JPH11204916A - Printed board and hole drilling machining method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To be able to form both through holes and blind via holes, by arranging a high vapor pressure element at a vapor pressure region and a laser beam irradiating position just before a completion of forming holes of a printed board. SOLUTION: A printed board 10 comprises a layer of core material 5 provided as to be center in the perpendicular direction of the board, each layer so provided as the layer of core material 5, an inner layer copper foil 4, a high vapor pressure layer 3 and an insulator layer 2 as to contrast in order and semiconductor parts to be able to provided on the both surfaces. A beam spot of laser beam L is set at a required machining position on the surface of the insulator layer and to obtain required blind via holes a tapered degree of the via holes which are previously and experimentally selected based upon a relation with respect to a proper known laser beam output, a diameter, a pulse number and the tapered degree or a relation with respect to a particle diameter of machining residual number is set as a pulse number to be reduced. The insulator layer 2 is locally ground in the board thickness direction by the laser beam, and the high vapor pressure layer 3 is vaporized to spout to the outside of the via holes 7.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for drilling a printed circuit board using a laser beam, and more particularly to a method for forming a through hole and a blind via hole in a printed circuit board.

[0002]

2. Description of the Related Art In general, through holes and blind via holes in a printed circuit board required for placing semiconductor components are formed by a mechanical drilling method using a drill. On the other hand, in the current situation where computers and mobile phones tend to have higher performance and are lighter, thinner and smaller, with the miniaturization of semiconductor parts themselves and the densification between these parts, fine processing of print patterns, There is a demand for finer hole diameters of holes and blind via holes.

[0003] However, in the mechanical drilling method using the above-mentioned drill, there are problems in mechanical strength of the drill,
It is difficult to reduce the hole diameter to 0.2 mm or less because the drill itself requires fine processing such as creation of a twist groove. In view of the above, fine drilling by various methods has been attempted at present, and among them, a drilling method using a laser beam has attracted particular attention.

For example, in a method for boring a printed circuit board disclosed in Japanese Patent Application Laid-Open No. Hei 4-37494, a window hole is formed by drilling in an outer layer copper foil of a printed circuit board to be processed, and the window hole is formed. A desired blind hole is formed by irradiating the inner insulating layer with a laser beam. Here, the insulating layer is a glass epoxy resin impregnating glass fiber, and since the melting points of the glass fiber and the epoxy resin are different, the problem that the thermal energy of the laser beam is not uniformly transmitted into the insulating layer. Occurs.

Therefore, the method disclosed in Japanese Patent Application Laid-Open No. 4-37494 discloses a method of irradiating a glass fiber in an insulator layer by irradiating a laser beam in a pulsed manner to prevent the effect of heat conduction in the insulator layer. Drilling can be performed without leaving the inside or making the inner surface of the epoxy resin gouge largely with respect to the diameter of the window hole formed in the outer layer copper foil.

[0006] However, the method for boring a printed circuit board has a problem that its workability is greatly affected by the type of the material of the insulating layer and the properties of the base material contained in the insulating layer. For example, in the method:
When forming the blind hole, the resin or the melt of the base material cannot be completely removed and remains on the wall surface of the formed hole as spherical processing dust.

FIG. 5 shows the relationship between the degree of taper of the formed blind hole and the particle size of the processing residue remaining on the inner wall surface of the formed blind hole when the insulating layer 2 is irradiated with the laser beam L in a pulsed manner. Shows the relationship. Here, FIG.
(A), (b), and (c), the number of pulses of the irradiated laser beam L increases.

As shown in FIG. 5A, at a stage where the number of pulses is small, the spherical processing residue 6a remaining on the inner wall surface of the formed blind hole 7a is very small. However, the difference in hole diameter between the incident side and the exit side of the laser beam L increases. That is, the degree of taper of the formed blind hole 7a increases. And FIG.
As shown in (b) and (c), as the number of pulses of the irradiated laser beam L increases, the processing residues 6b and 6c increase, and the blind holes 7b and 7c
Becomes smaller.

FIG. 6 is a diagram showing the relationship between the number of pulses of the laser beam applied to the insulator layer and the degree of taper of the formed blind hole. As shown in FIG. 6, in order to reduce the degree of taper of the formed blind hole,
What is necessary is just to increase the number of pulses of the laser beam.

However, the relationship between the pulse number of the laser beam and the particle size of the processing residue remaining on the inner wall surface of the formed blind hole is, as shown in FIG. 7, proportional to the pulse number of the laser beam. The particle size of the residue increases. This means that small processing chips generated in the early stage with a small number of pulses become nuclei, and the particle size of the processing residue grows and enlarges with the increase in the number of pulses of the subsequently irradiated laser beam. Is attributed to

Therefore, when forming a via hole having a small taper degree in the above method, the problem of machining residue remaining on the inner wall surface of the via hole cannot be ignored, and a good inner wall surface cannot be obtained.

In a laser drilling method disclosed in Japanese Patent Application Laid-Open No. 56-144890, a portion to be processed is covered with a low boiling point liquid such as water or oil, and the portion to be processed is irradiated with a solid laser beam. While the laser processing is proceeding, the liquid is exploded by irradiating the liquid pool with a gas laser beam, and it is possible to take out the remaining melt inside the hole which could not be scattered outside from the formed hole.

However, in order to remove the processing residue inside the hole to be formed, a new different kind of laser beam system (in this case, a gas laser) is required. Therefore, there is an apparatus configuration for executing the drilling method. It is complicated and leads to high costs. In addition, when forming a fine hole, particularly a deep hole, in order to utilize a pool of liquid, the bottom of the hole to be formed is completely covered with the liquid due to the adsorption force and surface tension of the liquid. This makes it difficult to achieve the effect of the laser drilling method sufficiently.

A laser drilling method disclosed in Japanese Patent Application Laid-Open No. 58-218387 discloses a method of irradiating a work with a laser beam from one side to form a through-hole penetrating to the other side. A backing material is brought into contact with the through-hole forming portion on the side to prevent spatter of the work generated during processing from being scattered from the other side of the work by the backing material. Since the evaporated matter is blown out from the formed through hole, it is possible to prevent the spatter from adhering to the inside of the through hole.

However, in forming a blind via hole in a printed circuit board, the backing material cannot be brought into contact with the surface opposite to the surface irradiated with the laser beam because the formed hole does not penetrate. .

[0016]

As described above, in the conventional processing method using a laser beam, the relationship between the reduction of processing debris when forming a hole in a printed circuit board and the formed hole taper is contradictory. It cannot be controlled only by the laser beam irradiation conditions. In addition, the condition that both the through hole and the blind via hole are finely formed without processing residues inside the hole is not satisfied. Especially the problem of processing residue
In forming the blind via hole, plating around in a later plating process becomes poor, which causes a significant decrease in reliability such as insulation characteristics.

According to the present invention, in order to efficiently remove resin and substrate processing residues remaining on the inner wall of a hole during drilling of a substrate by a laser beam, the constitution of the substrate material itself is devised, and through holes and blind vias are provided. An object of the present invention is to provide a printed circuit board capable of forming both holes and a method of forming a hole in the printed circuit board.

[0018]

In order to achieve the above object, a printed circuit board according to the present invention has at least one high vapor pressure region which is a material having a high vapor pressure. Is located at a position where the laser beam is irradiated immediately before the formation of the hole in the printed circuit board is completed. By irradiating the high vapor pressure area with the laser beam, explosive melting and evaporation occurs in the area, and the reaction force can remove the resin and the processing residue of the base material remaining on the wall surface of the processing hole.

In the printed circuit board according to the next invention, the thickness of the high vapor pressure region is selected according to the diameter of the hole formed. In order to increase or decrease the volume of the insulating layer in the workpiece to be removed in proportion to the diameter of the hole to be formed, by changing the thickness of the layer of the material having a high vapor pressure in the workpiece, the wall surface of the processed hole is changed. The removal of the resin residue and the processing residue of the base material can be effectively performed.

In the printed circuit board according to the next invention, the thickness of the high vapor pressure region is selected according to the depth of the hole to be formed. Even if the diameter of the hole to be formed is constant, since the volume of the insulating layer in the work to be removed increases or decreases in proportion to the depth of the hole to be formed, the material having a high vapor pressure in the work By changing the thickness of the layer, the resin remaining on the wall surface of the processing hole and the processing residue of the base material can be effectively removed.

According to a second aspect of the present invention, there is provided a drilling method for forming a hole in a printed circuit board using a laser beam, wherein the printed circuit board has at least one high vapor pressure region which is a material having a high vapor pressure. And irradiating the laser beam immediately before the formation of the hole in the printed board in the high vapor pressure region is completed. The layer explosively melts and evaporates, and the reaction force removes the resin remaining on the wall surface of the processing hole and the processing residue of the base material. By irradiating the high vapor pressure area with the laser beam, explosive melting and evaporation occurs in the area, and the reaction force can remove the resin and the processing residue of the base material remaining on the wall surface of the processing hole.

In the hole drilling method according to the next invention, the thickness of the high vapor pressure layer is selected according to the diameter of the hole to be formed. In order to increase or decrease the volume of the insulating layer in the workpiece to be removed in proportion to the diameter of the hole to be formed, by changing the thickness of the layer of the material having a high vapor pressure in the workpiece, the wall surface of the processed hole is changed. The removal of the resin residue and the processing residue of the base material can be effectively performed.

In the drilling method according to the next invention, the thickness of the high vapor pressure layer is selected according to the depth of the hole to be formed. Even if the diameter of the hole to be formed is constant, since the volume of the insulating layer in the work to be removed increases or decreases in proportion to the depth of the hole to be formed, the material having a high vapor pressure in the work By changing the thickness of the layer, the resin remaining on the wall surface of the processing hole and the processing residue of the base material can be effectively removed.

[0024]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of a printed circuit board according to an embodiment of the present invention;

Embodiment 1 The first embodiment of the present invention will be described below. FIG. 1 (a), (b), (c)
Shows a cross-sectional view of the printed circuit board in a step of forming a blind via hole. FIG. 2A,
(B), (c) is the schematic diagram which showed the characteristic of this invention more clearly.

In FIG. 1, a printed circuit board 10 is composed of a plurality of layers of different materials such as an insulator layer 2, a high vapor pressure layer 3, an inner copper foil 4, and a core material 5. Also,
The printed circuit board 10 is arranged such that the layers of the core material 5 are located at the center in a direction perpendicular to the substrate surface, and each layer is
, The inner copper foil 4, the high vapor pressure layer 3, and the insulator layer 2 in this order, and the semiconductor component can be disposed on both sides.

In processing the printed circuit board 10,
First, a beam spot of the laser beam L is set at a desired processing position on the surface of the printed circuit board 10, that is, the surface of the insulator layer. Further, in order to obtain a desired blind via hole, an appropriate laser beam output, a laser beam diameter, and a laser beam diameter as shown in FIG. The number of pulses selected based on the relationship between the number of pulses and the degree of taper or the relationship between the number of pulses of the laser beam and the particle size of the processing residue as shown in FIG. 7, for example, the taper of the formed blind via hole The number of pulses to reduce the degree is set.

Here, the insulator layer 2 is, for example, a glass epoxy resin, an epoxy resin impregnated with a ceramic filler, an epoxy resin, a polyimide resin, a ceramic substrate, or the like.

By irradiating the laser beam L appropriately set as described above, the insulating layer 2 is locally removed in the thickness direction. The insulating piece scraped off by the laser beam L is used as processing waste as the blind via hole 7.
Are partially scattered as processing residues 6 and remain on the inner wall surface of the blind via hole 7. The processing residue 6 remaining on the inner wall surface of the blind via hole 7 is
Subsequently, the laser beam L is partially melted by the thermal energy generated by the irradiated laser beam L, but remains as a nucleus of newly generated processing waste.

That is, the blind via holes 7 generated in the initial stage of the pulsed irradiation of the laser beam L
The processing residue 6 adhered to the inner wall surface grows as pulsed irradiation of the laser beam L continues, and even when the blind via hole processing of the insulating layer 2 is completed, it is blind as a spherical insulator. Stay on the inner wall of via hole 7.

The high vapor pressure layer 3 disposed adjacent to the insulating layer 2 is exposed at the bottom of the blind via hole 7 when the blind via hole processing of the insulating layer 2 is completed, and The exposed portion of the pressure layer 3 is continuously irradiated by the laser beam L.

Since the thermal energy of the laser beam L is much larger than the boiling point of the high vapor pressure layer 3, the high vapor pressure layer 3 irradiated with the laser beam L instantaneously explosively vaporizes, High pressure is applied to blow out the blind via hole 7. At this time, the processing residue 6 adhering to the inner wall surface of the blind via hole 7 melts the insufficiently vaporized high vapor pressure layer 3 due to the pressure of the high vapor pressure layer 3 as shown in FIG. Along with thing 8,
It is discharged to the outside of the blind via hole 7.

The blind via hole 7 at the stage when the blind via hole processing of the insulating layer 2 has been completed.
The exposed portion of the high vapor pressure layer 3 at the bottom is stripped off by the irradiation of the laser beam L to expose the surface of the inner copper foil 4 adjacent to the high vapor pressure layer 3. In general, the output of the laser beam L mainly for processing the insulating layer 2 does not have enough energy to sufficiently process the inner copper foil 4 which is a metal, and most of the incident energy. Is reflected and lost, so that no hole is formed in the inner layer copper foil 4.

6 and 7, the optimum number of laser beam irradiation pulses for obtaining a blind via hole having a desired depth is experimentally determined, and this pulse number is used. Insulator layer 2 and high vapor pressure layer 3
Only the part consisting of can be processed.

Therefore, a blind via hole 7 having a good wall surface with no adhesion of the processing residue 6 is formed, and in the subsequent plating process of the inner wall surface of the blind via hole 7, a good plated surface is inevitably obtained. Can be.

Embodiment 2 A second embodiment of the present invention will be described below. FIG. 3 shows the diameter of the hole to be formed and the thickness of the high vapor pressure layer sufficient to remove the processing residue attached to the inner wall of the hole when the thickness of the insulating layer portion to be processed is fixed to 100 μm. Shows the relationship. As shown in FIG. 3, the blind via hole 7 to be formed
Is proportional to the thickness of the high vapor pressure layer disposed adjacent to the insulator layer.

That is, when the diameter of the hole to be formed is small, the volume of the insulating layer to be stripped is small, so that the thickness of the high vapor pressure layer disposed adjacent to the insulating layer is reduced.
On the other hand, when the diameter of the formed blind via hole is large, the volume of the insulating layer to be removed is also large, so that the processing residue remaining on the inner wall surface of the blind via hole also increases.

Further, since the exposed area of the high vapor pressure layer at the bottom of the blind via hole at the stage when the blind via hole processing of the insulating layer portion has been completed is increased, the molten material which is vaporized and blown out by further irradiation with the laser beam and The reaction force also increases. However, as shown in FIG. 2, it is the high vapor pressure layer located near the inner wall surface that effectively removes the processing residue on the inner wall surface of the blind via hole. Therefore, the high vapor pressure layer located near the inner wall surface needs a sufficient thickness, and the thickness of the high vapor pressure layer disposed adjacent to the insulating layer is increased.

For example, when forming a hole with a hole diameter of 150 μm to be processed, setting the thickness of the high vapor pressure layer disposed adjacent to the insulating layer to about 30 μm will provide an effective processing residue removal effect. Is obtained.

Embodiment 3 A third embodiment of the present invention will be described below. FIG. 4 shows that the processing hole diameter is φ150.
This shows the relationship between the depth of the hole to be formed and the thickness of the high vapor pressure layer sufficient to remove the processing residue attached to the inner wall of the hole when the thickness is fixed to μm. As shown in FIG. 4, there is a proportional relationship between the depth of the via hole to be formed and the thickness of the high vapor pressure layer disposed adjacent to the insulator layer.

That is, when the depth of the hole to be formed is small, the volume of the insulating layer necessary for exfoliation is small, so that the thickness of the high vapor pressure layer disposed adjacent to the insulating layer is small. Is thinned. On the other hand, when the depth of the hole to be formed is large, the volume of the insulating layer to be removed is also large, so that the thickness of the high vapor pressure layer disposed adjacent to the insulating layer is also increased.

For example, when forming a hole with the depth of the hole of the insulating layer in the portion to be processed being 100 μm, the thickness of the high vapor pressure layer disposed adjacent to the insulating layer is reduced to about 30 μm. When set, an effective processing residue removal effect is obtained.

Although the blind via hole is formed on the printed circuit board in the above embodiment, the effect as described in the description of the above embodiment can be obtained by forming this through hole.

[0044]

As described above, according to the printed circuit board of the present invention, at least one high vapor pressure region which is a material having a high vapor pressure is provided. Since it is located at the position where the laser beam is irradiated immediately before the formation is completed, explosive melting and evaporation occurs in the area of the material with high vapor pressure, and the reaction force causes the resin remaining on the formed wall surface of the hole. And removal of processing residues from the substrate. Therefore, it becomes possible for the formed hole wall surface to have a smooth surface free of processing residues.

According to the printed circuit board of the next invention,
Since the volume of the insulator layer in the printed circuit board to be removed increases or decreases in proportion to the diameter of the hole to be formed, the thickness of the material layer having a high vapor pressure in the printed circuit board is changed, so that the material remains on the wall surface of the processed hole Reliable removal of resin and substrate processing residues, and
You can do it effectively.

According to the printed circuit board of the next invention,
Even if the diameter of the hole to be formed is constant, the volume of the insulator layer in the printed circuit board to be removed increases or decreases in proportion to the depth of the hole to be formed. By changing the thickness, the resin remaining on the wall surface of the processing hole and the processing residue of the base material can be reliably and effectively removed.

According to the drilling method according to the next invention, in the drilling method for forming a hole in a printed circuit board using a laser beam, the printed circuit board has at least one high vapor pressure region which is a material having a high vapor pressure. Since the laser beam is irradiated immediately before the formation of the holes in the printed circuit board in the high vapor pressure area, explosive melting and evaporation occurs in the high vapor pressure area, and the reactive force remains on the wall of the processed hole. Processing residues of resin and base material can be removed. Thus, a hole having a smooth inner wall surface can be obtained, which also enables the formation of a finer hole. That is, by forming fine holes in a printed circuit board by the method according to the present invention, semiconductor components can be arranged at a high density.

According to the drilling method of the next invention, the volume of the insulating layer in the printed circuit board to be removed is increased or decreased in proportion to the diameter of the hole to be formed. By changing the thickness of the layer, it is possible to reliably and effectively remove the resin remaining on the wall surface of the processing hole and the processing residue of the base material.

According to the drilling method of the next invention, even if the diameter of the hole to be formed is constant, the volume of the insulating layer in the printed circuit board to be removed in proportion to the depth of the hole to be formed is also increased or decreased. Therefore, by changing the thickness of the layer of the material having a high vapor pressure in the printed circuit board, it is possible to reliably and effectively remove the resin remaining on the wall surface of the processing hole and the processing residue of the base material.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a substrate showing each step of a processing according to an embodiment of the present invention.

FIG. 2 is a schematic diagram showing a mechanism of a processing process according to the embodiment of the present invention.

FIG. 3 is a graph showing the relationship between the thickness of a high vapor pressure layer disposed adjacent to an insulator layer and the diameter of a hole to be formed.

FIG. 4 is a graph showing the relationship between the thickness of a high vapor pressure layer disposed adjacent to an insulator layer and the thickness of an insulator layer portion to be formed.

FIG. 5 is a schematic view showing a conventional drilling method using a laser beam.

FIG. 6 is a graph showing a relationship between a hole taper degree and the number of laser pulses.

FIG. 7 is a graph showing the relationship between the particle size of a processing residue adhering to the inner wall surface of a hole and the number of laser pulses.

[Explanation of symbols] L laser beam, 2 insulator layers, 3 high vapor pressure layer, 4
Inner layer copper foil, 5 core material, 6, 6a, 6b, 6c Processing residue, 7, 7a, 7b, 7c Blind via hole, 8 melt, 10 printed circuit board.

Claims (6)

[Claims] 1. A high-vapor-pressure region which is at least one high-vapor-pressure material, wherein the high-vapor-pressure region is arranged at a position where a laser beam is irradiated immediately before formation of a hole in a printed circuit board is completed. A printed circuit board, comprising: 2. The printed circuit board according to claim 1, wherein the thickness of the high vapor pressure region is selected according to the diameter of a hole to be formed. 3. The printed circuit board according to claim 1, wherein the thickness of the high vapor pressure region is selected according to the depth of a hole to be formed. 4. A drilling method for forming a hole in a printed circuit board using a laser beam, wherein the printed circuit board has at least one high vapor pressure region that is a material having a high vapor pressure, and the high vapor pressure region And irradiating the laser beam immediately before the formation of the holes in the printed circuit board is completed. 5. The method according to claim 4, wherein the thickness of the high vapor pressure layer is selected according to the diameter of a hole to be formed. 6. The drilling method according to claim 4, wherein the thickness of the high vapor pressure layer is selected according to the depth of a hole to be formed.