Incremental printing of symbolic information – Light or beam marking apparatus or processes – Scan of light
Reexamination Certificate
2001-05-29
2003-10-14
Pham, Hai (Department: 2861)
Incremental printing of symbolic information
Light or beam marking apparatus or processes
Scan of light
C347S232000, C347S247000
Reexamination Certificate
active
06633322
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a light emitting element array constructed by arraying a plurality of light emitting elements such as light emitting diodes in a row, an optical printer head using such a light emitting element array and a method for driving such an optical printer head.
FIG. 17
is a plan view showing a first conventional light emitting element array which is a semiconductor light emitting device used for the construction of an optical printer head, for example, as shown in Japanese Unexamined Patent Publication No. 61-205153. In
FIG. 17
, identified by
101
,
103
and
113
are a light emitting element array as a semiconductor light emitting device, light emitting elements which are light emitting diodes (LEDs), and electrode pads, respectively. An array of the light emitting elements
103
are integrated at a density of 10 to 48 per mm. The electrode pads
113
are provided in one-to-one correspondence with the light emitting elements
103
and are connected with external circuits via bonding wires. Accordingly, power from a power supply is supplied to the light emitting elements
103
via the bonding wires.
In order to ensure a space sufficient to enable the connection of the bonding wires, the electrode pads
113
are arranged in an offset manner at the opposite sides of a substrate
1
. For example, 64 to 256 light emitting elements
103
are monolithically formed per chip, thereby constructing one light emitting element array
101
. An optical printer head is constructed by mounting such light emitting element arrays
101
on one or a plurality of circuit boards.
FIG. 18
is a perspective view of a first conventional optical printer head constructed using the aforementioned first conventional light emitting element arrays
101
. In
FIG. 18
, identified by
101
are light emitting element arrays; by
110
a circuit board on which light emitting element arrays
101
are mounted; by
111
conductive patterns provided on the circuit board; by
112
bonding wires for connecting electrode pads
113
of the light emitting element arrays
101
and the conductive patterns
111
on the circuit board
110
; by
120
a flexible printed circuit (FPC); by
119
drivers for driving the light emitting element arrays
101
; and by
121
wiring portions from data input terminals of the drivers
119
. The conductive patterns
111
on the circuit board
110
are substantially at the same pitches as the light emitting elements
103
.
Such an optical printer head is assembled as follows. First, the light emitting element arrays
101
are mounted on and bonded to the circuit board
110
by die bonding and then the electrode pads
113
of the bonded light emitting element arrays
101
and the conductive patterns
111
on the circuit board
110
are connected by the bonding wires
112
. On the other hand, output wires (extending toward the light emitting element arrays
101
) of the drivers
119
connected with the FPC
120
by, e.g., inner lead bonding are connected with the conductive patterns
111
on the circuit board
110
by a laser or thermal adhesion. In this way, the light emitting elements
103
and the output wires of the drivers
119
have a one-to-one correspondence, and a current is supplied to the light emitting elements
103
via the bonding wires
112
. Signals and voltages are supplied to the light emitting elements
103
and the drivers
119
via the wiring portion
121
of the FPC
120
.
FIG. 19
is a perspective view of a second conventional optical printer head. In
FIG. 19
, identified by
101
a light emitting element array; by
112
bonding wires; by
119
drivers; and by
121
input wiring portions (input signal patterns) provided on a circuit board
110
to feed input signals to the drivers
119
.
The optical printer head shown in
FIG. 19
is assembled as follows. First, the light emitting element array
101
and the drivers
119
are mounted on and bonded to the circuit board
110
by, e.g., die bonding and then the electrode pads
113
of the light emitting element array
101
and output electrodes of the drivers
119
are directly connected in one-to-one correspondence by the bonding wires
112
.
On the other hand, similar to the output electrodes, input electrodes of the drivers
119
are directly connected with the input signal patterns
121
on the circuit board
110
via the bonding wires
112
.
A comparison of the aforementioned two conventional printer heads shows that they adopt different methods for connecting the drivers
119
and the light emitting element arrays
101
. Specifically, in the first conventional optical printer head, the output wiring portions of the drivers
119
are connected with the light emitting element array
101
after being bonded to the conductive patterns
111
on the circuit board
110
as shown in FIG.
18
. However, in the second conventional optical printer head, the drivers
119
and the light emitting element arrays
101
are directly bonded to each other as shown in FIG.
19
.
Further, the first and second conventional optical printer heads are similar in that the drivers
119
provided on two chips are used for driving the light emitting element array
101
provided on one chip to emit a light.
Although the electrode pads
113
of the light emitting element array
101
are generally arranged in an offset manner along the arranging direction of the light emitting elements
103
as shown in
FIG. 17
, they may be formed only at one side of the light emitting elements
103
(one-side output method). In such a case, the light emitting element array
101
formed on one chip can be driven to emit light by the driver
119
formed on one chip.
However, in the first and second conventional optical printer heads, since fairly high bonding pitch precision is required, it has been difficult to improve productivity of the optical printer head.
Also, in the first and second conventional optical printer heads, half the number to the same number of drivers as a total number of the light emitting element arrays are provided. This necessitates a large space for mounting many drivers on the circuit board and a mounting process, which hinders a reduction of production cost of the optical printer head.
Further, since the light emitting element arrays and the drivers are provided in parallel in the first and second conventional optical printer heads, it has been difficult to narrow a width of the optical printer head along a sub-scanning direction, which stands as a large hindrance to making the optical printer head smaller.
Furthermore, in the first conventional semiconductor light emitting device used for the first and second conventional optical printer head, precision of the wire bonding process and a limit in narrowing the pitches of the electrode pads stand as a large hindrance to narrowing the pitches between the light emitting elements. For example, it makes it difficult to realize a pitch of 22 &mgr;m or smaller between the light emitting elements which is required for 1200 dpi (dots/inch).
In view of this problem, a method for monolithically forming drivers on the light emitting element arrays
101
on which only the light emitting elements
103
and the electrode pads
113
were formed has been proposed to remarkably reduce the number of bonding as compared to the prior art, improve reliability, reduce production cost and enable high-quality printing resulting from the narrow-pitch-arrangement of the light emitting elements.
FIG. 20
is a plan view of a second conventional light emitting element array which is a semiconductor light emitting device used to construct an optical printer head, for example, as shown U.S. Pat. No. 4,587,717. Light emitting elements
103
which are GaP light emitting diodes, an output circuit
122
a
and a signal processing circuit
122
b
forming a driving circuit
122
for the light emitting elements
103
are monolithically formed on the same chip, i.e., a silicon substrate
102
. Image data from the output circuit
122
a
are fed in parallel, serial or serial/pa
Iwameji Kazuaki
Ogawa Motokazu
Sakai Hisashi
Kyocera Corporation
Pham Hai
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