Patent Publication Number: US-2004043536-A1

Title: Method of producing integrated circuit package units

Description:
BACKGROUND OF THE INVENTION  
       [0001] 1. Field of the Invention  
       [0002] The invention relates to a method of producing integrated circuit package units, more particularly to a method in which a plurality of integrated circuit package units are produced through a singulation process from a preformed substrate.  
       [0003] 2. Description of the Related Art  
       [0004] Referring to FIGS. 1, 2 and  3 , a conventional matrix type substrate  1  for producing integrated circuit package units includes a grid-like array of preformed QFN (Quad Flat Non-Leaded) package precursors  11  formed on a leadframe  12 , and a plurality of intersecting singulation streets  13  extending along the borderlines of the package precursors  11 . The center-to-center distance between two adjacent package precursors  11  is represented by (L 1 ). Each package precursor  11  includes a semiconductor chip  111 , and inner leads  122  electrically connected to the semiconductor chip  111 . The dimension of each inner lead  122  is denoted by (Wo) A continuous encapsulating epoxy layer  112  encloses the semiconductor chips  111  of the package precursors  11 , and is bonded integrally to the leadframe  12 . The leadframe  12  includes a plurality of intersecting connection bars  121  which extend along the borderlines of the package precursors  11  and which are formed integrally with the inner leads  122  of the package precursors  11 . FIG. 2 is provided with dotted lines at the left side thereof to show one part of the substrate  1  which has not been cut, and with solid lines at the right side thereof to show another part of the substrate  1  which has been cut. The singulation streets  13  cover the metal layer of the leadframe  12  (i.e., the connection bars  121 ) and parts of the encapsulating epoxy layer  112  underlying the connection bars  121 . A cutting device, which has a cutting blade  2  made of a material containing diamond, is used to cut off the connection bars  121  and the underlying epoxy layer  112  so as to separate structurally and electrically the package precursors  11  to form individual integrated circuit package units, one of which is shown in FIG. 3. The inner leads  122  are left in each package unit after singulation. However, since the connection bars  121  are made of copper or similar material, which is soft and ductile, the cutting blade  2  must operate in a slow and toilsome manner like spooning up ice cream with a scoop. Furthermore, the metal chips produced upon cutting can stick to the cutting blade  2 , loaded the blade, and deteriorate the blade cutting ability. Although the conventional cutting device provides a water jet to spray on the cutting point, since the cutting is performed continuously along the singulation streets  13 , it is difficult to self-sharpen the blade grit or remove the metal chips from the cutting blade  2 . This phenomenon tends to attenuate the sharpness of the cutting blade  2 , increases the rate of wear of the cutting blade  2 , and decreases the rate of cutting. Generally, the cutting rate of the cutting blade  2  is as slow as 1-5 mm/sec. Moreover, in order to match the width of the connecting bars  121 , it is necessary to properly select a suitable width for the cutting blade  2 . In addition, there is an incidence of burring at the edge of the inner leads  122  after singulation, as shown in FIG. 4, which can result in short-circuiting in the semiconductor chip  111  especially when the burr size is large enough.  
       [0005] Although the prior art has suggested a process of manufacturing integrated circuit package units, which utilizes a half etching technology to reduce the thickness of a metal layer of a leadframe, this manufacturing process still cannot solve the aforesaid problems encountered in the conventional singulation process.  
       SUMMARY OF THE INVENTION  
       [0006] Therefore, the object of the present invention is to provide a method of producing integrated circuit package units that is capable of overcoming the aforementioned drawbacks of the prior art.  
       [0007] According to this invention, a method of producing individual integrated circuit package units comprises the steps of: providing a base which includes a leadframe and a plurality of package precursors formed on the leadframe; and singulating the package precursors. Each of the package precursors has inner leads, and a semiconductor chip connected electrically to the inner leads. The leadframe has a plurality of metallic connection bars extending along borderlines of the package precursors, and extension parts branching from two sides of the connection bars. The extension parts are formed integrally with the connection bars, and are connected respectively and directly to the inner leads of the package precursors. The base further has a continuous encapsulating epoxy layer that encloses the semiconductor chips of the package precursors and that are bonded integrally with the leadframe. The package precursors are singulated by cutting the leadframe and the encapsulating epoxy layer along first and second cutting streets which extend respectively along and at two opposite sides of the connection bars and which extend through the extension parts. The cutting of the base is performed by cutting into the first and second cutting streets with a cutting tool, thereby separating the connection bars from the inner leads. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0008] Other features and advantages of the present invention will become apparent in the following detailed description of the preferred embodiment with reference to the accompanying drawings, of which:  
     [0009]FIG. 1 is a fragmentary schematic view of a conventional matrix type substrate;  
     [0010]FIG. 2 is a fragmentary sectional view of the conventional substrate of FIG. 1;  
     [0011]FIG. 3 illustrates a single package unit after singulation of the conventional substrate;  
     [0012]FIG. 4 illustrates burrs occurring at the edge of inner leads of the conventional substrate after singulation;  
     [0013]FIG. 5 is a fragmentary schematic view of a matrix base used in a preferred embodiment of a method of producing integrated circuit package units according to the present invention;  
     [0014]FIG. 6 is an enlarged schematic view of an encircled portion of FIG. 5;  
     [0015]FIG. 7 is a fragmentary sectional view of the matrix base of FIG. 5;  
     [0016]FIG. 8 is a fragmentary sectional view of a singulated integrated circuit package unit with the inner leads thereof being sectioned; and  
     [0017]FIG. 9 is a fragmentary schematic view showing the extension parts of a leadframe of the matrix base to be cut by a cutting tool. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
     [0018] Referring to FIGS.  5  to  7 , a method of producing individual integrated circuit package units embodying the preferred embodiment of the present invention comprises first and second steps.  
     [0019] The first step is to provide a matrix base  100 , which includes a plurality of preformed integrated circuit package precursors. In this embodiment, the matrix base  100  includes a leadframe  30 , and is preformed with a grid-like array of QFN package precursors  20  formed on the leadframe  30 . Each of the package precursors  20  has inner leads  21 , and a semiconductor chip  22  connected electrically to the inner leads  21 . The center-to-center distance (L 2 ) between two adjacent ones of the package precursors  20  is greater than the center-to-center distance (L 1 ) between two adjacent ones of the package precursors  11  of the conventional substrate  1  shown in FIG. 1. The leadframe  30  is made of copper or a similar material, and has a plurality of intersecting metallic connection bars  31  extending along borderlines of the package precursors  20 , and extension parts  32  branching from two sides of the connection bars  31 . The extension parts  32  are formed integrally with the connection bars  31 , and are connected respectively and directly to the inner leads  21  of the package precursors  20 . The extension parts  32  extend towards the inner leads  21  from two opposite sides of the connection bars  31 . The extension parts  32  are spaced apart so that gaps  33  are formed therebetween. Furthermore, the length of the inner leads  21  of the package precursors  20  is equal to that of the inner leads  122  of the conventional package precursors  11 , which is a standard length of a QFN package unit. The matrix base  100  further has a continuous encapsulating epoxy layer  23  that encloses the semiconductor chips  22  of the package precursors  20  and that are bonded integrally with the leadframe  30 . The encapsulating epoxy layer  23  is made of an epoxy resin, and the epoxy resin fills the gaps  33  between the extension parts  32 .  
     [0020] In the second step, the package precursors  20  are singulated by cutting the leadframe  30  and the encapsulating epoxy layer  23  along first and second cutting streets  41 ,  42  which extend respectively along and at two opposite sides of the connection bars  31  and which extend through the extension parts  32 .  
     [0021] The cutting of the matrix base  100  is performed by using two rotary cutting tools  210  and by cutting respectively into the first and second cutting streets  41 ,  42  so as to cut away the extension parts  32  and so as to separate the connection bars  31  from the inner leads  21 , as illustrated by the solid lines at the right side of FIG. 7, thereby obtaining a plurality of singulated package precursors  20  (not shown).  
     [0022] It should be noted that the cutting of the leadframe  30  along the first and second cutting streets  41 ,  42  can be performed simultaneously by a dual-blade cutting tool  210  or can be performed by using a single-blade cutting tool (not shown) that cuts through the first and second cutting streets  41 ,  42  consecutively.  
     [0023] Therefore, the present invention provides the following advantages:  
     [0024] 1. In the present invention, the first and second cutting streets  41 ,  42  are kept away from the connection bars  31 , and are arranged to fall within the extension parts  32  which are easier to be cut by the cutting tools  210  as compared to the connection bars  31 . Since the gaps  33  between the extension parts  32  are filled by the encapsulating epoxy layer  23 , as shown in FIG. 9, the metal of the leadframe  30  along the first and second cutting streets  41 ,  42  is discontinuous and is interrupted by the epoxy layer  23 . During the cutting operation, the cutting tools  210  simultaneously cut into the metal of the leadframe  30  and the epoxy layer  23 . Since the cutting tools  210  cut into the extension parts  32  intermittently, rather than cut into the connection bars  31  continuously, and since the cutting tools  210  reach and cut the hard epoxy layer  23  before the cut metal chips (not shown) of the extension parts  32  are able to stick to the cutting tools  210 , the cut metal chips are pushed away from the cutting tools  210  by the chips or particles of the epoxy layer  23  resulting from the cutting of the epoxy layer  23 . Thus, the cut metal chips can be easily washed away by a water jet from the first and second cutting streets  41 ,  42 . As a result, the sharpness of the cutting tools  210  can be maintained in a good condition, and the wear of the cutting tools  210  can be lessened. Although the number of the cutting streets used in the present invention is twice of that used in the conventional process, experiments show that the cutting speed in the present invention can be 80 mm/sec, which is much faster than that of the cutting operation performed in the conventional process for manufacturing QFN package units so that the production rate is relatively increased in the present invention.  
     [0025] 2. The quality of the package units produced by the present invention is good since the blade sharpness is maintained in a good condition. As a result, the incidence of burring at the inner leads  21  of the package units is reduced, as illustrated in FIG. 8.  
     [0026] 3. Since the connection bars  31  are not cut directly by the cutting tools  210 , the width of the cutting tools  210  is not limited by the connection bars  3 l. Therefore, as compared with the conventional cutting blade  2 , the cutting tools  210  used in the present invention can be thinner and can thus have a reduced contact area with the metal. Furthermore, the present invention eliminates the incomplete cutting problem occurring often in the conventional process.  
     [0027] 4. The matrix base  100  used in the present invention can be produced by the same process as that used in the conventional process except that the center-to-center distance of the package precursors  20  is enlarged and that the leadframe  30  is provided with the extension parts  32  and the inner leads  21 .  
     [0028] Although the preferred embodiment of the present invention is directed to the production of QFN package units, the present invention is not limited thereto. The present invention is applicable to the production of any integrated circuit package unit other than QFN package units.  
     [0029] While the present invention has been described in connection with what is considered the most practical and preferred embodiment, it is understood that this invention is not limited to the disclosed embodiment but is intended to cover various arrangements included within the spirit and scope of the broadest interpretation so as to encompass all such modifications and equivalent arrangements.