1. Field of the Invention
The present invention generally relates to systems for supporting and electrically grounding metallic covers for electronic control modules.
2. Description of the Known Technology
Electronic control modules, such as those commonly found in automobiles, typically include a housing containing a circuit board. Generally, the housing has an opening large enough to easily place the circuit board within the housing. In order to protect the circuit board from environmental harm, a metallic cover is placed over the opening of the housing, thereby enclosing the circuit board within the housing.
In addition to protecting the circuit board from environmental harms, the metallic cover may also be utilized as a heat sink for dissipating heat generated by the circuit board. In order to accomplish this, the cover must be in thermal communication with the circuit board. Generally, this is accomplished by connecting one or more wires between the ground plane of the circuit board and the cover. By so doing, not only is the cover in thermal communication with the circuit board, but the wires electrically ground the cover, thereby shielding emissions radiating from the module. The primary drawback is the expense of manufacturing this system because of additional steps needed for attaching the wires to both the circuit board and the cover. Therefore, there is a need for a low cost system that places the cover in electrical and thermal communication with the circuit board.
In satisfying the above need, as well as overcoming the enumerated drawbacks and other limitations of the known technology, the present invention provides a system for supporting and electrically grounding metallic covers for electronic control modules. The system generally includes a circuit board located within a cavity of a housing. Wall portions of the housing define an opening, wherein a cover is placed over the opening of the housing, thereby enclosing the circuit board.
The supports for supporting the cover when placed over the opening are located on a top side of the circuit board. The supports may be a solder ball formed on a mask opening of the circuit board, a plurality of wire spring members located on a contact portion formed adjacent to the perimeter of the top side of the circuit board or a plurality of spring members located adjacent to the perimeter of the circuit board.
Further objects, features and advantages of this invention will become readily apparent to persons skilled in the art after a review of the following description, with reference to the drawings and claims that are appended to and formed part of this specification.
Referring to
The cover 22 covers the opening 16 of the housing 12, thereby enclosing the circuit board 18 within the cavity 14. The cover 22 is attached to the housing 12 via a series of fasteners 24 or other mechanisms that mechanically engage both the cover 22 and the housing 12. For example, the fasteners 24 may be threaded and engage a series of threaded holes 26 formed within the housing 12 and the cover 22. When assembled, the cover 22 seals the circuit board 18 within the cavity, protecting the circuit board 18 from external environmental elements.
The top side 20 of the circuit board 18 includes a plurality of supporting means or supports 28 that provide structural support to the cover 22. Additionally, the supports 28 may be in electrical communication with a ground plane formed within the circuit board 18. When the cover 22 is attached to the opening 16 of the housing 12, the cover 22 is electrically and mechanically in contact with the supports 28. By so doing, the cover 22 will be grounded to the ground plane of the circuit board 18, thereby shielding emissions radiating from the module 10. Additionally, the cover 22 can act as a heat sink for the circuit board 18, whereby heat generated by the circuit board 18 is transferred to the cover 22 via the supports 28. Furthermore, a dielectric spacing is formed between the cover 22 and the circuit board 18. This dielectric spacing may range between 2 to 20 thousandths of an inch (“mils”).
Referring to
Surrounding the mask opening 30 is a trough 36 made of a non wettable material. As particularly seen in
Preferably, the mask opening 30 and the bond pad perimeter 34 are substantially square in shape, however, any suitable shapes may be utilized. The width D1 of the mask opening 30 is approximately 28 mils, however this may vary between 15 and 35 mils. The width D2 of the bond pad perimeter 34 is approximately 68 mils. As stated previously, the trough 36 surrounds the bond pad perimeter 34 and is also generally square in shape, however, any suitable shape may be utilized. The dimension D3 across one side of the trough 36 in the above application is approximately 108 mils.
When the solder ball 32 is formed on the mask opening 30, excess solder remaining from the formation of the solder ball is repelled by the non-wetting bond pad perimeter 34 and received by the trough 36. For example, assume that a solder paste 38 is applied to an area covering the mask opening 30 and portions of the bond pad perimeter 34. The amount of solder paste 38 is critical. Too much solder paste (overprinting) would result in solder balling. Too little solder paste would not create a solder ball with a height of at least 10 mils. Generally, the ratio of the printed area (solder paste 38) to the solderable area (mask opening 30) should be between 1.2 and 2.4 to achieve the necessary critical height of at least 10 mils for the solder ball 38.
The solder paste 38 should completely cover the mask opening 30. If portions of the mask opening 30 are exposed, the solder ball 38 may be “robbed” of solder. Conversely, if too much solder paste 38 is used, the trough 36 may fill up with solder, increasing the possibility that excess solder would roll onto other portions of the circuit board 18.
When the solder paste 38 is heated to a molten state, the solder paste 38 will, by reflow action, form the solder ball 32 via the use of a stencil having a thickness between 3 to 7 mils. Any additional solder is repelled by the bond pad perimeter 34 and flows to the trough 36. By so doing, the height of the solder ball 32 can be consistently achieved because the mask opening 30 will retain a limited maximum amount of the molten solder. Assuming that the mask opening 30 of each supports 28 is of a consistent size, the height of each solder ball 32 will therefore be substantially the same. This is beneficial since having each solder ball at a consistent height, the plurality of supports 28 define a level support plane for the cover 22 that is of a specific and predictable height. The solder balls 38 may be placed in a staggered or aligned configuration and with a density dependant on the type of application. For example, in applications where thermal conductivity is important, additional solder balls 38 may be required to increase thermal conductivity.
Referring to
A plurality of conductive wire spring members 42 are attached to the contact portion 40. Generally, the conductive wire spring members 42 are made from tin, copper, gold, beryllium and combinations thereof. The conductive wire spring members 42 are ribbon bonds or wire bonds that form a compressible perimeter. As best shown in
Referring to
The first set of contact pads 46 includes an interior contact pad 52, a middle contact pad 54 and a side contact pad 56. In like manner, the second set of contact pads 48 includes a top contact pad 58, a middle contact pad 60 and a side contact pad 62. The contact pads of both the first and second sets 46, 48 are formed on or within the top side 18 of the circuit board 18 and are in electrical communication with the ground plane of the circuit board 18. While shown with three, it should be understood that any number of individual contact pads may be formed as part of the set of contact pads within the top side 18 of the circuit board 18. Notches 64, 66, 68 are formed in contact pads 52, 54, 56, respectively. In like matter, notches 70, 72, 74 are formed in the contact pads 58, 60, 62, respectively.
The spring member 46 generally includes base portion 76 fixedly attached to the top side 18 of the circuit board 18. The base portion 76 of the spring member 49 has notches 80, 82, 84, 86, 88, 90 formed within. The notches 64, 66, 68, 70, 72, 74 mechanically engage notches 80, 82, 84, 86, 88, 90, respectively. By having each pin mechanically engage a separate notch, the base portion of the spring member 49 can be held in place while being manufactured. Generally, solder paste 92 is deposited in and around the first and second sets 46, 48 of contact pads. The spring element 49 is then placed on top of the solder paste. When heat is applied to the solder paste, the solder paste melts 92 while the notches guide the spring member 49 into its appropriate location. Two generally opposing flexible portions 78, 80 extend from the base portion 76 away from the top side 20 of the circuit board 18. After the solder paste 92 cools, the spring member 49 is then fixedly attached to the circuit board 18.
Referring to
As a person skilled in the art will readily appreciate, the above description is meant as an illustration of implementation of the principles this invention. This description is not intended to limit the scope or application of this invention in that the invention is susceptible to modification, variation and change, without departing from the spirit of this invention, as defined in the following claims.