Semiconductor device manufacturing: process – Making device or circuit emissive of nonelectrical signal
Reexamination Certificate
1999-06-02
2001-05-08
Mulpuri, Savitri (Department: 2812)
Semiconductor device manufacturing: process
Making device or circuit emissive of nonelectrical signal
C438S558000, C438S795000
Reexamination Certificate
active
06228669
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an light emitting diode (LED) element used for display apparatus, indication lamp or similar applications, and particularly to an LED element that makes it possible to reduce man-hours required in the operation of mounting the LED element on a circuit board and allows high-density packaging on the circuit board.
2. Background Art
An example of a method for manufacturing an LED element
90
of the prior art is shown in
FIGS. 1 and 2
. First, as shown in
FIG. 1
, an N layer
91
b
of GaAsP and then an N+ layer
91
c
of GaAsP are formed on one side of a heavily-doped N type base layer
91
a
of GaP by diffusion or other proper means, thereby to obtain an LED substrate
91
. Insulation films
92
,
93
made of SiO
2
or the like are formed on the front and back sides of the LED substrate
91
, respectively. Provided in the insulation film
92
on the front side are apertures
92
a
at portions that will be subjected to a subsequent diffusion process.
The LED substrate
91
and a P-type diffusing substance
94
(for example Zn) are put into a quartz tube
81
under vacuum condition, as shown in
FIG. 2
, and subjected to heat treatment at a temperature from 700 to 800° C. This causes the P-type diffusing substance
94
to be diffused over the apertures
92
a
, thereby forming PN junctions
95
(refer to FIG.
3
).
After the process described above, the LED substrate
91
is taken out of the quartz tube
81
and undergoes such processes as removal of unnecessary portions of the insulation film
93
, formation of a P electrode
96
and an N electrode
97
and cut-off. Thus the LED element
90
as shown in
FIG. 3
is obtained. The LED element
90
thus obtained is mounted on a circuit board, a lead frame or the like to suit the application, fitted with wiring to the P electrode
96
using gold wire or the like and is provided with a case, thereby to make a product such as an LED display or LED lamp.
In the LED element
90
of the prior art described above, however, the P electrode
96
and the N electrode
97
are formed on different sides, the former on the front side and the latter on the back side, of the LED element
90
. Consequently, wiring for the electrodes
96
and
97
must be done separately in different processes. Thus the manufacturing processes for the LED element of this configuration becomes complicated.
Particularly the P electrode
96
, because of the location thereof being on the top surface of the LED element
90
when mounted, requires three-dimensional wiring that involves wires running over other components. This makes it necessary to provide a certain clearance around the LED element
90
, making it impossible to mount the LED elements
90
with a high density. As a result, there occurs such a problem that display quality cannot be improved due to the packaging density when a display apparatus is formed.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a method for manufacturing a planar mount LED element that makes it possible to simplify a wiring process when forming an LED display apparatus.
Another object of the present invention is to provide a method for manufacturing a planar mount LED element that makes it possible to arrange the manufactured LED elements with a high density and, as a result, to improve the display quality of an LED display apparatus.
Further another object of the present invention is to provide a planar mount LED element that can be used for achieving the objects described above.
The present invention provides a method a planar mount light emitting diode (LED) element comprising: forming a P type metal film at a predetermined portion on one surface of an N type LED substrate at a portion where a PN junction is to be formed on said surface of the N type LED substrate; forming an N type metal film at a predetermined portion on said surface of said N type LED substrate at a portion where an N electrode is to be formed on the surface of said N type LED substrate; covering said two films with an insulation film to form a capped construction; applying heat treatment at a diffusing temperature to the portion where the PN junction is to be provided, thereby to form the PN junction; irradiating a laser beam to the portion where the N electrode is to be provided, thereby to form a heavily-doped N type alloy portion that reaches said N type LED substrate; removing said insulation film; and forming the P electrode on said PN junction and forming the N electrode on said heavily-doped N type alloy portion, thereby to form the P electrode and the N electrode on the same side of the LED substrate.
While the method described above is applied to the N type LED substrate, the method may also be applied to a P type LED substrate by modifying the diffusing metal or the like.
The present invention also provides a planar mount LED element having at least a pair of P electrode and N electrode formed on the same side of the LED substrate made by the manufacturing method described above.
The manufacturing method described above makes it possible, first, to mount the P electrode and the N electrode formed on the same side of the LED element. This in turn makes it possible, when mounting the LED elements on a circuit board, to connect wirings of the P electrode and the N electrode on the board in a single process. Thus the manufacturing method simplifies the wiring process when assembling a display apparatus and achieves a remarkable effect of cost reduction.
Second, since the P electrode and the N electrode are formed on the same side of the LED element according to the manufacturing method of the present invention, the clearance that has been required in the prior art to be secured around the LED element for making wiring with gold wires can be minimized. Thus, according to the manufacturing method the density of mounting the LED elements can be increased when assembling a display apparatus having the LED elements arranged in a matrix, and achieves a remarkable effect also in improving the display quality.
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Kondo Hideo
Tamura Hiromoto
Mulpuri Savitri
Ostrolenk Faber Gerb & Soffen, LLP
Stanley Electric Co. Ltd.
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