JP2004335655A - Hole forming method, printed wiring board, and hole forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a hole forming method for drilling a substantially straight hole on a board, a printed wiring board having a hole formed by this method, and a hole forming device for forming the hole. <P>SOLUTION: The printed wiring board 10 is irradiated with a laser 24 from its front surface to form a halfway hole 18a, and the board 10 is irradiated with the laser 24 from its rear surface to form a penetrated hole 18. Since the hole 18 is formed by irradiating the board 10 with the laser 24 from its both surfaces, the substantially straight hole 18 can be formed, and a plating liquid can smoothly flow inside the hole 18. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a hole forming method for a substrate, a printed wiring board having holes formed therein, and a hole forming apparatus.
[0002]
[Prior art]
Hole formation in the printed wiring board is performed using a mechanical drill or a laser. Through holes are formed by plating the inner walls of the holes.
[0003]
When forming a hole with a mechanical drill, if the hole diameter of the through-hole of a printed wiring board becomes small, or the pitch between through-holes becomes narrow, it is necessary to make a mechanical drill thin. A thin mechanical drill cannot form a desired hole because the shaft fluctuates during rotation or bends during hole formation. The thinner the machine drill, the easier it is to break and the higher the price. Therefore, when a mechanical drill is used, the manufacturing yield of the printed wiring board is deteriorated.
[0004]
Therefore, a laser is used instead of a mechanical drill. The type of laser is a CO ₂ (carbon dioxide) laser, a UV (ultraviolet) laser, or the like. 6A, first, a printed wiring board 11 is prepared in which metal foils 14a and 14b such as copper foil are laminated on both surfaces of an insulating substrate 12. As shown in FIG. In the present specification and drawings, the metal foil 14 a is a metal foil on the front side of the printed wiring board 11, and the metal foil 14 b is a metal foil on the back side of the printed wiring board 11.
[0005]
As shown in FIG. 6B, alignment marks 32 are provided as reference marks at positions where holes are formed at the four corners of the printed wiring board 11. The alignment mark 32 is provided by a known patterning technique. Positioning is performed by irradiating a laser with the alignment mark 32 as a reference. In the positioning method, the alignment mark 32 is photographed with a CCD (Charge Coupled Device) camera, and the position to which the laser is irradiated is determined by using the position of the photographed alignment mark 32 as a reference. The determined position is irradiated with a laser, and a hole 34 is formed in the printed wiring board 11.
[0006]
However, the energy of the laser is absorbed by the insulating substrate 12 constituting the printed wiring board 11. Further, when the insulating substrate 12 is irradiated with a laser, a gas due to melting of an epoxy resin or the like that is a material of the insulating substrate 12 is generated, and the energy of the laser is absorbed. The laser is tapered in the insulating substrate 12. As shown in FIG. 6B, the hole 34 formed by the laser is tapered, that is, the hole diameter φ5 on the back surface is smaller than the hole diameter φ4 on the surface of the printed wiring board 11. For example, when the thickness of the printed wiring board 11 is about 300 μm, the hole diameter φ4 on the surface of the printed wiring board 11 is about 100 μm, and the hole diameter φ5 on the back surface is about 80 μm. Since the hole diameter φ5 on the back surface is small, the flow of the plating solution may be deteriorated and the plating layer may not be formed.
[0007]
Patent Document 1 discloses a method for forming holes using two types of lasers. A hole is formed in the insulating layer containing glass fiber with a carbon dioxide laser so that the bottom of the hole becomes a copper foil. The copper foil at the bottom of the hole is removed with a YAG laser to form a through hole. By properly using the two types of lasers, holes can be formed without the interface between the copper foil and the insulating layer being removed. That is, even a small-diameter hole can be formed with high accuracy. However, when the hole is formed in the insulating layer, the energy of the laser is absorbed by the insulating layer. Therefore, the hole may be tapered and plating may not be possible.
[0008]
Patent Document 2 describes a method in which a plurality of glass plates are overlapped, a laser is irradiated from both surfaces of the stacked glass plates to form holes, and a plurality of glass plates are bonded. By moving the focal point of the laser, the inner wall of the hole melts and the two glass plates can be bonded. Although Patent Document 2 has a hole drilled with a laser, the purpose is to bond a glass plate, and the purpose is to create a through hole in a printed wiring board by drilling a straight hole and plating the hole. I have not done it. Since the laser is irradiated from both sides of the overlapped glass plates, the lasers reach each other's oscillator, and the oscillator may be destroyed.
[0009]
[Patent Document 1] Japanese Patent Laid-Open No. 2001-244606 (FIG. 1)
[Patent Document 2] Japanese Patent Laid-Open No. 2001-247321 (FIG. 1)
[0010]
[Problems to be solved by the invention]
An object of the present invention is to provide a hole forming method for forming a substantially straight hole in a substrate, a printed wiring board in which holes are formed by the method, and a hole forming apparatus for forming holes.
[0011]
[Means for Solving the Problems]
The gist of the hole forming method of the present invention is to prepare a substrate having a front surface and a back surface, to form a reference mark on the substrate, and to irradiate a laser from the surface of the substrate to form a hole halfway through the substrate And a step of irradiating a laser from the back surface of the substrate and penetrating a hole formed partway through the substrate. In the present invention, holes are formed by sequentially irradiating a laser on the front and back surfaces of a substrate. Therefore, since the hole diameters on both sides of the substrate are made uniform and almost straight holes are formed, the plating solution can flow smoothly into the holes. Further, when laser is irradiated from the front surface, a hole penetrating the substrate may be formed, and the laser beam may be irradiated to the hole penetrating from the back surface.
[0012]
The gist of the printed wiring board of the present invention is that the substrate, the hole penetrating through the substrate and having the same hole diameter on both surfaces of the substrate, the hole diameter in the substrate being smaller than the hole diameter on both surfaces of the substrate, and the hole And a reference mark serving as a reference for the position of. The hole diameters on both sides of the substrate are uniform, making it easier for the plating solution to pass through. Even if the substrate is turned over, the position where the hole is made can be determined by the reference mark.
[0013]
The gist of the hole forming apparatus of the present invention includes an oscillator that oscillates a laser for making a hole in a substrate, a means for forming a reference mark for determining a position for forming the hole, and the laser from both sides of the substrate. Means for irradiating, and means for determining an irradiation position of the laser with reference to the reference mark. A hole is formed by irradiating a laser on both sides of the substrate. The laser irradiation position is determined based on the reference mark.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of a hole forming method and a hole forming apparatus according to the present invention will be described with reference to the drawings. The substrate on which the hole is formed is a printed wiring board. In the specification and drawings, one surface of the substrate is the front surface, and the surface opposite to the front surface is the back surface. In the specification and drawings, reference numeral 16 generally represents reference numerals 16a, 16b, 16c, and 16d.
[0015]
The hole forming apparatus 20 of the present invention shown in FIG. 2 includes an oscillator 22 that oscillates a laser 24 for forming a hole in the printed wiring board 10, and means for forming a reference mark for determining a position for forming the hole. And means for irradiating the laser 24 from both sides of the printed wiring board 10 and means for determining the irradiation position of the laser 24 with reference to a reference mark provided on the printed wiring board 10.
[0016]
As the laser 24, a CO ₂ laser or a UV laser is used. As shown in FIG. 1A, the printed wiring board 10 has a metal foil 14 such as copper laminated on both surfaces of an insulating substrate 12. The output of the laser 24 is changed when a hole is formed in the metal foils 14a and 14b and when a hole is formed in the insulating substrate 12. For example, the output of the laser 24 when forming holes in the metal foils 14a and 14b is about 5 mJ / 7 μsec per shot. The output of the laser 24 when forming a hole in the insulating substrate 12 is about 5 mJ / 100 μsec per shot. The metal foil 14a is on the front surface side of the printed wiring board 10, and the metal foil 14b is on the back surface side.
[0017]
Means for irradiating the laser 24 from both sides of the printed wiring board 10 includes means for turning the printed wiring board 10 upside down. The means for turning over is a robot arm or the like that can be flipped over with the printed wiring board 10 interposed therebetween. After irradiating the laser 24 from the surface of the printed wiring board 10, the printed wiring board 10 is turned over using a robot arm or the like, and the laser 24 is irradiated. Further, the printed wiring board 10 may be turned over by a human hand instead of the robot arm.
[0018]
The means for determining the irradiation position of the laser 24 based on the reference mark provided on the printed circuit board 10 is a CCD camera 28 and a computer for determining the position of the laser 24 irradiation from the position of the reference mark photographed by the CCD camera 28. Including. The reference mark of the present invention is an alignment hole that penetrates the printed wiring board 10. For example, as shown in FIG. 3, assume that there are alignment holes 16a, 16b, 16c, and 16d at the four corners of the printed wiring board 10, respectively. The computer determines which position of the printed wiring board 10 is irradiated with the laser 24 based on the positions of the photographed alignment holes 16a, 16b, 16c, and 16d. It is not necessary to strictly determine the placement position of the printed wiring board 10 in the stage 30 described later.
[0019]
As a means for forming the reference mark, an oscillator 22 that oscillates a laser 24 for forming a hole in the printed wiring board 10 is used. The reason for using the oscillator 22 is that the alignment holes 16 a, 16 b, 16 c, and 16 d that are reference marks are holes that penetrate the printed wiring board 10.
[0020]
Two collimating lenses CL shown in FIG. 2 change the focal point of the laser 24. The mask adjusts the diameter of the laser 24. The bend mirror BM is a mirror for reflecting the propagating laser 24. The condensing lens 26 is a lens that irradiates the laser 24 perpendicularly to the printed circuit board 10 when the laser 24 passes through the center. By adjusting the angles of the two Galvan mirrors GM, the position through which the laser 24 passes through the condenser lens 26 can be adjusted.
[0021]
The hole forming apparatus 20 includes a stage 30 on which the printed wiring board 10 is placed and moved. The irradiation position of the laser 24 on the printed wiring board 10 can be changed.
[0022]
A hole forming method using the hole forming apparatus 20 will be described. As shown in FIG. 1A, a printed wiring board 10 in which metal foils 14a and 14b such as copper foil are laminated on both sides of an insulating substrate 12 is prepared. The thickness of the printed wiring board 10 described in the present embodiment is, for example, about 300 μm.
[0023]
As shown in FIG. 1B, an alignment hole 16 as a reference mark is opened in the printed wiring board 10 using a laser 24. As the laser 24, the same laser 24 as that used when forming a hole in a later process is used. Accordingly, the hole diameter of the alignment hole 16 is such that the hole diameter on the front surface is larger than the hole diameter on the back surface. The laser 24 used is a CO ₂ laser or a UV laser. For example, as shown in FIG. 3, alignment holes 16a, 16b, 16c, and 16d are opened in the four corners of the printed wiring board 10.
[0024]
The position where the laser 24 is irradiated is determined with the alignment hole 16 as a reference. First, the alignment hole 16 is photographed by the CCD camera 28. The computer determines the x and y positions at which the laser 24 is irradiated from the x (horizontal direction) and y (vertical direction) positions of the photographed alignment hole 16 on the printed wiring board 10.
[0025]
As shown in FIG. 1C, the printed wiring board 10 is irradiated with a laser 24 to form a hole 18 a halfway through the printed wiring board 10. The depth of the hole 18 a is set to the depth to the middle of the printed wiring board 10. If a plurality of holes 18 a are to be formed, the laser 24 is irradiated to a plurality of positions on the printed wiring board 10. Since the metal foil 14a and the insulating substrate 12 are made of different materials, the output of the laser 24 is changed. For example, the output of the laser 24 when opening the hole 18a in the metal foil 14a is about 5 mJ / 7 μsec per shot. The output of the laser 24 when opening the hole 18a in the insulating substrate 12 is about 5 mJ / 100 μsec per shot. When a hole having a desired depth is not formed by one shot, a hole having a desired depth is formed by a plurality of shots.
[0026]
As shown in FIG. 1D, the printed wiring board 10 is turned over, and the irradiation position of the laser 24 is determined with the alignment hole 16 as a reference. The position determination method is the same as the position determination method using the alignment hole 16 described above.
[0027]
After determining the position where the laser 24 is irradiated, the laser 24 is irradiated to the position. The laser 24 is irradiated to penetrate the hole 18a formed partway through the printed wiring board 10. The through holes 18 have the same hole diameters φ1 and φ2 on both sides of the printed wiring board 10. In the middle of the printed wiring board 10, the hole diameter φ3 is the smallest. For example, the hole diameters φ1 and φ2 are 100 μm, and the hole diameter φ3 is 90 μm. The hole diameter φ3 is larger than the hole diameter φ5 shown in FIG. 6, and the plating solution can flow smoothly.
[0028]
A plating resist is formed on both surfaces of the printed wiring board 10. A plating solution is flowed into the hole 18 to form a plating layer on the inner wall of the hole 18 to complete the through hole.
[0029]
Through the above steps, the holes 18 are formed, and the printed wiring board 10 of the present invention is manufactured. Since the holes 18 are formed by sequentially irradiating the front surface and the back surface of the printed wiring board 10 with the laser 24, the hole diameters φ1 and φ2 of the holes 18 are aligned on both sides of the printed wiring board 10. The hole 18 has the smallest hole diameter φ3 at the center of the hole 18, but is larger than the hole diameter φ5 on the back surface of the laser 24 described in the prior art. That is, the hole 18 is substantially straight, and the inner wall of the hole 18 can be plated without adversely affecting the flow of the plating solution. Through holes having a large aspect ratio can be provided, and the circuit pattern of the printed wiring board 10 can be miniaturized. The aspect ratio is a value obtained by dividing the depth of the hole 18 by the hole diameter. Since the alignment hole 16 is provided, the hole 18 can be formed by irradiating the laser 24 without causing a positional shift even after the printed wiring board 10 is turned over.
[0030]
Although the printed wiring board 10 is turned upside down after forming the hole 18a with the laser 24 partway through the printed wiring board 10, the printed wiring board 10 may be turned upside down after the hole penetrating the printed wiring board 10 is formed. As shown in FIG. 4A, a printed wiring board 10 in which metal foils 14 are laminated on both surfaces of an insulating substrate 12 is prepared.
[0031]
As shown in FIG. 4B, an alignment hole 16 is formed in the printed wiring board 10. The alignment holes 16 are formed at the four corners of the printed wiring board 10. The position where the laser 24 is irradiated is determined using the alignment hole 16. A laser beam 24 is irradiated to the determined position to form a hole 18b penetrating the printed wiring board 10.
[0032]
After the hole 18b penetrating the printed wiring board 10 is formed from the surface of the printed wiring board 10, the printed wiring board 10 is turned over as shown in FIG. To complete the hole 18. Before irradiating the laser 24, the position where the laser 24 is irradiated is determined using the alignment hole 16.
[0033]
When the hole 18a is first drilled, the hole diameter on the back surface is the same as that of the conventional hole smaller than the hole diameter on the front surface, but by irradiating the laser 24 from the back surface, the hole diameters on the front surface and the back surface are made uniform. Can do. By irradiating the laser 24 from both sides of the printed wiring board 10, the substantially straight hole 18 can be formed. The plating solution flows smoothly through the hole 18, and the inner wall of the hole 18 can be plated.
[0034]
Although the laser 24 is irradiated on each side of the printed wiring board 10, the holes 18 may be formed by irradiating the laser 24 from both sides of the printed wiring board 10 at a time. In this case, the hole forming apparatus prepares two sets of the oscillator 22 of the laser 24 shown in FIG. Instead of the stage 30, a means for holding the printed circuit board 10 is used. If the oscillation of the laser 24 is not stopped immediately after the hole 18 is formed, the laser 24 is irradiated to the other oscillator 22. The oscillator 22 is destroyed by the lasers 24 of each other. Therefore, a half mirror is provided between the oscillator 22 and the printed wiring board 10 so that the partner laser 24 does not reach the oscillator 22.
[0035]
As the reference mark, the alignment hole 16 penetrating the printed wiring board 10 is formed, but another reference mark may be formed. For example, as shown in FIGS. 5A and 5B, the printed wiring board 10 may be provided with notches 17a and 17b having round or square corners. Since the notches 17a and 17b can be confirmed from both sides of the printed wiring board 10, the position where the laser 24 is irradiated can be determined even after the printed wiring board 10 is turned over.
[0036]
Although the formation of holes in the printed wiring board 10 has been described, the present invention may be applied to other boards. If it is a transparent substrate, the reference mark may be other than the alignment hole 16 penetrating the substrate. For example, a point or circle as a reference mark is drawn on one side of the substrate.
[0037]
As mentioned above, although embodiment of this invention was mentioned above, this invention is not limited to said embodiment. In addition, the present invention can be implemented in a mode in which various improvements, modifications, and changes are made based on the knowledge of those skilled in the art without departing from the spirit of the present invention.
[0038]
【The invention's effect】
According to the present invention, a substantially straight hole can be formed by forming a hole by irradiating a laser from both sides of the substrate. The flow of the plating solution does not deteriorate in the hole, and the inner wall of the hole can be plated. Since reference marks penetrating the substrate are provided at the four corners of the substrate, it is possible to position the laser irradiation position when the substrate is turned over.
[Brief description of the drawings]
1A and 1B are diagrams showing a hole forming method according to the present invention, in which FIG. 1A is a cross-sectional view of a printed wiring board, FIG. 1B is a view in which alignment holes are formed, and FIG. It is the figure which formed the hole to the middle, (d) is the figure which turned the printed wiring board over and completed the hole.
FIG. 2 is a diagram showing a configuration of a hole forming apparatus according to the present invention.
FIG. 3 is a front view of a printed wiring board in which alignment holes are formed at four corners.
4A and 4B are diagrams showing another hole forming method of the present invention, in which FIG. 4A is a cross-sectional view of a printed wiring board, and FIG. 4B is a view in which an alignment hole and a hole penetrating the printed wiring board are formed. Yes (c) is a view in which the printed wiring board is turned over to complete the hole.
5A and 5B are views showing another hole forming method of the present invention, in which FIG. 5A is a plan view in which round cutouts are provided at corners of a printed wiring board, and FIG. 5B is a plan view showing square cutouts. It is the provided top view.
6A and 6B are diagrams showing a conventional hole forming method, wherein FIG. 6A is a cross-sectional view of a printed wiring board, and FIG. 6B is a diagram in which alignment marks and holes are formed.
[Explanation of symbols]
10, 11: Printed wiring board 12: Insulating substrates 14a, 14b: Metal foils 16, 16a, 16b, 16c, 16d: Alignment holes 17a, 17b: Notches 18, 18a, 18b, 34: Holes 20: Hole forming device : Oscillator 24: Laser 26: Condensing lens 28: CCD camera 30: Stage 32: Alignment mark

Claims (10)

Providing a substrate having a front surface and a back surface;
Forming a reference mark on the substrate;
Irradiating a laser from the surface of the substrate, forming a hole halfway through the substrate;
Irradiating a laser from the back surface of the substrate, penetrating a hole formed partway through the substrate;
A hole forming method including: The hole forming method according to claim 1, further comprising the step of turning the substrate upside down after the step of forming the hole partway through the substrate. Providing a substrate having a front surface and a back surface;
Forming a reference mark on the substrate;
Irradiating a laser from the surface of the substrate to form a hole penetrating the substrate;
Irradiating the through hole with a laser from the back surface of the substrate;
A hole forming method including: The hole forming method according to claim 3, further comprising a step of turning the substrate over after forming the hole penetrating the substrate. The hole forming method according to claim 2, further comprising a step of determining a laser irradiation position on the basis of the reference mark after the step of turning the substrate over. A substrate,
Through the substrate, the hole diameter on both sides of the substrate is the same, the hole diameter in the substrate is smaller than the hole diameter on both sides of the substrate, and
A reference mark serving as a reference for the position of the hole;
Including printed wiring board. The printed wiring board according to claim 6, wherein the reference mark includes an alignment hole penetrating the board. The printed wiring board according to claim 6 or 7, wherein a plating layer is provided on an inner wall of the hole. An oscillator that oscillates a laser for forming a hole in the substrate;
Means for forming a reference mark for determining a position for forming the hole;
Means for irradiating the laser from both sides of the substrate;
Means for determining a laser irradiation position with reference to the reference mark;
Including a hole forming device. The hole forming apparatus according to claim 9, wherein the means for irradiating the laser from both sides of the substrate includes means for turning the substrate over.

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