JP2002271009A - Printed wiring board for high density mounting and base material therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve all of various defects caused by a positional deviation of an SR film coating the surface of a printed wiring board at the same time, in the printed wiring board having such a structure that a solder resist film is formed on an insulation substrate formed with a wiring pattern and the SR film of the minimum width is disposed between two conductor pads disposed adjacently to each other with a very small spacing. SOLUTION: The distance between the two adjacent conductor pads 2a is made very small, and an area of each pad is made larger a than an area necessary for bonding an electrode 10a of an electronic component. A solder resist 3 is formed with openings 20 to expose each conductor pad, and an opening area of each opening is small enough for the opening to be included in the area of the conductor pad. In a normal state in which there is no positional deviation of the solder resist, each opening stays at the center of each conductor pad, with the distance between the periphery of the opening and that of the conductor pad being equal to or smaller than the maximum positional deviation of the solder resist.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solder disposed between conductive pads even when the space between the conductive pads is reduced to less than 0.2 mm, which is the conventional limit value, to increase the mounting density of mounted components. The present invention relates to a printed wiring board for high-density mounting and a printed wiring board base material in which various problems due to a displacement of a resist film do not occur.

[0002]

2. Description of the Related Art In a printed wiring board, a wiring pattern made of a conductive film such as copper is formed on an insulating substrate, and a surface of the insulating substrate which avoids conductive pads for mounting components constituting the wiring pattern is coated with a solder resist film ( Hereinafter, referred to as SR film)
And a configuration covered by That is, since the space between the conductor patterns on which the components are mounted becomes smaller as the mounted components become smaller and higher in density, the cream solder protrudes from the conductor pads when the cream solder is applied on the respective conductor pads, and the insulating substrate There is an increased likelihood of flowing over and causing defects such as solder bridges, short circuits, etc. with other conductor parts. For this reason, conventionally, an SR film made of a resin material having a property of preventing the flow of solder is coated on the wiring pattern and the insulating substrate excluding the conductive pad so that the solder does not flow outside the conductive pad. Has been done.

FIG. 3 is a plan view showing a state in which electronic components are mounted on a printed wiring board.
After the wiring pattern 2 is formed on the insulating substrate 1, the SR film 3 is formed by screen printing using a mask (silk screen) (not shown). The electronic component 10 is fixed by cream solder in a state where the electrodes 10a located at both ends are placed on the conductor pads 2a constituting the wiring pattern 2, respectively. When the two conductor pads 2a on which different electronic components are mounted are close to each other, or when the interval between the two conductor pads on which one component is mounted is narrow, the narrow strip-shaped SR film 3 is provided between the conductor pads.
The arrangement of “a” prevents the cream solder on each conductor pad from flowing. As is well known, screen printing has a configuration in which a film that does not transmit SR is fixed at a position corresponding to each conductive pad on the surface of a silk screen through which a liquid solder resist passes. As a result, no SR film is formed only on the portion of the conductor pad concealed.

FIG. 4 shows a structure in which a narrow strip-shaped SR film 3a is arranged on the surface of an insulating substrate 1 located between adjacent conductive pads 2a.
It is an enlarged view which shows the structure which interrupt | blocks the flow of cream solder between two conductor pads. The width of the narrow strip-shaped SR film 3a is limited by the material constituting the SR film 3a. In order to sufficiently secure the adhesion strength between the SR film 3a and the substrate 1,
At least 0.1 mm is required. SR film 3a
Is formed on a surface of an insulating substrate provided with a wiring pattern by using a mask (not shown).
In addition to the case where a film is formed at an intermediate position between both conductor pads with high positional accuracy as shown in (b), the film is often displaced toward one of the conductor pads as shown in (b). The maximum width of the positional shift of the SR film depends on the performance of the SR film forming apparatus, but is often about ± 0.05 mm. Also, the SR film 3 a
Is formed so as to cover the electrode 1 of the electronic component 10.
As a result, the area of the conductor pad necessary for mounting the Oa is reduced, and the component holding strength by soldering is reduced and the mounted component 10 is displaced. For this reason,
The distance between the conductor pads is the maximum width of the above positional deviation ±
Considering 0.05mm, at least 0.2mm (0.1m
m + 0.05 mm × 2) will be required. That is, this means that the space between the mounted components cannot be reduced to 0.2 mm or less.

In recent years, as chip components, small ones having a vertical and horizontal dimension of about 0.6.times.0.3 mm have come to be marketed, and electronic components mounted on a printed wiring board have been reduced in size. Correspondingly, further densification of the wiring pattern is required, and as a result, the spacing between the conductor pads is also strongly required to be less than 0.2 mm. However, when the above-mentioned conductor pad interval is reduced to less than 0.2 mm, the SR film 3a becomes smaller than the conductor pad 2a due to the relationship with the SR film 3a in which the minimum width that can be formed is limited to 0.1 mm.
The probability that the conductive pad reduces the area where the conductive pad supports the electrode of the component is greatly increased. That is, FIG.
(B) is a diagram showing a state where the conductor pad interval is reduced to 0.15 mm. In this case, the interval between the SR film 3a having a width of 0.1 mm and the edge of both conductor pads 2a is further reduced. Therefore, when the formation position of the SR film 3a is displaced within a range of ± 0.05 mm, the probability that the SR film 3a overlaps the conductor pad 2a as shown in FIG. 5B is further increased. If the SR film covers even a part of the conductor pad as described above, the effective bonding area of the conductor pad varies, and the area of the conductor pad that joins the electrode 10a of the component is reduced. The strength to be reduced. Ideally, it is preferable that the bonding is performed in a state where the proper position of the electrode 10a of the component is aligned with the center position of the conductor pad 2a.
If the position is shifted due to the covering with the R film, the position is shifted from the proper position of the electrode 10a of the component to be bonded on the conductive pad, which causes a bonding failure or a component position shift.

FIGS. 6 (a), 6 (b) and 6 (c) are plan views of a printed wiring board base material for explaining this situation, an enlarged view of an individual piece with electronic components mounted thereon, and a state in which no components are mounted. It is an enlarged view of an individual piece. That is, the printed wiring board base material is
A solder resist film (hereinafter, referred to as an SR film) is formed on the component mounting area 1A of the insulating substrate 1 constituting the base material with only the conductor pads 2a constituting the wiring pattern 2 exposed.
3 to cover almost the entire surface. Also,
A recognition mark 5 made of a conductor pattern is formed at an appropriate position, for example, at four corners of an outer region (exposed region of the insulating substrate surface) 1B located outside the component mounting region 1A. The recognition mark 5 is a portion serving as a reference point for knowing a component mounting position when one electronic component 10 is mounted on the pair of conductor pads 2a. That is, the device that automatically mounts the electronic component uses the information about the coordinate position of the recognition mark 5 obtained by the image reading means or the like as a reference, and calculates the x and y coordinate values for each of the conductor pads stored in advance. The position of the conductive pad 2a is determined, and the component is mounted at the determined coordinate position. Outer area 1
Also on B, the SR film 3 is formed over the entire area excluding the recognition mark 5.

[0007] The SR film 3 is placed on the component mounting area 1 on the insulating substrate 1.
In the case where the SR film 3 is formed on the area A, a silk screen configured so that the SR film 3 does not adhere only to the portion corresponding to the conductor pad 2a is used, and the SR film 3 is collectively screened on other portions. Print, but at this time
When the printing position is shifted in the x direction, the y direction, or other directions within the range of 0.05 mm, a part of the conductor pad 2a is formed by the SR film 3a as in the electronic component on the right side of FIG. After being covered, the actual center position of the conductor pad moves to the center position C ′ indicated by a chain line with respect to the center position C of the original conductor pad (shown by a solid line). However, since the automatic component mounting apparatus cannot recognize that the SR film covers the conductor pattern, the work of uniquely mounting the electronic component on each conductor pad is performed using the coordinate position of the read recognition mark 5 as a clue. I do. Therefore, the electrode 10a of the electronic component is
The conductive pad is placed on the conductive pad with reference to the original center position C (shown by a solid line). For this reason, a part of the electrode is placed over the SR film (the overlap portion with the conductor pad) to which the cream solder 6 is not easily attached, and the area of the conductor pad (solder amount) contributing to the bonding is reduced. Because of the decrease, it is difficult to obtain sufficient bonding strength. As a result, the bonding strength varies among the conductive pads, and the quality becomes unstable. FIG.
(B) As shown in FIG.
When a part of the electrode is placed on the film portion via the cream solder 6, the component is misaligned (actually exposed surface) due to the self-alignment action of the solder generated in the process of melting and hardening during reflow. To the center position C '). Further, when the cream solder 6 is printed on the SR film covering the conductor pad, the cream solder 6 on the SR film is hardly melted and fixed, so that a defective phenomenon such as a solder ball 6a occurs. Since the solder balls roll easily on the substrate and move, they adhere to other conductor parts and cause a short circuit between the conductors.

[0008]

SUMMARY OF THE INVENTION The present invention has been made in view of the above, and has been made in consideration of the above problem.
The distance between two conductive pads adjacent to each other at a distance of less than 0.1.
A printed wiring board for high-density mounting in which a printed wiring board having a configuration in which an SR film having a width of 1 mm is disposed is free from various problems due to a displacement of the SR film covering the printed wiring board surface. It is an object to provide a method for forming a substrate and a solder resist film. More specifically, it is an object of the present invention to solve at once a poor mounting of an electronic component, a solder bridge between the conductive pads, and other problems that have been caused by the SR film being displaced and covering the conductive pads. And

[0009]

In order to solve the above problems, a first aspect of the present invention is an insulating substrate, a wiring pattern including a conductive pad formed on the insulating substrate surface, and an insulating pattern excluding at least the conductive pad. A solder resist that covers the surface of the substrate, and in a printed wiring board for high-density mounting, comprising: The solder resist is provided with an opening for exposing each conductive pad, and the opening area of the opening is included in the area of the conductive pad. In a normal state where the solder resist has not been misaligned,
Each opening is included in the center of the conductor pad, and the interval between the periphery of the opening and the periphery of the conductor pad at this time is
It is characterized in that it is equal to or larger than the maximum displacement of the solder resist.

According to a second aspect of the present invention, there is provided a component mounting region having a structure in which a plurality of insulating substrate pieces each having a wiring pattern including a component mounting conductor pad on a surface are connected, and an outer peripheral edge of the component mounting region. And an outer region provided with at least one recognition mark, and at least a component mounting region excluding the conductor pad and an outer region excluding at least the recognition mark. Each is covered with a solder resist, and the interval between the adjacent conductor pads is set to a minute width, while the area of each conductor pad is increased by a required value larger than the area required for joining the electrodes of the electronic component. The solder resist covering the component mounting area includes an opening for exposing each conductive pad, and the opening area of the opening is included in the area of the conductive pad. Uni narrowed, in the state of regular the solder resist is not misaligned, the
Each opening is included in the center of the conductor pad, and the interval between the periphery of the opening and the periphery of the conductor pad at this time is
The maximum displacement amount of the solder resist is equal to or greater than the maximum, and the solder resist covering the outer region is
An outer opening for exposing the recognition mark is provided, and the opening area of the outer opening is narrowed so that the outer opening is included in the area of the recognition mark. In the state of the above, the outer opening is included in the center of the recognition mark, and the interval between the outer opening periphery and the recognition mark periphery at this time is equal to or larger than the maximum displacement amount of the solder resist. Is set to.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to embodiments shown in the drawings. FIGS. 1A and 1B are enlarged plan views showing the configuration of a main part of a printed wiring board for high-density mounting according to an embodiment of the present invention. The description will be made with reference to FIG. This printed wiring board for high-density mounting (hereinafter simply referred to as a printed wiring board)
A solder resist film (hereinafter, referred to as a screen resist) formed on the insulating substrate 1 provided with the wiring pattern 2 by screen printing so that a part of the conductor pad 2a constituting the wiring pattern 2 is exposed.
SR film 3).
Specifically, in the present embodiment, the interval between the adjacent conductor pads 2a is reduced by twice (0.1 mm) twice the maximum variation value of 0.05 mm when the SR film 3 is formed, and at the same time, the distance between the adjacent conductor pads 2a is reduced. The pad 2a has a configuration in which the area of the pad 2a is larger than the originally required bonding area shown in FIGS. On the other hand, regarding the SR film 3, an opening 20 having an opening area smaller than the area of the conductor pad 2a is provided at a position corresponding to the conductor pad 2a, and the conductor pad 2 is provided in the opening 20.
It is configured to expose a part of “a”. The opening area of the opening 20 is set to be equal to the area originally required for soldering the electrode 10a of the electronic component 10 to be joined. Therefore, for example, when the interval between the conductor pads 2a is set to a small width, for example, less than 0.2 mm (for example, 0.15 mm), the SR film 3 is not displaced on the substrate 1 as shown in FIG. Is printed so that the opening 20 completely fits in the center of the area of the conductive pad 2a. Note that S located between the conductor pads 2a
Since the width of the R film 3 exceeds 0.1 mm, the bonding strength with the insulating substrate surface is sufficiently ensured. When the SR film 3 is printed at a regular position as shown in FIG. 1A, the width between the inner peripheral edge of the opening 20 and the outer peripheral edge of the corresponding conductor pad 2a is at least at the time of forming the SR film 3. Therefore, even if the formation position of the SR film 3 is displaced by a maximum of 0.05 mm to the right as shown in FIG.
Does not exceed the edge of each conductor pad 2a and can still fit within the area of the conductor pad. This means that the area of the conductive pad exposed in the opening 20 always maintains a sufficient and necessary area for bonding the electrodes of the electronic component.

Further, the characteristic configuration of the present invention is that the SR film 3 is formed so as to cover the insulating substrate surface corresponding to the outer region 1B shown in FIG. The SR film 3 on the outer region 1B has a small-diameter circular outer opening 25 at a position corresponding to the circular recognition mark 5. The outer opening 25 formed to expose the recognition mark 5 is set to have a narrow (small diameter) opening area such that the outer opening is included in the area of the recognition mark. In other words, a normal state where the solder resist has not been displaced (FIG. 2A)
In the state (2), the outer opening 25 is concentrically included in the center of the recognition mark 5. At this time, the distance L between the outer opening periphery and the recognition mark periphery is determined by the solder resist SR film 3. Maximum displacement (± 0.05mm)
Is equal to or greater than In other words, the area of the recognition mark 5 corresponding to the outer opening 25 is
Since the diameter is enlarged by twice the maximum displacement amount of the solder resist film SR3, even if the solder resist film is displaced in any direction, the outer opening 2 is formed.
5 does not fall out of the area of the recognition mark 5. In addition, since the solder resist in the component mounting area 1A and the solder resist in the outer area 1B are formed collectively by using a single silk screen, a positional shift occurs in the same direction and the same distance as a whole. I do. Therefore, when a position shift occurs in the outer opening 25, the position shift also occurs in the opening 20 by the same distance in the same direction.

As with the relationship between the outer opening 25 and the recognition mark 5, the relationship between the opening 20 and the conductor pad 2a is the maximum allowable deviation regardless of the direction in which the SR film 3 is displaced. As long as the width is within a range (for example, ± 0.05 mm), the opening 20 is within the area of the conductive pad 2a. On the other hand, the automatic component mounting device
After recognizing the center of the circular recognition mark 5 exposed in the reading means 5 by the reading means, the position of each conductor pad 2a is determined based on the coordinates of the center, and the electrode of the electronic component is correctly positioned on the conductor pad. The electronic components are mounted so as to be mounted. Accordingly, as long as the positional shift width of the SR film 3 is within the range of the maximum allowable shift width, the positional coordinates of the conductor pads determined with reference to the center of the recognition mark 5 are always accurate, and Are correctly mounted on the conductor pad surface exposed in the opening 20. Therefore, the bonding area between the conductive pad and the electrode of the component and the amount of solder that can be used for bonding are necessary and sufficient, and the occurrence of poor bonding can be effectively prevented. The displacement of the component mounting position due to the self-alignment due to the variation in the bonding force between the conductive pads can be prevented. Prior to component mounting, the opening 2
The cream solder can be accurately applied by aiming only on the surface of the conductor pad exposed in the inside of the solder pad, so that the cream solder does not adhere to the SR film covering the conductor pad surface, and the solder ball And the problems caused by the formation are solved. Also, 0.1
Since the SR film having a sufficient width of at least mm is interposed, the occurrence rate of the solder bridge between the conductor pads can be significantly reduced.

The structure of the conductor pad according to the present invention is as follows.
The present invention can be applied to the case where the distance between at least two adjacently arranged conductor pads is set to a value smaller than 0.2 mm and the SR film having the minimum width is formed within the distance. Therefore,
Not only is the distance between each of the conductor pads on which two adjacent electronic components are mounted less than 0.2 mm, but also the distance between the plurality of conductor pads on which one electronic component is mounted is 0.
The present invention is applicable to a case where the distance is less than 2 mm. The shape of the outer region of the printed wiring board base material is shown in FIG.
As shown in (a), the shape is not limited to the shape surrounding the whole component mounting area 1A in a ring shape, but may be any shape as long as it is an area connected along the outer peripheral edge of the component mounting area 1A. .

[0015]

As described above, according to the present invention, a solder resist film is formed on an insulating substrate provided with a wiring pattern, and the solder resist film is disposed adjacently at a small interval (for example, an interval of less than 0.2 mm). In a printed wiring board having a configuration in which an SR film having a minimum width (for example, 0.1 mm width) is disposed between two conductive pads, various problems caused by a displacement of the SR film covering the printed wiring board surface More specifically, the mounting failure of the electronic component, the solder bridge between the conductive pads, and other problems caused by the SR film being displaced and covering the conductive pads can be solved at once.

[Brief description of the drawings]

FIGS. 1A and 1B are enlarged plan views showing a configuration of a main part of a printed wiring board for high-density mounting according to an embodiment of the present invention.

FIGS. 2A and 2B are views for explaining a positional relationship between solder resists.

FIG. 3 is a plan view showing a state where electronic components are mounted on a printed wiring board.

FIGS. 4A and 4B show a configuration in which a narrow strip-shaped SR film is arranged on the surface of an insulating substrate 1 located between adjacent conductive pads to block the flow of cream solder between two conductive pads; FIG.

FIGS. 5 (a) and 5 (b) show conductor pad intervals of 0.15 mm.
FIG.

6 (a), (b) and (c) are a plan view of a conventional printed wiring board base material, an enlarged view of an individual piece with electronic components mounted thereon, and an enlarged view of an individual piece with no components mounted thereon.

FIGS. 7A and 7B are diagrams for explaining the drawbacks of the conventional example.

[Explanation of symbols]

1 insulating substrate, 2 wiring pattern, 2a conductive pad,
3, 3a Solder resist film (SR film), 5 recognition mark, 6 cream solder, 10 electronic components, 10a
Electrodes, 20 openings, 25 outer openings.

Claims (2)

[Claims] An insulating substrate, a wiring pattern including a conductive pad formed on the insulating substrate surface, a solder resist covering at least the insulating substrate surface excluding the conductive pad,
In the printed wiring board for high-density mounting provided with, while setting the interval between the adjacent conductor pads to a minute width, the area of each conductor pad is larger than the area required for joining the electrodes of the electronic component. The solder resist is provided with an opening for exposing each conductive pad, and the opening area of the opening is narrowed so that the opening is included in the area of the conductive pad. In a normal state where no displacement has occurred, each opening is included in the center of the conductor pad, and the interval between the periphery of the opening and the periphery of the conductor pad is the maximum displacement of the solder resist. A printed wiring board for high-density mounting, which is equal to or more than. 2. A component mounting region having a structure in which a plurality of insulating substrate pieces each having a wiring pattern including a component mounting conductor pad on a surface are connected, and at least one of the component mounting regions is connected to an outer peripheral edge of the component mounting region. A printed wiring board base material integrated with an outer region provided with two recognition marks, and at least on a component mounting region excluding the conductor pad and at least on an outer region excluding the recognition mark. While covering with a resist, the interval between the adjacent conductor pads is set to a very small width, while the area of each conductor pad is made larger by a required value than the area required for joining the electrodes of the electronic component, The solder resist covering the component mounting area has an opening for exposing each conductive pad, and the opening area of the opening is reduced so that the opening is included in the area of the conductive pad. However, in a normal state where the solder resist has not been displaced, each opening is included in the center of the conductor pad, and the gap between the periphery of the opening and the periphery of the conductor pad at this time is The maximum displacement of the resist is equal to or greater than the maximum, and the solder resist covering the outer region includes an outer opening for exposing the recognition mark, and the outer opening has an opening area of the outer opening. In a normal state in which the solder resist has not been displaced, the outer opening is in the state of being included in the center of the recognition mark. The distance between the periphery of the opening and the periphery of the recognition mark is set to be equal to or larger than the maximum positional deviation amount of the solder resist. Cement wiring substrate base material.