Method of forming an overmolded electronic assembly

Details Method of forming an overmolded electronic assembly Method of forming an overmolded electronic assembly

1998-05-20

2001-01-30

Ortiz, Angela (Department: 1732)

Plastic and nonmetallic article shaping or treating: processes

Mechanical shaping or molding to form or reform shaped article

To produce composite, plural part or multilayered article

C264S272150, C264S272170, C264S275000

Reexamination Certificate

active

06180045

ABSTRACT:

FIELD OF THE INVENTION
The present invention generally relates to electronic assemblies. More particularly, this invention relates to an overmolded electronic assembly that is compatible with automated assembly methods and yields an enclosure of the type that conducts heat away from a flip chip or other circuit device enclosed within the assembly.
BACKGROUND OF THE INVENTION
Circuit boards with semiconductor devices such as flip chips must often be protected from the environment in which the board is employed. A widely practiced method is to enclose such circuit boards in an assembly that includes a pair of case halves that must be assembled together by hand to form an enclosure that supports the circuit board within. Connectors secured to one of the case halves provide for electrical interconnection to the circuit board. Sealing elements are also typically required to exclude moisture from the enclosure. Finally, fasteners are required to secure the assembly together. Such assembly processes are labor intensive, and the resulting package must be tested for leakage to ensure the package was properly assembled.
From the above, it can be appreciated that a less complicated assembly process for electronic assemblies would be highly desirable from the standpoint of a labor, material and process costs, as well as reliability.
SUMMARY OF THE INVENTION
According to the present invention, there is provided an overmolded electronic assembly and a method for forming the assembly that entails enclosing a circuit board having one or more circuit devices mounted to its surface. The assembly includes a heat-conductive member in thermal contact with one or more of the circuit devices mounted to the circuit board. An overmolded body encloses the circuit board and the circuit device with the heat-conductive member, such that the overmolded body and heat-conductive member form a moisture-impermeable seal around the circuit board and circuit device. The overmolded body also has a connector housing integrally-formed in its outer surface. The method for manufacturing the overmolded electronic assembly generally entails supporting the circuit board on the heat-conductive member such that the heat-conductive member thermally contacts the circuit device. An overmolded enclosure is then formed by molding a material over the surface of the circuit board to form the overmolded body that, with the heat-conductive member, encloses the circuit board and its circuit device.
In a preferred aspect of the invention, the heat-conductive member includes pedestals that contact the circuit devices, supports space the circuit board from the heat-conductive member, and the circuit board has input/output pins that extend through the overmolded body and into the connector housing. In this manner, the circuit board, supports and heat-conductive member define a cavity into which the material for the overmolded enclosure flows during molding to encase the circuit board. In one embodiment of the invention, the assembly further includes a snap-fit member that is mechanically locked to the heat-conductive member, with the circuit board being enclosed between the snap-fit member and the heat-conductive member. The snap-fit member preferably biases the circuit device against the heat-conductive member, and provides EMI shielding for the circuit board. The overmolded body is formed by molding a material over the exterior surface of the snap-fit member, such that the overmolded body and heat-conductive member enclose and encase the circuit board and snap-fit member.
From the above, one can see that the overmolded electronic assembly of this invention provides an uncomplicated method for encasing a circuit board and its circuit devices in a protective enclosure. More particularly, the assembly eliminates the prior art requirement for separate connectors, individual case assemblies, fasteners and seals. In the manufacturing process, there is no assembly of seals to case halves, no fastening of case halves, reduced inventory of parts and no leak test requirement. Furthermore, the electronic assembly can be manufactured on a completely automated final assembly line. Finally, the electronic assembly can exhibit improved heat transfer from the circuit devices, resistance to vibration and shock, and improved reliability due to more closely matched coefficients of thermal expansion (CTE) of the overmolding and circuit board materials.
Other objects and advantages of this invention will be better appreciated from the following detailed description.


REFERENCES:
patent: 4843520 (1989-06-01), Nakatani et al.
patent: 4868638 (1989-09-01), Hirata et al.
patent: 5444909 (1995-08-01), Mehr
patent: 5570272 (1996-10-01), Variot
patent: 5722161 (1998-03-01), Marrs
patent: 5935502 (1999-08-01), Ferri et al.
patent: 06411541 (1995-01-01), None

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