Electrolytic plating method and device for a wiring board
A plating bath which accommodates an insoluble node and a printed-circuit board, and a copper dissolved bath which supplies copper ions are arranged. The insoluble anode Is arranged as opposed to the printed-circuit board being a cathode, and a forward/reverse current is applied between both of the electrodes. Iron ions are added to a plating solution.
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1. Field of the Invention
The present invention relates to an electrolytic plating method and device filling up a microvia hole formed on a wiring board with metal plating.
2. Description of the Related Art
For electric appliances such as a cellular phone, a video camera, a notebook computer, etc., it is demanded to mount high-density components. As an implementation of high-density mounting, a buildup board on which a wiring layer and an insulation layer are sequentially formed, a printed-circuit board of an all-layer microvia type to which wiring boards on which microvias are formed are attached with heat and pressure, etc. are proposed.
For a conventional buildup board, micro holes (microvia holes) are formed on an insulation layer, and the inner side and the bottom of the holes are metal-plated, so that wiring layers above and below the insulation layer are electrically connected.
With this method, however, it is difficult to further form one microvia hole on another, and to securely connect the holes in an electric manner. Therefore, a land cannot be arranged on a microvia hole after microvia holes are stacked. Due to such a restriction on a pattern design, the whole of a pattern design cannot be made with an automatic wiring tool, and part of the design must be made manually. As a result, the time period required to design a printed-circuit board becomes long.
To overcome such a problem, a technique filling up microvia holes with electrolytic plating is proposed. For example, Japanese Laid-open Patent Publication No. 8469 discloses the technique filling up microvia holes by performing electric metal plating with PR electrolysis after an electroless metal film is formed.
However, with the plating method using PR electrolysis disclosed by the above described publication, plating must be performed for a long time (for example, two hours or longer) to fill up microvia holes. Therefore, the manufacturing cost of a printed-circuit board increases, and it is difficult to use a printed-circuit board on a mass-production level. Additionally, attempts are made to improve the density of an electric current in order to shorten a plating time. However, problems such that a void occurs during plating, or a plated surface becomes rough occur.
Furthermore, to solve the problems occurring when a soluble anode is used, for example, Japanese Laid-open Patent Publication No. 507106 discloses a metal plating method using an insoluble anode and a plating solution to which an oxidization-reduction compound is added.
The above described invention assumes electrolytic plating using a direct current power source, and does not present a plating method for filling up microvia holes on a printed-circuit board for a short time.
SUMMARY OF THE INVENTIONAn object of the present invention aims at filling up microvia holes on a printed-circuit board for a short time.
According to the present invention, a printed-circuit board is used as one pole and an insoluble electrode is used as the other, and electrolytic plating is performed by applying a forward/reverse current with the use of a metal plating solution including iron ions by 0.1 gram/liter or more, so that microvia holes formed on a printed-circuit board are filled up with metal plating.
According to the present invention, electrolytic plating is performed by applying a forward/reverse current with the use of a metal plating solution including iron ions by 0.1 gram/liter or more, whereby microvia holes can be filled up for a time shorter than a conventional method, and a metal film having a smooth surface characteristic can be formed. As a result, microvias which electrically connect wiring layers above and below an insulation layer can be formed for a short time, thereby significantly reducing the manufacturing cost of a multi-layer printed-circuit board.
As an electrolytic plating method, for example, a pulse reverse electrolytic method applying a forward/reverse pulsed current is available.
Additionally, a plating solution may be stirred to flow in parallel with the surface to be plated of a printed-circuit board. At this time, the flow quantity of the plating solution may be controlled depending on the diameter or the depth of a microvia hole.
With the above described configuration, the deposit speed of metal plating on the surface of a printed-circuit board and that of metal plating within a microvia hole can be suitably controlled. Consequently, a deep microvia hole with a short diameter can be filled up without causing a void, etc. within the hole.
BRIEF DESCRIPTION OF THE DRAWINGS
Hereinafter, a preferred embodiment according to the present invention will be described by referencing drawings. First of all, the manufacturing process of a multi-layer printed-circuit board is explained by referencing
A wiring pattern (wiring layer) 11′ is formed by etching a copper foil (conductor layer) stacked onto a core resin 12 such as glass epoxy, etc. (process steps (1) and (2) in
The technique filling up microvia holes with pulse reverse electrolytic plating is recited, for example, in “Gist of the 100th Lecture (held on Oct. 6 and 7, 1999) by Surface Finishing Society of Japan.
Next, an electrolytic plating method for a printed-circuit board according to this preferred embodiment will be explained by referencing
A plating bath 21 is composed of insoluble anodes 22, a cathode 23 being a printed-circuit board, a power source 24 for applying a forward/reverse current between the electrodes, and a copper plating solution including iron ions. To widen the surface areas of the electrodes, a multi-aperture electrode such as an expanded metal, etc. is used as each of the insoluble anodes 22.
Besides, copper dissolved baths 25 are arranged to supply copper ions to the plating bath 21, and a solution within the copper dissolved baths 25 and the plating solution within the plating bath 21 are circulated by a circulation pump 26.
According to this preferred embodiment, an iron ion “Fe2+” is added to the plating solution, so that “Fe3++e” is generated from “Fe2+” in the proximity of the insoluble anodes 22 as shown in
In the copper dissolved baths 25, “Cu2+” and “Fe2+” are generated by the dissolution reaction between the copper material within the copper dissolved baths 25 and “Fe3+” which is generated by each of the insoluble anodes 22 and carried to the copper dissolved baths 25.
At the cathode 23, Cu is deposited from “Cu2+” which is carried from the copper dissolved baths 25, so that a copper plated layer is formed on the printed-circuit board. At the same time, “Fe2+” is produced from “Fe3++e” which is generated by the insoluble anodes 22.
Namely, “Fe3+” is generated from the iron ion “Fe2+” included in the plating solution as a result of the electrolytic reaction of the insoluble anodes 22, and “Cu2+” and “Fe2+” are generated by “Fe3+” and the copper material within the copper dissolved baths 25. Therefore, the copper ion “Cu2+” and the iron ion “Fe2+”, which is added to the plating solution and consumed by the reaction of the insoluble anodes 22 continue to be supplied from the copper dissolved baths 25.
The cathode (printed-circuit board) 23 is arranged in the middle of the plating bath 21, and the two insoluble anodes 22 in a meshed state are arranged as opposed to the printed-circuit board 23. The plating solution is circulated by the circulation pump 26 in the right direction of
Described next are plating conditions and evaluation results of plating when a microvia hole having a depth of 50 μm, which is formed on an insulation layer, is filled up with the plating method according to this preferred embodiment.
The fundamental composition of the plating solution used in this preferred embodiment is as follows:
-
- copper sulfate·5 hydrates: 235.7 g/liter (L)
- sulfuric acid: 60 g/L
- organic additive (surface active agent such as Impulse Leveler provided by Atotec Co., Ltd.)
- organic additive (brightener such as Impulse Brightener provided by Atotec Co., Ltd.)
- chloric ion: 40 mg/L
- iron ion: 15 g/L (or 0.1 g/L)
In this preferred embodiment, pulse reverse electrolytic plating is performed by applying a forward/reverse pulsed current to the electrodes. The plating current applied to both of the electrodes is a forward/reverse pulsed current having a forward current duration T1 that is 40 ms, and a reverse current duration T2 that is 2 ms, as shown in
Sample 1 indicates the plating performed for 33.3 minutes with the average current density 3 Å/dm2 in a plating solution that does not include iron ions.
Sample 2 indicates the plating performed for 33.3 minutes with the average current density 3 Å/dm2 in a plating solution that includes iron ions by 15 g/L.
Sample 3 indicates the plating performed for 33.3 minutes with the average current density 3 Å/dm2 in a plating solution that includes iron ions by 0.1 g/L.
In this figure, the average value of the degree of roughness of the plated surface of Sample 1, for which the pulse reverse electrolytic plating is performed for 33.3 minutes with the plating solution that does not include iron ions, is 3.496 μm, whereas the average value of the degree of roughness of the plated surface of Sample 3, for which the pulse reverse electrolytic plating is performed for 33.3 minutes with the plating solution that includes iron ions by 0.1 g/L, is 2.830 μm. Namely, it can be verified that a smoother plated surface can be obtained by Sample 3 for which the plating is performed with the plating solution including iron ions.
Additionally, the average value of the degree of roughness of the plated surface of Sample 2, for which the pulse reverse electrolytic plating is performed for 33.3 minutes with the plating solution that includes iron ions by 15 g/L is 1.821 μm, and a further smoother plated surface than that with the plating solution which includes iron ions by 0.1 g/L can be obtained.
Furthermore,
Note that a microvia hole tapers, the diameter of the aperture of the hole is 40 μm, the diameter of the bottom of the hole is 25 μm, and the depth is 50 μm.
If the pulse reverse electrolytic plating is performed for 33.3 minutes with the plating solution which includes iron ions by 15 g/L, the microvia hole is completely filled up, and the copper plated surface is smooth as shown in
If the pulse reverse electrolytic plating is performed for 33.3 minutes with the plating solution which includes iron ions by 0.1 g/L, the microvia hole is completely filled up a shown in
It can be verified from the results of the comparisons between the degrees of roughness of the plated surface and the cross-sectional views of the microvias in
According to the above described preferred embodiment, iron ions are added to a copper dissolved solution and pulse reverse electrolytic plating is performed, whereby microvia holes can be filed up for a short time, and its surface can be almost smoothed.
Additionally, a plating solution is made to flow in parallel to the surface to be plated (the surface on which microvia holes are formed) of a printed-circuit board being a cathode, thereby further improving the plating characteristic. Furthermore, by controlling the flow quantity of a plating solution to be a suitable value, the deposit speed of the surface of the cathode 23 and that of copper within a microvia hole my be set to a desired value.
In the above described preferred embodiment, “Fe2+”, is added to a copper plating solution. However, the present invention is not limited to “Fe2+”, and other oxidization-reduction compounds may be added. The present invention may also be applied to metal plating other than copper. Furthermore, the application time of a forward/reverse plating current, the current density of an electrode, the composition of a plating solution, a plating time, etc. are not limited to those implemented in the above described preferred embodiment. For example, any composition can be used if it is available to electrolytic plating of copper, and other metals.
Still further, the direction in which a plating solution is made to flow upward or downward, not limited to the right and the left. The essentiality is to make a plating solution flow in parallel to the surface desired to be plated of a printed-circuit board. The present invention may be applied to a multi-layer substrate on which a semiconductor device is mounted, etc., not limited to a multi-layer printed circuit board.
According to the present invention, microvia holes are filled up for a short time, and a metal film having a smooth surface characteristic can be formed. Namely, microvias which electrically connect wiring layers above and below an insulation layer can be formed for a short time, thereby significantly reducing the manufacturing cost of a multi-layer wiring board.
Claims
1-6. (canceled)
7. An electrolytic plating device, comprising;
- a wiring board with microvia holes, each having a bottom made of copper foil provided on a surface of the wiring board as an electrode;
- an insoluble electrode, which is an electrode opposed to the wiring board;
- a metal plating solution containing iron ions of at least 0.1 gram/liter;
- a power source for performing electrolytic plating by applying a forward/reverse current between the wiring board and said insoluble electrode; and
- a stirring unit stirring said metal plating solution to make the solution flow in parallel to the surface to be plated of said wiring board so that the microvia holes having the copper foil at the bottom, which are formed on the surface of said wiring board, may be filled up with said metal plating.
8. The electrolytic plating device according to claim 7, wherein:
- the metal plating solution is comprised of copper plating solution; and
- the stirring unit adjusts a flow rate of the copper plating solution to a level at which copper deposition speeds both on the surface and inside microvia holes of the wiring board are optimum.
9. The electrolytic plating device according to claim 8, wherein
- the string unit adjusts the flow rate of the copper plating solution to bring the iron ion amount present near to wiring board surface to a level at which all the microvia holes are almost fully filled and the plating layer thickness on the wiring board surface becomes optimum.
10. The electrolytic plating device according to claim 9, further comprising:
- a plating bath accommodating the insoluble electrode and the wiring board; and
- a copper dissolved bath supplying copper ions to said plating bath, wherein
- said stirring unit circulates a solution within the copper dissolved bath and the plating solution within the plating bath.
11. The electrolytic plating device according to claim 7, wherein:
- said insoluble electrode is implemented by a multi-aperture electrode; and
- said plating solution is implemented by a copper plating solution.
Type: Application
Filed: Jul 22, 2004
Publication Date: Jun 9, 2005
Applicant:
Inventors: Toshiki Inoue (Aichi-ken), Kyoko Kumagai (Aichi-ken)
Application Number: 10/896,488