JP4345742B2 - Wiring board and manufacturing method thereof - Google Patents

Description

  The present invention relates to a wiring board used for various electric devices and a manufacturing method thereof, and more specifically, in a wiring board in which copper wiring is formed on an insulating film by a semi-additive method, the surface before plating is smooth. The present invention relates to a wiring board having copper wiring and a manufacturing method thereof.

In recent years, semiconductor packages have been reduced in size and increased in density, and the mounting method has become suitable for high-density mounting such as chip-on-board (COB), ball grid array (BGA), and chip-size package (CSP). Yes.
By the way, as a method for obtaining a wiring board used for a semiconductor package, a subtractive method mainly including the following steps is employed.
a. A step of forming a resist layer by applying a liquid resist to the surface of the conductor layer provided on the substrate surface or attaching a film-like resist.
b. A step of forming an etching mask by exposing the resist layer to ultraviolet rays using a mask having a desired wiring pattern, exposing the resist layer, and developing the resist layer.
c. A process of forming a wiring pattern by etching away the conductor layer exposed in the opening of the etching mask.
d. A process for producing a copper wiring by removing the etching mask remaining on the surface of the wiring pattern.

However, if an attempt is made to obtain the above-described miniaturized and high-density wiring board by the subtractive method, there arises a problem that good etching results cannot be obtained in the step c. This is because the phenomenon that the etching solution does not sufficiently enter the opening portion of the etching mask occurs in the wiring substrate that has been miniaturized and increased in density because the wiring interval is extremely narrow. As a result, a defect called a short circuit due to defective etching occurs.
In order to avoid such a problem, a wiring board that has been reduced in size and increased in density by an additive method or a semi-additive method has been created. Specifically, for example, a resist pattern is formed by photolithography on a seed layer formed by an electroless copper plating method on an insulating substrate, and a circuit pattern (by an electrolytic copper plating method is used by using the formed resist pattern. The copper wiring pattern referred to in the present invention is formed, and then the resist pattern is removed, and the seed layer existing under the resist pattern is removed by etching (hereinafter, this etching is referred to as flash etching). (See, for example, Patent Document 1, paragraph [0002]).

By the way, in such a semi-additive method, since the seed layer and the circuit pattern are both formed by copper plating, not only the seed layer but also the circuit pattern is etched by flash etching. As a result, the corners of the circuit pattern are rounded by flash etching, making it difficult to manage the pad width and the like required during mounting (see, for example, Patent Document 1, paragraph [0003]).
In order to solve such a problem, it is disclosed that the temperature of an etching solution used for flash etching is lower than normal temperature and is used after cooling in the step of removing flash etching (see, for example, Patent Document 1, paragraph [0010]). .
In the method disclosed in Patent Document 1, the etching rate is lowered by lowering the temperature of the etching solution from room temperature, facilitating the control at the end of etching of the seed layer, and the corner portion of the circuit pattern is caused by overetching. It tries to prevent it from becoming round. Although what can be used as an etchant is only an acid, the disclosed etchant is specifically an aqueous solution of SPS (Sodium per sulfate) and H ₂ O ₂ —H ₂ SO _4. It is only an aqueous solution (see paragraph [0024] of Patent Document 1), and it has not been clarified at all how other acids affect the same effect or the surface state of the circuit pattern.
In addition, since the etching solution is used at a temperature lower than room temperature, an etching solution cooling facility is required, and the apparatus must be large.
JP 2004-335751 A

By the way, recently, as lead removal has been promoted, tin has been used as a plating material applied to the surface of the copper wiring. In such a case, in the conventional flash etching, the surface of the copper wiring after etching is rough, and in the subsequent tin plating process, granular crystals of tin are deposited on the surface of the copper wiring. When tin granular crystals are deposited on the surface of the copper wiring, whiskers peculiar to tin are likely to be generated from the granular crystals. It is known that tin whiskers grow with time and cause a short circuit between wirings, and a wiring board in which granular crystals of tin are deposited on the surface of the copper wiring is considered to have a problem in reliability.
Even if the etching method described in Patent Document 1 is applied and the amount of etching in flash etching can be managed as described above, the surface roughness of the copper wiring after flash etching is smoothed to form granular crystals in the tin plating process. It cannot be made to prevent precipitation.

Further, if the surface of the copper wiring before tin plating becomes smoother than the conventional one, the surface after plating becomes smoother than the conventional one, and the wire bonding property and the solder wettability are improved. In addition, if the flash etching can be performed at room temperature, a special cooling facility is not necessary, and the size and complexity of the apparatus can be prevented.
The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a wiring board having a smoother copper wiring surface after flash etching than the conventional one and a manufacturing method thereof.

A first aspect of the present invention that solves the above problem is a wiring board in which a copper wiring made of a plating layer is provided on the insulator surface, and the surface roughness (Rz) of the copper wiring surface made of the plating layer is 0. .25μm Ri der less, tin plating layer on the surface of the copper wiring is a wiring board ing provided.
If such a wiring board is used, it becomes a highly reliable board without generation of whiskers, and a board with improved wire bonding and solder wettability can be obtained.
The second aspect of the present invention is a wiring board in which copper wiring is provided on the insulator surface via a metallized layer or a seed layer and a metallized layer in addition to the first invention.
With such a wiring substrate, a substrate having circuit wiring having a strong adhesive force with the substrate is obtained.

According to a third aspect of the present invention, in addition to the first aspect or the second aspect, the metallized layer is a wiring board made of copper or a metal or an alloy having the same solubility characteristics as copper.
According to a fourth aspect of the present invention, in addition to the first aspect or the second aspect, the metallized layer is a wiring board made of a metal or an alloy having a different solubility characteristic from copper.
Although copper is heavily used as the circuit board, the metallized layer is most preferably made of a metal or alloy having the same melting characteristics as copper, but it is also possible to use a metal or alloy having different melting characteristics from copper, which is inexpensive. There is an advantage that the selection range of materials and manufacturing methods is expanded.

5th of this invention is related with the manufacturing method of a wiring board,
(1) providing a metallized layer on the insulator surface;
(2) providing a resist layer on the surface of the metallized layer;
(3) A step of exposing the resist layer using a desired mask and then developing to form a plating mask made of the resist layer;
(4) applying copper plating to form a copper wiring on the exposed metallized layer;
(5) The resist layer is peeled off, and the metallized layer existing between the copper wirings and the surface of the copper wirings are removed by flash etching using a flash etching solution containing chlorine, so that the surface roughness (Rz) is 0. Forming a copper wiring of 25 μm or less ,
(6) A method of manufacturing a wiring board including a step of forming a tin plating layer on the surface of the copper wiring as a main step.

The sixth of the present invention is
(1) A step of providing a metal seed layer on the insulator surface (2) A step of providing a metallization layer on the seed layer surface,
(3) providing a resist layer on the surface of the metallized layer;
(4) a step of exposing the resist layer using a desired mask and then developing to form a plating mask made of the resist layer;
(5) applying copper plating to form copper wiring on the exposed metallized layer;
(6) The resist layer is peeled off, and the metallized layer existing between the copper wirings and the surface of the copper wirings are removed by flash etching using a flash etching solution containing chlorine, so that the surface roughness (Rz) is 0. Forming a copper wiring of 25 μm or less ,
(7) forming a tin plating layer on the surface of the copper wiring;
Is a manufacturing method of a wiring board including the above as a main process.

According to a seventh aspect of the present invention, in addition to the fifth or sixth aspect, a method of manufacturing a wiring board using copper or a metal or an alloy having the same dissolution characteristics as the copper as the metallized layer.
This is to obtain a copper circuit having a strong bonding force.

Eighth invention, the fifth or in addition to the seventh aspect, the flash etching solution is mainly composed of sulfuric acid and hydrogen peroxide, Ru etchant der chlorine ions are added thereto.

  The ninth aspect of the present invention is a method of manufacturing a wiring board having a sulfuric acid concentration of 5 to 50 g / l, a hydrogen peroxide concentration of 10 to 60 g / l, and a chlorine concentration of 5 to 40 ppm.
  This is to smooth the surface roughness of the obtained copper circuit.

Since the wiring board of the present invention has a smooth surface roughness (Rz) of 0.25 μm or less on the surface of the copper wiring before the plating layer is provided, even if tin plating is applied to the surface of the copper wiring, the granular crystals of tin Does not occur. As a result, the wiring board of the present invention is a highly reliable wiring board because no whisker peculiar to tin is generated even though tin plating is performed.
In addition, the surface of the plating layer provided on the smooth copper wiring surface is also smoother than the conventional one due to the influence of the copper wiring surface, so the wire bonding property and solder wettability are improved. The If the tin plating layer is applied, there are advantages that the copper circuit is prevented from being corroded by moisture and soldering in the mounting process is facilitated.

When the method of the present invention is applied, when the metallized layer or the metallized layer and the seed layer are removed by flash etching, the etching of the copper wiring surface that occurs at the same time becomes uniform, and as a result, the copper wiring having the above smooth surface state is obtained. Can be obtained. As a result, the generation of granular crystals of tin on the surface of the copper wiring can be prevented in the tin plating process which is a subsequent process.
In addition, since the metallized layer and the metallized layer and the seed layer of the present invention can be etched at room temperature, no special cooling equipment is required, and an increase in the size of the apparatus can be avoided.

  As a substrate material for manufacturing a wiring board used recently, mainly (a) a substrate having a metallized layer having the same melting characteristics as copper or copper alloy, etc. directly on the insulating layer, and (b) an insulating layer (C) A substrate with a seed layer and a metallized layer that have the same dissolution characteristics as copper or copper alloy, or (c) a seed layer that uses a metal or alloy that has a different dissolution characteristic from copper for the insulating layer. There are three types: a metallized layer having the same dissolution characteristics as copper and copper alloy, etc., and having a metallized layer on the seed layer. The present invention can be applied to any of them. The main difference when these three types of substrates are used is that when the substrate material (c) is used, a step of flash etching the seed layer is added after the metallized layer is flash etched. Since the etching solution used at the time of seed layer flash etching does not usually commit copper, the surface roughness (Rz) of the copper wiring surface obtained at the time of removing the copper metallization layer does not deteriorate.

In the present invention, the surface roughness of the copper wiring before the corrosion-resistant plating is defined after the corrosion-resistant plating. For example, when annealing is performed after the corrosion-resistant plating, the corrosion-resistant plating material and copper are alloyed to form a surface roughness of the copper wiring. This is because it may be impossible to define the length.
Hereinafter, the wiring board of the present invention is manufactured using a seed layer provided with a metal, an alloy or the like other than copper on the insulator surface, and a substrate provided with a metallized layer with copper on the seed layer. This will be explained with an example.

First, FIG. 1 (a) uses a polyimide film as an insulator 4, a seed layer 3 having a Ni—Cr alloy coating formed on one surface thereof by a sputtering method, and a copper metallization layer 2 formed thereon by an electroplating method. FIG. 2 is a cross-sectional view of the metallized layer and the plating mask 1 whose opening is a wiring pattern on the surface of the metallized layer.
The insulator 4 used may be any insulating material such as polyamide resin, PET resin, polyester resin, etc., regardless of the polyimide resin, but is preferably a film-like material and has processability, flexibility, heat resistance, resistance to resistance. A polyimide film is more preferable than chemical properties.

  The seed layer 3 provided on the surface of the insulator 4 functions as a cathode in a wiring formation process by electroplating described later. The seed layer 3 may be made of a metal or alloy other than copper, or other conductive material as in this example, or may be made of copper. When the seed layer 3 is composed of a metal or alloy other than copper, nickel, chromium, tungsten, or an alloy film thereof is often used, and is provided by, for example, a sputtering method or a vapor deposition method. For this reason, the thickness is usually 0.01 μm. In addition, when the thickness of the seed layer 3 is insufficient for performing electroplating to be described later, copper may be formed on the seed layer 3 by dry deposition to form a part of the seed layer.

  As an example of the seed layer 3 and the metallized layer 2 made of copper, for example, the seed layer 3 is made of an electroless copper plating method or a sputtering method, and the copper metallized layer 2 is made of an electrolytic copper plating method. There is. Whether or not the seed layer 3 is made of copper is related to the adhesion strength between the seed layer 3 and the insulator 4 to be obtained. If the wiring width is 45 μm or less as in recent times, the adhesion strength of the finally obtained wiring is determined. In order to increase the thickness, it has become common to form the seed layer 3 with a metal or alloy other than copper.

The metallized layer 2 is generally constituted by an electroplating method. The thickness of the metallized layer 2 is usually 0.1 μm, which is thicker than the seed layer 3. In this example, the metallized layer 2 is made of copper. However, any material can be used as long as it has conductivity and can be etched. However, in order to take advantage of the present invention, it is preferable that the dissolution characteristics with respect to the etching solution are the same as those of the wiring material. Usually, copper is used as the wiring material as in this example, so that the metallized layer 2 is also made of copper or an equivalent of copper in the etching solution, such as a copper alloy containing copper as a main component. preferable.
If the metallized layer 2 is made of a metal having a different melting characteristic from copper and a metal or conductive material different from that of the seed layer 3, the copper wiring surface is first flash-etched to smooth the copper wiring surface and then metallized. Since the layer 2 is removed by flash etching and then the seed layer 3 is flash-etched, there is a disadvantage that the number of flash etching steps increases, which is not preferable.

Further, when the metallized layer 2 is made of the same copper as the seed layer 3 and a metal or alloy having a different melting characteristic, the copper wiring surface is first flash-etched to smooth the copper wiring surface, and then the metalized layer 2 and the seed are formed. The layer 3 is removed by flash etching, but it takes time to remove the metallized layer 2 and the seed layer 3, and the time required for the production becomes longer and the production cost increases. This is not preferable because it may be disadvantageous.
In addition, the board | substrate which consists of such an insulator 4, the seed layer 3, and the metallizing layer 2 is marketed as what is called a two-layer board | substrate, or a copper / poly board | substrate, and selects the thing according to the objective among these. Can be used.

In order to form the plating mask 1, the resist layer provided on the surface of the metallized layer of the substrate may be provided using a liquid resist, or may be provided by laminating a film-like resist film. As a material of the resist layer, any material can be used as long as it is used for manufacturing an ordinary wiring board, and may be a positive type or a negative type. This is because it is only necessary to select a mask to be used. The resist material and the mask are selected so that the opening of the resist layer becomes a wiring pattern to be obtained.
The exposure conditions and development conditions for the resist layer may be selected as recommended for the resist material to be used. Usually, the recommended conditions are disclosed when the resist material is purchased.
Next, FIG. 1B shows a cross-sectional structure after copper is deposited by electroplating on the opening (metallized layer surface) of the plating mask 1 of FIG. 1A and then the plating mask 1 is removed. FIG. Reference numeral 5 denotes a wiring formed by the deposited copper.

  In the present invention, the metal deposited by plating forms copper wiring as copper, but it is a metal that can be handled by a plating method such as nickel or chromium, and can be applied to the present invention as long as the electrical characteristics satisfy the requirements. is there. However, in this case, the material of the metallized layer 2 is preferably the same material.

FIG. 1C is a cross-sectional view after the metallized layer 2 is removed by flash etching of the copper wiring side of the substrate of FIG. When a commercially available two-layer substrate is used, a nickel-chromium alloy is usually used as the seed layer, and copper is used as the metallization layer. The dissolution characteristics of the seed layer and the metallization layer are different (c). Is embodied.
FIG. 1D is a cross-sectional view after the seed layer 3 is removed by flash etching. As described above, the seed layer 3 is as thin as about 0.01 μm, and the etching solution used for flash etching of the seed layer does not erode copper. Therefore, when the seed layer 3 is removed, the copper wiring obtained in (c) is removed. The exposed surface is not substantially affected.
The “copper wiring surface” which is a requirement of the present invention refers to the exposed surfaces 5a and 5b of the copper wiring 5 in a state before the plating layer is provided in the stage (d). The surface roughness (Rz) of the surfaces 5a and 5b corresponds to the present invention when it is 0.25 μm or less.

In order to set the surface roughness (Rz) of the surfaces 5a and 5b of the copper wiring 5 to 0.25 μm or less, the composition of the etching solution used for removing the metallized layer 2 by flash etching is changed to a sulfuric acid concentration of 5 to 5. It is preferable that the concentration is 50 g / l, the hydrogen peroxide concentration is 10 to 60 g / l, and the chlorine content is 5 to 40 ppm. In particular, if the chlorine concentration is out of this range, the surface roughness (Rz) of the copper wiring surface before the plating layer is provided is less likely to be 0.25 μm or less when flash etching is performed at room temperature.
Further, a desired amount of hydrogen chloride or alkali metal chloride can be added to a commercially available etching solution, for example, CPE800 manufactured by Mitsubishi Gas Chemical Co., Ltd. and used.

FIG. 1E is a cross-sectional view after the plating layer 6 is formed by performing corrosion-resistant metal plating such as tin on the surface of the exposed copper wiring 5 pattern. The metal plating layer 6 is used to ensure corrosion prevention of the copper wiring and soldering in the mounting process, and tin plating having good wettability with the solder is preferably used.
For metal plating of tin or the like, a conventional method may be followed, and a special plating solution or plating method is not required.
From the object of the present invention to prevent whiskers generated when tin plating is applied to the copper wiring surface, which is one of the objects of the present invention, the surface roughness (Rz) of the copper wiring surface before the plating layer is provided is determined. Although the thickness is 0.25 μm or less, it is important to smooth the surface of the copper wiring from the viewpoint of obtaining good wire bonding properties, solder wettability, and the like, which are other purposes. After that, if necessary, plating is performed at a predetermined place, and a solder resist is printed to obtain a wiring board.
[Example]

Using the chlorine concentration flash etching solution shown in Table 1, a wiring board was fabricated in the same steps as in FIG.
In this example, a polyimide film with a thickness of 38 μm, a Ni / Cr seed layer with a thickness of 170 mm formed thereon by a sputtering method, and a copper metallization with a thickness of 0.3 μm provided on the seed layer. A wiring board was prepared using a copper / polyimide substrate composed of layers.
First, a dry film resist (RY-3315 manufactured by Hitachi Chemical Co., Ltd.) is laminated on the surface of the copper metallization layer of the copper / polyimide substrate, exposed and developed using a mask having a predetermined wiring pattern, and the opening is wired. A dry film resist mask for plating to be a pattern was formed.
Next, copper was deposited on the surface of the copper metallized layer exposed in the plating mask opening by electrolytic copper plating to form a copper wiring, and then the plating mask was peeled off to expose the copper metallized layer.

Next, an etching solution for flash etching prepared by adding hydrochloric acid to a commercially available etching solution (product name: CPE800, manufactured by Mitsubishi Gas Chemical Co., Ltd.) in advance so that the chlorine concentration becomes the value shown in Table 1, The copper wiring side surface was sprayed at a temperature of 30 ° C. for 30 seconds to flash-etch the copper metallized layer exposed between the wirings and the copper wiring surface.
Next, the seed layer was dissolved and removed using a commercially available nickel / chromium selective etching solution (product name: Mekkuri Mover CH 1920, manufactured by MEC Co., Ltd.).
Thereafter, the roughness of the copper wiring surface was measured with an ultra-deep color 3D shape measurement microscope. Table 1 shows the relationship between the chlorine concentration of the etching solution for etching the copper metallization layer and the roughness of the copper wiring surface.

Next, tin plating was performed on the surface of the exposed copper wiring according to a conventional method to obtain a flexible wiring board having a smooth tin plating surface. The surface of the tin plating layer was observed with a scanning electron microscope and examined for the presence of granular tin crystals. Those that did not occur were marked with a circle, those that did not occur were marked with an X, and the results are shown in Table 1.
Next, as a result of conducting gold plating on the surface of tin plating and investigating wire bonding properties, those which were better than the conventional ones were marked with ○, and those which were equal to or less than the conventional ones were marked with X.

From the results shown in Table 1, the roughness of the copper wiring surface before tin plating once decreased with an increase in the amount of chlorine added, took a minimum value with the addition of 10 ppm, and thereafter the surface roughness gradually increased with an increase in the amount added. Further, when no chlorine is added, when 1 ppm is added, and when 50 ppm is added, granular crystals of tin are generated in the tin plating layer, and the wire bonding property after gold plating is not different from the conventional case. However, addition of 5 to 40 ppm does not generate tin granular crystals in the tin plating layer and improves wire bonding after gold plating.
From the above, the chlorine addition amount in the etching solution is preferably 5 to 40 ppm, and more preferably 20 to 30 ppm in consideration of the liquid management and analysis accuracy.

It is sectional process drawing which shows the manufacturing process of a wiring board, (a) is the figure which formed the mask for plating, (b) is the figure which formed the copper wiring, (c) is the figure which etched the metallization layer, (d) (E) is the figure which formed the metal plating layer in the copper wiring surface.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Mask for plating 2 Metallization layer 3 Seed layer 4 Insulator 5 Copper wiring 6 Metal plating layer

Claims (5)

(1) providing a metallized layer on the insulator surface;
(2) providing a resist layer on the surface of the metallized layer;
(3) A step of exposing the resist layer using a desired mask and then developing to form a plating mask made of the resist layer;
(4) applying copper plating to form a copper wiring on the exposed metallized layer;
(5) The resist layer is peeled off, and the metallized layer existing between the copper wirings and the surface of the copper wirings are removed by flash etching using a flash etching solution containing chlorine, so that the surface roughness (Rz) is 0. Forming a copper wiring of 25 μm or less,
(6) forming a tin plating layer on the surface of the copper wiring;
A method for manufacturing a wiring board, comprising: (1) providing a seed layer made of a metal on the insulator surface;
(2) providing a metallized layer on the seed layer surface;
(3) providing a resist layer on the surface of the metallized layer;
(4) A step of exposing the resist layer using a desired mask and developing to form a plating mask made of the resist layer;
(5) applying copper plating to form copper wiring on the exposed metallized layer;
(6) The resist layer is peeled off, and the metallized layer existing between the copper wirings and the surface of the copper wirings are removed by flash etching using a flash etching solution containing chlorine, so that the surface roughness (Rz) is 0. Forming a copper wiring of 25 μm or less,
(7) forming a tin plating layer on the surface of the copper wiring;
A method for manufacturing a wiring board, comprising:   3. The method for manufacturing a wiring board according to claim 1, wherein the metallized layer is made of copper or a metal or an alloy having the same dissolution characteristics as copper.   4. The method for manufacturing a wiring board according to claim 1, wherein the flash etching solution is an etching solution containing sulfuric acid and hydrogen peroxide as main components and chlorine ions added thereto. .   5. The composition of the flash etching solution according to claim 1, wherein the composition of the flash etching solution is a sulfuric acid concentration of 5 to 50 g / l, a hydrogen peroxide concentration of 10 to 60 g / l, and a chlorine concentration of 5 to 40 ppm. Wiring board manufacturing method.

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