Patent Publication Number: US-2005121139-A1

Title: System and method used in attaching die for ball grid arrays

Description:
TECHNICAL FIELD OF THE INVENTION  
      This invention relates generally to the field of integrated circuit packaging and, more specifically, to a system and method for attaching die for ball grid arrays (“BGAs”).  
     BACKGROUND OF THE INVENTION  
      Because of the sheer volume of integrated circuits in the marketplace, packaging of integrated circuits in a manner that is cost-effective with high yield is important for semiconductor manufacturers in order to be competitive in the marketplace. One important process in the fabrication of integrated circuits, such as ball grid arrays (“BGAs”), is the die attach process.  
      One problem during the die attach process for BGAs with large die size is insufficiency of epoxy coverage. Epoxy voids may occur once the dispense pattern is not properly optimized because there is a possibility of air entrapment. This may lead to material rejection, which hurts yield, or poor reliability. Package cratering is also a possibility due to insufficient epoxy coverage.  
     SUMMARY OF THE INVENTION  
      According to one embodiment of the invention, a method used in attaching die to a substrate includes providing a substrate having a plurality of die attach regions, positioning a dispensing tool having an aperture adjacent a respective one of the die attach regions, positioning the aperture proximate the respective die attach region, dispensing an adhesive through the aperture and onto the respective die attach region, and translating the dispensing tool in a direction perpendicular to a length of the aperture while dispensing the adhesive to form an adhesive region on the respective die attach region. A length of the aperture is greater than a width of the aperture.  
      Some embodiments of the invention provide numerous technical advantages. Other embodiments may realize some, none, or all of these advantages. For example, a modified dispense tool that includes an aperture with a length approximately equal to the length of a die desired to be attached to a substrate assures sufficient epoxy coverage when the travel of the dispense tool approximately equals the width of the die. Sufficient epoxy coverage substantially reduces or eliminates epoxy voids and package cratering, which enhances yield and quality/reliability of the completed integrated circuits.  
      Other technical advantages are readily apparent to one skilled in the art from the following figures, descriptions, and claims.  
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      For a more complete understanding of the invention, and for further features and advantages, reference is now made to the following description, taken in conjunction with the accompanying drawings, in which:  
       FIG. 1  is perspective view of a dispensing tool according to one embodiment of the invention; and  
       FIGS. 2A through 2C  are perspective views illustrating the dispensing of an adhesive on a die attach region of a substrate utilizing the dispensing tool of  FIG. 1  according to one embodiment of the invention.  
    
    
     DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS OF THE INVENTION  
      Example embodiments of the present invention and their advantages are best understood by referring now to  FIGS. 1 through 2 C of the drawings, in which like numerals refer to like parts.  
       FIG. 1  is a perspective view of a dispensing tool  100  according to one embodiment of the present invention. As described in more detail below in conjunction with  FIGS. 2A through 2C , dispensing tool  100  functions to dispense an epoxy or other suitable adhesive on a substrate to ensure sufficient epoxy coverage for integrated circuit die that are subsequently attached to the substrate. This substantially reduces or eliminates epoxy voids and/or package cratering that may develop during the fabrication of integrated circuit packages. These problems have been discovered using prior die attach techniques, such as the writing dispense method and the stamping dispense method. The writing dispense method utilizes a dispensing tool have a circular aperture that creates a pattern of adhesive on a substrate by directing the dispensing tool in a particular pattern while dispensing the epoxy. The most common configuration is an “X” shape. The stamping dispense method utilizes a plurality of circular apertures arranged in a particular pattern that create a pattern of adhesive by “stamping” the material onto the surface of the substrate in a vertical stamping motion only. This pattern is also in the general shape of an “X”. Both of these die attach techniques often lead to epoxy voids and/or package cratering, especially for the larger die sizes that have recently become more prevalent. The apertures used in these prior techniques are circular because most epoxy materials in the industry are easy to dispense (less viscous). Using non-circular apertures, such as square or rectangular, that have corners would generate residue on the corners, thus making the aperture smaller over time.  
      The present invention addresses these problems by providing, in one embodiment, dispensing tool  100  with a rectangular aperture  102  having a greater length  104  than a width  106 . This facilitates the dispensing of an amount of epoxy or other suitable adhesive to a die attach region of a substrate that matches the general shape of a die desired to be attached to the substrate when the dispensing tool is translated in a direction that is perpendicular to length  104 . This is described in more detail below in conjunction with  FIGS. 2A through 2C . Although illustrated in  FIG. 1  as being the shape of a rectangle, aperture  102  may resemble other suitable configurations having a greater length than width. For example, aperture  102  may resemble the shape of a parallelogram, a trapezoid, a triangle, an ellipse, an oval, or other suitable shapes. Dispensing tool  100  may be formed from any suitable material, such as a tool steel, and any suitable automated machinery may be utilized to translate dispensing tool  100 .  
      In one embodiment, the size and shape of aperture  102  depends on the size and shape of the integrated circuit die that is desired to be attached to a substrate. Because most integrated circuit die are generally rectangular, aperture  102  includes length  104  being approximately equal to a length of the particular die that is desired to be attached to the substrate. In one embodiment, length  104  is between approximately three millimeters and nine millimeters and width  106  is between approximately 0.09 millimeters and 0.11 millimeters. Other suitable dimensions for aperture  102  is contemplated by the present invention.  
       FIGS. 2A through 2C  are perspective views illustrating the dispensing of an adhesive  202  on a die attach region  206  of a substrate  200  utilizing dispensing tool  100  according to one embodiment of the invention. Adhesive  202  is typically an epoxy; however, adhesive  202  may be any suitable adhesive adapted to attach integrated circuit die to substrate  200 . In addition, substrate  200  may be formed from any suitable flexible or rigid material; however, in one embodiment, substrate  200  is a tape substrate formed from polyimide. In the illustrated embodiment, adhesive  202  is delivered to dispensing tool  100  by an adhesive delivery system  204  for the purpose of dispensing adhesive  202  on one of a plurality of die attach regions  206  on substrate  200 . Adhesive delivery system  204  may be any suitable delivery system operable to deliver adhesive to dispensing tool  100 .  
      Referring to  FIG. 2A , aperture  102  of dispensing tool  100  is positioned adjacent a respective die attach region  206 . In order to dispense adhesive  202  on die attach region  206 , aperture  102  is positioned with respect to die attach region  206  by an offset  208  that may be any suitable distance depending on the amount of adhesive  202  desired to be dispensed on die attach region  206 . In one embodiment, offset  208  is approximately 0.10 to 0.11 millimeters from surface of die attach region  206 ; however, other suitable distances may also be utilized. Adhesive delivery system  204  then delivers adhesive  202  to dispensing tool  100  at a suitable rate. Once adhesive  202  starts forming on the surface of die attach region  206 , dispensing tool  100  is translated in a direction perpendicular to length  104  of aperture  102  while continuing to dispense adhesive  202 . The translation of dispensing tool  100  is illustrated in  FIG. 2A  by an arrow  210 .  
      Referring to  FIG. 2B , dispensing tool  100  has translated along a width  212  of die attach region  206  to form an adhesive region  214  thereon. The distance of width  212  is dependent upon the width of a particular die  216  ( FIG. 2C ) desired to be attached to die attach region  206 . The adhesive delivery system  204  then stops the flow of adhesive  202  to dispensing tool  100  so that dispensing tool  100  may be moved to the next die attach region  206  to repeat the process of dispensing adhesive  202  thereon.  
      Referring to  FIG. 2C , the movement of dispensing tool  100  to the next die attach region  206  is illustrated. As described above, any suitable method, such as automated machinery, may be utilized to control dispensing tool  100 . Also illustrated is adhesive region  214  completed on the first die attach region  206 . As illustrated, the configuration of adhesive region  214  resembles the configuration of die  216 . As illustrated by arrow  218 , die  216  may be attached to adhesive region  214  that now has sufficient adhesive coverage to substantially reduce or eliminate any voids or package cratering that have occurred in prior systems. This greatly enhances yield and quality/reliability of the completed integrated circuits. An advantage of utilizing dispensing tool  100  to form adhesive region  214  that resembles the configuration of die  216  is that large die sizes, such as die used for ball grid array packages, may be attached to die attach regions  206  of substrate  200  with greater assurance that no problems will occur during the die attach process.  
      Also illustrated in  FIG. 2C  is a length  220  of die  216  that, in one embodiment, approximately equals a length  104  of aperture  102 . In this manner, and with reference to  FIGS. 2A and 2B , a single sweeping motion by dispensing tool  100  may create adhesive region  214  in a cost efficient manner.  
      Although embodiments of the invention and their advantages are described in detail, a person skilled in the art could make various alterations, additions, and omissions without departing from the spirit and scope of the present invention, as defined by the appended claims.