Active solid-state devices (e.g. – transistors – solid-state diode – Housing or package
Reexamination Certificate
2000-12-15
2003-01-07
Fahmy, Wael (Department: 2823)
Active solid-state devices (e.g., transistors, solid-state diode
Housing or package
C257S777000, C257S785000, C257S794000
Reexamination Certificate
active
06504240
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to a semiconductor device having a wiring substrate formed by using glass fabrics impregnated with resin. More particularly, the present invention relates to a semiconductor device in which pad electrodes formed on the wiring substrate and projected electrodes or bump electrodes of a semiconductor pellet are opposed and superposed, and the pad electrodes and the projected electrodes superposed on each other are pressed toward each other and heated to electrically couple the projected electrodes and the pad electrodes.
BACKGROUND OF THE INVENTION
It is desired that portable type electronic circuit devices, such as a note type personal computer, a portable telephone and the like, are compact and lightweight. Therefore, the external size of each electronic component used in the portable type electronic devices is reduced by reducing the sizes of one or more electronic parts used in the electronic component. In other way, each electronic component is substantially downsized by increasing the mounting density of the electronic parts included in the electronic component although the external size of the electronic component is the same as before.
Also, each lead as an electrode for coupling the electronic component and an external circuit is shaped into a surface mountable form and, thereby, projection length of the lead is reduced. Further, each lead is replaced by a projection type electrode such that an external size of the electronic component can be reduced as small as possible. In this way, the electronic components are downsized.
As an example of such electronic components, a semiconductor device having a Chip Size Package (CSP) structure is generally used. In the semiconductor device having the CSP structure, a semiconductor pellet is flip-chip bonded on a wiring substrate and the semiconductor pellet and the wiring substrate are bonded by using resin.
With reference to the drawings, an explanation will be made on a conventional semiconductor device having the CSP structure.
FIG. 3
is a side cross sectional view showing a schematic structure of a conventional semiconductor device having the CSP structure. The conventional semiconductor device
110
shown in
FIG. 3
comprises a wiring substrate
104
, and a semiconductor pellet
101
mounted on the wiring substrate
104
. The semiconductor pellet
101
has a semiconductor substrate
102
and many projected electrodes
103
formed on one of the main surfaces of the semiconductor substrate
102
. In the semiconductor substrate
102
, a number of electronic elements (not shown in the drawing) are formed and wired internally to form circuits.
A wiring substrate
104
comprises an insulating substrate
105
, pad electrodes
106
formed on one of the main surfaces of the insulating substrate
105
, and electrodes
107
for external connection formed on the other of the main surfaces of the insulating substrate
105
. The pad electrodes
106
are formed at locations corresponding to those of the projected electrodes
103
of the semiconductor pellet
101
. The pad electrodes
106
are electrically coupled with the electrodes
107
for external connection via conductor patterns not shown in the drawing.
The projected electrodes
103
of the semiconductor pellet
101
are superposed on the pad electrodes
106
of the wiring substrate
104
and coupled therewith by soldering, pressure welding, thermal compression bonding or ultrasonic bonding. Thereby, the projected electrodes
103
and the pad electrodes
106
are electrically connected to each other. Also, the semiconductor pellet
101
and the wiring substrate
104
are bonded by resin
108
.
Further, on each of the electrodes
107
for external connection, there is formed a solder ball
109
. Each of the solder balls
109
is shaped into a spherical form by melting a solder on the electrode
107
for external connection.
In the semiconductor device
110
, only a main portion of the semiconductor pellet
101
is bonded to the wiring substrate
104
by using a minimum necessary amount of resin
108
. Thereby, it becomes possible to reduce the external size of the semiconductor device.
As a semiconductor device of this kind, there is proposed a semiconductor device which has still higher mount density. In such semiconductor device, for example, electrodes are further formed on the other of the main surfaces of the semiconductor pellet
101
, and another semiconductor pellet is coupled to the electrodes. Alternatively, another semiconductor pellet is mounted on the surface of the wiring substrate
104
on which surface the solder balls
109
are formed.
In the conventional semiconductor device, coefficients of thermal expansion differ largely among the semiconductor pellet
101
, the wiring substrate
104
and the resin
108
. Therefore, at a high temperature, the wiring substrate
104
warps due to the bimetal effect. Thus, stress concentrates into coupling portions of the electrodes
103
and
106
, so that there is a possibility that the projected electrodes
103
peel off from the joined interface portion of the electrodes
103
and the electrodes
106
, or the projected electrodes
103
peel off from the semiconductor substrate
102
. Therefore, there is a possibility that electrical connection between the semiconductor pellet
101
and the wiring substrate
104
is damaged. In order to avoid such disadvantages, in the resin
108
, filler such as silica, alumina and the like which has a thermal expansion coefficient close to that of the semiconductor pellet
101
is dispersed within base resin such as epoxy resin and the like. Thereby, a thermal expansion coefficient of the base resin is lowered, and the effect of difference of the thermal expansion coefficients between the semiconductor pellet
101
and the wiring substrate
104
is reduced.
As an insulating substrate
105
used in the wiring substrate
104
, an insulating board is generally known which is fabricated by impregnating resin into a laminated glass fabric body and curing the resin. The laminated glass fabric body are fabricated by stacking a plurality of glass fabrics each of which is made by weaving glass fibers into a cloth.
Also, in each of Japanese patent laid-open publication No. 6-204632 (hereafter referred to as prior art 1) and Japanese patent laid-open publication No. 7-112506 (hereafter referred to as prior art 2), there is disclosed a metal-clad laminated board for a printed circuit board. In the metal-clad laminated board disclosed in these publications, a surface resin layer having a low modulus of elasticity is disposed between a substrate layer of glass fabrics impregnated with epoxy resin and a metal layer formed on a surface of the metal-clad laminated board. Therefore, even when a temperature of the environment in which the metal-clad laminated board is used becomes high and the difference of thermal expansion coefficients between a wiring substrate and surface mounted devices becomes large, the surface resin layer which is in a rubber-like state deforms and a stress caused by the difference of the thermal expansion coefficients between the surface mounted devices and the wiring substrate is mitigated. Therefore, it is possible to prevent a stress from occurring in the solder coupling portions between the surface mounted devices and the wiring substrate.
Here, the inventor of the present invention considered on the case a semiconductor device shown in
FIG. 3
is fabricated by using the wiring substrate disclosed in the prior art 1 and prior art 2, and found the following fact.
As a method of coupling the projected electrodes
103
and the pad electrodes
106
, it is considered possible to form the projected electrodes
103
by using solder balls and to couple the projected electrodes
103
and the pad electrodes
106
by melting the solder balls. In this case, even if the wiring substrate
104
is heated when coupling the electrodes
103
and
106
, there occurs no problem. However, as another method of coupling the electrodes
103
Choate Hall & Stewart
Coleman William David
Fahmy Wael
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