Electronic Control Modules (ECMs) are now commonplace in under-hood vehicular applications and are used to provide computer control of various functions of the vehicle. The ECM enclosure or housing provides a number of functions including: (1) conducting thermal power away from the electronics to the environment; (2) protecting the electronics from environmental elements; and (3) providing a shield to minimize electromagnetic energy from entering or exiting the ECM. This invention leverages the state-of-the-art approaches to address each of these functions and integrates them into one design approach.
Current designs typically use die-cast aluminum material for the housing or enclosure. Die-cast aluminum is a cost-effective approach to provide part geometry and material properties to efficiently pull thermal power away from the electronics and transfer that heat to the larger environment. Unfortunately, these materials are susceptible to corrosion and/or deterioration over time. Additionally, The automotive industry continues to require ECM products to have higher reliability and endure a harsh environment for greater durations than used in prior vehicular applications. Consequently, corrosion resistance requirements for ECMs have increased significantly in recent years. The state-of-the-art has evolved to address this issue through the use of environmental coatings such as powder coats, epoxy electrostatic coatings, and anodizes, to protect the ECM enclosure from weather and a corrosive environment.
Electromagnetic Compatibility (EMC) requirements such as radiated radio frequency (RF) emissions and electromagnetic interference (EMI) susceptibility have also become more stringent during this time frame. Additionally, increased microprocessor speeds, proliferation of communication buses, faster data transfer rates, and use of expanded memory modes have also become more prevalent thus generating more electromagnetic energy at higher frequencies. One solution to mitigate these issues is to create a Faraday cage around the circuit board assembly using the structure of the ECM. This cage is created by having continuous or closely spaced contact points between the ECM housing and the aluminum cover that covers, seals, and/or protects the module. This design approach requires electrical conductivity between the top half and the bottom half of the enclosure. Unfortunately, the environmental coatings discussed in the previous paragraph are typically electrically-insulating materials. Thus, the requirements to provide a protective coating and provide an electromagnetic shield, all in an integrated housing, are mutually exclusive with the current design approaches.
There are two methods to circumvent this problem. The first is to apply a protective spray to the completely assembled ECM in order to seal it from the environment. Unfortunately, the processes involved in coating the ECM after assembly can damage the electronics inside the assembly. The second approach that has been used in the past is for the assembly screws to electrically connect the top half and bottom half of the enclosure for creating the integrated Faraday cage. However, new design guidelines, based on high frequency operation, call for these connections to be less than 0.5 inches (12.7 mm) apart. This quantity of screws is neither cost-effective nor practical in many applications.