In the first week of 2010, 102 U.S. Patents referencing nanotechnology were granted setting a pace for more than 5,500 nanotechnology patents this year. More than 4,400 nanotechnology patents were granted in 2009, the record year to date for nanotechnology patents. More than 49,000 nanotechnology patent applications are pending.
The new year's first "nano" Patent is 7,640,659, awarded to Panasonic Corporation (Osaka, JP) for a cheaper nanofabrication process involving a method for forming a conductive pattern on a wiring board using a conductive paste that includes metal nanoparticles.
Panasonic inventors Seiji Karashima, Takashi Kitae and Seiichi Nakatani developed a bubbly method for forming a conductive pattern that is simpler than the conventional complicated processes involving photolithography and etching, hence a conductive pattern can be formed at a comparatively low cost.
The inventors made various examinations on a method for forming a bump through self-assembly of conductive particles (such as a solder powder) on an electrode of a wiring board or a semiconductor chip, or on a flip-chip mounting method by forming a connecting body between electrodes of a wiring body and a semiconductor chip through self-assembly of conductive particles between the electrodes resulting in a novel bump formation method and a novel flip-chip mounting method.
The Panasonic method provides a wiring board on which a wiring pattern is formed. The wiring pattern is formed by providing a flat plate with a convex pattern on a surface thereof in facing relation to the wiring board, supplying a fluid body including conductive particles and a gas bubble generating agent into a gap between the wiring board and the flat plate, and heating the fluid body for allowing the fluid body to self-assemble between the convex pattern formed on the flat plate and the wiring board, whereby forming the wiring pattern made of an aggregate of the conductive particles included in the fluid body having self-assembled.
The fluid body is forced out of the gas bubbles by the growing gas bubbles, so that the fluid body can be allowed to self-assemble between a convex pattern formed on the flat plate and the substrate owing to the interfacial force. As a result, an aggregate of the conductive particles included in the fluid body having self-assembled forms a conductive pattern, and thus, the conductive pattern can be easily formed in a simple way of heating.
Furthermore, since the conductive pattern is formed in a self-assembly manner in accordance with the convex pattern, the conductive pattern can be formed in a fine shape.
In addition, when a curable material such as a resin is used as the fluid body, the conductive pattern made of the aggregate of the conductive particles can attain a structure stable in the strength by curing the fluid body of the resin or the like after forming the conductive pattern through the self-assembly.
Furthermore, since the conductive pattern is formed in a self-assembly manner in accordance with the convex pattern, the conductive pattern can be formed in a fine shape.
In addition, when a curable material such as a resin is used as the fluid body, the conductive pattern made of the aggregate of the conductive particles can attain a structure stable in the strength by curing the fluid body of the resin or the like after forming the conductive pattern through the self-assembly.
FIGS. 4A through 4E are cross-sectional views for showing basic procedures in Panasonic’s conductive pattern formation
11 substrate | 14 a fluid body |
12 the flat plate | 16 conductive particles |
13 convex patterns | 20 gas bubbles |
At this point, the are formed on the flat plate in the same layout as a conductive pattern to be formed on the substrate. Also, in the case where the substrate is, for example, a wiring board on which electronic components and the like are built, the flat plate is provided above the substrate with necessary alignment.
It is noted that these procedures may be performed by previously providing the substrate and the flat plate so as to oppose each other with a given gap and then supplying the fluid body including the conductive particles and the gas bubble generating agent into the gap therebetween.
When the fluid body is heated under this condition, gas bubbles are generated from the gas bubble generating agent included in the fluid body as shown in FIG. 4C. At this point, the fluid body is forced out of the gas bubbles as the gas bubbles grow.
The fluid body thus forced out self-assembles between the convex patterns formed on the flat plate and the substrate owing to the interfacial force as shown in FIG. 4D. When the flat plate is removed, patterns of the fluid body 14 obtained through the self-assembly is formed on the substrate.
At this point, an aggregate of the conductive particles included in the fluid body having self-assembled forms the conductive patterns with the conductive particles in contact with one another
The last nano-patent of 2009 was U.S. Patent 7,640,226 for self-welded metal-catalyzed carbon nanotube bridges and solid electrolytic non-volatile memories, awarded to Case Western Reserve University See Nano Patents and Innovations: http://tinyurl.com/yefwhgb
