JPH11330649A - Board for forming circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form cylindrical vias having microdiameters with their opening diameters made equal at both surfaces of an insulation board by avoiding forming taper vias opened by a laser beam, having different diameters at the front and rear surfaces. SOLUTION: An aramide fiber base 1 which has the highest thermal shrinkage start temperature is disposed on the top, a plurality of the kinds of aramid fiber bases 2, 3, 4, 5, 6 are laminated in the ascending order of the thermal shrinkage start temperature on the back surface of an insulation base and is impregnated with a thermosetting resin 7. Thus, they are disposed from the top face to the bottom face of an insulation board 8, in the order of the thermal shrinkage start temperature, ST1>ST2>ST3>ST4>ST5>ST6 of the aramide fiber bases.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a via hole having a small diameter for forming a circuit board having a plurality of wirings on both sides or an inner layer, thereby increasing the density of component mounting and having excellent high frequency characteristics. The present invention relates to a circuit forming substrate that can be used.

[0002]

2. Description of the Related Art In recent years, as electronic devices have become smaller, thinner, lighter, and more sophisticated, various electronic components constituting electronic devices have become smaller and thinner. Various technology developments are being actively carried out to enable high-density mounting of printed wiring boards to be mounted.

In recent years, in particular, with the rapid development of mounting technology, there has been a strong demand that multilayer printed wiring boards capable of mounting semiconductor chips such as LSIs at high density and corresponding to high-speed circuits be supplied at low cost. . In such a multilayer wiring circuit board, it is important to have high electrical connection reliability and excellent high frequency characteristics between a plurality of wiring patterns formed at a fine wiring pitch. In response to the demands of such high-performance, high-performance electronic equipment, multi-layer printed wiring boards, in which electrical connection between layers is made with a conventional through-hole structure by drilling and etching or plating of a copper-clad laminate, It is now extremely difficult to satisfy these requirements, and in order to solve such problems, printed wiring boards having a new structure and manufacturing methods aimed at high-density wiring are being developed.

One of the typical examples is to replace the copper plating conductor on the inner wall of the through hole, which has been the mainstream of the conventional interlayer connection of the multilayer wiring board, with a conductor filled in the inner via hole to improve the connection reliability. There is a resin multilayer substrate having an all-layer IVH structure (JP-A-6-268345) that can improve the size and form an inner via hole directly under the component land or between arbitrary layers, and can realize a reduction in the size of the substrate and high-density mounting. .

[0005]

In the above-mentioned wiring board having an all-layer IVH multilayer structure, it is possible to form high-density wiring. Also, in a general method of forming a printed wiring board, accurately forming a via hole or a through hole having a small diameter is an important issue in creating a high-density wiring and a high-density mounting board. . Therefore, in general, an optical aperture method using a laser beam instead of the mechanical aperture method has become popular.

However, there is a problem with the laser beam aperture method, and the phenomenon is shown in FIG. FIG. 5 is an enlarged sectional view showing a part of the insulating substrate 30 constituting the wiring board having the all-layer IVH multi-layer structure, in which a thermosetting resin 32 such as an epoxy resin is applied to a fiber base material 31 such as aramid fiber. Is impregnated. When a laser beam is irradiated from above the insulating substrate 30 to form a via hole having a required hole diameter D in the insulating substrate 30 as shown in the drawing, the laser beam is irradiated by thermal energy concentrated on the surface of the insulating substrate 30. Insulating substrate 30 around point
Is thermally decomposed or melted to open a pore diameter d1 larger than the target pore diameter D. Next, as the laser beam enters the inside of the insulating substrate 30, its thermal energy is absorbed by the substrate material and decreases, so that the diameter of the perforated hole also decreases in proportion to the decreasing thermal energy. Is smaller than the target hole diameter D. That is, when a via hole having a hole diameter D is to be formed in the insulating substrate 30 having the conventional material configuration by a laser beam processing method, as shown in FIG. 5, D, d1, and d2 have a relationship of d1>D> d2. Occurs. That is, an inverted truncated-cone-shaped via hole 33 having a taper in which the diameter differs between the opening surface 33a and the back surface 33b of the via hole opened by the laser beam is formed.

The via hole 3 having such a taper
In the case of performing high-density wiring as the diameter of the wiring becomes smaller, the wiring 3 becomes an obstacle and lowers the accuracy of forming the wiring pattern.

In order to solve such a problem, it is conceivable to use a processing method in which a short-pulse laser beam is irradiated a plurality of times. However, the processing tact becomes longer and the processing cost is increased.

The present invention has been made to solve the above-mentioned problem, and can reduce the processing cost by using a gas laser or the like, and has a cylindrical shape in which the diameter of the upper end and the lower end of a via hole is almost equal at a required portion of the insulating substrate. An object of the present invention is to provide a circuit forming substrate on which a via hole can be formed.

[0010]

According to the present invention, in order to achieve the above object, as an insulating substrate used for forming a circuit board, physical characteristics are changed continuously or stepwise from the front surface to the back surface of the insulating substrate. By using an insulating substrate, it is intended to form a cylindrical via hole having an equal opening diameter without taper when the via hole is opened by laser processing.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention according to claim 1 of the present invention is directed to an insulating substrate used for forming a circuit board, wherein the physical characteristics of the insulating substrate are continuously changed from the front surface to the back surface of the insulating substrate. And a relatively accurate cylindrical via hole can be formed by a laser processing method.

According to a second aspect of the present invention, in the insulating substrate used for forming the circuit board, the physical characteristics of the insulating substrate are changed stepwise from the front surface to the back surface of the insulating substrate. Thus, the same effect as that of the first aspect can be obtained.

According to a third aspect of the present invention, in the insulating substrate used for forming a circuit board, the insulating substrate is impregnated with a thermosetting resin by laminating fiber base materials having different physical characteristics. By sequentially stacking fiber base materials having different physical characteristics, the physical characteristics can be continuously changed from the front surface to the back surface of the insulating substrate.

According to a fourth aspect of the present invention, there is provided an insulating substrate used for forming a circuit board, wherein the insulating substrate is obtained by impregnating a fiber base material having a specific physical property with a thermosetting resin. An insulating substrate formed by laminating a plurality of single-layer substrates having different physical characteristics, the physical characteristics of which are changed stepwise from the front surface to the rear surface of the insulating substrate. The substrate can be formed easily and at low cost.

According to a fifth aspect of the present invention, in an insulating substrate used for forming a circuit board, a plurality of resin films having different physical characteristics are respectively applied to the insulating substrate from the front surface to the back surface of the insulating substrate. It is intended to be an insulating substrate configured by overlapping so that the characteristics change stepwise, especially when forming a via hole having a small diameter, it is possible to smooth the inner wall surface of the via hole,
The filling of the conductive material into the via hole can be easily performed.

According to a sixth aspect of the present invention, there is provided an insulating substrate used for forming a circuit board, wherein the insulating substrate is formed of a plurality of resin films and resin-impregnated fiber substrates each having different physical characteristics. This is an insulating substrate formed by composite lamination such that the physical characteristics change stepwise from the front surface to the back surface, and the adhesiveness with the copper foil provided on the front surface of the insulating substrate can be improved.

According to a seventh aspect of the present invention, there is provided the circuit-forming substrate according to the fifth or sixth aspect, wherein the resin film is a polyimide film, a wholly aromatic aramid having different thermal decomposition onset temperatures. the film,
It is composed of a resin film selected from aromatic polyester films, it is possible to accurately control the thermal decomposition onset temperature, with an extremely accurate minute diameter, and
It is possible to form a via hole whose inner wall is extremely smooth and can easily be filled with a conductive material such as a conductive paste.

According to an eighth aspect of the present invention, there is provided a circuit forming substrate according to any one of the first to sixth aspects, wherein:
The physical properties are defined as the heat shrinkage start temperature or the thermal decomposition start temperature, and by setting the heat shrinkage start temperature or the thermal decomposition start temperature low from the front surface to the back surface of the insulating substrate, the melting of the substrate material by the laser beam or Thermal decomposition can be accelerated, and as a result, a cylindrical via hole can be formed.

According to a ninth aspect of the present invention, in the circuit forming substrate according to any one of the third, fourth and sixth aspects, the fibrous base material is provided with different heat shrinkage initiation temperatures or different thermal decomposition initiation temperatures. It is composed of a single fiber selected from among aramid fibers, aromatic polyester fibers or glass fibers, or a blended fiber of two or more types, and can accurately control a heat shrinkage initiation temperature or a thermal decomposition initiation temperature. In addition, it is possible to form a very accurate micro via hole.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings. (Embodiment 1) FIG. 1 shows a partial cross section of a circuit-forming substrate according to a first embodiment of the present invention, in which aramid fibers or aromatics having different heat shrinkage initiation temperatures or thermal decomposition initiation temperatures, respectively. This figure shows a configuration in which a plurality of fiber bases made of polyester fibers are stacked and impregnated with a thermosetting resin such as an epoxy resin.

Next, specific examples of the present embodiment using aramid fibers as a base material will be described.

Generally, a PPTA-type para-aramid fiber obtained by polymerizing paraphenylenediamine and terephthalic acid chloride has a heat shrinkage initiation temperature of about 400 ° C.
Temperature of Thermal Shrinking (hereinafter, STTS
And about 560 ° C, thermal decomposition onset temperature Start Tem
It has a perature of thermal decomposition (hereinafter referred to as STTD). On the other hand, a copolymerized para-aramid fiber obtained by copolymerizing 3,4-diaminodiphenyl ether in addition to paraphenylenediamine as a diamine component is about 200%.
C. STTS and about 500.degree. C. STTD. Therefore, by adjusting the copolymerization molar ratio of paraphenylenediamine and 3,4 diaminodiphenyl ether,
An aramid fiber substrate as shown in (Table 1) was prepared.

[0023]

[Table 1]

In order to form the insulating base material having the structure shown in FIG. 1 using the aramid fiber base material shown in Table 1, the aramid fiber base material 1 having the highest STTS is arranged at the top, and the insulating base A plurality of types of aramid fiber substrates 2, 3, 4, 5, and 6 were laminated in the order of STTS on the back surface of the material, and a thermosetting resin 7 made of an epoxy resin was impregnated to form an insulating substrate 8.

That is, S of each aramid fiber substrate
TTS is ST1> ST2 from the upper surface to the lower surface of the insulating substrate.
>ST3>ST4>ST5> ST6. Therefore, the STTD of each aramid fiber substrate is also DT1> DT2.
>DT3>DT4>DT5> DT6.

As shown in FIG. 1, when the insulating substrate 8 having the above-described structure is formed by irradiating, for example, a carbon dioxide gas laser from above the insulating substrate 8, the uppermost layer of the substrate is STT.
Since S (or STTD) is the highest, it is difficult to process. Even if it receives relatively high thermal energy at the start of laser beam irradiation, unnecessary thermal decomposition or melting of the insulating substrate 8 does not occur. Drilling can be performed in a state close to the via hole diameter D. Next, once the perforation is started, the thermal energy of the laser beam is absorbed by the internal substrate layer and gradually decreases, but the STTS of the substrate layer at that time is configured to be lower in order than the surface layer of the insulating substrate 8. Therefore, via holes 9 having an appropriate diameter are formed by the substrate layer having the STTS corresponding to the energy of the laser beam. Further, as described above, the insulating substrate 8 formed by sequentially laminating fiber base materials having different STTSs and impregnating with a thermosetting resin has its physical characteristics, ie, STTS or STTD, continuously in the thickness direction of the insulating substrate 8. This has the effect of smoothing the inner wall of the perforated via hole 8.

(Embodiment 2) Next, a second embodiment of the present invention will be described with reference to FIG.

2 (a) to 2 (e) show a process of manufacturing a circuit forming substrate according to the present embodiment. In the present embodiment, only a fiber base material having a certain STTS (or STTD) is used. Is impregnated with a thermosetting resin such as an epoxy resin to form a single-layer substrate, and a single-layer substrate having a different STTS is sequentially laminated to form a circuit-forming substrate.

That is, as shown in FIG. 2A, the first single-layer substrate 10 in which the fiber base material 1 having the highest STTS (ST1) is impregnated with the epoxy resin 7 and the same STTS
A second single-layer substrate 11 (b) in which the fiber substrate 2 having (ST2) is impregnated with the epoxy resin 7, and a third single substrate in which the fiber substrate 3 having STTS (ST3) is impregnated in the epoxy resin 7; The layer substrate 12 (c) and the fourth single-layer substrate 13 (d) in which the fiber base material 4 having STTS (ST4) is impregnated with the epoxy resin 7 are laminated to form the insulating substrate shown in FIG. 14 is obtained.

As shown in FIG. 3, a via hole 15 having a diameter D is formed in the insulating substrate 14 thus formed by a laser beam as in the first embodiment, as shown in FIG. STTS (or STT)
The change in D) is step-like because the single-layer substrates 10, 11, 12, and 13 are stacked, and the manufacturing cost of the circuit-forming substrate can be reduced. As in the case of the first embodiment, the shape is not smooth but a cylindrical shape having a bellows shape in which a step is formed for each single-layer substrate.

(Embodiment 3) Next, a third embodiment of the present invention will be described. FIG. 4 shows a cross section of a circuit-forming substrate according to a third embodiment of the present invention. In this embodiment, a plurality of resin films having different STTDs are used without using a fiber base material. As in the case of the embodiment, the insulating substrates are stacked from the top to the bottom in the descending order of STTD. That is, a resin film 16 made of a thermosetting polyimide having an STTD of about 560 ° C. is placed on the top, and a resin film 17 made of a wholly aromatic aramid film having an STTD of about 500 ° C.
Are placed in the middle and STTD is about 4 at the bottom of the insulating substrate.
By arranging and laminating a resin film 18 made of aromatic polyester at 70 ° C., the insulating substrate 19 in the present embodiment can be manufactured.

Via holes 20 having a diameter d are formed in the insulating substrate 19 formed in this manner by a laser beam in the same manner as in the above-described embodiments. The change of STTD in the present embodiment is shown in FIG.
Although the steps 17 and 18 are laminated, the circuit-forming substrate in the present embodiment is characterized by a stepped shape. Suitable when a via hole is required,
The inner wall surface of the via hole 20 is extremely smooth, and can be easily filled with a conductive material such as a conductive paste despite its small diameter.

As is apparent from the above embodiments, as a development of another embodiment of the circuit forming substrate according to the present invention, a plurality of resin-impregnated fiber base materials and resin fills having different STTSs or STTDs are laminated. It is also possible to form an insulating base material, especially by arranging a resin film on both sides of the insulating base material, it is possible to increase the adhesive strength with a copper foil for a wiring pattern formed on both sides of the insulating substrate. And reliability can be improved.

The glass fiber is prepared by appropriately combining the amounts of the respective inorganic oxides constituting the glass material.
Since the physical properties can be adjusted in an extremely wide range, the insulating substrate suitable for the required laser beam output conditions can be produced by impregnating the glass fiber alone or with the aramid fiber together with the resin.

In each of the above-described embodiments of the present invention, as a processing method other than the carbon dioxide gas laser used as the via hole processing means, a gas laser other than a carbon dioxide gas, a solid laser such as a YAG laser, or an excimer laser is used. Law.

As described above, according to the above-described embodiment, since the thermal shrinkage starting temperature or the thermal decomposition starting temperature of the circuit forming substrate is sequentially changed in the thickness direction of the circuit forming substrate, holes are formed by the laser beam. In the process, since the substrate material is melted or thermally decomposed in response to the change in the thermal energy of the laser beam, the diameters of the upper end and the lower end of the opening are almost equal and do not have a taper, and thus have the required small diameter. Via holes can be accurately formed.

[0037]

As is clear from the above embodiments, according to the present invention, as an insulating substrate used for forming a circuit board, the physical characteristics are changed continuously or stepwise from the front surface to the back surface of the insulating substrate. Using an insulating substrate,
There is an effect that a cylindrical via hole having a so-called opening diameter having the same diameter on both sides of the circuit forming substrate and having a small diameter can be formed without causing taper in the insulating substrate when the via hole is opened by laser processing.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a circuit forming substrate according to a first embodiment of the present invention, in which a via hole is formed.

FIG. 2 is a sectional view showing a method of forming a circuit forming substrate according to the second embodiment.

FIG. 3 is a sectional view of the circuit forming substrate according to the embodiment, in which a via hole is formed;

FIG. 4 is a cross-sectional view of the circuit forming substrate according to the third embodiment in which a via hole is formed.

FIG. 5 is a cross-sectional view in which a via hole is formed in a conventional circuit forming substrate.

[Explanation of symbols]

 8 Insulating substrate

Continuation of the front page (72) Inventor Yoshihiro Kawakita 1006 Kadoma Kadoma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (9)

[Claims] 1. An insulating substrate used for forming a circuit substrate, wherein a physical characteristic of the insulating substrate continuously changes from a front surface to a back surface of the insulating substrate. 2. An insulating substrate used for forming a circuit board, wherein a physical characteristic of the insulating substrate changes stepwise from a front surface to a back surface of the insulating substrate. 3. An insulating substrate used for forming a circuit board, wherein the insulating substrate is formed by laminating a plurality of fiber base materials having different physical characteristics and impregnating with a thermosetting resin, and A substrate for circuit formation, wherein physical characteristics are continuously changed from a front surface to a back surface of the insulating substrate. 4. An insulating substrate used for forming a circuit board, wherein the insulating substrate is formed by impregnating a fiber base material having specific physical characteristics with a thermosetting resin, and a plurality of single layers each having different physical characteristics. A substrate for circuit formation, wherein the substrates are laminated, and the physical characteristics change stepwise from the front surface to the back surface of the insulating substrate. 5. An insulating substrate used for forming a circuit board, wherein the insulating substrate changes a plurality of resin films having different physical characteristics from the front surface to the rear surface of the insulating substrate in a stepwise manner. A circuit forming substrate, characterized in that the substrate is an insulating substrate configured to be superposed as described above. 6. An insulating substrate used for forming a circuit board, wherein the insulating substrate is provided with a plurality of resin films and resin-impregnated fiber substrates each having different physical characteristics from the front surface to the rear surface of the insulating substrate. A circuit-forming substrate, wherein the substrate is an insulating substrate formed by compounding and laminating so as to change stepwise. 7. The circuit formation according to claim 5, wherein the resin film is a resin film selected from a polyimide film, a wholly aromatic aramid film, and an aromatic polyester film having different thermal decomposition onset temperatures. Substrate. 8. The circuit forming substrate according to claim 1, wherein the physical property is a heat shrinkage starting temperature or a thermal decomposition starting temperature. 9. The fiber base material is a single fiber selected from aramid fibers, aromatic polyester fibers or glass fibers having different heat shrinkage initiation temperatures or different thermal decomposition initiation temperatures, or two or more mixed fibers. Item 3,
7. The circuit-forming substrate according to any one of 4 and 6.