Drying and gas or vapor contact with solids – Process – With contacting of material treated with solid or liquid agent
Reexamination Certificate
2001-09-21
2002-10-29
Lazarus, Ira S. (Department: 3749)
Drying and gas or vapor contact with solids
Process
With contacting of material treated with solid or liquid agent
C034S307000, C034S352000, C034S416000, C034S417000, C034S472000, C257S099000, C257S100000
Reexamination Certificate
active
06470594
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to control of moisture inside a packaged electronic device and relates particularly to highly moisture-sensitive electronic device elements having multiple highly moisture-sensitive electronic devices and methods for their fabrication to prevent premature device failure or premature degradation of device performance.
BACKGROUND OF THE INVENTION
In manufacturing, electronic devices are typically produced by fabricating large substrates containing multiple electronic devices. These substrates are typically selected from the group consisting of glass, plastic, metal, ceramic, silicon and other semiconductor materials, or combinations of these materials. The substrates may be rigid or flexible and may be handled as individual units or continuous rolls. The primary reason for fabricating multiple electronic devices on large individual substrates or a continuous roll substrate is to reduce manufacturing cost by decreasing handling, increasing throughput, and increasing yield. In the micro-electronics industry silicon wafer processing has increased from 2 inch wafers to 12 inch wafers resulting in significant cost reductions. In the liquid crystal display (LCD) industry glass substrate processing has increased from 300 mm×400 mm substrates to lover 600 mm×700 mm substrates with the same result. In manufacturing of highly moisture-sensitive electronic devices, such as organic light-emitting devices (OLED), polymer light-emitting devices, charge-coupled device (CCD) sensors, and micro-electro-mechanical sensors (MEMS), the same economies of scale are achieved by fabricating large individual substrates or a continuous roll substrate with multiple highly moisture-sensitive electronic devices.
FIG. 1A
shows an unencapsulated highly moisture-sensitive electronic device element
14
containing multiple highly moisture-sensitive electronic devices
12
on an individual substrate
10
, and
FIG. 1B
is a schematic sectional view of the highly moisture-sensitive electronic device element
14
taken along section line
1
B—
1
B of FIG.
1
A. Fabricating large individual substrates or a continuous roll substrate with multiple highly moisture-sensitive electronic devices, however, introduces a problem that is not important for less moisture-sensitive electronic devices in that highly moisture-sensitive devices must be protected from even short term exposure to moisture during fabrication.
Typical electronic devices require humidity levels in a range of about 2500 to below 5000 parts per million (ppm): to prevent premature degradation of device performance within a specified operating 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 or by sealing the device and a desiccant within a cover. Desiccants such as, for example, molecular sieve materials, silica gel materials, and materials commonly referred to as Drierite materials, are used to maintain the humidity level within the above range. Short term exposure to humidity levels greater than 2500 ppm during the fabrication and encapsulation of these types of electronic devices typically does not cause measurable degradation of device performance. For this reason, encapsulation of these types of electronic devices is done after the electronic devices are separated from the initial substrate.
In the manufacture of liquid crystal displays the electronics and the liquid crystal materials are not highly moisture-sensitive; therefore, the process for encapsulating the electronics and the liquid crystal materials does not require protection from ambient moisture during fabrication.
FIG. 2A
shows a typical multiple LCD element
28
before separation into single LCD devices, and
FIG. 2B
is a schematic sectional view of the multiple LCD element
28
taken along section line
2
B—
2
B of FIG.
2
A. In LCD manufacturing the LCD back-plane
22
and the LCD front-plane
24
contain multiple LCD devices. The LCD back-plane
22
and the LCD front-plane
24
are bonded together with a sealing material
20
that surrounds each LCD device except for a gap in the sealing material
20
. After fabrication of the multiple LCD element
28
the LCD devices are separated and filled with liquid crystal material. After filling the LCD devices, the gap in the sealing material
20
is sealed with a gap sealing material to retain the liquid crystal material and to protect the LCD back-plane electronics
26
and the liquid crystal material from moisture. Because LCD devices are not highly moisture-sensitive, the separation process of the multiple LCD element is typically performed in an ambient air environment with no measurable degradation of the LCD devices.
Particular highly moisture-sensitive electronic devices, for example, organic light-emitting devices, (OLED) or panels, polymer 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 are not achievable with desiccants of silica gel materials and of 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 capacity at humidity levels at or below 1000 ppm, and the minimum achievable humidity level of molecular sieve materials is a function of temperature within an enclosure: moisture absorbed, for example, at room temperature, can be released into the enclosure or package during temperature cycling to higher temperature, such, as, for example, to a temperature of 100° C. Desiccants used within such packaged devices include powders of metal oxides, alkaline earth metal oxides, sulfates, metal halides, or perchlorates, i.e. materials having desirably relatively low values of equilibrium minimum humidity and high moisture capacity. However, such materials often chemically absorb moisture relatively slowly compared to the above-mentioned molecular sieve, silica gel, or Drierite materials, Such relatively slow reaction with water vapor leads to a measurable degree of device degradation of performance following the sealing of the desiccant inside a device cover due to, for example, moisture absorbed on the inside of a device, moisture vapor present within the sealed device, and moisture permeating through the seal between the device and the cover from the outside ambient. In addition, highly moisture-sensitive electronic devices typically cannot be exposed to moisture levels greater than 1000 ppm even during fabrication and encapsulation, requiring control of the moisture levels until the devices are completely encapsulated. For these reasons, control of the moisture level during fabrication and encapsulation is required to prevent degradation of performance.
To reduce the quantity of moisture absorbed on the inside of a device or present within the sealed device, highly moisture-sensitive devices, such as organic light-emitting devices (OLED) or panels, polymer light-emitting devices, charge-coupled device (CCD) sensors, and micro-electro-mechanical sensors (MEMS), are often sealed within a low humidity environment, such as a drybox at humidity levels less than 1000 ppm moisture. To ensure low levels of moisture within the sealed device, these highly moisture-sensitive devices are completely sealed within the low humidity environment prior to any additional processing steps, such as bonding of interconnects and module assembly. To achieve this low humidity sealing, highly moisture-sensitive devices, such as charge-coupled device (CCD) sensors and micro-electro-mechanical sensors (MEMS), are typically sealed individually as single elements with separate cover elements after separation from a multiple element substrate or wafer. Other devices, such as organic light-emitting devices (OLED), are sealed as multiple de
Bessey Peter G.
Boroson Michael L.
Schmittendorf John
Serbicki Jeffrey P.
Eastman Kodak Company
Lazarus Ira S.
Owens Raymond L.
Rinehart K. B.
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