Electrically conductive cement containing agglomerate, flake and powder metal fillers

• US 5,180,523 A
• Filed: 11/14/1989
• Issued: 01/19/1993
• Est. Priority Date: 11/14/1989
• Status: Expired due to Term

• Current Assignee: Parlex USA, Inc.
• Original Assignee: Poly-Flex Circuits Incorporated
• Inventors: Weiu, Tai S., Durand, David, Chu, Ang-Ling, Vieau, David P.
• Primary Examiner(s): Lieberman, Paul
• Assistant Examiner(s): SWOPE, BRADLEY
• Application Number:
  US07/436,199
• Time in Patent Office: 1,162 Days
• Field of Search: 252/512, 252/514, 252/513
• US Class Current: 252/512
• CPC Class Codes: C08L 2666/54 Inorganic substances
• CPC Class Codes: C09J 163/00 Adhesives based on epoxy resins; Adhesives based on derivatives of epoxy resins
• CPC Class Codes: H01B 1/22 the conductive material comprising metals or alloys
• CPC Class Codes: H01R 4/04 using electrically conductive adhesives
• CPC Class Codes: H05K 1/181 associated with surface mounted components
• CPC Class Codes: H05K 2201/0125 Shrinkable, e.g. heat-shrinkable polymer
• CPC Class Codes: H05K 2201/0218 Composite particles, i.e. first metal coated with second metal
• CPC Class Codes: H05K 2201/023 Hard particles, i.e. particles in conductive adhesive at least partly penetrating an electrode
• CPC Class Codes: H05K 2201/0245 Flakes, flat particles or lamellar particles
• CPC Class Codes: H05K 2201/0272 Mixed conductive particles, i.e. using different conductive particles, e.g. differing in shape
• CPC Class Codes: H05K 2203/0307 Providing micro- or nanometer scale roughness on a metal surface, e.g. by plating of nodules or dendrites
• CPC Class Codes: H05K 2203/0568 Resist used for applying paste, ink or powder
• CPC Class Codes: H05K 2203/1105 Heating or thermal processing not related to soldering, firing, curing or laminating, e.g. for shaping the substrate or during finish plating
• CPC Class Codes: H05K 2203/1453 Applying the circuit pattern before another process, e.g. before filling of vias with conductive paste, before making printed resistors
• CPC Class Codes: H05K 3/0023 by exposure and development of a photosensitive insulating layer
• CPC Class Codes: H05K 3/321 by conductive adhesives
• CPC Class Codes: Y10S 428/901 Printed circuit
• CPC Class Codes: Y10T 428/24917 including metal layer
• CPC Class Codes: Y10T 428/25 Web or sheet containing structurally defined element or component and including a second component containing structurally defined particles

Abstract

An electrically conductive cement having substantially stable conductivity and resistance characteristics under high humidity conditions comprises a mixture of two epoxy resins with the proportion of each epoxy resin adjusted to provide a volumetric shrinkage in the mixture in the 4 to 16% and a conductive silver particular filler including agglomerates having size and surface characteristics that maintain stable electrical contact with an electrical component lead. The epoxy mixture is preferably a combination of a high-shrinkage epoxy resin and a lower-shrinkage epoxy resin in the appropriate amounts of each so as to produce the desired volumetric shrinkage characteristic. The conductive particle filler is preferably an admixture of silver flakes, silver powder, and an effective amount of silver agglomerates. The agglomerates are irregularly shaped particles having multiple surface indentations and recesses to produce many rough-edged salients or ridges and having a particle length, width, and thickness aspect ratio of about 1:1:1. An effective amount of such agglomerates appears to effect penetration of surface oxides when establishing the cemented connection as a result of the volumetric shrinkage of the polymeric carrier upon curing.

Claims

1. An electrically conductive element for establishing electrical contact between and adhering surfaces, comprising:

a polymeric carrier having a volumetric shrinkage characteristic of about 4 to about 16%; and

a filler comprising about 60 to about 90% by weight of the cement including conducive particles consisting of;

i) agglomerate particles having a mean particle size of about 4.5 microns, an aspect ratio of about 1;

1;

1 and a rough external appearance characterized by sufficient recesses and ridge-like boundaries so as to effect enhanced electrical contact between surfaces adhered with the cement,

ii) a mixture of flake particles hang a FSSS of about 0.90 to about 1.30 microns and a surface area of about 0.3 to 0.6 m² /g and a particle size distribution of about 90% <

14 microns, 50% <

7 microns and 10% <

2 microns, and

iii) powder particles having a mean particle size of about 1.6 microns.

2. The electrically conductive cement of claim 1 wherein:

the polymeric carrier is comprised of at least two resins with the proportions of the resins adjusted to provide volumetric shrinkage in the desired range.

3. The electrically conductive cement of claim 2, wherein:

the polymeric carrier comprises a mixture of about one part bisphenol F diglycidyl ether resin and about one part liquid phenol epoxy novolac resin and about one part of a mixture of hardener, diluent and coupling agent.

4. The electrically conductive cement of claim 3, wherein:

wherein the filler comprises about 30% by weight agglomerate particles;

about 40% by weight flake particles and about 30% by weight powder particles;

the agglomerate particles are silver and have a FSSS of about 0.6 microns, a tap density of about 1.85 g/cc, a Scott apparent density of about 16.7 g/in³ and a surface area of about 1.62 m² g/;

the flake particles are silver and have a tap density of about 3.0 to 3.5 g/cc and a Scott apparent density of about 30 to 35 g/in³ ; and

the powder particles are silver and have a FSSS of about 0.75 microns, a tap density of about 2.70 g/cc, a Scott apparent density of about 20.1 g/in³ and a surface area of about 1.41 m² /g.

5. The electrically conductive cement of claim 4 wherein the filler comprises about 75% by wight of the cement.

6. The electrically conductive cement of claim 2 wherein each of the two resins is an epoxy resin.