Grounding method for baseplate sealed enclosures

This application claims the benefit of U.S. Provisional Application No. 61/870,464 filed Aug. 27, 2013. The disclosure of the above application is incorporated herein by reference.

The invention relates generally to an attachment structure for use with a standalone control unit having a sealed enclosure.

Various types of control units are generally known. Some types of control units are standalone, and are designed to withstand operating in harsh environments. Standalone controllers use an aluminum sheet metal base plate to attach and provide a rigid support for a printed circuit board (PCB). A cover or housing is placed and sealed over a rigidizer creating a sealed PCB enclosure. It is difficult to ground the PCB for electromagnetic interface (EMI) and radio frequency interface (RFI) purposes because typical methods of using a screw create a leak path in the base plate. In addition, exposed screw threads through the bottom of the sheet metal base plate increase the risk of handling damage from the exposed screw threads.

Transmission control units (TCU) that are sealed and use an aluminum sheet metal base plate require a method of grounding the PCB to the base plate for EMI/RFI control. Any holes or screws in the base plate create a leak path which occurs typically during thermal cycles.

Accordingly, there exists a need for a standalone control unit which provides for a connection between a PCB and a base plate, and is also encapsulated and provides a proper seal.

The present invention is an attachment structure for use with a standalone control unit. A threaded insert in an enclosed cavity allows screws to be used for EMI/RFI board grounding along with creating a sealed, enclosed pocket.

The attachment structure of the present invention allows for grounding of the PCB to the sheet metal base plate without creating a leak path to the outside. The attachment structure is suitable for electrical grounding, and is not limited to use with grounding an EMI/RFI board. This grounding approach encapsulates the screw to prevent the formation of a leak path.

In one embodiment, the present invention is a transmission control unit having an attachment structure, which includes a base plate, a material layer disposed on at least a portion of a top surface of the base plate, and a printed circuit board at least partially disposed on the material layer.

A cavity is formed as part of the base plate, and an insert is located in the cavity such that at least a portion of the printed circuit board is supported by the insert. A screw is inserted through an aperture of the printed circuit board and an aperture of the insert, connecting the printed circuit board and the insert to the base plate. At least one protrusion is formed as part of the base plate in proximity to the insert, and at least one recess is formed as part of the insert, such that the protrusion extends into the recess to connect the insert to the base plate.

The cavity includes at least one side wall, and a bottom wall connected to the side wall. The protrusion is formed as part of the side wall.

There is also an axis, and the insert is non-circular, such that as the fastener is inserted through the insert and rotated, the insert is prevented from rotating about the axis and remains stationary relative to the base plate. At least part of the cavity is shaped to correspond to the shape of the insert, preventing rotation of the insert about the axis as the screw is inserted through the aperture of the insert and the aperture of the printed circuit board. At least a portion of the screw is substantially parallel to the axis.

The base plate is made of a metal material, such as aluminum, but it is within the scope of the invention that other types of metal may be used, such as, but not limited to, steel or copper.

Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.

The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein:

FIG. 1 is a sectional side view of an attachment structure for a standalone control unit, according to embodiments of the present invention; and

FIG. 2 is a sectional side view of an insert attached to a base plate, which is used as part of an attachment structure for a standalone control unit, according to embodiments of the present invention;

FIG. 3 is an exploded sectional side view of an insert and a base plate, prior to undergoing a swaging process, which are used as part of an attachment structure for a standalone control unit, according to embodiments of the present invention;

FIG. 4 is an exploded sectional side view of an insert shown separately from a base plate, after undergoing a swaging process, which are used as part of an attachment structure for a standalone control unit, according to embodiments of the present invention; and

FIG. 5 is an exploded view of an insert and a base plate, prior to undergoing a swaging process, which are used as part of an attachment structure for a standalone control unit, according to embodiments of the present invention.

The following description of the preferred embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses.

A section of a transmission control unit (TCU) having an attachment structure according to the present invention is shown in the Figures generally at 10 . The TCU 10 includes a printed circuit board (PCB) 12 , an insert 14 , and a base plate 16 . Also included is a fastener 18 , which in this embodiment is a threaded screw, but it is within the scope of the invention that other types of fasteners may be used.

The screw 18 extends through a first aperture 20 formed as part of the PCB 12 , and a second aperture 22 formed as part of the insert 14 . There is an axis 44 which also extends through the first aperture 20 and the second aperture 22 , and is substantially perpendicular to the PCB 12 . The threaded portion of the screw 18 is inserted through the apertures 20 , 22 along the axis 44 . The screw 18 is substantially parallel to the axis 44 . The second aperture 22 is threaded and receives the screw 18 to secure the connection between the screw 18 , the PCB 12 , and the insert 14 .

The insert 14 is also connected to the base plate 16 through the use of a retention feature, shown generally at 30 . The base plate 16 includes a cavity, shown generally at 24 , the insert 14 is located in the cavity 24 , and the screw 18 partially extends into the cavity 24 . The cavity 24 includes sidewalls 26 and a bottom wall 28 . Integrally formed as part of the sidewalls 26 is a protrusion 32 a , which is part of the retention feature 30 and circumscribes the sidewalls 26 . The protrusion 32 a extends into a recess 32 b formed as part of the insert 14 . The recess 32 b circumscribes the insert 14 , best shown in FIGS. 1-2, and 4 , and is also part of the retention feature 30 . The protrusion 32 a is formed by a swaging process, and produces an interference fit between the protrusion 32 a and the recess 32 b , connecting the protrusion 32 a and the recess 32 b , and therefore properly positioning the insert 14 in the recess 32 b relative to the base plate 16 . The retention feature prevents the insert 14 from being removed from the cavity 24 , and more specifically, from being pulled out of the cavity 24 due to the pulling force applied to the insert 14 as the screw 18 is inserted into the apertures 20 , 22 .

The thickness of the insert 14 is such that the PCB 12 is not in contact with the base plate 16 , but rather the thickness and positioning of the insert 14 locates the inner surface 40 of the PCB 12 at a distance 34 away from the top surface 46 the base plate 16 . The distance 34 in this embodiment ranges from 0.13 mm to 0.30 mm, but it is within the scope of the invention that other distances may be used.

Located between the PCB 12 and the base plate 16 is a material layer 42 . The material layer 42 is of a thickness approximately equal to the distance 34 between the inner surface 40 of the PCB 12 and the top surface 46 of the base plate 16 . The material layer 42 is made of a thermal interface material which performs the functions of transferring heat away from the PCB 12 , and the thermal interface material provides a dielectric isolation function.

The cavity 24 is formed as part of the base plate 16 such that the inner surface 36 of the bottom wall 28 is located at a distance 38 from the outer surface 48 of the insert 14 . The location of the insert 14 is also such that the outer surface 48 of the insert 14 is also about the same distance 34 away from the top surface 46 of the base plate 16 as the lower surface 40 of the PCB 12 . This ensures that the outer surface 48 of the insert 14 is in alignment with the outer surface 50 of the material layer 42 , and therefore the PCB 12 is properly supported by the material layer 42 and the insert 14 . The cavity 24 formed as part of the base plate 16 seals and encloses the entire area around the screw 18 and the insert 14 , ensuring there is no leak path where liquid or other debris may enter the TCU 10 .

During assembly, the insert 14 is placed into the cavity 24 , and the protrusion 32 a is formed by the swaging process, as previously described, such that the protrusion 32 a fits into the recess 32 b . The insert 14 is a non-circular shape, and in this embodiment, the insert 14 is hexagonal in shape as shown in FIGS. 4-5 , but it is within the scope of the invention that the insert may be other shapes as well, such as, but not limited to, triangular, rectangular, heptangular, and the like. The cavity 24 , or at least the portion of the cavity 24 surrounding the insert 14 , is of a shape that corresponds to the shape of the insert 14 , which in this embodiment is hexagonal. After the insert 14 is placed in the cavity 24 , and the swaging process is completed, the screw 18 is inserted through the first aperture 20 and is rotated, which then moves the screw 18 through the second aperture 22 of the insert 14 . The hexagonal shape of the insert 14 and the corresponding hexagonal shape of the cavity 24 prevents the insert 14 from being rotated about the axis 44 relative to the base plate 16 as the screw 18 is inserted into the second aperture 22 and rotated.

Once the screw 18 is in place, the PCB 12 is connected to and positioned correctly relative to the base plate 16 . The shape of the base plate 16 , and more specifically the shape of the sidewall 26 and the bottom wall 28 creates the sealed cavity 24 , and therefore prevents the existence of a leak path around the screw 18 and insert 14 .

While it has been shown that the attachment structure of the present invention may be used with a TCU, it is within the scope of the invention that the attachment structure may be used with any other type of standalone controller, such as an electronic control unit, or the like. Furthermore, the base plate 16 shown in the drawings is made of aluminum, but it is within the scope of the invention that other types of materials may be used, such as steel, copper, or the like. The attachment structure of the present invention is also not limited to use with EMI/RFI board grounding, but it is within the scope of the invention that the attachment structure may be used to provide electrical grounding as well.

The description of the invention is merely exemplary in nature and, thus, variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.