Stock material or miscellaneous articles – Composite – Of epoxy ether
Reexamination Certificate
1997-11-24
2001-01-16
Pianalto, Bernard (Department: 1762)
Stock material or miscellaneous articles
Composite
Of epoxy ether
C174S050510, C361S500000, C427S079000, C427S096400, C427S103000, C427S117000, C428S901000
Reexamination Certificate
active
06174606
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to silver/polymer composites and more particularly to a chemical coating to form a Ag-complex in the composite to reduce silver dissolution and electrolytic migration.
BACKGROUND OF THE INVENTION
Insulating thermoset and thermoplastic polymers can be made conductive by loading them with metallic powder particles such as silver, palladium, tin, graphite or gold. The resulting conductive composite or paste has many potential applications. Such a material can be used for electrostatic discharge protection, electromagnetic interference shielding, and as an adhesive for interconnect technology that could replace PbSn solder. Ag is the metal of choice for these latter applications owing to its high conductivity and oxide free surface. The widespread use of Pb-containing solder in electronics is an environmental concern, and regulations banning Pb are being considered. Whereas Ag particles filled composite possesses high conductivity for interconnection applications, the corrosion and dissolution resistance are also of utmost importance specifically, when the interconnect are in close proximity less than
1
mm. In order to be conductive, the composite has to have a high loading level, i. e. it should contain more than 50 weight % of the metal powder. Interconnections are expected to perform under a variety of environmental conditions, and with an applied voltage, where Ag ion dissolution can result in electrolytic migration, dendrite formation and eventually electrical shorts or opens. Thus, the susceptibility of the metal in the composite to dissolve in the presence of moisture under an applied potential indicates a problem for a device in operation.
In U.S. Pat. No. 4,821,148 which issued Apr. 11, 1989 to Kobayashi et al., a semiconductor device having an aluminum electrode, a lead frame having a silver electrode, and a copper wire connecting the electrodes was immersed in a solution of benzotriazole in ethyl alcohol for 3 minutes to form a metal-organic compound thereon. An Ag-benzotriazole film was formed on the surface of the silver electrode, a Cu-benzotriazole film was formed on the surface of the copper wire, and an Al-benzotriazole film was formed on the surface of the aluminum electrode. The films are effective in enhancing not only the corrosion resistance to water but also adhesion to the molding resin used to package the device.
SUMMARY OF THE INVENTION
In accordance with the present invention a structure is described having reduced electrochemical mobility of Ag when exposed to moisture comprising a first substrate having a first conductive region on a surface of the substrate, a conductive composite containing silver particles and a polymer, the conductive composite positioned on and in electrical contact with the first conductive region and a coating containing a heterocyclic organic compound containing nitrogen positioned on the conductive composite.
The heterocyclic organic compound may be selected from the group consisting of imidazole, benzimidazole, benzotriazole (BTA), and 5 methyl benzotriazole and derivatives thereof with chemical moities attached to the aromatic ring. The heterocyclic organic compound containing nitrogen may be a cyclic azo-compound containing nitrogen.
REFERENCES:
patent: 4821148 (1989-04-01), Kobayashi et al.
Brusic Vlasta Agnes
Roldan Judith Marie
Saraf Ravi F.
International Business Machine Corporation
Pianalto Bernard
Tropp Robert M.
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