Electrical devices containing multiple regions for the performance of different electrical functions are common in the field of automotive sensors. Typically, a region containing a sensing element is exposed to some type of corrosive environment. For example, pressure sensors incorporated in automotive subsystems can be exposed to corrosive gases within, for example, an exhaust manifold. In other applications, sensors can be exposed to corrosive liquid environments. For example, sensors can be submerged in automotive fluids, such as power steering fluid, engine lubricating oils, and the like. While the electronic device must function in a corrosive environment, it is also necessary that the electrical device be connected to external electronic circuitry. The external circuitry sends and receives electrical signals to and from the electrical device. To avoid corrosion of electrical connections, the portion of the device exposed to the corrosive environment must be effectively isolated from the portion of the device in which external electrical connections are made.
In addition to the need for internal isolation of the various regions of an electrical device, during fabrication thermal processing steps are carried out to form electrical connections within the electrical device. For example, sensing elements are usually wire bonded to a leadframe position within the electrical device. The formation of reliable wire bond connections requires that the electrical device be subjected to elevated temperatures during the bonding operation. Typically, the elevated temperatures necessary to form the wirebonds are achieved by heating the entire electrical device, including the housing and internal components. Because of the large thermal mass, the heating of the housing and internal components is costly and takes an extended period of time in order to reach the desired temperature. The elevated temperatures can soften the molded plastic material used to fabricate structural components of the electronic device. Additionally, at high temperature the plastic housing material can flow. The flow of plastic can coat bonding areas of the leadframe with an insulative plastic layer. The plastic layer hinders the formation of electrical connections to the leadframe. In addition, the flow of plastic can result in undesirable deformation of the electrical device housing.
Existing electrical devices require multiple sealing locations in order to achieve sufficient environmental protection required for applications in corrosive environments. To form the multiple seals, custom dispensing operations are necessary to provide sealant at several locations within the device housing. Accordingly, a need existed for an electrical device having an improved means for sealing and atmospherically isolating various regions within the device housing. Additionally, a need existed for an improved electrical device design, in which electrical connections can be reliably formed without compromising the integrity of the electrical device.