Abstract:
A multi-chip package is disclosed that has a construction capable of preventing and/or reducing electrical shorts caused by shifts in bond wires. The multi-chip package includes a die attach formed between connection points of a bond wire. The die attach is made of a non-conductive material and can be constructed so as to support or encompass a portion of the bond wire. By contacting the bond wire, the die attach restricts the motion of the bond wire by acting as a physical barrier to the bond wire&#39;s movement and/or as a source of friction. In this manner, undesired position shifts of the bond wires can be prevented, reducing device failures and allowing for improved manufacturing allowances.

Description:
BACKGROUND 
     1. Field of Invention 
     The disclosure relates to chip package assembly, and specifically to a chip package assembly manufactured to maintain bond wire separation to prevent electrical shorts, and a corresponding method therefor. 
     2. Related Art 
     There has been a significant effort over the last several years to continue to reduce the size of electronics devices. As a consequence of this effort, chip packages have likewise become smaller, and the contents of those chip packages have been condensed. Therefore, bond wires that connect semiconductor dies within the chip package to the chip package fingers are manufactured to be extremely close to one another, which has increased the likelihood that electrical shorting will occur. Electrical shorts can cause substantial interference and data errors, as well as chip damage, and are therefore extremely detrimental to proper chip performance. 
       FIG. 1  shows some examples of chip package configurations having a high likelihood for electrical shorting. In  FIG. 1A , a semiconductor die  110  is connected to a plurality of substrate fingers  130  by a plurality of bond wires  120 . As the number of bond wires  120  increases, the pitch p between each of the bond wires  120  and/or fingers  130  decreases. Consequently, the bond wires  120  become arranged so close to each other that extremely small shifts from their originally-manufactured positions can cause contact with neighboring bond wires  120 . This is an example of wire-to-wire shorting. 
       FIG. 1B  illustrates a second example, in which a relatively small die  110  is positioned above a relatively large die  140 . In order to make contact with the substrate fingers  130 , the bond wires  120  that connect contacts  115  of the die  110  to the fingers  130  must travel a significant distance. Consequently, the bond wires  120  are prone to sagging, in which the weight of the bond wire pulls the bond wire down. Depending on the orientation of the package when sagging occurs, the bond wires  120  may short to each other (wire-to-wire shorting) or to the die  110  or  140  (wire-to-die shorting). 
       FIG. 1C  illustrates a third example, in which the die  110  is positioned over the die  140 . Bond wires  160  connect the contacts  145  of the die  140  to the contacts  130  of the substrate  150 . Similarly, bond wires  120  connect the contacts  115  of the die  110  to the contacts  130  of the substrate  150  (For ease of illustration, only a single bond wire  120  is shown. However, any or all of the remaining contacts  115  may be connected to the remaining contacts  130  using a similar configuration).  FIG. 1D  illustrates a side view of the configuration shown in  FIG. 1C . In this configuration, the die  110  and the die  140  may be positioned very close to each other, making the clearance between the bond wires  120  and the bond wires  160  very small. As such, sagging in the bond wires  120  may cause an electrical short with the bond wires  160 . 
       FIG. 1E  shows a modification to the configuration of  FIGS. 1C and 1D . In this example, the bond wire  120  has a reverse-loop configuration, which is designed to provide greater clearance between the wire  120  and wire  160 . However, although the clearance has been increased, the wire  120  is still prone to sagging, especially since the shape of the reverse-loop configuration leaves a long flat wire portion between contacts. 
     As these examples show, conventional chip packages suffer from the potential for electrical shorts. In addition, as device and chip package sizes continue to decrease, this problem will grow. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS/FIGURES 
       Embodiments are described with reference to the accompanying drawings. In the drawings, like reference numbers indicate identical or functionally similar elements. Additionally, the left most digit(s) of a reference number identifies the drawing in which the reference number first appears. 
         FIG. 1A  illustrates a plan view of a first example of a conventional chip package configuration; 
         FIG. 1B  illustrates a plan view of a second example of a conventional chip package configuration; 
         FIG. 1C  illustrates a three-dimensional view of a third example of a conventional chip package configuration; 
         FIG. 1D  illustrates a side view of the third example conventional chip package configuration; 
         FIG. 1E  illustrates a side of a modified third example conventional chip package configuration; 
         FIG. 2  illustrates a three-dimensional view of an exemplary chip package configuration; 
         FIGS. 3A-3D  illustrate side views of exemplary die attach configurations; 
         FIGS. 4A and 4B  illustrate plan views of exemplary die attach formations; 
         FIGS. 5A-5D  illustrate side views of exemplary die attach shapes; and 
         FIG. 6  illustrates a block diagram of an exemplary method of constructing the bond wires and die attach in a multi-chip package. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The following Detailed Description refers to accompanying drawings to illustrate exemplary embodiments consistent with the disclosure. References in the Detailed Description to “one exemplary embodiment,” “an exemplary embodiment,” “an example exemplary embodiment,” etc., indicate that the exemplary embodiment described may include a particular feature, structure, or characteristic, but every exemplary embodiment may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same exemplary embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an exemplary embodiment, it is within the knowledge of those skilled in the relevant art(s) to affect such feature, structure, or characteristic in connection with other exemplary embodiments whether or not explicitly described. 
     The exemplary embodiments described herein are provided for illustrative purposes, and are not limiting. Other exemplary embodiments are possible, and modifications may be made to the exemplary embodiments within the spirit and scope of the disclosure. Therefore, the Detailed Description is not meant to limit the invention. Rather, the scope of the invention is defined only in accordance with the following claims and their equivalents. 
     Method embodiments may be implemented in hardware (e.g., circuits), firmware, software, or any combination thereof. Method embodiments may also be implemented as instructions stored on a machine-readable medium, which may be read and executed by one or more processors. A machine-readable medium may include any mechanism for storing or transmitting information in a form readable by a machine (e.g., a computing device). For example, a machine-readable medium may include read only memory (ROM); random access memory (RAM); magnetic disk storage media; optical storage media; flash memory devices; electrical, optical, acoustical or other forms of propagated signals (e.g., carrier waves, infrared signals, digital signals, etc.), and others. Further, firmware, software, routines, instructions may be described herein as performing certain actions. However, it should be appreciated that such descriptions are merely for convenience and that such actions in fact results from computing devices, processors, controllers, or other devices executing the firmware, software, routines, instructions, etc. Further, any of the implementation variations may be carried out by a general purpose computer. 
     The following Detailed Description of the exemplary embodiments will so fully reveal the general nature of the invention that others can, by applying knowledge of those skilled in relevant art(s), readily modify and/or adapt for various applications such exemplary embodiments, without undue experimentation, without departing from the spirit and scope of the disclosure. Therefore, such adaptations and modifications are intended to be within the meaning and plurality of equivalents of the exemplary embodiments based upon the teaching and guidance presented herein. It is to be understood that the phraseology or terminology herein is for the purpose of description and not of limitation, such that the terminology or phraseology of the present specification is to be interpreted by those skilled in relevant art(s) in light of the teachings herein. 
     Those skilled in the relevant art(s) will recognize that this description may be applicable to many various apparatuses in which connections between electrical contacts have a likelihood of shorting due to wire shifting. 
     An Exemplary Multi-Chip Package 
       FIG. 2  illustrates an exemplary chip package  200 . The chip package includes a substrate  250  having a plurality of lead fingers  230 . Stacked on the substrate is a first semiconductor die  240 . The first semiconductor die  240  includes a fabricated integrated circuit, such as a microprocessor, microcontroller, or other integrated circuit. The first semiconductor die  240  may include a plurality of metal contacts  245 , which are connected to corresponding lead fingers  230  of the substrate  250  via bond wires  260 . The metal contacts are connected to various portions of the integrated circuit of the first semiconductor die  240 , and facilitate communication with the integrated circuit using the bond wires  260  and lead fingers  230 . 
     In an embodiment, a second semiconductor die  210  may be stacked above the first semiconductor die  240 . Similar to the first semiconductor die  240 , the second semiconductor die  210  may include an integrated circuit that may be the same as or different from the integrated circuit of the first semiconductor die  240 . The second semiconductor die  210  includes a plurality of metal contacts  215 , which are connected to lead fingers  230  via bond wires  220  (For simplicity, only a single bond wire  220  is shown). Overlapping bond wires  220  and bond wires  260  may be connected to the same or different lead fingers  230 . 
     It will be understood that the chip package  200  is illustrated as including both a first semiconductor die  240  and a second semiconductor die  210  only for illustrative purposes. Embodiments may include only a single semiconductor die or multiple semiconductor dies (2 or more) within the spirit and scope of the present disclosure. 
     In order to prevent electrical shorts caused by shifting bond wires, the first semiconductor die  240  includes a first die attach  290   a . The die attach  290   a  is preferably formed at or proximate to the edge of the first semiconductor die  240  on the side of the metal contacts  245 . However, the die attach  290   a  can alternatively be positioned anywhere between the metal contacts  245  and lead fingers  230 . For example, in one embodiment, the die attach  290   a  may be formed on the substrate  250  between the edge of the first semiconductor die  240  and the first row of lead fingers  230 . For purposes of discussion, the die attach  290   a  is presumed to have been formed at the edge of the first semiconductor die  240 , as shown in  FIG. 2 . 
     The die attach  290   a  is preferably made of any non-conductive material capable of being molded to a particular form before being cured into its final solidified form. Several such materials are already qualified for use in multi-chip packages, and are currently being employed in other capacities within multi-chip packages. Those skilled in the relevant art(s) will be able to readily identify these materials and understand how to apply those materials to the current disclosure. Because the material can be any qualified material already used in other multi-chip package applications, the cost of adding the die attach  290   a  is relatively small. 
     In an embodiment, the die attach  290   a  has a minimum height equal to the distance between the bond wires  260  and the surface on which die attach  290   a  sits. For example, in the embodiment of  FIG. 2 , the minimum height of the die attach  290   a  is equal to the distance between the bond wires  260  and the surface of the first semiconductor die  240 . This is to ensure that the die attach  290   a  at least contacts the bond wires  260 . Other embodiments may employ different heights for die attach  290   a . For example, and without limitation, in some embodiments, it may be useful to form the die attach  290   a  to have a height that exceeds the distance between the bond wires  260  and the corresponding surface in order to have the bond wires pass through the die attach  290   a.    
     By contacting the bond wires  260 , the die attach  290   a  places vertical pressure on the bond wires, which prevents vertical wire sagging. In addition, the contact places a friction source on the bond wires  260 , which prevents horizontal shifting. Passing the bond wires  260  through the die attach  290   a  increases their stability, because their movement is greatly restricted in both the vertical and horizontal directions by the presence of the die attach material, as will shown in further detail below. 
     In addition to the die attach  290   a  formed on the first semiconductor die  240 , additional die attaches can be formed on other components within the multi-chip package and/or on the substrate to enhance electrical short prevention. For example, as shown in  FIG. 2 , the second semiconductor die  210  includes a second die attach  290   b . Like the first die attach  290   a , the second die attach  290   b  is positioned between the metal contacts  215  of the second semiconductor die  210  and its corresponding edge. The second die attach  290   b  can have the same or different size and shape as the first die attach  290   a , depending on application and size restrictions. 
     By employing one or more die attaches  290  in the multi-chip package  200 , the shifting of bond wires can be substantially prevented, which greatly reduces the chances of both wire-to-wire and wire-to-die shorting. Consequently, the life and reliability of multi-chip packages can be greatly increased. Several additional advantages also result from the use of die attaches. For example, because the bond wires are substantially held stationary by the die attaches, bond wires and lead fingers can be manufactured even closer to each other, allowing for increased data throughput. In addition, arrangement of semiconductor dies can be diversified, allowing for improved product density. Further, process windows for manufacturing bond wires become wider because wires can be manufactured closer to each other without fear of shorting, thereby reducing manufacturing costs. 
     Those skilled in the art will recognize that the die attaches  290   a  and  290   b  depicted in  FIG. 2  are not necessarily drawn to scale/shape. For example, although the die attaches  290   a  and  290   b  are illustrated as having a rectangular cross-section, the die attaches  290   a  and  290   b  may instead have a semi-circular or semi-ovular cross-section depending on the method used to form the die attaches  290   a  and  290   b , as discussed in further detail below. 
     Exemplary Die Attach Configurations 
     Height and Support Configurations 
       FIGS. 3A-3D  illustrate side views of exemplary die attach height configurations in an exemplary multi-chip package  300 . The multi-chip package  300  includes semiconductor dies  310  and  320  stacked above a substrate  330 . The substrate includes a plurality of lead fingers  335 . At least one of the lead fingers are connected to a metal contact (not shown) of the semiconductor die  320  via a bond wire  325 . Another of the lead fingers  335  is connected to a metal contact (not shown) of the semiconductor die  310  via a bond wire  315 . 
     In the embodiment of  FIG. 3A , a die attach  350  is disposed on the edge of the semiconductor die  320 , and has a height such that it contacts the bond wire  325 . In this configuration, the die attach  350  prevents vertical sagging of the bond wire  325  by exerting an upward pressure on the bond wire  325 . In addition, the die attach  350  substantially reduces horizontal shifting of the bond wire  325  by providing a source of horizontal friction. In addition, this embodiment employs minimal die attach material, which may be beneficial in several applications. 
       FIG. 3B  illustrates another embodiment, in which the height of the die attach  350  exceeds the distance between the bond wire  325  and the surface of the semiconductor die  320 , but does not reach the bond wire  315 . In this configuration, the bond wire  325  passes through the die attach  350 . Consequently, its movement after manufacturing is greatly restricted, which significantly reduces the chances of both vertical sagging and horizontal shifting. 
     Because the die attach  350  illustrated in  FIG. 3A  does not support any pass-through bond wires, the die attach of  FIG. 3A  can easily be formed to have a rectangular cross-section or a semi-circular or semi-ovular cross-section. However, the die attach illustrated in  FIG. 3B  (as well as the die attaches illustrated in  FIGS. 3C and 3D ) includes a pass-through bond wire, and is therefore formed to have a semi-circular or semi-ovular cross-section. As discussed in detail below, a rectangular cross-section is preferably achieved using a manufacturing process that is different from the manufacturing process used to create a semi-circular or semi-ovular cross-section. It may be relatively difficult to form the die attach so as to include pass-through bond wires when using the rectangular manufacturing process, as is discussed in further detail below. 
     The embodiments of  FIGS. 3A and 3B  illustrate die attach configurations that can reduce the likelihood of electrical shorts deriving from shifts in the positions of the bond wires  325 . However, because the die attach  350  does not reach the bond wire  315 , the die attach  350  may not be able to prevent sagging and/or shifting of the bond wire  315 . Therefore, additional die attaches can be employed at other locations (such as on the substrate or the surface of the semiconductor die  310 ) to support the bond wire  315 . 
     Alternatively,  FIG. 3C  illustrates another embodiment of the die attach, in which the height of the die attach is sufficient to contact the bond wire  315 . In this configuration, the bond wire  325  passes through the die attach  350 , and is held in place by the die attach  350 . In addition, through its contact with the bond wire  315 , the die attach  350  also restricts movement of the bond wire  315 . In particular, by providing an upward pressure on the bond wire  315 , the die attach  350  prevents vertical sagging of the bond wire  315 . In addition, the contact also creates a source of horizontal friction to restrict horizontal movement of the bond wire  315 . In this manner, a single die attach  350  is capable of reducing potential shifts in both the bond wire  325  and the bond wire  315 . This helps to further prevent wire-to-wire shorting between the bond wires  315 , as well as between the bond wire  315  to the bond wire  325 . 
       FIG. 3D  illustrates another embodiment of the die attach  350  in which the die attach  350  has a height such that the die attach extends beyond the bond wire  315 . In this configuration, both the bond wire  325  and the bond wire  315  pass through the die attach  350 . Consequently, each are supported both vertically and horizontally by the die attach  350 . This substantially reduces the likelihood that either bond wire  315  or bond wire  325  will shift from its manufactured position, which greatly reduces shorting. 
     As one of ordinary skill in the relevant art(s) will readily recognize, a multi-chip package that includes multiple die attaches can include any combination of die attach configurations from among the configurations depicted in  FIGS. 3A-3D , as well as any other die attach configuration based on the teaching contained herein. 
     In addition, as one or ordinary skill in the relevant art(s) will readily recognize, the height of the die attach operates in conjunction with the position of the bond wires to create the support structure. Therefore, the height configuration of the die attach, and the desired support configuration, will depend largely on bond wire positions within the multi-chip package. Conversely, bond wires can be positioned based on the height of the die attach to achieve the desired support configuration. 
     Formation 
       FIGS. 4A and 4B  illustrate plan views of exemplary die attach formations on an exemplary semiconductor die  410 . Depending on application and arrangement within the multi-chip package, many different formation options are available for the die attach  420 . 
     In the embodiment of  FIG. 4A , the die attach  420  is formed individually on or proximate to each edge of the die  410  at which bond wires extend. For example, as shown in  FIG. 4A , a first die attach portion  420   a  is formed on one edge of the die  410  and a second die attach portion  420   b  is formed on an opposite edge of the die  410 . These edges preferably correspond to edges over which bond wires will extend, such as is shown in  FIG. 1B . By forming the die attach  420  as individual portions, the amount of die attach material used and the amount of occupied space can be minimized. 
     In the embodiment of  FIG. 4B , the die attach  420  is formed as a single continuous portion. This configuration may be particularly beneficial in instances where bond wires extend over every edge of the die  410 , such as is shown in  FIG. 1A . However, this configuration can similarly be used in other instances where fewer than all edges include overpassing bond wires. By forming the die attach  420  as a single continuous portion, manufacturing processes can be simplified the process need not be concerned with chip orientation to ensure that bond wires pass over portions of the die attach  420 . 
     In addition, a single die may include any combination of the above die attach formation configurations. For example, in an embodiment, a die may include a first die attach portion on one edge that is separate from a second die attach portion formed continuously on two or more other edges. Those skilled in the relevant art(s) will recognize that many alternative configurations may be available within the spirit and scope of the present disclosure. 
     Die Attach Shape 
       FIGS. 5A-5D  illustrate side views of exemplary die attach shapes in an exemplary multi-chip package. The multi-chip package includes a semiconductor die  510  formed on a substrate  505 . A bond wire  530  is connected to the semiconductor die  510 , and extends over a die attach  520 . 
     In the embodiment shown in  FIG. 5A , the die attach  520  is formed to have a semi-cylindrical shape with a semi-circular or semi-ovular cross-section. This configuration increases surface contact with the bond wire  530  and provides a smooth surface on which the bond wire  530  can rest. 
     In the embodiment shown in  FIG. 5B , the die attach  520  is formed to have a semi-cylindrical shape with a rectangular cross-section. This configuration allows for the possibility of having multiple contact points with the bond wire  530 . For example, as shown in  FIG. 5B , the die attach  520  contacts the bond wire  530  at both a leading and following edge. In addition, because of the sharp edge of the rectangular die attach, the bond wire  530  may embed or depress into those edges. These features further enhance motion suppression of the bond wire  530 . It should be understood that, due to the manufacturing process used to form a die attach with a rectangular cross-section (discussed below), such die attaches may be incapable of supporting pass-through bond wires. 
     In the embodiment shown in  FIG. 5C , the die attach  520  is formed of multiple portions. For example, as shown in  FIG. 5C , the die attach  520  includes a first portion  520   a  and a second portion  520   b . Each of these portions contacts the bond wire  530  at different points. This provides the advantage of having multiple points of motion suppression, while reducing die attach material. 
     As shown in the embodiment of  FIG. 5D , the multiple portions of the die attach  520  can be formed as different shapes and on different surfaces depending on application and design needs. For example, as shown in  FIG. 5D , the first die attach portion  520   a  is formed on a surface of the die  510  with a semi-ovular cross-section. A second die attach portion  520   b  is formed on a surface of the substrate  505  with a rectangular cross-section. This configuration not only provides multiple points of support and motion suppression to the bond wire  530 , but also has different motion suppression properties at each of those points. Therefore, manufacturing of the die attach can be specifically tailored to meet the needs of the multi-chip package. Although two die attach portions are illustrated, any number of die attach portions may be used. 
     Those of ordinary skill in the relevant art(s) will recognize that any combination of the embodiments depicted in  FIGS. 5A-5D  as well as other shapes and combinations thereof (including 1, 2, or more die attach portions) can be employed in a single multi-chip package and/or in relation to a single semiconductor die. In addition, each of the die attach portions in any combination can be individually configured to allow corresponding bond wires to pass therethrough, or rest thereon. 
     Exemplary Method for Forming Die Attach and Bond Wires in Multi-Chip Package 
       FIG. 6  illustrates a block diagram of an exemplary method of constructing the bond wires and die attach in a multi-chip package. Once the multi-chip package is ready to have its bond wires formed, only the “pass-through” bond wires are initially formed ( 610 ). The “pass-through” bond wires are those that will pass through the die attach in the finally-manufactured chip package. 
     Once the “pass-through” bond wires have been formed, the die attach material is dispensed ( 620 ). The die attach should be dispensed onto the desired locations and at the desired heights, and at least some of the die attach material should be formed to surround a portion of the “pass-through” bond wires previously formed. Once the die attach material has been dispensed, the die attach material is cured ( 630 ) using, for example, an oven. The curing of the die attach material should be sufficient to transition the matter state of the die attach material from liquid, gel, or other non-/semi-solid state to a solid state. 
     A first exemplary method of dispensing the die attach material includes dispensing die attach material in a substantially liquid form. The liquidity of the die attach material will allow for the material to be formed around previously-formed bond wires (pass-through bond wires), and will result in a naturally semi-circular or semi-ovular cross-sectional shape. A second exemplary method of dispensing the die attach material includes dispensing one or more die attach films along the desired location using a film cut and paste method. Because the films are pre-formed, they may be incapable of encompassing previously-formed bond wires (pass through bond wires), and will naturally result in a rectangular cross-sectional shape. 
     After the die attach has been cured, the remaining bond wires are formed ( 640 ). The bond wires that are to be supported by the previously-formed die attach are manufactured so as to contact upper surfaces of the previously-formed die attach, while the remaining wires are formed as normal. This method of forming the die attach and bond wires can be repeated as necessary for multiple layers of bond wires and/or semiconductor dies. 
     Those skilled in the relevant art(s) will recognize that the above method can additionally or alternatively include any of the functionality of the multi-chip package  200 / 300  and/or the die attach  420 / 520  discussed above, as well as any of their modifications. Further, the above description of the exemplary method should neither be construed to limit the method nor the description of the multi-chip package  200 / 300  and/or die attach  420 / 520 . 
     CONCLUSION 
     It is to be appreciated that the Detailed Description section, and not the Abstract section, is intended to be used to interpret the claims. The Abstract section may set forth one or more, but not all exemplary embodiments, and thus, is not intended to limit the disclosure and the appended claims in any way. 
     The invention has been described above with the aid of functional building blocks illustrating the implementation of specified functions and relationships thereof. The boundaries of these functional building blocks have been arbitrarily defined herein for the convenience of the description. Alternate boundaries may be defined so long as the specified functions and relationships thereof are appropriately performed. 
     It will be apparent to those skilled in the relevant art(s) that various changes in form and detail can be made therein without departing from the spirit and scope of the disclosure. Thus, the invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.