JPH01306111A - Small diameter drill for boring printedboard - Google Patents

Abstract

PURPOSE:To facilitate boring through two laminated substrates by forming an undercut type tip edge section and a twisted groove in a drill body and setting the ratio of core thickness, the ratio of groove width, the core thickness taper per 1mm, the twist angle and the tip angle of the twisted groove within a specific range. CONSTITUTION:In a small diameter drill 1 for boring two laminated printedboard, an undercut type tip edge section 5 and a twisted groove 4 are formed in the drill body 2. The core thickness ratio (core thickness W/edge diameter D) is set to 0.10-0.20, the groove width ratio (groove F/land L) is set to 1.2-1.5, the core thickness taper per 1mm is set to 0.022-0.030, the twist angle theta of the twisted groove 4 is set to 33-37 deg., and the tip angle alphais set to 125-135 deg.. When a drill having such shape is employed, the twist angle thetais strengthened, cutting resistance is reduced through reduction of the core thickness, cutting chips are discharged smoothly. Furthermore, since the rigidity reduced through reduction of the core thickness is compensated through selection of the groove width ratio, the rigidity is improved and the cutting chips can be discharged smoothly.

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 two-thick printed circuit boards.

(Prior Art) Drills for processing printed circuit boards are increasingly used to drill small diameter holes of 0.6 mm or less due to the increasing density of printed circuit boards.

On the other hand, as seen in JP-A-62-181815, the helix angle is set to 30° or more, the depth of the drill groove is set to 50 to 70% of the drill diameter, in other words, the core thickness ratio is set to 0. .3
~0.5. A proposal for a contoured surface with a uniform core thickness has been disclosed.

(Problem to be solved by the invention) However, with small diameter drills for processing printed circuit boards,
Drill breakage, hole position accuracy, epoxy smear, and chip clogging were cited as processing problems, and the small diameter drill seen in the publication mentioned above was insufficient in terms of performance.

For this reason, the present invention aims to improve the core thickness ratio, groove width ratio, core thickness taper, and
The above-mentioned problems are attempted to be solved by optimizing the helix angle and the tip angle.

(Means for Solving the Problems) The present invention has been made in view of the above-mentioned points, and aims at specialization by using a small-diameter drill for processing printed circuit boards for drilling holes in two stacked printed circuit boards. This is done in consideration of its optimal shape.

That is, in the present invention, the core thickness ratio (core thickness/cutting edge diameter) is 0. + -0.2, groove width ratio (groove/land): 1.2 to 1.5. Regarding the core thickness taper per I+++m, o, oz ~ 0.030. For the helix angle, 33° to 37° and for the tip angle.

It is set at 125@ to 135'. In particular, these shapes have a strong helix angle and a small core thickness to reduce cutting resistance and improve chip evacuation. This is done in such a way that the groove width ratio is compensated for. Therefore, the small diameter drill for processing printed circuit boards of the present invention has achieved the contradictory objectives of high rigidity and good chip evacuation.

(Function) The small diameter drill for printed circuit board processing in the present invention has two
This is for drilling holes in stacked printed circuit boards.

In the present invention, the core thickness ratio, etc., are optimized to provide high rigidity and excellent chip evacuation properties. This is because consideration was given to increasing the chip evacuation performance by increasing the helix angle and decreasing the core thickness, while supplementing rigidity with the full width ratio.

Therefore, the small diameter drill for processing printed circuit boards of the present invention works to improve hole position accuracy.

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

In Figures m1 to 3, (1) indicates the drill body (2
) and a shank portion (3), this is a small diameter drill for processing printed circuit boards, and is made of, for example, a cemented carbide grade equivalent to Mho. 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, the two-layer printed base jft
(10a) and (10b) are drilled together with the backing plate (11) by so-called simultaneous optical machining.

Therefore, in this case, the groove length L3 of the twisted groove (4) is
) and the thickness of the waste board (12) 6
In this example, the thickness of the printed circuit board (10al (IOb) is 1.6++++w, and the thickness of the Afl patch plate (11) is 0.15mm, so the groove length is □
, Ll was set to 4.7 mm. Therefore, this groove length [7° is generally 4.5 to 5.0+s
It is within the range of +w.

Therefore, the tip cutting edge portion (5) formed on the drill body (2) has a margin length l-, which is L, = 0.4.
Applicable to undercut types with a ff of about 1 m. A pair of tip cutting edge ridges (6) are formed in the tip cutting edge portion (5) by the tip cutting edge angle α. In this case, the tip cutting edge angle α is set within the range of α·125° to 135°. This means that the tip cutting edge ff+a is 12
If the diameter is less than 5'', the tip of the drill tends to bend due to the glass fibers contained in the workpiece, as shown in FIG. 5, and the accuracy of the hole position deteriorates accordingly, so it was excluded. Furthermore, if the tip cutting edge angle a exceeds 135°, the probability of breakage of the drill during machining increases due to the increase in thrust force, which is not practical.

Therefore, the tip cutting edge angle a is 125° to 13
A range of 5° 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 33° to 37°.

Rotation 1fi 60.0 for generally processing printed circuit boards
For 00 to ao and oo mouth rprn, there is a tendency as shown in Table 1. In small-diameter drills intended for drilling holes without step machining, chip evacuation is only good within an extremely narrow range of helix angle, and the range of the helix angle θ is 33° to 37°. . When the helix angle θ is less than 33°, the pumping action of the helical groove (4) is low, and when the helix angle θ exceeds 37°, the path through which the chips pass until they are discharged is narrow and the chips do not become loose. The chip evacuation becomes worse because of the dirt.

The small diameter drill (+) of the present invention has improved the core thickness ratio (core thickness/cutting edge diameter), groove width ratio (groove/land), and core thickness taper compared to the standard cross-sectional shape of the undercut type. By doing so, a two-layer printed circuit board (IQa) (1
Suitable for drilling 0bl.

That is, in the small diameter drill (1) of the present invention, the core thickness ratio is 0. IO≦W/D≦0.20. Regarding the groove width ratio, 1.2≦F/L≦1.5. Regarding core thickness taper,
It was set within the range of teo, oz ≦wt≦o, and o3'o per 1 mm.

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. Figure 6 shows the results of actually calculating this.

In Figure 6, the horizontal axis is the cross-sectional area ratio of the drill compared to that of a round bar, and the vertical axis is the moment of inertia in the weakest direction in the cross section perpendicular to the drill shaft. There is.

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. Additionally, generally speaking, increasing the core thickness ratio simultaneously increases the core thickness and the diesel blade, which increases the thrust force and worsens the biting ability of the drill at the start of machining. The drill rigidity increases by increasing the core thickness ratio and decreasing the groove width ratio, that is, the closer it is to a round bar, the greater the drill rigidity becomes, and the hole position accuracy improves, but on the other hand, the helical groove (4) for discharging chips becomes narrower. This may make it difficult to eject the chips, or in some cases, the drill may break due to chip clogging.

Therefore, the results of a study comparing these factors in terms of chip evacuation after actual drilling are explained below.

First, as shown in FIG. 7, in the region where the groove width ratio is less than 1.0 and the core thickness ratio is more than 0.20, the chip evacuation performance becomes poor. In addition, even in areas with good chip evacuation, if the flute width ratio exceeds 1.5 and the core thickness ratio becomes 0.1 or less, the drill rigidity decreases, and the drill bends, resulting in a decrease in accuracy. You can see that the drill is broken.Therefore, 1
Small diameter drill for processing printed circuit boards in the present invention +11
Now, regarding the core thickness ratio, 0.10≦Ill/D≦0.
20. Regarding the groove width ratio, a range of 1.2≦F/L≦1.5 was selected.

In addition, regarding core thickness taper, if it is less than o, oz,
The section modulus becomes smaller, resulting in insufficient strength, and 0.030
Exceeding this was excluded because chip evacuation would be poor.

The small-diameter drill (1) for processing printed circuit boards of the present invention configured in this manner is set to have a shape and size similar to a drill bit, for example. In this case, the groove width ratio is F
/L≦1.3-1.4. For core thickness taper, Wt≦
It was set at 0.025/l.

Margins Below Next, examples of drilling in the product of the present invention and the conventional product will be described.

The tool specifications of the present invention are the drill diameter D = φ0.40 mm in Table 2 mentioned above, and the cutting conditions were 1 revolution = 70.000 rpm and feed = 21a+/s+n. The workpiece was a two-layered printed circuit board (lOa) (IObl) as shown in FIG. 4, and the backing plate (II) was an Ai plate with a thickness of O,I5n+w+.

As a result, in the product of the present invention, the hole position accuracy at 4,000 hits was mostly within the range of 50μ as shown in FIG. 8, and the maximum deviation was also small at 54μ. Note that the number of sampling points in this case is 50 points.

On the other hand, the conventional product is 50 μm as shown in Figure 9.
The hole position accuracy was poor as some of the holes were out of alignment, and the maximum deviation was as large as 75μ. In this case, the cutting conditions for the conventional product cannot be the same as those described above, and 1.
Rotation speed = 60.000rpII+, feed = 1.8a
The conditions are lowered to +/win. In addition, the tool specifications for the conventional product are core thickness ratio = 0.175. Groove width ratio = 1.
8. Core thickness taper Wt =0.02/1. Torsion angle = 30
°, tip angle = 120°, and for groove length 3, etc.,
This is similar to the product of the present invention.

(Effects of the Invention) As explained above, the present invention aims at optimizing the shape of the drill so that it is suitable for simultaneous drilling of two stacked printed circuit boards. Therefore, it is possible to provide a small-diameter drill with good performance and chip evacuation. Therefore, according to the present invention, the following specific effects can be obtained.

■ High-efficiency machining can be performed in one shot without the drill breaking 7 This can be seen from the comparison of conditions shown in Figures 8 and 9.

■ Hole position accuracy due to drill bending is ±50μ50μ
Can be processed with precision. This is clear from a comparison of FIGS. 8 and 9.

■ It is now possible to drill holes of good quality without any problems such as poor chip evacuation.

[Brief explanation of the drawing]

FIG. 1 is a front view showing an embodiment of a small diameter drill for processing printed circuit boards of the present invention, FIG. 2 is an enlarged side view thereof, and FIG. 3 is a partially enlarged iE side view showing the cutting edge portion. Figure 4 is a conceptual explanatory diagram showing the drilling situation, Figure 5 is an explanatory diagram showing the relationship between the tip angle α and hole position accuracy, and Figure 6 is the core thickness ratio and groove width in the cross-sectional shape of the drill. Figure 7 is an explanatory diagram showing the relationship between the core thickness ratio and groove width ratio in terms of chip evacuation. FIG. 9 is an explanatory diagram showing the hole position accuracy obtained by the conventional product. (1)・-Small diameter drill for printed circuit board processing (21-・
Drill body (31--Shank part (4)
...Twisted groove +5) -...Tip cutting edge portion (6)...Tip cutting edge ridge Patent applicant Toshiba Tungaloy Corporation 4-: Twisted groove f: Sakibori scattering rod 7-shade diagram

Claims (1)

[Scope of Claims] A small diameter drill for drilling holes in two stacked printed circuit boards, the drill body having an undercut type tip cutting edge portion and a helical groove formed therein,
A small diameter drill for processing printed circuit boards, characterized by satisfying the following conditions (a) to (e). (a) Core thickness ratio (core thickness/cutting edge diameter) is 0.10 to 0.20
To be. (b) The groove width ratio (groove/land) is 1.2 to 1.5. (c) Core thickness taper per 1 mm is 0.022 to 0.0
Must be 30. (d) The helix angle of the helix groove is 33° to 37°. (e) The tip angle is 125° to 135°.