Ultrasonically sealing the cover plate to provide a hermetic enclosure for ...

(12) United States Patent

Ghosh et al.

US006706316B2

(io) Patent No.: US 6,706,316 B2 (45) Date of Patent: Mar. 16,2004

(54) ULTRASONICALLY SEALING THE COVER PLATE TO PROVIDE A HERMETIC ENCLOSURE FOR OLED DISPLAYS

(75) Inventors: Syamal K. Ghosh, Rochester, NY (US); Fugui He, Penfield, NY (US); Harold Moore, Pittsford, NY (US)

(73) Assignee: Eastman Kodak Company, Rochester, NY (US)

( * ) Notice: Subject to any disclaimer, the term of this patent is extended or adjusted under 35 U.S.C. 154(b) by 231 days.

(21) Appl. No.: 09/850,788

(22) Filed: May 8, 2001

(65) Prior Publication Data

US 2002/0187254 Al Dec. 12, 2002

(51) Int. CI.7 B05D 5/12; B32B 31/16

(52) U.S. CI 427/58; 427/74; 427/284;

427/369; 427/375; 427/600; 156/73.1

(58) Field of Search 427/58, 600, 66,

427/74, 375, 271, 277, 359, 369; 156/73.1;

174/52.1-52.5

(56) References Cited

U.S. PATENT DOCUMENTS

3,951,327 A * 4/1976 Snow et al 228/121

5,304,419 A 4/1994 Shores

5,401,536 A 3/1995 Shores

5,591,379 A 1/1997 Shores

5,771,562 A * 6/1998 Harvey et al 29/592.1

6,195,142 Bl * 2/2001 Gyotoku et al 349/69

6,210,815 Bl * 4/2001 Ooishi 428/690

2001/0046579 Al * 11/2001 Ishii et al 428/68

2002/0045397 Al * 4/2002 Tanaka 445/24

FOREIGN PATENT DOCUMENTS

EP 0776147 5/1997

* cited by examiner

Primary Examiner—Brian K. Talbot

(74) Attorney, Agent, or Firm—Raymond L. Owens

(57) ABSTRACT

A method of providing a hermetically sealed enclosure for a highly moisture sensitive electronic device including depositing an electrical conductor on the substrate which provides an electrical connection with the electronic device and depositing an electrically insulating thin layer over the electrical conductor; providing a low melting point indium metal or alloy in the form of a wire having diameter ranging from 1 mil to 10 mils on the electrically insulating thin layer on the substrate so that the wire is situated around the periphery of the electronic device; placing an ultrasonic horn over the cover plate so that ultrasonic energy can be delivered through the cover plate to the wire and applying a pressure between 20 and 100 psi; and providing an acoustic wave to melt the wire.

6 Claims, 2 Drawing Sheets

1

ULTRASONICALLY SEALING THE COVER
PLATE TO PROVIDE A HERMETIC
ENCLOSURE FOR OLED DISPLAYS

5

FIELD OF THE INVENTION

This invention relates to an ultrasonic encapsulation of electronic devices. More particularly, this invention relates to hermetically sealing a moisture sensitive electronic device, such as organic light emitting devices (OLED). 10

BACKGROUND OF THE INVENTION

It is known in microelectronic industry that in order to be functionally efficient for their intended purposes, certain types of electronic devices must be sealed to protect them from the ambient environment. Various electronic devices require humidity levels in a range of about 2500 to maximum 5000 parts per million (ppm) to prevent premature degradation of device performance within a specified oper- 2Q ating and/or storage life of the device. Control of the environment to this range of humidity levels within a packaged device is typically achieved by encapsulating the device and a desiccant within a cover.

Particular electronic devices, for example, OLED, poly- 25 mer light-emitting devices, charge-coupled device (CCD) sensors, and micro-electro-mechanical sensors (MEMS) require humidity control to levels below about 1000 ppm and some require humidity control below even 100 ppm. Such low levels of humidity are not achievable using 30 commonly used desiccants like silica gel or Drierite® materials. Molecular sieve materials can achieve humidity levels below 1000 ppm within an enclosure if dried at a relatively high temperature. However, molecular sieve materials have a relatively low moisture absorption capacity at humidity 35 levels at or below 1000 ppm. Therefore, the minimum achievable humidity level using molecular sieve materials as a desiccant is a function of temperature within an enclosure. Moisture adsorbed by molecular sieve material, for example, at room temperature, can be released into the enclosure or 40 package during temperature cycling to higher temperature, such as, for example, to a temperature of 100° C. Desiccants used within such packaged devices include metal oxides, alkaline earth metal oxides, sulfates, metal halides, or perchlorates, i.e., materials having desirably relatively low 45 values of equilibrium minimum humidity and high moisture capacity. However, such materials often chemically absorb moisture relatively slowly compared to the abovementioned molecular sieve, silica gel, or Drierite® materials. Such relatively slow reaction of desiccant with water 50 vapor leads to a measurable degree of device degradation in terms of performance.

Numerous publications describe methods and/or materials for controlling humidity levels within enclosed or encapsulated electronic devices. For example, Kawami et al., Euro- 55 pean Patent Application EP 0776 147 Al discloses an organic EL element enclosed in an airtight container which contains a desiccant comprised of a solid compound for chemically absorbing moisture. The desiccant is spaced from the organic EL element, and the desiccant is consoli- go dated in a predetermined shape by vacuum vapor deposition, sputtering, or spin coating.

Shores discloses in U.S. Pat. No. 5,304,419 a moisture and particle getter for enclosures which enclose the electronic device. A portion of an inner surface of the enclosure 65 is coated with a pressure sensitive adhesive containing a solid desiccant.

2

Shores discloses in U.S. Pat. No. 5,401,536 a method of providing a moisture-free enclosure for an electronic device in which the enclosure contains a coating or adhesive with desiccant properties. The coating or adhesive comprises a protonated alumina silicate powder dispersed in a polymer.

Shores discloses in U.S. Pat. No. 5,591,379 a moisture gettering material composition for hermetic devices. The composition is applied as a coating or adhesive on the interior surface of a device packaging, and the composition comprises a water vapor permeable binder, which has dispersed therein a desiccant which is preferably a molecular sieve material.

However, the use of proper desiccant inside the enclosure of an electronic device may extend the service life, but it does not make the device immune to failure due to moisture permeation from the outside ambient. True hermetic sealing of the electronic components can provide a controlled environment in which the electronic devices function, however, a true and effective hermetic seal is difficult to achieve in all the cases. More particularly it is difficult for OLED because of the temperature restraint. The organic layers in the OLED tend to deteriorate if they are exposed to over 100° C. for any length of time. In the traditional hermetic sealing, as for example, vacuum tube and lamp manufacturing method, elevated temperatures, high vacuum and other means are employed to accomplish that. The OLED displays do not withstand traditional methods of hermetic sealing as mentioned above.

SUMMARY OF THE INVENTION

It is an object of the invention to provide a highly effective hermetically sealed enclosure for moisture sensitive electronic devices.

It is another object of the present invention to provide a method of sealing a cover plate to provide an enclosure using a low temperature metal alloy.

These and other objects are achieved by a method of providing a hermetically sealed enclosure for a highly moisture sensitive electronic device comprising the steps of:

(a) depositing an electrical conductor on the substrate which provides an electrical connection with the electronic device and depositing an electrically insulating thin layer over the electrical conductor;

(b) providing a low melting point indium metal or alloy in the form of a wire having diameter ranging from 1 mil to 10 mils on the electrically insulating thin layer on the substrate so that the wire is situated around the periphery of the electronic device;

(c) placing an ultrasonic horn over the cover plate so that ultrasonic energy can be delivered through the cover plate to the wire and applying a pressure between 20 and 100 psi; and

(d) providing an acoustic wave from the ultrasonic horn through the cover plate to melt the wire.

It is an advantage of the present invention that the hermetically sealed enclosure provided by the above method prevents moisture from permeating through the seal and thus degrading the enclosed electronic device. The present invention is particularly suitable for use with highly moisture sensitive electronic devices like OLED display.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts an ultrasonic sealing arrangement for a moisture-sensitive electronic device; and

FIG. 2 is an end view of an ultrasonically sealed moisturesensitive electronic device.