Patent Application
20090197478
This invention relates to overmolding of the electronic assemblies and more particularly to an electronic assembly having features that enhance overmolding integrity.
In a conventional electronic assembly having a circuit device contained in an overmold package, the overmold material is typically bonded to a thermoplastic body of an electrical connector, with a seal between the electronic device contained in the package housing and the external environment being provided in part by an adhesive bond between the thermoplastic body of the electrical connector and the overmolding material. This arrangement provides several benefits including durability, mechanical resistance to shock and vibration, and protection of the circuit device from the surrounding environment. However, there is a compound delamination issue at the interface between the thermoplastic body of the electrical connector and the overmolding material when the package is exposed to thermal cycling. It is believed that this delamination problem is attributable to a substantial difference between the coefficient of thermal expansion of the thermoplastic body of the electrical connector in a direction that was transverse to the direction of flow of the thermoplastic material during the molding process as compared with the coefficient of thermal expansion of the thermoplastic body in a direction that was parallel to flow during the molding process. For example, with a typically glass-filled thermoplastic material, the coefficient of thermal expansion in a direction that was transverse to the flow direction during the molding process is about three times the coefficient of thermal expansion in a direction that was parallel to flow during the molding process.
Regardless of the exact cause of the delamination problems which occur during thermal cycling at the interface between a thermoplastic body of an electrical connector and an overmolding material, it has been found that this problem can be eliminated or substantially reduced by incorporating integrally molded protuberances at the interface between an overmold body and the thermoplastic body of the electrical connector to achieve an interlocking relationship between these components.
In accordance with certain aspects of the invention, there is provided an overmolded electronic assembly having a backplate, a circuit substrate on the backplate, a circuit device defined on the circuit substrate, an electrical connector joined to the backplate, and an overmold body having a peripheral edge in adhesive contact with a thermoplastic body of the electrical connector, with the thermoplastic body including a plurality of protuberances projecting from the thermoplastic body and arranged in a closed circuitous pattern circumscribing external connector pins of the electrical connector. During molding of the overmold body, which extends over the protuberances, indentations conforming with the protuberances are formed in the overmold body to provide an interlocking relationship between the overmold body and the thermoplastic body of the electrical connector, thereby reducing or eliminating delamination problems which could otherwise occur during thermal cycling of the electronic assembly.
These and other features, advantages and objects of the present invention will be further understood and appreciated by those skilled in the art by reference to the following specification, claims and appended drawings.
The present invention will now be described, by way of example, with reference to the accompanying drawings, in which:
As shown in
Backplate 12 is a generally planar base member onto which the other components of the electronic assembly are added or assembled and serves as a part of a housing encasing the circuit substrate and circuit device defined on the circuit substrate. In order to avoid delamination issues at the interface between overmold body 18 and backplate 12, backplate 12 may be comprised or may consist of a metal or metal alloy. A suitable metal backplate 12 may be comprised or consist of aluminum or an aluminum alloy.
Circuit substrate 14 may comprise generally any printed circuit board, wiring board or the like on which electronic components may be mounted and on which electrically conductive traces may be defined.
Generally, any electronic component 20 or combination of electronic components may be mounted on circuit substrate 14 to define a circuit device that may be incorporated into an overmolded electronic assembly in accordance with the invention. Such electronic components include, without limitation, integrated circuits, transistors, diodes, resistors, capacitors, and the like. The circuit device may include a plurality of electronic components or a single electronic component such as an integrated circuit chip.
The electrical connectors 16 used in an electronic assembly 10 of the invention generally comprise a thermoplastic body 22 with embedded (e.g., insert molded) electrically conductive elements 24 that extend through a wall member 26 defined by the thermoplastic body, with opposite sections of each of the electrically conductive elements 24 projecting away from opposite sides of wall member 26 to provide external connector sections 27 that extend outwardly from the electronic assembly housing and internal connector sections 29 that are connected with the circuit device defined on circuit substrate 14.
Electrically conductive traces 28 on circuit substrate 14 together with at least one electronic component 20 define the circuit device on circuit substrate 14. The interface or electrical connection between electrical traces 28 and electrically conductive elements 24 of the electrical connector may be achieved by any known or suitable means, such as by soldering. Alternatively, compliant pin technology may be employed.
A more detailed front perspective view of electrical connector 16 is shown in
Except for the addition of protuberances 36 and overmolding of the assembly to achieve an interlocking relationship between edges of overmold body 18 and thermoplastic body 22 of connector 16, other aspects of the process for fabricating overmolded electronic assembly 10 are generally conventional. In general, a circuit device is first fabricated on circuit substrate 14, and then electrical connector 16 is attached to circuit substrate 14 to provide a printed circuit board assembly in which electrical connections with the circuit device defined on circuit substrate 14 are achieved by electrical connection with external connector sections 27 projecting outwardly away from a housing defining the completed assembly 10 (as shown in
Overmold body 18 may be formed from a thermoset resin, which may be filled or not filled. Examples of thermoset resins which may be employed include epoxy resins, polyester resins, melamine resins, urea-formaldehyde resins, and the like. Fillers that may be employed include talc, silica, glass beads, etc. Overmold body 18 serves to join connector 16 to backplate 12 and complete a sealed housing for the electronic device defined on circuit substrate 14.
It has been found that the improved structure and processes of the invention eliminate or reduce delamination problems that occur during thermal cycling, eliminate or minimize the need for stringent control on cleanliness and texture of the surfaces of outer side of thermoplastic body 22, and reduce costs associated with overcoming the delamination problem.
It will be understood by those who practice the invention and those skilled in the art, that various modifications and improvements may be made to the invention without departing from the spirit of the disclosed concept. The scope of protection afforded is to be determined by the claims and by the breadth of interpretation allowed by law.
