(1) Field of the Invention
The present invention generally relates to packaging for circuit devices. More particularly, this invention relates to an electronic package and packaging method by which a leadframe is used to form electrical leads as well as thermal convectors for the package.
(2) Description of the Related Art
Semiconductor IC devices are at times enclosed in a protective housing to form an IC package, which can then be mounted on a circuit board or other suitable substrate using well known bonding techniques, such as soldering and brazing. The IC devices are typically mounted to a substrate or leadframe, and the resulting assembly is enclosed within a molded housing to form the IC package. Input/output (I/O) leads project through the walls of the housing and are electrically connected to the components within the housing by wire bonding or another suitable technique. The leads may be formed as part of a leadframe around which the housing is molded. Electronic components, typically active IC devices (e.g., transistors and diodes), are mounted on enlarged portions (“paddles”) of the leadframe. The package is then electrically connected and possibly mounted to a circuit board with the leads.
An example of an IC package that makes use of a leadframe is represented in
IC devices generate heat during their operation, resulting in increased junction temperatures for the devices. Because IC reliability and function are adversely affected by high junction temperatures, many IC packages require features to remove heat from the IC device. Various solutions for removing heat from IC packages have been proposed. Most of these approaches involve placing the IC device in contact with a metal slug or an internal frame, which conduct thermal energy from the IC device to a surface of the package. Heat is then removed from the package surface by conduction into a separate heat sink or into the circuit board on which the package is mounted. In many existing concepts, thermal energy is eventually dissipated by convection into the surrounding air using fins thermally connected to the heat sink or circuit board.
While effective, the above approaches require secondary assembly processes and separate heat sinks, which add cost to the electronic assembly. It would be desirable to dissipate heat from an IC package having simplified construction and assembly requirements.
The present invention provides an electronic package and packaging method, in which the package has integral convective fins for dissipating heat from the package. The fins can be formed from portions of a leadframe that would otherwise be removed and discarded from the package during forming of electrical leads for a circuit device housed in the package.
The package of this invention generally includes a molded housing, a circuit device encased within the housing, multiple electrical leads extending from the housing, and a thermally-conductive support structure electrically separate from the electrical leads. Each of the electrical leads has an interior end within the housing, adjacent but separate from the circuit device, and electrically connected to the circuit device. Each of the electrical leads also has an exterior end outside of the housing and adapted for electrical connection to a substrate. The thermally-conductive support structure comprises a base portion within the housing and multiple thermal leads integral with and extending from the base portion. The circuit device is attached to the base portion for thermal coupling therewith. The thermal leads protrude outside the housing and have distal ends configured to dissipate heat that has been conducted away from the circuit device through the base portion. According to a preferred aspect of the invention, the electrical leads are originally part of the support structure and separated from the base portion and the thermal leads during processing of the housing.
The packaging method of this invention generally entails providing a thermally and electrically conductive leadframe comprising a base portion and at least two sets of leads extending from the base portion. First and second sets of these leads correspond to the electrical and thermal leads, respectively, of the package described above. The first set of leads is separated from the base portion and from the second set of leads, such that each lead of the first set of leads has an interior end adjacent but separate from the base portion, and each lead of the second set of leads has an interior portion that remains attached to the base portion. A circuit device is mounted to the base portion, and the circuit device is electrically connected to the interior ends of the first set of leads. The circuit device, the base portion of the conductive leadframe, the interior ends of the first set of leads, and the interior portions of the second set of leads are then encased within a molded housing. The exterior ends of the first set of leads project outside of the housing as connector terminals for the circuit device, and the distal ends of the second set of leads project outside of the housing as thermal dissipaters for the circuit device.
From the above, one can see that the package and method of this invention are able to provide a simplified construction and assembly through the use of an initially single structure to produce two sets of leads that perform either an electrical connection function or a thermal dissipation function. As such, separate manufacturing steps previously required to form and then assemble and attach a discrete thermal dissipation element to an electronic package is eliminated. Notably, the second (thermal) set of leads of this invention can be formed with material conventionally discarded following the process of forming the first (electrical) set of leads from a conventional leadframe, in which case the thermal leads would typically be interdigitized with the electrical leads as a result of being formed from the same leadframe. Alternatively or in addition, unused electrical leads can be used to form some or all of the thermal leads, in which case the electrical leads designated to form the thermal leads would not be separated from the base portion (paddle) of the leadframe. In any case, the thermal leads are present during the molding operation and are subsequently deformed as required for the particular application. For example, the thermal leads can be configured to perform as convection fins or to support a separate finned heat sink. The number, locations, and widths of the thermal leads can be chosen to accommodate different packages, forming operations and molding operations. The thermal leads can also be adapted to transfer thermal energy to a variety of media, including air, liquids, solids, and phase change materials.
Other objects and advantages of this invention will be better appreciated from the following detailed description.
Those skilled in the art will appreciate that the IC package 10 represented in
While the invention has been described in terms of a particular embodiment, it is apparent that other forms could be adopted by one skilled in the art. For example, the leadframe could be configured differently from that shown in the Figures and yet achieve the objects of this invention, the package could contain various electrical components for a variety of applications, and different materials could be used than those noted. Accordingly, the scope of the invention is to be limited only by the following claims.
Number | Name | Date | Kind |
---|---|---|---|
5644164 | Roh | Jul 1997 | A |
5861669 | Sono et al. | Jan 1999 | A |
6242797 | Ichikawa et al. | Jun 2001 | B1 |
6262475 | Liu et al. | Jul 2001 | B1 |
6262489 | Koors et al. | Jul 2001 | B1 |
6396133 | James | May 2002 | B1 |
20040000703 | Lee et al. | Jan 2004 | A1 |
Number | Date | Country | |
---|---|---|---|
20050082660 A1 | Apr 2005 | US |