Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Reexamination Certificate
2000-06-28
2003-03-25
Ball, Michael W. (Department: 1733)
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
C156S308600, C156S309300, C427S536000
Reexamination Certificate
active
06537411
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
Polyimides and derivatives of polyimides are of great importance to the microelectronics packaging and encapsulation industries. This invention relates to a method for the low temperature lamination of metals, especially copper, to the surface of polyimides and derivatives of polyimides.
When thermally induced grafting or graft copolymerization occurs on the pristine or the pre-activated surface and interface of polyimides or derivatives of polyimides in contact with a metal surface, lamination occurs simultaneously. The surface and interfacial polymerization or graft copolymerization with concurrent lamination of the metal are carried out under atmospheric conditions, and in the complete absence of an added polymerization initiator or system degassing. Polymerization initiators may also be used to enhance the graft copolymerization reaction. The process and properties can be imparted on surfaces of pristine or pre-activated polyimides and derivatives of polyimides in contact with a preferred metal.
Thermal grafting or graft copolymerization with concurrent lamination can be carried out in the presence of one or more functional monomers including, but not limited to, 1-vinyl imidazole (VIDZ), 1-ally imidazole (AIDZ), 2-vinyl pyridine (2VP), 4-vinyl pyridine (4VP), 2,4,6-triallyoxy-1,3,5-triazine, trially-1,3,5-benzenetricarboxylate, epoxide-containing monomers, monomers of polyelectrolyte and polyampholyte.
The lap shear adhesion strength of the so-laminated polyimide-copper interface can readily exceed the fracture strength of the substrate polyimide film. The T-peel adhesion strengths of the so-laminated polyimide-copper interfaces are greater than 16 N/cm, with delamination occurs via cohesive failure in the polymer film. The strong adhesion between the polymer and the metal arises from the strong adhesion/adsorption of the functional chains and the covalent tethering of the grafted functional chains on the surfaces of polyimides or derivatives of polyimide on one hand, and the strong adhesion, with or without charge transfer interaction, of the grafted functional chains to the metal surface on the other. Strong adhesion of the metal to the polymer depends on the proper annealing of the polyimide-copper interface after thermal grafting, interfacial polymerization and lamination.
The present invention distinguishes itself from prior art lamination of metals to polyimides in that the one-step grafting/lamination process is carried out at temperature substantially below the melt processing and curing temperatures of the polyimides, does not involve the polyamic acid precursor and no adhesive is required to affect the lamination process.
2. Description of Related Arts
Polyimides are considered specialty plastics because of their outstanding, high performance engineering properties particularly suited for the microelectronics packaging industries and composite applications. Polyimides offer good thermal and mechanical stability, low dielectric constants and chemical resistance. Polyimides for electronic applications have been reviewed by P. K. Mukerji and G. Demet in
Polym. Adv. Technol.
4, 309 (1992). Good adhesion of polyimides to metals, copper in particular, is essential for applications in microelectronics. Depending on the configuration of the particular assembly, the copper metal is either introduced onto the polyimide surface through vacuum evaporation/deposition, or by means of the direct lamination of the metal foil, films or sheet to the polymer surface.
The strategies of surface chemical and physical modification have been widely implemented in polyimides and other polymers for adhesion improvement with metals and with other polymer substrates. They have been described, for example in, E. Sacher, J. J. Pireaux and S. P. Kowalczyk (Eds.),
Metallization of Polymers,
ACS Symposium Series 440, Am. Chem. Soc., Washington, D.C. (1990); in M. Strobel, C. S. Lyons and K. L. Mittal (Eds.),
Plasma Surface Modification of Polymers: Relevance to Adhesion,
VSP, Zeist, The Netherlands (1994); and in K. L. Mittal (Ed.),
Polymer Surface Modification: Relevance to Adhesion,
VSP, Zeist, The Netherlands (1995).
The patent literature contains numerous disclosures of surface modification of polyimides for adhesion enhancement. However, most of the prior art is related to plasma or chemical surface treatment. A few of the prior art disclosures are related to surface modification via graft copolymerization. Almost no prior art is directed to the modification of polyimides via surface graft copolymerization for the improvement of adhesion to metals. Throughout our exhaustive patent literature search, there is no relevant process which involves the simultaneous modification of polyimide surface via grafting or graft copolymerization and the lamination of a metal in the complete absence of an adhesive.
For further background reading, reference is made to the following patent publications:
European Patent Nos. 310803, 388888, 419845, 456972 and 478975;
U.S. Pat. Nos. 4,382,101, 4,775,449 and 4,842,946;
British Patent publication No. 9004392;
Japanese Patent Publication Nos. 1132772, 3150392, 4072070, 5001160, 7070335, 61116531A, 90-025779, 04-359585, 04064280, 06-316759, 06-279996, 07-186324, 7316776A, 08-230108, 08-325713; and
Russian Patent Publication Nos. 262015, 315079 and 339042.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a new method for the low temperature direct lamination of a metal, such as copper, to surfaces of polyimides under atmospheric conditions. It is also an object of the present invention to effect the said lamination in the absence of an added adhesive. These and other objects and advantages of the present invention are obtained by providing a method for modification of pristine, pretreated, or preactivated polyimide surfaces via low temperature thermal graft copolymerization or interfacial polymerization of an appropriate functional monomer in the presence of the contacting metal. A desirable low grafting/lamination temperature is selected to be substantially below the melting or curing temperature of the polyimides. Desirable radio frequency gas plasma with low plasma power is selected for the pretreatment of the polyimides to minimize the undesirable over-oxidation, etching or sputtering of the polyimide surface. The surfaces of the polyimides can also be activated by corona discharge, ozone treatment, UV irradiation and electron beam bombardment.
The objects and advantages of the present invention can be achieved when the monomer used for the surface graft copolymerization or interfacial polymerization with concurrent lamination are selected from a group of vinyl monomers which contain nitrogen heteroatoms or nitrogen functionalities in the pendent group or groups. The monomers are also selected from the family containing multiple vinyl group functionalities, which can also promote chain crosslinking, as well as from the family which contains epoxide functional groups.
The objects and advantages of the present invention can be achieved when the monomer concentrations used for graft copolymerization or interfacial polymerization range from 2 to 100 weight per cent. Desirable solvents are selected from the group which provide good solubility for the vinyl monomer, and which promote free radical polymerization.
The objects and advantages of the present invention are obtained when the monomers used for the simultaneous interfacial polymerization grafting and lamination process also contains a small quantity of a polymerization initiator. The initiators are selected from the families of organic peroxides, hydroperoxides, azo and diazo compounds, and the like.
The objects and advantages of the present invention are obtained when the metals for lamination are preferably selected from copper metal and its alloys.
The objects and advantages of the present invention are obtained when the polymers for lamination are selected from polyimides and their derivatives.
The objects and adva
Ang Arthur Khoon Siah
Cui Cheng Qiang
Kang En-Tang
Lim Thiam Beng
Neoh Koon Gee
Ball Michael W.
Haran John T.
The National University of Singapore
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