Electricity: conductors and insulators – Boxes and housings – Hermetic sealed envelope type
Reexamination Certificate
1999-02-24
2002-08-06
Reichard, Dean A. (Department: 2831)
Electricity: conductors and insulators
Boxes and housings
Hermetic sealed envelope type
C174S050510, C257S783000, C257S787000
Reexamination Certificate
active
06429372
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a semiconductor device of surface mounting type having a BGA (Ball Grid Array) structure which is one kind of IC package, and relates to its fabrication method.
2. Description of the Related Art
In recent years, semiconductor devices are made to become higher in integration and functions, as the performance of electronic apparatuses becomes higher. Such higher integration and functions increase the total number of external terminals. The number of terminals (pins) is increased more and more. Such an advance of increased terminals causes a decrease in external terminal pitch. In packages such as the QFP (Quad Flat Package) of conventional semiconductor devices, therefore, there have occurred problems such as lowering in external terminal strength or aggravation in positional precision at the time of mounting.
In order to avoid the above described problems, therefore, there has been developed a semiconductor device using a plastic substrate called BGA, which is a package of surf ace mounting type having solder balls instead of external terminals of the package.
FIG. 1
is a sectional view showing a configuration example of a conventional semiconductor device of BGA type. An element plane of an IC chip (semiconductor chip)
1
is stuck to a thin chip mounting substrate
3
(which may be replaced by tape). The IC chip
1
is electrically connected to the chip mounting substrate
3
. On a back face of the chip mounting substrate
3
, a plurality of solder balls (ball electrodes)
4
are attached in a matrix form. These solder balls
4
are electrically connected to the IC chip
1
via wiring of the substrate
3
. The semiconductor device is mounted on a printed board (mounting board)
5
by soldering the solder balls
4
onto the printed board
5
.
If the printed board
5
having a semiconductor device of the conventional BGA structure mounted thereon as described above is housed in a casing or the like of an electronic apparatus and actually used, the temperature becomes high when the electronic apparatus is operating and the temperature returns to normal when not operating. A temperature cycle is thus generated. By this temperature cycle, therefore, the printed board
5
and the semiconductor substrate mounted thereon are warmed and cooled. At that time, a coefficient of thermal expansion (3.5 ppm) of the IC chip
1
made of silicon is different from a coefficient of thermal expansion (18 ppm) of the printed board
5
made of resin. In addition, the IC chip
1
is stuck to the substrate
3
securely.
Eventually, therefore, thermal stress caused by the above described difference in coefficient of thermal expansion is applied to the solder balls
4
. Because of fatigue of a metal in the solder balls
4
, a crack or the like is caused. This crack develops and results in breakdown of joint to the printed board
5
. Thus there is a fear of occurrence of an electric open circuit. If the above described temperature cycle is repeated a large number of times, electric connection between the printed board
5
and the semiconductor device becomes different from predetermined connection. There is a problem that a failure is caused by this.
Furthermore, the area of the substrate
3
cannot be made wider than the area of the IC chip
1
. Therefore when the IC chip
1
has a large number of functions and consequently a large number of solder balls
4
must be attached to the substrate
3
, the size of each of the solder balls must be made small. As a result, it becomes necessary to fabricate solder balls of various sizes. This results in a problem that the fabrication becomes troublesome and the cost of the solder balls
4
becomes high.
SUMMARY OF THE INVENTION
The present invention has been made in order to solve the above described problems of the conventional technique. An object of the present invention is to provide a semiconductor device and its fabrication method, capable of stably maintaining electric connection between a printed board and solder balls even if a temperature cycle is repeated, and capable of attaching a large number. of solder balls without reducing the size of the solder balls.
In order to achieve the above described object, there is provided a semiconductor device including a semiconductor chip, hangover portions formed by hardening resin on side planes of the semiconductor chips, insulative tape having signal wiring and ball electrodes electrically connected to the signal wiring on a main plane thereof, an adhesive agent layer having elasticity for sticking the semiconductor chips and the hangover portions to a back plane of the insulative tape, and insulative tape having signal wiring and ball electrodes electrically connected to the signal wiring on a main plane thereof, an adhesive agent layer having elasticity for sticking the semiconductor chips to a back plane of the insulative tape, and an electric connection portion for electrically connecting the semiconductor chips to the signal wiring of the insulative tape.
According to the invention, after ball electrodes of semiconductor chips are soldered to a printed board or the like and mounting is conducted, a temperature cycle is caused by operation and operation cease of the semiconductor chip. Since at this time the semiconductor chip made of silicon is different from the printed board made of resin in coefficient of thermal expansion, thermal stress occurs between them. According to the present invention, the adhesive agent layer has elasticity, and consequently the thermal stress is absorbed by the elasticity and it is not applied to the ball electrodes. As a result, little fatigue of a metal occurs in the ball electrodes. Since cracks are not generated, the ball electrodes do not come into an open state with respect to wiring of the printed board. Over a long period of time, therefore, electric connection between the semiconductor chip and the printed board is stably maintained via the ball electrodes. Furthermore, the area of the insulative tape can be increased by the area of the hangover portions as compared with the size of the semiconductor chip. As a result, a larger number of ball electrodes can be disposed on the insulative board without reducing the size of each of the ball electrodes.
In a preferred embodiment of the present invention, the adhesive agent layer has a Young's modulus value in the range of 1 MPa to 5000 MPa.
According to this embodiment, if the Young's modulus of the adhesive agent layer is smaller than 1 MPa, the elasticity of the adhesive agent layer is too great. When conducting wire bonding on the semiconductor chip to the insulative tape, therefore, the adhesive agent layer cannot support the insulative tape and consequently sufficient joint strength cannot be obtained. If the Young's modulus of the adhesive agent layer is larger than 5000 MPa, the elasticity of the adhesive agent layer is small. In this case, therefore, the stress caused between the semiconductor chip and the printed board by the temperature cycle cannot be absorbed. Consequently, fatigue of the metal in the ball electrodes advances in a short period of time, and the electric connection between the semiconductor chip and the printed board comes into an open state in a short period of time.
In a preferred embodiment of the present invention, the electric connection portion includes wires for connecting electrode pads of the semiconductor chip to electrode pads disposed on the signal wiring of the insulative tape, and a seal portion seals the electric connection portion with seal resin so as not to expose the wires.
According to this embodiment, the wires are buried within the seal resin, and are not exposed. Therefore, the wires are not cut, and the electric connection between the semiconductor chip and the insulative board can be stably maintained over a long period of time.
In a preferred embodiment of the present invention, resin forming the overhang portions of the semiconductor chip is resin of the same fami
Asada Jun-ichi
Iijima Toshitsune
Mino Toshikazu
Okumura Naohisa
Omori Jun
Kabushiki Kaisha Toshiba
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Oliva Carmelo
Reichard Dean A.
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