# US 4,398,975 A · Conductive paste

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- Number: US 4,398,975 A
- Document ID: US4398975A
- Status: Granted
- Kind: A
- Application number: 06/331,229
- Filed: 1981-12-16
- Granted: 1983-08-16
- Earliest claimed: 1980-12-25
- Assignees: Sony Corporation
- Inventors: Kenji Ohsawa; Takao Ito; Koichiro Tanno; Masayuki Ohsawa; Keiji Kurata
- Web page: https://patentgrep.com/patent/US4398975A

## CPC

- C22C 28/00: Alloys based on a metal not provided for in groups C22C5/00 - C22C27/00
- H01B 1/02: mainly consisting of metals or alloys
- H01R 4/58: characterised by the form or material of the contacting members (H01R4/01 takes precedence)
- H05K 3/3485: Application of solder paste, slurry or powder (using printing techniques to form the desired conductive pattern of the printed circuit by applying conductive material H05K3/12)
- H05K 3/4038: {Through-connections; Vertical interconnect access [VIA] connections (H05K3/403, H05K3/42 take precedence)}
- H05K 3/346: Solder materials or compositions specially adapted therefor
- H05K 3/4644: {by building the multilayer layer by layer, i.e. build-up multilayer circuits (making via holes in the insulating layers H05K3/0011; special circuit boards as base or core whereon the multilayer is built H05K3/4602)}
- H05K 2201/0215: Metallic fillers
- H05K 2201/0305: Solder used for other purposes than connections between PCB or components, e.g. for filling vias or for programmable patterns
- H05K 2201/09845: Stepped hole, via, edge, bump or conductor
- C22C: ALLOYS (treatment of alloys C21D, C22F)
- H01B: CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES (selection for magnetic properties H01F1/00; waveguides H01P {; printed circuits H05K})
- H01R: ELECTRICALLY-CONDUCTIVE CONNECTIONS; STRUCTURAL ASSOCIATIONS OF A PLURALITY OF MUTUALLY-INSULATED ELECTRICAL CONNECTING ELEMENTS; COUPLING DEVICES; CURRENT COLLECTORS
- H05K: PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS

## Abstract

A novel conductive paste and a method of making the same in which metallic gallium is combined with a metal or alloy which forms a eutectic with gallium in an amount in excess of its limit of solubility in gallium at a specific temperature. This melt is then treated with a metal powder of a second metal or alloy which alloys with gallium to produce a higher melting alloy, the second metal powder being coated on its surface with the eutectic-forming metal.

## Claims

### Claim 1

A conductive paste comprising:
a continuous phase of metallic gallium in combination with a first metal which forms a eutectic with gallium, said metal being present in excess of its solubility limit in gallium at a predetermined temperature,
in combination with a second metal powder capable of alloying with gallium, said powder being pre-coated with said first metal and being dispersed through said continuous phase.

### Claim 2 (depends on 1)

A conductive paste according to claim 1 in which:
said first metal includes indium, tin, zinc, or bismuth, or an alloy thereof.

### Claim 3 (depends on 1)

A conductive paste according to claim 1 in which said second metal is copper, nickel, cobalt, gold, or an alloy of such metal.

### Claim 4 (depends on 2)

A conductive paste according to claim 2 which contains about 10% by weight tin.

### Claim 5 (depends on 2)

A conductive paste according to claim 2 which contains about 6% by weight zinc.

### Claim 6 (depends on 2)

A conductive paste according to claim 2 which contains about 20% by weight indium.

### Claim 7 (depends on 1)

A conductive paste according to claim 1 in which:
said metal powder has a size of from 0.5 to 500 microns.

### Claim 8 (depends on 1)

A conductive paste according to claim 1 in which:
said metal powder has a size of about l0 to l00 microns.

### Claim 9

A method for making a conductive composition which comprises:
providing a molten mixture of gallium and a first metal which forms a eutectic with gallium at a temperature in excess of the melting point of said metal,
cooling the resulting melt to a lower temperature,
adding to the cooled melt a powder having a central core of a second metal or alloy capable of alloying with gallium to form a gallium alloy of a higher melting point than the gallium itself, said core being pre-coated with said first metal, and
agitating the resulting mixture to disperse said powder within said melt.

### Claim 10 (depends on 9)

A method according to claim 9 in which said first metal includes indium, tin, zinc or bismuth.