JPH06296070A - Manufacture of printed wiring board - Google Patents

Abstract

(57) [Abstract] [Purpose] A print that has a narrow-pitch connection pad group, and can adhere and form the required solder layer on the narrow-pitch connection pad surface in a form that is surely separated from each other. An object is to provide a method for manufacturing a wiring board. A step of integrally forming a required circuit pattern including a group of pads with a narrow pitch on at least one main surface of a supporting substrate by a photo etching process, and removing an etching resist used for the photo etching process to form a circuit pattern. Exposing the formation surface and exposing the exposed circuit pattern formation surface to a connection pad surface including at least a narrow pitch pad surface, and coating a solder resist layer so that the circuit pattern formation surface is planarized. And a step of forming the connection pad, and another means is to achieve the above-mentioned object by embedding the connection pad so as to be flush with the surface of the supporting substrate.

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, and more particularly to a method for manufacturing a printed wiring board having surface mounting pads.

[0002]

2. Description of the Related Art For the purpose of making electronic devices lighter or more compact, circuit structures have been downsized.
That is, a mounting circuit device (mounting circuit unit) in which required electronic components are mounted on the main surface of a printed wiring board is being widely put to practical use in various electronic devices, and for this reason, for example, 0.4 Development of a high-density printed wiring board with a narrow-pitch connection pad group of less than mm is underway.

By the way, as a method of manufacturing the above-mentioned high-density printed wiring board for surface mounting, the following means known as subtractive method is known. That is,
After patterning an etching resist on the copper foil surface of the copper foil-clad laminate, the copper foil is selectively etched using the etching resist as a mask to form a conductor circuit including connection pads with a narrow pitch. Then, the etching resist is removed by peeling or melting to expose the formed conductor circuit formation surface. After that, as a surface finish, at least the connection pad surface including at least a narrow pitch pad is exposed on the exposed circuit pattern forming surface, and a solder resist layer is coated / formed. In addition, this solder resist layer coating / formation allows the connection pad surface to be exposed in response to soldering in a later process, while avoiding (preventing) solder from adhering to other conductor circuit surfaces. It is intended to serve as a solder dam by providing a protective function such as preventing oxidation of the conductor circuit and forming it between the QFP pads. Next, if necessary, on the exposed connection pad surface of the coating / forming surface of the solder resist layer, for example, by printing cream solder, or by a hot-air leveling method, a preliminary solder layer is formed by adhesion. Commercially available for practical use. In any case, when a printed wiring board is used for surface mounting, it is necessary to selectively supply and adhere solder to the connection pad surface.

Other known methods for manufacturing a high-density printed wiring board for surface mounting include an additive method, a partial solder peeling method using an electrolytic solder layer as an etching resist, and a super solder technology method. However, there is a problem in that it is relatively complicated and the cost is low, including equipment.

[0005]

The manufacturing method referred to as the subtractive method has many practical advantages as compared with other manufacturing methods. However, in the case of the manufactured surface mounting printed wiring board, However, there are the following problems in practice.
That is, when used for surface mounting, a solder layer needs to be attached / applied to the connection pad surface, and this solder layer attachment / applying requires surface finishing in the manufacturing process or mounting circuit formation (assembly). Done in stages. However, with the high-density surface mounting, 0.4mm or less (for example,
In the case of a printed wiring board having a connection pad group with a narrow pitch of 0.3 mm), it is difficult to form a solder resist between each pad with a narrow pitch, and therefore the connection pad surface should be separated from each other and secured. In addition, there is a problem that it is difficult to deposit sufficient solder, and a highly reliable high-density mounting circuit cannot be configured. That is, when the pitch of the connecting pads is less than 0.4 mm, the occurrence of so-called solder bridges is observed when the solder is applied by the hot air leveling method. The pitch of the connecting pads is 0.3.
If the thickness is less than mm, the solder bridging is similarly observed when the solder is applied by printing the cream solder, and in any case, it is difficult to achieve highly reliable mounting. In other words, although these connecting pad groups and the like have a small protruding height from the supporting substrate surface, they not only form irregularities on the supporting substrate surface, but also because the connecting pad pitch is narrow, It can be said that it is practically difficult to selectively separate and deposit the solder layer on the surface of each connecting pad only by surely separating them from each other only by the concave portion between the adjacent connecting pads.

The present invention has been made in view of the above circumstances, and has a narrow pitch connecting pad group, and a required solder layer on the narrow pitch connecting pad surface so as to be surely separated from each other. An object of the present invention is to provide a method for manufacturing a printed wiring board capable of depositing and forming

[0007]

According to a first method of manufacturing a printed wiring board of the present invention, a predetermined circuit pattern including a pad group of a narrow pitch is integrally photo-etched on at least one main surface of a supporting substrate. And a step of removing the etching resist used for the photoetching process to expose the circuit pattern forming surface, and a connecting pad surface including at least a narrow pitch pad surface on the exposed circuit pattern forming surface. And a step of coating and forming a solder resist layer so that the surface on which the circuit pattern is formed is flattened. Further, the second method for manufacturing a printed wiring board is characterized in that Forming a required circuit pattern including a group of pads with a narrow pitch integrally on at least one main surface of the substrate by photoetching; The etching resist used in the etching process to expose the circuit pattern forming surface, and the connecting pad surface including at least the narrow pitch pad surface of the exposed circuit pattern forming surface is subjected to a pressure treatment, and the connection is performed. And the step of making the upper surface of the pad for use flush with the surface of the supporting substrate.

[0008]

According to the method of manufacturing a printed wiring board according to the present invention, the printed wiring board has a structure in which the connecting pad surface including at least the narrow-pitch pad group forms the same flat surface as the supporting substrate (wiring substrate) surface. Can be manufactured. That is, in the method of the present invention, the connection pad surface including the narrow-pitch pad group that functions as the surface to be soldered is substantially filled with the support substrate by filling the peripheral region with a solder resist or by applying pressure / embedding to the support substrate. By adopting a configuration in which the surfaces are substantially the same, it is possible to form a preliminary solder layer on a narrow pitch pad of less than 0.3 mm pitch by cream solder printing or hot air leveling method. In other words, it is possible to form a highly reliable electrical connection while having a connection pad that includes a pad group with a high wiring density and a narrow pitch.
It is possible to provide a printed wiring board suitable for the configuration of a high-density mounted circuit to be held.

[0009]

EXAMPLES Examples of the present invention will be described below with reference to FIGS. 1 (a) to 1 (g) and 2 (a) to 2 (e).

Example 1 FIGS. 1 (a) to 1 (g) are sectional views schematically showing an example of an embodiment of the first method for manufacturing a printed wiring board according to the present invention.

First, a printed wiring board having required inner layer circuits and having copper foil layers with a thickness of about 18 μm integrally disposed (formed) on both main surfaces is prepared, and is provided at required positions (positions). An electrical connection hole 3 is formed. Then, a dry film was laminated on the copper foil layer surface of the perforated printed wiring board, and exposure and development were performed to perform pattern masking. Then, the pattern-masked printed wiring board was subjected to an etching treatment to remove the copper foil layer by 0.3
After forming a connection pad including a group of 1 mm narrow pitch pads and forming a circuit portion, a through-hole connection layer 2a was formed on the inner wall surface of the connection hole 2 by selective plating (FIG. 1).
(a)). In FIG. 1 (a), 3 is a printed wiring board, 3a
Indicate inner layer circuits, respectively.

Then, on the patterned surface of the printed wiring board 3, the first solder resist layer 4a is coated / formed by, for example, screen printing on a region which does not require soldering (FIG. 1 (b)). A second solder resist layer is formed by, for example, screen printing on the connection pad region including the narrow pitch pad group 1 forming the soldered portion.
Apply and cure 4b (Fig. 1 (c)). In the formation of the second solder resist layer 4b, the surface of the connecting pad 1 is inevitably covered, so that the surface of the connecting pad 1 is covered while being monitored by, for example, an optical pattern inspection device. The second solder resist layer 4b is scraped off by, for example, a buffing machine 5 to expose the surface of the connection pad 1 substantially uniformly (FIG. 1 (d)). In the above,
The solder resist layers 4a and 4b may be formed by using either dry film or liquid solder resist.
In the case of a dry film, a vacuum laminating method may be used, and in the case of a liquid solder resist, a screen printing method or a spray method may be used. Further, when the second solder resist layer 4b covering the surface of the connection pad 1 is scraped off, sufficient care and caution should be taken so as not to damage the surface of the connection pad 1 or the like.

When the surface of the connection pad 1 is exposed by the buffing, on the other hand, the space between the connection pads 1 of this connection pad group is formed into the second solder resist layer 4b which has not been polished or removed. The group of connection pads 1 is entirely filled with the same plane, and the circuit forming surface of the printed wiring board 3 is substantially flat (FIG. 1 (e)). ). In this state, for example, cream solder is printed on the surface of the printed wiring board 3 where the connection pad 1 is exposed, and then reflow processing is performed to selectively and solder bridge the surface of the connection pad 1. A printed wiring board provided with a required solder (preliminary solder) layer 6 can be obtained without generation (FIG. 1 (f)).

In the above manufacturing process, when the solder layer 6 is deposited / formed on the exposed surface of the connection pad 1 by the so-called hot air leveling method, the exposed surface of the connection pad 1 is Not only was the required solder layer 6 formed selectively without generation of solder bridges, but a solder layer 6 ′ could also be deposited on the through-hole connection layer 2a (FIG. 1).
(g)).

In the above description, the first solder resist layer 4a and the second solder resist layer 4a are divided into a region that does not require soldering and a connection pad region that includes a group of narrow pitch pads 1 that form a portion to be soldered.
Although the solder resist layer 4b of 1 is sequentially coated / formed, the same method can be applied by grinding the connection pad region forming the soldered portion and exposing the one surface of the connection pad after coating / forming at the same time. The action and effect can be achieved.

Example 2 FIGS. 1 (a) to 1 (e) are sectional views schematically showing an example of an embodiment of the second method for manufacturing a printed wiring board according to the present invention.

First, a substrate 3'having a required inner layer circuit 3a using a glass nonwoven fabric-resin system as an insulator is prepared (see FIG. 2).
(a)) A copper foil layer having a thickness of about 18 μm is integrally provided (formed) on both main surfaces of this substrate 3'through a glass nonwoven fabric-resin prepreg layer to form a printed wiring board. The electric connection hole 2 is formed at a required position (position). Then, for example, a dry film was laminated on the copper foil layer surface of the perforated printed wiring board, and exposure and development were performed for pattern masking. Then, the pattern-masked printed wiring board is subjected to etching treatment so that the copper foil layer has a narrow pitch pad of 0.3 mm.
After forming a connection pad including a group and forming a circuit portion, a through-hole connection layer 2a was formed on the inner wall surface of the connection hole 2 by selective plating (FIG. 2 (b)).

Next, of the patterned surface of the printed wiring board 3, the narrow-pitch pad 1 forming the soldered portion is formed.
For example, a temperature of about 170 ° C. and a pressure of about 20 kg / cm ² are applied to the connecting pad area including the groups by the heating and pressurizing body 7 (FIG. 2 (c)), and the connecting area including the narrow pitch pad 1 group. The pads are embedded in the printed wiring board 3 so that the upper surface thereof is flush with the printed wiring board (supporting substrate) 3 surface. In this way, the surface of the connection pad 1 is made flush with the surface of the printed wiring board (supporting substrate) 3 and then the solder resist layer 5a is coated / formed by, for example, screen printing on the area where soldering is not required. Here, the formation of the solder resist layer 4a may be either dry film or liquid solder resist, vacuum drying method when dry film, screen printing method or spray method when liquid solder resist. You can go in.

Next, for example, cream solder is printed on the exposed surface of the connection pad 1 of the printed wiring board 3,
By applying a reflow process, the connection pad 1
A printed wiring board having a desired solder (preliminary solder) layer 6 selectively provided on the surface without generation of a solder bridge is obtained (FIG. 2 (d)).

In the above manufacturing process, when the solder layer 6 is deposited / formed on the exposed surface of the connection pad 1 by a so-called hot air leveling method, the exposed surface of the connection pad 1 is selected. Not only the required solder layer 6 was formed without causing the occurrence of solder bridges, but also the solder layer 6 ′ could be formed on the through-hole connection layer 2a (FIG. 2).
(e)).

The present invention is not limited to the above embodiments, but can be carried out in various modified modes without departing from the spirit of the present invention.

[0022]

As described above, according to the method for manufacturing a printed wiring board of the present invention, a pad with a narrow pitch is provided without requiring complicated operations or using special means. Therefore, a printed wiring board that can be mounted with high density and high reliability can be obtained easily and at low cost. That is, not only the manufacturing method is conventional and the yield is good, but also the solder layer having a substantially uniform thickness (quantity) is securely formed by being separated from each other on the pad surface with a narrow pitch. Therefore, the lead connection of the mounted electronic component can be achieved with high reliability. And, it can be said that the low cost, the good yield, and the ability to form a highly reliable high-density packaging circuit bring many advantages in practical use, and a preliminary solder layer is formed on a narrow pitch pad. Therefore, the individual mounting method such as the hot bar method can be applied.

[Brief description of drawings]

FIG. 1 schematically shows an embodiment example of a method for manufacturing a first printed wiring board according to the present invention, in which (a) is a cross-sectional view of a state in which an outer layer is patterned, and (b) shows a non-soldered region. First
Sectional view of the state where the solder resist layer is covered, (c) is a sectional view of the state in which the soldered area is covered with the second solder resist layer, (d) is the second solder resist cured layer A cross-sectional view of the connection pad surface exposed, (e) a cross-sectional view of the connection pad surface exposed by polishing the second solder resist hardened layer, (f) an exposed connection pad Sectional view of a state in which a solder layer is deposited on the surface by a printing method,
(g) is a cross-sectional view of a state in which a solder layer is adhered and formed on the exposed connection pad surface by a hot air leveling method.

FIG. 2 schematically shows an embodiment example of a second method for manufacturing a printed wiring board according to the present invention, in which (a) is a sectional view of a printed wiring board having an inner layer circuit and (b) is an outer layer. A cross-sectional view of a patterned state, (c) a cross-sectional view of a state in which a connection pad is embedded in a printed wiring board, (d) a connection pad surface is flush with the printed wiring board surface and embedded. Cross-sectional view of the state, (d) is a cross-sectional view of the state in which the non-soldered area is covered with the first solder resist layer and the solder layer is formed by the printing method on the connection pad surface, and the formation by the printing method FIG. 3E is a cross-sectional view of a state in which the solder layer is deposited on the connection pad surface by a hot air leveling method.

[Explanation of symbols]

1 ... Connection pad (narrow pitch pad, etc.) 2 ... Connection hole 2a ... Through hole connection layer 3 ... Printed wiring board
3a ... Inner layer circuit 3 '... Printed wiring board 4a ... First solder resist layer 4b ... Second solder resist layer 5 ... Buffing device 6 ... Solder layer 7
... Heating / pressurizing body

Claims (2)

[Claims] 1. A step of integrally forming on a at least one main surface of a supporting substrate a required circuit pattern including a narrow-pitch pad group by photoetching, and removing the etching resist used for the photoetching, Exposing the circuit pattern forming surface, and exposing the exposed circuit pattern forming surface to at least the connection pad surface including the narrow pitch pad surface, and making the circuit pattern forming surface flat. A method for manufacturing a printed wiring board, comprising the steps of coating and forming layers. 2. A step of integrally forming a required circuit pattern including a pad group of a narrow pitch on at least one main surface of a supporting substrate by photoetching, and removing an etching resist used for the photoetching, Exposing the circuit pattern forming surface, and applying pressure treatment to the connecting pad surface including at least the narrow pitch pad surface of the exposed circuit pattern forming surface, and the connecting pad upper surface is flush with the supporting substrate surface. A method of manufacturing a printed wiring board, comprising the steps of: