JPH04250690A - Manufacture of printed circuit board - Google Patents

Abstract

PURPOSE:To prevent generation of a precipitation malfunction in a photoresist to be formed by electrodepositing. CONSTITUTION:A circuit board provided on the surface with a metal layer is dipped in electrodeposition photoresist liquid, energized, and coated on the surface of the layer with a photoresist by electrodepositing. In this case, the board is vibrated in the liquid from dipping of the board in the liquid at least to an initial period of the energization. Bubbles adhered to the board when dipping of the board in the liquid, bubbles adhered to the board upon generation in the liquid are removed by vibration to be applied to the board in the liquid, thereby preventing precipitation malfunction of the photoresist.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a printed wiring board, which includes a step of electrodepositing a photoresist on a metal layer.

0002

[Prior Art] Conventionally, in manufacturing printed wiring boards, photoresist is applied to the surface of a metal layer such as copper foil that is placed on the surface of a wiring board made of a laminate, etc., and then a predetermined pattern is applied. This is done by exposing a photoresist to light, developing it, and then etching it to form a circuit. And the above photoresist application is
This is done using the spray method, roll coater method, dip method, etc., but it is difficult to uniformly apply a thin film of photoresist, and the pattern formed by exposing and developing the photoresist is sharp. However, there is a problem in that it is difficult to create microcircuits with fine patterns, which are in high demand in the market.Also, when manufacturing printed wiring boards with through holes, it is necessary to apply photoresist to the plating surface on the inner periphery of the through holes. However, there is a problem in that these coating methods are difficult.

[0003] For this reason, a technique in which electrodeposition coating is applied to photoresist coating has recently been developed and put into practical use. That is, as disclosed in JP-A-63-17592 and JP-A-63-23389, a wiring board covered with a metal layer is immersed in an electrodeposition type photoresist solution, and then the wiring board is electrodeposited. When a direct current is passed between the photoresist solution and the metal layer, the resin component of the electrodeposited photoresist solution is deposited on the surface of the metal layer by an electrode reaction based on the same principle as electroplating, and the photoresist is deposited on the surface of the metal layer. Can be electroplated. Since the photoresist deposited on the surface of the metal layer is electrically insulating, if there is a difference in the amount of photoresist deposited locally on the surface of the metal layer, the amount of photoresist deposited is smaller and will be deposited in areas with low insulation. As a result, the photoresist can be coated with a very uniform film thickness, and the photoresist can also be coated evenly on recessed areas such as through holes.

0004

However, when applying photoresist by electrodeposition, the occurrence of abnormal deposition of the photoresist due to the presence of air bubbles becomes a problem. In other words, when the wiring board is immersed in the electrodeposition photoresist solution, air bubbles may become entangled, air bubbles may remain in the through holes provided in the wiring board, or gases generated during electrodeposition may form bubbles on the wiring board. Bubbles often exist on the surface or inside the through-holes of wiring boards, such as by adhering to the surface or inside the through-holes, and photoresist can be deposited by electrodeposition in areas where these bubbles exist. First, as a result, pinholes occur in the photoresist coating, which ultimately results in defective defects in the circuit formed by etching.

The present invention has been made in view of the above points, and it is an object of the present invention to provide a method for manufacturing a printed wiring board that can prevent the occurrence of abnormal precipitation of photoresist due to air bubbles. .

[0006]

[Means for Solving the Problems] The present invention involves electrodepositing a photoresist on the surface of the metal layer by immersing a wiring board with a metal layer on the surface in an electrodeposition photoresist solution and applying electricity. When manufacturing printed wiring boards by exposing and developing a photoresist and then etching it to form a circuit, the wiring board is immersed in the electrodeposited photoresist solution until at least the initial stage of energization. It is characterized by applying vibration to the wiring board.

[0007] Alternatively, a shock may be applied to the wiring board in the electrodeposited photoresist solution. The present invention will be explained in detail below. The wiring board is not limited in any way as long as it is used in the manufacture of printed wiring boards, such as phenol resin laminates and epoxy resin laminates with metal foil such as copper foil pasted on the surface and a metal layer laminated thereon. , a metal-clad laminate such as an imide resin laminate can be used. After this wiring board is pretreated as necessary, an electrodeposition type photoresist is electrodeposited on the surface of the metal layer.

[0008] For electrodeposited photoresists, the previously published Japanese Patent Application Laid-open No. 6
As reported in Japanese Patent No. 3-23389, there are cationic and anionic types, but any commonly available types can be used. Then, the wiring board is immersed in the electrodeposition photoresist solution, and an electrode is inserted into the electrodeposition photoresist solution. In the case of a cationic electrodeposition photoresist solution, connect the electrodes to the anodes respectively, and
In the case of an anionic electrodeposition photoresist solution, the photoresist can be deposited on the surface of the metal layer by connecting each to the cathode and passing a direct current, thereby performing electrodeposition coating of the photoresist.

[0009] When performing electrodeposition coating as described above, the wiring board is immersed in an electrodeposition photoresist solution and held in the solution for a predetermined period of time, and then the current value is gradually increased from zero over a predetermined period of time. It is preferable to start the energization in this manner (referred to as a soft start), and after reaching a predetermined current value, to control the energization so as to maintain it at a constant voltage. In the present invention, vibration is applied to the wiring board in the electrodeposited photoresist solution while the wiring board is immersed in the electrodeposition photoresist solution and during at least the initial period of energization. When a wiring board is immersed in an electrodeposited photoresist solution, air may be drawn in and bubbles may adhere to the surface of the wiring board, or air may remain in the through holes provided on the wiring board and air bubbles may adhere to the through holes. However, in the present invention, while the wiring board is immersed and held in the electrodeposited photoresist solution as described above, these bubbles are removed in order to give vibration to the wiring board in the electrodeposition photoresist solution. It can be peeled off and removed from the wiring board. Also, when electricity is applied and electrodeposition coating is performed, H2 and O2 are generated due to electrolysis of the electrodeposited photoresist solution.
etc. are generated as a gas in the electrodeposited photoresist solution, and this gas may adhere as bubbles to the surface of the wiring board or enter the through holes as bubbles. This is especially noticeable at the beginning of energization. To this end, as described above, the present invention applies vibration to the wiring board in the electrodeposited photoresist solution at least during the initial period of energization, and these bubbles can be peeled off and removed from the wiring board by the vibration. It is something. Of course, the vibration may be applied throughout the energization until the end, and the longer the vibration is applied, the better the results can be obtained. Sufficient results can be obtained by applying vibration. Furthermore, in place of this vibration, or in combination with the vibration, a shock may be applied to the wiring board in the electrodeposited photoresist solution. This impact is preferably applied at predetermined time intervals from the time the wiring board is immersed in the electrodeposited photoresist solution until the end of the electrodeposition coating.

[0010] When electrocoating is performed by dipping the wiring board suspended on a hanger or the like in an electrodeposition photoresist solution, the electrodeposition photoresist is applied by applying vibration to the hanger using a vibrator or the like. It is capable of applying vibrations to the wiring board in the resist liquid, and it is also possible to apply impact to the wiring board in the electrodeposition photoresist liquid by applying impact to the hanger with a hammering device or the like. Vibration is 30-10
It is preferable to apply the impact at a frequency of about 0,000 Hz, and it is preferable to apply the impact with a force of about 4 to 100 kg. By applying vibration and impact to the wiring board in this way, air bubbles can be removed from the surface of the wiring board and inside the through holes as described above.
It is possible to prevent abnormal precipitation of photoresist and to prevent pinholes from occurring in the photoresist coating.

After electrodepositing a photoresist on the surface of the metal layer of the wiring board as described above, a photomask is placed on the surface of the photoresist and brought into close contact with the surface, and exposure is performed by irradiating light such as ultraviolet rays. The unnecessary parts of the photoresist are removed by further treatment with a developer, and the parts of the metal layer that are not covered with the photoresist are etched by immersion in or spraying an etching solution. can be dissolved and removed to form a circuit.

0012

EXAMPLES The invention will now be illustrated by examples. Example 1 An FR-4 type epoxy resin laminate laminated with 18μ thick copper foil was used as a wiring board, and the surface of the copper foil was buffed and treated with a 3% meta-silicic acid solution adjusted to 40-50°C for 60 seconds. Pretreatment was carried out by performing a degreasing treatment, a soft etching treatment using a soft etching solution manufactured by Shipley for 5 minutes, and a neutralization treatment using a 10% sulfuric acid solution for 1 minute.

Next, as an electrodeposition photoresist solution, 25±1
"Photo ED P-1" manufactured by Nippon Paint Co., Ltd. adjusted to ℃
A wiring board hung vertically with a hanger was immersed in this electrodeposited photoresist solution and energized, thereby electrodepositing a photoresist on the surface of the copper foil. When performing electrodeposition coating, the wiring board is immersed in the electrodeposition photoresist solution and held for 30 seconds (this 30 seconds is called the holding period), and then the electrodeposition photoresist solution is applied using the copper foil of the wiring board as a cathode. Start applying direct current using the electrode as an anode, and it takes 30 seconds to gradually increase the distance from zero to 50m.
The current density is increased to A/dm2 (this 30 seconds is called a soft start period), and then the current is controlled so that the current is maintained for 105 seconds while keeping the voltage constant (this 105 seconds is called a voltage hold period). Do it, 6~
A photoresist was electrodeposited on the surface of the copper foil to a coating thickness of 7 μm.

[0014] When performing electrodeposition coating in this manner, vibrations at a frequency of 60 Hz were applied to the wiring board by applying vibration to the hanger with a vibrator during a 30-second holding period and a 30-second soft start period. . Example 2 Vibrations were applied to the wiring board during a 30-second holding period and a 30-second soft start period, and
The wiring board was shocked by hitting the hanger with a pin cylinder every 5 seconds throughout the period that the wiring board was immersed in the electrodeposited photoresist solution, and the rest was as in Example 1.
Photoresist was electrodeposited in the same manner as above.

Example 3 30 seconds of holding period, 30 seconds of soft start period and first 3 seconds of voltage holding period
Electrodeposition of photoresist was performed in the same manner as in Example 1 except that vibration was applied to the wiring board for 0 seconds. Example 4 Vibration was applied to the wiring board throughout the 30 seconds of the holding period, 30 seconds of the soft start period, and the first 30 seconds of the voltage holding period, and vibration was applied every 5 seconds throughout the period of immersing the wiring board in the electrodeposited photoresist solution. Electrodeposition of photoresist was carried out in the same manner as in Example 1 except that the wiring board was subjected to impact.

Example 5 30 seconds of the hold period, 30 seconds of the soft start period and the first 6 seconds of the voltage hold period
Electrodeposition of photoresist was performed in the same manner as in Example 1 except that vibration was applied to the wiring board for 0 seconds. Example 6 Vibrations were applied to the wiring board throughout the 30 seconds of the hold period, 30 seconds of the soft start period, and the first 60 seconds of the voltage hold period, and vibrations were applied every 5 seconds throughout the period of immersing the wiring board in the electrodeposition photoresist solution. Electrodeposition of photoresist was carried out in the same manner as in Example 1 except that the wiring board was subjected to impact.

Comparative Example 1 Electrodeposition of photoresist was carried out in the same manner as in Example 1 except that no vibration or impact was applied to the wiring board. Comparative Example 2 Electrodeposition of photoresist was carried out in the same manner as in Example 1 except that vibration was applied to the wiring board for only 30 seconds during the holding period. Comparative Example 3 Vibration was applied to the wiring board only for 30 seconds during the holding period, and impact was applied to the wiring board every 5 seconds throughout the period in which the wiring board was immersed in the electrodeposited photoresist solution, but the rest was the same as in Example 1. Then, the photoresist was electrodeposited.

Comparative Example 4 Vibrations were applied to the wiring board only for 30 seconds during the holding period, and shocks were applied to the wiring board every 1.5 seconds throughout the period in which the wiring board was immersed in the electrodeposited photoresist solution. Electrodeposition of photoresist was performed in the same manner as in Example 1. Comparative Example 5 The photoresist was coated in the same manner as in Example 1 except that the wiring board was subjected to impact every 5 seconds throughout the period of immersion of the wiring board in the electrodeposited photoresist solution without applying vibration to the wiring board. Electrodeposition painting was performed.

The wiring boards on which the photoresists were electrodeposited in Examples 1 to 6 and Comparative Examples 1 to 5 were examined for abnormal deposition of the photoresists. The inspection was carried out by counting the number of pinholes formed in the photoresist coating formed on the inner periphery of 800 through holes with a diameter of 0.3 mm that were previously provided on the wiring board. In this case, among the 800 through holes, the upper 400 through holes are group A, and the lower 400 are
Through-holes were defined as Group B, and measurements were taken for each group. The results are shown in the table below.

[0020]

[Table 1]

As can be seen from the results in the table, applying vibration only during the holding period is insufficiently effective (Comparative Example 2).
), it is confirmed that it is necessary to apply vibrations from the holding period to at least the soft start period. It is also confirmed that although the effect can be enhanced by using impact in combination, it is not possible to obtain a sufficient effect with impact alone.

[0022]

[Effects of the Invention] As described above, the present invention applies vibration to the wiring board in the electrodeposited photoresist solution from the time the wiring board is immersed in the electrodeposition photoresist solution until at least the initial stage of energization. Bubbles that adhere when the wiring board is immersed in the electrodeposited photoresist solution, or bubbles that are generated in the electrodeposition photoresist solution and adhere to the wiring board, are caused by vibrations applied to the wiring board in the electrodeposition photoresist solution. It can be removed, and it can prevent abnormal precipitation of photoresist and pinholes from occurring in the photoresist coating.

Claims (2)

[Claims] Claim 1: A wiring board with a metal layer provided on the surface is immersed in an electrodeposition photoresist solution and electricity is applied to electrodeposit a photoresist on the surface of the metal layer, and after this photoresist is exposed and developed. When manufacturing a printed wiring board by etching to form a circuit, the wiring board is immersed in an electrodeposited photoresist solution and the wiring board is subjected to vibration in the electrodeposition photoresist solution until at least the initial stage of energization. A method for manufacturing a printed wiring board, characterized by: 2. The method for manufacturing a printed wiring board according to claim 1, wherein the wiring board is subjected to an impact in an electrodeposited photoresist solution.