Optical contact bonding
Encyclopedia
Optical contact bonding is a glueless process whereby two closely conformal surfaces are joined together, being held purely by intermolecular forces.
has been credited with the first description of conformal interaction observed through the interference phenomenon known as Newton's rings
, though it was S. D. Poisson
in 1823 who first described the optical characteristics of two identical surfaces in contact. It was not until the 19th century that objects were made of such precision that the binding phenomenon was observed. The clinging together was described as "wringing together", or as "ansprengen" in German. By 1900 optical contact bonding was being employed in the construction of optical prisms, and the following century saw further research into the phenomenon at the same time that ideas of inter-atom interactions were first being studied.
However, if the bodies are conformal to an accuracy of better than 10 angstrom
s (1 nanometer), then a sufficient surface area is in close enough contact for the intermolecular interactions to have an observable real world physical manifestation—that is, the two objects stick together. Such a condition requires a high degree of accuracy and surface smoothness, which is typically found in optical components, such as prisms.
or glue, the physical properties of the bound object are the same as the objects joined. Typically, glues and binders are more heat sensitive or have undesirable properties compared to the actual bodies being joined. The use of optical contact bonding allows the production of a final product with properties as good as the bulk solid.
History
Isaac NewtonIsaac Newton
Sir Isaac Newton PRS was an English physicist, mathematician, astronomer, natural philosopher, alchemist, and theologian, who has been "considered by many to be the greatest and most influential scientist who ever lived."...
has been credited with the first description of conformal interaction observed through the interference phenomenon known as Newton's rings
Newton's rings
The phenomenon of Newton's rings, named after Isaac Newton who first studied them in 1717, is an interference pattern caused by the reflection of light between two surfaces - a spherical surface and an adjacent flat surface...
, though it was S. D. Poisson
Siméon Denis Poisson
Siméon Denis Poisson , was a French mathematician, geometer, and physicist. He however, was the final leading opponent of the wave theory of light as a member of the elite l'Académie française, but was proven wrong by Augustin-Jean Fresnel.-Biography:...
in 1823 who first described the optical characteristics of two identical surfaces in contact. It was not until the 19th century that objects were made of such precision that the binding phenomenon was observed. The clinging together was described as "wringing together", or as "ansprengen" in German. By 1900 optical contact bonding was being employed in the construction of optical prisms, and the following century saw further research into the phenomenon at the same time that ideas of inter-atom interactions were first being studied.
Explanation
Intermolecular forces such as Van der Waals forces, hydrogen bonds, and dipole-dipole interactions are typically not sufficiently strong to hold two apparently conformal rigid bodies together, since the forces drop off rapidly with distance, and the actual area in contact between the two bodies is small due to surface roughness and minor imperfections.However, if the bodies are conformal to an accuracy of better than 10 angstrom
Ångström
The angstrom or ångström, is a unit of length equal to 1/10,000,000,000 of a meter . Its symbol is the Swedish letter Å....
s (1 nanometer), then a sufficient surface area is in close enough contact for the intermolecular interactions to have an observable real world physical manifestation—that is, the two objects stick together. Such a condition requires a high degree of accuracy and surface smoothness, which is typically found in optical components, such as prisms.
Production of an optical contact bond
In addition to both surfaces' being practically conformal (in practice often completely flat), the surfaces must also be extremely clean and free from any small contamination that would prevent or weaken the bond—including grease films and specks of dust. For bonding to occur, the surfaces need only to be brought together; the intermolecular forces draw the bodies into the lowest energy conformation, and no pressure needs to be applied.Advantages
Since the method requires no binder, balsamCanada balsam
Canada balsam, also called Canada turpentine or balsam of fir, is a turpentine which is made from the resin of the balsam fir tree of boreal North America...
or glue, the physical properties of the bound object are the same as the objects joined. Typically, glues and binders are more heat sensitive or have undesirable properties compared to the actual bodies being joined. The use of optical contact bonding allows the production of a final product with properties as good as the bulk solid.
Uses
Originally the process was confined to optical equipment such as prisms—the earliest examples being made around 1900. Later the scope of use was expanded to microelectronics and other miniaturised devices.External links
- Description of production of experimental 'Lab on a chip' via contact bonding RSC Publishing (Royal Society of Chemistry)
- 100% Bond Strength Characterization of Laser Materials Modern optical bonding technique utilized by Precision Photonics Corporation.
- Optical Fabrication: Optical Contacting Grows More Robust by Chris Myatt, Nick Traggis, and Kathy Li Dessau.