Patent Publication Number: US-10764994-B2

Title: Circuit boards and circuit board assemblies

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a divisional application of U.S. application Ser. No. 14/947,437 filed on Nov. 20, 2015 the contents of which is incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present disclosure relates to electrical assemblies, and more particularly to circuit board assemblies mounting electrical components like integrated circuits. 
     2. Description of Related Art 
     Printed circuit board (PCB) assemblies commonly include a PCB structure and one or more electronic components. The PCB structure typically supports the one or more electronic components mechanically, and includes one or more conductive features formed within the PCB structure. The conductive features, such as tracks or pads, are generally etched from a conductive material like copper or aluminum and electrically connect to the electronic component through a structure like a pin or a jumper. The electrical connection between the electronic component and the conductive features of the PCB structure provide connectivity between the various electronic component(s) within the PCB assembly as well as to other external electronic components. The electrical characteristics of the electrical connection between the electronic component and the conductive feature of the PCB structure can influence the performance of the electronic component and/or the PCB assembly. For example, in some PCB assemblies, the resistance of the electrical connection between the electronic component and the conductive features of the PCB structure can generate heat sufficient to influence the reliability of the electronic component or PCB assembly. 
     Such conventional methods and systems have generally been considered satisfactory for their intended purpose. However, there is still a need in the art for improved PCB structures and PCB assemblies. The present disclosure provides a solution for this need. 
     SUMMARY OF THE INVENTION 
     A printed circuit board (PCB) includes a body and a belly pad seated within with the body. The belly pad is electrically separated into a first pad and a second pad. The first pad and the second pad are arranged to be electrically connected to one another by an interconnect electrically connecting the belly pad to a conductive plane of an electrical component, thereby allowing continuity testing across an interface between the first pad and the interconnect. 
     In certain embodiments, body can be an electrically insulative body. The insulative body can include a body portion intermediate the first pad and the second pad. The electrically insulative body can electrically separate the first pad from the second pad within the PCB. The PCB can include a ground via. The ground via can be electrically connected to the first pad. The PCB can also include a ground interface disposed on the external face of the PCB, and the ground interface can be electrically connected to the first pad through the ground via, thereby forming a ground trace for connecting the electrical component to an external ground bus. The PCB can include a test via. The test via can be electrically connected to the second pad. The PCB can also include a test interface disposed on an external face of the PCB, and the test interface can be electrically connected to the second pad through the test via, thereby forming a test trace. 
     In accordance with certain embodiments, the PCB can include a component-mounting surface. The component-mounting surface can include a plurality of pin pads and the belly pad. A plurality of the pin pads can be disposed on opposite sides of the second pad of the belly pad. A plurality of the pin pads can be disposed on opposite sides of the body portion intermediate the first pad and second pad of the belly pad. A plurality of the pin pads can be disposed on opposite sides of the first pad of the belly pad. The second pad can occupy an area of the component-mounting surface of the PCB smaller than an area of the component-mounting surface occupied by the first pad. A portion of the second pad can extend beyond an overlay area of the electrical component and the component-mounting surface of the PCB. The interconnect can overlay a portion of the second pad extending beyond the overlay area of the electrical component and PCB. 
     It is also contemplated that, in accordance with certain embodiments, the interconnect can be electrically connected to both the first pad and the second pad of the belly pad. The interconnect can span the body portion of the PCB intermediate the first pad and the second pad. The interconnect can overlay and be in intimate mechanical contact with the body portion of the PCB intermediate the first pad and second pad of the belly pad. An electrically conductive interface can be defined between the interconnect and the second pad of the belly pad. An electrically conductive interface can be defined between interconnect and the first pad of the belly pad. An electrically conductive interface can be defined between the interconnect and the conductive plane of the electrical component. An electrically insulating joint can be defined between interconnect and the body portion of the PCB intermediate the second pad and first pad of the belly pad. It is contemplated that continuity across interface between the interconnect and the first pad can be determined using the second pad of the belly pad, such as by applying a voltage across the second pad and first pad, measuring the current flow through the interconnect, and calculating the electrical resistance therethrough. 
     A method of testing continuity in an electrical assembly as described above includes measuring resistance through an interface defined between the interconnect and the first pad of the belly pad, comparing one or more of the measured resistances against a predetermined resistance value, and reworking the interconnect if one or more of the measured resistances are greater than the predetermined resistance value. In embodiments, the method can also include determining resistance through an interface defined between the interconnect and the second pad of the belly pad that is connected in series with the first pad through the interconnect. In certain embodiments, the method can include measuring resistance through an interface between the interconnect and a conductive plane of an electrical component. In accordance with certain embodiments, resistance can be measured through two of more of the interfaces to determine resistance of one of the interfaces. 
     These and other features of the systems and methods of the subject disclosure will become more readily apparent to those skilled in the art from the following detailed description of the preferred embodiments taken in conjunction with the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       So that those skilled in the art to which the subject disclosure appertains will readily understand how to make and use the devices and methods of the subject disclosure without undue experimentation, embodiments thereof will be described in detail herein below with reference to certain figures, wherein: 
         FIG. 1  is a perspective view of an exemplary embodiment of a printed circuit board (PCB) assembly constructed in accordance with the present disclosure, schematically showing an electrical component connected by an interconnect to a belly pad of a PCB; 
         FIG. 2  is a cross-sectional side elevation view of the PCB assembly of  FIG. 1 , schematically showing the interconnect spanning the belly pad and electrically connecting a first pad with the second pad; 
         FIG. 3  is a plan view of the PCB assembly of  FIG. 1 , schematically showing the electrical component and interconnect overlaying belly pad and pin pads arranged on opposite sides of the belly pad; and 
         FIG. 4  is a diagram of a method of testing the electrical connectivity between the interconnect and the PCB using the first pad and the second pad of the belly pad. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Reference will now be made to the drawings wherein like reference numerals identify similar structural features or aspects of the subject disclosure. For purposes of explanation and illustration, and not limitation, a partial view of an exemplary embodiment of a printed circuit board (PCB) assembly in accordance with the disclosure is shown in  FIG. 1  and is designated generally by reference character  100 . Other embodiments of PCB assemblies and methods of making such assemblies, or aspects thereof, are provided in  FIGS. 2-4 , as will be described. The systems and methods described herein can be used for motor controllers in aircraft electrical systems, however the invention is not limited to either motor controllers or aircraft electrical systems. 
     Referring to  FIG. 1 , PCB assembly  100  is shown. PCB assembly  100  includes a PCB  102  mechanically supporting an electrical component  104  and an electrically conductive interconnect  106  connected between the electrical component  104  and PCB  102 . PCB  102  includes a plurality of electrically insulative layers (shown as an integral structure for purposes of clarity) laminated together and having therein a plurality of electrically conductive features arranged within the electrically insulative layers. A belly pad  108  is seated within a component-receiving surface  148  of PCB facing electrical component  104 . A ground plane  116  is disposed within an interior of PCB  102  and is electrically connected to belly pad  108 . 
     Belly pad  108  includes a first pad  110  and an adjacent second pad  112 . Electrical component  104  overlays first pad  110  and second pad  112 , and includes a conductive plane  126 . Second pad  112  is electrically separated from first pad  110  within PCB  102  by a body portion  136  (shown in  FIG. 2 ) intermediate the first pad  110  and second pad  112  of belly pad  108 . A ground via  114  extends from first pad  110  to ground plane  116  within an interior of PCB  102 , electrically connecting first pad  110  with ground plane  116 . A test via  118  extends from second pad  112  through the interior of PCB  102  to a test interface  120 , providing electrical access to second pad  112  from the exterior of PCB  102 . Optionally, a ground terminal  122  can be disposed on a side of PCB  102  opposite electrical component  104  and electrically connected to ground plane  116  through ground via  114  to provide electrical access to first pad  110  from the exterior of PCB  102 . It is contemplated the plurality insulative layers forming PCB  102  can include a material such as FR-4 glass epoxy. One or more of the electrically conductive features of PCB  102 , e.g., belly pad  108 , ground plane  116 , ground via  116 , and/or test via  118 , can be formed from copper, such as from etched copper sheet or similar conductive material. 
     With reference to  FIG. 2 , electrical component  104 , PCB  102 , and interconnect  106  are shown. Electrical component  104  includes a housing  124  with an interior and an exterior, a conductive plane  126  disposed on the exterior of housing  124 , and a grounded element  128  disposed within the interior of housing  124 . It is contemplated that electrical component  104  can be a chip package, housing  124  can be a ceramic housing, and grounded element  128  can include an integrated circuit defined within a silicon body. Conductive plane  126  is disposed on an exterior face of housing  124  facing PCB  102  and a plurality of vias  130  extend through ceramic housing  124  to electrically connect electrical component  104  with conductive plane  126 . One or more of the plurality of vias  130  can be a thermal via thermally coupling grounded element  128  with conductive plane  126  for cooling grounded element  128  through PCB  102 . 
     PCB  102  includes an electrically insulative body  132 . Electrically insulative body  132  is formed from an electrically insulative material  134  that bounds ground plane  116 , ground via  114 , and test via  118 . Electrically insulative material  134  of insulative body  132  also bounds first pad  110  and second pad  112  on a side of PCB  102  opposite electrical component  104 . An intermediate portion  136  of insulative body  132  electrically separates first pad  110  of belly pad  108  from second pad  112  of belly pad  108  within insulative body  132  of PCB  102 . Ground plane  116  is disposed within insulative body  132  and is electrically connected to first pad  110  through ground via  114 , which in turn extends to a ground terminal  122  disposed on an external surface  140  of PCB  102  to form a ground trace  110 / 114 / 122 . External surface  140  also includes a test terminal  120 , which is connected to second pad  112  by test via  118  and thereby forms a test trace  112 / 118 / 120 . 
     Interconnect  106  is formed from an electrically conductive material  142 , such as solder or similar material, and is interposed between PCB  102  and electrical component  104 . Interconnect  106  spans both first pad  110  of belly pad  108  and second pad  112  of belly pad  108 , connecting first pad  110  in electrically in series with second pad  112 . Interconnect  106  also spans conductive plane  126  of electrical component  104 , electrically connecting conductive plane  126  of electrical component  104  with both first pad  110  of belly pad  108  and second pad  112  of belly pad  108 . An electrically conductive interface A is disposed between interconnect  106  and second pad  112  of belly pad  108  that is connected electrically in series with an electrically conductive interface C is disposed between interconnect  106  and first pad  110  of belly pad  108 . An electrically conductive interface D is disposed between interconnect  106  and ground plane  116  of electrical component  104 , and an electrically insulative joint B is disposed between interconnect  106  and intermediate portion  136  of PCB  102 . 
     As will be appreciated by those of skill in the art in view of the present disclosure, the quality of the ground reference provided to electrical component  104  PCB  102  is influenced by the resistivity of interface C, interconnect  106 , and interface D. Belly pad  108  allows for testing electrical continuity across each of these elements by applying voltages across various structures on PCB  102 , measuring current flow through the structures, and comparing the measured current to a predetermined value. Based on the comparison, PCB  102  can be dispositioned as suitable for use or requiring rework/or repair, such as by removing and replacing interconnect  106 . As will be appreciated, resistance can be determined through the interface defined between interconnect  106  and first pad  110  of belly pad  108 , allowing for assessment of the connectivity between the components. 
     For example, a voltage can be applied across external test terminal  120  and external ground connect  122 , and current flow therebetween measured. This provides an indication the resistivity of through interface A, interface C, and interconnect  106 . The measured current flow can be compared to a predetermined threshold, and based on the comparison of the measured current flow, determination made regarding continuity across the various interfaces bounded by interconnect  106 . Alternatively or additionally, a voltage can be applied to a first face  144  of interconnect  106  and external ground terminal  122  or external test terminal  120 , current measured, and resistivity of the intervening interface (e.g., interface C or interface A) inferred from the current flow and compared to a predetermined threshold for disposition. Voltage can be applied to a second face  146  of interconnect  106  and external ground terminal  122  or external test terminal  120 , current measured, and resistivity of the intervening interface (e.g., interface C or interface A) inferred from the current flow and compared to a predetermined threshold for disposition. This allows for determining which of the interfaces bounded by interconnect  106  is driving elevated resistance through the interface, simplifying rework by allowing for rework of a portion of the interconnect  106 . 
     With reference to  FIG. 3 , a component-receiving surface  148  of PCB  102  is shown. Surfaces of first pad  110 , electrically intermediate body portion  136 , and second pad  112  are disposed within component-receiving surface  148 . Pin pads  150  (only one identified for purposes of clarity) are also defined within component-receiving surface  148  and are electrically isolated from conductive plane  126  (shown in  FIG. 2 ). PCB  102  also includes a pin  1  locating indicator  152  arranged adjacent to pin  1  pad of PCB  102 , facilitating assembly of PCB  102  by allowing alignment of pin  1  indicator  154  of electrical component  104  with PCB  102  for coupling a first pin  156  between electrical component  104  and PCB  102 . 
     Electrical component  104  overlays component-receiving surface  148  of PCB  102  such that electrical component  104  laterally spans first pad  110  and second pad  112 . A pair of pin pads  150  are disposed on laterally opposite sides of first pad  110 . A pair of pin pads  150  are also disposed on laterally opposite sides of body portion  136 . A pair of pin pads  150  are additionally disposed on laterally opposite sides of second pad  112 . 
     Belly pad  108  is disposed within the overlay area defined between electrical component  104  and PCB  102 . A portion of first pad  110  extends beyond the overlap area between electrical component  104  and PCB  102 , providing a test location that allows for acquiring current measurements for assessing the continuity across individual interfaces within PCB assembly  100 . Similarly, a portion of second pad  112  extends beyond the overlap area between electrical component  104  and PCB  102 , providing a further test location that allows for acquiring current measurements for assessing the continuity across individual interfaces within PCB assembly  100 . In the illustrated exemplary embodiment, first pad  110  has a greater area than second pad  112 . The greater area of first pad  110  allows first pad  110  to serve as a heat sink for electrical component  104 , notwithstanding the relative area occupied by second pad  112 . 
     With reference to  FIG. 4 , a method testing continuity in an electrical assembly, e.g., PCB assembly  100  (shown in  FIG. 1 ) is generally indicated with reference numeral  200 . Method  200  includes measuring resistance through an interface between a second pad and an interconnect, e.g., first interface A shown in  FIG. 2 , disposed between a second pad, e.g., second pad  112  (shown in  FIG. 1 ), and an interconnect, e.g., interconnect  106  (shown in  FIG. 1 ), as shown with box  210 . Method  200  also includes measuring resistance through an interface between a first pad and an interconnect, e.g., third interface C (shown in  FIG. 2 ) disposed between a first pad, e.g. first pad  110  (shown in  FIG. 1 ), and the interconnect, as shown with box  220 . Method  200  further includes measuring resistance in a circuit including a conduction plane of an electrical component and the interconnect, e.g., conductive plane  126  of electrical component  104  (shown in  FIG. 1 ) disposed between an electrical component and the interconnect, as shown with box  230 . 
     Once current has been measured and/or resistance determined, the current measurement and/or calculated resistance can be compared against a predetermined value, as shown with box  240 . Based on the comparison, the interconnect can be reworked in the event that current flow is too low and/or resistance too high, as shown with box  250 . In embodiments, the method includes acquiring at least current measurement and/or calculating one resistance value. In certain embodiments, the method includes acquiring a plurality of current measurements and/or calculating a plurality of resistances using measurements acquired at different locations, and determining continuity through individual interfaces to disposition the assembly. 
     The methods and systems of the present disclosure, as described above and shown in the drawings, provide for electrical assemblies with superior properties including an assembly interconnect that is testable at the piece part level. While the apparatus and methods of the subject disclosure have been shown and described with reference to preferred embodiments, those skilled in the art will readily appreciate that changes and/or modifications may be made thereto without departing from the scope of the subject disclosure.