Patent Document

BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to an apparatus for manufacturing electrical device packages. More particularly, the invention relates to an apparatus for dispensing a liquid encapsulant to encapsulate a semiconductor chip that is attached a tape.  
           [0003]    2. Description of the Related Art  
           [0004]    In a typical process for fabricating a plastic semiconductor package, a semiconductor chip after being attached and wire-boned to a lead frame is encapsulated with a molding compound by transfermolding. However, other packaging process can employ different encapsulation methods. For example, a micro ball grid array (μBGA) package, which includes a tape instead of a leadframe of the plastic package, is encapsulated by a liquid encapsulant coating process.  
           [0005]    The tape typically has windows exposing parts of the beam leads for connection to the semiconductor chip. A fabrication method, which employs the tape with windows, is described below. A typical assembly process for assembling μBGA package begins with providing a tape made of, for example, polyimide, and having windows and metal beam leads across the windows. A semiconductor chip is attached to the tape using an adhesive, and the beam leads are connected to bonding pads on the chip through the windows. Then the windows are filled with an encapsulant to protect the chip and the electrical connections.  
           [0006]    [0006]FIG. 1 is a schematic diagram showing a conventional reel-to-reel dispensing apparatus  100  for filling the windows with an encapsulant. Apparatus  100  includes: a dispensing station  40  for coating a liquid encapsulant on a tape  10  to which a semiconductor chips  11  are attached; a reel-to-reel handling track  60  for moving tape  10  at dispensing station  40 ; a tape feed station  20  for feeding tape  10 ; and a tape take-up station  70  for unloading tape  10  from dispensing station  40  after the coating process. The structure of apparatus  100  will be explained based on the order of the movement of tape  10 .  
           [0007]    A tape feed reel  22  of tape  10  is loaded into tape feed station  20 . A protection tape  30  which is wound with tape  10  in reel  22  to protect chips  11  is removed from the reel as tape  10  is supplied to dispensing station  40 . When removed, protection tape  30  is wound to a protection tape take-up reel  26 , while tape  10  moves to a support plate  50  in dispensing station  40 . In dispensing station  40 , a syringe  42  above support plate  50  dispenses a liquid encapsulant through a needle  44  to an upper surface  12  (FIG. 2) of tape  10 , which includes chips  11 . An actuator  46  coupled to syringe  42  controls the movement of syringe  42 . Tape  10  is then transferred to tape take-up station  70  which winds tape  10  on a reel  72 . At the same time, a protection tape  80  for protecting chips  11  on tape  10  is wound as an interleaf. Reel-to-reel handling track  60  controls the movement of tape  10  from tape feed station  20  to tape take-up station  70 .  
           [0008]    Dispensing of the liquid encapsulant on the top of tape  10  is further described with reference to FIG. 2. In FIG. 2, chip  11  is attached to tape  10  by an elastomer adhesive  18 , and beam leads  16  electrically connect chip  11  to tape  10  at windows  14 . For encapsulation, tape  10  is placed on support plate  50 . A suction port  52  connected to a vacuum pump (not shown) holds tape  10  to support table  50 .  
           [0009]    Then, syringe  42  (FIG. 1) dispenses a liquid encapsulant  47  along periphery of chip  11  to protect the electrical connection area between chip  11  and beam leads  16 . When dispensed, liquid encapsulant  47  fills windows  14  ( 47   b ), covers the periphery of chip  11  ( 47   a ), and undesirably runs out through a gap between tape  10  and support table  50  ( 47   c ). This may eventually contaminate support plate  50  and adversely affect dispensing encapsulant on following tapes.  
           [0010]    To stop the encapsulant from running into the gap, several methods have been proposed. Two representative examples are depicted in FIG. 3 and FIG. 4. FIG. 3 shows a tape  10  covered with a photo solder resist (PSR) film  90 , which can be removed by etching after dispensing, and FIG. 4 shows a piece of tape  10  temporarily held on a magazine substrate  94 .  
           [0011]    With reference to FIG. 3, tape  10  having windows  14  and sprocket holes  19  has PSR film  90  formed on the bottom surface of tape  10  before the encapsulant coating step. PSR film  90  can prevent the liquid encapsulant from running onto support table  50  (FIG. 2). After the encapsulant is cured, etching can remove PSR film  90 .  
           [0012]    With reference to FIG. 4, tape  10 , which is cut to size, is placed on a magazine substrate  94 . Magazine substrate  94  has a surrounding lip that prevents the liquid encapsulant from running onto support table  50  (FIG. 2). However, the method of FIG. 3 requires costly processing steps including forming PSR film  90  on the bottom of tape  10  before the encapsulant coating step, and partly removing PSR film  90  to expose windows  14  and solder ball pads (not shown). The method of FIG. 4 reduces manufacturing efficiency by requiring an addition of tape cutting step, and because a batch-type process using tape strips is less efficient than a reel-to reel process.  
         SUMMARY OF THE INVENTION  
         [0013]    According to an aspect of the present invention an apparatus for dispensing a liquid encapsulant to encapsulate a semiconductor package includes: a dispensing station for dispensing the liquid encapsulant to a tape; a tape transfer station for transferring the tape to the dispensing station; a cover film attaching station for attaching a cover film to the bottom of the tape before transferring the tape to the dispensing station; and a cover film detaching station for separating the cover film from the tape after dispensing of the liquid encapsulant. The cover film prevents the liquid encapsulant from flowing into a gap between the tape and a stage with which the tape is in contact.  
           [0014]    The cover film attaching station includes an attaching means which moves vertically with respect to the cover film. When the cover film is under the tape, the attaching means flattens the cover film and the tape, and uses a press roller to apply pressure to the cover film and attach the cover film to the tape. The cover film detaching station includes a separator which helps the cover film separate from the tape so that an excessive force is not applied to the cover film or the tape.  
           [0015]    According to another aspect of the present invention, a method for dispensing a liquid encapsulant on the top of a tape of a semiconductor package employs a removable cover film attached to the tape to prevent leakage of encapsulant. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]    These and various other features and advantages of the present invention will be readily understood with reference to the following detailed description taken in conjunction with the accompanying drawings. In the drawings, like reference numerals designate like structural elements, and, in which:  
         [0017]    [0017]FIG. 1 is a schematic diagram showing a conventional reel-to-reel dispensing apparatus;  
         [0018]    [0018]FIG. 2 is an enlarged view of part A in FIG. 1;  
         [0019]    [0019]FIG. 3 is a perspective view of a tape with a PSR film formed thereon;  
         [0020]    [0020]FIG. 4 is a plan view of a conventional tape on a magazine substrate;  
         [0021]    [0021]FIG. 5 is a schematic diagram of a dispensing apparatus according to the present invention;  
         [0022]    [0022]FIG. 6 is an enlarged view of part B of FIG. 5;  
         [0023]    [0023]FIG. 7A is a partial longitudinal sectional view of a cover film attaching station in the apparatus of FIG. 5;  
         [0024]    [0024]FIG. 7B is a partial traverse sectional view of a cover film attaching station in the apparatus of FIG. 5;  
         [0025]    [0025]FIG. 8 is a partial sectional view of a cover film detaching station in the apparatus of FIG. 5;  
         [0026]    [0026]FIG. 9 is a schematic diagram depicting another embodiment of the dispensing apparatus according to the present invention;  
         [0027]    [0027]FIG. 10 is a flow chart of one embodiment of the dispensing process according to the present invention; and  
         [0028]    [0028]FIG. 11 is a flow chart of another embodiment of the dispensing process according to the present invention.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0029]    The present invention is described in detail hereinafter with reference to the accompanying drawings, in which embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein.  
         [0030]    [0030]FIG. 5 is a schematic diagram of a dispensing apparatus  200  according to an embodiment of the present invention. Apparatus  200  includes a dispensing station  140 , a tape transfer station  160 , a tape feed station  120  and a tape unloading station  170 . Apparatus  200  further includes a cover film attaching station  230  for attaching a cover film  210  to a tape  110 , a cover film feed station  220  for feeding cover film  210  to cover attaching station  230 , a cover film detaching station  250 , and a cover film unloading station  260 .  
         [0031]    A tape feed reel  122 , in which tape  110  having semiconductor chips  111  and an interleaf protection tape  130  are wound together, is held to an axle  124 . When tape  110  feeds out of tape feed reel  122 , protection tape  130  from tape feed reel  122  is wound around a protection tape take-up reel  126  which is held to an axle  128 . At the same time that tape  110  feeds into cover film attaching station  230 , a cover film reel  222  held to an axle  224  feeds cover film  210  to cover film attaching station  230  via a guide roller  226 .  
         [0032]    An upper attach means  240  and a lower attach means  232  of cover film attaching station  230  bond cover film  210  to tape  110 . To promote the bonding, cover film  210  includes an adhesive layer on a surface that is bonded to tape  110 . The adhesive layer bonds cover film  210  and tape  110  temporarily, for example, for 20 to 40 minutes, so as to separate cover film  210  and tape  110  easily after encapsulation. A film such as REVALFA made by Nitto Denko Corporation in Japan is suitable for cover film  210 . An assembly including tape  110  and cover film  210  moves to dispensing station  140 . Dispensing station  140  includes a syringe  142 , a motor  146  coupled to syringe  142 , and a support plate  150 . While the assembly is on support table  150 , motor  142  moves syringe  142 , and syringe  142  dispenses a liquid encapsulant through a needle  144  to encapsulate chip  111  and tape  110 . Motor  146  can freely move a lower end of syringe  142  to position syringe  142  for dispensing liquid at desired locations on tape  110 . After passing through dispensing station  140 , tape  110  and cover film  210  are separated from each other at cover film detaching station  250 . Then tape  110  is wound with a protection film  180  to a reel  172  in tape unloading station  170 . At this time, cover film  210  moves to cover film unloading station  260  and is wound to a cover film take-up reel  262 .  
         [0033]    A tape transfer station  160  controls movement of tape  110  and cover film  210  in apparatus  200  by controlling driving axles  128 ,  174  and  264  coupled to respective reels  126 ,  172  and  262 . Supporting axles  124 ,  178  and  224  simply support reels  122 ,  176 , and  222 , respectively.  
         [0034]    A part of tape  110  where the liquid encapsulant is dispensed is described in more detail with reference to FIG. 6 which depicts part ‘B’ in FIG. 5. Chip  111  is attached on the top surface  112  of tape  110  by an elastomer adhesive  118 . Tape  110  includes windows  114  for connecting beam leads  116  to chip  111 . When tape  110  is on support plate  150 , cover film  210  is on the bottom surface  113  of tape  110  and firmly held to support plate  150  by a suction port  152  connected to a vacuum pump(not shown). Liquid material  147 , e.g., an encapsulant, is applied around chip  111  to protect the electrical connections between chip  111  and beam leads  116 , and the surface of chip  111  not covered by tape  110 . Cover film  210  dams or blocks windows  114  of tape  110  and prevents encapsulant  147  from flowing onto support table  150 .  
         [0035]    [0035]FIGS. 7 a  and  7   b  are partial sectional views of cover film attaching station  230  of FIG. 5 in longitudinal and traverse directions of cover film  210 , respectively.  
         [0036]    Cover film attaching station  230  includes upper attach means  240  and lower attach means  232 . With reference to FIG. 7A, upper attach means  240  flattens tape  110 . In particular, a suction plate  241  of upper attach means  240  includes a number of suction holes  243  and  244  respectively for holding tape  110  and chips  111 , and a number of cavities  246  for receiving chips  111 . Each cavity  246  has a protective layer  247  to protect chip  111  on a surface where chip  111  is held by suction hole  244 . Suction holes  243  and  244  are in communication with a vent  242  connected to an external vacuum pump, and a plate transfer means  248  attached to plate  241  moves plate  241  up and down.  
         [0037]    Referring to FIG. 7B, while upper attach means holds tape  110  flat, a roller  234  of lower attach means  232  rolls under cover film  210  pressing bottom of cover film  210  to bond cover film  210  to tape  110 . It is preferable that cover film  210  is narrower than tape  110 , and roller  234  and plate  241  are narrower than tape  110  but wider than cover film  210 . Roller  234  moves in directions of F-C-D-E of FIG. 7A in that order. When moving upward in direction F, roller  234  presses cover film  210  to tape  110 , and then roller  234  moves in direction C rolling and pressing cover film  210  so as to bond cover film  210  to tape  110 . Then, roller  234  moves downward in direction D and back to the original position in direction E to prepare for a next bonding. Roller  234  is coupled via a roller transfer means  238  to an external driving means (not shown), and a rotating axis  236  rotates roller  234 .  
         [0038]    [0038]FIG. 8 is a partial sectional view of cover film detaching station  250  in apparatus  200  of FIG. 5. With reference to FIG. 8, cover film detaching station  250  has a guide pin  252 , which is positioned so as to separate tape  110  and cover film  210  after the liquid is applied to tape  110 . Sharp end  254  of guide pin  252  is placed between cover film  210  and tape  110 , and cover film  210  separates from tape  110  as tape  110  moves forward.  
         [0039]    [0039]FIG. 9 is a schematic diagram of a dispensing apparatus  400  according to another embodiment of the present invention. Like apparatus  200  of FIG. 5, apparatus  400  has a dispensing station  320 , a tape transfer station  330 , a tape feed station  310 , a tape unloading station  340 , a cover film feed station  350 , a cover film attaching station  360 , a cover film detaching station  370  and a cover film unloading station  380 . Apparatus  400  further includes a curing station  390  for curing a liquid encapsulant after encapsulation of a chip. Curing station  390  heats the encapsulated chip and tape, and is preferably located between dispensing station  320  and tape unloading station  340 .  
         [0040]    [0040]FIG. 10 is a flow chart of one embodiment of a dispensing process according to the present invention. With reference to FIG. 10, the dispensing process includes supplying a tape (step  410 ), attaching a cover film to the bottom of the tape (step  420 ), dispensing a liquid (e.g. a liquid encapsulant) on the top of the tape (step  430 ), separating the cover film from the bottom of the tape (step  440 ), and unloading the tape (step  450 ). The tape includes windows and a semiconductor chip attached to the tape by an adhesive.  
         [0041]    [0041]FIG. 11 is a flow chart of another embodiment of a dispensing process according to the present invention. With reference to FIG. 11, the dispensing process includes supplying a tape (step  510 ), attaching a cover film to the bottom of the tape (step  520 ), dispensing a liquid encapsulant on the top of the tape (step  530 ), curing the liquid encapsulant (step  535 ), separating the cover film from the bottom of the tape (step  540 ), and unloading the tape (step  550 ).  
         [0042]    As described in the hereinbefore, the present invention provides apparatuses and methods for dispensing a liquid and encapsulating semiconductor chips on a tape. Although the present invention has been described with reference to specific embodiments of the invention, the concept thereof can be applied without restriction to other embodiments.

Technology Category: 4