Abstract:
An apparatus and system, as well as fabrication methods therefor, may include a substrate coupled to a first material and a second material. The first and second materials may comprise adjacent metals, and may have different coefficients of thermal expansion sufficient to reduce the amount of substrate warp that can occur due to heating and cooling.

Description:
TECHNICAL FIELD 
     The subject matter relates generally to apparatus, systems, and methods that can be used to assist in controlling substrate warp due to environmental temperature variations. 
     BACKGROUND INFORMATION 
     Electronic components, such as integrated circuits, may be assembled into component packages by physically and electrically coupling them to a substrate. During some packaging operations, such as reflow assembly processes, heat may be applied to the substrate. Sometimes heating and cooling substrates in this manner, including substrates used in ball grid array (BGA) packages, results in warping the substrate. Heat spreaders and other heat dissipating elements may be attached to the package, reducing the amount of warp in the substrate. However, even when heat dissipating elements are attached, substrate warp may result in low solder ball attach yield, and open joints. Various types of substrates, including circuit boards, may benefit from controlling substrate warp over temperature. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a side cut-away view of apparatus and systems according to various embodiments; 
         FIG. 2  is a top cut-away view of an apparatus according to various embodiments; and 
         FIG. 3  is a flow chart illustrating several methods according to various embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     In the following detailed description of various embodiments, reference is made to the accompanying drawings that form a part hereof, and in which are shown by way of illustration, and not of limitation, specific embodiments in which the subject matter may be practiced. In the drawings, like numerals describe substantially similar components throughout the several views. The embodiments illustrated are described in sufficient detail to enable those skilled in the art to practice the teachings disclosed herein. Other embodiments may be utilized and derived therefrom, such that compositional, structural, and logical substitutions and changes may be made without departing from the scope of this disclosure. The following detailed description, therefore, is not to be taken in a limiting sense. 
       FIG. 1  is a side cut-away view of an apparatus  100  and system  110  according to various embodiments. For example, an apparatus  100  may comprise a substrate  114 , a first material  118 , and a second material  122 . The first material  118  may have a first coefficient of thermal expansion (CTE) that is different than the CTE of the second material  122 . Thus, when the first and second materials  118 ,  122  are bonded, attached, or otherwise coupled to the substrate  114 , such as by being embedded within the substrate  114 , and placed in close proximity to each other, or adjacent each other (as shown in  FIG. 1 ), environmental temperature changes may result in the first and second materials  118 ,  122  bending in a controlled direction Y, the amount of which can be selected to offset a tendency by the substrate  114  to bend or warp in the opposite direction X. 
     For example, such activity may occur during packaging reflow operations, or when the substrate  114  is heated or cooled. In some embodiments, the first material  118  may be located between the second material  122  and a die  124  coupled to the substrate  114 , wherein the first material  118  has a higher CTE than the CTE of the second material  122 . 
     In some embodiments, environmental temperature changes may result in a tendency by the substrate  114  to bend or warp in the opposite direction, that is, in direction Y. In this case, the combination of the first and second materials  118 ,  122  should be selected so as to bend in the controlled direction X, the amount of such bending selected to offset the tendency of the substrate  114  to bend in the direction Y. In this situation, it may be desirable to select the second material  122  so as to have a higher CTE than the CTE of the first material  118 . 
     Thus, for example, if the substrate  114  tends to warp in the X direction by 10 mils, violating an arbitrary coplanarity specification which limits surface warp to 8 mils or less, then the first a second materials  118 ,  122  can be embedded within the substrate  114 , and selected so that each has a CTE which differs from the other by an amount sufficient to reduce the warp in the surface  126  of the substrate to less than about 8 mils. Still further, the first and second materials  118 ,  122  can be selected so that each has a CTE which differs from the other by an amount sufficient to reduce the warp in the surface  126  of the substrate  114  to less than about 5 mils, or some other limit, such as less than about 2 mils across the surface  126  of the substrate. 
     Therefore, judicious selection of the first and second materials  118 ,  122  may operate to reduce the amount of warp across a surface  126  of the substrate  114  within a selected temperature range. For example, the selected temperature range may be between about 20° C. and about 280° C. 
     In most embodiments, the difference between the CTE of the first material  118  and the CTE of the second material  122  should not be so great that excessive stress is applied to the substrate over a selected temperature range. Thus, in some embodiments, the CTE difference ratio between the first material  118  and the second material  122  may be less than about 10:1. That is, the CTE of the first material  118  may be selected to be as high as about ten times greater than the CTE of the second material  122  (for bending in one direction), and the CTE of the first material  118  may be selected to be as low as about one-tenth the CTE of the second material  122  (for bending in the opposite direction), or any value in-between, including a ratio of about 1:1. 
     In some embodiments, the first material  118 , the second material  122 , or both may comprise a metal, including but not limited to aluminum (CTE of about 22 ppm/K), steel (CTE of about 13 ppm/K), copper (CTE of about 17 ppm/K), gold (CTE of about 15 ppm/K), nickel (CTE of about 13 ppm/K), tin (CTE of about 24 ppm/K), and alloys of these. In other embodiments, either one or both of the first and the second materials  118 ,  122  may comprise any substance that provides a CTE differential sufficient to reduce the amount of warp in a surface  126  of the substrate  114  by a desired amount over a desired temperature range. The substrate  114  may comprise any number of materials or items, including but not limited to silicon (e.g., a silicon wafer), film, tape, one or more resins, fire-retardant 4 (FR-4) material, and/or and one or more polymers. The substrate  114  may comprise a part of any number of packages, assemblies, and/or systems, including but not limited to a tape carrier package (TCP), a system on film (SOF), a chip on board (COB), a chip size package (CSP), a BGA, a fine-pitch BGA (FPBGA), and/or a printed circuit board. 
     The substrate  114  may be coupled to a dielectric  130 , and/or one or more conductors  134 , such as copper foil conductors, and/or one or more layers of solder resist  138 . The substrate  114  may also be coupled to solder bumps  142 , and include vias  146 . 
       FIG. 2  is a top cut-away view of an apparatus  200  according to various embodiments. Here it can be seen that the substrate  214  may have a surface  226 , the area  248  of which may be defined by a plurality of sides  252 . The first material  218  and the second material  222  may each have a substantially similar amount of surface area, and may be located directly on top of each other so as to be completely overlapping, and to occupy a substantially similar portion of the substrate  214 . The first material  218  and the second material  222  may also be located such that one partially overlaps the other. The area  248  may be a planar surface area. The first material  218  and the second material  222  may be coupled to the surface  226  of the substrate  214 , or embedded within the substrate  214 . In many embodiments, the first material  218  and the second material  222  may each have a surface area  258 ,  262 , respectively, which is greater than about 60% of the surface area  248  associated with the substrate  214 . 
     Still other embodiments may be realized. For example, referring now to  FIGS. 1 and 2 , a system  110  may comprise a wireless transceiver  166  coupled to the substrate  114 ,  214 . The system  110  may also comprise a first material  118 ,  218  coupled to the substrate  114 ,  214  and a second material  122 ,  222  coupled to the substrate  114 ,  214 . The first material  118 ,  218  may have a CTE different from the CTE of the second material  122 ,  222 , such that the difference between the CTE of the first and second materials  118 ,  218  and  122 ,  222  operates to reduce the amount of warp across a surface  126 ,  226  of the substrate  114 ,  214  within a selected temperature range. 
     The system  110  may also comprise a display  170  coupled to a processor  174  and the wireless transceiver  166 , which may be a radio frequency transceiver coupled to an antenna  178 . The substrate  114 ,  214  may have a surface area  248 , such as a planar surface area, wherein the first material  118 ,  218  and the second material  122 ,  222  each have a surface area  258 ,  262  which is greater than about 60% of the surface area  248  of the substrate  114 ,  214 . 
     It should be noted that the first material  118 ,  218  and the second material  122 ,  222  may each have a surface area  258 ,  262  which is coextensive with the surface area  248  of the substrate  114 ,  214  (e.g., see  FIG. 1 ). In some embodiments, the first material  118 ,  218  and the second material  122 ,  222  may each have a surface area which is greater than the surface area  248  of the substrate  114 ,  214  (not shown). The first material  118 ,  218  may be adjacent the secondary material  122 ,  222  (see  FIG. 1 ), or the first material  118 ,  218  may be located proximate to the second material  122 ,  222  (see  FIG. 2 ), wherein other materials  282  are located between the first material  118 ,  218  and the second material  122 ,  222 . 
     It should also be understood that the apparatus and systems of various embodiments can be used in applications other than for coupling and heat transfer between dice and heat dissipating elements, and thus, the embodiments shown are not to be so limited. The illustrations of an apparatus  100 ,  200  and system  110  are intended to provide a general understanding of the elements and structure of various embodiments, and they are not intended to serve as a complete description of all the features of apparatus, and systems that might make use of the elements and structures described herein. 
     Applications that may include the novel apparatus and systems of various embodiments include electronic circuitry used in high-speed computers, communication and signal processing circuitry, data transceivers, modems, processor modules, embedded processors, and application-specific modules, including multilayer, multi-chip modules. Such apparatus and systems may further be included as sub-components within a variety of electronic systems, such as televisions, cellular telephones, personal computers, workstations, radios, video players, vehicles, and others. 
     Some embodiments include a number of methods. For example,  FIG. 3  is a flow chart illustrating several methods  311  according to various embodiments. Thus, a method  311  may (optionally) begin with coupling a first material and a second material to a substrate at block  325 , wherein the first material may have a CTE different from the CTE of the second material, such that the difference between the coefficients of thermal expansion in the first and second materials operates to reduce the amount of warp across a surface of the substrate within a selected temperature range. Coupling the first material and the second material to the substrate at block  325  may also include coupling the first material to the second material. Coupling the first material and the second material to the substrate at block  325  may further comprise embedding the first material and the second material in the substrate at block  335 . 
     The method  311  may continue with determining an amount of warp across a surface of the substrate over a selected temperature range at block at block  345 . The method  311  may also include coupling a die to the substrate  355 , and coupling a wireless transceiver to a circuit (perhaps located on the die) coupled to the substrate at block  365 . 
     It should be noted that the methods described herein do not have to be executed in the order described, or in any particular order. Moreover, various activities described with respect to the methods identified herein can be executed in serial or parallel fashion. 
     Although specific embodiments have been illustrated and described herein, it should be appreciated that any arrangement calculated to achieve the same purpose may be substituted for the specific embodiments shown. This disclosure is intended to cover any and all adaptations or variations of various embodiments. It is to be understood that the above description has been made in an illustrative fashion, and not a restrictive one. Combinations of the above embodiments, and other embodiments not specifically described herein will be apparent to those of skill in the art upon reviewing the above description. Thus, the scope of various embodiments includes any other applications in which the above compositions, structures, and methods are used. 
     It is emphasized that the Abstract of the Disclosure is provided to comply with 37 C.F.R. §1.72(b), requiring an abstract that will allow the reader to quickly ascertain the nature of the technical disclosure. It is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims. In addition, in the foregoing Detailed Description, it can be seen that various features are grouped together in a single embodiment for the purpose of streamlining the disclosure. This method of disclosure is not to be interpreted as reflecting an intention that the claimed embodiments require more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive subject matter lies in less than all features of a single disclosed embodiment. Thus the following claims are hereby incorporated into the Detailed Description, with each claim standing on its own as a separate preferred embodiment.