JPH08288658A - Printed wiring board for bga package mount - Google Patents

Abstract

PURPOSE: To provide a printed wiring board for BGA package which prevents short-circuit between electrode pads due to superfluous bonding agent and imperfect bonding due to insufficient bonding agent, and surely enables visual inspection of defect, and improve packaging density by effectively arranging electrode pads and through hole lands. CONSTITUTION: In a printed wiring board 1 for BGA package, through hole lands 3L are arranged. The through hole land is formed in the vicinity of periphery of an electrode pad 2 connected with a spherical outer electrode of a BGA package, and constituted as as unified body with the electrode pad 2. The electrode pad 2 and the through hole land 3L are formed in a plane where the width is gradually decreased. The fluidity of superfluous bonding agent is accelerated, and made to flow smoothly into through holes positioned in the central parts of the through hole lands 3L. The through hole lands 3L are arranged in the oblique direction, while the electrode pads 2 are set as the centers.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a printed wiring board on which a BGA (ball grid array) package is mounted. Particularly, the present invention relates to a printed wiring board having an electrode pad to which a spherical external electrode of a BGA package is connected.
The present invention relates to a printed wiring board capable of excellent electrical and mechanical bonding (for example, solder bonding) between a spherical external electrode of a BGA package and an electrode pad of the printed wiring board.

[0002]

2. Description of the Related Art In a BGA package, spherical external terminals are arranged on the lower surface of the package, and the connecting external terminals do not project around the outer surface of the package, so that high density mounting can be performed on the mounting surface of a printed wiring board. Furthermore, since the BGA package is a surface mount component and the BGA package can be mounted on each of the mounting surfaces of the front surface and the back surface of the printed wiring board, high density mounting can be performed on the mounting surface of the printed wiring board.

FIG. 4 is a plan view of a printed wiring board for mounting a BGA package according to the prior art, and FIG. 5 is a cutting line F shown in FIG. 4 in a state where the BGA package is mounted.
It is a longitudinal cross-sectional view of the printed wiring board cut along 5-F5. Figure 5
As shown in, the BGA package 6 is mounted on the mounting surface of the printed wiring board 1. As shown in FIGS. 4 and 5,
On the mounting surface of the printed wiring board 1, the spherical external electrodes 8 arranged on the lower surface of the package of the BGA package correspond to the arrangement position and the number of arrangements, and are regularly arranged in both the row direction and the column direction on the mounting surface. A plurality of formed electrode pads 2 are provided. The bonding between the spherical external electrode 8 of the BGA package 6 and the electrode pad 2 of the printed wiring board 1 is performed by the bonding agent 7, and solder is used as the bonding agent 7. A through hole land 3L is electrically connected to each of the plurality of electrode pads 2, and a connection wiring 23 is used to connect the electrode pad 2 and the through hole land 3L. Through hole land 3
L is electrically connected to a through-hole wiring 3T embedded in a through-hole formed in the printed wiring board 1 and an inner layer wiring (not shown) arranged inside the printed wiring board 1 is provided in the through-hole wiring 3T. ) Is electrically connected to.

A mounting method for mounting the BGA package 6 and other mounting components on the mounting surface of the printed wiring board 1 is performed in the following procedure.

First, at the time of manufacturing the printed wiring board, the solder resist is provided on the mounting surface of the printed wiring board 1 except for the electrode pads 2 (including the electrode pads to which other mounting components are connected) of the BGA package 6 and the through hole lands 3L. Is applied. In the first mounting step, cream solder is applied onto the electrode pads 2 of the BGA package 6. The cream solder is used as the bonding agent 7, and this cream solder is applied by a printing technique, for example. In the second step, the BGA package 6 is mounted on the mounting surface of the printed wiring board 1,
The spherical external electrodes 8 of the BGA package 6 are brought into contact with the electrode pads 2 of the printed wiring board 1 via cream solder.
The BGA package 6 is mounted by a mounting device or the like. In the third step, the printed wiring board 1 is conveyed to a reflow oven, the cream solder is heated and melted in the reflow oven, and solder reflow is performed. By this solder reflow, the electrode pad 2 and the spherical external electrode 8 are bonded with the bonding agent 7, and the BGA package 6 is mounted on the mounting surface of the printed wiring board 1.

However, when the BGA package 6 is mounted on the mounting surface of the printed wiring board 1, the bonding portion between the electrode pad 2 and the spherical external electrode 8 is hidden, and the bonding agent (bonding agent 7 The state of () is not inspected. Therefore, in the printed wiring board 1 on which this type of BGA package 6 is mounted, how to secure the reliability of the joint portion is an important issue.

Further, in the solder reflow, heat is applied to the printed wiring board 1 and the printed wiring board 1 is likely to be deformed such as warped or distorted. When the printed wiring board 1 is deformed, a gap is created between the electrode pad 2 and the spherical external electrode 8, and a bonding failure due to the lack of the bonding agent 7 occurs. Further, when the shortage of the bonding agent 7 is predicted and a large amount of the bonding agent 7 (cream solder) is applied in advance, on the contrary, the electrode pad 2
Excessive amount of the bonding agent 7 is present at a location where no gap is formed between the spherical external electrode 8 and the spherical external electrode 8. Therefore, as shown in FIG. 5, a short-circuit portion 7S is formed between the adjacent electrode pads 2 (between the spherical external electrodes 8) so that the excess bonding agent 7 is connected to each other, and a short circuit occurs between the electrode pads 2.

Japanese Unexamined Patent Publication (Kokai) No. 1-258454 discloses a technique capable of improving the difficulty of the above-described appearance defect inspection. In the technique disclosed in this publication, a through hole reaching the upper surface of the package is formed in the electrode portion on the lower surface of the package. When the package is mounted on the mounting board by soldering, the presence of the solder crawling in the through hole is confirmed, and whether the solder has crawled up or not is judged by the appearance defect inspection.

Further, Japanese Utility Model Laid-Open No. 4-87682 discloses a technique capable of preventing a short circuit between the electrode pads 2 due to the excess bonding agent 7. In the technique disclosed in this publication, a through hole is formed in the center of the solder pad (corresponding to the electrode pad 2 described above). Since excess solder is poured into the through holes, it is possible to prevent a short circuit between solder pads due to the excess solder.

[0010]

However, the following points have not been taken into consideration in the prior art. (1) In the printed wiring board 1 shown in FIGS. 4 and 5 described above, there is formed a path through which the excess bonding agent 7L connected to the through hole is released from the electrode pad 2 through the connection wiring 23 and the through hole land 3L. However, the connecting wiring 23 is formed with a width dimension smaller than the outer dimensions of the electrode pad 2 and the through-hole land 3L and a uniform width dimension. Further, the connection wiring 23 is formed in a layer different from that of each of the electrode pad 2 and the through hole land 3L and made of a different material. Therefore, in the route through which the excess bonding agent 7L is released, the route width is rapidly reduced in the portion from the electrode pad 2 to the connection wiring 23, and the excess bonding agent 7L is removed.
Is hard to escape, and actually does not function as a route for escaping the excess bonding agent 7L. Therefore, as described above, a short circuit occurs between the electrode pads 2 due to the excess bonding agent 7L.

(2) In the printed wiring board 1 shown in FIGS. 4 and 5, the through hole land 3L is arranged at the center of the area surrounded by the four adjacent electrode pads 2. For this reason, the outer layer wiring extending vertically and horizontally in FIG. 4 cannot be substantially passed between the electrode pad 2 and the through-hole land 3L, and therefore the outer layer wiring is arranged in the arrangement region of the electrode pads 2 and It is routed around the array area of the through hole land 3L. Therefore, since an extra layout wiring area is required on the mounting surface of the printed wiring board 1, the mounting efficiency of the printed wiring board 1 is reduced.

(3) According to the technique disclosed in the above-mentioned Japanese Patent Laid-Open No. 1-258454, it is possible to visually inspect for visual defects, but since the through holes are formed on the package side, the elements in the package and Through holes are formed while avoiding wiring. As a result, the size of the package is increased due to the formation of the through hole, so that the mounting efficiency is lowered on the mounting surface of the mounting substrate.

(4) In the technique disclosed in the above-mentioned Japanese Utility Model Laid-Open No. 4-87682, the solder reflow causes deformation of the printed wiring board 1, resulting in a through hole of solder even at a place where a gap is formed on the solder pad. It flows inside. For this reason, a joint failure occurs due to lack of solder at the place where the gap is generated.

The present invention has been made to solve the above problems, and the objects of the present invention are as follows.

(1) The present invention prevents a short circuit between electrode pads due to an excess bonding agent, prevents a bonding failure due to a shortage of the bonding agent, and can reliably perform a visual defect inspection. An object of the present invention is to provide a printed wiring board on which is mounted.

(2) According to the present invention, the electrode pads and the through hole lands can be efficiently arranged to improve the packaging density.
An object is to provide a printed wiring board on which a BGA package is mounted.

[0017]

In order to solve the above problems, the present invention according to claim 1 provides a printed wiring board on which a BGA package is mounted, which is electrically and mechanically connected to a spherical external electrode of the BGA package. And electrode pads arranged on the mounting surface according to the arrangement position and the number of arrangement of the spherical external electrodes, and arranged on the mounting surface at positions close to the periphery of the electrode pad, and the electrode pads. Through hole lands that are integrally formed of the same layer and the same material and that are electrically connected to the inner layer wiring provided inside the substrate.

According to the first aspect of the present invention, in order to absorb the gap between the printed wiring board and the BGA package, which is caused by heat treatment (for example, solder reflow), B is absorbed.
When an excessive bonding agent (for example, solder) is used between the spherical external electrode of the GA package and the electrode pad of the printed wiring board, the excess bonding agent can be poured into the through hole land (through hole). . Since the electrode pad and the through-hole land are integrally formed, and the surface of the electrode pad and the surface of the through-hole land, which is a path for the excess bonding agent to flow, are formed of smooth surfaces with reduced steps, the excess Fluidity is promoted in the cement. Therefore, it is possible to reduce the occurrence of a short circuit in which adjacent electrode pads are connected by an excessive bonding agent. Furthermore, since the surplus bonding agent is poured into the through holes, the appearance defect inspection can be performed based on the surplus bonding agent.

According to a second aspect of the present invention, in the printed wiring board according to the first aspect, the electrode pad and the through hole land which are integrally formed have a width from the electrode pad side toward the through hole land side. Is formed in a planar shape that is temporarily reduced.

According to the second aspect of the invention, the surplus of the bonding agent formed on the electrode pad can be gradually and smoothly poured from the electrode pad to the through hole land.

According to a third aspect of the present invention, in the printed wiring board according to the first or second aspect, a plurality of the electrode pads are arranged in each of a row direction and a column direction, and the through hole lands are formed. It is characterized in that the electrode pads integrally formed on the through hole land are arranged in an oblique direction having an inclination angle with respect to both the row direction and the column direction in which the electrode pads are arranged.

In the invention according to claim 3, when the positions where the through-hole lands are arranged are projected in the row direction and the column direction where the electrode pads are arranged, the electrode pads and the electrode pads are integrally formed. The distance between the formed through hole land can be apparently shortened. That is, in the row direction and the column direction in which the electrode pads are arranged, a space can be secured between the through hole land connected to the electrode pad and another adjacent electrode pad, so that the arrangement interval of the electrode pads can be reduced, Electrode pads can be arranged at high density on the mounting surface. Furthermore, since a space can be secured between the through hole land connected to the electrode pad and another adjacent electrode pad, wiring can be arranged in this space. If wirings can be arranged between the electrode pads, the number of wirings that bypass the electrode pads can be reduced, so that the wirings can be arranged at a high density on the mounting surface.

According to a fourth aspect of the present invention, in the printed wiring board according to the third aspect, a distance between the electrode pad and a through hole land connected to the electrode pad is equal to that of the through hole land. It is characterized in that it is set smaller than the distance between the through hole land and another electrode pad adjacent in the diagonal direction.

In the invention according to claim 4, since a space can be secured between the through hole land and another electrode pad adjacent to the through hole land, wiring can be arranged in this space.
Therefore, the number of wirings can be reduced, and the wirings can be arranged at a high density on the mounting surface.

According to a fifth aspect of the present invention, in the printed wiring board according to the first or second aspect, the electrode pad and the through-hole land connected to the electrode pad are arranged in the row direction on the row direction. Alternatively, they are arranged in the column direction.

In the invention according to claim 5, since the through hole lands are not arranged in the column direction or the row direction in which the electrode pads are arranged, a space can be secured between the electrode pads in this direction, and wiring can be provided in this space. Can be placed. Therefore, the number of wirings can be reduced, and the wirings can be arranged at a high density on the mounting surface.

[0027]

【Example】

Embodiment 1 FIG. 1 is a plan view showing a part of a printed wiring board for a BGA package according to Embodiment 1 of the present invention, and FIG. 2 is a cutting line F2-F shown in FIG. 1 in a state where a BGA package is mounted.
It is a longitudinal cross-sectional view cut in 2.

As shown in FIG. 2, the BGA package 6 is mounted on the mounting surface of the printed wiring board 1. As shown in FIGS. 1 and 2, BG is mounted on the mounting surface of the printed wiring board 1.
A plurality of electrode pads 2 are provided which are arranged regularly in both the row direction and the column direction on the mounting surface, corresponding to the arrangement position and the number of the spherical external electrodes 8 arranged on the lower surface of the package of the A package. A through hole land 3L is provided at a position close to the periphery of the electrode pad 2 on the mounting surface.
Is arranged.

The electrode pad 2 is formed to have a size and shape necessary for connecting to the spherical external electrode 8.
Is formed in a shape that is the same as or similar to the circular shape in which at least the spherical external electrode 8 is projected on the mounting surface. The through hole land 3L is integrally formed of the same layer and the same material as the electrode pad 2, and the through hole land 3L and the electrode pad 2 are electrically connected. When the electrode pad 2 and the through hole land 3L are integrally formed, the step difference between the surface of the electrode pad 2 and the surface of the through hole land 3L is reduced to form a smooth surface. The excess bonding agent 7L flows from the electrode pad 2 to the through hole land 3L, and the fluidity of the excess bonding agent 7L is promoted.

In the present embodiment, one through hole land 3L is connected to one electrode pad 2, but in the present invention, one electrode pad 2 is provided with a plurality of through hole lands 3L or a plurality of electrode pads 2. The case where one through-hole land 3L is connected is included.

The outer size of the through hole land 3L is set smaller than the outer size of the electrode pad 2.
The electrode pad 2 and the through hole land 3L formed integrally are the through hole land 3L from the electrode pad 2 side.
It is formed in a planar shape whose width is gradually reduced toward the side. When the bonding agent 7 is applied on the electrode pad 2, the excess bonding agent 7L of the applied bonding agent 7 gradually and smoothly moves from the electrode pad 2 into the through hole located in the central portion of the through hole land 3L. Can be poured into. Electrode pad 2
The minimum amount of the bonding agent 7 required for bonding between the spherical external electrode 8 and the spherical external electrode 8 is secured on the surface of the electrode pad 2 by wettability.

The through hole land 3L is the printed wiring board 1
Is electrically connected to the through-hole wiring 3T embedded in the through-hole formed in. Through hole wiring 3T
The inner layer wiring 5 disposed inside the printed wiring board 1 is electrically connected to the. The surplus bonding agent 7L poured into the through holes can be observed from the back surface of the printed wiring board 1, and the appearance defect inspection can be performed based on the surplus bonding agent 7L.

With respect to the arrangement of the electrode pads 2 in the row direction and the column direction, the through hole land 3L is arranged in the row direction in which the electrode pads 2 are arranged around the electrode pad 2 formed integrally with the through hole land 3L. , Are arranged in an oblique direction having an inclination angle with respect to any of the column directions. That is, as shown in FIG. 1, two electrode pads 2 adjacent to each other in the row direction and two electrode pads 2 adjacent to each other in the column direction are connected by connecting the respective center points of a total of four electrode pads 2 and are illustrated by broken lines for convenience. Through-hole lands 3L are formed along the diagonal line of the square. When the positions where the through-hole lands 3L are arranged are projected in the row direction and the column direction in which the electrode pads 2 are arranged, respectively, between the electrode pads 2 and the through-hole lands 3L formed integrally with the electrode pads 2. The distances La and Lb can be apparently shortened. That is, in the row direction and the column direction in which the electrode pads 2 are arranged, it is possible to secure a space between the through-hole land 3L connected to the electrode pad 2 and another electrode pad 2 adjacent thereto,
The arrangement intervals LA and LB of the electrode pads 2 can be reduced respectively.
In other words, a space can be secured between the through-hole land 3L connected to the electrode pad 2 and another adjacent electrode pad 2, so that the outer layer wiring 4 can be arranged in this space as shown in FIG. .

Further, the distance Lc between the electrode pad 2 and the through-hole land 3L connected to the electrode pad 2 is adjacent to the through-hole land 3L in the diagonal direction in which the through-hole land 3L is arranged. Is set smaller than the distance LC between the electrode pad 2 and the electrode pad 2. That is, the electrode pad 2 and the through hole land 3L are integrally formed in a size that does not reach the center point P of the quadrangle illustrated for convenience. Therefore, a space can be secured between the through-hole land 3L and another adjacent electrode pad 2. Outer layer wiring 4 in the secured space
Can be placed.

The spherical external electrode 8 of the BGA package 6
The connection between the printed wiring board 1 and the electrode pad 2 of the printed wiring board 1 is performed by a bonding agent 7, and for the bonding agent 7, for example, solder is used.

Next, a mounting method for mounting the BGA package 6 (and other mounting components) on the mounting surface of the printed wiring board 1 will be described.

First, at the time of manufacturing the printed wiring board, the solder resist is provided on the mounting surface of the printed wiring board 1 except for the electrode pads 2 (including the electrode pads to which other mounting components are connected) of the BGA package 6 and the through hole lands 3L. Is applied. In the first mounting step, cream solder is applied onto the electrode pads 2 of the BGA package 6. The cream solder is used as the bonding agent 7, and this cream solder is applied by a printing technique, for example. In the second step, the BGA package 6 is mounted on the mounting surface of the printed wiring board 1,
The spherical external electrodes 8 of the BGA package 6 are brought into contact with the electrode pads 2 of the printed wiring board 1 via cream solder.
The BGA package 6 is mounted by a mounting device or the like. In the third step, the printed wiring board 1 is conveyed to a reflow oven, the cream solder is heated and melted in the reflow oven, and solder reflow is performed. By this solder reflow, the electrode pad 2 and the spherical external electrode 8 are bonded with the bonding agent 7, and the BGA package 6 is mounted on the mounting surface of the printed wiring board 1.

The printed wiring board 1 thus constructed has the following effects.

(1) Excess bonding agent 7L from the electrode pad 2 to the through hole land 3L during mounting (during solder reflow)
Since the amount of the bonding agent 7 flows through the through holes to adjust the amount of the bonding agent 7, it is possible to prevent a short circuit between the electrode pads 2 due to the excess bonding agent 7L.

(2) Bonding agent 7L flowing into the through hole
Is the surplus, and the minimum amount of bonding agent required for bonding 7
Can be secured on the surface of the electrode pad 2 by wettability,
It is possible to prevent defective bonding due to the shortage of the bonding agent 7.

(3) Bonding agent 7L flowing into the through hole
With this, the appearance defect inspection can be reliably performed. (4) The electrode pads 2 and the through hole lands 3L are efficiently arranged, and the mounting density can be improved.

Example 2. FIG. 3 is a plan view showing a part of a printed wiring board for a BGA package according to the second embodiment of the present invention.

As shown in FIG. 3, in the printed wiring board 1 according to this embodiment, the electrode pad 2 and the electrode pad 2 are provided.
The through-hole land 3L connected to is arranged on the row direction (or on the column direction) where the electrode pads 2 are arranged. Through hole lands 3 are arranged in the column direction in which the electrode pads 2 are arranged.
Since L is not arranged, the electrode pad 2 in this direction
Space can be secured between them. Since the outer layer wiring 4 can be arranged in this space, the number of routing wirings can be reduced.

In the present embodiment, as shown in FIG. 3, the planar shape in which the electrode pad 2 and the through-hole land 3L are integrated is formed into an oval shape. In the present invention, the integrated shape is the same. May be rectangular.

In the printed wiring board 1 thus constructed, the same effects as those obtained by the printed wiring board 1 according to the first embodiment described above can be obtained.

[0046]

The following effects are obtained in the present invention. (1) The present invention can prevent a short circuit between electrode pads due to an excess bonding agent, prevent a bonding failure due to a shortage of the bonding agent, and reliably perform a visual defect inspection.
A printed wiring board on which a GA package is mounted can be provided.

(2) The present invention can provide a printed wiring board on which a BGA package is mounted, in which electrode pads and through-hole lands can be efficiently arranged and packaging density can be improved.

[Brief description of drawings]

FIG. 1 is a plan view showing a part of a printed wiring board for a BGA package according to a first embodiment of the present invention.

2 is a vertical cross-sectional view taken along the cutting line F2-F2 shown in FIG. 1 in a state in which a BGA package is mounted.

FIG. 3 is a plan view showing a part of a printed wiring board for a BGA package according to a second embodiment of the present invention.

FIG. 4 is a plan view showing a part of a printed wiring board for a BGA package according to a conventional technique.

5 is a vertical cross-sectional view taken along the line F5-F5 shown in FIG. 4 in a state where a BGA package is mounted.

[Explanation of symbols]

1 printed wiring board, 2 electrode pads, 3L through hole land, 3T through hole wiring, 4 outer layer wiring, 5
Inner layer wiring, 6 BGA package, 7,7L bonding agent,
8 Spherical external electrode.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Office reference number FI technical display location H05K 3/34 501 H01L 23/12 L

Claims (5)

[Claims] 1. A printed wiring board on which a BGA package is mounted is electrically and mechanically connected to spherical external terminals of the BGA package, and is mounted on a mounting surface according to the array position and the number of arrayed spherical external terminals. The electrode pad to be arranged is arranged on the mounting surface at a position close to the periphery of the electrode pad, and is formed integrally with the electrode pad in the same layer and the same material as the inner layer wiring arranged inside the substrate. A printed wiring board for mounting a BGA package, comprising: an electrically connected through hole land. 2. The printed wiring board according to claim 1, wherein the width of the electrode pad and the through-hole land formed integrally is gradually reduced from the electrode pad side toward the through-hole land side. A printed wiring board for mounting a BGA package, which is formed in a planar shape. 3. The printed wiring board according to claim 1 or 2, wherein a plurality of the electrode pads are arranged in each of a row direction and a column direction, and the through hole land is integrated with the through hole land. A printed wiring board for mounting a BGA package, characterized in that the electrode pads are formed in a diagonal direction having an inclination angle with respect to both a row direction and a column direction. 4. The printed wiring board according to claim 3, wherein a distance between the electrode pad and a through hole land connected to the electrode pad is such that the through hole land and the through hole land are arranged. A printed wiring board for mounting a BGA package, which is set to be smaller than a distance between other electrode pads adjacent to each other in an oblique direction. 5. The printed wiring board according to claim 1, wherein the electrode pad and the through-hole land connected to the electrode pad are arranged in a row direction or a column direction in which the electrode pads are arranged. A printed wiring board for mounting a BGA package, which is arranged.