Abstract:
Structures employed by a plurality of packages, printed circuit boards, connectors and interposers to create signal paths which reduce the deleterious signal quality issues associated with the use of through-holes. Disclosed structures can coexist with through-hole implementations.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of U.S. patent application Ser. No. 11/055,578, filed Feb. 9, 2005 and issuing as U.S. Pat. No. 7,652,381 on Jan. 26, 2010, which claims the benefit of, and incorporates by reference in its entirety, U.S. Provisional Application No. 60/543,130, filed Feb. 9, 2004. U.S. Pat. No. 7,652,381 is also a continuation-in-part of U.S. Pat. No. 7,280,372 filed on Nov. 15, 2004, which claims the benefit of U.S. Provisional Application No. 60/519,902 filed Nov. 13, 2003, all of which are incorporated by reference in their entirety. 
     
    
     TECHNICAL FIELD 
       [0002]    The present invention relates to generally to the field of printed circuit board (PCB), package, connector and interposer design, and more particularly to the methods by which these components form signal connections between each other. 
       BACKGROUND 
       [0003]    Today&#39;s technique of building electronic signal paths relies heavily upon interconnect structures invented over forty years ago.  FIG. 1 , for example, illustrates a prior art chassis system wherein through-holes are used to route signals from integrated circuits through packages, printed circuit boards (PCBs) and backplanes. Packages, PCBs and connectors can utilize these through-hole signal passage ways  7  for both signal conduction and in the case of connectors, for mechanical support. Inroads have been made towards the elimination of through-holes in certain types of component interfaces. Surface mount IC packages, for example, allow signals to connect between the bottom surface of an IC package and the top surface of a PCB without the use of through-holes by employing solder balls. However, through holes are still needed for packages and PCBs to transfer signals from their exterior surfaces to internal signal routing layers. 
         [0004]    Through-holes, for low frequency signals, may not significantly impact the quality of a signal traveling through them. As the frequency increases, signal quality does become affected and consequently designers must account for the deleterious effect of the through-hole on signal quality. In a typical chassis implementation,  FIG. 1 , a signal might have to travel through 12 through-holes 7 (inclusive of through-holes in the IC package) to reach its destination. In an optimized implementation for higher speed, the number of holes might be reduced by a factor of two. Even so, a signal path with six disruptive impedance variances (the through-holes) will impact the signal quality of a high speed signal. Manufacturers have devised ways to mitigate or reduce the effects of impedance disturbance of these through-holes. Blind vias and back drilling are among the most effective techniques in use. However, both blind vias and back drilling are time consuming and relatively expensive. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0005]    Drawings for the invention are divided into four general categories: planar printed circuit boards with apertures coupled with packages ( FIGS. 4 through 12 ); printed circuit boards coupled with planar packages ( FIGS. 13 through 16 ); planar printed circuit boards coupled with packages ( FIGS. 17 through 24 ) and printed circuit boards coupled with packages ( FIGS. 25 through 31 ). 
           [0006]      FIG. 1  illustrates prior art chassis connection system utilizing through-hole technology for the transmission of signals through multiple board connections; 
           [0007]      FIG. 2A  illustrates prior art of a stair-step IC package; 
           [0008]      FIG. 2B  illustrates prior art of a printed circuit board built with a stair-step apertures for stair-step packages and stair-step card edge for stair-step connectors; 
           [0009]      FIG. 2C  illustrates prior art of a stair-step connector; 
           [0010]      FIG. 3A and 3B  illustrates typical usage of shading and/or graphic representations used in drawings in the invention; 
           [0011]      FIG. 4  illustrates a package with multiple connection planes mounted into a printed circuit board with a cutout section; 
           [0012]      FIG. 5  illustrates an embodiment of the structure illustrated in  FIG. 4  incorporating stair-step packages with more than one stair step; 
           [0013]      FIG. 6  illustrates two packages which are mounted in opposition to each other through an opening of a printed circuit board and containing multiple signal paths between the packages and the printed circuit board; 
           [0014]      FIG. 7  illustrates an embodiment of the structures of  FIG. 6  incorporating stair-step packages with more than one stair step; 
           [0015]      FIG. 8  illustrates a single stair-step package mounted into a printed circuit board with multiple signal connection paths and a signal transmission package mounted underneath the package; 
           [0016]      FIG. 9  illustrates two stair-step packages mounted in two openings of a printed circuit board with each stair-step package mounted on opposite sides; 
           [0017]      FIG. 10  illustrates four stair-step packages mounted in a single opening of a printed circuit board wherein two of the stair-step packages are mounted in opposition to the other two stair-step packages and connected together through an intermediary package; 
           [0018]      FIG. 11  illustrates a stair-step package mounted into a connector substrate wherein the package serves as a method for connection; 
           [0019]      FIG. 12  illustrates stair-step packages mounted into connector substrates and providing for a method of connection; 
           [0020]      FIG. 13  illustrates a co-planar package connected into a stair-step printed circuit board; 
           [0021]      FIG. 14  illustrates an alternate embodiment of  FIG. 13  showing two coplanar packages mounted into a stair-step printed circuit board; 
           [0022]      FIG. 15  illustrates a co-planar package connected into a stair-step printed circuit board; 
           [0023]      FIG. 16  illustrates three co-planar packages coupled together physically and the combined coupled unit mounted into a stair-step printed circuit board; 
           [0024]      FIG. 17  illustrates a stair-step package mounted onto a planar printed circuit board wherein the step structure of the stair step package are facing away from the printed circuit board; 
           [0025]      FIG. 18  illustrates a refined embodiment of  FIG. 17  and also shows a different orientation of connections internal to the package; 
           [0026]      FIG. 19  illustrates a stair-step package mounted onto a planar printed circuit board wherein the stair-steps of the package are facing towards the surface of the printed circuit board; 
           [0027]      FIG. 20  illustrates a refined embodiment of  FIG. 19  and additionally shows two packages of varying size and connection method; 
           [0028]      FIG. 21  illustrates two stair-step packages mounted on a planar printed circuit board with their stair-steps facing away from the printed circuit board and the packages connected together through means other than the printed circuit board; 
           [0029]      FIG. 22  illustrates three stair-step packages mounted together and mounted onto a planar printed circuit board; 
           [0030]      FIG. 23  illustrates a more refined embodiment of  FIG. 22  and shows different interconnect within the package; 
           [0031]      FIG. 24  illustrates a stair-step package mounted onto a planar printed circuit board with a stair-step connector mounted onto one side of the package; 
           [0032]      FIG. 25  illustrates a stair-step package mounted onto a stair-step printed circuit board with the stair-steps of both elements facing in the same direction; 
           [0033]      FIG. 26  illustrates a stair-step package mounted onto a stair-step printed circuit board with the stair-steps of both elements facing towards each other; 
           [0034]      FIG. 27  illustrates a stair-step package mounted onto a printed circuit board wherein each element&#39;s stair-steps face each other and the stair-step package and the printed circuit board define the end or edge of the entire assembly; 
           [0035]      FIG. 28  illustrates a stair-step package mounted onto a stair-step printed circuit board wherein the stair-steps of the package on each side point in opposite directions with one side of the package mounted onto the exposed edge of the stair step printed circuit board; 
           [0036]      FIG. 29  illustrates two stair-step packages mounted next to each other with their stair-steps facing away from each other and, in combination, mounted on a printed circuit board; 
           [0037]      FIG. 30  illustrates a refined diagram of two stair-step packages mounted onto a planar printed circuit board with a planar connection made on the backside of the two packages; 
           [0038]      FIG. 31  illustrates a stair-step package mating with a stair-step printed circuit board providing for a straight signal path from the package onto the printed circuit board; 
           [0039]      FIG. 32  illustrates a refined diagram of two packages mounted onto a planar printed circuit board with a planar connection, containing a planar package, placed on the backside of the two packages; 
           [0040]      FIG. 33  illustrates two packages mounted in a mating fashion to a single printed circuit board cavity and providing for connection between the packages; 
       
    
    
     DETAILED DESCRIPTION 
       [0041]    In the following description reference is made to stair-step packages. Integrated circuit packages having stair-step structures described herein refer to, for example, any of the stair-step package structures disclosed in U.S. patent application Ser. No. 10/947,686 (“Multi-Surface IC Packaging Structures and Methods for Their Manufacture”), filed Sep. 23, 2004, which is incorporated herein by reference. An example of a stair-step package is illustrated in  FIG. 2A . 
         [0042]    In the following description reference is made to stair-step printed circuit boards. Stair-step printed circuit boards described herein refer to, for example, any of the stair step printed circuit board structures disclosed in U.S. patent application Ser. No. 10/990,280 (“Stair Step Printed Circuit Board Structures for High Speed Signal Transmissions”), filed Nov. 15, 2004, which is incorporated herein by reference. An example of a stair-step printed circuit board is illustrated in  FIG. 2B . 
         [0043]    In the following description reference is made to stair-step connectors. Connectors and interposers having stair-step structures described herein refer to, for example, any of the stair-step structures disclosed in U.S. Provisional Patent Application No. 60/543,141 (“High Speed, Direct Path, Stairstep, Electronic Connectors with Improved Signal Integrity Characteristics and Methods for Their Manufacture”), filed Feb. 9, 2004, which is incorporated herein by reference. An example of a stair-step printed circuit board is illustrated in  FIG. 2C . 
         [0044]    In the following description and in the accompanying drawings, specific terminology and drawing symbols are set forth to provide a thorough understanding of the present invention. In some instances, the terminology and symbols may imply specific details that are not required to practice the invention. For example, the interconnection between circuit elements or circuit blocks may be shown or described as multi-conductor or single conductor signal lines. Each of the multi-conductor signal lines may alternatively be single-conductor signal lines, and each of the single-conductor signal lines may alternatively be multi-conductor signal lines. Signals and signaling paths shown or described as being single-ended may also be differential, and vice-versa. 
         [0045]    In the following description and in the accompanying drawings, structures shown or described as being stair-step printed circuit boards may also be other electrical components having a stair-step electrical connection structure. Printed circuit boards may also include, without limitation, line cards, daughter boards, daughter cards, mother boards, backplanes and so forth. 
         [0046]    Typically a package refers to an embodiment of an integrated circuit contained within (or) on a substrate or encasement with multiple electrical or optical connection points. Other examples of technology which may be contained within a stair-step package include: optical processors, lasers, light emitting diodes, passive electrical devices (resistors, capacitors, inductors), electromagnetic devices (relays), energy storage technologies (batteries, fuel cells), memory storage elements of any technology, displays, transducers, mechanical actuators or simple electrical connection paths. Other technologies not mentioned specifically are allowed in other embodiments of a package. Although a single or double stair-step structure may be illustrated or presented, stair-stepping may be utilized to any number of levels as required. In addition, stair-steps, while presented as even or equally spaced may be implemented with different heights and/or widths between steps. While connection points illustrated on stair-step structures within the invention are shown in the horizontal direction, they may also be constructed in the vertical direction, or in both horizontal and vertical directions. References are made to stair-step printed circuit boards and connectors. While the invention describes methods for the use of printed circuit boards and enables the fabrication of printed circuit boards using materials not generally suitable in applications that require through-holes, it does not preclude the use of conventional printed circuit board materials and/or combinations of conventional printed circuit board materials with non-conventional materials. Furthermore, the stair-step printed circuit boards shown in the invention are not limited to the number of layers described or illustrated in the drawings in this disclosure and may be of any count. 
         [0047]    Through-hole connections may be used in any combination with the invention. Indeed, this is an important benefit of the invention. References are made to signal paths and connections. Signal paths can be made from wires, metal lead frames, flex material, fiber optics or any material suitable for achieving a desired electromagnetic transmission goal. Signal paths, although shown in the invention as a single point-to-point path in the plane of the disclosure drawing, may alternatively represent multiple signals, such as a bus or set of disparate signals (such signals would be occluded from view since the drawings are 2-dimensional). Connections can be made from solder, conductive adhesives, anisotropic films, capacitors, conductive films, springs, welding or any material or technique suitable for achieving a desired design goal. The number of connections is not limited to those illustrated in the invention. 
         [0048]    The present invention is illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings and in which like reference numerals refer to similar elements and in which: 
         [0049]      FIG. 3A and 3B  illustrate typical drawing styles for most of the illustrations used in describing the invention. In  FIG. 3A , a cross-hatched outline typically represents a printed circuit board  230 . Solid, thicker black lines typically represent conductive material  236  as part of the multiple surfaces (both internal and external) of the printed circuit board  230 . Outlined lines  237  typically represent signal paths connecting packages  231  to other packages  231  or printed circuit boards  230 , or to any other point normally reserved for connection on a device. These signal paths may be constructed from, but are not limited to wires, coaxial wires, metal lead frames, optical fibers, flexible circuits and need not be identical. Solid, thinner lines  232 ,  233 ,  234 ,  232   a,    233   b,    234   b  illustrated within the area of shading of a package  231  typically represent the signal paths between the outside of a package  231  and a device  235  within or on a package  231 . These signal paths  232 ,  233 ,  234 ,  232   a,    233   b,    234   b  may be constructed from, but are not limited to wires, coaxial wires, flexible circuits, springs, optical fibers or metal lead-frames. Signal paths  232 ,  233 ,  234 ,  232   a,    233   b,    234   b  are not required to be constructed with the same method: they may all be the same or different. For example, die bond wires and flexible circuits may be mixed in a package. The termination of signal path illustrated by  233 ,  233   a  is to be construed as terminating at the first stair-step while the termination of signal path  234 ,  234   a  is to be construed as terminating at the second stair-step and so forth. The termination of signal path  232 ,  232   a  is to be construed as terminating at the opposite surface of the stair-step surfaces. Devices  235  are typically illustrated in the invention drawings as solid rectangles. Devices may also be comprised of multi-devices  FIG. 3B  is a style of drawing referred to as refined and is used to add clarity. The style of these refined drawings dispenses with cross hatching of the PCB ( 230 ) and shows more realistic renderings of PCB construction (inclusive of through-holes and traces). Planar signal paths  239  within packages illustrated in the refined style appear white or gray. 
         [0050]    In interconnections according to embodiments of the invention, packages with at least one signal layer are connected to other packages or structures with at least one signal layer through tiered layers of exposed signal planes. By this structure, signals can enter or exit a package through the exposed layers of the package substrate and be connected to a similarly exposed set of signals on another package or structure thereby allowing a connection between two devices without the use of through-holes. 
         [0051]      FIG. 4  illustrates an embodiment of the invention: a planar printed circuit board  1  which has an opening  6  cut entirely through the substrate  1  with a stair-step package  3  mount allowing for the conveyance of signal paths  2   b,    2   c  to the opposite side  5 ,  5   a  of the planar printed circuit board  1  without the use of through-holes. The signal paths  2 ,  2   a,    2   b,    2   c  may be constructed through various means. For example, a common embodiment might be the use of flex material. Other embodiments might include single conductor wires, coaxial wires, metal lead frames or metalized plastic conductors. Electrical attachment of the package  3  to the planar printed circuit board  1  with a cutout  6  may be achieved through various means. 
         [0052]    Still referring to  FIG. 4 , the opening in the printed circuit board  1  can be of any arbitrary size or dimension. The thickness of the printed circuit board  1  can be of any depth. The material of the printed circuit board  1  can be made solidly made of a single material or a composition of layers of different materials with internal signals, power and ground layers. 
         [0053]    Still referring to  FIG. 4 , although only a single stair-step  4  in the package  3  is illustrated, multiple stair-steps in package  3  are allowed with the opening in the printed circuit board  1  to be sized to allow any level of stair-step to be mated. The depth of any particular stair-step on a package  3  may be independent or the same any other stair-step on the package  3 . 
         [0054]      FIG. 5  illustrates a different embodiment of a stair-step package coupled with a printed circuit board with an opening and shows how prior art construction utilizing through-holes  7  can coexist with the invention. The package  9  has three stair-step levels. 
         [0055]      FIG. 6  illustrates an embodiment of the invention which includes two stair-step packages  12 ,  14 , each with a single stair step, coupled together through an opening  17  in a printed circuit board  10 . Each package  12 ,  14  is oriented such that their stair-steps face each other. The packages  12 ,  14  connect through connection points  15 ,  15   a . Each package  12 ,  14  connects to the printed circuit board  10  through contact points  16 ,  16   a  of the packages and to traces on the surface  18 ,  18   b  of the printed circuit board  10 . Further connections are made from the packages  12 ,  14  to the printed circuit board  10  through signal paths  11 ,  11   b ,  13   a  and  13   b.    
         [0056]      FIG. 7  illustrates an embodiment of the invention which includes two stair-step packages  12 ,  14  coupled with a printed circuit board  10  with an opening. Both stair stepped packages have three stair steps. The embodiment also includes the addition of an interposing interconnection device  19  to effect the connection of the two stair stepped packages  12 ,  14  (instead of a direct connect between the packages) and shows how a conventional through-hole construction can be used in combination with the novel package structure. 
         [0057]      FIG. 8  illustrates an embodiment of the invention which includes a printed circuit board  20  with an opening  25  coupled with stair-step package  22 . The package has a single stair step. Additionally a connector  23  is placed opposite the opening  25  in the printed circuit board  20  which allows for signal path conduction across the opening  25  and allows for connection to the package  22 . The package  22  is connected to the printed circuit board  20  through contacts  29 ,  29   a  of the package  22 . Further connections are made from the package  22  to the printed circuit board  20  through signal paths  21  and  21   a . The package  22  is also connected to a connector  23  with signal conduction paths to the printed circuit board  24 ,  24   b.  The connector  23  also provides a signal path from one side of the printed circuit board opening  25  ( 26 ) to the other side of the opening  26   a.  The design methodology of the connector  23  may be constructed with any materials suitable to meet design goals. 
         [0058]      FIG. 9  illustrates an embodiment of the invention which includes a printed circuit board  30  with two openings  39 ,  39   a.  In one opening  39 , a stair-step package  32 , with a single stair step, is mounted on top of the printed circuit board  30  with its stair step facing towards the opening  39 . In the other opening  39   a,  a second stair-step package  33 , with a single stair step, is mounted on the bottom of the printed circuit board with its stair step facing towards the opening  39   a.  The openings  39 ,  39   a  are arranged to allow for the connection between package  32  and  33 . Each package  31 ,  33  is connected to the printed circuit board signal paths  38   a,    38   d,    38   c,    38   f.  Additionally, the packages  32 ,  33  are connected to the printed circuit board  30  through signal paths  31 ,  34 ,  35   a  and  37 . The packages  32 ,  33  are connected to each other through signal paths  35 ,  36 . Although only two packages are shown, the invention allows for unlimited cascading of packages. Furthermore, the invention allows for the packages to be of different shape, size, number and distance of stair steps. 
         [0059]      FIG. 10  illustrates an embodiment of the invention which includes four stair-step packages  47 ,  48 ,  49 ,  50 , each with a single stair step, mounted in an opening  55  within a printed circuit board  40 . Two packages  47 ,  48  are mounted over the top of the printed circuit board opening  55  with their stair-steps facing towards the opening  55 . Two packages  49 ,  50  are mounted over the bottom of the printed circuit board opening  55  with their stair-steps facing towards printed circuit board opening  55 . Sandwiched in between the four packages  47 ,  48 ,  49 ,  50  is an interposer  51  which provides for signal paths to connect the top packages  47 ,  48  to the bottom packages  49 ,  50 . Although illustrated as vertical signal paths through the interposer  56 , the interposer may be constructed in any configuration to allow horizontal and vertical connection schemes in order to achieve the desired connectivity. The interposer  51  is not limited to any particular construction technology and can be designed from the appropriate materials to achieve the desired design goals. Each package  47 ,  48 ,  49 ,  50  is connected to the printed circuit board  40  through signal paths  41 ,  44 ,  43 ,  46 . Additionally each package  47 ,  48 ,  49 ,  50  is connected to the printed circuit board  40  through connections  52   a,    52   c,    52   d ,  52   e.    
         [0060]      FIG. 11  illustrates an embodiment of the invention which includes a printed circuit board  62 , a stair-step package connector  61  and a stair-step package  60 , with a single stair step, arranged as a connector for the entire assembly ( 60 , 61 , 62 ). The package  60  may connect to a multitude of different devices such as cables, other packages, connectors or interposers. 
         [0061]      FIG. 12  illustrates an embodiment of the invention which includes two printed circuit boards  70 ,  71  each having the topology shown in  FIG. 11  but arranged such that the stair-step packages  74 ,  76  become the connecting point between each of the assemblies. 
         [0062]      FIG. 13  illustrates an embodiment of the invention which includes a planar package  84  coupled with a printed circuit board  80 , having two stair steps, wherein the body of the planar package is not touching the substrate  80 . The planar package  84  is connected to the printed circuit board through signal paths  81 ,  82 ,  83 ,  81   a,    82   a,    83   a.  The signal paths  81  and  81   a  connect the planar package  84  to the top of printed circuit board  80 . Signal paths  82 ,  82   a  connect the planar package  84  to the first exposed layer of the printed circuit board. Signal paths  83 ,  83   a  connect the planar package to the second exposed layer of the printed circuit board. The signal paths  81 ,  81   a,    82 ,  82   a,    83 ,  83   a,  in a typical embodiment common to Dual In-Line (DIP), Small or Swill Outline (SO), Quad Flat Pack (QFP) and Tape Automated Bonding (TAB) To adapt such devices, IC package leads are formed as the egress from the planar package. Other signal path conduction techniques may be used in alternative embodiments. 
         [0063]      FIG. 14  is a more refined illustration of the embodiment shown in  FIG. 13  and illustrates how the invention can coexist with prior art through-hole signal paths. It also shows how a planar package  86  can utilize varying height interconnects  87   88   89  to effect connection to the stair stepped substrate  80 . 
         [0064]      FIG. 15  illustrates an embodiment of the invention which includes a planar package  91  coupled with a printed circuit board  90  wherein the body of the planar package is mounted against the substrate  90 . 
         [0065]      FIG. 16  illustrates an embodiment of the invention which includes three planar packages  101 ,  102 ,  103  wherein each planar package has connection points integral to the package body. The packages  101 , 102 ,  103  are arranged in alternating orientation such that one side of planar package  101  rests on the first exposed layer  104  of the stair-step printed circuit board and the other end of planar package  101  rests upon planar package  102  such that connection is made between the two packages. Planar package  103 , in a similar arrangement, rests upon the opposite side of planar package  102 . Planar packages  101 ,  102  connect to the top layer of the stair-step printed circuit board through  108 ,  108   a.  Furthermore, planar packages  101 ,  102  connect to the first exposed layer of the printed circuit board through  109 ,  109   a.  Planar package  102  connects to the second exposed layer of the printed circuit board through signal paths  105 ,  105   a.  Although only three planar packages are illustrated, any arbitrary number of packages may be concatenated, placed and connected within a stair-step well. 
         [0066]      FIG. 17  illustrates an embodiment of the invention which includes a stair-step package  116 , with a single stair step, mounted onto a planar printed circuit board  110  which does not contain openings and where the stair-step in the package faces away from the printed circuit board  110 . Signal paths  111 ,  112 ,  111   a,    112   a  connect the package  116  to printed circuit board  110 . Signal paths  113 ,  113   a  connect the package  116  to traces disposed on the surface of substrate  110 . 
         [0067]      FIG. 18  illustrates an embodiment of the invention in which a stair-step package  241 , with a single stair step, similar to package  116  of  FIG. 17  is used in combination with a conventional through-hole printed circuit board. 
         [0068]      FIG. 19  illustrates an embodiment of the invention which includes a stair-step package  128 , with a single stair step, mounted onto a planar printed circuit board  120  which does not contain openings and where the stair-step in the package faces towards the printed circuit board  120 . Signal paths  121 ,  122 ,  123 ,  121   a,    122   a,    123   a  connect the package  128  to printed circuit board  120 . These connections can be wire, coax, flex circuit or any other material which provides a signal conduction path between the package  128  and the printed circuit board ( 120 ). 
         [0069]      FIG. 20  illustrates an embodiment of the invention in which two different kinds of packages  251 ,  252 , each similar to the package  128  of  FIG. 19  but having more stair steps, is coupled to a conventional planar printed circuit board  250 . 
         [0070]      FIG. 21  illustrates an embodiment of the invention which includes two stair step packages  131 ,  132 , each with a single stair step, mounted onto a planar printed circuit board  130  such that both packages are arranged with their stair-steps facing away from the surface of the planar printed circuit board  130 . Connections are made between the packages through signal paths  137 ,  138 ,  137   a,    138   a.  Between packages  131 ,  132  two signal paths exist  135 ,  136 . Signal path  135  connects the topmost surface of packaged  131  and the top most surface of package  132 . Likewise, signal path  136  connect the two packages together at their second stair-step level. Signal paths  133 ,  134  are shown to emphasize that the connection paths may continue to either side of the presented structure. Additionally, there is no requirement in this configuration for a signal path connection to start or terminate at same levels of stair steps between packages. A signal path may start at any stair-step level on one package and terminate at the same or any other stair-step level on a different package. 
         [0071]      FIG. 22  illustrates an embodiment of the invention which, while similar to the structure in  FIG. 21 , utilizes a third stair-step package  211  to bridge across two stair-step packages  213 ,  212  mounted onto a planar printed circuit board  210 . Direct signal path connections  217 ,  217   a,    218 ,  218   a  are made between the three packages  213 ,  211 ,  212  due to package  211  being “flipped” and directly resting upon the other two packages  212  and  213  and matching the stair step profiles of packages  212 ,  213 . Additional signal paths are possible as demonstrated by signal paths  215 ,  216 ,  216   a,    215   a.    
         [0072]      FIG. 23  illustrates an embodiment similar to that of  FIG. 22 , but where the packages  261 ,  263  have two levels of stair step and are used in combination with a planar printed circuit board. 
         [0073]      FIG. 24  illustrates an embodiment of the invention wherein a stair-step package  142  is attached to a planar printed circuit board  140  with its stair-steps facing away from the printed circuit boards  140 . This allows a stair-step connector  141 , or any other stair-step interposer device to attach not only to the printed circuit board  140  but also to the stair-steps on the package  142 . 
         [0074]      FIG. 25  illustrates an embodiment of the invention wherein a stair-step package  151  and interconnected stair-step printed circuit board  150  are arranged such that the stair-steps of the printed circuit board  150  and package  151  do not mate. The package  151  connects to the printed circuit board directly through signal paths  154 ,  154   a . Other signal paths  152 ,  153 ,  152   a,    153   a  connect the package  151  and printed circuit board  150 . 
         [0075]      FIG. 26  illustrates an embodiment of the invention wherein a stair-step package  161 , with a single stair step and interconnected stair-step printed circuit board  160 , with two stair steps, are arranged such that their respective stair-steps mate. Signal paths  164 ,  165 ,  164   a    165   a  are direct connections between the package  161  and the printed circuit board  160 . Other signal paths  162 ,  162   a  connect the package  161  and printed circuit board  160 . 
         [0076]      FIG. 27  illustrates an embodiment of the invention wherein a stair-step package  171  is connected to a printed circuit board  170  which has less than a full surrounding stair-structure, such as at a substrate edge. The portion of the package  171  not mated to the printed circuit board is thus usable as a launching point for signal paths  173 ,  174 . 
         [0077]      FIG. 28  illustrates an embodiment of the invention in which a stair-step package  181  has stair-stepping on both top and bottom of the structure  181   a,    181   b.  Other embodiments of stair-stepping are possible wherein any arbitrary surface (top-north, top-east, top-west, top-south, bottom-north, bottom-south, bottom-east, and/or bottom-west) may have selective stair-stepping. 
         [0078]      FIG. 29  illustrates an embodiment of the invention wherein two stair-step packages  191 ,  192  are connected together such that their stair-steps face away from one another and one of the packages  191  is mated to stair-steps within the printed circuit board. 
         [0079]      FIG. 30  illustrates an embodiment of the invention wherein two or more stair-step packages  201 ,  201  are connected to a stair-step printed circuit board  200  and in which not all sides of the packages mate with the printed circuit board. Instead, separate signal paths  203 ,  204 ,  205  are placed between the internal open space of the printed circuit board  200  opening (aperture). 
         [0080]      FIG. 33  illustrates an embodiment of the invention wherein a stair-step package  223  is mated to a printed circuit board  220  such that a direct connection path  228 ,  225  (i.e., the connection path  228 ,  225  has no turns). Often it is necessary or desirable to minimize right angles or other turns in signal paths to improve signal integrity. In this embodiment, a signal presented on a conductor  228  within the printed circuit board can travel through a small connection point  222  (which may be but is not limited to solder, conductive adhesive, gold dot, etc. . . ) to conductor  225  on a layer of the package  223  and, on conductor  225 , proceed through another connection point (which similarly may be but is not limited to solder, conductive adhesive, gold dot, etc . . . ) to device  227  which is mounted on (or) in the package  223 . In this way, the signal path remains in a single plane of travel and can provide the best opportunity for matching impedances between different signal paths. In one embodiment, as an example, device  227  could be a semiconductor device attached to the package  223  through the use of C4 pads and its associated bump  224 . 
         [0081]      FIGS. 32 and 33  illustrate embodiments of the invention in which stair-step packages are mated to a planar printed circuit board. On the planar side of the stair-step package, a substantially rigid substrate is added which allows for connection between the two packages. A variant allows the addition of smaller packages (or integrated circuits specifically) to be placed, and connected on the inflexible substrate. 
         [0082]    Although the invention has been described with reference to specific exemplary embodiments thereof, it will be evident that various modifications and changes may be made thereto without departing from the broader spirit and scope of the invention. Accordingly, the specification and drawings are, accordingly, to be regarded in an illustrative rather than a restrictive sense.