JPH1197841A - Method for manufacturing printed circuit board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form a through conductive path of high conductivity reliability. SOLUTION: A through-hole 14 is formed in a copper-clad laminated plate 10, in which a copper foil 12 is stuck on both faces of an insulating board 11. The through-hole 14 is filled with metal powder, and a resin sheet laminated on the copper foil 12 is separated, and ultrasonic vibrations are applied to metal powder. The particles of the metal powder scrape on each other, melted and welded to each other, and a metal pillar 18 is formed in the through-hole 14 as a through conductive path.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a printed circuit board having an improved conduction structure between circuits sandwiching an insulating layer.

[0002]

2. Description of the Related Art As a method of establishing conduction between copper foil patterns on both front and back surfaces of a printed circuit board, a plating through hole method and a method of embedding a conductive paste are known. The plating through hole is formed by forming a chemical plating layer on the inner peripheral surface of the through hole formed in the substrate, and further forming an electroplating layer thereon as necessary, and the thickness of the plating layer is 10 to 15 μm.
m. The method of embedding the conductive paste is as follows.
The conductive paste formed by kneading conductive particles of silver or copper into a resin paste is filled in the through holes formed in the substrate.

[0003]

In the plating through-hole method, when the diameter of the through hole is reduced, the amount of the electroplated layer deposited on the deep portion of the through hole decreases, so that the plating layer inside the through hole becomes thinner and the surface of the through hole becomes thinner. It is difficult to avoid the tendency that the plating layer of the copper foil portion becomes thick. This means that the copper foil is locally thickened in the through-hole portion, so that there is a problem that it is difficult to miniaturize a circuit in which it is essential to make the conductor thickness uniform. In addition, in the conductive paste embedding method, electrical conduction is ensured depending on the contact between the conductive particles in the conductive paste and the copper foil on the substrate surface. And may lack reliability.

Accordingly, an object of the present invention is to provide a method of manufacturing a printed circuit board which can miniaturize a circuit and has high reliability of conduction.

[0005]

According to a first aspect of the present invention, there is provided a method for manufacturing a printed circuit board, wherein a metal powder is filled in a through hole formed in an insulating layer, and ultrasonic vibration is applied thereto from a pressurized horn. This is characterized in that the metal powders are fixed to each other to form a through conductive path penetrating the insulating layer.

According to a second aspect of the present invention, in the method of manufacturing a printed circuit board according to the first aspect, a resin sheet is overlaid on the insulating layer, holes are formed in the resin sheet and the insulating layer at required positions, and a metal is formed in the hole. It is characterized in that the metal powder is filled in the through-hole by filling the powder and compressing the metal powder together with the resin sheet.

According to a third aspect of the present invention, there is provided the method for manufacturing a printed circuit board according to the first or second aspect, wherein the pressure horns are provided in pairs so as to sandwich the insulating layer, and the metal powder is filled in the through holes. It is characterized in that ultrasonic vibration is applied by sandwiching and pressurizing from both sides.

According to a fourth aspect of the present invention, in the method of any one of the first to third aspects, copper powder is used as the metal powder, and the surface thereof is coated with a metal having a lower melting point than copper. It has features in some places.

[0009]

According to the first aspect of the present invention, when ultrasonic vibration is applied to the metal powder filled in the through hole, the metal powders rub against each other and the surface thereof is melted by frictional heat. In addition, a metal pillar that is directly joined to metals and integrated into the through hole is formed as a through conductive path. Oxide film may be formed on the surface of each metal powder, but when ultrasonic vibration is applied while each metal powder is in contact with applying pressure, static pressure and contact surface The oxide film on the contact path is destroyed / removed by sliding, and clean surfaces are rubbed against each other, elastic deformation, plastic deformation, and even a temperature rise due to frictional heat is applied to the extent that an atomic attractive force acts between the joining surfaces. It comes close and the bonding area increases, leading to a strong bonding state. Then, the circuit on both the front and back surfaces of the insulating layer can be connected by the through conductive path. According to the through conductive path formed in this way, it is not necessary to form a conductive plating layer on the inner peripheral surface of the through hole, thereby preventing the thickness of the conductive layer on the surface of the insulating plate from becoming uneven. This makes it possible to miniaturize the circuit. In addition, since the through conductive path is formed by directly joining the metal powder, there is obtained an effect that the reliability of conduction is high and the resistance to aging is enhanced.

According to the second aspect of the present invention, holes are formed in the resin sheet superimposed on the insulating layer, and the holes are filled with the metal powder. Therefore, when this is compressed together with the resin sheet, the metal powder is densely filled in the through holes of the insulating layer. Then, when ultrasonic vibration is applied to this, the metal powders are efficiently coupled to each other, and a low-resistance through conductive path is formed.

According to the third aspect of the present invention, since the ultrasonic vibration is applied to the metal powder filled in the through hole from both sides, the operation of forming the through conductive path becomes efficient. According to the fourth aspect of the present invention, since the low-melting-point metal is coated on the surface while inexpensive copper powder can be used, the bonding between the metal powders is performed smoothly. When silver is used as the coating metal, it is effective in preventing oxidation of copper powder and reducing the resistance.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION

[First Embodiment] Hereinafter, a first embodiment of the present invention will be described with reference to FIGS. In the drawing, reference numeral 10 denotes an insulating substrate 1 made of glass epoxy having a thickness of, for example, 0.5 mm.
1 is a copper-clad laminate in which copper foils 12 are attached to both surfaces, and an electric circuit is formed by etching the copper foils 12 in a required pattern. On both sides of the laminated plate 10, for example, as shown in FIG.
Resin sheet 13 is further laminated, and as shown in (C), a through hole 1 for forming a conductive path penetrating the laminated plate 10 is formed.
4 are formed together with the resin sheet 13.

Next, FIG. 1D shows the inside of the through hole 14.
As shown in the figure, the metal powder 15 is filled. As the metal powder 15, for example, a copper powder for copper paste (specific gravity: 8.93) having a particle size of about 0.1 to 10 μm is used. A densely packed state can be obtained by combining a plurality of types of copper powder. Thereafter, the laminate 10 is planarly pressed together with the resin sheet 13 to increase the packing density of the metal powder 15, and the resin sheet 13 is peeled off to apply ultrasonic vibration to the metal powder 15. For this, as shown in FIG. 2, the laminated plate 10 is placed on a hard plate such as a metal plate 16 and a metal powder 15 is placed.
A horn 17 is applied to the filled portion, and a vertical ultrasonic vibration is applied with a static pressure of, for example, several tens kg. Then, the copper powders rub against each other and the surface melts due to frictional heat,
The copper powders are directly bonded to each other, and as shown in FIG.
The metal pillar 18 integrated in the 4 is formed as a through conductive path. This through conductive path (metal column 18) enables connection between the copper foil circuits 12 on both the front and back surfaces of the insulating substrate 11. Note that, if necessary, the laminated plate 10 may be turned upside down to apply ultrasonic vibration in the same manner as described above. In addition, the higher the frequency of the ultrasonic vibration, the shallower the vibration transmission depth, and the lower the frequency, the easier it is to obtain a large power. Therefore, an appropriate frequency should be set according to the required power and the thickness of the laminated board 10. Can be. In this embodiment, for example, a vibration of 28 kHz was the most effective.
If the through conductive path 18 is formed as in the present embodiment,
Since an electroplating process for conducting the front and back circuits is unnecessary, it is possible to prevent the thickness of the copper foil 12 of the laminated board 10 from becoming uneven, thereby enabling miniaturization of the circuit. . In addition, since the through-conducting path 18 is formed by directly joining the metal powders 15, the effect that the reliability of conduction is high and the resistance to aging is enhanced. Further, unlike the metal paste, since the resin composition does not contain the resin composition, the electric resistance of the through conductive path 18 can be reduced.
The physical strength of the connection portion with the second member 2 is increased.

[Second Embodiment] Next, referring to FIG.
A second embodiment in which a circuit pattern is applied to a build-up wiring board in which a plurality of circuit patterns are stacked will be described. As shown in FIG. 1A, a laminate obtained by attaching a copper foil 22 to both surfaces of an insulating substrate 21 is processed by an etching method to form a core substrate 20 having a predetermined circuit pattern. Next, a photosensitive insulating resin layer 23 is applied so as to cover the copper foil 22 of the core substrate 20 (FIG. 2B), and a through hole 24 is formed in the insulating resin layer 23 at a predetermined position by a photo process. (FIG. 2C).

The through hole 24 is formed in the insulating resin layer 2 as an insulating layer.
3 is filled with a metal powder 25 such as a copper powder in a state as dense as possible. Then, an ultrasonic horn (not shown) is applied to the filled metal powder 25, and while applying a required static pressure, ultrasonic vibration in the left-right direction (direction along the surface of the insulating substrate 21) is applied. As in the embodiment, the copper powders rub against each other and the surface thereof is melted by frictional heat. As a result, the copper powders are directly joined to each other, and a metal pillar 26 integrated in the through hole 24 is formed as a through conductive path as shown in FIG.

Then, as shown in FIG. 1E, electroless plating and electrolytic plating are performed to form a plating layer 27 on the entire surface, and this is etched with a required circuit pattern, thereby obtaining the structure shown in FIG. As shown, an upper layer circuit 28 is formed. The upper layer circuit 28 is connected to the copper foil circuit 22 on the insulating substrate 21 via the metal pillar 26 integrated in the through hole 24. Since this state corresponds to FIG. 2A, by repeating the above-described steps after (B),
Thus, a multilayer wiring board internally connected by the metal pillars 26 in the through holes 24 can be manufactured.

According to the above-described embodiment, the conduction reliability of the through conductive path is higher than that of the conventional method in which the through conductive path in the through hole 24 is formed by plating. can do. In addition, since the electroless plating and the electrolytic plating are performed on the smooth surface of the insulating resin layer 23, the plating thickness can be made uniform over the whole, and the circuit can be miniaturized.

[Other Embodiments] The present invention is not limited to the embodiment described above with reference to the drawings. For example, the following embodiments are also included in the technical scope of the present invention. In addition to the following, various changes can be made without departing from the scope of the invention.

(1) In the above embodiments, the through holes 14 and 2
Although the inner surface of 4 was filled with metal powder without plating, if the inner peripheral surfaces of the through holes 14 and 24 were thinly electrolessly plated, the metal powder would also contact the plating layer. Therefore, it is effective for improving the reliability of conduction and reducing the electric resistance. In the manufacturing method of the build-up board shown in the second embodiment, when the inner peripheral surface of the through hole 24 is to be subjected to electroless plating, first, as shown in FIG. The layer 31 may be formed, and then the metal powder 25 may be filled in the through hole 24 to apply ultrasonic vibration. Although the plating is performed, the thickness of the copper foil 12 of the insulating substrate 11 of the first embodiment is not made non-uniform because of the electroless plating of an extremely thin layer thickness, which prevents the miniaturization of the circuit. There is no risk of becoming.

(2) Although copper powder is used as the metal powder in each of the above embodiments, the present invention is not limited to this, and gold, silver, palladium, nickel, tin, lead, a mixture thereof, an alloy, or the like may be used. What is essential is that the conductive metal powder be self-fused by ultrasonic vibration. If a copper powder whose surface is coated with a metal having a lower melting point than that of the copper powder is used, bonding between the metal powders is performed smoothly. Also, if silver is used as the coating metal,
It is more effective for preventing oxidation of copper powder and reducing the resistance. Further, a small amount of organic or inorganic filler powder such as thermosetting resin powder or glass powder may be added to the metal powder.

(3) In each of the above embodiments, the ultrasonic vibration is applied to the metal powder from the rod-shaped ultrasonic horn. However, the present invention is not limited to this. Ultrasonic vibration may be applied, or a roller to which ultrasonic vibration is applied may be rolled on the substrate to sequentially apply vibrations to a large number of metal powders. Further, the frequency and the output can be appropriately set according to the depth and the diameter of the through-hole.
A range of kHz seems most preferred.

(4) In each of the above embodiments, the ultrasonic vibration is applied from one side to the metal powder filled in the through-hole. However, the present invention is not limited to this. The ultrasonic vibration may be applied while the vibration is being made.

(5) In the first embodiment, the resin sheet 13
Is stacked on the laminate 10 and filled with metal powder, and the metal powder is pressed by a flat press, so that a high packing density of the metal powder can be obtained.
Is not essential, and the packing density may be increased by, for example, a combination of different diameter particles or filling using liquid capillary force.

(6) In each of the above embodiments, the through conductive path is formed after the circuit pattern is formed. However, the present invention is not limited to this, and the metal powder is filled in the through hole of the insulating layer before the circuit pattern is formed. Then, a through-conducting path may be formed by applying ultrasonic vibration thereto, and then a circuit pattern may be formed.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a process of forming a through conductive path according to a first embodiment of the present invention.

FIG. 2 is a side view showing a state where ultrasonic vibration is applied to the laminated plate.

FIG. 3 is a cross-sectional view showing the laminated plate after the formation of the through conductive paths.

FIG. 4 is a sectional view showing a process of forming a through conductive path according to a second embodiment of the present invention.

FIG. 5 is a sectional view showing a circuit pattern forming process according to another embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Copper-clad laminated board 11 ... Insulating board 12 ... Copper foil 14 ... Through-hole 18 ... Metal pillar (through conductive path)

Claims (4)

[Claims] 1. A method of manufacturing a printed circuit board having a through conductive path for interconnecting circuits on both sides of an insulating layer through a through hole formed in the insulating layer, the method comprising: A method of manufacturing a printed circuit board, comprising: filling powder and applying ultrasonic vibration from a pressurized horn to fix the metal powder to each other to form the through conductive path. 2. A resin sheet is superimposed on the insulating layer, holes are formed in required positions in the resin sheet and the insulating layer, and the holes are filled with metal powder. 2. The method for manufacturing a printed circuit board according to claim 1, wherein the metal powder is filled in the through holes of the insulating layer by compressing. 3. The pressure horns are provided in pairs so as to sandwich the insulating layer, and apply ultrasonic vibration by pressing the metal powder filled in the through hole from both sides. The method for manufacturing a printed circuit board according to claim 1. 4. The printed circuit according to claim 1, wherein the metal powder is copper powder, the surface of which is coated with a metal having a lower melting point than copper. Substrate manufacturing method.