Tapes for heat sealing substrates

Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Adhesive outermost layer

Reexamination Certificate

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C428S040400, C428S041500

Reexamination Certificate

active

06218005

ABSTRACT:

TECHNICAL FIELD
The present invention relates to sealing tapes for heat-sealing substrates, methods of making the same, and methods of using the same to form a sealed article.
BACKGROUND
Glass sealants are used, in part, in making electronic parts such as semiconductor devices and fluorescent character display tubes. For example, U.S. Pat. No. 5,145,803 (Daimer et al.) reports a glass sealant comprising a lead borate glass used in the fabrication of integrated circuits. U.S. Pat. No. 4,883,777 (Yamanaka) reports a lead-containing glass sealant for the manufacture of semiconductors and other electronic devices. U.S. Pat. No. 4,058,387 (Nofziger) and U.S. Pat. No. 4,120,678 (Francel et al.) report a glass sealant used to seal a glass faceplate to a glass funnel of a cathode-ray tube. Glass sealants form a bond between two substrates when heated and when used on electronic devices are preferably made of low-softening point glass to avoid damage to the article being sealed. Some low-softening point glass sealants melt and flow at a temperature below 500° C., and most frequently between 400° C. and 475° C.
Most glass sealants are pastes applied by extrusion so that a continuous amount of paste is placed between two surfaces to be sealed. The fluid nature of the paste makes the application of a very thin and uniform layer of paste free of voids difficult to achieve. Gaps of paste, or uneven paste thickness along the surfaces to be sealed may result in poor substrate bonding. Excess paste, upon heating and cooling of the paste, may result in debris particles being formed external to the region being sealed. These debris particles may come loose and damage the internal components of the article being manufactured.
Pastes are soft, smooth, and thick mixtures that when used are messy. Pastes are easily transferred to other parts of the articles being manufactured, to technicians operating equipment, to equipment used in the manufacturing process, and to other work areas. Pastes may accidentally be applied to clothing or to skin creating a potential safety hazard depending upon the composition of the pastes. Furthermore, pastes may contain volatile solvents which emit unpleasant and possibly hazardous odors. Pastes may also have a short shelf life since the volatile solvent in the paste may evaporate leaving a dried material which cannot be applied to a substrate. As a result of this, often times a large percentage of paste is discarded as waste.
In addition to the foregoing, pastes may contain lead which is hazardous to workers when the lead-containing paste contacts skin or is ingested. Lead containing glass sealants must be disposed of properly to avoid environmental issues. Additional clean-up time may be necessary to remove unwanted paste.
SUMMARY
The present invention provides tapes made of glass sealants for heat sealing substrates. The tapes of the present invention comprise a self-supporting layer of glass sealant including a low-softening point glass, refractory particles, a dispersant, and a binder. These tapes can easily be applied to substrates without the mess associated with pastes. The tapes minimizes gap formation between two or more substrates being bonded and provide a layer of glass sealant having a uniform thickness. The thickness of the tape can be easily controlled and very thin tapes can be achieved.
In a preferred embodiment, the tape includes at least one adhesive layer attached to a major surface of the tape. The adhesive aids in holding the substrates in place during the early stages of the sealing process.
The present invention also provides a method of making tapes of glass sealants for heat sealing substrates. The method comprises the steps of mixing a low-softening point glass, a carrier, a dispersant, and refractory particles to form a slurry; adding a binder to the slurry to form a glass sealant; deaerating the slurry; and forming the slurry into a self-supporting layer.
The present invention also provides a method of making a sealed article using a tape of the present invention. The method comprises the steps of:
(i) placing a tape for heat sealing substrates in contact with a first substrate, the tape comprising a self-supporting layer of a glass sealant including a low-softening point glass, refractory particles, a dispersant, and a binder;
(ii) placing a second substrate in contact with the tape so that the tape is at least partially located between the first substrate and the second substrate thus forming an assembly in which the glass sealing tape is at least partially interposed between the first and the second substrates;
(iii) heating the assembly to a temperature capable of melting the glass sealant;
(iv) at least partially melting the glass sealant; and
(v) cooling the assembly so that the melted glass sealant hardens.
As used herein, with respect to the present invention, the following shall apply:
“Ceramic” refers to an inorganic, nonmetallic material, such as metal oxides, metal nitrides, and metal oxynitrides, preferably consolidated by the action of heat.
“Fired” refers to densification or consolidation by action of heat.
“Green Tape” refers to compositions having both inorganic and organic components, which have a definite shape, and which may be fired to produce a ceramic.
“Refractory” refers to a material that maintains its structural integrity at temperatures at least up to about 1000° C.
“Joint” refers to the seal and/or bond created by the tapes of the present invention located between the substrates which are bonded together by these tapes.
“Self-supporting” refers to a green body having sufficient mechanical integrity to be dispensed from a roll without breaking or significant disruption of the tape. For example, approximately one half inch of tape may overhang an edge without tearing.
“Fiber Softening Point” refers to the measurement obtained for a glass using the Standard Test Method for Softening Point of Glass, ASTM Designation No.: C 338-93.
“Low softening point glass” refers to a glass composition capable of viscous flow at temperatures in the range of about 280° C. to 500° C.


REFERENCES:
patent: 3669787 (1972-06-01), Cornell
patent: 3728185 (1973-04-01), Gray
patent: 3954486 (1976-05-01), Francel et al.
patent: 4058387 (1977-11-01), Nofziger
patent: 4120678 (1978-10-01), Francel et al.
patent: 4131478 (1978-12-01), Davis et al.
patent: 4310357 (1982-01-01), Matsuura et al.
patent: 4654095 (1987-03-01), Steinberg
patent: 4710479 (1987-12-01), Yamanaka
patent: 4883777 (1989-11-01), Yamanaka
patent: 5145803 (1992-09-01), Daimer et al.
patent: 5179046 (1993-01-01), Francis et al.
patent: 5246890 (1993-09-01), Aitken et al.
patent: 5280061 (1994-01-01), Haraguchi et al.
patent: 5516733 (1996-05-01), Morena
patent: 5539151 (1996-07-01), Hamzehdoost et al.
patent: 5700744 (1997-12-01), Park et al.
patent: 5747931 (1998-05-01), Riddle et al.
patent: 5795520 (1998-08-01), Scalia et al.
patent: 5800154 (1998-09-01), Watkins
patent: 0 498 409 (1992-08-01), None
patent: 0 893 813 A2 (1999-01-01), None
Patent Abstracts of Japan, vol. 12, No. 351, Sep. 20, 1998, Japanese Pat. No. 63 108754.
“A Test Method to Measure Shear Strength of Ceramic Jounts at High Temperatures” Unal et al.;Am. Ceram. Soc.,vol. 80, No. 5, 1997, pp. 1281-1284.
“Solder glass seals in semi-conductor packagin”, D.W.A. Forbes,Glass Technology,vol. 8, No. 2, Apr. 1967, pp. 32-42.
“Tape Casting Reactive Aluminas”, Anderson et al.,The American Ceramic Society Bulletin,vol. 76, No. 7, Jul. 1997, pp. 45-50.
“Standard Test Method for Softening Point of Glass”,ASTM C 338-93, pp. 101-103.
“Standard Test Method for Assignment of the Glass Transition Temperature by Thermomechanical Analysis”,ASTM E 1545 -95a,pp. 937-940.

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