Patent Publication Number: US-11641718-B2

Title: Electromagnetic compatibility contact between metal castings and printed circuit boards

Description:
TECHNICAL FIELD 
     The present disclosure relates to electromagnetic compatibility (EMC), and more particularly to optimizing electrical contact between metal castings and printed circuit boards. 
     BACKGROUND 
     EMC is a measure of an electronic device&#39;s ability to function acceptably in an operating environment without affecting the ability of other devices to operate in the same environment. This is particularly relevant for electronic devices that house one or more circuit boards, such as printed circuit boards (PCBs), that have an internal network of grounded conductive components mounted on the circuit board. Without proper shielding, other devices external to the electronic device or other components on the circuit board may adversely affect EMC. 
     For an electronic device having one or more circuit boards enclosed in metal castings, EMC may be affected by components on the circuit board itself, by components on multiple circuit boards stacked near each other, and by devices that are external to the enclosure. Properly shielding a component will prevent any adverse effects on EMC. 
     Typically, shielding is accomplished by attempting to create consistent connections to a common ground plane and in the case of electronic devices having circuit boards in metal enclosures, the enclosure is grounded for redirecting electrical interference. 
     To achieve a consistent connection to ground, circuit boards may have one or more contact points for fasteners around its perimeter to facilitate grounded contact with an enclosure. Typically, one or more circuit boards are attached to first and second faces of the enclosure with fasteners, such as screws or clips. The more fasteners that are used to attach the circuit boards, the more consistent the ground contact. However, for electronic devices having multi-layer circuit boards, or large enclosures, fasteners such as screws and clips may be unavailable as an option, Additionally, the number of fasteners needed for a consistent connection may become too numerous thereby adversely affecting the cost of the circuit board/enclosure assembly. Yet another drawback of fasteners is that the clamping force they provide, particularly if they are over-tightened, may introduce stress that deforms or otherwise damages the circuit board, which can adversely affect EMC. 
     When too few fasteners are used, retention may be inconsistent, which may lead to ineffective electrical grounding. Furthermore, vibrations, particularly in automotive applications, may also cause fasteners to come loose, causing a loss of contact to ground adversely affecting EMC. Manufacturing tolerances and deformation of parts may also adversely affect EMC. There is a need for a consistent connection to ground to shield the electronic device from internal and external interference. 
     SUMMARY 
     An electronic device having at least one circuit board. The circuit board has a predetermined pattern of solder bumps facilitating a ground connection with a first enclosure member and/or a second enclosure member. The at least one circuit board is sandwiched between the first and second enclosure members, each of the first and second enclosure members has a surface facing the circuit board and the surface facing the circuit board has a bead extending therefrom contacting the predetermined pattern of solder bumps to complete the ground connection. 
     In one or more embodiments, the predetermined pattern of solder bumps is a first predetermined pattern of solder bumps around a perimeter of the circuit board and at least a second predetermined pattern of solder bumps around at least one component on an interior of the circuit board. The bead extends from the surface of the enclosure member facing the circuit board in a manner that contacts the first and the at least second predetermined patterns of solder bumps. 
     In one or more embodiments, at least a third enclosure member is positioned between the first and second enclosure members. The at least a third enclosure member has a first edge with a bead extending therefrom, a second edge with a bead extending therefrom, and a planar surface parallel to the first and second enclosure members. A first circuit board has a predetermined pattern of solder bumps facilitating a ground connection is sandwiched between the first enclosure member and the third enclosure member. At least a second circuit board, also having a predetermined pattern of solder bumps facilitating a ground connection, is sandwiched between the second enclosure member and the third enclosure member. The bead on any one of the first enclosure member or the third enclosure member contacts the predetermined pattern of solder bumps on the first circuit board to complete the ground connection and the bead on any one of the second enclosure member or the third enclosure member contacts the pattern of solder bumps on the at least a second circuit board to complete the ground connection. The first enclosure member and the third enclosure member are parallel to the first circuit board and spaced to accommodate components on the circuit board. The at least a third enclosure member and the second enclosure member are also spaced a predetermined distance to accommodate components on the circuit board. 
    
    
     
       DESCRIPTION OF DRAWINGS 
         FIG.  1   . is a perspective view of an electronic device; 
         FIG.  2    is a cutaway view of the electronic device; 
         FIG.  3 A  is a close-up cutaway view of a bead contacting a pattern of solder bumps; 
         FIG.  3 B  is a perspective cutaway view of a bead contacting a pattern of solder bumps; 
         FIG.  4    is a circuit board having first and second predetermined patterns of solder bumps; and 
         FIG.  5    is a perspective cutaway view of the electronic device having multiple circuit boards mounted in parallel. 
     
    
    
     Elements in the figures are illustrated for simplicity and clarity and have not necessarily been rendered according to any sequence. For example, steps that may be performed concurrently or in different order are illustrated in the figures to help to improve understanding of embodiments of the present disclosure. 
     DETAILED DESCRIPTION 
     While various aspects of the present disclosure are described with reference to an electronic device in an automotive application, the present disclosure is not limited to such embodiments, and additional modifications, applications, and embodiments may be implemented without departing from the present disclosure. In the figures, like reference numbers will be used to illustrate the same components. Those skilled in the art will recognize that the various components set forth herein may be altered without varying from the scope of the present disclosure. 
       FIG.  1    is a simplified representation, in a perspective view, of an electronic device  100  having at least one circuit board  102  clamped between a first enclosure member  104  and a second enclosure member  106 . In practice, the circuit board  102  is sandwiched and fastened between the first and second enclosure members  104 ,  106  using fasteners  108 , such as screws or clips, strategically placed predetermined distances from each other around a perimeter of the device  100 . 
       FIG.  2    is a cutaway view of the electronic device  100 . The enclosure members  104 ,  106  are typically mounted to create an enclosure that is spaced a predetermined distance  110  around the circuit board  102  for clearance to accommodate electronic components on the circuit board and in the housing. Additionally, at least one enclosure member  104 ,  106  is configured to optimize EMC by providing a ground connection that shields components on the circuit board  102  from other components within the enclosure and shields the electronic device from electronic devices external to the enclosure. This is accomplished through a consistent contact to ground between the solder balls on the circuit board  102  and at least one of the first and second enclosure members  104 ,  106 . It should be noted that the solder balls may be on one, or both, sides of the circuit board  102 . At least one of the first and second enclosure members  104 ,  106  is formed from a material that provides shielding such as aluminum, magnesium, or steel. 
       FIG.  3 A  is a close-up view of the electronic device  100  showing the enclosure members  104 ,  106  and the circuit board  102  in contact with each other along one or more contact zones. The contact zones are areas where the circuit board  102  and the enclosures  104 ,  106  make contact, and in the case of the example shown in  FIG.  3 A , the contact zones are an entire perimeter of each of the circuit board  102 , the first enclosure member  104  and the second enclosure member  106 . 
     The contact zone of the circuit board  102  has a predetermined pattern of solder bumps  112 , such as one row around its perimeter on each surface as shown in  FIG.  4   . Referring to  FIG.  3 B , a surface  114  of each enclosure member  104 ,  106  that faces the circuit board  102  has a bead  116  that protrudes from the enclosure member. The bead  116  has a predetermined pattern that substantially matches the predetermined pattern of solder bumps so that when the circuit board  102  is clamped between the enclosure members  104 ,  106 , it consistently contacts the solder bumps  112 . Instead of contact being consistently made only at the fastener locations, contact occurs at contact zones along the bead  116  on each enclosure member  104 ,  06  where it contacts the solder bumps  112  on the circuit board  102 . In the example shown in  FIGS.  3 A and  3 B , the contact is made all along the perimeter (or any other location where the bead  116 , solder bump  112  connection may be introduced) to sustain sufficient electrical contact. 
     The bead  116  may be found on both enclosures (as shown) but it is necessary for the bead  116  on at least one of the enclosures  104 ,  106  to create an interference between the metallic casing of the enclosure  104  and/or  106  and a pattern of solder bumps  112  on the circuit board  102  to ensure electrical contact. In one or more embodiments, the bead  116  is triangular. A continuous bead  116  around the perimeter of the enclosures  104 ,  106  to sustain sufficient electrical contact and minimize any stresses that may be introduced into the circuit board  102 . However, the bead  116  may have a different profile shape to accommodate design specifications and limitations. 
     As discussed above, the bead  116  may be around a perimeter of the enclosures  104 ,  106  and contacts the pattern of solder bumps that are on the perimeter of the circuit board  102  to facilitate a ground connection that protects the electronic device  100  from external interference and from causing excessive emissions. However, the bead  116  on the surface of at least one of the enclosure members  104 ,  106  that faces the circuit board  102  may also be implemented in other areas and have points of contact between at least one of the enclosure members  104 ,  106  and the circuit board  102  other than just the perimeter. For example, the bead may contact at least a second pattern of solder bumps on an interior of the circuit board  102  that, for example, surrounds a particular component on the board, to isolate and protect the component form internal interference. 
     Contact of the bead  116  with the pattern of solder bumps  112  on the circuit board  102  provides consistent electrical contact. Gaps in a ground connection could adversely affect EMC. The perimeter bead  116  provides consistent electrical contact even in areas where circuit board deformation might typically occur, such as the areas between fasteners. When fasteners are over-clamped during assembly, or when the circuit board is otherwise warped or deformed, gaps in ground contact may occur. Gaps may also occur when one or more of the fasteners comes loose, for example from vibrations of the electronic, such as road vibrations of a vehicle. The continuous contact of the bead  116  with the solder bumps  112  addresses these problems. The bead  116  on the enclosure members contacting the pattern of solder bumps  112  on the circuit board  102  provides a more consistent contact to ground than the fasteners alone. 
       FIG.  5    shows one or more embodiments 500 of the inventive subject matter having first  504 , second  506  and at least a third  518  enclosure members. First  502  and second  520  circuit boards are enclosed by the enclosure members  504 ,  506 ,  518 . The first and second circuit boards  502 ,  520  have a predetermined pattern of solder bumps  512 , such as one row around a perimeter edge as shown in  FIG.  4   . Referring again to  FIG.  5   , The third enclosure member  518  is positioned between the first and second circuit boards  502 ,  520 . Each of the enclosure members  504 ,  506  has a bead  516  that has a predetermined pattern substantially matching the pattern of solder bumps  512  for contacting the pattern of solder bumps  512  on either, or both, of the circuit boards  502 ,  520 . 
     The third enclosure member  518  has a perimeter bead having a predetermined pattern, for example, along each edge so that it contacts the pattern of solder bumps  512  on at least one of the circuit boards  502 ,  520 . The third enclosure member  518  also has a planar surface section that divides the enclosure to provide structural support for multiple circuit boards in parallel. The planar surface may also function as a heat sink for hot components on any one of the circuit boards. Within the enclosure, there is spacing  510  between each of the circuit boards  502 ,  520  and spacing between circuit boards and enclosure members. The spacing is a predetermined distance to accommodate any board-to-board connectors (not shown). The at least a third enclosure member may have a bead  516  on each of its surfaces to contact solder bumps on each of the circuit boards  502 ,  520 . The third enclosure has a predetermined height so that, when it is connected between to the first and second circuit boards between the first and second enclosure members it completes the enclosure of the first and second circuit boards  502 ,  520 . The assembly includes spaces  510  above and below the circuit boards  502 ,  520  for component clearance. Contact between the bead  516  on the first, second and at least a third enclosure members  504 ,  506 ,  518  with the pattern of solder bumps  512  on the first and second circuit boards  502 ,  520  ensures a continuous contact zone for consistent electrical contact to ground for the assembly. 
     In the foregoing specification, the present disclosure has been described with reference to specific exemplary embodiments. The specification and figures are illustrative, rather than restrictive, and modifications are intended to be included within the scope of the present disclosure. Accordingly, the scope of the present disclosure should be determined by the claims and their legal equivalents rather than by merely the examples described. 
     For example, the components and/or elements recited in any apparatus claims may be assembled or otherwise operationally configured in a variety of permutations and are accordingly not limited to the specific configuration recited in the claims. 
     Benefits, other advantages, and solutions to problems have been described above regarding specific embodiments. However, any benefit, advantage, solution to problem or any element that may cause any particular benefit, advantage, or solution to occur or to become more pronounced are not to be construed as critical, required, or essential features or components of any or all the claims. 
     The terms “comprise”, “comprises”, “comprising”, “having”, “including”, “includes” or any variation thereof, are intended to reference a non-exclusive inclusion, such that a process, method, article, composition, or apparatus that comprises a list of elements does not include only those elements recited but may also include other elements not expressly listed or inherent to such process, method, article, composition, or apparatus. Other combinations and/or modifications of the above-described structures, arrangements, applications, proportions, elements, materials, or components used in the practice of the present disclosure, in addition to those not specifically recited, may be varied, or otherwise particularly adapted to specific environments, manufacturing specifications, design parameters or other operating requirements without departing from the general principles of the same.