° to 41 °.
The groove width ratio is 1.2 to 2.2, so that it can be applied over a wide range.

Further, FIG. 5 shows the results of breakage resistance of the product of the present invention and the comparative product. in this case,
The invention product and the comparative product both have a cutting edge diameter of φ0.2 mm, and the comparative product is described in Japanese Patent Publication No. 3-167.
It has a structure as seen in the publication. That is, the outer peripheral cutting edge ridge 4 extends to the vicinity of the groove length, does not form the so-called undercut portion 7, and does not form the strength buffering portion 10.

The work material has a thickness of 0.4 mm.
Three glass epoxy substrates (FR-4) each consisting of four layers were applied.

As a result, in the present invention, the feed rate was increased from 4 μm / rev to 15 μm / rev,
6μ of the comparative product, just by breaking one piece at 15μm / rev
It was found that the resistance to breakage was extremely high with respect to the m / rev breakage. As a result, it was confirmed that the present invention can be applied to a groove length of about 6 mm.

The hole position accuracy is 10 μm /
I compared by sending rev, but almost the same result was obtained,
It was also found to be extremely practical. In addition, the occurrence of chip clogging and smear was also reduced.

[0018]

As described above, according to the present invention, in addition to the construction of the margin 6 and the outer peripheral cutting edge 4 by processing the undercut portion 7 and the outer peripheral flank 8, the drill main body 2
Since the strength buffering portion 10 between the shank 9 and the shank 9 is configured, there is an advantage that fracture resistance is extremely high and a drill breakage accident during drilling is prevented.

[Brief description of drawings]

FIG. 1 is a front view showing an embodiment of a very small diameter drill for a printed wiring board according to the present invention.

FIG. 2 is a partially enlarged front view showing a main part of a cutting edge portion.

FIG. 3 is an enlarged side view.

FIG. 4 is a front view showing a modified example of an extremely small diameter drill for a printed wiring board according to the present invention.

FIG. 5 is an explanatory diagram of a feed rate test comparing the breakage resistance of the product of the present invention and that of the comparative product.

[Explanation of symbols]

 1 Micro drill for printed wiring board 2 Drill body 3 Tip cutting edge ridge 4 Perimeter cutting edge ridge 5 Twisted groove 6 Margin 7 Undercut part 8 Outer flank 9 Shank 10 Strength buffering part

Claims (2)

[Claims] 1. A print comprising a drill main body 2 having a spiral groove 5 and a shank 9 following the drill main body 2. A pair of tip cutting edge ridges 3 and a peripheral cutting edge ridge 4 are formed on the drill body 2, respectively. In a very small diameter drill for a wiring board, an intermediate strength buffer portion 10 composed of a cylindrical portion having a diameter smaller than the shank diameter or a tapered portion is interposed between the drill body 2 and the shank 9, and The outer peripheral cutting edge ridge 4 is formed by an intersecting ridge of a margin 6 and a helical groove 5 provided at the axial tip portion of the drill body 2, and the margin 6 is formed by machining the undercut portion 7 and the outer peripheral flank 8. A small diameter drill for a printed wiring board, characterized in that it remains at the axial tip of the drill body 2. 2. The margin according to claim 1 has a width of 40 to 60% of a core thickness d and an outer peripheral relief depth δ of 5 to 5 of a cutting edge diameter D.
The extremely small diameter drill for a printed wiring board according to claim 1, which is set to 15%.