Abstract:
Impedance control, and the uniformity of electrical and mechanical characteristics in electronic packaging are becoming more important as chip and bus speeds increase and manufacturing processes evolve. Current state of the art design and manufacture processes inherently introduce physical dielectric thickness variations into PCB cross sections. These thickness variations between the ground reference plane(s) and the signal layer(s) inject undesirable characteristic impedance variations and undesirable mechanical variations in thickness and surface topology. Therefore a process of generating equalization data and a design structure for multilayer electronic structures is presented.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present application is related to the following U.S. patent applications, which are hereby incorporated by reference herein in their entirety: 
     U.S. patent application Ser. No. 12/101,441, filed herewith titled “Controlling Impedance and Thickness Variations for Multilayer Electronic Structures”. 
     U.S. patent application Ser. No. 12/101,449, filed herewith titled “Controlling Impedance and Thickness Variations for Multilayer Electronic Structures”. 
     BACKGROUND 
       FIGS. 1A-1C  illustrate the current state of the art in developing at least one type of multilayer electronic structure. A core consists of at least one layer of copper (used as a reference ground layer), a layer of bonding film (e.g., FR4, etc.), and a second layer of copper. Selected locations of the second layer of copper are removed (e.g., etched), leaving intact copper signal traces that provide for the internal circuitry of the multilayer electronic structure. Bonding film is laminated between a first core and a second core to provide a continuous multilayer structure. When signal trace density changes (i.e., in a first location on the core there are numerous signal traces, and in a second location there are very few, if any, signal traces,) the distance from the signal traces to the reference ground layer varies across the multilayer electronic structure. This variation of distance results in variations in mechanical thickness, impedance, and electrical performance. 
     For example see  FIG. 1A .  FIG. 1A  depicts a prior art multilayer electronic structure having a single isolated signal trace. For instance if the signal trace is 4 mils wide, 0.7 mils thick, and the bonding film is 4 mils thick, after lamination the distance from the top of the signal trace to the adjacent reference ground layer approaches 3.3 mils. 
     Alternatively see  FIG. 1B .  FIG. 1B  depicts a prior art multilayer electronic structure having a signal trace nestled between two wide traces (e.g., power signal trace, ground signal trace, etc.). For instance if the signal trace is 4 mils wide, 0.7 mils thick, and the bonding film is 4 mils thick, after lamination the distance from the top of the signal trace to the adjacent reference ground layer approaches 4.0 mils. 
     Alternatively see  FIG. 1C .  FIG. 1C  depicts a prior art multilayer electronic structure having a single trace nestled between two other signal traces. For instance if each signal trace is 4 mils wide, 0.7 mils thick, and the bonding film is 4 mils thick, after lamination the distance from the top of the signal traces to the adjacent reference ground layer approaches 3.65 mils. 
     In the examples depicted in  FIGS. 1A ,  1 B, and  1 C, the distance from the top of the signal traces to the adjacent reference ground layer by itself leads to impedance differences of 48-51-53 Ohms respectively. 
     In the current state of the art, impedance and mechanical (i.e., thickness) tolerance requirements are tight and may in fact become tighter. Currently impedance tolerances of +/−10% are typical (e.g., 50 Ohms +/−5 Ohms). In the future, impedance tolerances of +/−7.5% or 5.0% may become more common. In the examples depicted in  FIGS. 1A ,  1 B, and  1 C, 50% of the +/−10.0% tolerance is taken up by the effect of the distance variations from the top of the signal trace to the adjacent reference ground layer. 
     SUMMARY 
     The present invention generally relates to multilayer electronic structures (i.e., printed circuit board (PCB), microstrip, coplanar PCB, stripline, ect., or any such equivalent multilayer structures.), method(s), and design structure(s) relating to the multilayer electronic structures. 
     Herein the terms multilayer electronic structure, printed circuit board, PCB, microstrip, etc. may be used interchangeably. 
     Impedance control, and the uniformity of electrical and mechanical characteristics in electronic packaging are becoming more important as chip and bus speeds increase and manufacturing processes evolve. Current state of the art design and manufacture processes inherently introduce physical dielectric thickness variations into PCB cross sections. These thickness variations between the ground reference plane(s) and the signal layer(s) inject undesirable characteristic impedance variations and undesirable mechanical variations in thickness and surface topology. 
     In an embodiment of the present invention characteristic impedance variations due to non uniformity in both signal density and dielectric bonding film thickness are improved. In other words, the cross section thickness across the entire electronic multilayer structure is more uniform. 
     In another embodiment a method of multilayer electronic structure manufacture comprises removing material of a dielectric layer, and laminating the dielectric layer to a core, wherein the material of the dielectric layer is removed in locations such that when the dielectric layer is laminated to the core the locations having material removed correspond to the locations upon the core having signal traces. In other words the dielectric layer is removed only in locations that mirror signal trace locations. In another embodiment the amount of dielectric material removed is proportional to the density of signal traces upon the core. In another embodiment the volume of removed dielectric material is approximately equal to the volume of the signal traces. 
     In another embodiment the method of multilayer electronic structure manufacture further comprises determining an optimum impedance, and adjusting the amount of dielectric material to be removed based on the optimum impedance. In another embodiment the method of multilayer electronic structure manufacture further comprises determining an optimum via size or via density, and adjusting the amount of dielectric material to be removed based on the via size or via density. In the present embodiment via size or via density relates to a via that is electrically contacting/formed to a signal trace. 
     In another embodiment a method of multilayer electronic structure manufacture comprises: providing a dielectric layer; selectively removing material of the dielectric layer resulting in at least a first section of the dielectric having had material removed, and a original section of the dielectric not having had material removed; positioning the dielectric layer versus a core such that the first section corresponds to a location of the core having at least one signal trace thereupon. In another embodiment the volume of characterized fill is approximately equal to the volume of signal trace material that is removed in the signal trace creation process. 
     In another embodiment the method of multilayer electronic structure manufacture further comprises: determining an optimum impedance and adjusting the amount of characterized fill to be add based on the optimum impedance. In another embodiment the optimum impedance at least in part relates to via size and/or via density. 
     In another embodiment a multilayer electronic structure comprises a dielectric layer having at least a displaced section of the dielectric layer having had material removed and a original section of the dielectric layer not having had material removed, and; a core layer having at least one signal trace thereupon; wherein when the dielectric is positioned versus the core layer the displaced section corresponds to a location of the core having at least one signal trace thereupon. 
     In another embodiment the removed location corresponds to the location of the at least one signal trace after the dielectric layer is laminated to the core layer. In another embodiment the amount of dielectric material removed is proportional to the volume of the at least one signal trace. In another embodiment the amount of dielectric material removed is approximately equal to the volume of the at least one signal trace. In another embodiment the volume of the at least one signal trace at least in part relates to an optimum impedance. In another embodiment the optimum impedance at least in part relates to signal trace geometry. 
     In another embodiment a multilayer electronic structure comprises a dielectric layer, a core layer having at least a first location with at least one signal trace thereupon, and a second location with no signal traces thereupon, and a characterized fill layer applied upon the second location. In another embodiment the amount of characterized fill applied is inversely proportional to the volume of the at least one signal trace. In another embodiment the amount of characterized fill applied is approximately equal to a volume equal to the area of the second group multiplied by the height of the at least one signal trace. In another embodiment the amount of characterized fill applied is based on an optimum impedance. In another embodiment the optimum impedance at least in part relates to via geometry. 
     In a particular embodiment a process of generating equalization data used to equalize thickness and/or impedance variations in multilayer electronic structure is described. The process comprises providing for the design of a multilayer electronic structure on a computer aided design package, generating finite element cells upon at least one layer of the multilayer electronic structure, calculating the signal trace density of each finite element cell, and generating equalization data. In another embodiment the equalization data is provided, for example, to a PCB card or other multilayer electronic structure manufacturer. 
     In another embodiment equalization data is generated/determined by identifying a baseline finite element cell having a baseline signal trace density, comparing the baseline signal trace density against an another signal trace density of an another cell, generating equalization data if the difference in the baseline signal trace density and the another signal trace density exceeds a maximum signal trace density value. 
     In another embodiment the equalization data provides the location and the amount of bonding film material to be removed. In another embodiment the equalization data provides the location and the amount of characterized fill to be added upon a layer of the multilayer electronic structure having signal traces thereupon. In another embodiment the equalization data is arranged into an equalization data matrix, thereby providing equalization data for the entire printed circuit card, and provided to, for example a PCB card or other multilayer electronic structure manufacturer. 
     In another embodiment the equalization data is generated/determined by identifying a baseline finite element cell having a baseline impedance, comparing the baseline impedance against another impedance of another cell, and generating equalization data if the difference in the baseline impedance and the another impedance exceeds a maximum impedance. In another embodiment the equalization data provides the location and the amount of dielectric material to be removed. In another embodiment the equalization data provides the location and the amount of characterized fill to be added upon a layer of the multilayer electronic structure having signal traces thereupon. 
     In another embodiment the equalization data is generated/determined by identifying a baseline finite element cell having a baseline thickness, comparing the baseline thickness against another thickness of another cell, and generating equalization data if the difference in the baseline thickness and the another thickness exceeds a maximum thickness tolerance. 
     In another embodiment, a computer program product for enabling a computer to generate equalization data is described. In particular embodiments the computer program product enables a computer to perform the processes described above. 
     In yet another embodiment a design structure is provided for a multilayer electronic structure that comprises a dielectric layer having at least a displaced section of the dielectric layer having had material removed and a original section of the dielectric layer not having had material removed, and; a core layer having at least one signal trace thereupon; wherein when the dielectric is positioned versus the core layer the displaced section corresponds to a location of the core having at least one signal trace thereupon. 
     In yet another embodiment a design structure is provided for a multilayer electronic structure wherein the removed location corresponds to the location of the at least one signal trace after the dielectric layer is laminated to the core layer. In yet another embodiment a design structure is provided for a multilayer electronic structure wherein the amount of dielectric material removed is proportional to the volume of the at least one signal trace. In yet another embodiment a design structure is provided for a multilayer electronic structure wherein the amount of dielectric material removed is approximately equal to the volume of the at least one signal trace. In yet another embodiment a design structure is provided for a multilayer electronic structure wherein volume of the at least one signal trace at least in part relates to an optimum impedance. In yet another embodiment a design structure is provided for a multilayer electronic structure wherein the optimum impedance at least in part relates to signal trace geometry. 
     In yet another embodiment a design structure is provided for a multilayer electronic structure comprising a dielectric layer, a core layer having at least a first location with at least one signal trace thereupon, and a second location with no signal traces thereupon, and a characterized fill layer applied upon the second location. In yet another embodiment a design structure is provided for a multilayer electronic structure wherein the amount of characterized fill applied is inversely proportional to the volume of the at least one signal trace. In yet another embodiment a design structure is provided for a multilayer electronic structure wherein the amount of characterized fill applied is approximately equal to a volume equal to the area of the second group multiplied by the height of the at least one signal trace. In yet another embodiment a design structure is provided for a multilayer electronic structure wherein the amount of characterized fill applied is based on an optimum impedance. In yet another embodiment a design structure is provided for a multilayer electronic structure wherein the optimum impedance at least in part relates to via geometry. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       So that the manner in which the above recited features of the present invention are attained and can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to the embodiments thereof which are illustrated in the appended drawings. 
       It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments. 
         FIG. 1A  depicts a prior art multilayer electronic structure section having a single isolated signal trace. 
         FIG. 1B  depicts a prior art multilayer electronic structure section having a signal trace nestled between two wide signal traces. 
         FIG. 1C  depicts a prior art multilayer electronic structure section having a single trace nestled between two other signal traces. 
         FIG. 2A  depicts an exploded view of the components of a multilayer electronic structure, utilizing characterized boding film, according to an embodiment of the present invention. 
         FIG. 2B  depicts the multilayer electronic structure of  FIG. 2A , after lamination, according to an embodiment of the present invention. 
         FIG. 2C  depicts an isometric exploded view of a particular multilayer electronic structure utilizing characterized bonding film, according to an embodiment of the present invention. 
         FIG. 2D  depicts an isometric view of an alternative example of the displaced sections of characterized bonding film. 
         FIG. 3A  depicts an exploded view of the components of a multilayer electronic structure, utilizing characterized boding film, according to an embodiment of the present invention. 
         FIG. 3B  depicts the multilayer electronic structure of  FIG. 3A  according to an embodiment of the present invention. 
         FIG. 4A  depicts an exploded view of the components of a multilayer electronic structure, utilizing characterized fill, according to an embodiment of the present invention. 
         FIG. 4B  depicts the multilayer electronic structure of  FIG. 4A  according to an embodiment of the present invention. 
         FIG. 5A  depicts an exploded view of the components of a multilayer electronic structure, utilizing characterized fill, according to an embodiment of the present invention. 
         FIG. 5B  depicts the multilayer electronic structure of  FIG. 5A  according to an embodiment of the present invention. 
         FIG. 5C  depicts an isometric exploded view of various layers of a particular multilayer electronic structure. 
         FIG. 6  depicts a process of generating equalization data used to equalize thickness and/or impedance tolerances in multilayer electronic structures, according to an embodiment of the present invention. 
         FIG. 7A  depicts a top view of a section of a multilayer electronic structure having a signal trace thereupon wherein cells are utilized to determine the signal trace density. 
         FIG. 7B  depicts a side view a section of a multilayer electronic structure having three signal traces thereupon wherein cells are utilized to determine thickness and/or impedance. 
         FIG. 8  depicts a process of generating equalization data utilizing the signal trace density of particular layers of multilayer electronic structure, according to an embodiment of the present invention. 
         FIG. 9  depicts a process of generating equalization data utilizing the thickness/impedance of a particular layer(s) of a multilayer electronic structure, according to an embodiment of the present invention. 
         FIG. 10  depicts a method of multilayer electronic structure manufacture according to an embodiment of the present invention. 
         FIG. 11  depicts an alternative method of multilayer electronic structure manufacture according to an embodiment of the present invention. 
         FIG. 12  is a flow diagram of a design process used in multilayer electronic structure design, manufacturing, and/or test according to an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to the drawings, wherein like numbers denote like parts throughout the several views, please refer to  FIG. 2A .  FIG. 2A  depicts an exploded multilayer electronic structure, according to an embodiment of the present invention. The exploded multilayer electronic structure comprises a first layer (e.g., core  20 , etc.), a second layer (e.g., copper ground  15 , etc.), and characterized bonding film  22  utilized to bond the first and second layers together. For example, characterized bonding film may bond two different core  20  layers together, or may bond a single core  20  layer with a copper ground  15  layer. Other layer types may be bonded together without deviation from the scope of the present invention. The copper ground  15  layer may itself be a layer, or may be the bottom of a second core  20 . 
     Core  20  comprises a copper ground  14  (used as a reference ground layer), a layer of bonding film  24  (e.g., FR4, etc.), and a second layer of copper. Selected locations of the second layer of copper are removed (e.g., etched), leaving intact copper signal traces that provide for the internal circuitry of the multilayer electronic structure. In the embodiment shown by  FIG. 2A , the second layer of copper is etched leaving a signal trace  18  nestled between two wide signal traces  16 . 
     Characterized bonding film  22  comprises a sheet of bonding film  21  with displaced sections  23 . Displaced sections  23  may be removed by various removal techniques or apparatus (drilling, etching, scraping, chemically, mechanically, laser, etc) without deviating from the scope of the present invention. The geometry of displaced sections  23  depend on the removal technique or apparatus utilized to remove the bonding film sections. The amount and location of the removal of sections  23  depend on the density and location of the various signal traces  18  upon core  20 . The more signal traces  18  on core  20 , the more displaced sections  23 . In certain embodiments the volume of displaced sections  23  is approximately equal to the volume of removed copper (the remaining copper being the various signal traces). In yet other embodiments the displaced sections  23  are located such that when the characterized bonding film is bonded to core  20 , the displaced sections  23  correspond the locations of the various signal traces (signal traces  16  and  18 , etc). In certain embodiments, bonding film  21  and bonding film  24  are the same type of material; however the materials need not be similar. 
       FIG. 2B  depicts the multilayer electronic structure of  FIG. 2A  after lamination, according to an embodiment of the present invention. By utilizing characterized bonding film, the effect of the distance variations from the top of signal trace  18  to the adjacent reference ground layer (i.e., copper ground  15 ) is greatly reduced, if not eliminated. Please refer back to  FIG. 1B , wherein a similar core configuration resulted in a distance (the distance from the top of the signal trace to the adjacent reference ground layer) of 4.0 mils as compared to a distance of 3.3 mils when utilizing the characterized bonding film  22 . 
     By utilizing characterized bonding film  22 , a designer may calculate a desired distance between the top of a signal trace to the adjacent reference ground layer or a desired impedance. Via size and signal trace density may be determined in order to provide the desired distance and/or impedance. The designer would then adjust the amount and location of displaced sections  23  accordingly, to achieve the desired distance/impedance. 
     The designer may also characterize the bonding film by removing a uniform thickness (or other geometry) from the bonding film in addition to the displaced sections  23  as described above. 
     Please refer to  FIG. 2C .  FIG. 2C  depicts an exploded multilayer electronic structure, according to an embodiment of the present invention. Upon core  20 , there comprises a high density signal trace area  27  at least having more signal traces  18  as compared to other locations upon core  20 . Similarly, on characterized bonding film  22  there comprises a characterized area  26  at least having an increased number of displaced sections  23  as compared to other portions of bonding film  22 . Characterized area  26  is arranged on characterized bonding film  22  such that when laminated to core  20 , the characterized area  26  corresponds to high density signal trace area  27 . In other words, there are more displaced sections  23  in higher dense signal trace areas. 
       FIG. 2D  depicts an alternative embodiment of characterized bonding film, having an alternative displaced section geometry, in accordance with the present invention.  FIG. 2D  shows characterized bonding film  22  having displaced sections  32  being rectangular; however in other embodiments displaced sections  32  are other geometries. Displaced sections  32  may be removed by various removal techniques or apparatus (drilling, etching, scraping, chemically, mechanically, laser, etc) without deviating from the scope of the present invention. The geometry of displaced sections  32  depend on the removal technique or apparatus utilized to remove bonding film mater. 
       FIG. 3A  depicts an exploded multilayer electronic structure, according to an embodiment of the present invention. The exploded multilayer electronic structure comprises a first layer (e.g., core  20 , etc.), a second layer (e.g., copper ground  15 , etc.), and characterized bonding film  22  utilized to bond the first and second layers together. For example, characterized bonding film may bond two different core  20  layers together, or may bond a single core  20  layer with a copper ground  15  layer. Other layer types may be bonded together without deviation from the scope of the present invention. The copper ground  15  layer may itself be a layer, or may be the bottom of a second core  20 . 
     Core  20  comprises a copper ground  14  (may be used as a reference ground layer), a layer of bonding film  24  (e.g., FR4, etc.), and a second layer of copper. Selected locations of the second layer of copper are removed (e.g., etched), leaving intact copper signal traces that provide for the internal circuitry of the electronic structure. In the embodiment shown by  FIG. 3A , the second layer of copper is etched leaving signal traces  18 . 
       FIG. 3B  depicts the multilayer electronic structure of  FIG. 3A  after lamination, according to an embodiment of the present invention. By utilizing characterized bonding film, the effect of the distance variations from the top of signal trace  18  to the adjacent reference ground layer (i.e., copper ground  15 ) is greatly reduced, if not eliminated. Please refer back to  FIG. 1C , wherein a similar core configuration resulted in a distance (the distance from the top of the signal trace to the adjacent reference ground layer) of 3.65 mils as compared to a distance of 3.3 mils when utilizing the characterized bonding film  22 . 
     By utilizing characterized bonding film  22  a constant distance from the top of the signal trace to the adjacent reference ground layer occurs in multiple signal trace configurations. This constant distance reduces the impedance tolerance across the multilayer electronic structure. 
     Please refer to  FIG. 4A .  FIG. 4A  depicts an exploded view of the components of a multilayer electronic structure, utilizing characterized fill  46 , according to an embodiment of the present invention. In an alternate embodiment to produce a uniform distance from the top of the signal trace to the adjacent reference ground layer, utilizes a dispersal apparatus (e.g., printer, sputter, spatter, etc.) to disperse upon core  20  characterized fill  46 . Characterized fill  46  is dielectric material similar to bonding film  21  and/or  24 . In certain embodiments characterized fill  46  may be partially cured epoxy. Characterized fill  46  is dispersed in a pattern that normalizes the distance variation from the top of bonding film  24  to the top of signal trace  18 . In certain embodiments additional characterized fill  46  is dispersed to effectively bond the first layer to the second layer. In other words characterized fill  46  may replace bonding film  24 . 
     In a particular embodiment, characterized fill  46  is made from the same material as bonding film  21  and/or  24 , thus minimizing variations. In certain embodiments, characterized fill may be dispersed thermally, wherein small amounts of epoxy material are dispersed upon core  20  and thereby adhere to core  20 . In this embodiment, the characterized fill may be cured/reflowed with the standard lamination process after dispersal. 
     In yet other embodiments, the dispersal pattern is ‘inverse’ of the density of the signal traces upon the core. As the density of signal traces increase, the amount of characterized fill  46  dispersed upon core  20  decreases. In certain embodiments, no characterized fill is dispersed in the highest dense signal trace location upon core  20 . In certain other embodiments, the amount of characterized film  46  dispersed is approximately equal to the amount (by volume, etc.) of copper that was etched away (thereby leaving the various signal traces). 
     In certain other embodiments, as shown in  FIG. 5C , characterized fill  46  is only dispersed in characterized fill areas  47 . Characterized fill areas  47  are locations upon core  20  that have a low density of signal traces. In another embodiment, characterized fill areas  47  are locations upon core  20  not having signal traces. 
     The amount and location of the characterized fill  46  depend on the density and location of the various signal traces  18  on core  20 . The less signal traces  18  on core  20 , the more characterized fill  46 . In certain embodiments the volume of characterized fill  46  is approximately equal to the volume of removed copper (the remaining copper being the various signal traces). 
     By utilizing characterized fill  46 , a designer may calculate a desired distance between the top of a signal trace to the adjacent reference ground layer or a desired impedance. Via size and signal trace density may be determined in order to provide the desired distance and/or impedance. The designer would then adjust the amount and location of dispersed characterized fill  46 , to achieve the desired distance/impedance. 
     Please refer to  FIG. 4B .  FIG. 4B  depicts the multilayer electronic structure of  FIG. 4A  after lamination, according to an embodiment of the present invention. By utilizing characterized film  46 , the effect of the distance variations from the top of signal trace  18  to the adjacent reference ground layer (i.e., copper ground  15 ) is greatly reduced, if not eliminated. Please refer back to  FIG. 1A , wherein a similar core configuration resulted in a distance (the distance from the top of the signal trace to the adjacent reference ground layer) of 3.3 mils as compared to a distance of 4.0 mils when utilizing the characterized bonding film  22 . 
     Please refer to  FIG. 5A .  FIG. 5A  depicts an exploded multilayer electronic structure, according to an embodiment of the present invention. The exploded multilayer electronic structure comprises a first layer, a second layer, characterized fill  46 , and bonding film utilized to bond the first and second layers together. Characterized fill  46  is dispersed, as described above, in the spaces not filled by signal traces  18 . 
       FIG. 5B  depicts the multilayer electronic structure of  FIG. 3A  after lamination, according to an embodiment of the present invention. By utilizing characterized fill  46 , the effect of the distance variations from the top of signal trace  18  to the adjacent reference ground layer (i.e., copper ground  15 ) is greatly reduced, if not eliminated. Please refer back to  FIG. 1C , wherein the similar core configuration resulted in a distance (the distance from the top of the signal trace to the adjacent reference ground layer) of 3.65 mils as compared to a distance of 4.0 mils when utilizing the characterized fill  46 . 
     By utilizing characterized fill  46  a constant distance from the top of the signal trace to the adjacent reference ground layer occurs in multiple signal trace configurations. This constant distance reduces the impedance tolerance across the multilayer electronic structure. 
     Please refer to  FIG. 6 .  FIG. 6  depicts a process  60  of generating equalization data utilized to equalize thickness and/or impedance variations across a multilayer electronic structure, according to an embodiment of the present invention. Process  60  begins at block  61 . In order to determine the geometrical and manufacturing properties (quantity, location, etc.) of characterized fill  46 , and/or alternatively characterized bonding film  22 , equalization data is created. Equalization data is utilized to equalize thickness and/or impedance variations across a multilayer electronic structure. Equalization data represents the data associated with characterized bonding film  22  (i.e., the locations of displaced sections  23 , etc.) or data associated with characterized fill  46  (i.e., the locations of where to disperse, etc). An equalization data matrix is the equalization data of at least two locations of the multilayer electronic structure. In an alternative embodiment, the equalization data matrix is the equalization data of the entire multilayer electronic structure. Creating equalization data may be dependent on determining the signal trace density of a particular area (block  64 ) of the multilayer electronic structure. In other embodiments, discussed infra, equalization data may be dependent on determining circuit board layer(s) thickness/impedance (block  64 ). The particular location of the printed circuit card considered is referred to as a cell. The cell may be a two dimensional area or a three dimensional volume. The area/volume of the cell is adjustable, however the smaller the area/volume of a cell, better equalization data may be created. When a generation of cells (block  62 ) in/from/to the computer aided design (CAD) data of the multilayer electronic structure occurs, equalization data may be created for each cell. When there is more than one cell, the equalization data matrix is created (block  66 ). Once generated, the equalization data, or equalization data matrix, may be transferred (block  68 ), for example to a card manufacturer. Process  60  ends at block  69 . 
     Please refer to  FIG. 7A  and  FIG. 8  concurrently.  FIG. 7A  depicts a top view of a multilayer electronic structure layer having a signal trace thereupon, further depicting a baseline cell  150 , and cells  151 - 153 .  FIG. 8  depicts another process  70  of determining the signal trace density of each cell and the generating equalization data, according to an embodiment of the present invention. Process  70  starts at block  72 . Upon generating of cells in/from/to the CAD data (block  62  shown in  FIG. 6 ), a baseline cell  150  is identified (block  74 ). The baseline cell  150  has a corresponding baseline signal trace density (for instance the percentage of the cell filled by the signal traces). In a particular embodiment, shown in  FIG. 7A , the baseline cell  150  is a cell having no signal trace(s) within. In another embodiment, the baseline cell is completely filled by a signal trace. In other embodiments the baseline cell may have any percentage of the cell encapsulating a signal trace, however it is preferable that the baseline entirely encapsulates a signal trace, or does not encapsulate any signal trace. The base line cell  150  (and/or baseline cell signal trace density) is compared to another cell (and/or another cell signal trace density) (block  76 ). If the delta exceeds a maximum signal trace comparison value (block  78 ), equalization data is generated for the another cell (block  82 ). Take for example,  FIG. 7A . The baseline cell  150  encapsulates no signal trace(s), cell  153  also encapsulates no signal trace(s), cell  152  is 50% filled by a signal trace and 50% not filled by a signal trace, and finally cell  151  entirely encapsulates a signal trace(s). A preset maximum comparison signal trace density value (block  78 ) is set, for example at 0.10, meaning that equalization data is generated for the another cell if the another cell has a signal trace density of greater than 10% of the baseline cell. The maximum preset comparison signal trace density value may be adjustable by a user. Cell  152  (50% filled, 50% not filled) has a signal trace density of 0.5 because it is half filled by a signal trace. Cell  153  has a signal trace density of 0.0 because it does not encapsulate a signal trace. Cell  151  has a signal trace density of 1.0 because it does entirely encapsulate a signal trace. Because 1.0 and 0.5, respectively exceeds the maximum comparison signal trace density value of 0.1, equalization data is generated for cell  152  and  151  (block  82 ). If however the actual signal trace density value does not exceed the preset maximum signal trace density value of 0.1, such as cell  153 &#39;s value of 0.0, equalization data is not generated for cell  153  (block  80 ). In another embodiment equalization data is generated for cell  153  indicating that no characterization shall occur in the location of the characterized bonding film in the corresponding location. Process  70  ends at block  84 . 
     In a particular embodiment equalization data is generated for use relating to characterized bonding film  22  utilizing the cell structure exemplified in  FIG. 7A . In this particular embodiment the equalization data indicates the locations and quantity of material to be removed from bonding film  21 . Please continue the example from above (i.e., baseline cell  150  encapsulates no signal trace(s), cell  153  also encapsulates no signal trace(s), cell  152  is 50% filled by a signal trace and 50% not filled by a signal trace, and finally cell  151  entirely encapsulates a signal trace(s)). Signal trace properties are determined or are known (i.e., height and width, etc.). The area of each cell is known or is determined. Each cell is analyzed whereby it is determined that 50% of the cell  152  is filled by a signal trace(s). Assume each cell&#39;s area is 0.5 mil square, and the thickness of the signal trace  18  is 1.4 mils. Therefore, 0.25 mil square of cell  152  is filled by the signal trace  18 , (50% of the cell area). Thus, 0.25 mil square×the signal trace  18  height (1.4 mils)=0.35 cubic mils. This volume therefore is the approximate volume that needs to be removed from bonding film  21  in the particular location that corresponds with cell  152 . Again the location corresponds if after lamination the particular location of the printed circuit card layer (where the particular cell was located) is laminated with the bonding film that has the particular displaced section. Any such volume approximately being 0.35 cubic mils may be removed from the bonding film in the corresponding location (i.e., the geometry of the displaced section may be any such geometry without departing from the scope of the present invention). 
     In another embodiment equalization data is generated for use relating to characterized fill  46  utilizing the cell structure exemplified in  FIG. 7A . In this particular embodiment the equalization data indicates the locations and quantity of characterized fill to be added upon core  20 . Please continue the example from above (i.e., baseline cell  150  encapsulates no signal trace(s), cell  153  also encapsulates no signal trace(s), cell  152  is 50% filled by a signal trace and 50% not filled by a signal trace, and finally cell  152  entirely encapsulates a signal trace(s)). Signal trace properties are determined or are known (i.e., height and width, etc.). The area of each cell is known or is determined. Each cell is analyzed whereby it is determined that 50% of the cell  152  is filled by a signal trace(s). Assume each cell&#39;s area is 0.5 mil square, and the thickness of the signal trace  18  is 1.4 mils. Therefore, 0.25 mil square of cell  152  is filled by the signal trace  18 , (50% of the cell area). Thus, 0.25 mil square×the signal trace  18  height (1.4 mils)=0.35 cubic mils. This volume therefore is the approximate volume of characterized fill  46  that is added upon core  20  in the particular location that corresponds with cell  152 . No characterized fill  46  would be added upon core  20  in the location corresponding to cell  151 . 0.7 cubic mills (0.5 square mills*1.4 mills) is the approximate volume of characterized fill  46  that would be added upon core  20  in the location corresponding cell  153 . Again the location “corresponds” if after lamination the particular location of the printed circuit card layer (where the particular cell was located) is laminated with the bonding film that has the particular displaced section. The geometry of the characterized fill  46  may be any such geometry without departing from the scope of the present invention. 
     Please refer to  FIG. 7B  and  FIG. 9  concurrently.  FIG. 7B  depicts a side view of a multilayer electronic structure core  20  having signal traces  18  thereupon, further depicting baseline cell  160 , and cells  161 - 163 .  FIG. 9  depicts yet another alternative process of determining the signal trace impedance/width of each cell and generating equalization data, according to an embodiment of the present invention. Process  90  starts at block  92 . Upon generating cells in/from/to the CAD data (block  62 , shown in  FIG. 6 ), a baseline cell  160  is identified (block  94 ). The cells (baseline and others), as contemplated in utilizing process  90 , are three dimensional volumes. The baseline cell  160  encapsulates a section of the at least one CAD circuit card layer. Therefore the baseline cell  160  has a particular first dimension, second dimension, and a third dimension that corresponds to the thickness of the at least one CAD circuit card layer. In a particular embodiment, the baseline cell is a cell encapsulating a section of core  20  and no signal trace(s) (not shown). In another embodiment the base line cell  160  encapsulates a section of core  20  and a signal trace (as shown in  FIG. 7B ). It may be preferred to create the baseline cell  160  such that the cell has the largest volume possible without empty space above and below the particular circuit board layer(s). In another embodiment the other cell (i.e., cells  161 - 163 ) volume equals the volume of baseline cell  160 . In other embodiments the volumes of the other cells do not equal the volume of the baseline cell. Further, the volume of cell  161  for instance, may not equal the volume of cell  162 . For example because there is empty space in cell  161 , cell  161  may be shortened such that the height would be similar to the height of the copper ground  14  and bonding film  24  stack. In another embodiment in an instance where there is empty space in a cell (i.e., cell  161  and  162 ) the height of those cells are shortened by a distance similar to the distance of the signal trace  18  height. 
     Baseline cell  160  has a baseline thickness/impedance. The baseline cell  160  thickness/impedance is compared to another cell&#39;s (cell  161 - 163 ) thickness/impedance (block  96 ). If the delta exceeds a maximum signal trace comparison value (block  98 ), equalization data is generated for the another cell (block  102 ). In a new example, the baseline cell  160  encapsulates the at least one layer of a printed circuit card (e.g., copper ground  14  and bonding film  24 ) and at least part of a signal trace  18 . In the present embodiment, as shown in  FIG. 7B , the dimension of cells  161 - 163  are set similarly to the dimensions of the baseline cell  160 , however as indicated above the volumes of each cell need not be similar. Cell  163  similarly encapsulates the at least one layer of a printed circuit card and at least part of a signal trace  18 . Cell  162  encapsulates the at least one layer of a printed circuit card and at least part of a signal trace  18 , but also encapsulates empty space (i.e., space without a section of signal trace  18 ). Cell  161  encapsulates the at least one layer of a printed circuit card and does not encapsulate at least part of a signal trace  18  (i.e., cell  161  has more empty space than  162 ). Thus cells  161 - 163  demonstrate the transition from a location of a multilayer electronic structure layer going from at least one layer without a signal trace there upon (cell  161 ), to a location where part of the cell encapsulates a signal trace and part of the cell does not (cell  162 ), to a location of a layer with a signal trace there upon (cell  163 ). 
     A preset maximum comparison impedance/thickness value (block  98 ) is generated, meaning that equalization data is generated (block  102 ) for the another cell if the another cell has thickness/impedance greater than the baseline cell. The maximum preset comparison value may be adjustable. If however the actual impedance/thickness value does not exceed the preset maximum comparison value, equalization data is not generated for the another cell (block  100 ). Process  90  ends at block  104 . 
     In a particular embodiment equalization data is generated for use relating to characterized bonding film  22 , utilizing the cell structure exemplified in  FIG. 7B . In this particular embodiment the equalization data indicates the locations and quantity of material to be removed from bonding film  21  (thereby creating characterized bonding film). Please consider the example depicted in  FIG. 7B . Cells may be generated in multiple configurations, two such configurations are depicted in  FIG. 7B . Cells  161 - 163  depict cells of similar geometries, and cells  164 - 166  depict cells of varying geometries. The volume of each cell is known or is determined. Equalization data is created for each cell. 
     For example cell  164  is compared with cell  166 . The volume differential of cell  166  and  164  would represent the equalization data for cell  166 . The impedance/height of the cells may also be translated into a volume. This volume differential would be the volume of material that is to be removed from characterized bonding film  22  in the location that corresponds to cell  166 . 
     In another embodiment equalization data is generated for use relating to characterized fill  46 , utilizing the cell structure exemplified in  FIG. 7B . In this particular embodiment the equalization data indicates the locations and quantity of characterized fill to be added upon core  20 . For example cell  164  is compared with cell  166 . The volume differential of cell  166  and  164  would represent the equalization data for cell  164 . The impedance/height of the cells may also be translated into a volume. This volume differential would be the volume of material that is to be added upon core  20  in the location that corresponds to cell  164 . 
       FIG. 10  depicts a method of multilayer electronic structure manufacture according to an embodiment of the present invention. Method  110  begins at block  112  and may be practiced, for example, by a card manufacturer. The equalization data matrix is read (block  114 ) to determine the particular locations to be removed from a sheet of bonding film, thus creating characterized bonding film  22 . The particular areas of the bonding film that will correspond to high signal trace density after lamination are removed (block  116 ) thereby creating characterized bonding film  22 . The characterized bonding film  22  is then laminated (block  118 ) to the core such that the characterized area  26  corresponds to the high density signal trace area  27 . Method  110  ends at block  120 . 
       FIG. 11  depicts an alternative method of multilayer electronic structure manufacture according to an embodiment of the present invention. Method  130  begins at block  132  and may also be practiced, for example, by a card manufacturer. The equalization data matrix is read (block  134 ) to determine the particular areas upon core  20  that characterized fill  46  are to be added. Characterized fill is dispersed (block  136 ) upon core  20  in characterized fill areas  47 . Bonding film is then laminated (block  138 ) to the characterized core (core  20  having characterized fill  46  thereupon). Method  130  ends at block  140 . 
       FIG. 12  shows a block diagram of an exemplary design flow  900  used for example, in multilayer electronic system design, simulation, test, layout, or manufacture. Design flow  900  includes processes and mechanisms for processing design structures to generate logically or otherwise functionally equivalent representations of the embodiments of the invention shown in  FIGS. 2A ,  2 B,  2 C,  2 D,  3 A,  3 B,  4 A,  4 B,  5 A,  5 B,  5 C,  7 A, and/or  7 B. The design structures processed and/or generated by design flow  900  may be encoded on machine-readable transmission or storage media to include data and/or instructions that when executed or otherwise processed on a data processing system generate a logically, structurally, or otherwise functionally equivalent representation of hardware components, circuits, devices, or systems. 
       FIG. 12  illustrates multiple such design structures including an input design structure  920  that is preferably processed by a design process  910 . Design structure  920  may be a logical simulation design structure generated and processed by design process  910  to produce a logically equivalent functional representation of a hardware device. Design structure  920  may also or alternatively comprise data and/or program instructions that when processed by design process  910 , generate a functional representation of the physical structure of a hardware device. Whether representing functional and/or structural design features, design structure  920  may be generated using electronic computer-aided design (ECAD) such as implemented by a developer/designer. When encoded on a machine-readable data transmission or storage medium, design structure  920  may be accessed and processed by one or more hardware and/or software modules within design process  910  to simulate or otherwise functionally represent an electronic component, mechanical component, circuit, electronic or logic module, apparatus, device, or system such as those shown in  FIGS. 2A ,  2 B,  2 C,  2 D,  3 A,  3 B,  4 A,  4 B,  5 A,  5 B,  5 C,  7 A, and/or  7 B. As such, design structure  920  may comprise files or other data structures including human and/or machine-readable source code, compiled structures, and computer-executable code structures that when processed by a design or simulation data processing system, functionally simulate or otherwise represent circuits or other levels of hardware logic design. Such data structures may include hardware-description language (HDL) design entities or other data structures conforming to and/or compatible with lower-level HDL design languages such as Verilog and VHDL, and/or higher level design languages such as C or C++. 
     Design process  910  preferably employs and incorporates hardware and/or software modules for synthesizing, translating, or otherwise processing a design/simulation functional equivalent of the components, circuits, devices, or logic structures shown in  FIGS. 2A ,  2 B,  2 C,  2 D,  3 A,  3 B,  4 A,  4 B,  5 A,  5 B,  5 C,  7 A, and/or  7 B to generate a netlist  980  which may contain design structures such as design structure  920 . Netlist  980  may comprise, for example, compiled or otherwise processed data structures representing other elements in multilayer electronic structure design. Netlist  980  may be synthesized using an iterative process in which netlist  980  is resynthesized one or more times depending on design specifications and parameters for the device. As with other design structure types described herein, netlist  980  may be recorded on a machine-readable data storage medium. The medium may be a non-volatile storage medium such as a magnetic or optical disk drive, a compact flash, or other flash memory. Additionally, or in the alternative, the medium may be a system or cache memory, buffer space, or electrically or optically conductive devices and materials on which data packets may be transmitted and intermediately stored via the Internet, or other networking suitable means. 
     Design process  910  may include hardware and software modules for processing a variety of input data structure types including netlist  980 . Such data structure types may reside, for example, within library elements  930  and include a set of commonly used elements, structures, and devices, including models, layouts, and symbolic representations, for a given manufacturing technology. The data structure types may further include design specifications  940 , characterization data  950 , verification data  960 , design rules  970 , and test data files  985  which may include input test patterns, output test results, and other testing information. Design process  910  may further include modules for performing standard circuit design processes such as timing analysis, verification, design rule checking, place and route operations, etc. 
     Design process  910  employs and incorporates well-known logic and physical design tools and simulation model build tools to process design structure  920  together with some or all of the depicted supporting data structures to generate a second design structure  990 . Similar to design structure  920 , design structure  990  preferably comprises one or more files, data structures, or other computer-encoded data or instructions that reside on transmission or data storage media and that when processed by an ECAD system generate a logically or otherwise functionally equivalent form of one or more of the embodiments of the invention shown in  FIGS. 2A ,  2 B,  2 C,  2 D,  3 A,  3 B,  4 A,  4 B,  5 A,  5 B,  5 C,  7 A, and/or  7 B. In one embodiment, design structure  990  may comprise a compiled, executable simulation model that functionally simulates the devices shown in  FIGS. 2A ,  2 B,  2 C,  2 D,  3 A,  3 B,  4 A,  4 B,  5 A,  5 B,  5 C,  7 A, and/or  7 B. 
     Design structure  990  may also employ a data format used for the exchange of layout data of multilayered electronic structure and/or symbolic data format (e.g., information stored in a Cadence, Gerber, GDSII (GDS2), GL1, OASIS, map files, or any other suitable format for storing such design data structures). Design structure  990  may comprise information such as, for example, symbolic data, map files, test data files, design content files, manufacturing data, layout parameters, wires, levels of metal, vias, shapes, data for routing through the manufacturing line, and any other data processed by semiconductor manufacturing tools to fabricate embodiments of the invention as shown in  FIGS. 2A ,  2 B,  2 C,  2 D,  3 A,  3 B,  4 A,  4 B,  5 A,  5 B,  5 C,  7 A, and/or  7 B. Design structure  990  may then proceed to a stage  995  where, for example, design structure  990 : proceeds to tape-out, is released to manufacturing, is released to a mask house, is sent to another design house, is sent back to the customer, etc. 
     The accompanying figures and this description depicted and described embodiments of the present invention, and features and components thereof. Those skilled in the art will appreciate that any particular program nomenclature used in this description was merely for convenience, and thus the invention should not be limited to use solely in any specific application identified and/or implied by such nomenclature.