Active solid-state devices (e.g. – transistors – solid-state diode – Combined with electrical contact or lead – Chip mounted on chip
Reexamination Certificate
1998-10-05
2002-08-27
Potter, Roy (Department: 2822)
Active solid-state devices (e.g., transistors, solid-state diode
Combined with electrical contact or lead
Chip mounted on chip
C257S723000, C257S786000, C257S784000
Reexamination Certificate
active
06441495
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a semiconductor device comprising a plurality of semiconductor chips stacked in the direction of thickness, and a method for making the same.
2. Background Art
There is known a type of semiconductor device in which a plurality of semiconductor chips are stacked and sealed in a resin package for drastically increased circuit mounting density. Such a semiconductor device is called “chip-on-chip” type because of the stacking arrangement in which one of the chips is mounted on another.
FIG. 29
shows an arrangement of a prior art chip-on-chip semiconductor device. As understood from the figure, in this arrangement, a plurality of semiconductor chips
9
a-
9
c
are stacked successively on a surface of a substrate
90
. According to such an arrangement, an area occupied by the semiconductor chips
9
a-
9
c
on the surface of substrate
90
is small, advantageously increasing the mounting density of the semiconductor devices.
However, the prior art has following problems.
Specifically, when the plurality of semiconductor devices
9
a-
9
c
are stacked, respective electrodes
94
a-
94
c
are elevated accordingly to higher locations. As a result, the electrodes
94
c
of the highest semiconductor
9
c
are located disadvantageously high (height difference Ha), away from the surface of substrate
90
formed with terminals
92
to which the electrodes
94
a-
94
c
are to be connected via respective pieces of wire
93
.
Under such a situation, it is sometimes difficult to make a proper connection between the electrode
94
c
and the terminal
92
because of the big height difference Ha. Specifically, in a conventional wirebonding machine, a capillary can perform a proper bonding only within a vertical range of ±300 &mgr;m away from its baseline height. Sometimes, however, the height difference Ha is greater than the upper limit (i.e. greater than the baseline height added with +300 &mgr;m), making it impossible to use the wirebonding machine for the wirebonding operation. In addition, when the height difference Ha is large, as shown in
FIG. 30
, the capillary
95
has to be significantly tilted when the capillary
95
presses the wire
93
to the electrode
94
c
or the terminal
92
. Under such a circumstance, there develops a space S between a tip portion of the capillary
95
and the electrode or the terminal, making it impossible to properly bond the wire
93
. As a result, according to the prior art, it is difficult to properly bond an end of the wire
93
to the electrodes
94
a-
94
c
or the terminal
92
, and there is a significant risk of causing a faulty connection at the location where the wire is bonded.
DISCLOSURE OF THE INVENTION
It is therefore an object of the present invention to provide a semiconductor device of a chip-on-chip type which allows proper connection via wire between the electrodes in each of the semiconductor chips and respective terminals.
Another object of the present invention is to provide a semiconductor device of a chip-on-chip type which allows more appropriate connection between the electrodes in each of the semiconductor chips and corresponding terminals.
According to a first aspect of the present invention, there is provided a semiconductor device with a following arrangement. Specifically, the semiconductor device comprises a plurality of semiconductor chips stacked in the direction of thickness. Each of the semiconductor chips includes an upper surface formed with electrodes. The semiconductor device further comprises a plurality of terminal portions beside the semiconductor chips, and plural pieces of wire for electrical connection from the electrodes to respective terminal portions. Further, each of the terminal portions is at an elevation lower than the highest electrodes, and higher than the lowest electrodes.
According to the above arrangement, it becomes possible to decrease the height difference between each of the electrode on the semiconductor chips and corresponding one of the terminal portions to be connected via the wire, even if there is a large height difference between the uppermost electrodes and the lowermost electrodes in the stack of plural semiconductor chips. Therefore, it becomes possible to properly connect all of the electrodes on each of the semiconductor chips to respective terminal portions by means of wirebonding, within the vertical moving range of the capillary of the wirebonding machine. Further, it becomes possible to press the capillary of the wirebonding machine to each of the electrodes and terminal portions at a smaller angle of tilt so that the wire can be tightly pressed against the surface of the electrode or terminal portion.
According to a preferred embodiment, the wire is bonded to the electrode as the first bonding, and thereafter to the terminal portion as the second bonding.
Further, according to the preferred embodiment, the plurality of semiconductor chips are mounted on a die-pad portion of a lead frame. The lead frame has internal lead portions formed beside the die-pad portion for serving as the terminal portions, and the die-pad portion is lower in elevation than the internal lead portion by a predetermined distance.
According to another preferred embodiment of the semiconductor device, the semiconductor device includes a first semiconductor chip disposed at a lower elevation and a second semiconductor chip disposed at a higher elevation. The first semiconductor chip and the second semiconductor chip are stacked via a plate type supporting member, and the plate type supporting member is formed with the plurality of terminal portions, as well as openings for the wire to communicate between the terminal portions and the electrodes of the first semiconductor chip for electrical connection.
The supporting member may be a film type substrate made of a thin film of synthetic resin formed with a conductive wiring region, a lead frame made of a metal, or a plate type substrate having a surface formed with a conductive wiring region.
According to the preferred embodiment, the first semiconductor chip and the second semiconductor chip are stacked to sandwich the plate type supporting member.
According to another preferred embodiment, the second semiconductor chip is smaller than the first semiconductor chip, and the two semiconductor chips being directly stacked together. Further, the second semiconductor chip and the electrodes of the first semiconductor chip face the opening, and the upper surface of the first semiconductor chip has its circumferential region bonded to a lower surface of the plate type supporting member.
It should be noted here that the second semiconductor chip may be stacked by another or a plurality of semiconductor chips other than the second semiconductor chip or the first semiconductor chip.
According to a second aspect of the present invention, there is provided a semiconductor device having a following arrangement. Specifically, the semiconductor device comprises a plurality of semiconductor chips stacked in the direction of thickness, and a plate type supporting member for supporting the plurality of semiconductor chips. The plate type supporting member is formed with terminal portions for electrical connection with the semiconductor chips. The plate type supporting member is at an intermediate elevation between an uppermost surface and a lowermost surface of the stack of semiconductor chips. The supporting member is a film type substrate made of a thin film of synthetic resin formed with a conductive wiring region, a lead frame made of a metal, or a plate type substrate having a surface formed with a conductive wiring region.
According to the above arrangement, it becomes possible to keep the height difference between the electrodes on each of the semiconductor chips and the terminal portions on the plate type supporting member corresponding not greater than a predetermined distance. Thus, connection can be properly made between the electrodes and the terminal portions by means
Hiromitsu Masaaki
Oka Hiroshi
Potter Roy
Rohm & Co., Ltd.
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