JPH1022628A - Method for filling conductor into via hole - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a conductor filling method to a via hole which can charge conductor paste precisely into via holes with very small bores and at narrow pitches. SOLUTION: Since the expected conductor filling is performed by heating, fusing, and evaporating conductor paste by the application of a laser beam L and allowing those fused evaporated particles Pa to enter a via hole 2 to stick thereto, a high-density wiring board can be made easily by performing the conductor charge into a via hole 2 precisely even in the case that the inside diameter of the via hole 2 made through a board 1 is micronized and that the formation pitch is small.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for filling a via hole formed in a substrate with a conductor.

[0002]

2. Description of the Related Art Via holes formed through a substrate include:
2. Description of the Related Art Conventionally, conductor filling has been performed by pushing in a conductor paste by a technique such as screen printing or pin transfer.

[0003]

In recent years, there has been a high demand for producing a high-density wiring board, and in order to cope with this, it is necessary to make the inside diameter of the via hole small and also to make the formation pitch narrow.

However, in the above-mentioned conventional method, it is extremely difficult to sufficiently fill a conductive paste into a via hole having a small inner diameter and a narrow pitch, and there is a problem that frequent filling problems occur.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and an object of the present invention is to provide a method of filling a via hole with a conductor paste which can accurately fill a via hole with a small inner diameter and a narrow pitch. It is in.

[0006]

According to the present invention, there is provided a laser light transmitting plate having a conductive paste applied thereto, which is disposed adjacent to one surface of a substrate having a via hole and opposed to the via hole. Irradiating a laser beam from the surface of the laser light transmitting plate opposite to the paste application surface toward the application paste, melting and evaporating the conductive paste by the irradiating laser light, and entering the molten / evaporated particles into the via hole. The main feature of the present invention is that the conductor is filled by being attached.

According to the method of filling a via hole according to the present invention, the conductor paste is heated and melted and evaporated by irradiating a laser beam, and the melted / evaporated particles enter the via hole and adhere to the via hole. Since the filling is performed, the inside of the via hole can be accurately filled even when the inside diameter of the via hole formed through the substrate is reduced and the forming pitch is narrowed.

[0008]

1 to 5 show a process chart of a conductor filling method according to an embodiment of the present invention, wherein 1 is a substrate, 2 is a via hole, and 3 is a laser beam transmitting plate. ,
Reference numeral 4 denotes a mask, 5 denotes a wall plate, P denotes a conductive paste, and L denotes a laser beam.

The substrate 1 is a fired one made of alumina, aluminum nitride, or the like. Via holes 2 having a predetermined inner diameter are formed in the substrate 1 at a predetermined pitch by drilling, punching, laser processing, or the like.

The laser light transmitting plate 3 is made of a material having transparency to the laser light L, for example, sapphire, zirconia,
The substrate 1 is made of ceramic or glass such as barium fluoride, calcium fluoride, aluminum nitride, and quartz, or a resin such as polyimide, acrylic, PET, or glass epoxy.
Are arranged at a predetermined interval below.

The mask 4 is made of a film or a thin plate made of a metal having a reflectivity to the laser beam L, for example, aluminum or stainless steel.
Are provided on the lower surface of the laser light transmitting plate 3 so as to face the via holes 2.

The wall plate 5 is for receiving the melted / evaporated particles Pa of the conductive paste P that has passed through the via hole 2 and is arranged above the substrate 1 at a predetermined interval.

The conductor paste P is capable of melting and evaporating by laser beam irradiation, for example, Sn-Pb alloy or A-Pb alloy.
It is formed by mixing powders of 1, Ag, Au, Cu, Ni, In, Ga, Bi and their alloys, a binder and a solvent. This conductive paste P is applied on the upper surface of the laser light transmitting plate 3 so as to face the via hole 2 in an appropriate amount.

The laser light L is in an infrared region irradiated by a YAG laser, a CO ₂ laser or the like, or an ultraviolet region irradiated by an excimer laser or the like. The lower surface of the laser light transmitting plate 3 is not shown by an optical system (not shown). Irradiation is performed from the side toward the conductor paste P.

Hereinafter, the conductor filling method according to the present embodiment will be described. First, as shown in FIG. 1, the wall plate 5 is disposed above the substrate 1 and the laser light transmitting plate 3 with the mask is disposed below the substrate 1, respectively. The laser beam L is emitted toward P so that its optical axis is perpendicular to the lower surface of the laser beam transmitting plate 3. The conductive paste P is applied in a dotted pattern on the upper surface of the laser light transmitting plate 3 in advance in accordance with the position of the via hole 2, and the paste application amount is adjusted according to the size of the via hole 2 to be filled.

The laser beam L is applied to the mask 4 as shown in FIG.
And only the laser light L that has passed through the light passage hole 4a is transmitted through the laser light transmitting plate 3. The conductor paste P on the upper surface of the laser beam transmitting plate 3 is the laser beam L after transmission.
Is heated and melted and evaporated.
a rises by hot air and enters the via hole 2, and gradually adheres to the inner surface of the via hole 2 and the lower surface of the wall plate 5.

The above-described irradiation with the laser beam L is continued until the gap between the inside of the via hole 2 and the wall plate 5 is filled with the melted / evaporated particles Pa as shown in FIG. Is stopped, and the wall plate 5 placed above and below the substrate 1 and the laser light transmitting plate 3 with the mask are removed.

When the wall plate 5 and the laser light transmitting plate 3 with the mask are removed, the conductor Pb filled in the via hole 2 has a shape which rises up and down from the via hole 2 as shown in FIG. If the bulge does not hinder, the upper and lower bulges are removed by performing appropriate polishing to ensure consistency between the upper and lower surfaces of the filled conductor Pb 'and the upper and lower surfaces of the substrate 1 as shown in FIG. .

As described above, according to the above-described conductor filling method, the conductor paste P is heated and melted and evaporated by the irradiation of the laser beam L, and the melted / evaporated particles Pa enter and adhere to the via hole 2. Since the intended conductor filling is performed, the inside diameter of the via hole 2 formed through the substrate 1 is reduced, and the conductor filling into the via hole 2 is accurately performed even when the formation pitch is narrowed. And a high-density wiring board can be easily produced.

In addition, since sintering by applying heat is not required for filling the conductor, defects due to sintering, such as the diffusion of the conductor paste into the substrate material and the occurrence of cracks due to the mismatch between the conductor paste and the shrinkage of the substrate are eliminated. Work reliability can be significantly improved.

Further, the amount of the conductor filling can be easily controlled by the irradiation time of the laser beam L and the amount of the conductor paste P applied, and it is possible to sufficiently cope with a via hole having a high aspect ratio.

Furthermore, since accurate positioning between the via hole 2 and the coating paste P or between the coating paste P and the irradiation laser beam R is unnecessary, the burden required for positioning can be reduced and the filling operation can be simplified. it can.

In the above-described embodiment, a fired substrate made of alumina, aluminum nitride, or the like is used as the substrate. However, since sintering by applying heat is not required for filling the conductor, the substrate is made of resin. They can also be used, and can be used for filling conductors in via holes of green sheets.

Further, in the above-described embodiment, the laser light transmission plate is provided with a mask on the lower surface to restrict the passage of the laser light. However, as shown in FIG. 6, the laser light transmission hole 14a is provided. The mask 14 is provided inside the laser light transmitting plate 13, or the laser light transmitting plate 23 itself is composed of a laser light transmitting region 23 a and a laser light non-transmitting region 23 b as shown in FIG. Restriction may be performed.

For example, in order to realize the latter with a crystallized glass substrate having no laser light transmission, only the region where the laser light is to be transmitted is heated and quenched to promote vitrification to improve light transmission. In addition, in order to realize the laser light transmitting glass / ceramic substrate, a light reflecting mask is provided on one surface of a region where the laser light is to be transmitted, and the entire surface is irradiated with the laser light. By heating and phase-separating this, crystallization or phase-separation can be advanced to devitrify other than the mask region.

Further, in the above-described embodiment, the coating paste is irradiated with the laser beam whose passage has been restricted by a mask or the like. However, as shown in FIG. If the light is condensed toward P, there is no need to restrict passage through a mask or the like.
Effective energy can be applied to the application paste P.

[0027]

As described in detail above, according to the present invention,
The conductor paste is heated and melted by laser light irradiation.
Evaporation is performed so that the molten / evaporated particles enter and adhere to the via hole to perform the intended conductor filling, so that the inner diameter of the via hole formed through the substrate is reduced, and the forming pitch is reduced. Even in such a case, the conductor can be accurately filled in the via hole, and a high-density wiring board can be easily produced.

Further, since sintering by applying heat is not required for filling the conductor, defects due to sintering, such as diffusion of the conductor paste into the substrate material and cracks caused by mismatch between the conductor paste and the substrate due to shrinkage, are eliminated. Work reliability can be significantly improved.

[Brief description of the drawings]

FIG. 1 is a process diagram of a conductor filling method according to an embodiment of the present invention.

FIG. 2 is a process chart of a conductor filling method according to an embodiment of the present invention.

FIG. 3 is a process chart of a conductor filling method according to an embodiment of the present invention.

FIG. 4 is a process diagram of a conductor filling method according to an embodiment of the present invention.

FIG. 5 is a process diagram of a conductor filling method according to an embodiment of the present invention.

FIG. 6 is a sectional view showing another example of the laser beam transmitting plate.

FIG. 7 is a sectional view showing another example of the laser light transmitting plate.

FIG. 8 is a cross-sectional view showing how laser light is focused and irradiated.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Substrate, 2 ... Via hole, 3 ... Laser light transmission plate, 4 ...
Mask, 4a: Light passage hole, 5: Wall plate, P: Conductive paste, Pa: Melted / evaporated particles, Pb: Filled conductor, L: Laser light, 13: Laser light transmitting plate, 14: Mask, 14a ...
Light passing holes, 23: laser light transmitting plate, 23a: laser light transmitting area, 23b: laser light non-transmitting area, L ': laser light.

Claims (6)

[Claims] 1. A laser light transmitting plate having a conductive paste applied thereto is disposed adjacent to one surface of a substrate having a via hole and opposed to the via hole, and the laser light transmitting plate is provided on a side opposite to the paste application surface of the laser light transmitting plate. Laser light is irradiated from the surface toward the application paste, the conductor paste is melted and evaporated by the irradiated laser light, and the melted / evaporated particles enter and adhere to the via holes to fill the conductor. To fill the via holes with a conductor. 2. The method according to claim 1, wherein a wall plate is provided adjacent to the other surface of the substrate having the via hole for receiving the molten and evaporated particles passing through the via hole. . 3. A method according to claim 1, wherein the upper and lower raised portions of the conductor filled in the via hole are removed by polishing so that the upper and lower surfaces of the filled conductor are aligned with the upper and lower surfaces of the substrate.
3. The method according to claim 1, wherein the via hole is filled with a conductor. 4. The laser light transmitting plate according to claim 1, wherein a mask having a light passing hole is provided on the laser light transmitting plate, and the laser light passing through the light passing hole is irradiated toward the coating paste. The method for filling a conductor into a via hole according to any one of the preceding claims. 5. The laser light transmitting plate comprises a laser light transmitting area and a laser light non-transmitting area, and the laser light transmitted through the laser light transmitting area is irradiated toward the coating paste. The method for filling a conductor into a via hole according to claim 1. 6. The method for filling a via hole with a conductor according to claim 1, wherein the laser light is focused toward the application paste.