JPH04239796A - Fabrication of printed wiring board - Google Patents

Abstract

PURPOSE:To provide a fabrication method capable of ensuring a high reliability printed wiring board suitable for packaging of electronic parts with high yield. CONSTITUTION:A feature is such that prior to forming a solder layer on a wiring board surface having a conductor circuit area including a surface packaging pad electroless plating is previously applied on a solder layer formation area surface. Hereby, the area surface on which the solder layer is selectively formed is pretreated by the electroless plating. Accordingly, a plating layer having fine uneven surface as a base is formed with separation of uniform fine particles so that deposition of a uniform thickness solder layer is easily and securely achieved and a high reliability printed wiring board is fabricated with high yield.

Description

[Detailed description of the invention]

0001

[Purpose of the invention]

0002

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a printed wiring board, and more particularly to a method of manufacturing a printed wiring board provided with surface mounting pads.

0003

2. Description of the Related Art In order to make electronic equipment lighter and more compact, attempts have been made to make circuit mechanisms smaller. In other words, mounted circuit devices (mounted circuit units), in which required electronic components are mounted on a printed wiring board surface equipped with surface mounting pads, are being widely put into practical use in various electronic devices. Therefore, the development of high-density printed wiring boards is also progressing.

The printed wiring board for surface mounting is (a) a solder-plated printed wiring board in which the surface mounting pad has a two-layer structure of Cu (base layer) and plated solder (upper layer); (b) In the conductor circuit, the area covered with solder resist is formed with a single layer of Cu1, and the area not covered with solder resist 3 is formed with a two-layer structure of Cu (base layer) and hot air leveled solder (upper layer). Solder leveler printed wiring boards, etc., are known.

[0005] The surface-mount printed wiring board having the above structure is generally manufactured in the following manner. For example, after selectively etching Cu foil to form a conductor circuit including required mounting pads, if necessary, the etching resist is peeled off and removed, and then a solder resist layer is deposited by printing. That is, parts other than the area where the required solder layer is to be formed are selectively masked. after that,
The oxide film on the conductor circuit surface, including the exposed mounting pads, is removed by soft etching or sulfuric acid treatment (pretreatment), the surface is cleaned or activated, and then immersed in a molten solder bath. A desired printed wiring board is obtained by selectively depositing a solder layer on the exposed surface.

[0006]

[Problems to be Solved by the Invention] However, the method for manufacturing the surface-mount printed wiring board has the following practical problems. That is, when a method is adopted in which the oxide film on the conductor circuit surface including the exposed mounting pad is removed by soft etching treatment or sulfuric acid treatment (pretreatment) prior to the adhesion formation (coating) of the solder layer. ,
The thickness of the solder layer to be coated tends to be non-uniform. Therefore, when conductor circuits including the exposed mounting pads have a narrower pitch due to higher wiring density, etc., bridges often occur between adjacent conductor circuits. In other words, the reality is that it is difficult to manufacture highly reliable printed wiring boards for surface mounting with a high yield.

The present invention has been made in response to the above-mentioned circumstances, and an object of the present invention is to provide a manufacturing method capable of obtaining a highly reliable printed wiring board suitable for mounting required electronic components at a high yield.

[0008]

[Structure of the invention]

[0009]

[Means for Solving the Problems] A method for manufacturing a printed wiring board according to the present invention is to selectively cover a wiring board surface having a conductor circuit area including surface mounting pads with a solder resist except for the area where a solder layer is to be formed. a step of performing electroless plating on the exposed surface of the solder layer formation region to form a plating layer; and a step of selectively depositing and forming a solder layer on the surface of the formed plating layer. It is characterized by comprising the following.

0010

[Operation] In the method for manufacturing a printed wiring board according to the present invention, the area surface on which the solder layer is to be selectively formed is pretreated by electroless plating. Through this pretreatment, a finely uneven underlying plating layer is formed through the precipitation of uniform particles, making it possible to easily and reliably form a solder layer with a uniform thickness, making it reliable. Printed wiring boards with high properties can be manufactured with high yield.

[0011]

Embodiments An embodiment of the present invention will be described below with reference to FIGS. 1 to 8.

FIGS. 1 to 8 are cross-sectional views schematically showing embodiments of the method for manufacturing a printed wiring board according to the present invention, which is carried out as follows. First, as shown cross-sectionally in Figure 1, C
A substrate 2 covered with U foil is prepared, and a hole 3 for forming a surface mounting pad area is bored in this substrate 2. Next, the board 2 with the holes drilled is plated using an electroless Cu plating solution, and a chemical Cu plating layer 4 having a thickness of, for example, about 0.3 μm is coated on the inner wall surface of the hole 3 and the surface of the Cu foil 1. After the deposition (FIG. 2), for example, an electrolytic Cu plating process is performed to form an electrolytic Cu plating layer 5 having a thickness of, for example, about 25 μm (FIG. 3).

After the plating layers 4 and 5 have been deposited, a dry film 6 is laminated on both main surfaces, and exposure and development are sequentially performed to form a conductive circuit including the required surface mounting pads. Image formation (masking for etching) is performed (FIG. 4). In this state, a necessary etching process is performed to form a conductive circuit 7 including a surface mounting pad 7a, and then the dry film 6 is peeled off and removed (FIG. 5).

Next, the surface mounting pad 7 of the substrate 2
A solder resist layer 8 is formed on the surface on which the conductor circuit 7 including the conductive circuit 7 (a) is formed, for example by a printing method, except for the solder layer forming area (FIG. 6). Thereafter, the oxide film on the surface of the conductor circuit 7 including the exposed mounting pad 7a is removed, for example, by sulfuric acid treatment, and then, for example, using an electroless Sn plating bath,
A Sn plating layer 9 is selectively deposited on the surface of the conductor circuit 7 including the exposed mounting pad 7a (FIG. 7). Thereafter, a desired solder layer 10 is selectively formed (solder coated) on the surface of the Sn plating layer 9 by immersion in a solder melting bath (FIG. 8). On the surface of the plating layer 9 formed by the electroless plating process, relatively fine irregularities exist almost uniformly, so that the solder adheres well and is easy to adhere in the solder coating process, so that the plated layer 9 is almost uniformly formed. In addition, a solder layer 10 having a large thickness was formed.

Note that in the above, the surface mounting pad 7
Although the conductor circuit 7 including a is formed by the so-called tinting method, it may be formed only with Cu foil, and if it is formed only with Cu foil, the Sn plating layer 9 and the solder layer 10
Prior to the selective adhesion formation (solder coating), it is preferable to form a chemical Cu plating layer 4 as a pretreatment. Furthermore, in the above, the oxide film was removed by sulfuric acid treatment prior to the formation of the Sn plating layer 9.
Treatment may be performed using a sulfuric acid-hydrogen peroxide system or sodium persulfate. Further, instead of the electroless Sn plating, for example, electroless solder plating or electroless Cu plating may be performed. Thus, the present invention is not limited to the above embodiments, but can be implemented in various ways within the scope of the invention.

[0016]

As described above, in the method of manufacturing a printed wiring board according to the present invention, a solder layer is deposited on a plating layer on which relatively fine irregularities are uniformly formed. In other words, since the solder layer has a sufficient thickness and is uniformly deposited without any variation in thickness, the possibility of bridging between adjacent conductor circuits at a narrow pitch can be easily avoided. In other words, it is possible to easily produce a highly reliable printed wiring board for high-density mounting with the required solder coating without reducing the wiring density and with a high yield.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing a state in which a hole for forming a pad region is formed in a Cu foil-covered substrate in the printed wiring board manufacturing method of the present invention.

FIG. 2 is a cross-sectional view showing a state in which a chemical Cu plating layer is deposited on the surface of a Cu foil-clad substrate in the printed wiring board manufacturing method of the present invention.

FIG. 3 is a cross-sectional view showing a state in which an electroplating layer is deposited on a chemical Cu plating layer on the surface of a Cu foil-clad substrate in the printed wiring board manufacturing method of the present invention.

FIG. 4 is a cross-sectional view showing a state in which an etching resist layer is formed on an electroplated layer surface in the printed wiring board manufacturing method of the present invention.

FIG. 5 is a cross-sectional view showing a conductive circuit including mounting pads formed by selective etching in the printed wiring board manufacturing method of the present invention.

FIG. 6 is a cross-sectional view showing a state in which a solder resist layer is adhered to a surface on which a conductor circuit including mounting pads is formed in the printed wiring board manufacturing method of the present invention.

FIG. 7 is a cross-sectional view showing a state in which a chemical Sn plating layer is deposited on the exposed surface after a solder resist layer is deposited in the printed wiring board manufacturing method of the present invention.

FIG. 8 is a cross-sectional view showing a state in which the surface on which the chemical Sn plating layer is formed is solder-coated in the printed wiring board manufacturing method of the present invention.

[Explanation of symbols]

1... Cu foil 2... Substrate 3... Hole (through hole) 4... Electroless Cu plating layer 5... Electroplating layer 6... Dry film
7...Conductor circuit 7a...Surface mounting pad
8...Solder resist layer 9...Electroless Sn plating layer 10...Solder coat (solder layer)

Claims (1)

[Claims] 1. A step of selectively covering a wiring board surface having a conductive circuit region including a surface mounting pad with a solder resist except for a solder layer formation region; A method for manufacturing a printed wiring board, comprising the steps of forming a plating layer by electroless plating, and selectively depositing a solder layer on the surface of the formed plating layer. .