Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Reexamination Certificate
1998-04-03
2001-09-04
Gallagher, John J. (Department: 1733)
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
C106S286700, C156S001000, C156S325000, C428S420000
Reexamination Certificate
active
06284085
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to the bonding of materials, and in particular to a method for bonding materials using hydroxide-catalyzed hydration and dehydration.
BACKGROUND OF THE INVENTION
The bonding of materials is critical in making high performance instruments or devices. The quality of a bonding method is judged, in dependence upon its application, in terms of the precision, the mechanical strength, the optical properties, the thermal properties, the chemical properties, and the process simplicity of the bonding. Three popular bonding methods are optical contacting, epoxy bonding, and high temperature frit bonding.
Optical contacting is a room-temperature process which employs no bonding material, and is thus suitable only for certain precision applications involving surfaces having reasonably good surface figure match. Ideally, if the bonding surfaces are thoroughly cleaned prior to bonding, the resulting interface will have low thermal noise and contain almost nothing susceptible to oxidation, photolysis, and/or pyrolysis. Optical contacting produces bonds which are generally unreliable in strength, however, due to sensitivity to surface chemical contamination (such as, by air-borne molecules) and other environmental factors (such as humidity). In addition, surface figure mismatch almost always exists to some extent. Consequently, strong chemical bonds rarely occur extensively across the interface, and voids are seen sometimes in the interface. The bonds produced by optical contacting do not consistently survive thermal shocks. Typically, optical contacting has a low first-try success rate. In case of failure, de-bonding usually degrades surface quality, and thus lowers success rate in re-bonding.
Epoxy bonding is usually a room-temperature process and has a good success rate for regular room-temperature applications. Because epoxy bonding is typically organic-based, however, the bonding is susceptible to pyrolysis (such as by high intensity lasers) and/or photolysis (such as by ultra-violet light) in high power density applications. The strength of the epoxy bond varies with temperature and chemical environment. Because the resulting wedge and thickness cannot be precisely controlled, epoxy bonding is unsuitable for precision structural work. It creates a relatively thick interface which makes optical-index matching more of a concern in optical applications.
Frit bonding is a high-temperature process which creates a high-temperature rated interface. The interface is mechanically strong and chemically resistant in most applications. Because the frit material is physically thick and thus thermally noisy, it is unsuitable for precision structural work. For example, when optimized for bonding fused silica, frit bonding usually creates good coefficient of thermal expansion (CTE) matching with the substrates at room temperature. The matching usually does not hold to a wider temperature range, however, resulting in strain and stress near the interface. Furthermore, a frit bond is opaque and inapplicable in transmission optics. Due to the high temperature requirement, frit bonding requires high-temperature rated fixturing for alignment, and is thus expensive. It is unsuitable if high temperature side effects, such as changes in the physical/chemical properties of the substrates, are of concern.
OBJECTS AND ADVANTAGES OF THE INVENTION
Accordingly, it is an object of the present invention to provide a method for producing bonds which are as precise and transparent as optical contact bonds and which also have the strength and reliability of frit bonds. It is a further object of the invention to provide such a method which may be performed simply and inexpensively at room temperature.
SUMMARY
These objects and advantages are attained by a method for bonding a first surface to a second surface through hydroxide-catalyzed hydration and dehydration. According to the method, hydroxide ions are applied to at least one of the surfaces and the surfaces are then placed sufficiently close to each other to form at least one chemical bond between the surfaces. The hydroxide ions are preferably contained in an aqueous solution which is applied to at least one of the surfaces. Suitable hydroxides for the aqueous solution include the ionic salts NaOH, KOH, NH
4
OH, sodium ethoxide, and potassium ethoxide.
At least one of the surfaces is preferably a surface of a material that can form a silicate-like network or that can be chemically linked to a silicate-like network through hydroxide-catalyzed hydration and dehydration. Examples of materials capable of forming a silicate-like network through hydroxide-catalyzed hydration and dehydration include silica, fused silica, silicon having a surface oxide layer, natural quartz, fused quartz, ZERODUR™ glass ceramic, ultra low thermal expansion coefficient (ULE
) glass, borosilicate, opal, granite, and other silica-based or silica-containing materials, including certain laser crystals. Examples of materials which cannot form but can be linked to a silicate-like network through hydroxide-catalyzed hydration and dehydration include alumina, alumina-based or alumina-containing materials including certain laser crystals, and iron. When hydrated, these two categories of materials both feature surface hydroxide groups.
Prior to bonding, both surfaces are preferably cleaned. If the surface figure match between the surfaces is favorable, such as in precision applications, a hydroxide solution can be employed for bonding substrate material(s) that can form silicate-like networks in situ. A solution containing both hydroxide and silicate can be used for substrate materials that cannot generate (or cannot generate at a reasonable rate) silicate-like networks through hydroxide catalysis. In all these precision applications, solutions containing both hydroxide and silicate can be used to control the settling time by adjusting their composition percentages.
If the surface figure match between the surfaces is unfavorable, such as in imprecision applications, a filling powder may be added as part of the hydroxide-containing (or also silicate-containing) bonding material to facilitate bridging the interface gap. The filling powder should be material(s) that can be hydrated to have surface hydroxyl groups, which can be chemically linked through hydroxide catalysis to a silicate network (either generated in situ from the powder material(s) and/or substrate material(s) to be bonded, or originally contained in the bonding material). In these imprecision applications, solution(s)/slurry(ies) containing hydroxide, silicate, and powder material can also be used to control the settling time by adjusting their composition percentages. Advantageously, the bonding method of the present invention may be performed at room temperature.
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Gallagher John J.
Lumen Intellectual Property Services
The Board of Trustees of the Leland Stanford Junior University
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