Eutectic bonding of metal to ceramic

• US 5,108,026 A
• Filed: 05/14/1991
• Issued: 04/28/1992
• Est. Priority Date: 05/14/1991
• Status: Expired due to Fees

• Current Assignee: CTS Corporation
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: Su, Ming-Yih, Somers, John W.
• Primary Examiner(s): Seidel, Richard K.
• Assistant Examiner(s): Knapp, Jeffrey T.
• Application Number:
  US07/699,534
• Time in Patent Office: 350 Days
• Field of Search: 228/122, 228/263.12, 228/903, 228/121, 228/124, 228/198
• US Class Current: 228/122.1
• CPC Class Codes: C04B 2235/6567 Treatment time
• CPC Class Codes: C04B 2235/658 Atmosphere during thermal treatment
• CPC Class Codes: C04B 2235/6584 at an oxygen percentage below that of air
• CPC Class Codes: C04B 2235/662 Annealing after sintering
• CPC Class Codes: C04B 2235/666 Applying a current during sintering, e.g. plasma sintering [SPS], electrical resistance heating or pulse electric current sintering [PECS]
• CPC Class Codes: C04B 2237/06 Oxidic interlayers
• CPC Class Codes: C04B 2237/09 wherein the active component for bonding is not the largest fraction of the interlayer
• CPC Class Codes: C04B 2237/12 Metallic interlayers
• CPC Class Codes: C04B 2237/124 based on copper
• CPC Class Codes: C04B 2237/126 wherein the active component for bonding is not the largest fraction of the interlayer
• CPC Class Codes: C04B 2237/343 Alumina or aluminates
• CPC Class Codes: C04B 2237/365 Silicon carbide
• CPC Class Codes: C04B 2237/366 Aluminium nitride
• CPC Class Codes: C04B 2237/403 Refractory metals
• CPC Class Codes: C04B 2237/405 Iron metal group, e.g. Co or Ni
• CPC Class Codes: C04B 2237/406 Iron, e.g. steel
• CPC Class Codes: C04B 2237/407 Copper
• CPC Class Codes: C04B 2237/52 Pre-treatment of the joining surfaces, e.g. cleaning, machining
• CPC Class Codes: C04B 2237/54 Oxidising the surface before joining
• CPC Class Codes: C04B 2237/56 Using constraining layers before or during sintering
• CPC Class Codes: C04B 2237/592 : whereby the interlayer is not continuous, e.g. not the whole surface of the smallest substrate is covered by the interlayer
• CPC Class Codes: C04B 2237/706 : of one or more of the metallic layers or articles
• CPC Class Codes: C04B 2237/708 : of one or more of the interlayers
• CPC Class Codes: C04B 2237/72 : Forming laminates or joined articles comprising at least two interlayers directly next to each other
• CPC Class Codes: C04B 37/025 : consisting of glass or ceramic material
• CPC Class Codes: C04B 37/026 : consisting of metals or metal salts
• CPC Class Codes: H05K 1/0306 : Inorganic insulating substrates, e.g. ceramic, glass
• CPC Class Codes: H05K 2201/0355 : Metal foils
• CPC Class Codes: H05K 3/38 : Improvement of the adhesion between the insulating substrate and the metal

Abstract

An improved eutectic oxide bonding method is applied for bonding a metallic copper foil to a nonmetallic substrate by forming a liquid phase derived from a eutectic oxide composition. A metallic copper thin film is initially deposited onto the substrate and heated in a low oxygen atmosphere under suitable conditions to form a cuprous oxide film. A metallic copper foil is positioned on the substrate in contact with the cuprous oxide film. Preferably, the assembly is initially heated at a temperature below the eutectic melting point to soften the foil and promote intimate contact between the foil and the cuprous oxide film. Thereafter, the assembly is heated above the eutectic melting point to form a liquid phase at the interface of the foil and the cuprous oxide film, and maintained at the temperature for a time sufficient to dissolve the oxide film, whereupon the liquid phase wets the substrate. The assembly is cooled, and the liquid phase is solidified to bond the foil to the substrate. In addition to copper, the method may be adopted to bond foils of other metals, including chromium, iron, cobalt and nickel, using low melting eutectic oxides thereof.

Claims

1. A method for bonding a metal foil to a nonmetallic substrate, said foil being formed of a metal reactable to produce an oxide compound and further suitable for producing in combination with said oxide compound a low melting eutectic oxide composition, said method comprising

depositing a thin film of said metal onto the substrate,

oxidizing the metal film to form said metal oxide compound,

arranging the metal foil and the substrate such that the foil lies in contact with the oxidized deposit,

heating the arrangement at a temperature above the eutectic melting point and below the metal melting point, whereupon a liquid phase forms at the interface between the metal foil and the oxidized film,

continuing to heat the arrangement at a temperature above the eutectic melting point for a time sufficient to dissolve the metal oxide compound into the liquid phase, whereupon the liquid phase wets the substrate, and

cooling the arrangement, whereby the liquid phase solidifies and bonds the metal foil to the substrate.

2. The method according to claim 1 wherein the metal is selected from the group consisting of chromium, iron, cobalt, nickel and copper.

3. A method for bonding a metallic copper foil to a nonmetallic substrate comprising

depositing a metallic copper thin film onto the substrate,

oxidizing the copper film under conditions suitable for forming cuprous oxide compound,

applying a metallic copper foil to the substrate to produce an arrangement comprising the foil in intimate contact with the oxidized copper film at an interface therebetween,

heating the arrangement at a temperature above the melting point of a eutectic copper oxide composition composed of about 0.34 weight percent oxygen and the balance copper, but less than the copper metal melting point, whereupon during said heating the copper metal and the oxidized deposit combine to form a liquid phase at the interface,

maintaining the arrangement at a temperature above the eutectic melting point and below the copper metal melting point for a time sufficient to dissolve the oxidized film into the liquid phase, whereupon the liquid phase wets the substrate, and

cooling and solidifying the liquid phase to bond the copper foil to the substrate.

4. A method for bonding a metallic copper foil to an alumina substrate comprising

vapor depositing a metallic copper thin film onto the substrate,

heating the copper film in contact with a suitably low oxygen atmosphere to form a cuprous oxide film,

applying a metallic copper foil directly onto the cuprous oxide film to form an assembly,

heating the assembly to a temperature above the melting point of a eutectic copper oxide composition composed of about 0.34 weight percent oxygen and the balance copper, and below the copper metal melting point to form a liquid phase that comprises the cuprous oxide from said film and wets the substrate, and

cooling the assembly to solidify the liquid phase and thereby bond the copper foil to the substrate.

5. A method for bonding a metallic copper foil to an alumina substrate comprising

vapor depositing onto the substrate a metallic copper film having a thickness between about 200 Å

and 3000 Å

,

heating the copper film to a temperature between 800°

C. and 1065°

C. while exposed to an atmosphere containing oxygen at a partial pressure less than 10^-3 atmosphere to react the metallic copper form a cuprous oxide film,

applying a metallic copper foil directly onto the cuprous oxide film to form an assembly,

heating the assembly to a temperature less than 1065°

C. to soften the metallic copper foil to produce intimate contact between the foil and the cuprous oxide film,

further heating the assembly to a temperature between about 1065°

C. and 1083°

C. to form a liquid phase derived from the cuprous oxide film in contact with the copper foil, which liquid phase wets the substrate, and

cooling the assembly to solidify the liquid phase and thereby bond the copper foil to the substrate.

6. A method for bonding a metallic copper foil to an alumina substrate comprising

vapor depositing onto the substrate a metallic copper thin film having a thickness between about 500 Å

and 1000 Å

,

heating the copper film to a temperature between 900°

C. and 1000°

C. while exposed to an atmosphere containing oxygen at a partial pressure between about 10^-5 and 10^-3 atmosphere to substantially react the metallic copper to form a cuprous oxide film,

applying a metallic copper foil directly onto the cuprous oxide film to form an assembly,

heating the assembly in an inert atmosphere to a temperature less than about 1065°

C. to soften the metallic copper foil to produce intimate contact at an interface between the copper foil and the cuprous oxide film,

further heating the assembly in an inert atmosphere to a temperature between about 1065°

C. and 1070°

C. to form a eutectic liquid phase at the interface and to dissolve the cuprous oxide film into the liquid phase, whereupon the liquid phase wets the substrate, and

cooling the assembly to solidify the liquid phase and thereby bond the copper foil to the substrate.