JP2604853B2 - Method of forming through hole in circuit board - Google Patents

Description

The present invention relates to a method for forming a through hole in a circuit board.

[Prior Art] When a method of forming a film on the surface of a circuit board by a vacuum deposition method or a sputtering method to obtain a circuit board is used, a conductor film or the like (insulator) is formed on a ceramic substrate as compared with the case of a plating method or the like. Film formation using resistors, resistors, and derivatives is also possible)
Can be formed relatively easily, and a high-quality conductor film with few impurities can be formed. According to the vacuum deposition method or the like, compared with the case of the plating method or the like,
Even if the surface roughness of the circuit board is fine, a sufficient degree of bonding to the conductor film can be obtained, so the thickness of the conductor film is sufficiently thin, the conductive resistance of the film portion is small, and a circuit board with excellent high frequency characteristics It can be obtained.

FIG. 5 shows that a conductor film is formed on one surface of a circuit board 1 made of alumina or the like in which holes 3 for through holes are formed by sputtering, and a conductor film is simultaneously formed on the inner periphery of the holes 3. An example of such a method is shown. The apparatus includes a vacuum container 5, which has an inlet 6 for Ar gas and an outlet 8 to which a vacuum pump 7 is connected. The circuit board 1 is set horizontally by a holder 9 above the space in the vacuum vessel 5, and a target (scattering portion) 2 provided above the cathode 10 is positioned below the space. By the operation of the vacuum pump 7, the inside of the vacuum vessel 5 is sucked and decompressed to be in a vacuum state, whereby the Ar gas is forcibly sucked through the suction port 6. Ar plasma is generated between the circuit board 1 and the target 2 by the Ar gas sucked into the vacuum vessel 5, and the Ar plasma is generated by the plasma.
From which copper atoms (scattering substances) are scattered. As a result, the copper atoms adhere to the surface of the circuit board 1 and also to the inner peripheral surfaces of the through-holes 3 of the board 1.

[Problems to be solved by the invention]

By the way, the above-mentioned method is carried out by supporting the circuit board 1 with a holder 9, and the board 1 has through holes 3.
Was supported to close on the back side,
The copper atoms reach one side surface of the circuit board 1 relatively easily, but the flow into the through holes 3... Has become very negative. This will be described more specifically with reference to FIG. 6 in which the main part is enlarged. In FIG. 6, the thickness of the circuit board 1 is T, the inner diameter of the through hole 3 is d, When the thickness of the conductor film 12 attached to the surface is t ₀ and the thickness of the conductor film 13 attached to the inner peripheral surface of the through hole 3 is t, π (d / 2) ² t ₀ ≒ πd (T + t ₀ ) Expression is approximated, and it can be seen that ∴t ≒ t ₀ × d / 4 (T + t ₀ ) Expression Taking the equation as an example, for example, T =
Table 1 shows how t becomes when the inner diameter d of the hole 3 is changed by substituting 0.635 t ₀ = 0.01.

As can be seen from the table, as the inner diameter d of the through hole 3 decreases, the thickness t of the conductor film 13 deposited in the hole 3 decreases, and d / T is 1 or less, that is, the circuit board. When the thickness d of the hole 3 is smaller than the thickness T of the circuit board 1, the conductor film adheres to the surface of the flat portion of the circuit board 1.
It would only be obtained following 20% the thickness t ₀ of 12. As shown in FIG. 7, the conductor film 13 formed by being deposited in the hole 3 is thicker on the target 2 side and gradually thinner on the back side thereof, so that the electric resistance value of the conductor film 13 is reduced. Becomes large, and in some cases, poor conduction may occur.

To solve these problems, Japanese Patent Application Laid-Open No. 62-2220
There is one described in No. 62 gazette. This relates to a sputtering method and a sputtering target.However, the method of forming a conductor film is limited to sputtering, and a rod-shaped target itself is inserted into a cylindrical body to perform sputtering. In order to perform uniform sputtering, it is necessary to form a uniform plasma. To maintain uniform distribution and discharge of Ar gas, a proper distance between electrodes (normally, about 5 mm, This method is not suitable for application to an inner peripheral surface having a small hole diameter such as a through hole of a circuit board.

In view of the above circumstances, the subject of the present invention is:
It is an object of the present invention to form a conductive film on the inner peripheral surface of a through-hole so as to have a substantially uniform thickness in the axial direction, a sufficient thickness, and a low conductive resistance.

[Means for solving the problem]

In order to solve the above-mentioned problems, a method for forming a through-hole in a circuit board according to the present invention includes a circuit board having a hole for a through-hole formed in a vacuum vessel having a portion where a conductive material is vaporized and ionized and scattered. Are arranged so that there is a space on the front and back sides of the substrate facing the scattered portion, and a negative voltage is applied to an electrode disposed on the opposite side of the scattered portion of the circuit board to apply the electrode and the circuit. By applying an electric field between the substrate and the substrate, the ionized and scattered substance is forcibly guided to the through-hole and adhered and deposited on the inner peripheral surface of the through-hole.

[Action]

When an ionized substance is introduced to the inner peripheral surface of the through-hole by applying an electric field between the electrode and the circuit board arranged on the opposite side of the scattered portion of the circuit board, the electric field effect The ionic particles are guided into the through-hole, and adhere to the inner peripheral surface of the through-hole in a large amount and over the entire surface with a substantially uniform thickness in the axial direction.

〔Example〕

Hereinafter, the present invention will be described in detail with reference to the drawings showing the embodiments.

FIG. 1 shows an embodiment of a method for forming a through hole in a circuit board according to the present invention as an apparatus. This figure shows an electric field utilizing an electric field for effectively guiding metal particles (scattering substances) ionized by plasma to the inner peripheral surface of the through hole. As shown in the drawing, the vacuum vessel 40 has an intake port 41 on one lower side and an exhaust port 43 connected to a vacuum pump 42 on the other side. A holder 44 is provided at an intermediate height of the container 40, and a circuit board 45 is set horizontally on the holder 44. The holder 44 and the circuit board 45 are members that also provide a space on the front and back sides thereof. The substrate 45 is provided with holes 46 for through holes. A magnetron sputter 47 as an evaporation source is provided at a lower portion of the container 40, and a circuit board 45 in the container 40 is provided.
At a position slightly apart upward, an electrode (cathode) 48 is provided horizontally so as to be opposite to the magnetron sputter 47. The cathode 48 is made of a flat plate like the circuit board 45,
The entire circuit board 45 is opposed from above.
The holder 44 is provided on the side of the container 40 on the side of the intake port 41.
Although the inside is vertically divided, the suction force can act on the space on the electrode 48 side on the exhaust port 43 side.

First, the inside of the vacuum container 40 is evacuated (eg, ×
In the 10 ^-4 ~ × 10 ^-6 about Torr), Ar gas through the inlet 41 ^{(e.g., × 10 -2 ~ × 10 -4} Torr) to an appropriate amount introduced.
Voltage (for example, 500 to 1000)
V) to form a plasma,
7 More conductive metal particles (Cu particles) are scattered and ionized by plasma. This Cu
A negative voltage (for example, several hundred volts to several hundred volts) is applied to the electrode 48 in order to stably attach and deposit particles in the through hole 46.
kV). Thereby, ionized Cu
The particles are guided to pass through the through holes 46.
As shown in FIG. 2, the Cu ions 50 are attracted by the force F in the direction of the electrode 48 together with the Ar ions 51. This force F is the electric field intensity E applied to the electrode 48.
F = eE (e is the ion charge) in proportion to As a result, as shown in FIG. 3, the trajectory of the Cu ions 50 is corrected in the direction of the inner peripheral surface of the through-hole 46 by the electric field effect of the electrode 48, and the Cu ions 50 fly to the inner peripheral surface. . The flight speed v of the ionized Cu ions 50 becomes an ultra-high speed of about 55,000 m / sec, when the applied voltage to the electrode 48 is 1 kV,
Since the ionized Cu particles 50 fly instantaneously toward the inner peripheral surface of the through-hole 46 while the trajectory is corrected by the electric field effect, the probability of adhesion of the Cu particles 50 to the inner peripheral surface is greatly improved. I do. Similarly, Ar ions 51 flying from the plasma fly toward the inner peripheral surface of the through-hole 46 due to the electric field effect, and a part of the Ar ions 51 is mixed into the conductor film 52. Since the surface of the conductor film 52 is impacted, a strong and uniform film 52 is formed.

As shown in FIG. 4, if the electrode 53 is provided with a needle-like projection 54 so that the tip faces the inside of the hole 46, the electric field effect becomes more effective and the ion Is greatly improved, and the effect of Ar ion bombardment can be further improved. The evaporation source may be any other than a magnetron cathode as long as it can ionize and scatter metal particles.For example, an electron beam evaporation source or a resistance heating evaporation source and an ion source or a plasma generation source may be used. It may be a combination or the like.

〔The invention's effect〕

The method for forming a through hole in a circuit board according to the present invention includes:
As described above, the conductor film is formed on the inner peripheral surface of the through-hole so as to have a substantially uniform thickness in the axial direction, a sufficient thickness, and a small conductive resistance.

[Brief description of the drawings]

FIG. 1 is a schematic view showing one embodiment of a method for forming a through hole in a circuit board according to the present invention as an apparatus, and FIGS. 2 and 3 are schematic views showing the flow of ions by enlarging the main part thereof. FIG. 4 is an enlarged view showing an embodiment in which needle-like projections are provided on the electrodes, FIG. 5 is a schematic view showing a conventional through-hole forming method as an apparatus, and FIG. 6 is a diagram showing a conductive film in the through-hole. FIG. 7 is an enlarged schematic view showing an estimated amount of deposition, and FIG. 7 is an enlarged view showing a state in which a conductive film is deposited on the entrance side in the hole. 45 …… Circuit board, 40 …… Vacuum container, 41 …… Suction port, 42…
... Vacuum pump, 46 ... Through hole, 47 ... Parts to be scattered, 50 ... Scattered substance, 52 ... Conducted film

 ────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shusuke Matsumura 1048 Oaza Kadoma, Kadoma, Osaka Prefecture Inside Matsushita Electric Works, Ltd. (56) References JP-A-58-223400 (JP, A) JP-A-59-200755 (JP, A)

Claims (1)

(57) [Claims] 1. A vacuum vessel having a portion for vaporizing and ionizing and scattering a conductive material, wherein a space is present on the front and back sides of the substrate where the circuit board having a hole for through holes is opposed to the portion for scattering. And applying an electric field between the electrode and the circuit board by applying a negative voltage to an electrode disposed on the opposite side of the scattered portion of the circuit board, thereby ionizing and scattering. A method for forming a through hole in a circuit board, in which a material to be forced is forcibly guided to a hole for the through hole to be attached and deposited on an inner peripheral surface of the hole.