JPH01306112A - Small diameter drill for machining printedboard - Google Patents

Abstract

PURPOSE:To facilitate boring of three sheets of printedboard by forming an undercut type tip cutter section and a twisted groove and setting the core thickness ratio, groove width ratio, core thickness taper per 1mm twist angle and tip angle of the twisted groove within a specific range. CONSTITUTION:An undercut type tip cutter section 5 and a twisted groove 4 are formed, where the core thickness ratio (core thickness W/edge diameter W) is set to 0.15-0.25, the groove width ratio (groove F/land L) is set to 1.4-1.7, the core thickness taper per 1mm is set to 0.03-0.04, the twist angle thetaof the twisted groove 4 is set to 27-33 deg., and the tip angle alpha is set to 125-135 deg.. An undercut type small diameter drill 1 for boring three laminated printedboards through step drilling has high rigidity and cutting chips can be discharged smoothly. Furthermore, boring position accuracy is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a small-diameter drill for processing printed circuit boards for drilling holes in three stacked printed circuit boards by step drilling.

(Conventional technology) Conventionally, drilling holes in three layers of printed circuit boards was
A method is adopted in which a patch plate at 8°C is placed on the top board, and then a small-diameter drill is given axial feed and rotation to drill holes in the printed circuit board together with the patch plate in a so-called one-shot process (for example, Publication No. 62-27161,
(See Japanese Unexamined Patent Publication No. 11207/1983, etc.).

On the other hand, small-diameter drills require a helix angle of 30° or more to drill a small-diameter deep hole with a diameter of 0.5 mm or less, and a drill groove depth of 50 to 70% of the drill radius, in other words, a core thickness ratio of 0.
．． 3 to θ, 5 A proposal for a shape surface formed with a web thickness (core thickness) of
(See Publication No. 181815).

(3m to be solved by the invention) On the other hand, in recent drilling methods, a step drilling method has been proposed in order to cope with the increasing density and multilayering of printed substrates.

It is attracting increasing attention due to its drilling efficiency.

However, when applying this method to drill holes with a conventional undercut type small-diameter drill that emphasizes versatility, chip clogging causes a decrease in chipping resistance and hole positioning accuracy, which makes the characteristics of step drilling There was a problem that it could not be used.

Therefore, the present invention provides a small-diameter drill for drilling three-layered printed circuit boards using a step drilling method, and a small-diameter drill that is specialized for processing printed circuit boards and has a tool shape suitable for the processing method. It is intended to provide a drill.

(Means for Solving the Problems) The present invention has been made in view of the above-mentioned points, and is a small-diameter drill for undercut type printed circuit board processing for drilling holes in three-layered printed circuit boards by step drilling. The thickness ratio, groove width ratio, core thickness taper, helix angle, and tip angle are optimized.

In other words, in step drilling, step feeding is performed 3 to 4 times, so chips can be ejected during pulling. Therefore, in terms of the shape of the drill, the core thickness ratio (core thickness /
The cutting edge diameter) is 0.15 to 0.25. Groove width ratio (
groove/land), 1.4 to l, 7. Regarding the core thickness taper, it is 0.03 to 0.04 per 1 mm.
Regarding the twist angle, 271 to 331. As for the tip angle! The angle is set between 25° and 135°. These numerical limitations are.

Particularly in step drilling, consideration was given to satisfying the contradictory conditions of high rigidity and good chip evacuation.

(Function) The small diameter drill for processing printed circuit boards of the present invention is for drilling holes in three stacked printed circuit boards by step drilling.

Therefore, when the small-diameter drill is pulled up, chips are discharged to the outside. Therefore, compared to conventional products, high-speed rotation and high-feeding are possible.

In addition, the small diameter drill of the present invention is specialized by setting the optimum shape such as the core thickness, so that the hole position accuracy is improved compared to conventional products.

(Example) An example of a small diameter drill for processing printed circuit boards according to the present invention will be described below.

In Figures 1 to 3, (1) represents the drill body (2).
) and a shank portion (3), it is a small diameter drill for processing printed circuit boards, and is made of cemented carbide of a grade equivalent to M20, for example. This small diameter drill (1) is usually applied to tools with a cutting edge diameter of φ0.6 mm or less,
As shown in Figure 4, three printed circuit boards (10
al (10b) (lQc) along with the backing plate (Ill) are drilled by step drilling. Therefore, in this case, the groove lengths I and 2 of the twisted groove (4) are the printed circuit board (10a) (lOb) (10cl, It is set based on the thickness of the backing plate (11) and the sacrificial plate (12).In addition, regarding the groove length L2, L2=5.1 to 6
．． A range of 5+am is suitable, and in this example, Lm=
It was set to 63n+m. The setting range of L2 is the general thickness 1 of the printed circuit board (10a) (10b) (Inc)
．． 3 times the 6ram (3 stacked) and through type 0.3 to 0.5
mm, the thickness of the backing plate (11) is 0.2 to 0.3 mm, and the chip discharge is 1 mm.

Therefore, the tip cutting edge portion (5) formed on the drill body (2) has a margin length of L s = 0.4 m.
Applicable to undercut type items that are approximately n+. And, the tip cutting edge part (5) has a tip cutting edge angle a! A pair of tip cutting edges (6) are formed. In this case, the tip cutting edge angle α is set within the range of α·125° to 135°. This is because when the tip cutting edge angle a is less than 125°, the drill tip tends to bend due to the glass fibers contained in the workpiece, as shown in Figure 5, resulting in poor hole positioning accuracy. It was excluded because of this. Furthermore, if the tip cutting edge angle a exceeds 135°, the probability of breakage during machining increases due to the increase in thrust force, which is not practical. Therefore, for the tip cutting edge angle α, 1
A range of 25° to 135° is optimal.

In addition, in the axial direction of the drill body (2), there is a twisted groove (4).
is formed, but the twist angle θ of this twist groove (4) is
θ=set within the range of 27° to 33°.

In this case, the helix angle θ depends on the correlation between the chip evacuation performance and the bending rigidity of the drill, and is therefore set in consideration of the relationship between the two.

That is, the relationship between the helix angle θ and the chip discharge performance is as shown in Table 1, and generally, as the helix angle θ becomes smaller, the chip discharge performance deteriorates.

In relation to chip evacuation performance, the helix angle θ is optimally around 35°, and step machining improves overall chip evacuation performance.

Margin below Table 1 shows drill diameter: φ0.4n+n+, test conditions: 1 revolution = 75.000rpH, feed = 0.
．． 03mm/rev.

The binding and processing board is glass-epoxy copper clad laminate 1
(4 layers) I 6m! It is made of three layers of one thickness.

On the other hand, the relationship between the helix angle θ and the hole position viscosity is
As shown in the figure, when the helix angle θ is 25° or more, the hole position accuracy 1 gradually decreases as the helix angle increases, and 3
At 5° or more, the performance target is maximum dispersion of 75 with 3
Exceeds μ. Therefore, the twist angle θ is θ=27°~
A range of 33° was selected.

Furthermore, in the small diameter drill (1) of the present invention, the amplifier 1
− Core thickness ratio (
By improving the core thickness/cutting edge diameter), groove width ratio (groove/land) 1, and core thickness taper, it has been made suitable for step drilling.

That is, in the small diameter drill (1) of the present invention, the core thickness ratio is 0.15≦W/D≦0.25. Regarding the groove width ratio, 1.4≦F/L≦1.7. Regarding core thickness taper,
0.03≦Wt≦0.04 per 1111Im
It was set within the range of .

The core thickness ratio and groove width ratio are the most important factors that determine the shape of the cross section perpendicular to the axis of the drill. Decreasing the core thickness ratio will reduce the rigidity of the drill, and conversely, decreasing the groove width ratio will increase the drill rigidity. becomes larger. The result of actually calculating this is shown in FIG. In Figure 7, the horizontal axis shows the new area ratio expressed as a ratio of the cross-sectional area of the drill compared to that of a round bar, and the vertical axis shows the moment of inertia in the most acute direction in a cross section perpendicular to the drill shaft. ing. As is clear from this, it can be seen that for the same cross-sectional area, the influence of the groove width ratio is greater than that of the core thickness ratio. Furthermore, increasing the core thickness ratio also increases the core thickness and the diameter of the drill bit, which increases the thrust force and worsens the biting ability of the drill at the start of machining. Drill rigidity is increased by increasing the core thickness ratio.
Decreasing the groove width ratio, in other words, the closer it is to a round bar, the larger the kerf and the better the hole position accuracy, but on the other hand, the twisted groove (4) for ejecting chips becomes narrower, making it difficult to eject the chips. In some cases, the drill bit may break due to chip jamming.

Therefore, the results of a study comparing these factors in terms of chip evacuation performance during actual drilling will be explained below.

First, as shown in FIG. 8, in the region where the groove width ratio is less than 1.4 and the core thickness ratio is more than 0.25, the chip evacuation performance becomes poor. In addition, even in areas with good chip evacuation, if the flute width ratio exceeds 97 and the core thickness ratio becomes less than 0.15, drill rigidity decreases, resulting in a decrease in hole position accuracy due to drill bending, and drill breakage. becomes visible. therefore,
Small diameter drill (+) for printed circuit board processing in the present invention
Now, regarding the core thickness ratio, 0.15≦Ill/D≦0.
25. Regarding the groove width ratio, a range of 1.4≦F/L≦1.7 was selected.

Regarding the core thickness taper, if it is less than 0.03, the section modulus will be small, resulting in insufficient strength, and if it exceeds 0.04, the chip evacuation will be poor, so it was excluded.

The small-diameter drill (+) for processing printed circuit boards of the present invention constructed in this manner is set to have a shape and dimensions similar to, for example, a robe. In this case, the groove width ratio is F
/L≦1.5-1.6. For core thickness taper, Wt≦
It was set at 0.035/l.

In the following margin, an example of drilling by step drilling in a product of the present invention and a conventional product will be described.

The tool specifications of the present invention are the drill diameter D=φ0.40m+a in Table 2 mentioned above, and the cutting conditions are as follows: rotation speed=To, 000rpm, feed=2. In+
/1lin. In addition, the workpiece is a three-layered printed circuit board (10al (10b) as shown in Figure 4).
l (lOcl, and the patch plate (11) is 0.I5n+
I decided to use mFI as a board.

As a result 1, the hole position accuracy of the product of the present invention at the time of 4,000 hits is 1 as shown in Figure 9.
It fell within the range of 00μ, and the maximum deviation was also small at 84μ. Note that the number of sampling points in this case is 50 points. On the other hand, with the conventional product, as shown in Figure 10, some of the holes deviate from 100μ, making the hole level r! 1 accuracy was poor, and the maximum deviation was large at 131μ. In this case, the tool specifications of the conventional product are core thickness ratio = 0.
175. Full width ratio = 1.8, core thickness taper W t = 0.
02/1. Helix angle = 30", tip angle = 120"
The groove length L3 etc. are based on the product of the present invention.

(Effects of the Invention) As explained above, the present invention provides a small-diameter drill (1) dedicated to drilling a three-hole printed circuit board (IOal (10b) (IOcl) by step drilling. This small-diameter drill (1) has an optimal shape for core thickness ratio, groove width ratio, etc., so it has high rigidity and good chip evacuation performance.Therefore, as shown in FIG. As can be seen, the hole position accuracy is high and the hole drilling efficiency is improved by -1.

[Brief explanation of the drawing]

Fig. 1 is a front view showing an embodiment of a small diameter drill for processing printed circuit boards according to the present invention, Fig. 2 is an enlarged side view thereof, Fig. 3 is a partially enlarged front view without showing the cutting edge portion, Figure 4 is an explanatory diagram showing the drilling situation, Figure 5 is an explanatory diagram showing the relationship between the tip angle a and the hole position accuracy (standard deviation), and Figure 6 is the relationship between the helix angle θ and the hole position rIt. Interval (maximum variation)
FIG. 7 is an explanatory diagram showing the relationship between core thickness ratio and flute width ratio in the cross-sectional shape of the drill, and FIG. 8 is an explanatory diagram showing the relationship between core thickness ratio and flute width ratio in chip evacuation. FIG. 9 is an explanatory diagram showing the hole position accuracy obtained by the small diameter drill for processing printed circuit boards of the present invention.
The figure is an explanatory diagram showing the hole position accuracy obtained with the conventional product. +11-...Small diameter drill for printed circuit board processing (21-
・・Drill body (3)・-Shank part (4
)・-Twisted groove (5)-Tip cutting edge part (6
)... Tip cutting edge ridge patent applicant: Toshiba Tungaloy Co., Ltd.; Jajidando Figure 3

Claims (1)

[Claims] A small diameter drill for drilling holes in three stacked printed circuit boards by step drilling, the drill body having:
In addition to forming an undercut type tip cutting edge portion and a twisted groove, the following conditions (a) to (e) are met.
A small diameter drill for processing printed circuit boards that satisfies the following requirements. (a) Core thickness ratio (core thickness/cutting edge diameter) is 0.15 to 0.25
To be. (b) The groove width ratio (groove/land) is 1.4 to 1.7. (c) Core thickness taper per 1 mm is 0.03 to 0.04
To be. (d) The helix angle of the helix groove is 27° to 33°. (e) The tip angle is 125° to 135°.