Active solid-state devices (e.g. – transistors – solid-state diode – Lead frame – With structure for mounting semiconductor chip to lead frame
Reexamination Certificate
2001-06-29
2004-10-19
Thomas, Tom (Department: 2815)
Active solid-state devices (e.g., transistors, solid-state diode
Lead frame
With structure for mounting semiconductor chip to lead frame
C257S687000, C257S690000, C257S701000, C257S738000
Reexamination Certificate
active
06806560
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a semiconductor device and a method for fabricating the same, and especially to a semiconductor device in which a semiconductor chip is assembled into a printed circuit board and a method for fabricating the same.
BACKGROUND OF THE INVENTION
In recent years, an electronic device has come to be integrated with high density, and a semiconductor chip with multiple terminals is packaged in accordance with an improvement of the function and thinning of an electronic circuit. Accordingly, a package of the semiconductor chip used in the electronic circuit is miniaturized and provided with multiple pins. In conformity with the aforementioned tendency, the semiconductor chip is assembled into a printed circuit board by means of a package of an area array type, such as a ball grid array package (BGA), a chip scale package (CSP) or a bare chip package (a flip chip package, FC).
FIG. 1
shows a typical example of the structure of the aforementioned packages of the semiconductor chips. In the package shown in
FIG. 1
, a chip-mounting substrate
103
on which a semiconductor chip
100
has been mounted by means of wire-bonding is assembled into a printed circuit board
104
by CSP, where the chip-mounting substrate
103
is composed of an insulating substrate
101
formed of ceramics, polyimide, etc. and conductor wirings
102
.
In the package having the aforementioned structure, a clearance formed between the chip-mounting substrate
103
and the printed circuit board
104
is filled with underfill material
105
in order to absorb a stress caused by a difference in the thermal expansion coefficient between the chip-mounting substrate
103
and the printed circuit board
104
and impacts caused by fallings to secure the reliability of soldered jointed portions.
However, if alien substances mix with underfill material
105
or the impacts exert on under fill material
105
for a long period of time, an adhesive strength of underfill material
105
is lowered, and underfill material
105
may exfoliate form the surface of the chip-mounting substrate
103
or of the printed circuit board
104
.
If underfill material
105
exfoliates from the chip-mounting substrate
103
or the printed circuit board
104
, since the stress concentrates on joined portions of the solder balls
106
, cracks occur on pads
107
,
108
which are respectively formed on surfaces of the chip-mounting substrate
103
and the printed circuit board
104
, and the joined portions become disincentive. As mentioned in the above, the reliability of the semiconductor device is lowered because of lowering of the adhesive strength of underfill material
105
.
In Japanese Patent Applications, Laid-Open, No.63-94646, an electronic device in which unevennesses are respectively provided for a predetermined part of a chip-mounting substrate and sealing resin for sealing a semiconductor chip is disclosed as a means for increasing an adhesive strength between the chip-mounting substrate and the basic substrate. That is to say, in the aforementioned semiconductor device, concave portions and convex portions are alternately formed on the chip-mounting substrate and on sealing resin for covering the semiconductor chip, and the chip-mounting substrate on which the semiconductor chip is mounted is buried in a cavity formed in the basic substrate. Accordingly, the aforementioned technology cannot be applied to a package of an area array type.
Although a semiconductor device in which a bonding wire is prevented from being disincentive by providing unevenness for a pad is disclosed in Japanese Patent No.2973988, underfill material is not prevented from being exfoliated according to this technology.
In a semiconductor device in which a semiconductor chip mounted on a lead frame is assembled into a printed circuit board, since there is a difference in a thermal expansion coefficient between the lead frame and a pad of the printed circuit board, the lead frame may exfoliate from the printed circuit board at a contact surface therebetween because of an impact caused by a thermal shock.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the invention to provide a semiconductor device in which a chip-mounting substrate or a lead frame adheres to a printed circuit board tightly, and a method for fabricating the same.
It is a further object of the invention to provide a semiconductor device operating in an electronic circuit with high reliability, and a method for fabricating the same.
A semiconductor device concerned with the first viewpoint of the invention comprises:
a semiconductor chip,
a chip-mounting substrate which is provided with the semiconductor chip mounted on a top surface thereof and the first conductive pads formed on a bottom surface thereof and connected with the semiconductor chip electrically,
solder balls formed on the first conductive pads,
a printed circuit board on which second conductive pads connected with the solder balls are formed, and
underfill material injected into a clearance formed between the chip-mounting substrate and the printed circuit board,
wherein unevenness is formed on a surface which is brought into contact with the underfill material of at least one of the chip-mounting substrate and the printed circuit board.
According to the aforementioned structure, since an area of a contact surface between the chip-mounting substrate and underfill material increases, an adhesive strength between the chip-mounting substrate and underfill material is heightened. Accordingly, the chip-mounting substrate becomes hard to exfoliate from underfill material, and an adhesive strength between the chip-mounting substrate and the printed circuit board is heightened. Moreover, since the adhesive strength between the chip-mounting substrate and the printed circuit board is heightened, a disconnection between the solder ball and the pad becomes hard to occur. Accordingly, the semiconductor device operating in the electronic circuit with high reliability can be obtained.
The aforementioned unevenness may be selectively formed on the first conductive pads or on the second conductive pads.
Moreover, the aforementioned unevenness may be shaped into a slit-like configuration or into a dimple-like configuration.
A semiconductor device concerned with the second view point of the invention comprises:
a semiconductor chip,
a lead frame which is provided with the semiconductor chip mounted thereon and electrically connected with the semiconductor chip, and
a printed circuit board including the third conductive pads which are formed thereon and brought into contact with the lead frame,
wherein at least one of the lead frame and the printed circuit board is provided with unevennesses at contact surfaces therebetween.
According to the aforementioned structure, since an area of a contact surface between the lead frame and the printed circuit board increases, the lead frame becomes hard to exfoliate from the printed circuit board, and the adhesive strength between the lead frame and the printed circuit board is heightened. Moreover, since the adhesive strength between the lead frame and the printed circuit board is heightened, a jointed portion between the lead frame and the printed circuit board becomes hard to be disincentive. Accordingly, the semiconductor device operating in the electronic circuit with high reliability can be obtained.
A method for fabricating a semiconductor device concerned with the third viewpoint of the invention comprises the steps of:
forming the fourth conductive pads on a bottom surface of a chip-mounting substrate,
forming unevenness on the bottom surface of the chip-mounting substrate,
mounting a semiconductor chip on a top surface of the chip-mounting substrate,
connecting the semiconductor chip with the fourth conductive pads electrically,
forming solder balls on the fourth conductive pads,
assembling the chip-mounting substrate into a printed circuit board by connecting solder balls with the fifth conductive pads formed on the printed circuit board, and
inj
Chu Chris C.
McGinn & Gibb PLLC
NEC Corporation
Thomas Tom
LandOfFree
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