Thick film getter paste compositions with pre-hydrated desiccant for use in atmosphere control

Abstract

The invention is directed to a screen-printable getter composition comprising: (a) glass frit; and (b) pre-hydrated desiccant material; dispersed in (c) organic medium. The present invention further relates to a getter composition utilizing low-softening temperature glasses comprising, based on weight %, 1-50% SiO2, 0-80% B2O3, 0-90% Bi2O3, 0-90% PbO, 0-90% P2O5, 0-60% Li2O, 0-30% Al2O3, 0-10% K2O, 0-10% Na2O, and 0-30% MO where M is selected from Ba, Sr, Ca, Zn, Cu, Mg and mixtures thereof. The glasses described herein may contain several other oxide constituents that can substitute glass network-forming elements or modify glass structure. The desiccant material is pre-hydrated to reach its saturation level of moisture absorption. The process of pre-hydration can be done by exposing the desiccant in a normal temperature / humidity environment of for example, 25° C. and 50-60% RH. for 24 to 48 hours or up to the time when weight gain (due to moisture absorption) stops increasing. An accelerated hydration process in a chamber with higher than normal humidity level (i.e. 50% Relative Humidity) is also applicable to shorten the time of exposure to fully hydrate the desiccant material.

Description

FIELD OF THE INVENTION

[0001] The invention is directed to thick film getter paste compositions with pre-hydrated desiccant for use in controlling moisture, oxygen, and small organic molecule levels in sensitive electronic and photonic devices. BACKGROUND OF THE INVENTION

[0002] The invention describes thick film getter compositions for use in controlling moisture, oxygen, and small organic molecule levels. Many packaged devices are susceptible to damage from undesired levels of moisture, oxygen, and small organic molecules and this is especially so in the case of various electronic, display, and light sensing or emitting devices. Examples of the types of damage caused or aggravated by the gas or condensed phase impurities include; hydration, oxidation, corrosion, and ion migration. In the case of FED (Field Emission Display) or SED (Surface Emission Display), the residue gasses may cause the undesirable modification of the emitter tip surface work function and degrade the performan...

Examples

examples 1-3

[0060] A series of bismuth or lead silicate-based glass compositions that have been found to be suitable in the present invention for application to thick film getter paste are shown in Table 2. The examples particularly illustrate silicate glasses containing more than 69 weight % bismuth.

[0061] All glasses were prepared by mixing raw materials and then melting in a platinum crucible at 1100-1400° C. The resulting melt was stirred and quenched by pouring on the surface of counter rotating stainless steel rollers or into a water tank. The glass powders prepared for the invention were adjusted to a 2-5 micron mean particle size by wet or dry milling using alumina ball media prior to being used as ingredients in the formulation of a paste composition. In the case of wet milling, the slurry after milling was dried in a hot air oven and the excessively large particles were removed by a sieving process.

[0062] It is noted that the examples of glass composition given below only serve as s...

examples 4-19

[0063] Thick film getter paste was prepared by mixing glass and pre-hydrated desiccant (3A or 13X powder) material (molecular sieve) with organic media based on the mixture of Texanol® and / or terpineol solvent and ethyl cellulose resin. Table 3 represents the examples of thick film compositions containing 7-10% glass and 47-60% pre-hydrated zeolite (3A or 13X). Although identical level of glass to pre-hydrated zeolite, namely, 1 to 6.1 for glass 1 to pre-hydrated 3A and 1 to 6.5 for glass 1 to pre-hydrated 13X, it is noted that a glass to pre-hydrated zeolite ratio other than the aforementioned value can be applicable in the getter paste compositions depending on the specific requirements in adhesion strength and the getter effect. Due to the density differential of glass among the glass compositions 1 to 3, the relative weight % glass in paste composition containing other than glass 1 was adjusted to maintain identical volume ratio of glass to zeolite 3A (Table 3) or 13X (Table 4)....

examples 20-22

[0068] Fired thick film samples were evaluated to quantify the degree of moisture absorption after exposure to certain humidity environment. Table 5 shows the absorption performance of selected getter samples 15 to 17 based on the thermal gravitational analysis (TGA) results. The moisture desorption and absorption results were expressed as weight loss and gain of thick films up to a given temperature. The TGA samples were prepared by firing at a peak temperature of 550° C. for 30 minutes and exposing to an 85° C. / 85% RH humidity condition for 2 hours including the time took to cool from 550° C. to room temperature. No additional firing for activation (i.e. to remove moisture absorbed by the zeolite materials) was used for the TGA analysis.

[0069] The weight loss proportionally increased with increasing temperature during the firing profile as expected, but it tends to demonstrate a much slower rate of weight loss after 400° C. Increasing the content of glass decreased the percentage...

FIELD OF THE INVENTION

[0001] The invention is directed to thick film getter paste compositions with pre-hydrated desiccant for use in controlling moisture, oxygen, and small organic molecule levels in sensitive electronic and photonic devices. BACKGROUND OF THE INVENTION

[0002] The invention describes thick film getter compositions for use in controlling moisture, oxygen, and small organic molecule levels. Many packaged devices are susceptible to damage from undesired levels of moisture, oxygen, and small organic molecules and this is especially so in the case of various electronic, display, and light sensing or emitting devices. Examples of the types of damage caused or aggravated by the gas or condensed phase impurities include; hydration, oxidation, corrosion, and ion migration. In the case of FED (Field Emission Display) or SED (Surface Emission Display), the residue gasses may cause the undesirable modification of the emitter tip surface work function and degrade the performan...

Examples

examples 1-3

[0060] A series of bismuth or lead silicate-based glass compositions that have been found to be suitable in the present invention for application to thick film getter paste are shown in Table 2. The examples particularly illustrate silicate glasses containing more than 69 weight % bismuth.

[0061] All glasses were prepared by mixing raw materials and then melting in a platinum crucible at 1100-1400° C. The resulting melt was stirred and quenched by pouring on the surface of counter rotating stainless steel rollers or into a water tank. The glass powders prepared for the invention were adjusted to a 2-5 micron mean particle size by wet or dry milling using alumina ball media prior to being used as ingredients in the formulation of a paste composition. In the case of wet milling, the slurry after milling was dried in a hot air oven and the excessively large particles were removed by a sieving process.

[0062] It is noted that the examples of glass composition given below only serve as s...

examples 4-19

[0063] Thick film getter paste was prepared by mixing glass and pre-hydrated desiccant (3A or 13X powder) material (molecular sieve) with organic media based on the mixture of Texanol® and / or terpineol solvent and ethyl cellulose resin. Table 3 represents the examples of thick film compositions containing 7-10% glass and 47-60% pre-hydrated zeolite (3A or 13X). Although identical level of glass to pre-hydrated zeolite, namely, 1 to 6.1 for glass 1 to pre-hydrated 3A and 1 to 6.5 for glass 1 to pre-hydrated 13X, it is noted that a glass to pre-hydrated zeolite ratio other than the aforementioned value can be applicable in the getter paste compositions depending on the specific requirements in adhesion strength and the getter effect. Due to the density differential of glass among the glass compositions 1 to 3, the relative weight % glass in paste composition containing other than glass 1 was adjusted to maintain identical volume ratio of glass to zeolite 3A (Table 3) or 13X (Table 4)....

examples 20-22

[0068] Fired thick film samples were evaluated to quantify the degree of moisture absorption after exposure to certain humidity environment. Table 5 shows the absorption performance of selected getter samples 15 to 17 based on the thermal gravitational analysis (TGA) results. The moisture desorption and absorption results were expressed as weight loss and gain of thick films up to a given temperature. The TGA samples were prepared by firing at a peak temperature of 550° C. for 30 minutes and exposing to an 85° C. / 85% RH humidity condition for 2 hours including the time took to cool from 550° C. to room temperature. No additional firing for activation (i.e. to remove moisture absorbed by the zeolite materials) was used for the TGA analysis.

[0069] The weight loss proportionally increased with increasing temperature during the firing profile as expected, but it tends to demonstrate a much slower rate of weight loss after 400° C. Increasing the content of glass decreased the percentage...