Abstract:
A method and apparatus is provided to identify defective laminate objects or package substrates having mounting sites for integrated circuit dies during the package substrate fabrication process. A hole is drilled or punched within the boundary of an individual package substrate contained within a larger laminate substrate and covered with a material layer coating composed of an opaque material such as a resist. The coating may then be selectively applied or removed at a later point during the fabrication process dependent upon whether the package substrate has been classified as defective or non-defective. After specific package substrates have been marked as defective, a light source and light collector are supplied to the fabrication process on opposite sides of the wafer. By shining the light source on the laminate substrate, defective package substrates can be identified by the passage of light through the hole which is no longer covered with resist. A package substrate may have one or many holes corresponding to one or many die mounting sites. Therefore, defective package substrates may be identified through the use of a simple light source and light collector and without the need for unnecessary expensive optical recognition or sorting machinery.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    This invention relates to the testing of laminated substrates used in packaging integrated circuit dies and, in particular, to a method and apparatus for identification of defective laminated substrates.  
           [0003]    2. Description of the Related Art  
           [0004]    Integrated circuit chips or dies are susceptible to damage and failure when exposed to environmental conditions such as heat and moisture. To protect a die and, therefore, extend its life span, it is packaged within a protective barrier of material which contains metallic pads and leads to provide electrical connection to the die itself. The fabrication of the package may involve the creation of a substrate capable of receiving an integrated circuit die and providing electrical connections to that die. Package substrates are typically laminate structures of insulating material having a die mounting site which secures the die and contains metal lines or layers which are fashioned to electrically connect the die to leads which extend outside the package. The leads may be contacted from outside the insulating material and used to connect the packaged die to another element, for example a circuit board. Advancements in processing techniques of package substrates have allowed both laminate substrates to be almost fully processed in an array and then divided from the array into numerous individual package substrates, and for one or multiple die mounting sites to be present on a single package substrate.  
           [0005]    The mounting of the dies within a package may be accomplished by placing the dies on a package substrate which is typically a ceramic or other insulating material combined with metal lines and/or layers to provide appropriate electrical connections. The package substrate is a laminate construction. In order to shield the dies, they are generally encased within the package by methods such as epoxy or resin encapsulation or by sealing in a container which is vacuum-sealed or filled with an inert gas.  
           [0006]    Several different packaging technologies are currently in use for semiconductor manufacturing, including thin quad flat packs (TQFPs), ball grid arrays (BGAs), tape automated bonding (TAB), ultra-thin packages, bare chips or chip-on-board (COB), flip-chip assemblies and multichip modules (MCMs).  
           [0007]    BGA packages, for example, are common and are generally constructed using a plastic or ceramic laminated substrate as shown in FIG. 5. The package substrate  20  is a laminate construction of a conducting (metal) patterned layer  54 , electrically insulating layers  52  and  56 , and conducting ball grid array  62 . A die mounting site  30  is formed in the layer  52  to accept an IC die. Insulating layers  52  and  56  may be, for example, a ceramic or plastic material having vias through which an electrical connection is made between the contacts  58  of the die site  30  and the ball grid array  62  through the metal pattered layer  54 . Electrical connections to the die itself are made through the contacts  58 . The die is typically wire bonded to the contacts  58  within the die mounting site  30 . The die is generally face up, with its back side bonded to the substrate package  20  through the wire bonds and, in some cases, through the use of an adhesive. The ball grid array  62  is comprised of a plurality of individual solder balls  64  which provide electrical contact to a circuit board or another package.  
           [0008]    Semiconductor packages are subject to a variety of heating and depositing processes during fabrication. Accordingly, a package substrate is susceptible to defects arising from any step in the fabrication process. A defective package substrate may render a die useless even if the die itself is flawless. Testing for defects within package substrates may occur at any point in the processing prior to introduction of the die. Commonly, it is accomplished after processing of the laminate layers is complete and prior to introduction of the die. Testing may be accomplished through a variety of methods, the most common being visual inspection by a human operator and by electronic probe testing. Visual inspection is accomplished by an operator utilizing a high resolution image of the die mounting sites on the laminate substrate to detect and analyze defects. Such a process is both expensive and time-consuming. In-line testing is also accomplished through the use of electronic probes which contact the die connection points of the individual die mounting sites within the laminated substrate and check for proper operation to determine the presence or absence of defects.  
           [0009]    Once an incapacitating defect has been found on an individual die mounting site, that die mounting site must be marked for analysis, repair, and/or destruction. Normally, this is accomplished by marking the die mounting site with a unique identification such as a print or ink media based tag. The laminated substrate may then be scored and separated into individual package substrates each having at least one die mounting site. The package substrates containing defective die mounting sites which have been marked as defective are eventually discarded or repaired. To implement this system, a code mark, such as a bar code, is applied to each individual package substrate or die mounting site prior to testing. After testing, the code mark is read and stored in a computer memory along with a designation of test results as defective or non-defective. The code mark is unique to each die mounting site and, therefore, the processing system may read the code mark at later time and redirect the defective die mounting sites to a repair station or a discard bin. However, ink-based marks or codes on the surfaces of substrates are subject to obfuscation and destruction during the laminate fabrication and/or package assembly processes.  
           [0010]    Another identification method is to retain order within the processing system by assigning each package substrate or die mounting site a unique number in that system. If a defect is found in a die mounting site that has been assigned, for example, the number  23 , the system will later skip or discard the 23 rd  die mounting site and associated substrate within the line. Such a process, however, requires complicated sorting and processing machinery to retain the order which has been assigned.  
           [0011]    Automated processes for the analysis, repair, and destruction of defective package substrates are preferred in light of the possible increases in efficiency and cost reduction it makes possible. Identifying the defective package substrates is essential within such a system. Currently no method or apparatus allows for in-line identification of defective individual package substrates without the use of complicated machinery or computing resources.  
         SUMMARY OF THE INVENTION  
         [0012]    The present invention provides a method and apparatus that is able to overcome some of the problems attendant the marking and subsequent analysis of defective laminate package substrates.  
           [0013]    The above and other features and advantages of the invention are achieved by providing an apparatus for the production of at least one hole within the boundary of an individual package substrate containing at least one die mounting site prior to the mounting of integrated circuit dies to the die mounting site(s). This hole is covered with a material layer coating composed of an opaque material such as a resist. The coating may then be selectively removed at a later point during the fabrication process dependent upon whether the individual package substrate has been classified as defective or non-defective. Later equipment can read the state of the hole as covered or not to determine the status of the individual package substrate as defective or not.  
           [0014]    After an individual substrate has been marked as defective, a light s source and light collector are used in the package fabrication process arranged on opposite sides of the package substrate to determine whether the hole is blocked or not by the resist, and thus whether the individual package substrate is defective or not. Therefore, defective individual package substrates may be identified through the use of a simple light source and light collector and without the need for a manual inspection or use of complicated optical recognition equipment.  
           [0015]    As a variant, for individual substrates employing multiple die mounting sites, it is also possible to provide a hole for each such site which is covered or not and thus be able to characterize each die mounting site on the individual package substrate as defective or not.  
           [0016]    The above and other advantages and features of the present invention will be better understood from the following detailed description of the preferred embodiment which is provided in connection with the accompanying drawings.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]    [0017]FIG. 1 a  is a perspective view of a preferred embodiment of the present invention;  
         [0018]    [0018]FIG. 1 b  is a perspective view of another preferred embodiment of the present invention;  
         [0019]    [0019]FIG. 2 is a perspective view of a package substrate prepared in accordance with a preferred embodiment of the present invention;  
         [0020]    [0020]FIG. 3 is a cross-sectional view of a package substrate production line using the invention of FIG. 1;  
         [0021]    [0021]FIG. 4 a -c are cross sectional views depicting the fabrication of a package substrate shown in FIG. 2; 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0022]    In the following detailed description, reference is made to the accompanying drawings which form a part hereof, and in which is shown 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, and it is to be understood that other embodiments may be utilized, and that structural, logical and electrical changes may be made without departing from the spirit and scope of the present invention. Wherever possible, like numerals are used to refer to like elements and functions in the various figures of the drawings and between the different embodiments of the present invention.  
         [0023]    A defective package substrate detection system  5  in accordance with the present invention is illustrated generally in FIG. 1 a . The detection system  5  is a portion of an automated package substrate fabrication line for processing a package substrate  20 . The individual package substrate  20  shown in FIG. 1 a  is of laminated construction containing the same insulating layers  52 ,  56 , conductive pattern layer  54  and die mounting site  30  as discussed previously with respect to FIG. 5. In addition, a hole  22  is formed through the laminated substrate  20 . The laminated substrate  20  further contains a coating layer strip  32  on one or both surfaces of substrate  20  which covers hole  22 . Package substrate  20  is preferably used to form a thin quad flat package (TQFP), a ball grid array (BGA) package, a tape automated bonding (TAB) package, or an ultra-thin package.  
         [0024]    The coating  32  is selectively removed from a location on the substrate covering hole  22  in order to indicate the status of substrate  20  as defective or not. For example, if after manual inspection or electrical testing substrate  20  is deemed defective, coating layer  32  is removed from covering hole  22 . Thus, light can pass through hole  22  to indicate a defective substrate. A light source  24  produces a light beam  28  which passes through hole  22  to intersect with a surface of a light detector  26  which is capable of detecting light beam  28 . The light beam  28  may have a cross-sectional area substantially equivalent to the cross-sectional area of the hole  22  or may have a cross-sectional area sufficient to intersect one entire major surface of package substrate  20 . A defective substrate detection employs the light source  24  and light detector  26 . The system can be set so that an unblocked hole  22  indicates a defective substrate  20 , as in the example just given, or it can be set so that a blocked hole  22  indicates a defective substrate in which case non-defective substrate will have the coating  32  removed from covering hole  22 . In either case, light beam  28  will be used and the signal output of light detector  26  will indicate whether the substrate  20  has been marked as defective or not. If the detector  26  provides an output signal indicating a defective substrate  20  it will either be repaired or remain unused and will be routed properly by an operator or machine to either a repair station or to a discard bin.  
         [0025]    In another embodiment of the invention shown in FIG. 1 b , package substrate  20  has a plurality of die mounting sites  12 ,  14 ,  16 ,  18  each capable of mounting a die and each having a corresponding marking hole  22  which extends through the package substrate  20 . Coating layer strips  32  are deposited on one or both sides of the package substrate  20  such that the holes  22  are covered. The coating layer strip  32  is removed from covering the holes  22 , or left intact, depending on whether the individual mounting sites are found to be defective or not. With this arrangement, even if one die mounting site is found to be defective it may be possible to still use the remaining non-defective mounting sites  30 . Accordingly, each mounting site  30  is provided with a respective marking hole  22  and associated coating layer strip  32  which can be selectively removed from carrying a hole to mark the status of the mounting site as defective or not. Although the package substrate  20  is shown in FIG. 1 b  to have a hole  22  and hole  34  for each die mounting site area  12 ,  14 ,  16 , or  18 , only one hole  22  may be formed for the package substrate  20  having a plurality of die mounting sites  30 . In such a case, if any die mounting site  30  is defective, the marking hole  22  is blocked or not by the coating layer strip  32  to expose hole  22  and indicate the status of substrate  20  as defective or not.  
         [0026]    [0026]FIG. 2 shows a laminate substrate array  10  which has two major processable surfaces and is composed of a plurality of individual substrates having respective die mounting sites  30  which will eventually be diced to form a plurality of individual package substrates  20 , each of which contains one die mounting site  30 . At least one hole  22  extends between the major surfaces of each individual package substrate  20  within the laminate substrate  10 . A coating layer strip  32  is placed over the array and on at least one major surface of each package substrate  20  such that it covers the hole  22 . To prevent the fouling of the die mounting site  30 , neither the holes  22  nor the coating layer strip  32  are located on the portions of the package substrates  20  which contain electrical connections for a die mounting site  30 .  
         [0027]    The laminate substrate  10  may be constructed of any material suitable for use as a package substrate for IC chips, preferably a rigid or flexible film laminate comprised of layers including, for example, ceramic, silicon, silicon dioxide, metal, or reinforced plastic with thermal vias e.g., glass reinforced epoxy, glass reinforced polyimide, glass reinforced polyester, glass reinforced PTFE, polyimide, polyester, and other high temperature thermoplastics, alone or in conjunction with glass or other reinforcing materials or metal cladding which may be further laminated to heat sinks, shielding materials, and a conducting sheet which provides electrical contact to an IC die. The coating layer strip  32  is preferably a resist which is capable of adhering to the surface of the laminate substrate  10  and is substantially opaque. A resist is a coating material normally used in package substrate fabrication processes to mask or to protect selected areas of a pattern from the action of an etchant, solder, or plating. The coating layer strip  32  may be, for example, a soldermask or solder resist normally used in the coating of material to protect or mask conductive traces or areas of a package substrate against solder bridging. Alternatively, the coating layer strip  32  may be a plating resist normally used to prevent the plating of the covered areas. Plating resists may be screened-on materials or may be dry-film photopolymer resists. In addition, dry-film resists may be used as the coating layer strip  32  in the form of laminated photosensitive sheets specifically designed for use in the manufacture of printed circuit boards and chemically machined parts. Dry-film resists are resistant to various electroplating and etching processes. It is essential that the coating layer strip  32  be able to be selectively removed through techniques such as ashing, the removal of photoresist from a substrate by high temperature oxidation, from selective areas, e.g. from the area over the holes  22 , as shown in FIG. 2.  
         [0028]    The coating layer strip  32  exists on one or both sides of the laminate substrate  10  and forms a barrier to the passage of light beam  28  through hole  22  in the package substrates  20  of laminate substrate  10 . The coating layer strip  32  must have a combination of opacity and thickness sufficient to block the passage of fight beam  28  through the holes  22 . The coating layer strip  32  is selectively removed on a package substrate  20  having a defective die mounting site  30  to expose the hole  22  which allows light beam  28  to pass through the package substrate  20 . Removal may occur through, ashing, chemical wash, or similar techniques known in the art. The coating layer strip  32  is not removed from non-defective package substrates  20  and, therefore, light beam  28  is blocked by the coating  32 . As noted, however, it is also possible to remove the coating layer strip  32  over holes of non-defective substrates, if desired.  
         [0029]    The light source  24  may be any device capable of producing a light beam  28  directed at the holes  22  of the laminate substrate  10 . Light source  24  may be a white light source or a wavelength-specific light source, such as a laser. In some cases, a wavelength-specific light source  24  may be used if it is important to reduce the possibility of false readings at the detector  26  from other light sources used in the package substrate fabrication process.  
         [0030]    In one embodiment of the present invention shown in FIG. 1, the light source  24  is mounted onto a mount  44  and may be either stationary or capable of movement. Detector  26  is any device capable of detecting a light beam  28  originating from light source  24 , preferably a photovoltaic cell activated by the wavelength of light beam  28 . The detector  26  is similarly mounted to a mount  46  and may be stationary or capable of movement. In the preferred arrangement shown in FIG. 2, the light source  24  on mount  44  is located below the laminate substrate  10  or package substrate  20  by a distance dictated by the existing package substrate fabrication production line into which the current system is integrated. The light detector  26  on mount  46  is located above the laminate substrate  10  or package substrate  20  by a distance dictated by the existing package substrate fabrication production line into which the current system is integrated and aligned with the light source  24 . Backlighting of the laminate substrate  10  or package substrates  20  allows for a simple and cost-efficient integration of the detection system  5  into currently existing package substrate fabrication production lines.  
         [0031]    A portion of a package substrate fabrication/production line is representatively shown in FIG. 3. A conveyor  50  transports a laminate substrate containing a plurality of individual package substrates  20  to a dicer  52 . The dicer cuts the laminate substrate  10  into individual package substrates  20  each having at least one die mounting site  30  which are then transported on conveyer  54  for further processing. The detection system  5  of the present invention may be implemented at any stage of the package substrate fabrication process including prior to dicing and after dicing of the laminate substrate  10 . The conveyors  50  and  54  are constructed to allow the light beam  28  from light source  24  to pass through to the laminate substrate  10 . This may be accomplished by the use of a transparent conveyor  50 ,  54  or through openings in the conveyor  50 ,  54 . The system  5  may include a single light source  24  and detector  26  or may be comprised of a number of light sources  24  and detectors  26  as shown in FIG. 3. The size of the light sources  24  and detectors  26  may vary in accordance with the area of the laminate substrate  10  or package substrates  20 . The use of multiple light sources  24  and detectors  26  may be desirable so that multiple package substrates  20 , laminate substrates  10 , or multiple die mounting sites  30  on a single package substrate  20  may be tested at the same time. In addition, the light sources  24  and detectors  26  may be placed in various positions within a package substrate fabrication production line to assist in both the classification of die mounting sites  30  as being either defective or non-defective or to assist in the analysis of defect placement on a laminate substrate  10 . Upon detection of a package substrate  20  having a defective die mounting site  30 , the detector  26  sends an output signal on line  42  signaling the conveyor or human operator to re-route the defective package substrate  20  to a repair station or discard bin.  
         [0032]    The process for forming the defective wafer identification detection system  5  will next be described with reference to FIGS. 4 a - 4   c . FIG. 4 a  shows a portion of the laminate substrate  10 , having two major surfaces, in a preliminary stage of construction having a plurality of defective die mounting sites  30  on package substrates  20  and non-defective die mounting sites  30  on package substrates  20 . The number and position of the defective die mounting sites  30  and non-defective die mounting sites  30  will vary from package substrate to package substrate. The laminate substrate  10 , which may ultimately yield many package substrates  20 , is subjected to the formation of holes  22  which extend through each package substrate  20 . The holes  22  are positioned on the laminate substrate  10  so that they do not intersect or contact the die mounting site  30  of the package substrates  20 . Formation of the holes  22  may be formed by etching, drilling or punching techniques with the holes  22  extending through the laminate substrate  10  leaving openings in both major surfaces of the package substrates  20 . Though the holes  22  shown in FIG. 1 are round, the holes may have any shape sufficient to allow light to pass from one end of a hole  22  through the laminate substrate  10  to the other end of hole  22 .  
         [0033]    [0033]FIG. 4 b  shows the laminate substrate  10  in a second preliminary stage of construction having package substrates  20  coated on both major surfaces with a coating layer strip  32 , preferably a resist coating, covering the holes  22 . The coating layer strip  32  has a thickness and/or opacity sufficient to block the passage of light through the holes  22 . Alternatively, coating layer strip  32  may be formed on only one or a part of one or both surfaces of the laminate substrate  10 , as desired. For purposes of further description of the invention, a laminate substrate  10  having a coating layer strip  32  on both sides of the laminate substrate  10  will be discussed.  
         [0034]    Referring now to FIGS. 4 b  and  4   c , once the coating layer strips  32  have been formed, the selective removal of a portion of the coating layer strips  32  may be carried out. Selective removal occurs when a die mounting site  30  is identified as defective through testing means known in the art, for example by electronic probe testing of the conducting lines within a die mounting site  30 . FIG. 4 c  shows the laminate substrate  10  after removal of the coating layer strip  32  from over the holes  22  on package substrate  20  having a defective die mounting site  30 . The coating layer strip  32  remains on the non-defective package substrate  20  covering corresponding hole  22 . Removal of the coating layer strips  32  from the defective die mounting sites  30  of the package substrate  20  may be accomplished by an ashing or chemical wash process which is directed at the holes  22  which correspond to defective package substrates  20  such that only the holes  22  corresponding to defective package substrates  20  are exposed. The formation and subsequent removal of the coating layer strip  32  from covering the holes  22  of defective package substrates  20  may be accomplished at any time during the fabrication process of the wafer after the testing and classification process during which the package substrates  20  are determined to be defective.  
         [0035]    In another embodiment of the invention, the laminate substrate  10  is diced or cut into individual package substrates  20  prior to die mounting sites  30  being identified as defective or non-defective. The package substrates  20  may then be passed over a fight source  24  and under a detector  26 . If a light beam  28  from light source  24  is detected by detector  26  through hole  22  of a defective package substrate  20  which has had coating  32  selectively removed to expose hole  22 , the package substrate  20  is identified as defective and can be redirected to a repair station or a discard bin.  
         [0036]    Although the present invention has been illustrated using one hole  22  which is selectively covered or not covered to identify a defective package substrate or a die mounting area thereon, it is also possible to provide a plurality of holes  22  for each package substrate  20  or die mount area. The plurality of holes  22  may be selectively covered or uncovered, as described above, to form a binary code, e.g. covered holes  22  representing “0” and uncovered holes  22  representing “1”, or vice versa. By reading the binary code using the light source  24  to produce a pattern of light and dark on the detector  26 , the binary code of each package substrate  20  may be used to represent a unique identification for a specific package substrate  20 , a code corresponding to the type or location of defects within the package substrate  20 , or a combination of both.  
         [0037]    With the present invention, the identification of defective package substrates  20  by a human or machine at any stage of a package substrate fabrication process is simplified and does not suffer from the marking reading problems attendant in current ink-package substrate systems and allows for a cost-effective method of identification without the need for sophisticated equipment which would require extensive revamping of current production line systems.  
         [0038]    It should be readily understood that the invention is not limited to the specific embodiments described and illustrated above. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, which are commensurate with the spirit and scope of the invention. Accordingly, the invention is not limited by the foregoing description, but is only limited by the scope of the appended claims.  
         [0039]    What is claimed as new and desired to be protected by Letters Patent of the United States is: