# US 5,708,056 A · Hot melt epoxy encapsulation material

> Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt

- Number: US 5,708,056 A
- Document ID: US5708056A
- Status: Granted
- Kind: A
- Application number: 08/566,519
- Filed: 1995-12-04
- Granted: 1998-01-13
- Earliest claimed: 1995-12-04
- Assignees: Delco Electronics Corporation; Hughes Electronics Corporation
- Inventors: Theresa Renee Lindley; Samuel R. Wennberg; Henry Morris Sanftleben; James M. Rosson; Ralph D. Hermansen
- Web page: https://patentgrep.com/patent/US5708056A

## CPC

- C08L 63/00: Compositions of epoxy resins; Compositions of derivatives of epoxy resins
- C08G 59/18: Macromolecules obtained by polymerising compounds containing more than one epoxy group per molecule using curing agents or catalysts which react with the epoxy groups {; e.g. general methods of curing}
- H05K 3/284: {for encapsulating mounted components (H05K1/185 takes precedence)}
- H05K 3/3421: {Leaded components}
- H05K 2201/10689: Leaded Integrated Circuit [IC] package, e.g. dual-in-line [DIL]
- H05K 2201/10977: Encapsulated connections
- Y02P 70/50: Manufacturing or production processes characterised by the final manufactured product
- C08L: COMPOSITIONS OF MACROMOLECULAR COMPOUNDS (compositions based on polymerisable monomers C08F, C08G; artificial filaments or fibres D01F; textile treating compositions D06)
- C08G: MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
- H05K: PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
- Y02P: CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS

## Abstract

A method and encapsulation material are provided for processing an electronic circuit assembly having surface mount integrated circuit packages mounted with soldered leads to its substrate, in which encapsulation of the soldered lead joints serves to enhance the fatigue life of the solder joints. The encapsulation material is a reactive hot melt epoxy that is curable at temperatures significantly lower than that required for previous epoxy-based encapsulation materials. As such, processing of the circuit assembly is greatly facilitated, while the benefit of encapsulated solder joints is achieved for the assembly. The encapsulation material further includes a latent curative and a filler material for lower the coefficient of thermal expansion of the encapsulation material.

## Claims

### Claim 1

An encapsulation material for encapsulating leads and solder joints of a surface mount integrated circuit device mounted on an electronic circuit assembly, the encapsulation material being a reactive hot melt material characterized by being a solid or semisolid at approximately room temperature, a liquid at an elevated application temperature of about 45.degree. to about 90.degree. C. at which the encapsulation material is applied to the leads and solder joints, and resolidifying upon cooling to room temperature so as to enable immediate handling of the electronic circuit assembly, the encapsulation material comprising at least two epoxy materials and a latent curative that triggers curing at a temperature of less than about 150.degree. C., a first epoxy of the at least two epoxy materials being a solid or semisolid at room temperature, a second epoxy of the at least two epoxy materials being a solid, semisolid or liquid at room temperature, the encapsulation material further comprising a filler material so as to have a coefficient of thermal expansion of about 25 to about 35 ppm/.degree. C., the encapsulation material having a viscosity of not more than about 5000 centipoise at the elevated application temperature.

### Claim 2 (depends on 1)

An encapsulation material as recited in claim 1 wherein the first epoxy is selected from the group consisting of bisphenol A and epoxy novolac, and constitutes at least about 20 weight percent of the at least two epoxy materials.

### Claim 3 (depends on 1)

An encapsulation material as recited in claim 1 wherein the second epoxy is a liquid epoxy resin selected from the group consisting of bisphenol A and bisphenol F, and constitutes at most about 80 weight percent of the at least two epoxy materials.

### Claim 4 (depends on 1)

An encapsulation material as recited in claim 1 wherein the encapsulation material is fully curable at a temperature in excess of about 150.degree. C. in about two minutes or less.

### Claim 5 (depends on 1)

An encapsulation material as recited in claim 1 wherein the filler material is glass spheres that constitute at least about 40 weight percent of the encapsulation material.

### Claim 6 (depends on 5)

An encapsulation material as recited in claim 5 wherein the filler material is a trimodal distribution of particles comprising a larger size particle range, an intermediate size particle range, and a smaller size particle range, and wherein the larger size particle range constitutes proportion of the filler material than the smaller size particle range and the intermediate size particle range combined.

### Claim 7 (depends on 1)

An encapsulation material as recited in claim 1 wherein the encapsulation material consists essentially of:
a first epoxy being a solid or semisolid at room temperature and constituting about 20 weight percent of the encapsulation material;
a second epoxy being a solid, semisolid or liquid at room temperature and constituting up to about 3 weight percent of the encapsulation material;
the latent curative triggering curing at a temperature of not more than 120.degree. C. and constituting up to about 3 weight percent of the encapsulation material; and
a filler material constituting about 75 weight percent of the encapsulation material.

### Claim 8

An electronic assembly having a substrate with a conductive member, the electronic assembly comprising:
a surface mount integrated circuit device mounted to the substrate;
a lead extending from the surface mount integrated circuit device and in electrical contact with the conductive member;
solder bonding the lead to the conductive member so as to form a solder joint; and
an encapsulation material encapsulating the solder joint, the encapsulation material being formed from a reactive hot melt material characterized by being a solid or semisolid at approximately room temperature, being a liquid at an elevated application temperature of about 45.degree. to about 90.degree. C. at which the encapsulation material is applied to the solder joint, and resolidifying upon cooling to room temperature so as to enable immediate handling of the electronic circuit assembly, the encapsulation material comprising at least two epoxy materials and a latent curative that triggers curing at a temperature of less than 150.degree. C., a first epoxy of the at least two epoxy materials being a solid or semisolid at room temperature, a second epoxy of the at least two epoxy materials being a solid, semisolid or liquid at room temperature, the encapsulation material further comprising a filler material so as to have a coefficient of thermal expansion of about 25 to about 35 ppm/.degree. C., the encapsulation material having a viscosity of not more than about 5000 centipoise at the elevated application temperature.

### Claim 9 (depends on 8)

An electronic assembly as recited in claim 8 wherein the reactive hot melt material has a viscosity of not more than about 1000 centipoise at the elevated application temperature.

### Claim 10 (depends on 8)

An electronic assembly as recited in claim 8 wherein the encapsulation material is heat curable at a temperature of not more than 120.degree. C.

### Claim 11 (depends on 8)

An electronic assembly as recited in claim 8 wherein the filler material is glass spheres that constitute at least about 40 weight percent of the encapsulation material, the filler material being a trimodal distribution of particles comprising a larger size particle range, an intermediate size particle range, and a smaller size particle range, and wherein the larger size particle range constitutes a greater proportion of the filler material than the smaller size particle range and the intermediate size particle range combined.

### Claim 12 (depends on 8)

An electronic assembly as recited in claim 8 wherein the first epoxy of the at least two epoxy materials is a solid or semisolid at room temperature and constitutes about 20 weight percent or more of the at least two epoxy materials, and wherein the second epoxy of the at least two epoxy materials is a solid, semisolid or liquid at room temperature.

### Claim 13 (depends on 8)

An electronic assembly as recited in claim 8 wherein the first epoxy is selected from the group consisting of bisphenol A and epoxy novolac and constitutes at least about 90 weight percent of the at least two epoxy materials, and wherein the second epoxy is liquid epoxy resin selected from the group consisting of bisphenol A and bisphenol F.