JP2002035977A - Piercing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form high-precision through holes capable of coping with increase in input/output pads of silicon chips and preventing deformation or deterioration in a sheet material, or deformation in the through holes caused by heat radiation failure of working heat when the through holes arranged in a nearly lattice state with narrow intervals are formed by irradiating a laser beam. SOLUTION: In a piercing method which forms the through holes arranged in a nearly lattice state by irradiating the laser beam on a preset sheet, a piercing point which positions nearly center part of the nearly lattice arrangement is used as a starting point and the laser beam is irradiated while the boring point is shifted from this starting point toward the outer side nearly concentrically. Especially, it is desirable to form the through holes at every boring point by repeating a process which irradiates the laser beam on every boring point arranged in a nearly lattice state at lest at every one pulse several times.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention forms a through conductor for connecting wiring layers to a prepreg used for a printed wiring board or the like suitable for a multilayer wiring board and a package for accommodating a semiconductor element, for example. Therefore, the present invention relates to a method for perforating through holes arranged in a lattice.

[0002]

2. Description of the Related Art In recent years, as the amount of information to be processed has increased in semiconductor devices, the number of terminals for inputting and outputting information (signals) has increased dramatically. For this reason, the number of pads (I / O pads) formed on the silicon chip increases, and it becomes necessary to form many pads on the lower surface of the silicon chip. For this reason, the density of the I / O pads of the silicon chip increases,
The distance (pitch) between the vertical conductors arranged in a lattice on the wiring board receiving the same must be 300 μm or less.

In order to meet such a demand for high-density wiring, a manufacturing method called a build-up method has been used. The basic structure of the build-up method is JP
According to the CA standard, there are two types: (1) base + build-up method and (2) all-layer build-up method.

(1) A method of manufacturing a base + build-up method is to apply a photosensitive resin to the front and back surfaces of a base substrate.
This is a method in which exposure-development-plating-resist formation-etching-resist removal is defined as one cycle, and a wiring layer is sequentially formed by repeating this. This method is advantageous in that the wiring layer formed by the build-up method can be finely wired. (2) Manufacturing method of all-layer build-up
For example, as in Japanese Patent No. 2587593, a via hole is formed in an insulating layer by a laser or the like, and a conductive paste is filled in the via hole to electrically connect a wiring circuit layer formed on the surface of the insulating layer to wiring. A layer is formed, and the wiring layer thus manufactured is multilayered.

A conventional printed wiring board serving as a base board is formed by drilling a hole in an epoxy resin insulating board reinforced with glass fiber, and plating the inner wall of the hole with copper to make electrical connection between the front and back of the board. I was

[0006]

However, in recent years, even in the base + build-up method, the wiring density of the base substrate itself, particularly the formation density of through conductors, is low, and a required number of electrical connections between the front surface and the rear surface of the base substrate are required. There is a new problem that cannot be done.

However, since high stress and heat are generated during conventional drilling when observed microscopically, a portion of the inner wall after processing, called a deteriorated layer, where the glass fiber and the resin are peeled off, is formed. As a result, an active plating solution penetrated into the peeled portion, and in a reliability test after completion of the substrate, metal was diffused along the peeled portion, resulting in insulation failure called migration. For this reason, in the conventional method using a drill or the like, it has not been possible to increase the via hole density by reducing the distance between vias.

Further, a through hole is formed by irradiating a high-energy laser beam instead of a drill, and an inner wall thereof is plated, or a conductive paste is filled in the through hole to perform electrical connection. Have also been tried. But,
In the case of plating, as in the case of a drill, a plating solution penetrates into this portion, and the reliability of insulation has been reduced. When the conductive paste was filled, the conductive metal diffused along the affected layer, and satisfactory insulation reliability could not be obtained.

On the other hand, (2) a method of forming a via-hole conductor by abutting a conductive paste, which is one of the all-layer build-up methods, makes it difficult to abut a projection if the via pitch is narrowed and the vias are densely packed. In addition, there is a problem that the density cannot be increased much because insulation reliability between vias is reduced. In the method using an aramid nonwoven fabric-epoxy resin-based insulating material, via processing with a laser is easy, but since the aramid resin has high hygroscopicity, the epoxy resin also absorbs moisture, and the reliability is reduced due to moisture absorption. Therefore, even with this method, the via density has not been improved.

Conventionally, when the through holes are formed in a substantially lattice shape by irradiating a laser beam, as shown in FIG. 4, for example, laser beams are sequentially irradiated from the upper stage to the lower stage of the lattice arrangement to form the holes. Was. However, in such a method, as the pitch interval of the through-holes becomes narrower, it becomes difficult to dissipate the processing heat at the time of irradiating the laser light, and the through-holes are deformed, thereby filling the through-holes with the conductive paste. There is a problem that a leak occurs between adjacent through conductors.

Particularly, when a through hole is formed in a so-called prepreg in which a thermosetting resin is impregnated in a woven fabric of glass fiber, it is conventionally difficult to form the through hole by laser irradiation, particularly carbon dioxide laser irradiation. there were. This is because processing heat accumulates in the through-hole dense area and the resin rises near the temperature, resulting in carbonization of the resin or partial thermal expansion, resulting in deformation and processing of the through-hole with the required precision. Could not. In addition, there is another problem that the interface between the glass fiber and the resin near the inner wall of the through-hole is separated due to the processing heat of the laser beam, and the insulation reliability is reduced.

According to the present invention, in forming through holes arranged in a substantially lattice shape with a narrow pitch and capable of coping with an increase in the number of I / O pads of a silicon chip by irradiating a laser beam as described above, An object of the present invention is to provide a perforation method capable of forming a highly accurate through-hole by preventing deformation and deterioration of a sheet material and deformation of a through-hole due to poor heat dissipation of processing heat.

[0013]

According to the present invention, there is provided a punching method for forming through holes arranged in a substantially lattice pattern on a predetermined sheet by irradiating a laser beam to the predetermined sheet. It has been found that the above object can be achieved by irradiating a laser beam while moving the piercing point substantially concentrically outward from the starting point with the piercing point located at the center as the starting point.

More specifically, irradiating a single drilling point with a laser beam a plurality of times to form a through-hole;
In particular, it is desirable to form through holes at all the drilling points by repeating the process of irradiating the laser light at least one pulse at a time to all of the drilling points arranged in a substantially lattice shape a plurality of times to prevent deformation. Also,
It is desirable to irradiate the laser beam while moving the perforation point spirally from the start point outward.

In the method of the present invention, when the sheet contains an uncured thermosetting resin, the sheet has 30 through holes.
In the case where the uncured thermosetting resin is at least one selected from the group consisting of an epoxy resin, a polyphenylene ether resin, and an imide resin when the perforations are formed in a substantially lattice shape at a pitch interval of 0 μm or less, the glass This is particularly effective when heat-resistant fibers made of woven or non-woven fibers or aramid fibers are included.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS (Laser Drilling) The drilling method of the present invention will be specifically described with reference to the drawings. According to the perforation method of the present invention, as shown in FIG. 1, a laser light 4 is guided to a predetermined sheet 1 from a laser light source 2 via a mirror 3 to a surface of the sheet 1, and a through hole 5 is formed in the surface of the sheet 1. Is formed. Further, the laser light 4 is configured so that the laser light 4 can be guided to an arbitrary portion of the sheet 1 by adjusting the angle of the mirror 3 or the like. Then, through holes 5 are formed in the sheet 1 by the energy of the laser beam 4. (Punching Method) According to the present invention, as shown in FIG. 2, for example, the through holes 5 are formed in the sheet 1 in such a manner that m through n through holes 5 are arranged in a substantially lattice shape.

According to the present invention, in forming the through holes 5 as described above, the perforation point p1 located substantially at the center of the substantially lattice array is set as a starting point, and the laser is concentrically formed outward from the starting point. The hole is pierced at the piercing point while moving the light irradiation position.

More specifically, as shown in FIG. 2A, the irradiation position of the laser beam is sequentially moved in a spiral shape from the perforation point p1 toward the outside. FIG.
As shown in (b), it has a spiral shape as in (a), but the irradiation position of the laser beam may be moved along the diagonal of the lattice. Further, as shown in FIGS. 2C and 2D, the irradiation position can be moved substantially concentrically while having a folded portion in the middle.

As described above, according to the method in which the laser beam irradiation position is moved substantially concentrically outward from the start point with the perforation point p1 as the starting point, the conventional laser shown in FIG. As is clear from the embodiment described later, the deformation of the through-hole can be effectively prevented as compared with the method of moving the light irradiation position. It is considered that this is because according to the method of the present invention, the processing heat accompanying the irradiation of the laser beam is evenly diffused in the perforation process, and the stagnation of the heat can be effectively removed. (Punching Method-Cycle Shot) According to the drilling method of the present invention, when a through-hole is formed by irradiating one pulse of laser light, a large amount of processing heat is applied to the drilling point, and as a result, the through-hole is formed. Deformation may be caused.

Therefore, it is desirable to set the energy of the laser beam per pulse to be low enough to form a through hole by irradiating two or more pulses. Thus, by irradiating two or more pulses, processing is performed gradually while dissipating the processing heat for each pulse, so that deformation of the through-hole can be prevented.

Also, in the above case, 1 is set at the piercing point.
While irradiating the laser light of the pulse or two or more pulses, by irradiating the laser light to all the perforation points arranged in a substantially lattice shape by the method of moving the irradiation position of the laser light as described above, as a cycle, Return to the starting point of the drilling point again and perform drilling in the same way,
By repeating a plurality of cycles, through holes are formed at all drilling points. Thereby, the diffusion of heat can be made more uniform, and the through holes can be formed in a lattice shape without deformation of the through holes. (Printed circuit board) The perforation method of the present invention is used for forming a through hole in a predetermined sheet. As the sheet, a sheet containing at least an organic resin and having a thickness of 20 to 200 μm is particularly preferable. It is. Examples of such a sheet include an organic resin, or a composite of an organic resin and an inorganic powder, or an inorganic or organic fibrous body.

The perforation method of the present invention is most suitable particularly for producing a printed wiring board. Specifically, the sheet to be perforated contains at least one uncured thermosetting resin selected from the group of epoxy resin, polyphenylene ether resin, and imide resin, and furthermore, glass fiber generally called prepreg or It is suitable when a through-hole is formed in a sheet in which the above-mentioned thermosetting resin is impregnated into a heat-resistant fiber made of a woven or non-woven aramid fiber.

In particular, when the number of terminals through which information (signals) are taken in and out is dramatically increased, when applied as a wiring board on which a semiconductor element is mounted, a high-density through hole having a pitch interval of 300 μm or less in the wiring board. It is necessary to perforate. At the same time, the diameter of the through hole is 100
It is desired that the thickness be not more than μm. If the diameter of the through-hole exceeds 100 μm, the effect of heat at the time of processing the through-hole by the laser beam increases, so that the processing speed tends to be unable to be increased.

According to the drilling method of the present invention, the pitch interval between the through holes (the interval between the center of the through hole and the center of the nearest through hole) is 300 μm or less, particularly 250 μm.
Even in the following cases, the through holes can be formed while preventing the resin-containing sheet from being deformed or deteriorated by the processing heat and the through holes from being deformed.

In the case of piercing the above prepreg,
If the irradiation amount per pulse of laser light is too small,
A large amount of irradiation is required to form the through-hole. Conversely, if it is too large, the processing heat increases, heat stagnation tends to occur, and prepreg deformation, alteration, and deformation of the through-hole easily occur. Therefore, the irradiation amount per pulse of the laser beam is suitably 2 to 20 mJ, particularly 3 to 10 mJ. (Method of Manufacturing Printed Circuit Board) Next, an example of a method of manufacturing a multilayer printed circuit board using the above-described punching method will be described. First, as shown in FIG. 3A, a prepreg 10 containing an uncured resin and glass fibers is prepared. The uncured resin contained in the prepreg 10 is PPE
(Polyphenylene ether), BT resin (bismaleimide triazine), epoxy resin, polyimide resin, polyamide bismaleimide
Some resins are desirable.

Next, as shown in FIG. 3B, through holes 12 are formed in the uncured prepreg 11 based on the above-described method. The energy of the laser at this time is 2 to 20 mJ per pulse, particularly 3 to 10 mJ.
mJ is appropriate.

Next, as shown in FIG.
2 is filled with a conductive paste made of a mixture of a metal powder such as copper and a resin to form the through conductor 13.

Next, the surface of the prepreg 11 and / or
Alternatively, a wiring circuit layer is formed on the back surface. For example, FIG.
As shown in (d), a copper foil 15 is applied on the film 14, etched to form a mirror image wiring circuit layer 16, and transferred to the surface of the prepreg 11 on which the penetrating conductor 13 is formed.
The wiring layer 17 is formed.

Thereafter, as shown in FIG. 3E, the plurality of wiring layers 18 and 19 manufactured in the same manner as described above are connected to the wiring layer 1.
After the laminate is aligned with No. 7 and heated to a temperature at which the thermosetting resin in the prepreg is completely cured, a multilayer printed wiring board can be manufactured.

In the above-described manufacturing method, prepreg is used as the insulating sheet. However, the insulating sheet is not limited to this, and the inorganic material such as silica, alumina, mullite, zirconia, etc. may be used for the thermosetting resin. 5 to 70
The prepreg may be used in combination with the prepreg described above.

[0031]

EXAMPLES (1) As a core substrate, a prepreg was prepared by impregnating a woven fabric made of glass fiber with a polyphenylene ether (PPE) resin. Fig. 2
(A) to (d) and any of the methods in FIG.
1 mm diameter within a 10 mm square area with a CO ₂ laser
00 μm, pitch interval 250 μm, 200 μm, 150
The through-holes arranged in μm were processed. Further, the state of the through hole was observed.

Thereafter, a conductor paste containing copper powder and an organic binder was filled in the through-hole by a screen printing method to form a through conductor.

On the other hand, P with a 12 μm thick copper foil adhered thereto
A transfer wiring circuit layer was formed on the copper foil of the ET resin film by a photoresist method. Next, on the prepreg, the resin film is aligned and laminated,
The wiring circuit layer was transferred by heating and pressing at 120 ° C. and 30 kg / cm ² to peel off the resin film.

Similarly, three prepregs each having a through conductor and a wiring circuit layer formed thereon are laminated, and heated at 200 ° C. for 1 hour while applying a pressure of 20 kgf / cm ² using a vacuum press to completely cure the substrate. Was.

The through conductor forming portion of the obtained wiring board was cut, and the cross-sectional shape was observed. Further, this wiring board was subjected to (a) an atmosphere of 121 ° C., 2.1 atm, and 100% humidity,
(B) Insulation reliability was evaluated by standing for 300 hours under conditions of 130 ° C., 85% humidity, and 5.5 V, respectively. The results are shown in Table 1.

[0036]

[Table 1]

As is apparent from the results shown in Table 1, the sample N in which the through-hole was formed by the conventional laser light moving method was used.
o. In Nos. 9 to 11, discoloration and deformation of the through-hole were observed around the through-hole, and insulation failure occurred between adjacent through-conductors even in the through-conductor.

On the other hand, the samples in which the through-holes were formed according to the present invention did not show any discoloration or deformation around the through-holes or in the through-holes, and showed good results in the reliability test. .

[0039]

As described in detail above, according to the present invention,
When forming through holes arranged in a substantially lattice pattern with a narrow pitch interval by irradiating laser light, deformation and deterioration of the sheet material due to poor heat dissipation of processing heat and deformation of the through holes are prevented, and high precision penetration is achieved. Holes can be formed. Therefore, a wiring board that can cope with an increase in the number of I / O pads of a silicon chip can be manufactured.

[Brief description of the drawings]

FIG. 1 is a view for explaining an outline of a perforation method according to the present invention.

FIG. 2 is a diagram for explaining a moving direction of a laser beam in a perforation method according to the present invention.

FIG. 3 is a process chart for explaining a method for manufacturing a multilayer printed wiring board.

FIG. 4 is a diagram for explaining a method of moving a laser beam in a conventional perforation method.

[Explanation of symbols]

 1 sheet 2 laser light source 3 mirror 4 laser light 5 through hole

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Claims (8)

[Claims] 1. A perforation method for forming through-holes arranged in a substantially lattice shape by irradiating a predetermined sheet with a laser beam, wherein a perforation point located substantially at the center of the substantially lattice arrangement is set as a starting point, A perforation method comprising irradiating a laser beam while moving the perforation point substantially concentrically from the starting point toward the outside. 2. The perforation method according to claim 1, wherein a laser beam of two or more pulses is applied to one perforation point to form a through-hole. 3. The method according to claim 1, wherein a step of irradiating all the drilling points arranged in a substantially lattice pattern with laser light at least one pulse at a time is repeated a plurality of times to form through holes at all drilling points. 2. The perforation method according to 2. 4. The drilling method according to claim 1, wherein the laser beam is irradiated while moving the drilling point spirally from the starting point outward. 5. The perforating method according to claim 1, wherein the sheet contains an uncured thermosetting resin. 6. The drilling method according to claim 1, wherein the through holes are drilled in a substantially lattice shape at a pitch interval of 300 μm or less. 7. The uncured thermosetting resin is an epoxy resin,
The perforation method according to claim 1, wherein the perforation method is at least one selected from the group consisting of a polyphenylene ether resin and an imide resin. 8. The perforation method according to claim 5, wherein the sheet contains heat-resistant fibers made of a woven or non-woven fabric of glass fibers or aramid fibers.