Abstract:
A power converter includes electrical contacts arranged on a first surface and a connection device. The converter has a top surface above the first surface and a bottom surface below the first surface. A border of the bottom surface is inset from a border of the second surface. The connection device includes a pair of conductive legs, each leg comprising a first end and a second end. The pair of legs lie opposite each other in a pair of evenly spaced planes that intersect the first surface. The first ends are adapted to connect to one or more of the contacts on the first surface and the second ends are adapted to connect to one or more conductive pads on a surface of a substrate. The connection device is adapted to enable the first ends of the two legs to connect to the contacts from below the first surface.

Description:
BACKGROUND 
   This description relates to surface mounting a power converter. 
   In some modular DC—DC power conversion products, the DC input voltage is greater than the DC output voltage, e.g., the input voltage may be 48 VDC, and the DC output voltage may be 1.8 VDC. With electronic circuits trending towards lower operating voltages, the output currents delivered by many DC—DC converters have increased. 
   DC—DC converters provide a so-called “pinout”, for making connections to their inputs and outputs. An example of one such pinout is shown in FIG.  1 . In the Figure, which is an exploded view of a DC—DC converter module  10  mounted on a printed circuit board  12 , the DC—DC converter pinout comprises output voltage connection pins  14 , input voltage connection pins  16  and input and output control pins  17 . Because the output pins typically carry more current than the input pins their diameter (e.g., 0.080″ (2.0 mm)) may be larger than the diameter (e.g., 0.040″ (11.0 mm)) of the input and control pins. All of the pins are inserted into mating holes  18 ,  20  in the printed circuit board  12  and are soldered to etches  22 ,  24 ,  26  in and around the holes. Pins of the kind described above are useful up to about 40 Amperes. Above 40 Amperes, either larger diameter pins, or a plurality of pins, may be used. 
   DC—DC converters may also be mounted using surface mount power interconnections involving solder-ball-grid arrays or “J-lead” lead frames, examples of which are described or illustrated in U.S. patent application Ser. No. 10/303,613, “Power Converter Package and Thermal Management”, filed on Nov. 25, 2002, and in U.S. Design Patent Application No. 29/175,342, “Power Converter Body” (referred to, respectively, as the “&#39;613 application” and the “&#39;342 application”), filed on Feb. 3, 2003, both assigned to the same assignee as this application and both incorporated here by reference. As described in the &#39;342 application, and shown in  FIG. 2 , a power converter module  30  may be surface mounted to a substrate  34  by connecting the solder-ball-grid arrays  31   a ,  31   b  to corresponding conductive etch patterns  33   a ,  33   b  on the surface of the substrate  34 . In the example shown in  FIG. 2 , the bottom surface of the power converter module extends through an aperture  35  in the substrate. 
   SUMMARY 
   In general, in one aspect, the invention features an apparatus comprising a power converter including electrical contacts arranged on a first surface and a connection device. The converter has a top surface above the first surface and a bottom surface below the first surface. A border of the bottom surface is inset from a border of the second surface. The connection device includes a pair of conductive legs, each leg comprising a first end and a second end. The pair of legs lie opposite each other in a pair of evenly spaced planes that intersect the first surface. The first ends are adapted to connect to one or more of the contacts on the first surface and the second ends are adapted to connect to one or more conductive pads on a surface of a substrate. The connection device is adapted to enable the first ends of the two legs to connect to the contacts from below the first surface. 
   Implementations of the invention may include one or more of the following features. The first ends and second ends of respective legs are spaced apart by a distance that is greater than a distance between the first surface and the bottom surface. The top and bottom surfaces are planar and are parallel to each other and to the first surface. The electrical contacts comprise a ball-grid array. The conductive pads comprise conductive etch. There are two or more pairs of legs in the pair of planes. The pair of legs are part of a strip of conductive material bent to form the pair of legs, each leg connected at a right angle to a spanning portion of the strip, the pair of legs being electrically connected together by the spanning portion. The spanning portion comprises the first ends of each of the two pair of legs. The legs of the pair are formed from separate pieces of conductive material. The second end of each leg is formed into a J. The J end of each leg is directed inward toward the other leg so that the two ends of the Js lie between the pair of legs. There are two or more pairs of legs held together by a non-conductive rib. The rib comprises a hole that exposes a portion of a pair of legs to form a first end. Each of the pairs of legs comprises a strip of conductive material bent to form the pair of legs, each leg connected at a right angle to a spanning portion of the strip, the pair of legs being electrically connected together by the spanning strip, and the rib comprises a hole that exposes a portion of the spanning strip to form a first end. The legs of a pair are formed from separate pieces of conductive material and the rib comprises holes that expose a portion of each leg to form a first end. The rib connects the pairs of legs so that the legs lie in the pair of planes. 
   In general, in another aspect, the invention features a method for making connections between (a) electrical contacts that are inset from a bottom surface of a power converter and (b) conductive pads located on a substrate. The method includes interposing between the contacts and the bottom surface, conductive segments that comprise two generally parallel conductive legs, each leg comprising a first end and a second end, the first ends of the two legs being connected to one or more of the electrical contacts and the second ends extending to a location below the bottom surface and connecting to one of more of the pads. 
   Implementations of the invention may include one or more of the following features. Additional conductive segments are provided, each conductive segment comprising pairs of generally parallel legs. The segments are arranged in a row using a non-conductive rib so that the generally parallel legs in each segment lie in two generally parallel planes. A ball-grid array of electrical contacts is provided on the power converter. Holes are provided in the rib to expose portions of first ends at locations along the rib that align with the locations of the balls in the ball-grid array. The ball-grid array is soldered to the exposed locations of the spanning portions. The free ends of the legs are folded into a J, and the J-shaped portions of the free ends are soldered to the conductive pads on the substrate. The distance is essentially equal to the maximum distance between the first surface and the bottom surface so that the bottom surface is just above, and in close proximity to, the surface of the substrate. The distance is greater than the maximum distance between the first surface and the bottom surface so that a gap exists between the bottom surface and the surface of the substrate. The distance may be twice the value of the maximum distance between the first surface and the bottom surface. 
   Other advantages and features of the invention will become apparent from the following description and from the claims. 

   
     DESCRIPTION 
     We first briefly describe the drawings: 
       FIGS. 1 and 2  show exploded views of power converters and printed circuit boards. 
       FIG. 3  shows an exploded view of a power converter and a connector system. 
       FIGS. 4A-4D  show orthographic views of the converter of FIG.  3 . 
       FIG. 5  shows an end view of the converter of  FIG. 4  mounted to a substrate. 
       FIG. 6  shows a conductive metal piece used as part of a connector system. 
       FIG. 7  shows an assembly of the metal piece of FIG.  6  and plastic ribs. 
       FIGS. 8A-8D  show orthographic views of the assembly of FIG.  7 . 
       FIGS. 9A-9E  show perspective and orthographic views of the assembly of  FIG. 8  after cutting away portions of the conductive plate. 
       FIGS. 10A-10F  show perspective and orthographic views of the connector segments of  FIG. 9  after forming the leads. 
       FIG. 11  shows a cross section of the assembly of FIG.  7 . 
       FIG. 12  shows a cross section of a mold during the molding of the assembly of FIG.  7 . 
       FIG. 13  shows a conductive metal piece used to form another connector system according to the invention. 
       FIG. 14  shows an assembly comprising the metal piece of  FIG. 13 and a  plastic rib. 
       FIG. 15  shows the assembly of  FIG. 14  including a slot. 
       FIG. 16  shows an end view of an assembly. 
       FIG. 17  shows a perspective view of the assembly of FIG.  16 . 
       FIG. 18  shows an exploded perspective view of the assembly of  FIG. 17  comprising components underneath the body of the power converter. 
   

     FIG. 3  shows an exploded perspective view, and  FIGS. 4A through 4D  show, respectively, top, end, side, and bottom plan views, of an assembly comprising a power converter module  30  and two bilateral J-lead connectors  28 ,  29 , described below. In the Figures, the power converter module  30  comprises solder-ball-grid arrays  31   a ,  31   b  for making electrical connections (e.g., the power converter module is of the kind described or illustrated in the &#39;613 and &#39;342 applications (and shown in FIG.  2 )). The bilateral J-lead connectors  28 ,  29  are attached to the power converter module  30  by means of the solder-ball-grid arrays  31   a ,  31   b  to form a surface mount connector system for the power converter module  30 . As illustrated in  FIG. 5 , which shows the J-lead connectors  28 ,  29  of  FIG. 4  connected by solder  62  to conductive pads  36   a ,  36   b  on a substrate  34  (e.g., a printed circuit board), an advantage of the structure is that the power converter module  30  may be surface mounted to a substrate  34  without the need for an aperture ( 35 ,  FIG. 2 ) in the substrate. To avoid the need for an aperture, the minimum height of the J-lead connectors (i.e., the minimum value of the distance labeled “H” in FIG.  5 ), is no less than the vertical distance between the bottom surface of the power converter  95  and the surfaces  100  on which the ball grid array is mounted, if that surface is coplanar with the surface of the substrate that is adjacent to the bottom surface of the power converter. Another advantage of the structure is that its use does not materially affect the thermal performance of the power converter  30 , because the J-leads can efficiently conduct heat generated within the power converter from the ball-grid array into the substrate  34 . This heat may then be removed by convection from, or a flow of cooling air over, the leads and the substrate. 
   Referring to  FIGS. 3 ,  4  and  5  the power converter module  30  comprises a top surface  102 , two generally planar second surfaces  100  comprising the ball-grid arrays  31   a ,  31   b , the second surfaces being located below the top surface, and a bottom surface  95  located below the second surfaces. Portions of the border of the bottom surface  95  are inset from the corresponding portions of the border of the top surface  102  to make the ball-grid array of contacts on the second surfaces  100  accessible from underneath the second surfaces. Because the J-lead connectors fit essentially entirely within the regions underneath the second surfaces, the assembly of  FIGS. 4 and 5  occupies essentially the same surface area on a substrate  34  as does the power converter module  30  of FIG.  2 . 
   Each of the bilateral J-lead connectors  28 ,  29  comprises several electrically independent connection segments. For example, connector  29  comprises four essentially identical segments  37   a - 37   d . Each of the segments  37   a - 37   d  comprises two parallel rows (e.g., rows  35   a ,  35   b ,  FIG. 4   b ) of connections, each parallel row comprising slots (e.g., slots  40 ,  FIG. 3 ) that form four compliant fingers (e.g., fingers  33   a - 33   d ) within each segment. In a similar fashion, connector  28  comprises five segments: essentially identical segments  41   a ,  41   e , each segment comprising two parallel rows (e.g., rows  35   c ,  35   d ,  FIG. 4   b ) of connections, each row of connections comprising six compliant fingers (e.g., compliant fingers  33   e - 33   j , FIG.  3 ); and essentially identical segments  41   b ,  41   c ,  41   d , each segment consisting of a single pair of compliant fingers (e.g., fingers  33   k ,  33 L, FIG.  3 ). 
   The arrangement of segments, slots and fingers illustrated in  FIGS. 3 and 4  is but one example of many possible arrangements that can include, for example, other numbers of segments, other numbers of fingers per segment, unequal lengths of segments, and so forth. The number of fingers in a segment will be selected based upon, e.g., how much current the segment must carry and the permissible heat loss in the segment. Thus, e.g., segment  41   e  (FIG.  4 ), comprising six rows of fingers, might carry a relatively high converter output current, while segments  41   b ,  41   c  and  41   d , each comprising a single row of fingers, might be used for connection to low current control signals. 
   Opposing pairs of fingers (e.g., fingers  33   e  and  33   m ) may be formed from a single piece of conductive material, to form a common connection contact, or they may be formed from separate pieces of conductive material to form a pair of independent connection contacts. Because of their close proximity, pairs of opposing fingers in segments formed of pairs of independent connections will exhibit relatively low values of parasitic inductance compared, e.g., to the parasitic inductance between segments formed of common connection contacts located at different positions along a row. For example, if rows of opposing fingers  35   a  and  35   b  in  FIG. 4B  are formed of independent connections and the rows are used for making connection to the positive and negative voltage terminals of the converter, the parasitic inductance associated with the two rows of contacts will be relatively low owing to the close proximity of the opposing rows of fingers. On the other hand, if the positive and negative voltage terminals of the converter are brought out by use of adjacent segments (e.g., segments  37   a ,  37   b , FIGS.  3  and  4 D), with each segment being formed of common connection contacts that form a single contact point, the relatively wide spacing between the segments will result in a relatively much higher value of parasitic inductance for the connections. 
     FIGS. 6 through 12  show steps in the manufacture of bilateral J-lead connectors  28 ,  29 , in which the segments comprise common connection contacts having opposing fingers formed from a single piece of conductive material. 
     FIG. 6  shows a flat piece of conductive metal  39  (e.g., palladium plated copper, of thickness 0.010 inches (0.25 mm), and of width A=1.224 inches (3.11 cm) and length B=1.565 inches (3.98 cm) comprising slots and holes  40 ,  42 ,  44 ,  46 ,  48 . Some of the slots (e.g., slots  40 ) define the finger locations and some (e.g., slots  44 ,  46 ) define spaces between electrically isolated segments. 
   The conductive metal piece  39  is placed in a mold and plastic ribs  50 ,  52  ( FIG. 7 ) are molded in place.  FIG. 7  shows an exploded perspective view, and  FIGS. 8A through 8D  show, respectively, top, end, side and bottom plan views, of an assembly  51  comprising the conductive metal piece  39  and molded plastic ribs  50 ,  52 , after the molding process is completed. As shown in  FIG. 11 , which shows a sectional view of the assembly  51  taken at the location marked AA in  FIG. 7 , the plastic material that forms the rib  50  fills the anchor holes  42  ( FIG. 6 ,  12 ) in the conductive piece  39 , to firmly affix the rib  50  to the conductive piece  39 . Holes  48  are used to locate the piece  39  in the mold during the molding of the rib. 
   The pattern of holes  54  in the ribs  50 ,  52  on the top side of the assembly  51  defines regions free of plastic for making connections between the solder-ball-grid array (e.g., grid-array  31   a ,  FIG. 3 ) on a converter module  30  and the conductive segments of the finished bilateral J-lead connectors  28 ,  29 . Another pattern of holes  55 , located in the rib on the bottom side of the assembly  51  (FIG.  8 D), each hole  55  being located concentric with and directly beneath one of the top side holes  54 , and each hole  55  having a smaller diameter than the holes  54 , is used to aid in the molding process, as described below. 
   It is useful to keep the surface of the conductive piece  39  within the region of each of the top-side holes  54  free of plastic molding compound. Otherwise, it may not be possible to form a proper solder joint when the connectors are soldered to the ball-grid array on the power converter. To ensure that the regions remain free of plastic material, the conductive piece  39  may be insert-molded using a mold design of the kind illustrated in FIG.  12 .  FIG. 12  shows a schematic cross sectional view of the assembly  51  of  FIG. 7 , taken at the location marked BB in  FIG. 7 , with the assembly  51  in the mold after the plastic which forms the rib  50  has been injected into the mold. A left mold half comprises left mold plate  47   a  and a plurality of round pins  49   a , each pin corresponding to one of the top side holes  54  in rib  50 . A right mold half comprises right mold plate  47   b  and a plurality of pins  49   b , each pin corresponding to one of the bottom-side holes  55  in rib  50 . When the mold is closed, pins  49   a  and  49   b  are forced to be in contact with the surfaces of conductive piece  39  at concentric locations on opposite sides of the piece. During the molding process the material that forms the rib (shown as portions of molded rib  50  in  FIG. 12 ) is injected into the mold under pressure. Without pins  49   b , this pressure (as indicated in one location in  FIG. 12  by the arrows  45 ) might cause a small gap to form at region  43  between the bottoms of pins  49   a  and the surface of the conductive piece  39 . The force exerted by the presence of the pins  49   b  directly beneath pins  49   a , however, provides support within the mold that prevents this gap from forming. By this means, the surface of the conductive piece  39  below the pins  49   a  is kept free of extraneous plastic material. 
   After the ribs have been molded onto the conductive piece  39 , portions of the conductive piece are cut away to yield two connector sections  28   a ,  29   a , as illustrated in the perspective view of FIG.  9 A and the orthographic views of  FIGS. 9B through 9E . In a later manufacturing step, the flat portions of the conductive pieces that extend from the ribs are folded to form the final configuration of the bilateral J-lead connectors  28 ,  29 , as illustrated in the perspective view of FIG.  10 A and the orthographic views of  FIGS. 10B through 10F . 
   Steps in the manufacture of bilateral J-lead connectors  28 ,  29 , in which the segments comprise independent connection contacts having opposing fingers formed from separate pieces of conductive material, are illustrated schematically in  FIGS. 13 through 15 . 
     FIG. 13  shows a piece of conductive metal  66  comprising slots and holes  40 ,  68 . The conductive piece, which may be of the same material and be of the same thickness as the piece shown in  FIG. 6 , has been pre-folded from a flat piece of material into a generally U-shaped arrangement. Slots  40  separate portions of the conductive piece  66  that comprise opposing pairs of legs (e.g., opposing pairs of legs  76   a ,  76   b ; opposing pair of legs  76   c ,  76   d ; opposing pair of legs  76   e ,  76   f ), the legs in each opposing pair being parallel to each other and connected at an essentially right angle to a spanning portion (e.g., spanning portions  104   a ,  104   b ,  104   c ,  FIG. 13 ) that connects the pair of legs. The separated portions are connected to each other by means of straps (e.g., straps  71   a ,  71   b ,  71   c ). The ends of the legs (e.g., ends  72   a ,  72   b ) may be unformed, as shown in  FIG. 13  (and be formed into J-leads in a later step) or they may be pre-formed into a J-lead arrangement (not shown). 
   As illustrated schematically in  FIG. 14 , the conductive metal piece  66  is placed in a mold and a plastic rib  74  is molded in place. A pattern of holes  54  in the rib  74  defines regions free of plastic for making connections between the solder-ball-grid array (e.g., grid-array  31   a ,  FIG. 3 ) on a converter module  30  and regions on the surface of the conductive segments of the finished connector  77   a - 77   f , analogous to the counterpart holes  54  described with respect to  FIGS. 6-10 . Another pattern of holes  55 , located in the rib on the bottom side of the assembly  51  (not shown in FIG.  14 ), perform the same support function during the molding process as the counterpart holes  55  described above with reference to FIG.  8 . The plastic material that forms the rib  74  fills anchor holes  68  ( FIG. 13 ) in the conductive piece  66 , thereby firmly affixing the rib  74  to the conductive piece  66 . 
   As illustrated in  FIG. 15 , in another manufacturing step a slot  82  is cut along the top of the rib  74 . The slot is sufficiently wide to completely cut away the straps (e.g., straps  71   a - 71   c ,  FIG. 13 ) and sever each U-shaped portion into a pair of electrically disconnected legs. Severed ends  80   a ,  80   b ,  80   c  of, respectively, legs  76   a ,  76   e ,  76   e  are illustrated in FIG.  15 . In a subsequent manufacturing step, the slot  82  may be filled with material (not shown) to, e.g., provide insulation between opposing severed ends of legs or to prevent contamination of severed ends. In a further manufacturing step, the ends of the legs (e.g., ends  72   a ,  72   b ) may be formed into J-leads. 
   Extending the length of the J-lead connectors may provide additional advantages.  FIGS. 16 and 17  show end and perspective views of an assembly having the same general features of the assembly of  FIGS. 3 and 5 , except that the bilateral J-connectors  90 ,  92  in the assembly of  FIGS. 16 and 17  are of longer length than the bilateral J-connectors  28 ,  29  in the assembly of  FIGS. 3 and 5 . The longer length of the bilateral J-connectors result in a greater distance, X ( FIG. 16 ) between the lower surface  95  of the power converter  30  and the top surface of the substrate  34 . The longer length also causes an increase in the exposed surface area of the bilateral J-connectors  90 , 92 . 
   Cooling of the power converter module  30  of  FIGS. 16 and 17  is improved over that of the power converter module of  FIGS. 3 and 5  because the increased distance, X, provides a relatively larger space through which cooling air can flow, thereby enabling the cooling air to more easily extract heat from the lower surface  95  of the power converter  30  and from the increased surface area of the inner surfaces (e.g., surfaces  97   a ,  97   b ,  FIG. 16 ) of the bilateral J-connectors. In addition, the increased surface area of the outer surfaces (e.g., surfaces  98   a ,  98   b ,  FIG. 16 ) of the bilateral J-connectors provide for more efficient transfer of heat into the surrounding air. 
   In some cases the distance X is arranged to be twice the minimum length that would otherwise be required to avoid putting an aperture in the substrate (e.g., twice the value of “H”, discussed above with reference to FIG.  5 ). 
   Another advantage of longer length is that components  94 ,  95 ,  96  may be mounted on the substrate  34  in the region underneath the power converter  30 , as illustrated in FIG.  18 . 
   Other implementations are also within the scope of the following claims. For example, the ends of the legs may be formed into a shape different from a J-lead.