JP2002038295A - Electroplating method for circuit board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electroplating method for a circuit board, which provides a plated film of high quality even on a minute conductor surface by surely removing air bubbles in a chemical solution, which are trapped on the conductor surface, without requiring a large remodeling of a present plating equipment, in a continuous, chemical treatment process for electrolytically depositing metal on the conductor of the circuit board. SOLUTION: The electroplating method for the circuit board is characterized by applying an ultrasonic vibration to a surface to be treated of the circuit board with a facing manner, in at least one process including a degreasing process, out of a degreasing process of pretreatment in an electroplating process, a soft etching process, and an activation process, in a continuous solution- treatment process for electrolytically depositing metal on a conductor in a manufacturing process for the circuit board.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electroplating method in a circuit board manufacturing process.

[0002]

2. Description of the Related Art Conventionally, in electroplating, electrical connection between wiring layers by a through hole in a circuit board as represented by copper plating, formation of wiring by plating represented by an additive method or semi-additive method, and the like. , Such as electrical connection between wiring layers by non-through holes in the build-up multilayer method,
It is used as a means for forming conductors on circuit boards.Solder plating, tin plating, silver plating, nickel plating, gold plating, etc. are used to add connection functions to mounted components. It is widely used in the manufacture of circuit boards, for example, for forming bumps.

[0003] With the recent demand for higher functionality and lighter, thinner and smaller electronic devices, high-density integration and high-density mounting of electronic components have been rapidly progressing. The circuit board to be mounted is required to have high density wiring and high multilayer wiring, and accordingly, it is necessary to form plating on through holes and non-through holes with small diameter and high aspect ratio, and to form fine wiring by plating There is a demand for high-precision, high-quality plating techniques, such as the need to perform plating and the plating of minute terminals.

[0004] In performing the fine plating as described above, a particular problem is that in the various chemical treatments in the plating process, air bubbles remain on the surface of the circuit board to be plated, and the air bubbles form the chemical treatment or the plating itself. And cause quality defects such as abnormal deposition of plating and non-adhesion of plating. This problem has become more apparent as the parts of the circuit board to be plated become finer and have a higher aspect ratio. As a solution, there are mechanical methods that vibrate the circuit board or chemical solution to remove air bubbles, and circuit boards. Various chemical methods have been attempted to improve the wettability of chemicals and chemicals to make air bubbles difficult to adhere.

[0005]

A method of removing air bubbles by generating mechanical vibration has been widely used from the past. As a typical method, a method utilizing vibration generated by a vibrator is known. Have been. The vibrator is vibrated at a frequency of 50 to 60 Hz, and the vibration energy is directly applied to a jig for supporting a circuit board to be plated, or to a jig receiving base itself of a swinging device. This is a method for removing bubbles from the surface of the substrate. However, this method has a disadvantage that the vibration energy is attenuated due to the material and structure of the jig itself, the mounting method of the object to be plated, the liquid resistance of the chemical solution, and the like, and the effect of removing bubbles is weakened. Was.

As a method for solving the above-mentioned disadvantage, recently,
A super vibration stirring method proposed by Nippon Techno Co., Ltd. can be mentioned. In this method, a plurality of metal wings are arranged in a chemical solution, and the wings are arranged outside the liquid by a vibrator at 50 to 60 Hz.
By vibrating the liquid crystal, vibrations are generated in the chemical solution and also a liquid flow is generated. By the vibration and the energy of the liquid flow, bubbles on the surface of the circuit board are removed. However, in this method, vibration is transmitted not only to the chemical solution but also to the plating apparatus itself. Therefore, it is necessary to take measures against vibrations in the plating apparatus, and the installation space for the vibrator is limited to just above the plating tank.
Considering the application of this method to existing plating equipment, large-scale equipment remodeling is necessary, and in most cases, it cannot be adopted due to the limitations of the equipment space and substrate transport mechanism.
The fact is that it is only used for new plating equipment. Furthermore, since the vibration frequency is limited to the low frequency band by using the vibrator, for a part having a small aspect ratio of 1 or more,
There is a disadvantage that the bubble removing effect is extremely reduced.

On the other hand, in addition to the above-described method of mechanically removing air bubbles, a method of removing air bubbles and preventing the adhesion of air bubbles by improving the wettability of the surface of a circuit board has been proposed as a chemical method. The most typical method is to slightly etch the surface of a circuit board to be plated with plasma, clean the surface, and modify the surface to be hydrophilic to improve wettability. There is. A plasma is generated in a dilute argon gas or oxygen gas, and the circuit board is exposed to this atmosphere to clean the surface to be plated and modify the surface to be hydrophilic. Since the gas enters the minute part, not only the surface but also the wall surface and the bottom surface such as the fine holes can be uniformly treated. However, in the method using the plasma, there is a drawback in that the production cost is increased by adding one step, a drawback that a sufficient reforming effect is not obtained depending on the type of the material of the circuit board, and generation of heat. For this reason, a circuit board having low heat resistance has a disadvantage that dimensional changes and deformations are likely to occur.

As a method for imparting wettability to a chemical solution, a method of adding a surfactant to the chemical solution is generally adopted, and various chemical solutions having high wettability are commercially available from various chemical solution manufacturers. However, since the wettability is treated as a secondary function that does not impair the processing effect of the chemical solution such as degreasing and etching, the effect of removing air bubbles and preventing air bubble adhesion is sufficient. Absent.

[0009] Further, the above-mentioned method of mechanical bubble removal and the method of chemical bubble removal are also used in combination. However, this method also corresponds to a conductor surface of a circuit board which is increasingly miniaturized. Things are getting harder.

Accordingly, the present invention provides a continuous chemical treatment process for depositing a metal on a conductor of a circuit board by electroplating without the need for a major modification of the existing plating equipment, and without the need for extensive modification of the existing plating equipment. An object of the present invention is to provide a method for electroplating a circuit board which can reliably remove attached air bubbles and obtain a high quality plating film even on a fine conductor surface.

[0011]

SUMMARY OF THE INVENTION The present invention is a pretreatment step of electroplating in a continuous chemical solution treatment step for depositing a metal on a conductor of a circuit board by electroplating during a circuit board manufacturing process. In at least one of the degreasing step, the soft etching step and the activation step, including at least the degreasing step, ultrasonic vibration is applied so as to directly face the entire surface of the surface to be plated of the circuit board, This is a method for electroplating a circuit board.

In the present invention, the conductor for electroplating the circuit board is preferably made of copper, a copper alloy or an iron-nickel alloy.

The metal deposited by electroplating used in the present invention is preferably copper, nickel, silver, gold, tin, a tin alloy, or a lead alloy.

In the electroplating apparatus used in the present invention, an ultrasonic oscillator having desired performance is installed in a chemical solution tank for removing air bubbles at a position facing and in parallel with a surface to be plated of a circuit board. If there is space available, even with the carrier transport method,
Either a horizontal transfer system or a reel-to-reel transfer system electroplating apparatus may be used. Generally, an electroplating apparatus having a continuous chemical treatment step has a degreasing step, a soft etching step, and an activation step as a chemical treatment step which is a pretreatment for electroplating, and the degreasing step is the first step among these. Therefore, it is most effective and preferable to install an ultrasonic oscillator at least in this degreasing tank.

The ultrasonic oscillator has an oscillation frequency of 35 to 10
What is necessary is just to be in the range of 0 kHz and the output in the range of 200 to 1000 W. When the oscillation frequency is lower than 35 kHz, the surface uniformity of the energy distribution of the ultrasonic waves impinging on the circuit board surface is remarkably reduced, so that air bubbles are easily generated, and when the oscillation frequency is higher than 100 kHz,
Since the entire energy density is significantly reduced, air bubbles are likely to remain. Also, even within the above range, depending on the type of tank structure or tank material or chemical solution used, cavitation may occur, in this case, increase the oscillation frequency or lower the output, It is desirable that cavitation does not occur. If the chemical treatment is performed in a state where cavitation has occurred, depending on the structure and material of the circuit board, a problem such as peeling of the conductor or destruction of the resin may occur.

In the present invention, the ultrasonic vibration may be applied continuously or intermittently.
It is preferable that the power be adjusted to an appropriate condition in a range of 00 kHz and an output of 200 to 1000 W.

In the present invention, the non-plated surface of the circuit board is installed in the chemical treatment tank so that the surfaces of the non-plated surfaces face each other, and the chemical treatment is performed while applying vibration under the above-described conditions. By performing pretreatment of electroplating such as degreasing, soft etching, and acid activation treatment, good normal electroplating can be performed.

[0018]

EXAMPLES The present invention will be described below with reference to examples.
The present invention is not limited thereby.

(Embodiment 1) CREST was installed in a degreasing treatment tank, a soft etching treatment tank, and an acid activation treatment tank of a carrier transport type electro-copper plating apparatus capable of continuously performing the process shown in FIG.
As shown in FIG. 2, each of the ultrasonic oscillators manufactured by
The object to be plated (the circuit board 25) and the vibration surface of the ultrasonic vibration device 21 face each other, and were placed so as to be immersed in the chemical solution 23 in the processing tank 22. The frequency of the ultrasonic oscillator is 39 kHz
, And the one having a maximum output of 500 w was used. The chemical solution was PC-590M manufactured by Meltex Co., Ltd. as a degreasing solution, AD-485 manufactured by Meltex Co., Ltd. as a soft etching solution, a 5% sulfuric acid solution as an active solution, and a brightener Sparthrow 2000 manufactured by LPW as a copper plating solution. Copper sulfate plating solutions were used.

The object to be plated has a thickness of 50 as shown in FIG.
A thin film conductor layer 32 having a thickness of 0.2 μm is formed on one side of a polyimide substrate 31 having a thickness of 0.2 μm by sputtering, and a plating resist having a thickness of 25 μm is patterned on this thin film conductor layer with a minimum opening width of 25 μm. The plating resist opening was plated with 20 μm thick copper using the thin film conductor layer 32 as a cathode electrode. In order to obtain the optimum conditions of the ultrasonic oscillator, plating was performed by changing the output and the time, and the results of evaluating the yield were as shown in Table 1.

[0021]

[Table 1]

From these results, it is possible to obtain a high plating yield if the output is set in the range of 300 to 400 W and the time is set to 15 seconds or more.

(Example 2) An ultrasonic oscillator made by CREST was placed in a degreasing tank of a carrier-conveying type electric solder plating apparatus capable of continuously performing the process shown in FIG. 4 as shown in FIG. The circuit board 25) was placed so as to be immersed in the chemical solution 23 in the processing tank 22 with the vibrating surface of the ultrasonic vibrator 21 facing the vibrating surface. The ultrasonic oscillator has a frequency of 68 kHz
And the maximum output was 1000 w. The chemical solution is PC-455 manufactured by Meltex Co., Ltd. as a degreasing solution, Metex G-5S manufactured by McDermid Co., Ltd. as a soft etching solution, FF-451 manufactured by McDermid Co., Ltd. as an active solution, and FF-100HS manufactured by MacDermid Co., Ltd. as a solder plating solution. Kerbert No. 70 manufactured by McDermid Co. was used as the neutralizing solution.

The object to be plated is coated on the circuit board 51 on which the conductor wiring 54 is formed as shown in FIG.
A 5 μm insulating resin layer 52 is formed, and a hole diameter of 2
A non-through hole 53 of 5 μm was formed, and the non-through hole was filled with solder plating using the conductor wiring as a cathode electrode. In order to obtain the optimum conditions of the ultrasonic oscillator, plating was performed while changing the output and time, and the yield was evaluated. The results are as shown in Table 2.

[0025]

[Table 2]

From these results, it is possible to obtain a high yield if the output is set in the range of 800 W or more and the processing time is set in 30 seconds or more. Furthermore, if air bubbles can be removed in the first chemical solution treatment, a high plating yield can be obtained without an ultrasonic oscillator in the subsequent chemical solution treatment process.

[0027]

According to the method for electroplating a circuit board of the present invention, it is necessary to greatly modify an existing plating apparatus in a continuous chemical solution treatment process for depositing a metal on a conductor of a circuit board by electroplating. Instead, bubbles adhered to the conductor surface in the chemical solution can be reliably removed, and high quality and high yield plating can be obtained even on a fine conductor surface.

[Brief description of the drawings]

FIG. 1 is a process chart of Example 1.

FIG. 2 is a schematic diagram of installation of an ultrasonic vibration device in Examples 1 and 2.

FIG. 3 is a sectional view of an object to be plated in Example 1.

FIG. 4 is a process chart of Example 2.

FIG. 5 is a sectional view of an object to be plated in Example 2.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 21 Ultrasonic vibration device 22 Processing tank 23 Chemical solution 24 Circuit board conveyance jig 25, 51 Circuit board 31 Polyimide base material 32 Thin film conductor layer 33 Plating resist layer 52 Insulating resin layer 53 Non-through hole 54 Conductor wiring

Continued on the front page (72) Inventor Jin Aoki 2-5-8 Higashishinagawa, Shinagawa-ku, Tokyo Sumitomo Bakelite Co., Ltd. F-term (reference) 4K024 AA03 AA07 AA09 AA10 AA11 AA21 AA22 AB01 BA02 BA09 BB11 BC01 DA10 5E343 AA02 AA11 BB16 BB23 BB24 BB25 BB34 BB43 BB44 BB53 BB54 BB71 BB72 DD03 DD44 EE01 EE52 FF16 FF23 GG02

Claims (4)

[Claims] In a continuous chemical solution treatment process for depositing a metal on a conductor of a circuit board by electroplating during a manufacturing process of a circuit board, a degreasing process, a soft etching process, and an activity, which are pretreatment processes for electroplating, are performed. A method for electroplating a circuit board, characterized in that ultrasonic vibration is applied so as to directly oppose the entire surface of the surface to be plated of the circuit board in at least one step including at least a degreasing step among the conversion steps. 2. The electroplating of a circuit board according to claim 1, wherein the ultrasonic vibration is applied at a frequency in the range of 35 to 100 kHz and adjusted with an output in the range of 200 to 1000 W. Method. 3. The method for electroplating a circuit board according to claim 1, wherein the conductor of the circuit board is made of copper, a copper alloy, or an iron nickel alloy. 4. The method according to claim 1, wherein the metal deposited by electroplating is copper, nickel, silver, gold, tin, a tin alloy, or a lead alloy. Electroplating method for circuit boards.