Patent Publication Number: US-2023135089-A1

Title: Release film and method of manufacturing semiconductor package using the same

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This U.S. non-provisional patent application claims priority under 35 U.S.C. § 119 to Korean Patent Application No. 10-2021-0149730, filed on Nov. 3, 2021, in the Korean Intellectual Property Office, the entire contents of which are hereby incorporated by reference. 
     BACKGROUND OF THE INVENTION 
     The present disclosure relates to a release film and/or a method of manufacturing a semiconductor package using the same. 
     A molding process, which is a part of a semiconductor device packaging process, is performed to encapsulate a substrate and a semiconductor device mounted thereon with a molding material. A mold and a molding material may be used to hermetically encapsulate the semiconductor device. An epoxy molding compound (EMC), which is composed of an epoxy resin and various inorganic and subsidiary materials added therein, is mainly used as the molding material. The molding material is injected into the mold, during a shaping process. In the packaging process, a release film, which is interposed between the mold and the molding material, is used to detach the shaped product from the mold, after hardening the molding material. 
     SUMMARY 
     Example embodiments of the inventive concepts provide a way of suppressing an issue of static electricity, which may occur when a molding material is detached from a release film. 
     According to an embodiment of the inventive concepts, a release film may include a conductive polymer substrate layer, and release layers on a top surface and a bottom surface of the conductive polymer substrate layer. Each of the release layers may include a fluorine-based polymer, and a density of the conductive polymer substrate layer ranges from 0.1 g/cm 3  to 0.5 g/cm 3 . 
     According to an embodiment of the inventive concepts, a release film may include a conductive polymer substrate layer, and release layers on a top surface and a bottom surface of the conductive polymer substrate layer. Each of the release layers may include a fluorine-based polymer, the conductive polymer substrate layer may have a thickness between 40 μm to 80 μm, and each of the release layers may have a thickness between 0.5 μm to 5 μm. 
     According to an embodiment of the inventive concepts, a method of manufacturing a semiconductor package may include disposing a release film to cover a cavity of a mold, disposing a molding member on the release film, positioning a substrate such that a semiconductor device mounted on a first surface of the substrate is over the cavity; moving the mold toward the first surface of the substrate such that the molding member covers at least a portion of the first surface of the substrate, hardening the molding member to form a molding structure, and detaching the molding structure from the release film. The release film may include a conductive polymer substrate layer and release layers on a top surface and a bottom surface of the conductive polymer substrate layer. Each of the release layers may include a fluorine-based polymer. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a sectional view schematically illustrating a release film according to some example embodiments. 
         FIG.  2    is an enlarged sectional view illustrating a portion ‘aa’ of  FIG.  1   . 
         FIG.  3    is a sectional view illustrating a structure obtained by stretching the release film of  FIG.  1   . 
         FIG.  4    is an enlarged sectional view illustrating a portion ‘bb’ of  FIG.  3   . 
         FIGS.  5 ,  6 ,  7 ,  9 , and  10    are sectional views illustrating a process of manufacturing a semiconductor package using the release film. 
         FIG.  8    is an enlarged sectional view illustrating a portion ‘cc’ of  FIG.  7   . 
     
    
    
     DETAILED DESCRIPTION 
     Example embodiments of the inventive concepts will now be described more fully with reference to the accompanying drawings, in which example embodiments are shown. Example embodiments, however, may be embodied in various different forms, and should not be construed as being limited to only the illustrated embodiments. Rather, the illustrated embodiments are provided as examples so that this disclosure will be thorough and complete, and will fully convey the concepts of this disclosure to those skilled in the art. Unless otherwise noted, like reference characters denote like elements throughout the attached drawings and written description, and thus descriptions will not be repeated. 
     Spatially relative terms, such as “top,” “bottom,” and/or the like, may be used herein for ease of description to describe one element or feature&#39;s relationship to another element(s) or feature(s) as illustrated in the figures. It will be understood that the spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, the device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly. 
       FIG.  1    is a sectional view schematically illustrating a release film  10  according to some example embodiments.  FIG.  2    is an enlarged sectional view illustrating a portion ‘aa’ of  FIG.  1   . 
     Referring to  FIGS.  1  and  2   , a release film  10  may include a conductive polymer substrate layer  11  and a pair of release layers  12 . 
     The conductive polymer substrate layer  11  may include a first surface  11   a  and a second surface  11   b , which are opposite to each other. The release layers  12  may be respectively provided on the first and second surfaces  11   a  and  11   b  of the conductive polymer substrate layer  11 . Each of the release layers  12  may be in contact with the conductive polymer substrate layer  11 . 
     The conductive polymer substrate layer  11  may have a woven or non-woven fabric structure. In some embodiments, the conductive polymer substrate layer  11  may include a porous conductive fiber and/or the conductive polymer substrate layer  11  may include a porous fiber and a conductive polymer material coated on the porous fiber. For example, as shown in  FIG.  2   , the conductive polymer substrate layer  11  may include fibers and a plurality of pores  101  which are empty spaces defined between the fibers. 
     The porous fiber may be formed of and/or include at least one of polyethylene naphthalate, polyimide, nylon, polyester, and/or the like. The conductive polymer material may include at least one of poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS), polypyrrole, polythiophene, polyaniline, and/or the like. 
     The release layer  12  may include a fluorine-based polymer. For example, the release layer  12  may be formed of and/or include at least one material including one or more C—F bonds (e.g., fluoropolymer and perfluoropolymer). For example, the release layer  12  may be formed of and/or include at least one fluorine-based polymer (e.g., ethylene tetrafluoroethylene (ETFE), polytetrafluoroethylene (PTFE), and perfluorooctanoic acid (PFOA)). As shown in  FIG.  2   , the release layer  12  may have an uneven surface (such as a fine concavo-convex structure), which is placed opposite to the conductive polymer substrate layer  11 . In some embodiments, the conductive polymer substrate layer  11  may include a contact portion  11 C, which is located near the release layer  12  and is coated with the release layer  12 . 
     The conductive polymer substrate layer  11  may have a first thickness T 1 , and each of the release layers  12  may have a second thickness T 2 . The first thickness T 1  may be at least ten times larger than the second thickness T 2 . As an example, the first thickness T 1  may range from 30 μm to 150 μm and/or the second thickness T 2  may range from 0.1 μm to 20 μm. In some example embodiments, the first thickness T 1  may range from 40 μm to 80 μm, and/or the second thickness T 2  may range from 0.5 μm to 5 μm. 
     Due to the presence of the pores  101 , the conductive polymer substrate layer  11  may have a density lower than the release layer  12 . As an example, the density of the conductive polymer substrate layer  11  may range from 0.1 g/cm 3  to 0.5 g/cm 3  and/or the density of the release layer  12  may range from 1.5 g/cm 3  to 2.3 g/cm 3 . 
     If the density of the conductive polymer substrate layer  11  is lower than 0.1 g/cm 3 , the pores  101  may be clogged with the release layer  12  when the conductive polymer substrate layer  11  is coated with the release layer  12 , as will be described below. In addition, in a stretching process on the release film  10 , which will be described with reference to  FIGS.  7  and  8   , the release film  10  may not exhibit a conductive property or the conductive polymer substrate layer  11  may be torn. 
     If the density of the conductive polymer substrate layer  11  is higher than 0.5 g/cm 3 , the conductive polymer substrate layer  11  may have a poor stretching property. As a result, in steps of  FIGS.  6  and  7   , the release film  10  may not be in close contact with an inner bottom surface  312  and an inner side surface  322  of a mold  30 , and in these cases, it may be difficult to realize a desired molding shape. 
     In the case where the second thickness T 2  of the release layer  12  is large (e.g., larger than 20 μm), the conductive polymer substrate layer  11  may not be exposed by the stretching process on the release film  10  to be described with reference to  FIGS.  7  and  8   . 
     In the case where the second thickness T 2  of the release layer  12  is small (e.g., smaller than 0.1 μm), the conductive polymer substrate layer  11  may have a portion that is in direct contact with a molding member  42  even in the step before the stretching process on the release film  10 . In this case, the conductive polymer substrate layer  11  may be strongly attached to the molding member  42  in a process of hardening the molding member  42  of  FIG.  9    to be described below, and thus, it may not be easily detached from the molding member  42  in the detaching process. 
     A weight of the release layers  12  may account for 1% to 10% of a total weight of the release film  10 . As an example, a weight ratio of the conductive polymer substrate layer  11  to the release layers  12  may range from 8:1 to 9:1. 
     A sheet resistance of the release film  10  may be greater than or equal to 10 8  Ω/sq and/or may be smaller than 10 10  Ω/sq. In some example embodiments, the sheet resistance of the release film  10  may be about 10 9  Ω/sq. 
       FIG.  3    is a sectional view illustrating a structure obtained by stretching the release film of  FIG.  1   .  FIG.  4    is an enlarged sectional view illustrating a portion ‘bb’ of  FIG.  3   . 
     Referring to  FIG.  3   , the release film  10  may be stretched by an external force. During the stretching process, a length of the release film  10  may be increased in a direction parallel to the external force but may be decreased in a direction perpendicular to the external force. As a result, both of the first and second thicknesses T 1  and T 2  may be decreased by the stretching process. 
     In some embodiments, during the stretching process, the release layer  12  may be cut to form a plurality of portions. As a result, the conductive polymer substrate layer  11  may be exposed through regions between the cut portions of the release layer  12 . The exposed portion  11 N of the conductive polymer substrate layer  11  may protrude toward the outside of the release layer  12 , depending on a direction of the external force applied during the stretching process. 
     In some example embodiments, the release layer  12  may have a stretching property that is better than the conductive polymer substrate layer  11 , under the same condition on the external force. However, since the release layer  12  has a very small thickness, it may not be continuously stretched and may be torn by the external force. Thus, when the same external force is exerted on layers, the release layer  12  having the second thickness T 2  may be torn before the conductive polymer substrate layer  11  having the first thickness T 1 . For example, in some example embodiments, the release layer  12  may be formed on the conductive polymer substrate layer  11  at such a thickness that the release layer  12  undergoes inelastic deformation and tearing (and/or fracturing) while the polymer substrate layer  11  undergoes elastic deformation. 
     A release film according to some example embodiments may be fabricated by the following method. 
     Porous fibers, which are formed to have a woven and/or non-woven fabric structure, may be prepared. A conductive polymer substrate layer may be formed by coating the porous fibers with a conductive polymer material. For example, the conductive polymer substrate layer may be formed by coating a conductive polymer material on a non-woven fabric using a spray coating process. 
     Alternatively, the conductive polymer substrate layer may be formed by fabricating a material, which contains polymer powder (e.g., polyethylene terephthalate (PET)) and conductive polymer (0.1% to 1%) in a shape of a non-woven fabric, using a spun bond method. 
     A solution may be prepared by supplying a fluorine-based polymer composite in a solvent. In some example embodiments, the solvent may include an organic and/or a fluorine-based solvent. In some example embodiments, the fluorine-based polymer composite may include at least one material containing one or more C—F bonds (e.g., fluoropolymer and perfluoropolymer). For example, the fluorine-based polymer composite may include at least one of ethylene tetrafluoroethylene (ETFE), polytetrafluoroethylene (PTFE), perfluorooctanoic acid (PFOA), and/or the like. In some example embodiments, an additive agent, such as catalyzer, may be further added in the solvent. 
     Release layers may be formed on opposite surfaces (e.g., top and bottom surfaces) of the conductive polymer substrate layer by performing a coating process on the conductive polymer substrate layer (e.g., in a manner of dipping the substrate layer into the solution) and performing a drying process thereon. 
       FIGS.  5 ,  6 ,  7 ,  9 , and  10    are sectional views illustrating a process of manufacturing a semiconductor package using the release film.  FIG.  8    is an enlarged sectional view illustrating a portion ‘cc’ of  FIG.  7   . 
     Referring to  FIG.  5   , a mold  30  with a cavity  302  may be provided. The mold  30  may be formed of and/or include at least one of conductive or metallic materials. The mold  30  may be, for example, grounded and/or may serve as a ground. The mold  30  may include a base portion  31  and a frame portion  32  enclosing the base portion  31 . 
     A top surface  312  of the base portion  31  may be referred to as the inner bottom surface  312  of the mold  30 . A side surface  322  of the frame portion  32  adjacent to the base portion  31  may be referred to as the inner side surface  322  of the mold  30 . A space, which is defined by the inner bottom surface  312  of the mold  30  and the inner side surface  322  of the mold  30 , may correspond to the cavity  302 . 
     The release film  10  may be provided on the mold  30 , and a molding powder  41  may be provided on the release film  10 . In some example embodiment, the molding powder  41  may be formed of and/or include an epoxy molding compound and/or an epoxy molding pre-cursor. 
     A carrier substrate  70  may be provided on the mold  30 , and the release film  10  may be interposed between them. A package substrate  60  and semiconductor devices  50  may be provided on a surface of the carrier substrate  70  adjacent to the mold  30 . In some example embodiments, the package substrate  60  may be a printed circuit board (PCB). The semiconductor devices  50  may be mounted on a first surface  602  of the package substrate  60  adjacent to the mold  30 . 
     Referring to  FIG.  6   , the mold  30  may include at least one pathway (not shown), which is connected to the cavity  302  of  FIG.  5   , and a vacuum suction operation may be performed through the pathway. As a result, the release film  10  may be in close contact with the inner bottom surface  312  of the mold  30  and the inner side surface  322  of the mold  30 . In some example embodiment, the release film  10  may be in contact with a top surface of the frame portion  32 . The molding member  42  having a fluidic property may be formed, e.g., by heating the molding powder  41  of  FIG.  5   . 
     Referring to  FIG.  7   , the semiconductor devices  50  may be disposed into the molding member  42 . In some example embodiments, the mold  30  may be moved toward the first surface  602  of the package substrate  60 . The molding member  42  of  FIG.  6    may cover the first surface  602  of the package substrate  60  and the semiconductor devices  50 . The frame portion  32  may be immobilized, and the base portion  31  may be moved in an upward direction to further press the molding member  42  against the semiconductor device  50  and the package substrate  60 . A portion (e.g., P 2 ) of the release film  10  on a top surface  324  of the frame portion  32  may be in contact with the first surface  602  of the package substrate  60 . 
     The release film  10  may be stretched and/or deformed during this process. The stretching and/or deformation of the release film  10  may occur most actively near a portion P 1 , where the inner bottom surface  312  of the mold  30  is connected to the inner side surface  322  of the mold  30 . 
     Referring to  FIG.  8   , as a result of the stretching of the release film  10 , the conductive polymer substrate layer  11  may have one or more portions  11 N, which are exposed from the release layers  12 , as shown in  FIGS.  3  and  4   . 
     As an example, the exposed portion  11 N of the conductive polymer substrate layer  11  may be formed on the first surface  11   a  to be in contact with the molding member  42  and may be formed on the second surface  11   b  to be in contact with the base portion  31  and/or the frame portion  32 . In some examples, the exposed portion  11 N may correspond to an area of greatest deformation in the release film  10 . 
     Referring to  FIG.  9   , a molding structure  43  may be formed by hardening the molding member  42  of  FIG.  8   . The package substrate  60 , the semiconductor devices  50 , and the molding structure  43  may form a package structure  80 . Thereafter, the package structure  80  may be detached from the release film  10 . 
     In the case where a separation process is performed to detach layers, which are formed of different kinds of materials and are in contact with each other, from each other, an electrostatic phenomenon may occur. In a comparative example, where a single film, which is made of fluorine compound, has been used as the release film. According to the known triboelectric series, the fluorine-compound-based single release film is negatively charged with ease, while positively charging an object which is in contact with the same, during the detaching process, and thus, it may easily cause an electrostatic phenomenon. For example, the use of the fluorine-compound-based release film may lead to an electrostatic discharging issue and the consequent failure of the semiconductor device. 
     According to some example embodiments of the inventive concepts, in the case where the release film  10  is stretched, the conductive polymer substrate layer  11  may be exposed to the outside of the release layer  12 . The exposed portion  11 N of the conductive polymer substrate layer  11  may be in contact with the molding structure  43  and the mold  30 . In these cases, during the process of detaching the release layer  12  from the molding structure  43 , electric charges may be discharged to the mold  30  through the conductive polymer substrate layer  11 , and thus, it may be possible to lower a discharging voltage and/or to suppress the electrostatic discharging phenomenon. 
     Since the conductive polymer substrate layer  11  is provided to have a porous woven or non-woven fabric structure, it may have elongation that is suitable for the release film. As an example, the conductive polymer substrate layer  11  may not be torn or cut by the release film stretching process, which is performed for the vacuum suction, the motion of the base portion, and/or the separation of the package structure. 
     In addition, the release layer  12  may include a material that can be easily detached from the molding structure  43 , may have a contact area that is larger than that of the conductive polymer substrate layer  11 , and/or may have a sufficiently small thickness, compared with the conductive polymer substrate layer  11 , and thus, the conductive polymer substrate layer  11  may be exposed to the outside of the release layer  12  by the stretching process. 
     Referring to  FIG.  10   , a sawing process of cutting the package structure  80  along a sawing line SL may be performed to form a plurality of semiconductor packages  100 . 
     Hereinafter, some features in the inventive concepts and the consequent effects will be described in more detail by comparing some example embodiments of the inventive concepts with comparative examples. However, the following example embodiments will be given to describe the inventive concepts more specifically, and the example embodiments are not limited to these examples. 
     Example Embodiment 1 
     A substrate layer including a spun bond non-woven fabric of polyethylene terephthalate (PET) was prepared. Top and bottom surfaces of the substrate layer were coated with conductive polymer (PEDOT:PSS) using a spray coating process. Thereafter, the substrate layer was dipped into solution containing fluorine-containing composite (AGC&#39;s CYTOP™ Type S). Next, the substrate layer was taken out of the solution and was hardened. 
     Example Embodiment 2 
     A substrate layer was prepared in the same manner as the example embodiment 1, except for that the spun bond non-woven fabric was prepared to have a thickness lager than that in the example embodiment 1. 
     Comparative Example 1 
     A substrate layer was prepared to include an ethylene tetrafluoroethylene (ETFE) film, instead of the spun bond non-woven fabric. Thereafter, any additional process is not performed. 
     Comparative Example 2 
     A substrate layer was prepared to include a polyethylene terephthalate (PET) film (TACS&#39;s TS-502S), instead of the spun bond non-woven fabric. Top and bottom surfaces of the substrate layer were not coated with a conductive polymer. The subsequent process was performed in the same manner as the example embodiment 1. 
     Experimental Example 
     1. Measurement of Density of Substrate Layer 
     In the example embodiments 1 and 2 and the comparative example 2, after the spray coating step of the conductive polymer, the substrate layer was cut to form a sample having an area of 5 cm×5 cm. A weight of the cut sample was measured, and a density of the sample was calculated by dividing the weight by a volume of the sample. In the comparative example 1, the density was measured in the same manner 
     2. Measurement of Elongation of Substrate Layer 
     In the example embodiments 1 and 2 and the comparative example 2, after the spray coating step of the conductive polymer, the substrate layer was cut to form a sample having a size of 2.5 cm×10 cm. Elongation of the cut sample was measured through a process of stretching the sample until it is torn. In the comparative example 1, the elongation was measured in the same manner 
     3. Measurement of Weight Ratio of Release Layer 
     In the example embodiments 1 and 2 and the comparative example 2, a mass of the substrate layer was measured before and after the solution dipping coating step. A weight ratio of the release layer was calculated by dividing a value, which was obtained by subtracting the mass of the substrate layer before the dip coating step from the mass after the dip coating step, by the mass of the substrate layer before the dip coating step. 
     4. Measurement of Thickness of Release Layer 
     In the example embodiments 1 and 2 and the comparative example 2, a thickness of the substrate layer was measured before the solution dipping coating step and after the solution dipping coating step. 
     5. Measurement of Sheet Resistance of Release Film 
     Sheet resistances in the example embodiments 1, and 2, and comparative examples 1 and 2 were measured by applying a voltage of 100V for 10 seconds using a sheet resistance measuring apparatus (e.g., MCA-HT800 Nittoseiko analytech). 
     6. Measurement of Failure Rate after Semiconductor Package Molding Process 
     An ESD failure rate (parts per million (ppm)) was measured on 10000 package samples, which were fabricated according to the example embodiments 1, and 2, and comparative example 1 and 2, using a DC test apparatus. 
     
       
         
           
               
               
               
               
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                   
                   
                   
                   
                 Sheet 
                   
               
               
                   
                   
                   
                   
                 Thickness 
                 resistance 
                 Failure 
               
               
                   
                   
                   
                   
                 (μm) of 
                 (Ω/sq) of 
                 rate (ppm) 
               
               
                   
                 Density 
                 Elongation 
                 Weight 
                 release 
                 release 
                 after 
               
               
                   
                 (g/cm 3 ) of 
                 (%) of 
                 ratio (%) 
                 layer (B/A 
                 film after 
                 package 
               
               
                   
                 substrate 
                 substrate 
                 of release 
                 solution 
                 molding 
                 molding 
               
               
                   
                 layer 
                 layer 
                 layer 
                 coating) 
                 process 
                 process 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
            
               
                 Embodiment 1 
                 0.2 
                 100 
                 10 
                 50/52 
                 10 9   
                 0 
               
               
                 Embodiment 2 
                 0.2 
                 100 
                 10 
                 100/103 
                 10 9   
                 0 
               
               
                 Comparative 
                 1.4 
                 300 
                 100 
                 65/65 
                 very high 
                 400 
               
               
                 example 1 
                   
                   
                   
                   
                 (over) 
               
               
                 Comparative 
                 1.1 
                 10 
                 10 
                 50/53 
                 very high 
                 &gt;400 
               
               
                 example 2 
                   
                   
                   
                   
                 (over) 
               
               
                   
               
            
           
         
       
     
     As shown in Table 1, although the substrate layer of the same material (e.g., PET) were prepared in the example embodiments 1 and 2 and the comparative example 2, the densities in the example embodiments 1 and 2 were smaller than that in the comparative example 2, and the elongation values were greater in the example embodiments 1 and 2 than in the comparative example 2. This shows that the samples in the example embodiments 1 and 2 (e.g., composed of the porous non-woven fabric) can have a relatively small density and a good stretching property. In the example embodiments 1 and 2, the release layer formed on the substrate layer had about 10% of a total weight and had a thickness of 2 μm to 3 μm. Table 1 also shows that the sheet resistance was smaller in the example embodiments 1 and 2 than in the comparative examples 1 and 2. This shows that, by using the thin release layer and the conductive polymer substrate layer, it may be possible to reduce the sheet resistance. 
     Table 1 shows that a failure rate measured after the semiconductor package molding process was smaller in the example embodiments 1 and 2 than in the comparative examples 1 and 2. This shows that the electrostatic discharging issue was reduced in the process of detaching a package structure from a mold. 
     According to some example embodiments of the inventive concepts, a release film may include a conductive polymer substrate layer and release layers provided on top and bottom surfaces thereof. In the case where the release film is stretched, the conductive polymer substrate layer may be exposed through the release layer, and such an exposed portion may be in contact with a molding material and a metal mold. When the release layer is detached from the molding material, electric charges may be discharged to the metal mold through the conductive polymer substrate layer. Accordingly, it may be possible to suppress a static electricity issue. 
     While some example embodiments of the inventive concepts have been particularly shown and described, it will be understood by one of ordinary skill in the art that variations in form and detail may be made therein without departing from the spirit and scope of the attached claims.