Method of Making Display Structure Having Light Emitting Diodes

This invention relates to a novel method of making a display device of the type having a light emitting semiconductor diode in which the diode is securely supported by a simple structure.

It is an object of the present invention to provide a novel method for making a display device in which a semiconductor element is securely supported by supporting members for solid connection to conductive members with a simple construction.

Another object of this invention is to provide a novel method of making a display device having a light emitting diode with positive and negative electrodes and in which the diode has its electrodes easily and positively soldered to conductive members.

A further object of the present invention is to provide a novel method for making a display device which has an effective enlargement when being observed.

Yet another object of this invention is to provide a novel method of making a display device which is easy to manufacture and low in cost.

Additional and other objects, features and advantages of this invention will be apparent from the following description, taken in conjunction with the accompanying drawings.

FIGS. 1A, 1B and 1C are diagrammatic sectional views of initial steps in one embodiment of the present invention;

FIGS. 1D and 1D' are diagrammatic views of a pn junction diode which is to be mounted by the novel method of the present invention;

FIGS. 2A to 2D are diagrammatic cross-sectional views illustrating one embodiment of the manufacturing process of the present invention;

FIGS. 3A to 3D are diagrammatic sectional views illustrating a different embodiment of the present invention;

FIG. 4A is a diagrammatic plan view of still another type of display device which is manufactured in accordance with a further embodiment of the present invention; and

FIG. 4B is a cross-sectional view taken along the line C--C of FIG. 4A.

In this invention, a light-transparent insulating sheet 1 is attached at its opposite surfaces with metal layers or copper plates 2 and 3 by adhesive agent to form a substrate 4 as shown in FIG. 1A. In this case, as the sheet 1, it is preferred to use a relatively thin film such as a light-transparent resin film consisting of polyimide resin, polyester resin or the like and having a thickness of about 50.mu. (micron). In addition, the copper plates 2 and 3 are preferred to have a thickness of about 70.mu. each.

Next, the surface of the copper plate 3 formed on one surface of the sheet 1 is subjected to a blackening process. The blackening process is effected by applying a so-called black-nickel plating 5 consisting of alloy plating of zinc, sulphur and nickel. In this case, the thickness of the black-nickel plating 5 is made about 1.mu. maximum, by way of example (see FIG. 1B).

After the copper plate 3 is applied with a black nickel plating 5, portions of the copper plate 2 and the copper plate 3 are removed by etching in a manner hereafter to be described (see FIG. 1C). The sandwich composed of the copper layer 2, the light transparent insulating sheet 1, and the nickel plating layer 5 comprises an initial construction for commencing the method of manufacture which forms one preferred embodiment of the present invention. After the sandwich shown in FIG. 1B is formed, the copper layer 2 is etched to provide an opening having a width l.sub.2 and the copper layer 3 and nickel layer 5 are etched to provide an opening having a larger width l.sub.1.

The light emitting semiconductor element 12 which is to be mounted in accordance with the method of the present invention is a pn junction type semiconductor device as depicted in FIGS. 1D and 1D'. FIG. 1D' is a cross sectional view of the diode 12 taken along the line B--B of FIG. 1D. Electrodes 13p and 13n are connected by deposition to the end surfaces of the diodes of the p-type and n-type regions in ohmic contact therewith to form a light emitting diode.

Referring now to FIGS. 2A to 2D, the element 12 is positively secured to the substrate 4 (which is the sandwich formed by layers 1, 2 and 3) in the manner now to be described. In advance of the etching process, which forms the opening in the copper layer 2 and the opening in the copper layer 3, a nickel layer 22 is plated on the copper plate 2 to be disposed with the elements 12. Thereafter, in the case of etching the copper plate 2, firstly the nickel layer 22 and the copper plate 2 are etched with narrow etching width, and then the copper plate 2 is over-etched in a predetermined width with the nickel layer 22 being used as a mask. During the etching the conductive layer 22 is etched in such a way that the portion thereof on one side of the opening 8 is separate and distinct from the portion on the other side of the opening 8. These two portions thus provide two electrically separated conductive paths for appropriate connection in a circuit. In other words, as depicted in FIG. 2A, eaves 22a of the nickel layer 22 are formed by the above over-etching process, at least, at a portion over the groove 8 wherein the element 12 is disposed. In the above etching process, the final etching width l.sub.2 of the copper plate 2 obtained by the over-etching is selected in a predetermined size which has been described with reference to FIG. 1.

After the eaves 22a of the nickel layer 22 are thus formed, a tin plating layer 23, by way of example, is formed by deposition on the surface including the nickel layer 22 and a copper plate 2 as shown in FIG. 2B. Next, the element 12 is inserted into each groove 8 having the eaves 22a thereon by pressing down the respective eaves 22a. In this case, the element 12 is resiliently supported by the eaves 22a as shown in FIG. 2C. Besides, the electrodes 13p and 13n of the element 12 are electrically brought into contact with the copper plates 2 through the tin plating layers 23 and the nickel layer 22. After flux 24 is applied on the tin plating layers 23 with the above described condition as shown in FIG. 2C, an alloy process is applied thereto. Thus, the tin plating layers 23 are subjected to an alloy process as shown in FIG. 2D to connect the electrodes 13p and 13n of the element 12 to the copper plates 2 or wiring portions 9 in an electrical and mechanical manner.

Meanwhile, with a condition where the eaves 22a are formed, the element 12 is inserted into the groove 8 by pushing down the eaves 22a directly and the element is then supported resiliently by the curved portions of the eaves 22a of the nickel layers as shown in FIG. 2B', and thus the electrical and mechanical connections between the element 12 and conductive portions 9 are completed. Also, as shown in FIG. 2C', a tin plating layer 23 is further deposited on the nickel layer 22, and then an alloy process may be used to obtain a construction as shown in FIG. 2D.

When the eaves 22a are provided at the end edges of the wiring portions 9 facing the groove 8 and the eaves 22a are pushed down to insert the element 12, the element 12 is securely supported by the eaves 22a in a mechanical manner. Accordingly, the operation in the following process can be smoothly carried out, that is, the element can be prevented from being shaken and falling out in its transportation and precise coupling with no positional shift can occur.

FIGS. 3A to 3D show another improved method of this invention, in which the light emitting display is made to look larger, particularly even with small light emitting semiconductor elements. That is, a so-called effect of enlargement is achieved. In other words, there is first provided a sheet 1 which is previously applied with aventurine lacquer 25 on its opposite surfaces and then the copper plates 2 and 3 are formed by deposition on both the surfaces of this sheet 1 to form the substrate 4 as shown in FIG. 3A. Further, the surface of one copper plate 3 is subjected to the black-nickel plating 5 as occasion demands. Thereafter, in the case where the eaves are to be provided similar to the case of FIGS. 2A to 2D, the nickel layer 22 is deposited on the surface of the copper plate 2 (see FIG. 3B) and then the copper plates 2 and 3 together with the nickel layer 22 are subjected to etching process to form the eaves 22a on the nickel layer 22, thus a predetermined pattern is formed as shown in FIG. 3C. In this case, the aventurine lacquer 25 comes out to the outside at etched portions. Further, the recess 6 formed in the copper plate 3 is made larger than the groove 8 of the copper plate 2.

Next, the element 12 is inserted into the groove 8 of the copper plate 2 and they are connected by the solder paste 14 as shown in FIG. 3D.

With such a construction, the light emitted from the element 12 is observed through the transparent sheet 1 from the side of copper plate 3. In this case, since the surface of the sheet 1 is applied with the aventurine lacquer 25, the light is reflected diffusively to perform a display with a moderate by bold figure.

FIGS. 4A and 4B show a further embodiment of this invention. At first, an iron plate 31 with a thickness of about 250.mu. is applied with a copper plating having a thickness of about 20.mu. at its opposite surfaces with a photo resist being used as a mask to form a copper layer 32 and copper marks 32' in predetermined patterns. In this case, a gap between the copper layers 32 on the upper side is made substantially 0.6 mm and both the layers 32 have projected therefrom comb-like electrodes each being substantially 0.5 mm in pitch, 100.mu. in width and 225.mu. in length.

Next, a black ceramic substrate 34 having a thickness of about 8 mm is secured to the lower surface of the iron plate 31 through epoxy resin 33 or the like with the copper marks 32' formed on the bottom surface being used as its guide.

Thereafter, the iron plate 31 is etched in a lead-frame shape 35 with the copper layer 32 being used as a mask as shown in FIG. 4A. In this case, the iron plate 31 is over-etched by 100 to 150.mu. to form eaves 32a of the copper layer 32. Then, a solder plating with thickness of about 20.mu. is applied on the surface including the copper layer or electrodes 32 and the iron plate 31. Next, a GaP light emitting semiconductor element, which is substantially 4 mm long, 0.5 mm wide and 180.mu. high, is inserted between the eaves 32a of the copper layer 32 with the PN-junction of the element being perpendicular to the substrate 34 and finally subjected to a soldering process.

In the embodiment of the invention shown in FIGS. 4A and 4B, the diode is viewed from the side of the structure opposite to that where the opaque black ceramic layer lies, i.e., from above as seen in FIG. 4B.

It will be apparent to those skilled in the art that many modifications and variations may be effected without departing from the spirit and scope of the novel concepts of the present invention.