Patent Application
20070267972
In the following detailed description, for purposes of explanation and not limitation, example embodiments disclosing specific details are set forth to provide a thorough understanding of the present invention. However, it will be apparent to one having ordinary skill in the art, having had the benefit of the present disclosure, that the present invention may be practiced in other embodiments that depart from the specific details disclosed herein. Moreover, descriptions of well-known devices, methods and materials may be omitted so as not to obscure the description of the present invention. Finally, wherever applicable, like reference numerals refer to like elements.
For purposes of discussion and not limitation, the following description will be presented in terms of an OLED display device. The skilled artisan will appreciate that the techniques disclosed herein may be applicable to the temporary encapsulation of other devices where hermeticity over a pre-determined length of time is desired. Examples of other devices include a photovoltaic device, a thin-film sensor, or an evanescent waveguide sensor.
In an exemplary OLED display device manufacturing operation, at least one OLED device is deposited onto a first glass substrate. The at least one OLED device comprises a cathode, one or more layers of an organic, light emitting material, and an anode. A second glass substrate is then placed overtop the first glass substrate. The second glass substrate includes a line of glass frit deposited on the second substrate in a closed, frame-like pattern about a periphery of the substrate, forming a wall. The frit wall is disposed between the first and second substrates, thereby forming a glass envelope between the two substrates, with the at least one OLED device disposed therein. The first and second substrates may thereafter be sealed by heating the frit with a laser beam. Such laser sealing techniques are known in the art and will not be described further so as not to obscure the present invention. However, in brief, a laser beam having a suitable wavelength whereby energy from the laser beam is absorbed by the frit is traversed over the frit wall (typically through one or both of the substrates), thereby heating and melting the frit to join the first and second substrates.
A plurality of OLED devices may be formed using the first and second substrates. For example, a plurality of frit walls may be formed on one substrate in an m×n matrix, while a plurality of OLED devices may be formed on the second substrate. The first and second substrates may then be joined by heating the frit frames, such as with a laser, until an hermetic seal in formed around each OLED device.
In certain circumstances, it may be desirable to join the first and second substrates temporarily. For example, assembly of the substrates and one or more display devices may occur at one facility, while the heating and sealing of the frit may occur at a second facility distant from the first facility. The distance between the assembly facility and the frit sealing facility can be on the order of several miles, to many thousands of miles. Transportation of the assemblies from the assembly facility to the frit sealing facility can include air transport, meaning significant pressure changes can occur in the surrounding environment.
In accordance with an embodiment of the present invention, a temporary hermetic seal between the first and second substrates can be formed by depositing sealant grease between the first and second substrates, about a periphery of the substrates. By periphery what is meant is that the sealant grease is deposited in close proximity to, but inward of, the edges of the glass substrate. The first and second substrates may later be frit sealed, and the temporary grease seal removed by cutting away the portions of the first and second substrates having the sealing grease disposed thereon.
Suitable sealing greases include readily available commercial vacuum greases such as, for example, Dow-Corning High Vacuum Grease 15 V 2645 Stopcock/Vacuum Grease, Dow Corning 976V High Vacuum Grease, Santovac 5 GB Ultra High Vacuum Grease, Braycote 600EF High Vacuum Grease, and Apiezon M High Vacuum Grease as a sealant. In the alternative, ordinary dental fixative, for use with dentures, such as Polygrip brand dental fixative, has been found to be effective, and considerably less expensive than commercially available vacuum greases. Other materials suitable for forming a temporary hermetic seal include a UV curable acrylate, high modulus monomers (e.g. DSM 950-111 or DC Q3-6696), UV curable cationic epoxy adhesives (e.g. Loctite 3337), and UV curable acrylates. As used herein, the term sealant grease is intended to encompass any of the above materials, combinations thereof, or similar materials which may serve to form a temporary hermetic seal.
As shown in
Several steps may be taken to improve the hermeticity of the seal. For example, it has been found that a more uniform bead of vacuum grease may be obtained by employing an automated dispensing apparatus, such as a pneumatic syringe. Also, assembly within a glove box is preferred over assembly in open air, to minimize exposure to the ambient environment. Preferably, the glove box has a negative internal pressure relative to the ambient pressure. A dry, inert atmosphere within the glove box may be employed to prevent initial contamination of the OLED device(s).
Increased longevity of the temporarily hermetically sealed OLED device may be obtained by including a desiccant 20 within the envelope formed between the first and second substrates, but is not required. For example, a desiccant may be included between the first and second substrates inside (interior to) the vacuum grease seal, but outside (exterior to) the frit wall. When the vacuum seal portion of the assembly is cut away, the desiccant is also removed. For example, a channel (22) may be formed in one or both of the substrates, and the channel filled with a desiccant. Also, the temporarily sealed assembly may be further vacuum sealed in a polymer bag (not shown) for transport. For example, an ordinary food sealing system may be used to seal the assembly in a polymer bag.
In some embodiments, as shown in
It has been found that temporary hermetic seals of the type described above can maintain their hermeticity in excess of at least about 300 hours, and in some instances, 800 hours. For most applications contemplated herein, this has been found to be satisfactory.
A first and second glass cover substrate was provided. Each substrate was about 0.7 mm in thickness and 6 inch (15.24 cm) square. Each of the glass cover substrates included frit frames disposed thereon in an m×n pattern.
First and second back plane substrates were also provided having dimensions the same as the cover substrates. To represent individual OLED display devices and to provide a visual confirmation of hermeticity, calcium metal films were deposited in an m×n matrix on the surface of each back plane substrate. If exposed to air, the calcium metal film transforms from having a silvery surface to being milky in appearance. The thickness of the calcium films on the first substrate were approximately 600 nm, while the thickness of the calcium films on the second substrate were approximately 700 nm.
A vacuum grease (Dow-Corning High Vacuum Grease (15 V 2645 Stopcock/Vacuum Grease, 150 g. Tube) was dispensed with a syringe around the perimeter of each cover substrate, creating a grease bead. The first sample had a thinner bead, while the other sample had a slightly thicker bead of the vacuum grease.
The sample substrates were stored in a glove box having an argon atmosphere during preparation. A single cover substrate and a single back plane substrate were then removed from the glove box and the cover glass substrate was quickly placed on top of the back plane substrates, using manual alignment, such that each calcium film on the back plane substrate was contained within each frit frame of the cover substrate. Uniform pressure was applied to the assembly using a steel plate to create a temporary seal. The above procedure was repeated for the second set of cover and back plane substrates. The 600 nm calcium sample substrate was assembled with the thinner bead of vacuum grease while the 700 nm calcium sample substrate was assembled with the thicker bead of vacuum grease. Initial observations showed a seal width ranging between about 4 mm to 8 mm. On each sample, there were narrow sections as thin as about 1 to 2 mm, and there appeared to be some air entrapment in the start stop positions of the grease deposition.
After approximately 48 hours, the 700 nm calcium assembly showed slight degradation, most likely attributed to the non-uniformity in the manual application of the vacuum grease bead. The 600 nm calcium assembly still indicated as good hermetic seal.
A second experiment was conducted similar to that described in Example 1 above. Six assemblies were constructed. Two assemblies were constructed using Santovac 5 GB Ultra High Vacuum Grease as a sealant, two assemblies were constructed using Braycote 600EF High Vacuum Grease as a sealant, and two assemblies were constructed using Apiezon M High Vacuum Grease as a sealant. The sealant in all cases was dispensed using an air-powered syringe application tips and adapters from the EFD® company. One calcium film (emulating an OLED device) on a single Bracote assembly failed after 337 hours, a second “device” failed after 33381 hours, and a third device failed after 522 hours. All other samples exceeded 882 hours of hermeticity.
It should be emphasized that the above-described embodiments of the present invention, particularly any “preferred” embodiments, are merely possible examples of implementations, merely set forth for a clear understanding of the principles of the invention. Many variations and modifications may be made to the above-described embodiments of the invention without departing substantially from the spirit and principles of the invention. All such modifications and variations are intended to be included herein within the scope of this disclosure and the present invention and protected by the following claims.
This application claims the benefit of priority under 35 U.S.C. § 119(e) of U.S. Provisional Application Ser. No. 60/802,835 filed on May 22, 2006, the content of which is incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 60802835 | May 2006 | US |
