Electronic-component mounting structure

Details Electronic-component mounting structure Electronic-component mounting structure

1999-09-20

2001-12-11

Gaffin, Jeffrey (Department: 2841)

Electricity: electrical systems and devices

Housing or mounting assemblies with diverse electrical...

For electronic systems and devices

C361S774000, C029S840000, C257S737000, C257S738000, C257S774000, C257S778000, C257S786000, C174S260000

Reexamination Certificate

active

06330166

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention generally relates to a structure in which an electronic component and a base board are connected by an array of solder bumps provided on one surface of the electronic component. This invention particularly relates to an electronic-component mounting structure suited for use in a portable electronic apparatus.
2. Description of the Related Art
There are known techniques for increasing the life time of interconnecting solder bumps in BGA-package (ball grid array package) mounting structures.
Japanese published unexamined patent application 7-321247 discloses a BGA-package mounting structure. In Japanese application 7-321247, electrodes in an array on one side of a BGA package have elliptical shapes whose major axes correspond to dimensions along lines passing through the centers of deformations caused by thermal distortions. In addition, electrodes in an array on a base board have elliptical shapes substantially equal to those of the package electrodes. The package electrodes and the base-board electrodes are connected by solder balls. The BGA-package mounting structure in Japanese application 7-321247 suppresses the adverse affection of thermal distortions on the interconnecting solder balls, and thereby increases the life time of the interconnecting solder balls.
In general, a portable electronic apparatus is sometimes subjected to a mechanical shock. For example, when the portable electronic apparatus is accidentally dropped, such a mechanical shock occurs. Conventional solder bumps tend to be damaged by 5 mechanical shocks. Thus, it is desirable that portable electronic apparatuses use solder bumps which withstand mechanical shocks.
In the BGA-package mounting structure of Japanese application 7-321247, since the package electrodes and the base-board electrodes are substantially equal in shape, the solder bumps (the solder balls) have barrel-like shapes of
FIG. 33
after a reflowing process is complete. The barrel-like solder bumps have such angles of contact with the electrodes that stresses tend to be applied to the bumps by mechanical shocks. Thus, it seems that the interconnecting solder bumps in the BGA-package mounting structure of Japanese application 7-321247 are easily damaged by mechanical shocks.
Japanese published unexamined patent application 9-45733 discloses a method of mounting electronic components. According to the method in Japanese application 9-45733, electrodes on an electronic component are connected to electrodes on a base board by solder bumps. After a reflowing process is complete, some of the interconnecting solder bumps have drum-like shapes with constricted middle portions as shown in FIG.
34
. The constricted middle portions cause low strengths of the interconnecting solder bumps. Thus, the interconnecting solder bumps in Japanese application 9-45733 seem to be short in life time.
SUMMARY OF THE INVENTION
It is an object of this invention to provide an improved electronic-component mounting structure.
A first aspect of this invention provides an electronic-component mounting structure comprising an electronic component (
2
) having a surface; first electrodes (
1
) provided on the surface of the electronic component (
2
) and arranged in a first array; a base board (
4
); second electrodes (
3
) provided on the base board (
4
) and arranged in a second array corresponding to the first array, the second electrodes (
3
) corresponding to the first electrodes (
1
) respectively; and solder bumps (
9
) connecting the first electrodes (
1
) and the second electrodes (
3
) respectively; wherein the first electrodes (
1
) include first outermost electrodes (
1
b
) located in an outer area of the first array, and the second electrodes (
3
) include second outermost electrodes (
3
b
,
3
c
) located in an outer area of the second array, the second outermost electrodes (
3
b
,
3
c
) corresponding to the first outermost electrodes (
1
b
) respectively; wherein an outer edge (X
1
, Z
1
) of each of the second outermost electrodes (
3
b
,
3
c
) extends outward of an outer edge (Y
1
) of a corresponding first outermost electrode (
1
b
) with respect to the first and second arrays; and wherein a distance between an outer edge (X
1
, Z
1
) of each of the second outermost electrodes (
3
b
,
3
c
) and an outer edge (Y
1
) of a corresponding first outermost electrode (
1
b
) is greater than a distance between an inner edge (X
2
, Z
2
) of the second outermost electrode (
3
b
,
3
c
) and an inner edge (Y
2
) of the corresponding first outermost electrode (
1
b
) with respect to the first and second arrays.
A second aspect of this invention provides an electronic-component mounting structure comprising an electronic component (
2
) having a surface; first electrodes (
1
) provided on the surface of the electronic component (
2
) and arranged in a first array; a base board (
4
); second electrodes (
3
) provided on the base board (
4
) and arranged in a second array corresponding to the first array, the second electrodes (
3
) corresponding to the first electrodes (
1
) respectively; and solder bumps (
9
) connecting the first electrodes (
1
) and the second electrodes (
3
) respectively; wherein the first electrodes (
1
) include first outermost electrodes (
1
b
) located in an outer area of the first array, and the second electrodes (
3
) include second outermost electrodes (
3
b
,
3
c
) located in an outer area of the second array, the second outermost electrodes (
3
b
,
3
c
) corresponding to the first outermost electrodes (
1
b
) respectively; and wherein an angle (&thgr;1) between a surface of each of the second outermost electrodes (
3
b
,
3
c
) and a surface of a corresponding solder bump (
9
) at an outer edge (X
1
, Z
1
) of the second outermost electrode (
3
b
,
3
c
) is acute, and is different from an angle (&thgr;2) between a surface of the second outermost electrode (
3
b
,
3
c
) and a surface of the corresponding solder bump (
9
) at an inner edge (X
2
, Z
2
) of the second outermost electrode (
3
b
,
3
c
) with respect to the first and second arrays.
A third aspect of this invention is based on the second aspect thereof, and provides an electronic-component mounting structure wherein the first electrodes (
1
) have a greater strength of bond to the solder bumps (
9
) than a strength of bond between the second electrodes (
3
) and the solder bumps (
9
).
A fourth aspect of this invention provides an electronic-component mounting structure comprising an electronic component (
2
) having a surface; first electrodes (
1
) provided on the surface of the electronic component (
2
) and arranged in a first array; a base board (
4
); second electrodes (
3
) provided on the base board (
4
) and arranged in a second array corresponding to the first array, the second electrodes (
3
) corresponding to the first electrodes (
1
) respectively; and solder bumps (
9
) connecting the first electrodes (
1
) and the second electrodes (
3
) respectively; wherein the first electrodes (
1
) have a greater strength of bond to the solder bumps (
9
) than a strength of bond between the second electrodes (
3
) and the solder bumps (
9
); wherein the first electrodes (
1
) include first outermost electrodes (
1
b
) located in an outer area of the first array, and the second electrodes (
3
) include second outermost electrodes (
3
b
,
3
c
) located in an outer area of the second array, the second outermost electrodes (
3
b
,
3
c
) corresponding to the first outermost electrodes (
1
b
) respectively; and wherein an outer edge (X
1
, Z
1
) of each of the second outermost electrodes (
3
b
,
3
c
) extends outward of an outer edge (Y
1
) of a corresponding first outermost electrode (
1
b
) with respect to the first and second arrays.
A fifth aspect of this invention is based on the first aspect thereof, and provides an electronic-component mounting structure wherein the second electrodes (
3
) have greater areas of bond to the solder bumps (
9
) than areas of bond between the first electrodes (
1
) an

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