Patent Publication Number: US-2023164923-A1

Title: Solder joint inspection features

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims priority to U.S. Provisional Patent Application No. 63/281,327 dated Nov. 19, 2021, the contents of which are incorporated by reference herein in its entirety for all purposes. 
    
    
     FIELD OF THE DISCLOSURE 
     The subject disclosure relates to inspection of solders on printed circuit boards (PCBs), and more particularly to features to inspect conductor wire solder connections to solder pads. 
     BACKGROUND 
     Soldering delivers a robust and efficient bond between a solder pad of a PCB or a microchip and a conductor wire, enabling component integration and the attachment of electronic packages thereto. Soldering processes accommodate through-hole leaded components as well as surface-mounted packages. 
     When soldering conductor wire to a board, the solder joint formed requires inspection in order to avoid producing a defective connection, and thus a defective board. Some compromised solder joints are intermittent and problems only manifest when mechanical strain is applied to the PCB. Inspection is particularly critical due to ever-growing industry trends towards using surface mounted components. Solder joint inspection is typically a subjective determination of how much of conductor wire is placed on a solder pad, and how much solder needs to be applied thereto. 
     Solder joint inspection is required for the manufacturing of electronic components, systems and methods, particularly for the inspection of ball grid array solder contacts. X-rays have been employed to inspect solder joints because the penetrating illumination enables visualization of hidden features between an integrated circuit component and a printed circuit board. However, X-ray sources and detectors add unnecessary complexity to the process of inspecting visible solder joints. UV light and fluorescing materials may also be employed to aid in the inspection of solder joints. However, the integration of special materials to the manufacturing process requires compatibility testing and qualification for utilization, especially in applications requiring high reliability or those with environmental sensitivity. 
     Solder joint inspection methods often employ machine vision systems. In such systems, images of the solder joint to be inspected are acquired and stored digitally. A computational device then performs image processing, calculations, and or pattern matching against reference images stored in memory devices. These systems may attempt to calculate the height or volume of solder, the curvature of the exterior surface of the solder, or the contact angle between the solder and substrate. The criteria for the sufficiency of solder in these cases is based on a calculation that must be performed by a CPU. Comparisons are then made between the result of the calculation and a reference value stored in non-transitory memory. 
     Though, the quantity of solder present is not a sufficient criteria for determining the quality of a soldered contact. And, these methods introduce unnecessary sophistication, and as such, a system for solder joint quality inspection may be devised that eliminates the need for avoidable calculations. 
     The position of an electrically active component with respect to the solder pad on a printed circuit board is also critical to the functionality of the resulting circuit. Furthermore, encasing the conducting lead of an electrically active component is important for the structural integrity of the solder joint subject to mechanical stress. A system for inspecting both the position of the conducting lead with respect to the solder pad on a printed circuit board and the quantity of solder applied is desired to ensure high quality soldered connections. 
     The subject disclosure is contemplated for use in an electric motor such as a permanent magnet brushless motor that is disclosed by U.S. Pat. No. 7,105,973 BS, issued Sep. 12, 2006, the entirety of which is corporate by reference herein. The subject disclosure may also be implemented by those skilled in the art to other electric motor types and topologies including, but not limited to linear motors, outside rotating motors, hybrid steppers, permanent magnet steppers, variable reluctance motors, switched reluctance motors, or other polyphase electric motors. 
     An electric motor using a printed circuit board with solder joint inspection features includes a rotor and a stator having a plurality of coils wrapped thereon, the coils comprising field windings. The plurality of field winding coils may be wound around one or more stator teeth but may also be wound into a slat-less stator that does not include individual stator teeth. 
     The field windings of the electric motor stator are of any material capable of conducting electricity, preferably insulated conductors called magnet wire. The separate stator field winding coils may be connected in either series groups or in parallel groups to achieve the appropriate winding parameters necessary for the application of the electric motor. 
     Electric motors may have single or multi-phase windings, and it is common for multiphase stators to be connected in either a star-wye connection pattern or a delta connection pattern with each motor phase having one or more stator field windings coils. 
     The interconnections of the electric motor&#39;s individual field windings into series and/or parallel groups and those groups further into either a star-wye or delta connection maybe done using a printed circuit board. 
     Individual conducting magnet wires of the electric motor&#39;s field windings must be securely soldered on to the printed circuit board, which then will use the subject disclosure described herein to confirm the quality of the solder joint. 
     The flow of current into the field windings can be controlled and adjusted by motor control electronics to produce a desired magnetic field and corresponding motor performance. 
     SUMMARY 
     The subject technology is directed to a printed circuit board (PCB) having a solder joint inspection system. The printed circuit board includes a substrate surface having at least one solder pad thereon, at least one conductor wire having an end attached to the at least one solder pad, and a first inspection feature marked on the substrate surface. The first inspection feature is adjacent to the at least one solder pad to define a conductor end zone on the at least one solder pad. The end of the conductor wire is in the conductor end zone when properly attached. 
     In one embodiment, the at least one solder pad may define a second inspection feature to mark an extent to which the at least one solder pad is covered by a flow of solder when the wire is properly attached. The at least one solder pad may include a proximal end, a distal end, and a lateral side extending between the proximal end and distal end. The second inspection feature may include a notch disposed on the lateral side of the at least one solder pad. The first inspection feature may be silkscreened onto the substrate surface. 
     The subject technology is directed to a method of inspecting a solder joint including providing a substrate surface having at least one solder pad. The method includes forming a first inspection feature on the substrate surface adjacent to the at least one solder pad to define a conductor end zone on the at least one solder pad, and providing an end of a conductor wire in the conductor end zone. The method includes inspecting the position of the conductor wire, and thereafter flowing solder over the at least one solder pad to create a solder joint. The method includes inspecting the solder joint in view of a second inspection feature on the at least one solder pad. The second inspection feature marks an extent to which the at least one solder pad is covered by a flow of solder when the wire is properly attached. 
     In one embodiment, the first inspection feature may include silkscreening the first inspection feature onto the substrate surface. The at least one solder pad may include a proximal end, a distal end, and a lateral side extending between the proximal end and distal end. The second inspection feature may include a notch disposed on the lateral side of the at least one solder pad. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Various aspects of the present disclosure are discussed herein with reference to the accompanying Figures. It will be appreciated that for simplicity and clarity of illustration, elements shown in the drawings have not necessarily been drawn accurately or to scale. For example, the dimensions of some of the elements can be exaggerated relative to other elements for clarity or several physical components can be included in one functional block or element. Further, where considered appropriate, reference numerals can be repeated among the drawings to indicate corresponding or analogous elements. For purposes of clarity, however, not every component can be labeled in every drawing. The Figures are provided for the purposes of illustration and explanation and are not intended as a definition of the limits of the disclosure. 
         FIG.  1    is an overhead perspective view of two solder pads defined by a printed circuit board. 
         FIG.  2    is an overhead perspective view of the two solder pads of  FIG.  1   , including a conductor end zone. 
         FIG.  3    is an overhead perspective view of a solder joint formed on one of the two solder pads of  FIG.  1   . 
         FIG.  4   a - 4   b    are overhead and side perspective views of a printed circuit board used in a motor assembly with solder joint inspection features as described herein. 
         FIG.  5    is a close-up view of two solder pads defined by a printed circuit board, including a conductor wire end zone. 
         FIG.  6   a    is a close-up view of two solder pads defined by a printed circuit and a conductor wire positioned outside of the conductor wire end zone. 
         FIG.  6   b    is a close-up view of two solder pads defined by a printed circuit and a conductor wire positioned inside of the conductor wire end zone. 
         FIG.  7   a    is a close-up view of two defective solder joints, requiring a reflow of solder. 
         FIG.  7   b    is a close-up view of one proper solder joint, where solder has flowed beyond a second inspection feature. 
     
    
    
     DETAILED DESCRIPTION 
     The subject technology overcomes many of the prior art problems associated with solder joint inspection. The advantages, and other features of the technology disclosed herein, will become more readily apparent to those having ordinary skill in the art from the following detailed description of certain exemplary embodiments taken in combination with the drawings and wherein like reference numerals identify similar structural elements. It should be noted that directional indications such as vertical, horizontal, upward, downward, right, left and the like, are used with respect to the figures and not meant in a limiting manner. 
     A coordinate system is used herein to help characterize embodiments of the printed circuit board  100 . For example, a transverse axis  114  and an axial axis  116  are referenced. The transverse axis  114  is disposed at a 90 degree angle relative to the axial axis  116  and defines a lateral direction of the printed circuit board  100 . The axial axis  116  is disposed at a 90 degree angle relative to the transverse axis  114  and defines an axial direction along the length of a conductor wire  118 . A vertical axis  115  is disposed at a 90 degree angle relative to the transverse axis  114  and axial axis  116  and defines a thickness of the printed circuit board  100  for example. 
       FIG.  1   , illustrates a conventional printed circuit board  100  which may include one or more typical flat laminated composites made from non-conductive substrate materials with one or more layers of copper circuitry buried internally or on an external surface. The circuit board may include a top surface and a bottom surface with conventional conductors etched on either the top or bottom surfaces. 
     In some embodiments, the printed circuit board  100  may be amenable to through-hole technology. In turn, the printed circuit board  100  may include a number of plated or non-plated through-holes which provide electrical continuity through the printed circuit board  100 , referred to herein as vias. The vias include the electrical interconnection between layers of the printed circuit board  100  that are otherwise insulated in the laminate structure, and provide for a third dimension of connection between conductive layers in a controlled manner. 
     In the embodiment shown in  FIG.  1   , the printed circuit board  100  is amenable to surface-mount technology. The printed circuit board  100  may mechanically support surface-mounted electronic components in designated locations by soldering the electronic components to the printed circuit board  100 . The electronic components may include integrated circuits, or discrete components, such as resistors and diodes. Where an electronic component is to be placed on the printed circuit board  100 , the printed circuit board  100  may have, define, or otherwise contain a flat, usually tin-lead, silver, or gold plated copper pad, referred to herein as a solder pad  102 . 
     The solder pad  102  embodied on the printed circuit board  100  is an exposed region, typically including metal, that an electronic component lead, referred to herein as a conductor wire  118 , can be soldered to. The conductor wire  118  may pass through a slot  117  in the edge of a printed circuit board  100  and connect to a chip, resistor, capacitor, amplifier, diode, or other electronic component. The conductor wire  118  may be a magnet wire or sensor wire for an electric motor for which the printed circuit board  100  makes electric connection. In one embodiment, the conductor wire  118  is a strippable magnet conductor wire. As such, insulation is removed from the conductor wire  118  before making the solder connection to the printed circuit board  100 . In another embodiment, the conductor wire  118  is a magnet conductor wire that does not require stripping before making the solder connection to the printed circuit board  100 . 
     Solder pad  102  may include a surface mount pad such that surface mounted electronic components may be soldered directly to the printed circuit board  100 . Alternatively, solder pad  102  may include a plated or non-plated thru-hole pad such as when the printed circuit board  100  is amenable to through-hole technology. 
     The solder pad  102  embodies a shape having a semi-circular portion defining a proximal end  106  of the solder pad  102 , in conjunction with a rectangular portion defining a distal end  108 . The shape of the solder pad  102  resembles that of a Norman window, wherein the rectangular distal end  108  has a length dimension, extending in the transverse direction  114  of  FIG.  1   , which is less than a length dimension, also extending in the transverse direction  114  of  FIG.  1   , of the semi-circular proximal end  106 . In other embodiments, the solder pad  102  may embody the shape of an elongated semi-circle, a rectangle with two rounded corners, a rectangle with a semi-circular top portion, or a similar shape. Alternatively, the solder pad  102  may include: a square or rectangular solder pad  102 , used in conjunction with large and few circuit board components; a circular solder pad  102 , typically used in single and double-sided printed circuit boards  100  with regularly arranged components; an island-shaped solder pad  102 , typically used in a vertical irregular arrangement; a teardrop solder pad  102 , often used in high-frequency circuits; a polygonal solder pad  102 , used to distinguish pads with close outer diameter but different apertures for easy processing and assembly; an oval solder pad  102  used in dual in-line devices; or an open-shaped solder pad  102 . In yet another embodiment, the solder pad  102  may embody any shape feasible for the printed circuit board  100  application. 
     Referring now to  FIGS.  1  and  2    together, the printed circuit  100  includes a solder joint inspection system. The solder joint inspection system includes a first inspection feature  110  and a second inspection feature  112 . 
     The first inspection feature  110  is printed, inked, marked, screened, silkscreened, scored, stained, shaped, or otherwise indicated on the printed circuit board  100 . The first inspection feature  110  on the printed circuit board  100  is adjacent or proximate to the solder pad  102  to define a conductor end zone  122 . In this regard, by referencing the first inspection feature  110 , a conductor end zone  122  may be defined on the solder pad  102  by an inspector. The conductor end zone  122  marks an appropriate area for the end portion  119  of the conductor wire  118  to make contact with the solder pad  102 . 
     In one embodiment, the first inspection feature  110  includes a white fiducial marking silkscreened onto the printed circuit board  100  surface, adjacent to the solder pad  102 . The first inspection feature  110  may be visually transposed onto the solder pad  102 , defining the conductor end zone  122  within which the end portion  119  of the conductor wire  118  must be positioned for proper attachment. As such, the first inspection feature  110  can be referenced by an inspector when determining if an adequate length of conductor wire  118  is disposed on the solder pad  102 . 
     The first inspection feature  110  includes a length  120 , as shown in  FIG.  2   . The length  120  dimension extends in the axial direction  116  as depicted in  FIG.  1   . The length  120  provides a first dimension of the conductor end zone  122 , while the width in the transverse direction of the solder pad  102  defines a second dimension of the conductor end zone  122 . 
     The first inspection feature  110  extends along the transverse direction  114  relative to the solder pads  102  and conductor wire  118 , whereas the conductor wire  118  extends along an axial direction  116 . Though it will be appreciated by one of pertinent skill in the art that the first inspection feature  110  may extend along a transverse  114  or axial  116  direction relative to the conductor wire  118 , the printed circuit board  100 , the solder pad  102 , or another point of reference. 
     Referring now to  FIG.  3   , the second inspection feature  112  of the solder joint inspection system is defined by the solder pad  102 . The second inspection feature  112  marks an extent to which the solder pad  102  is covered by a flow of solder when a conductor wire  118  is properly attached. 
     The second inspection feature  112  may include a v-shaped, u-shaped, circular, straight, or other shaped notch, indentation, or step in the solder pad  102 . In another embodiment, the second inspection feature  112  may include an indicator that is printed, inked, marked, screened, silkscreened, scored, stained, shaped, or otherwise indicated on the printed circuit  100  instead of, or in addition to, the solder pad  102 . The second inspection feature  112  may preferably be disposed on a lateral side of the solder pad  102 , the lateral side including a sidewall or peripheral of the solder pad  102 , extending between the proximal end  106  and the distal end  108  of the solder pad  102 . However, any surface or location of the solder pad  102  may suffice as a second inspection feature  112  position. 
     The second inspection feature  112  may be disposed on more than one lateral side of the solder pad  102 . In this regard, in some embodiments, the solder pad  102  is symmetrical, including two second inspection features  112  formed on opposing lateral sides of the solder pad  102 , separated along the transverse direction  114 . In such an embodiment, the second inspection features  112  may define an indicator line  126  therebetween to show the extent to which the solder pad  102  is covered by a flow of solder when the conductor wire  118  is properly attached. 
     Relative to the length of the solder pad  102 , that is, the axial direction  116  defined in  FIG.  1   , the second inspection feature  112  may be disposed at a point on the solder pad  102  that is 0%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, or 100% the length of the solder pad  102 . For example, in the embodiment shown in  FIG.  3   , the second inspection feature  112  is disposed at a point on the solder pad  102  that is roughly 40% of the length of the solder pad  102 . Depending on the solder pad  102 , the conductor wire  118 , or the electronic component to be mounted to the printed circuit board  100 , the second inspection feature  112  may be adjusted in order to mark an appropriate amount of solder for the application. 
     Referring now to  FIGS.  1 - 3    together, in operation, the solder joint inspection system provides a method of inspecting a solder joint  124 . As discussed prior, a substrate surface on the printed circuit board  100  is provided having at least one solder pad  102  defined by, attached to, or otherwise on the printed circuit board  100 . The first inspection feature  110  is formed on the substrate surface, adjacent to the at least one solder pad  102  to define the conductor end zone  122  on the at least one solder pad  102 . In order to affix a surface-mounted electronic component (not shown) or to the printed circuit board  100 , an end of a conductor wire  118  of the electronic component is provided in the conductor end zone  122 , marking a proper length or portion of conductor wire  118  that must be affixed to the solder pad  102  for proper connection. Similar to the surface-mounted electronic component, in order to affix a conductor wire  118  of an electric motor to the printed circuit board  100 , the end of a conductor wire  118  of the electronic component is provided in the conductor end zone  122 , marking a proper length or portion of conductor wire  118  that must be affixed to the solder pad  102  for proper connection. 
     Thereafter, the position of the conductor wire  118  may be inspected to ensure an end of the conductor wire  118  is within the conductor end zone  122  of the solder pad. 
     The conductor wire  118  may then be attached to the board through a variety of heating techniques, including laser soldering, induction soldering, fiber focus infrared soldering, resistance soldering, active soldering, silver soldering, mechanical and aluminum soldering, hand soldering, wave soldering, reflow soldering, and brazing. As such, flowing solder over the at least one solder pad  102  creates the solder joint  124 . The solder joint  124  may be inspected in view of the second inspection feature  112  on the at least one solder pad  102 . This is because the second inspection feature  112  marks an extent to which the at least one solder pad  102  is covered by a flow of solder when the conductor wire  118  is properly attached. If the solder does not extend to the second inspection feature  112 , then the solder joint  124  can be resoldered. 
     In a preferred example, the printed circuit board  100  is subjected to reflow soldering. A solder paste is used to temporarily attach the conductor wire  118  to the solder pad  102 , after which the entire printed circuit board  100  is subjected to controlled heat. The solder paste eventually reaches the eutectic temperature at which the particular alloy composing the solder paste undergoes a phase change to a liquid or molten state. The solder paste thereafter exhibits properties of adhesion, thus creating one or more permanent or semi-permanent solder joints  124 , joining the conductor wire  118  and the solder pad  102 . The second inspection feature  110  shows the extent to which the solder paste covers the conductor wire  118  on the solder pad  102  following the reflow soldering process. 
     Referring now to  FIGS.  4   a ,  4   b   , and  FIG.  5   , overhead, side, and close-up views of a printed circuit board  100  for an electric motor are shown in accordance with the subject disclosure. The printed circuit board  100  makes an electrical connection with conductor magnet wires of the electric motor&#39;s field windings. As shown in greater detail with respect to  FIG.  5   , the printed circuit board  100  includes one or more solder pads  102  and a first inspection feature  110  silkscreened adjacent thereto. The conductor end zone  122  is apparent on the solder pad  102  based on the location of the first inspection feature  110  relative to the solder pad  102  and the printed circuit board  100 . The first inspection feature  110  aids in solder joint  124  inspection of the electrical connection between the conductor magnet wires of the electric motor&#39;s field windings and the printed circuit board  100 . 
     Referring now to  FIG.  6   a   , a slot  117  is defined by the circuit board, through which a conductor wire  118  is fed. The end portion  119  of the conductor wire  118  is located outside of the conductor end zone  122 . By marking or noting the conductor end zone  122  defined by the first inspection feature  110 , an inspector can adjust the position of the end portion  119  of the conductor wire  118  to that shown in  FIG.  6   b    to ensure a higher probability of an operational solder joint. 
     Referring now to  FIG.  7   a   , a close-up view of two defective solder joints  724  is depicted. The second inspection feature  112 , marks an extent to which the solder pads  102  are covered by a flow of solder when the conductor wire  118  is properly attached. In comparison to  FIG.  7   b   , the flow of solder in  FIG.  7   a    did not reach the second inspection feature  112  while flowing from the proximal end  106  of the solder pad  102  to the distal end  108 , thus indicating a defective joint.  FIG.  7   b    is a close-up view of a proper solder joint  124 . As shown, solder has flowed beyond the second inspection feature  112  from the proximal end  106  of the solder pad  102  to the distal end  108 . 
     As can be seen, the subject disclosure provides many improvements to solder joint  124  inspection systems. For example, without limitation, the use of the first inspection feature  110  and the second inspection feature  112  described herein provide a reliable way to aid an inspector in the visual inspection of a machine in determining whether the solder joint  124  is acceptable. The solder joint  124  inspection system facilitates this inspection process manually and automatically with and without visual magnification. Further, the subject technology can be adapted to any kind of soldering technique. 
     It will be appreciated by those of ordinary skill in the pertinent art that the functions of several elements can, in alternative embodiments, be carried out by fewer elements, or a single element. Similarly, in some embodiments, any functional element can perform fewer, or different, operations than those described with respect to the illustrated embodiment. Also, functional elements shown as distinct for purposes of illustration can be incorporated within other functional elements in a particular embodiment. 
     While the subject technology has been described with respect to various embodiments, those skilled in the art will readily appreciate that various changes and/or modifications can be made to the subject technology without departing from the scope of the present disclosure.