JP2007262456A - Copper ball for anode for copper plating, plating apparatus, copper plating method and method of manufacturing printed board - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve plating characteristics such as uniformity of electrodeposition by suppressing the peeling-off of a black film formed on the surface of a copper ball of an anode for copper plating. <P>SOLUTION: The copper ball for the anode is used as the anode for copper plating and comprises crystal grains of copper containing phosphorus element, wherein ≥70% of the number of the crystal grains in total crystal grains constituting the copper ball for the anode has ≥10 μm minor axis and ≥60% of the number of the crystal grains in total crystal grains constituting the copper ball for the anode has ≥30 mμ major axis. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a copper ball for a positive electrode for copper plating, a copper plating apparatus, a copper plating method, and a method for manufacturing a printed circuit board.

  When performing copper plating, it is common to use a copper ball containing a small amount of phosphorus element and having a diameter of 60 mm or less as a positive electrode, while using a plating object as a negative electrode. This copper ball is installed in a copper sulfate plating solution and gradually dissolves in the plating solution with the electrolysis of the plating, so that it is appropriately supplied according to its consumption.

On the surface of the copper ball containing phosphorus element, in the electrolysis process, as shown in FIG. 2, such as copper chloride (Cu ₂ Cl ₂ ), copper oxide (Cu ₂ O), copper phosphide (Cu ₃ P), A compound called a black film is formed (see, for example, Patent Documents 1 and 2).

JP2003-171797 JP 2003-268595 A

  However, the black film formed on the surface of the copper ball is so brittle that it can be easily peeled off by hand, so that the black film may peel off from the surface of the copper ball during the plating process.

  The peeled black film is deposited as sludge in the plating solution, and the deposited sludge diffuses into the plating solution, thereby causing a reduction in plating characteristics such as uniform electrodeposition.

  Accordingly, an object of the present invention is to suppress peeling of a black film formed on the surface of a copper ball for a positive electrode for copper plating, thereby improving plating characteristics such as uniform electrodeposition.

  A first invention for solving the above-described problems is a positive electrode copper ball used as a positive electrode for copper plating, wherein the positive electrode copper ball is composed of copper crystal grains containing a phosphorus element, and Of the total number of crystal grains constituting the electrode copper ball, the minor axis of 70% or more of the crystal grains is 10 μm or more, and 60% of the total number of crystal grains constituting the positive electrode copper ball The major axis of the above number of crystal grains is 30 μm or more.

  In the first invention, the positive electrode copper ball has a copper element content of 99.95% or more, and the positive electrode copper ball has a phosphorus element content of 300 ppm or more and 400 ppm or less. Also good.

  According to a second aspect of the present invention for solving the above problems, a plating tank for storing a plating solution therein, an immersion means for immersing a plating object as a negative electrode in the plating solution in the plating tank, and in the plating tank A copper plating apparatus comprising: dipping means for dipping a copper ball for a positive electrode for copper plating according to claim 1 or 2 as a positive electrode in the plating solution.

  According to a third aspect of the present invention for solving the above problems, a plating solution is stored in a plating tank, a plating object as a negative electrode is immersed in the plating solution in the plating tank, and a positive electrode is formed in the plating tank. The copper ball for a positive electrode for copper plating according to claim 1 or 2 as an electrode is immersed in the plating solution and energized from the positive electrode to the negative electrode to form a copper plating layer on the plating object. It is a copper plating method.

  According to a fourth aspect of the present invention for solving the above problems, a plating solution is stored in a plating tank, and a wiring substrate as a negative electrode is immersed in the plating solution in the plating tank. A copper plating layer is formed on the wiring substrate by immersing the copper ball for a positive electrode for copper plating according to claim 1 or 2 as an electrode in the plating solution and energizing the negative electrode from the positive electrode. It is a manufacturing method of a printed circuit board.

  The copper ball for the positive electrode for copper plating according to the present invention can suppress the peeling of the black film formed on the surface of the copper ball for the positive electrode for copper plating, thereby improving the plating characteristics such as uniform electrodeposition. be able to.

Next, an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a cross-sectional view of a copper plating apparatus using copper balls for a positive electrode for copper plating according to an embodiment of the present invention. FIG. 2 is an explanatory view of a black film formed on the surface of a copper ball for a positive electrode for copper plating according to an embodiment of the present invention. FIG. 3 is an enlarged view of a cross-sectional structure of a copper ball for a positive electrode for copper plating according to an embodiment of the present invention. FIG. 4 is a cross-sectional view of a printed circuit board that has been subjected to copper plating, (a) is a cross-sectional view of a via hole when copper plating is performed using a conventional positive electrode copper ball, (b) The sectional view of the via hole at the time of performing copper plating using the copper ball for positive electrodes concerning one embodiment of the present invention is shown.

(1) Positive Electrode Copper Ball First, a copper plated positive electrode copper ball according to an embodiment of the present invention will be described with reference to FIGS.

  FIG. 3 is an enlarged view of a cross-sectional structure of a copper plating positive electrode copper ball B according to an embodiment of the present invention. The positive electrode copper ball B is composed of a plurality of crystal grains 11.

  Here, among the intervals between two parallel lines sandwiching the cross section of each crystal grain 11, the minimum width is called the minor axis 11S, and the maximum width is called the major axis 11L. The minor axis 11S and the major axis 11L contribute to the size of the cross-sectional area of the crystal grain 11.

  In one embodiment of the present invention, 70% or more of the crystal grains 11 out of the total number of the crystal grains 11 constituting the positive electrode copper ball B for copper plating have a short diameter 11S of 10 μm or more. Moreover, out of the total number of crystal grains 11 constituting the positive electrode copper ball B, 60% or more of the crystal grains 11 have a major axis 11L of 30 μm or more.

  In other words, out of the total number of crystal grains 11 constituting the positive electrode copper ball B, the number of crystal grains 11 having a minor axis 11S of less than 10 μm is less than 30% and the major axis 11L is less than 30 μm. The number of 11 is less than 40%.

  As shown in FIG. 2, the outer shape of the positive electrode copper ball B has a ball shape, but it does not matter whether or not the ball shape is a true sphere. Moreover, although it is preferable that the diameter of a ball | bowl is about 60 mm or less, it does not necessarily restrict | limit to said conditions. In addition, the cross section of the positive electrode copper ball B may be elliptical, polygonal, or a combination thereof.

  Each crystal grain 11 is made of a copper element containing a small amount of phosphorus element. The composition of each crystal grain 11 is, for example, preferably a copper element content of 99.95% or more and a phosphorus element content of 300 ppm to 400 ppm, but is not necessarily limited to the above conditions.

(2) Copper Plating Apparatus Subsequently, the configuration of the copper plating apparatus according to one embodiment of the present invention will be described with reference to FIG.

  An electrolytic copper plating apparatus 1 according to an embodiment of the present invention includes a plating tank 2, a holder 3 as an immersion means for immersing a plating object as a negative electrode in a plating solution, and a positive electrode copper ball as a positive electrode. And a basket 4 as a dipping means for dipping in the plating solution.

  The plating tank 2 is configured to store a copper sulfate plating solution 9 therein.

  The holder 3 fixes the wiring substrate 6 as a plating object so as to be suspended from above the wiring substrate 6. And it is comprised so that raising / lowering is possible so that the wiring base material 6 can be immersed in the copper sulfate plating solution 9, or can be pulled up from the copper sulfate plating solution 9. FIG.

  In addition, the holder 3 is good also as a structure which fixes the wiring base material 6 so that it may support from a bottom face or a side surface. Furthermore, as another dipping means, the long wiring substrate 6 may be configured as a conveyance roller that dipped in the copper sulfate plating solution 9 while being conveyed inside the plating tank 2.

  The basket 4 has a function of accommodating a plurality of positive electrode copper balls B as positive electrodes. And the basket 4 is installed in the plating tank 2 so that the accommodated positive electrode copper ball B faces the wiring substrate 6, and at this time, a part of the basket 4 is together with the positive electrode copper ball B. Then, it is immersed in the copper sulfate plating solution 9.

  The basket 4 needs to have electrical conductivity so that power can be supplied from the outside to the accommodated positive electrode copper ball B, and must have corrosion resistance to the copper sulfate plating solution 9. Therefore, it is made of a material such as titanium or platinum.

  Further, in the storage portion of the positive electrode copper ball B in the basket 4, the stored positive electrode copper ball B is immersed in the copper sulfate plating solution 9 and the copper ions eluted from the positive electrode copper ball B are transferred to the basket. The entire surface or a part thereof is configured in a mesh shape so that it can freely flow out to the outside.

  Further, the upper surface of the basket 4 is opened or can be opened and closed so that the positive electrode copper balls B can be appropriately replenished in accordance with the amount of consumption during the plating process.

  The basket 4 is installed by being wrapped in a mesh bag called an anode bag 5. The anode bag 5 is a bag made by knitting polypropylene fibers, for example. By wrapping the basket 4 with the anode bag 5, sludge generated from the positive electrode copper balls B does not diffuse into the copper sulfate plating solution 9. So that it has a filtering function. However, in the electrolytic copper plating apparatus 1 according to one embodiment of the present invention, the anode back 5 is not necessarily essential.

  Further, the negative electrode of the DC power source 10 is connected to the wiring substrate 6 via the holder 3 so that a potential difference for plating electrolysis is applied, and the positive electrode of the DC power source 10 is connected to the positive electrode copper ball B. Are connected via the basket 4.

(3) Copper plating method and printed board manufacturing method Next, a copper plating method and a printed board manufacturing method according to an embodiment of the present invention using the copper plating apparatus 1 will be described with reference to FIG. To do.

  First, the copper sulfate plating solution 9 is stored in the plating tank 2.

  Thereafter, the holder 3 is used to fix the wiring substrate 6 as a plating object so as to be suspended from above. Thereafter, the holder 3 is lowered and the wiring substrate 6 is immersed in the copper sulfate plating solution 9.

  In the above description, the wiring substrate 6 refers to a substrate provided with a conductor layer 8a and a conductor layer 8b on both surfaces of a film-like or plate-like insulating layer 7, for example. In addition, the wiring base material 6 does not necessarily need to have a conductor layer on both surfaces, and may be only one surface.

  The wiring substrate 6 is a through-hole penetrating the one conductor layer 8a and the insulating layer 7, and a blind via hole BH in which one opening of the through hole is closed by the other conductor layer 8b, A through hole TH penetrating the conductor layers on both sides and the insulating layer 7 is formed in advance.

  In addition to the wiring substrate 6, any substrate having a base surface on which copper plating can be deposited can be used as a plating object.

On the other hand, a plurality of positive electrode copper balls B as positive electrodes are stored in the basket 4.
At this time, by making the outer shape of the positive electrode copper ball B into a ball shape of 60 mm or less, it is possible to increase the surface area of the copper in the positive electrode while improving the filling property of the positive electrode copper ball B into the basket 4. it can.

  Thereafter, the basket 4 is placed in the plating tank 2 so that the stored positive electrode copper ball B faces the wiring substrate 6. At that time, a part of the basket 4 is immersed in the copper sulfate plating solution 9 together with the accommodated copper ball B for the positive electrode.

In the above, the copper sulfate plating solution 9 is first stored in the plating tank 2, and then the wiring substrate 6 and the positive electrode copper ball B are immersed. At this time, the wiring substrate 6 and the basket are immersed. Any of 4 may be immersed first, or these may be simultaneously immersed.
As another embodiment, both or one of the wiring substrate 6 and the positive electrode copper ball B is fixed in advance in an empty plating tank 2, and then copper sulfate plating is performed in the plating tank 2. Liquid 9 may be stored.

  Thereafter, the positive electrode copper ball B as the positive electrode is energized to the wiring substrate 6 as the negative electrode to start plating electrolysis.

After the start of plating electrolysis, a black film BF such as copper chloride (Cu ₂ Cl ₂ ), copper oxide (Cu ₂ O), and copper phosphide (Cu ₃ P) is formed on the surface of the positive electrode copper ball B. The Among the black films, Cu ₃ P in particular is a compound in which the copper element in the copper ball and the phosphorus element added in a small amount in the copper ball form a compound. Elution into the plating solution 9 serves to keep the amount of copper ions in the copper sulfate plating solution 9 constant.

On the other hand, a copper plating layer 12 shown in FIG.
When the consumption of the positive electrode copper balls B stored in the basket 4 progresses during the plating process, the positive electrode copper balls B are appropriately replenished according to the amount of consumption.

  After the copper plating layer 12 having a desired thickness is formed on the surface of the wiring substrate 6, the plating process is completed, and the production of the printed circuit board 6 'is completed. Thereafter, the holder 3 is raised and the printed board 6 ′ is pulled up from the copper sulfate plating solution 9.

  According to the above, by the copper ball B for the positive electrode for copper plating according to one embodiment of the present invention, the peeling of the black film BF formed on the surface of the copper ball B for the positive electrode for copper plating is suppressed. It is possible to improve plating characteristics such as uniform electrodeposition on the wiring substrate 6.

    Below, a comparative example is demonstrated with an Example.

  First, two types of positive electrode copper balls A and positive electrode copper balls B having different crystal grain sizes were prepared. Thereafter, six copper balls were randomly extracted from the positive electrode copper ball A and the positive electrode copper ball B, respectively.

  The positive electrode copper ball A and the positive electrode copper ball B have a diameter of about 25 mm and are common. Further, the composition of the positive electrode copper ball A and the positive electrode copper ball B is common, with the copper element content being 99.95% or more and the phosphorus element content being 300 ppm or more and 400 ppm or less. .

  Thereafter, these copper balls are cut to expose the cross section, and the exposed cross section is mirror-finished using a buff and a diamond grindstone, and then a mixed solution of ammonia and hydrogen peroxide is used. Sectional crystal grains as shown in FIG.

  Then, about the cross section which made the crystal grain appear, using a metal microscope, it is 1000 magnification | multiplying_factor, and 10 places per copper ball (namely, about the copper ball A for positive electrodes, and the copper ball B for positive electrodes each) The cross-sectional structure | tissue photography of each 60 places was performed.

  Then, in each of the photographed photographs, the minor axis 11S and the major axis 11L at 20 locations were measured. That is, for each of the positive electrode copper ball A and the positive electrode copper ball B, the measurement is 6 balls × 10 photo shooting locations × 20 crystal grain measurements = 1200 locations (short axis and long axis respectively) about).

As a result, the results shown in Table 1 were obtained.

  Thereafter, a transfer test and a uniform electrodeposition characteristic test of the black film BF were sequentially performed using the positive electrode copper ball A (comparative example) and the positive electrode copper ball B (example) described above.

(1) Transfer test of black film BF First, 30 pieces of positive electrode copper balls A and positive electrode copper balls B were randomly extracted from the remaining copper balls (94 pieces each). 2 pieces are immersed in a copper sulfate plating solution 9 bathed in the plating tank 2 and 12.0 A (0.4 A per copper ball) is energized for 150 minutes, and the copper ball surface is shown in FIG. Such a black film BF was formed.
Thereafter, the formation of the black film BF was repeated under the same conditions (10 times), and the black film BF was formed for all 30 positive electrode copper balls A and 30 positive electrode copper balls B.

  Thereafter, 15 pieces are taken out from each of the 30 positive electrode copper balls A and the positive electrode copper balls B on which the black film BF is formed, and rolled about 50 mm on plain paper, so that the black film BF becomes plain paper. The state of transcription was observed.

As a result, in all the positive electrode copper balls B, the black film BF was not transferred to the plain paper in all 15 pieces.
On the other hand, in the positive electrode copper ball A, it was confirmed that the black film BF was transferred to the plain paper in all 15 balls.
Therefore, in the positive electrode copper ball B, it was confirmed that the dropout of the black film BF could be suppressed as compared with the positive electrode copper ball A.

(2) Uniform electrodeposition characteristic test First, two wiring base materials 6 provided with conductor layers (8a, 8b) on both surfaces of the insulating layer 7 on the film were prepared as plating objects. In the examples and comparative examples, the insulating layer 7 was 25 μm thick, and the material was polyimide. The conductor layers 8a and 8b were both 12 μm in thickness and made of copper.
Each wiring substrate 6 was formed with 100 blind via holes BH having a diameter of 60 μm by using a laser method. A conductive film made of Sn-Pd colloid was formed on the inner wall of the blind via hole BH.

  Thereafter, a plating tank 2 is prepared for each of the positive electrode copper ball A and the positive electrode copper ball B (two tanks in total), and 3 liters of copper sulfate plating solution 9 is newly built in each plating tank 2. did.

  Then, using the remaining positive electrode copper balls A and positive electrode copper balls B (15 each) on which the black film BF was formed, the wiring substrate 6 was subjected to copper plating.

Thereafter, a copper plating layer 12 having a predetermined thickness was formed on the surface of the conductor layer 8a, and the production of the printed circuit board 6 ′ was completed. The energization current density was 3.0 A / dm ² and the energization time was 18 minutes.

  Thereafter, the printed circuit board 6 ′ is cut so as to divide the center of the blind via hole BH, the thickness of the copper plating layer 12 deposited on the surface of the conductor layer 8a, and the copper plating layer 12 deposited in the blind via hole BH. The thickness was observed.

As a result, when the positive electrode copper ball B was used, the plating thickness on the inner surface of the blind via hole BH was equivalent to the plating thickness on the surface of the conductor layer 8a as shown in FIG.
On the other hand, when the positive electrode copper ball A was used, the plating thickness on the inner surface of the blind via hole BH was 1/5 as compared with the plating thickness on the surface of the conductor layer 8a, as shown in FIG.
Therefore, it was confirmed that the positive electrode copper ball B can obtain uniform electrodeposition characteristics including the inside of the blind via hole BH.

It is sectional drawing of the copper plating apparatus using the copper ball for positive electrodes of the copper plating concerning one Embodiment of this invention. It is explanatory drawing of the black film formed on the surface of the copper ball for positive electrodes of the copper plating concerning one Embodiment of this invention. It is an enlarged view of the cross-sectional structure of the copper ball for positive electrodes of copper plating concerning one Embodiment of this invention. It is sectional drawing of the printed circuit board which performed the copper plating process, (a) shows sectional drawing of the via hole at the time of performing copper plating using the copper ball for conventional positive electrodes, (b) is one of this invention Sectional drawing of the via hole at the time of performing copper plating using the copper ball for positive electrodes concerning embodiment is shown.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Electro copper plating apparatus 2 Plating tank 3 Holder (immersion means)
4 Basket (Dipping means)
6 Wiring substrate (Plating object)
6 'Printed circuit board 9 Copper sulfate plating solution 11 Crystal grain 11L Long diameter 11S Short diameter B Copper ball for positive electrode

Claims (5)

A copper ball for a positive electrode used as a positive electrode for copper plating,
The positive electrode copper ball is composed of copper crystal grains containing phosphorus element,
The short diameter of 70% or more of the crystal grains constituting the positive electrode copper ball is 10 μm or more, and
A copper ball for a positive electrode for copper plating, wherein a major axis of 60% or more of the total number of the crystal grains constituting the positive electrode copper ball is 30 μm or more. A copper ball for a positive electrode for copper plating according to claim 1,
The copper element content in the positive electrode copper ball is 99.95% or more,
The copper ball for a positive electrode of copper plating, wherein the content of phosphorus element in the copper ball for a positive electrode is 300 ppm or more and 400 ppm or less. A plating tank for storing a plating solution inside;
In the plating tank, immersion means for immersing a plating object as a negative electrode in the plating solution,
A copper plating apparatus comprising: dipping means for dipping the copper ball for a positive electrode of copper plating according to claim 1 or 2 as a positive electrode in the plating solution in the plating tank. Plating solution is stored inside the plating tank,
In the plating tank, the plating object as a negative electrode is immersed in the plating solution,
In the plating tank, the positive electrode copper ball for copper plating according to claim 1 or 2 as a positive electrode is immersed in the plating solution,
Forming a copper plating layer on the plating object by energizing the cathode to the cathode;
The copper plating method characterized by the above-mentioned. Plating solution is stored inside the plating tank,
In the plating tank, immersing the wiring substrate as a negative electrode in the plating solution,
In the plating tank, the positive electrode copper ball for copper plating according to claim 1 or 2 as a positive electrode is immersed in the plating solution,
Forming a copper plating layer on the wiring substrate by energizing from the positive electrode to the negative electrode;
A printed circuit board manufacturing method characterized by the above.

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