Abstract LED displays with integrated logic are typically formed by bonding the LED devices and often the logic chips to large alumina or other ceramic substrates, lead frame substrates or other substrates. Typically the arrangement has a large area of uncovered substrate due to the large display area compared with the smaller chip size. Reflection of bright light from the substrate detracts from the contrast of the display. It has been found that photoresist materials conventionally in use turn black when heated to temperatures in excess of those recommended for post-baking (e.g., > 200* C). It is convenient to cover the inactive portion of the substrate with a patterned layer of photoresist (leaving windows for chip and circuit bonding) and then, through a heat treatment, which may already exist in the IC process, to blacken the photoresist layer. The photoresist layer forms a part of the finished device. Adhesion of the photoresist is surprisingly tenacious.
A METHOD FOR ENHANCING THE CONTRAST OF AN ELECTROLUMINESCENT DISPLAY DEVICE IN WHICH LIGHT-EMITTING DEVICES ARE AFFIXED TO PORTIONS OF A SUBSTRATE AND IN WHICH OTHER PORTIONS OF THE SUBSTRATE NOT COVERED WITH LIGHT-EMITTING DEVICES ARE REFLECTIVE AND TEND TO REDUCE THE CONTRAST OF THE LIGHT-EMITTING REGIONS WITH RESPECT TO THE BACKGROUND OF THE DISPLAY, THE METHOD CHARACTERIZED BY PHOTOLITHOGRAPHICALLY APPLYING SELECTIVELY TO THE LIGHT-REFLECTING PORTIONS A PHOTORESIST, AND BAKING THE PHOTORESIST AT A TEMPERATURE SUFFICIENT TO DARKEN THE PHOTORESIST SIGNIFICANTLY AND CAUSE IT TO ADHERE PERMANENTLY TO THOSE PORTIONS SO AS TO REMAIN A PART OF THE FINISHED DEVICE.
Claim 2
Independent Claim
100 words
A METHOD FOR ENHANCING THE CONTRAST OF AN ELECTROLUMINESCENT DISPLAY DEVICE IN WHICH LIGHT-EMITTING DEVICES ARE AFFIXED TO PORTIONS OF A SUBSTRATE AND IN WHICH OTHER PORTIONS OF THE SUBSTRATE NOT COVERED WITH LIGHT-EMITTING DEVICES ARE REFLECTIVE AND TEND TO REDUCE THE CONTRAST OF THE LIGHT-EMITTING REGIONS WITH RESPECT TO THE BACKGROUND OF THE DISPLAY, THE METHOD CHARACTERIZED BY PHOTOLITHOGRAPHICALLY APPLYING SELECTIVELY TO THE LIGHT-REFLECTING PORTIONS A PHOTORESIST, AND BAKING THE PHOTORESIST AT A TEMPERATURE SUFFICIENT TO DARKEN THE PHOTORESIST SIGNIFICANTLY AND CAUSE IT TO ADHERE PERMANENTLY TO THOSE PORTIONS SO AS TO REMAIN A PART OF THE FINISHED DEVICE.
Claim 3
Dependent Claim
24 words
The method of claim 1 in which the reflecting portions over which the photoresist is applied include portions of a highly reflecting ceramic substrate.
Claim 4
Dependent Claim
23 words
The method of claim 1 in which the reflecting portions over which the photoresist is applied include conductor patterns of highly reflecting metallization.
Claim 5
Dependent Claim
16 words
The method of claim 1 in which the photoresist is baked at a temperature exceeding 200*C.
Claim 6
Dependent Claim
16 words
The method of claim 1 in which the photoresist is baked at a temperature exceeding 300*C.
Claim 7
Dependent Claim
15 words
The method of claim 1 in which the light-emitting devices are gallium compound semiconductor diodes.
Claim 8
Dependent Claim
22 words
The method of claim 1 in which the photoresist is applied with a thickness in the range of 0.1 to 10 microns.
Claim 9
Dependent Claim
42 words
The method of claim 1 in which at least parts of the light-emitting devices are affixed to the substrate by a bonding technique that uses a heat treatment step, and the photoresist is darkened as a result of this heat treatment step.
Claim 10
Dependent Claim
14 words
The method of claim 1 in which the substrate is a metal lead frame.
Claim 11
Dependent Claim
18 words
The method of claim 1 in which the photoresist is applied also to portions of the light-emitting devices.