Driver IC

Details Driver IC Driver IC

1999-09-28

2001-02-27

Zweizig, Jeffrey (Department: 2816)

Miscellaneous active electrical nonlinear devices, circuits, and

Specific identifiable device, circuit, or system

Integrated structure

C327S515000

Reexamination Certificate

active

06194960

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a driver IC having a group of drive elements that individually drive external elements such as light-emitting diodes for an exposing unit for an electrophotographic printer, heat-generating resistors for a thermal printer, display elements for a display.
2. Description of the Related Art
One conventional driver IC is an LED driver IC that drives a plurality of light-emitting diodes (LED) of an LED array. The LED driver ICs and LED arrays are combined to form an LED head for use in the electrophotographic printer.
FIG. 17
illustrates a layout of the conventional driver IC fabricated using the technique disclosed in Japanese Patent Preliminary Publication (KOKAI) No. 6-297765.
FIG. 17
also shows a see-through view of a layout of an LED array
100
for convenience of explanation. The LED array
100
includes 192 LEDs. Each chip of the driver IC
400
drives 192 LEDs.
The driver IC includes a shift register
201
, a set of latches
202
, a set of pre-buffers
204
, a set of drive transistors
205
, a set of input electrode pads
210
, a set of drive electrode pads
220
, a supply electrode
230
, and supply electrode pads
431
. The shift register
201
includes flip-flops FF
1
-FF
192
. The set of latches
202
includes latches LT
1
-LT
192
. The set of pre-buffers
204
includes pre-buffers G
1
-G
192
. The set of drive transistors
205
includes drive transistor Tr
1
-Tr
192
. The set of drive electrode pads
220
includes drive electrode pads DO
1
-DO
192
. The reference “A” denotes the region between even-numbered drive electrode pads (DO
2
, DO
4
, . . . , DO
192
) and the supply electrode
230
.
The driver IC
400
is in the shape of a rectangle chip having long sides and short sides. The set of the drive electrode pads
220
extends along one of the long sides of the driver IC
400
and includes drive electrode pads DO
1
-DO
192
arranged in two rows with one row staggered with respect to the other. The drive electrode pads DO
1
-DO
192
are used to drive 192 LEDs of the LED array
100
, each pad being connected to a corresponding LED. The sets of input electrode pads
210
are aligned along the other long side of the driver IC
400
and receive signals from outside.
The shift register
201
, set of latches
202
, set of pre-buffers
204
, set of drive transistors
205
are aligned in this order from the input electrode pads
210
side to the drive electrode pads
220
side. The flip-flops FF
1
-FF
192
, latches LT
1
-LT
192
, pre-buffers G
1
-G
192
, and drive transistors Tr
1
-Tr
192
are all aligned in the direction of the long side of the driver IC
400
at the same intervals as the drive electrode pads
220
.
The supply electrode
230
is an aluminum electrode having a width W, and is formed between the set of drive transistors
205
and the set of pre-buffers
204
. The supply electrode
230
extends from one short side of the driver IC
400
to the other in the direction of the long side of the driver IC
400
.
Provided on the supply electrode
230
are two electrode pads
431
via which drive supply VDDH is supplied from outside. The sources of the drive transistors Tr
1
-Tr
192
are connected to corresponding nearby supply electrodes
230
.
The two supply electrode pads
431
are at locations corresponding to the drive transistors T
64
and Tr
132
, respectively.
The LED array
100
is in the shape of a rectangle chip having long sides and short sides, and has a set of anode electrode pad
120
that includes anode electrode pads LI
1
-LI
192
. The set of the anode electrode pads
120
extends along one of the long sides of the chip of LED array
100
. The anode electrode pads LI
1
-LI
192
are arranged in two rows with one row staggered with respect to the other. The anode electrode pads LI
1
-LI
192
are connected to the corresponding drive electrode pads DO
1
-DO
192
using a later described ACF. An i-th anode electrode pad LIi is at a location corresponding to an i-th drive electrode pad DOi. The input electrode pads
210
are aligned along the other long side of the LED array
100
.
FIG. 18
is a lateral cross-sectional view of a chip module having the LED array
100
and prior art driver IC
400
, taken along lines C-C′ of FIG.
17
.
Referring to
FIG. 18
, there are provided light emitting elements
101
, individual anode electrodes (Al electrode)
102
, and anode electrode pads (Al electrode pad)
103
on the surface of the LED array
100
. Each combination of light emitting element
101
, individual anode electrode
102
, and anode electrode pad
103
forms one of a plurality of LEDs. Each anode electrode pad
103
is connected to a corresponding anode electrode pad (LI
1
-LI
192
) of FIG.
17
. There is provided a common cathode electrode
104
on the opposite surface of the LED array
100
.
The LED array
100
has LEDs of an end-surface emission type in which light is emitted in a direction parallel to the surface of the pn junction of the light emitting element
101
. The anode electrode pad
103
is formed in integrally continuous with the anode electrode
102
, and is connected to one end of a corresponding drive electrode pad
221
of the driver IC
400
. The other end of the anode electrode
102
is connected to the p-type region of the light-emitting element
101
. The common cathode electrode
104
is connected to the n-type region of all the light emitting elements
101
(i.e., n-type substrate of the LED array).
The driver IC
400
has the input electrode pad
211
that is a part of the set of input electrode pad
210
(FIG.
17
), the drive electrode pad
221
that is a part of the set of drive electrode pads
220
(FIG.
17
), and the supply electrode pad
431
.
The input electrode pad
211
includes an Al-electrode pad
211
a
and an Au (gold)-bump
211
b
formed on the Al electrode pad
211
a
. The drive electrode pad
221
is the i-th drive electrode pad DOi of FIG.
17
and includes an Al-electrode pad
221
a
and an Au (gold)-bump
221
b
formed on the Al electrode pad
221
a.
The supply electrode pad
431
includes an Al-electrode pad
431
a
and an Au-bump
431
b
. The Al-electrode pad
431
a
is on an area of the supply electrode
230
near the drive transistor Tr
132
(i.e., near drive electrode pad DO
132
).
The set of drive electrode pads
220
of the driver IC
400
is electrically connected with the LED array
100
through an anisotropic conductive film (referred to ACF), thereby forming a chip module. Dispersing electrically conductive gold-plated particles
303
b
in a thermosetting ACF resin
303
a
forms an ACF
303
.
The driver IC
400
and LED array
100
are connected in an ACF connection process as follows:
The LED array is placed on the driver IC with the ACF sandwiched between the anode electrode pads
103
and the drive electrode pads
221
. The LED array is mounted to the driver IC such that the anode electrode pads
103
of the LED array
100
are aligned with the corresponding drive electrode pads
221
of the driver IC
400
. Then, the assembly of the driver IC
400
and LED array
100
is heated so that the ACF resin
303
a
is softened. Then, the LED array
100
is pressed against the driver IC
400
and the assembly is again heated at an elevated temperature. Thereafter, the assembly is cooled so that the ACF resin is set. In this manner, the both chips are mechanically bonded to each other and the gaps between the two are sealed. The conductive particles
303
b
sandwiched between the anode electrode pads
103
and Au-bumps
221
b
allows electrical connection between anode electrode pads
103
and corresponding drive electrode pads
221
without using wires.
The chip module is bonded to a printed circuit in the die-bonding process. During the die-bonding process, the input electrode pads
211
and the supply electrode pads
431
of the driver IC
400
are connected to corresponding signal output electrode pads and supply electrode pads on the printed circuit board through bonding wires (gold wires)
302
a
and
302

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