Abstract:
A method may provide thermal interface material. The method comprises providing a first coating layer on a top side of a base metal layer and a second coating layer on a bottom side of the base metal layer, wherein the coating layer has a melting point lower than a melting point of the base metal layer; attaching the base metal layer to a die and a heat spreader; and melting the first coating layer and the second coating layer to bond to the die and the heat spreader.

Description:
BACKGROUND 
       [0001]    Indium solder is typically used as thermal interface material (TIM) for central processing unit (CPU) packages or any other packages that may use heat spreader. However, using Indium may increase the cost of the packages. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0002]    The invention described herein is illustrated by way of example and not by way of limitation in the accompanying figures. For simplicity and clarity of illustration, elements illustrated in the figures are not necessarily drawn to scale. For example, the dimensions of some elements may be exaggerated relative to other elements for clarity. Further, where considered appropriate, reference labels have been repeated among the figures to indicate corresponding or analogous elements. 
           [0003]      FIGS. 1 and 2  are schematic diagrams of a method that may be used to form a semiconductor package. 
           [0004]      FIG. 3  is a schematic diagram of an embodiment of a semiconductor package that may be formed by the method of  FIGS. 1 and 2 . 
       
    
    
     DETAILED DESCRIPTION 
       [0005]    In the following detailed description, references are made to the accompanying drawings that show, by way of illustration, specific embodiments in which the invention may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention. It is to be understood that the various embodiments of the invention, although different, are not necessarily mutually exclusive. For example, a particular feature, structure, or characteristic described herein, in connection with one embodiment, may be implemented within other embodiments without departing from the spirit and scope of the invention. In addition, it is to be understood that the location or arrangement of individual elements within each disclosed embodiment may be modified without departing from the spirit and scope of the invention. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present invention is defined only by the appended claims, appropriately interpreted, along with the full range of equivalents to which the claims are entitled. In the drawings, like numbers refer to the same or similar functionality throughout the several views. 
         [0006]    References in the specification to “one embodiment”, “an embodiment”, “an example embodiment”, etc., indicate that the embodiment described may include a particular feature, structure, or characteristic, but every embodiment may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is submitted that it is within the knowledge of one skilled in the art to effect such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described. 
         [0007]    The following description may include terms, such as upper, lower, top, bottom, first, second, etc. that are used for descriptive purposes only and are not to be construed as limiting. 
         [0008]      FIGS. 1 and 2  illustrate an exemplary embodiment of a method that may be used to form, e.g., a semiconductor package  130  of  FIG. 3 . Referring to  FIG. 1 , in one embodiment, a preform  100  may be provided. The solder preform  100  may comprise a base metal layer  104 . In one embodiment, the base metal layer  104  may comprise a solder layer that may comprise Sn. For example, the base metal layer  104  may comprise SnPb, Sn and/or SnAg or the combination thereof. In another embodiment, any other metallic material that has a melting point higher than a temperature such as around 150° C. may be utilized. As shown in  FIG. 1 , one or both sides of the base metal layer  104  may be coated with a coating layer  102 . In one embodiment, the coating layer  102  may comprise Bi, such as eutectic SnBi (e.g., 42Sn58Bi), eutectic SnBiAg (e.g., 42Sn57Bi1Ag), and/or Bi. In another embodiment, any other coating material may be utilized, such as that has a melting point lower than a melting point of the base metal layer  104  and may melt to bond to the heat spreader  120  and the die  114  at around the melting point of the coating material such as 140-180° C. 
         [0009]    Referring to  FIG. 2 , an assembled package  110  may be provided. The package  110  may comprise a substrate  112 . A die  114  may be bonded to the substrate  112 , e.g., on the upper side thereof. As shown in  FIG. 2 , the die  114  may comprise a bump die that may comprise one or more bumps  116  to couple the die  114  to the substrate  112 ; however, in some embodiments, other interconnects may be utilized, including land grid arrays (LGA), ball grid arrays (BGA), etc. While  FIG. 2  illustrates one die  114 , some embodiments may comprise more dies  114  that have a different arrangement. Referring to  FIG. 2 , if the coating layer  102  comprises Bi only, no flux may be need for the coating layer  100 . If the coating layer  102  utilizes other metal than Bi, such as eutectic SnBi and/or SnBiAg, a flux may be applied to the coating layer  102 . 
         [0010]    Referring to  FIGS. 2 and 3 , the preform  100  may be placed on the die  114 , e.g., a back side (the top of  FIG. 2 ) with no interconnect. A heat spreader  120  such as integrated heat spreader (IHS) may be attached to the assembled package  110  with the preform  100  interleaved between the die  114  and the heat spreader  120 . In one embodiment, a sealant or adhesive  118 , e.g., epoxy, silicone or any other adhesives, may be provided on the substrate  112  to secure the heat spreader  120  to the substrate  112 . In one embodiment, if the coating layer  102  comprises eutectic SnBi or eutectic SnBiAg, with a temperature being ramped up to e.g., about 140-180° C., the coating layer  102  may melt to bond the heat spreader  120  and the die  114  and may form TIM bonding between the heat spreader  120  and the die  114 . For example, the Bi component in the melt coating layer  102  may diffuse into the base metal layer  104 , e.g., Sn matrix of the base metal layer  104  to form TIM  132 . The TIM  132  may bond to the heat spreader  120  and the die  114 , and may have a re-melting point higher than that of the eutectic SnBi or eutectic SnBiAg. In another embodiment, the sealant  118  may be cured around the temperature. 
         [0011]    In another embodiment, if the coating layer  102  comprises a Bi layer, the Bi component in the coating layer  102  and Sn component in the base metal layer  104  may form eutectic phase (e.g., eutectic SnBi) with the temperature being ramped up to about 140-180° C. and the euctectic SnBi may then melt around the temperature to diffuse Bi component into the Sn matrix of the base metal layer  104 , so as to form the TIM bonding. The obtained TIM  132  may have a melting point that is higher than that of the eutectic SnBi or SnBiAg. 
         [0012]    While the methods of  FIGS. 1 and 2  are illustrated to comprise a sequence of processes, the method in some embodiments may preform illustrated processes in a different order. Further, while the embodiments of  FIGS. 1 ,  2  and  3  are illustrates to comprise a certain number of dies, interconnects, substrates, interconnects, chips, some embodiments may apply to a different number. 
         [0013]    While certain features of the invention have been described with reference to embodiments, the description is not intended to be construed in a limiting sense. Various modifications of the embodiments, as well as other embodiments of the invention, which are apparent to persons skilled in the art to which the invention pertains are deemed to lie within the spirit and scope of the invention.