JPH02310992A - Forming method for through hole of circuit board - Google Patents

Abstract

PURPOSE:To so form a conductor film in a sufficient amount on the inner peripheral wall of a through hole as to reduce its conductive resistance by forcibly introducing substance to be scattered from a part to be scattered from a vacuum unit to a space of a downstream side via the hole from a space of an upstream side by the flow of gas, adhering and depositing it on the inner peripheral surface of the hole. CONSTITUTION:An Ar plasma 30 is generated in a low vacuum chamber 27 with Ar gas to be introduced into the chamber 27 through a suction port 22 by suction by the operation of a vacuum pump 23, and Cu atoms (conductive material) are scattered from the surface of a target 25 by sputtering with the plasma. The scattered atoms 31,... are adhered and deposited to the flat surface of lower side of a circuit board 20 not only to become a conductor film 35 but to be introduced into through hole 29 according to the flow of Ar atoms 32,..., and adhered and deposited also on the inner peripheral surface of the hole 29. Since the deposition is forcibly conducted by the flow, a thicker conductor film 33 than a conventional one is formed to become a through hole 34.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a method for forming through holes in a circuit board.

[Conventional technology]

When using a method to obtain a circuit board by forming a film on the surface of the circuit board by vacuum evaporation or sputtering, it is possible to form a conductor film, etc. (insulator, resistor, It is also possible to form a film using a dielectric or the like) with relative ease, and it is also possible to form a high-quality conductor film with few impurities. According to the vacuum evaporation method, etc., compared to the case of the plating method, etc., even if the surface roughness of the circuit board is fine, a sufficient degree of bonding can be obtained for the conductor film, so that the thickness of the conductor film can be made sufficiently thin. This has the advantage that the conductive resistance of the film portion is reduced, and a circuit board with excellent high frequency characteristics can be obtained.

Fig. 7 shows that a conductor film is formed on one side of a circuit board 1 made of alumina or the like with holes 3 for through-holes made by sputtering, and at the same time a conductor film is also formed on the inner periphery of the holes 3. An example of a method for forming a film is shown below. The device includes a vacuum container 5, which includes:
An Ar gas intake port 6 and an exhaust port 8 connected to a vacuum pump 7 are open. The circuit board 1 is set horizontally by a holder 9 in the upper part of the space in the vacuum container 5, and the target (splashing part) 2 provided above the cathode 10 is located in the lower part of the space. Due to the operation of the vacuum pump 7, the inside of the vacuum container 5 is suctioned and depressurized to become a vacuum state.
r gas will be forcibly sucked. The Ar gas sucked into the vacuum container 5 generates A plasma between the circuit board 1 and the target 2, and the plasma causes copper atoms (a flying substance) to fly away from the target 2. As a result, copper atoms adhere to the surface of the circuit board 1, and the through-hole holes 3 of the circuit board 1...
・It also comes to adhere to the inner peripheral surface of.

Problem to be solved by the invention C] By the way, in the above method, the circuit board 1 is supported by the holder 9, but the board 1 has holes 3 for through holes.
Since the copper atoms are supported so as to be closed on the back side, the copper atoms can reach one side of the circuit board 1 relatively easily, but the inflow into the through-hole holes 3 is extremely difficult. I was becoming reluctant to do so. To explain this more specifically using FIG. 8, which shows an enlarged view of the main parts, in the same figure,
The thickness of the circuit board l is T, the inner diameter of the hole 3 for the through hole is d, and the thickness of the conductive film 12 attached to the surface of the circuit board 1 is t.
. , a conductive film 13 attached to the inner peripheral surface of the through-hole hole 3
When the thickness of is t, π(d/2)' t, ζπd (T+to)...0
It is approximated by the formula 1, -, t # toX d/4 (T+ to)
・It can be seen that the formula is old...−・−■. ■ Taking the formula as an example, for example, T=0.635 t, =o, o 1
Table 1 shows how much t becomes when the inner diameter d of the hole 3 is changed by substituting .

As shown in Table 1, the smaller the inner diameter d of the through-hole hole 3, the thinner the thickness t of the conductor film 13 deposited inside the hole 3 becomes, and d/T is 1 or less, i.e. , circuit board 1
If d is smaller than the thickness T and the hole 3 tends to be elongated, the thickness of the conductor film 12 attached to the surface of the flat part of the circuit board 1 will be less than 20% of the thickness to. . The conductor film 13 deposited and formed in the hole 3 is the ninth
As shown in the figure, it is thick on the target 2 side and gradually becomes thinner toward the back, which increases the electrical resistance value of the conductive film 13 and, in some cases, may cause conduction failure. As a solution to these problems, there is a method described in Japanese Patent Laid-Open No. 62-222062. This method relates to a sputtering method and a sputtering target, but the method for forming a conductive film is limited to sputtering, and the rod-shaped target itself is inserted into a cylindrical body to perform sputtering. In order to perform uniform sputtering, it is necessary to form plasma uniformly, and for this purpose, it is necessary to maintain an appropriate distance between the electrodes (usually about 51 m) in order to maintain a uniform Ar gas distribution and discharge. , about 4 am) in the above-mentioned publication, and for this reason, this method is not suitable for application to the inner circumferential surface of a minute hole such as a through hole of a circuit board.

In view of the above circumstances, it is an object of the present invention to form a conductive film on the inner peripheral surface of a through-hole in a sufficient amount and to reduce conductive resistance.

[Means to solve the problem]

In order to solve the above problem, a method for forming a through hole in a circuit board according to the invention according to claim 1 includes forming a hole for a through hole in a vacuum container having a portion inside which vaporizes and scatters a conductive material. A printed circuit board is arranged to face the part to be scattered, and the circuit board is used to sweep inside the vacuum container so that the part to be scattered is a space on the upstream side of the scattering path, and the other side is a space on the downstream side of the scattering path. By suctioning a vacuum on the downstream side of the partition, the downstream space becomes a high vacuum and the upstream space becomes a low vacuum, and the gas introduced into the upstream space is drawn into the through-hole hole. through the through-hole to the downstream space, and the scattered substances from the part to be scattered are forced by the gas flow from the upstream space through the through-hole to the downstream space. During this time, it is allowed to adhere and deposit on the inner peripheral surface of the hole.

The method for forming through-holes in a circuit board according to the invention as set forth in claim 2 includes scattering the circuit board with holes for through-holes in a vacuum container having a portion in which a conductive material is vaporized, ionized, and scattered. between the electrode and the circuit board, which are arranged so that a space exists on the front and back sides of the circuit board, and the substance to be ionized and scattered is placed on the opposite side of the part of the circuit board to be scattered. By applying an electric field to the through-hole, the material is forcibly guided into the through-hole and attached and deposited on the inner circumferential wall of the hole.

[For production]

If the scattered substances are made to flow together with the introduced gas from the low vacuum chamber to the high vacuum chamber and guided into the through-hole holes placed in the middle, the scattered substances guided by the difference in the degree of vacuum will flow through the through-holes. It comes to adhere to the inner circumferential surface of the hole in large quantities and over the entire area.

The ionized and scattered substance is guided to the inner circumferential surface of the through hole by applying an electric field between the circuit board and an electrode disposed on the opposite side of the part of the circuit board to be scattered, Ion particles are guided into the through-hole by the electric field effect and adhere to the inner peripheral surface of the hole in large numbers and over the entire surface.

〔Example〕

Hereinafter, embodiments of the present invention will be explained in detail with reference to the accompanying drawings.

FIG. 1 shows an embodiment of the method for forming through holes in a circuit board according to the present invention as an apparatus. The device forms a conductive film on the surface of an alumina circuit board 20 by sputtering, and is equipped with a vacuum container 21, which has an Ar gas inlet 22 on one side and an Ar gas inlet 22 on the other side. The exhaust port 19 is fighting for its opening. A vacuum pump 23 such as a Talio pump is connected to the exhaust port 19. A cathode 24 is provided in the lower part of the vacuum container 21, and a target (splashing part) 25 made of a copper material (conductive material) is provided above the cathode 24. The internal space of the vacuum container 21 is vertically divided by a partition wall 26 and a circuit board 20 such that the lower part is a space on the upstream side of the scattering path and the upper part is a space on the downstream side of the scattering path. The circuit board 20 is supported by a partition wall (holder) 26 so as to be parallel to and above the target 25 . The downstream space becomes a high vacuum chamber 28, and the upstream space becomes a low vacuum chamber 27,
These chambers 27, 28 are created by the operation of the vacuum pump 23. Note that the circuit board 20
The axes of the through-hole holes 29 are directed upward and downward.

By operating the vacuum pump 23, the high vacuum chamber 28 is brought to a pressure of, for example, 10-' to 10-' Torr, and the low vacuum chamber 27 is brought to a pressure of 10-'' to 10-'' Torr. As a result, each hole 2 for through hole
In the chamber 9, gas and the like flow from the low vacuum chamber 27 to the high vacuum chamber 28. Then, Ar plasma 30 is generated in the low vacuum chamber 27 by the Ar gas introduced into the low vacuum chamber 27 through the intake port 22 by the suction action, and
Target 25 is sputtered with the same plasma.
The CU ring atom conductive material) is scattered from the surface of the CU ring atom.

The scattered Cu atoms 31... not only adhere and deposit on the lower flat surface of the circuit board 20 to form the conductive film 35, but also as shown in the schematic diagram of FIG. 2, the Ar atoms 32...・・・
is guided into the through-hole hole 29 according to the flow of
It also begins to adhere and deposit on the inner peripheral surface of the assimilation 29. Since this deposition is forcibly carried out by the flow, the conductor film 33 is formed thicker than before and becomes the through hole 34, and the conductor film 33 is not too thick in the low vacuum chamber 27.
The thickness is approximately uniform in the axial direction. The scattered substances are guided into the downstream space through the through-hole 29 by the flow of the Ar atoms 32.

FIG. 3 shows a device in which an electric field is used to effectively guide metal particles (scattering substances) ionized by plasma to the inner peripheral surface of a through hole. As shown in the figure, the vacuum container 40 has an inlet port 41 at the bottom thereof, and an exhaust port 43 connected to a vacuum pump 42 at the other side. A holder 44 is located at the middle height of the container 40.
A circuit board 45 is set horizontally in the holder 44. The holder 44 and the circuit board 45 are members that allow a space to exist on both sides of the holder 44 and the circuit board 45. The substrate 45 is provided with holes 46 for through holes. A magnetron sputter 47 serving as an evaporation source is installed at the bottom of the container 40, and an electrode (cathode) is installed at a position slightly away above the circuit board 45 in the container 4θ on the opposite side of the magnetron sputter 47. 48 are provided horizontally. The cathode 48 is made of a flat plate like the circuit board 45, and faces the entire circuit board 45 from above. Note that the holder 44 is attached to the container 4 on the intake port 41 side.
0 is divided into upper and lower parts, but on the exhaust port 43 side, suction force can act on the space of the electrodes 48.

First, the inside of the vacuum container 40 is evacuated to a vacuum (for example, x
to -'~Xl0-' Torr), and Ar gas (for example,
0-' Torr) is introduced in an appropriate amount. Plasma is formed by applying a voltage (for example, 500 to 100 OV) to the magnetron sputter 47, and conductive metal particles (CU particles) are scattered from the baffle 47 and ionized by the plasma. This Cu
In order to attach and deposit particles within the through-hole hole 46 with high probability, a negative voltage (for example, several tens of ohms) is applied to the electrode 48.
(Ov to several kV). Thereby, the ionized Cu particles are guided to pass through the through holes 46. This state is shown in FIG. 4, where the Cu ions 50 and the Ar ions 51 are drawn toward the electrode 48 by a force F. This person F is
In proportion to the electric field strength E applied to the electrode 48, F=eE
(e is the charge amount of the ion). As a result, as shown in FIG. 5, the Cu ions 50 are corrected in trajectory toward the inner circumferential surface of the through-hole hole 46 due to the electric field effect of the electrode 48, and fly onto the inner circumferential surface. .

The flight speed V of the ionized Cu ions 50 is
When the applied voltage is 1kV, 55000m per second
The ionized CU particles 50 instantly fly toward the inner peripheral surface of the through-hole hole 46 while being corrected in trajectory by the electric field effect, so that the Cu particles 50 are not attached to the inner peripheral surface. The probability of Similarly, Ar ions 51 flying from the plasma fly toward the inner circumferential surface of the through-hole hole 46 due to the electric field effect, and some of them also mix into the conductive film 52, but they are always mixed with C.
Since the surface of the conductive film 52 of u is impacted, a strong and uniform film 5 is formed.
2 will be formed.

In addition, as shown in FIG. 6, the electrode 53 has a needle-like protrusion 54.
By providing a hole so that its tip faces into the hole 46, the electric field effect becomes more effective and the probability of ions adhering to the hole 46 is greatly improved, and the impact caused by the Ar ion bombardment becomes more effective. The effect can also be improved. The evaporation source may be anything other than a magnetron cathode, as long as it can ionize and scatter metal particles. For example, an evaporation source using an electron beam method, a resistance heating method, an ion source, or a plasma generation source may be used. It may be a combination or the like.

〔Effect of the invention〕

In the method for forming through holes in a circuit board according to the present invention, as described above, a conductive film is formed on the inner circumferential wall of a through hole in a sufficient amount and with a low conductive resistance.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of an apparatus for forming a through hole in a circuit board according to an embodiment of the present invention, and FIG. 2 is a schematic cross-sectional view of an enlarged main part showing the flow of ions.
Figure 3 is a schematic diagram showing another embodiment, Figures 4 and 5 are enlarged schematic diagrams of the main parts showing the flow of ions, and Figure 6 is a schematic diagram showing the flow of ions on the electrode. Fig. 7 is a schematic diagram showing a conventional through-hole forming method as an apparatus, and Fig. 8 is an enlarged view showing an example of a conventional through-hole forming method. The enlarged schematic diagram and FIG. 9 are enlarged diagrams showing the conductor film deposited on the entrance side of the hole. 20.45...Circuit board 21.40...Vacuum container 22.41...Intake port 23.42...Vacuum pump 25.47...Part to be scattered 27...Low vacuum chamber (downstream side space) 28... High vacuum chamber (upstream space) 2
9.46...Through hole hole 31.50...Scattered substances 33.52...Conductor film 34...Through hole agent Patent attorney Takehiko Matsumoto Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6

Claims (1)

[Scope of Claims] 1. A circuit board having a through-hole is placed in a vacuum container having a part inside which vaporizes and scatters a conductive material so as to face the part to be scattered. By partitioning the inside of the vacuum container using the same substrate so that the part to be scattered is a space on the upstream side of the scattering path and the other side is a space on the downstream side, and vacuum suction is performed on the downstream side,
The space on the downstream side is made to have a high vacuum and the space on the upstream side is made to be a low vacuum, and the gas introduced into the space on the upstream side is made to flow through the through hole to the space on the downstream side, and The scattered substances from the part to be scattered are forcibly guided from the upstream space through the through-hole hole to the downstream space by the gas flow, and during this time, they adhere to the inner circumferential surface of the hole.・A method for forming through-holes in circuit boards by depositing them. 2. In a vacuum container having a part where the conductive material is vaporized, ionized, and scattered, a circuit board with through-hole holes is arranged so as to face the part where the conductive material is to be scattered and that there is a space on the front and back sides of the board. At the same time, the ionized and scattered substance is forced into the through hole by applying an electric field between the circuit board and an electrode placed on the opposite side of the part of the circuit board to be scattered. A method for forming through-holes in circuit boards in which the material is guided and deposited on the inner circumferential surface of the hole.