Abstract:
A resin sealing method for sealing a gap between a substrate and a semiconductor chip mounted thereon includes the following steps: applying a predetermined amount of resin at and along the circumference of the semiconductor chip in such a manner so as to maintain a space between the resin and a side face of the semiconductor chip; reducing the pressure of the atmosphere around the substrate to exhaust air from the gap; reducing the viscosity of the applied resin to partially fill the gap with resin, thereby leaving a closed cavity reduced in pressure; pressurizing the atmosphere around the substrate to compress the closed cavity due to the pressure difference from the surrounding atmosphere to entirely fill the gap with resin. The exhausting of the air is very stable, and a concentration of resin at the corner of the semiconductor chip can be suppressed, thereby avoiding the spattering of resin onto the top of the chip.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a resin sealing method and apparatus of effecting resin sealing after the pad of a semiconductor chip mounted on a substrate is joined to the electrode of the substrate through a bump. Particularly, the present invention relates to a resin sealing method and apparatus filling the gap between a semiconductor chip and a substrate with resin. 
     2. Description of the Background Art 
     In a semiconductor device having the pad of the semiconductor chip and the electrode of the substrate electrically connected via a bump, resin is inserted or filled into the gap between the semiconductor chip and the substrate and is then cured. This resin sealing is carried out in order to prevent generation of cracks at the junction due to thermal stress, and intrusion of a substance that adversely affects the semiconductor chip such as intrusion of impurities and moisture. 
     Conventionally, the method shown in FIGS. 5A-5D is employed in order to insert and cure resin in the gap between a semiconductor chip and a substrate. FIGS. 5A-5D are plan views of a semiconductor device corresponding to respective steps of a conventional resin sealing method. 
     Referring to FIG. 5A, liquid resin  102  is applied around a semiconductor chip  101  mounted on a substrate  100  so as to substantially surround the circumference thereof. A portion of the circumference of semiconductor chip  101  that is to serve as an outlet  103  is left absent of liquid resin  102 . 
     Referring to FIG. 5B, the atmosphere around substrate  100  is reduced in pressure. Accordingly, the air present between substrate  100  and semiconductor chip  101  is output from outlet  103  as exhaust  104 . 
     Referring to FIG. 5C, the viscosity of the applied liquid resin  102  is reduced by applying heat under the state where the atmosphere around substrate  100  is reduced in pressure. As a result, liquid resin  102  reduced in viscosity flows into the gap between substrate  100  and semiconductor chip  100  by the capillary action to be connected at the portion absent of the resin to become annular. Thus, the gap between substrate  100  and semiconductor chip  101  is filled with liquid resin  102  leaving a closed cavity  105  that is reduced in pressure. 
     Referring to FIG. 5D, the atmosphere around substrate.  100  is pressurized up to the atmospheric pressure. Under atmospheric pressure, closed cavity  105  in the gap between substrate  100  and semiconductor chip  101  is compressed by the pressure difference from the surrounding space to be eliminated. In other words, the entire region of the gap between substrate  100  and semiconductor chip  100  is filled with liquid resin  102 . Then, heating is applied to cure liquid resin  102 . By the foregoing steps, cured seal resin is formed at the gap between substrate  100  and semiconductor chip  100 , and also at the circumference of semiconductor chip  101 . 
     The conventional resin sealing method poses the following problems shown in FIGS. 6A-6D. FIGS. 6A-6D are plan views of a semiconductor device corresponding to respective steps of a conventional resin sealing method representing the problems. Referring to FIG. 6A, liquid resin  102  is applied on substrate  100 , likewise FIG.  5 A. In reducing the pressure of the atmosphere around substrate  100 , there is the case where abnormal exhaust  106  penetrates through liquid resin  102  to be output from a region other than outlet  103  due to uneven application of liquid resin  102 , as shown in FIG.  6 B. Also, in pressurizing the atmosphere around substrate  100 , there is the case where liquid resin  102  compressed towards closed cavity  105  by the pressure difference from the surrounding space is partially concentrated at the corner of semiconductor chip  101  to rise over the top surface of semiconductor chip  101 . There is also the case where abnormal exhaust  106  is output from substantially the entire circumference of semiconductor chip  101  when the area of the cross section of outlet  103  is not large enough. 
     In the foregoing cases, a portion of liquid resin  102  will be blown off by the abnormal exhaust  106  to adhere on the top surface of semiconductor chip  101  as shown in FIG.  6 C. The adhered liquid resin  102  will remain on the top surface of semiconductor substrate  101  as resin covering  107 . This resin covering  107  is cured by the heating process as shown in FIG. 6D to cause appearance defect in the completed semiconductor device to degrade the yield. 
     SUMMARY OF THE INVENTION 
     In view of the foregoing, an object of the present invention is to provide a resin sealing method and apparatus to improve the yield by preventing generation of a resin covering in filling the gap between a substrate and a semiconductor chip with resin. 
     According to an aspect of the present invention, a resin sealing method achieving the above object has resin inserted and cured in the gap formed between a substrate and a semiconductor chip mounted on the substrate. The resin sealing method includes the steps of applying resin of a predetermined amount, which is set corresponding to the circumferential configuration of the semiconductor chip, at or along the circumference of the semiconductor chip under a state retaining a predetermined void or space between the resin and a side face of the semiconductor chip, reducing the pressure of the atmosphere around the substrate to exhaust air from the gap, reducing the viscosity of the applied resin to partially fill the gap with resin and thereby leaving a closed cavity reduced in pressure, and pressurizing the atmosphere around the substrate to compress the closed cavity from the surrounding atmosphere due to the pressure difference therebetween to entirely fill the gap with resin. 
     According to this resin sealing method, resin of a predetermined amount is applied at or along the circumference of the semiconductor chip in such a manner so as to retain a void or space between the resin and the side face of the semiconductor chip. Accordingly, a region absent of resin is formed surrounding the semiconductor chip at the substrate plane. By reducing the pressure of the atmosphere around the substrate, the air present between the substrate and the semiconductor chip is exhausted through the region where resin is not applied, i.e. through the gap or space formed between the resin applied at the circumferential position of the semiconductor chip and the side face of the semiconductor chip. Since this resin-free space forms a region where air can be exhausted having a large area of cross, section at the circumference of the semiconductor chip, exhaust can be effected stably. 
     At the corner of the semiconductor chip, the amount of resin to be applied is reduced or a region absent of applying resin is provided. As a result, exhaust can be effected in stability at the corner region where exhaust is concentrated so that the exhaust pressure is increased. Thus, there is the advantage superior in practical usage of providing a resin sealing method and apparatus that can prevent generation of a resin covering caused by abnormal exhaust and resin concentration. 
     In the above resin sealing method, the step of applying resin preferably has the amount of resin applied at the circumferential position of the site where the circumferential configuration of the semiconductor chip corresponds to a corner set lower than the amount of resin applied at the circumferential position of other sites of the semiconductor chip. 
     In a preferable embodiment of the resin sealing method of the present invention, the step of applying resin includes the step of applying resin of a predetermined amount at the circumferential position of the semiconductor chip excluding the site where the circumferential configuration of the semiconductor chip corresponds to a corner. 
     According to another aspect of the present invention, a resin sealing method of inserting and curing resin in a gap formed between a substrate and a semiconductor chip mounted on the substrate includes the steps of applying resin of a predetermined amount, which is set corresponding to the circumferential configuration of the semiconductor chip, at or along the circumference of the semiconductor chip in contact with a portion of the side face of the semiconductor chip at one region and retaining a predetermined void or space between the resin and another region of the side face, reducing the pressure of the atmosphere around the substrate to exhaust air from the gap, reducing the viscosity of the applied resin to partially fill the gap with resin and thereby leaving a closed cavity reduced in pressure, and pressurizing the atmosphere around the substrate to compress the closed cavity from the surrounding atmosphere due to the pressure difference therebetween to entirely fill the gap with resin. 
     In a preferable embodiment of the resin sealing method of the present invention, the step of exhausting includes the step of reducing the pressure of the atmosphere around the substrate from the atmospheric pressure down to a predetermined pressure over a predetermined period of time. 
     The resin sealing apparatus of the present invention fills a gap formed between a substrate and a semiconductor chip mounted on the substrate with resin. The resin sealing apparatus includes an application unit applying resin of a predetermined amount, which is set corresponding to the circumferential configuration of the semiconductor chip, at the circumference of the semiconductor chip in a manner retaining a predetermined void or space between the resin and the side face of the semiconductor chip, a pressure reduction unit to reduce the pressure of the atmosphere around the substrate to exhaust air from the gap, a viscosity reduction unit reducing the viscosity of the applied resin to partially fill the gap with resin leaving a closed cavity reduced in pressure, and a pressurization unit pressurizing the atmosphere around the substrate to compress the closed cavity from the surrounding atmosphere due to the pressure difference therebetween to entirely fill the gap with resin. 
     According to this resin sealing apparatus, resin of a predetermined amount is applied at the circumferential position of the semiconductor chip under a state retaining a void or space relative to the side face of the semiconductor chip. Accordingly, a region absent of resin is formed at the substrate plane, surrounding the circumference of the semiconductor chip. When the atmosphere around the substrate is reduced in pressure, the air present in the gap between the substrate and the semiconductor chip is exhausted through the region where resin is not applied, i.e. through the space formed between the resin applied at the circumferential position of the semiconductor chip and the side face of the semiconductor chip. Since the region from which air is exhausted is formed to have a large area of cross section at the circumference of the semiconductor chip, exhaust can be effected stably. 
     In a preferable embodiment of the resin sealing apparatus of the present invention, the atmosphere around the substrate is reduced in pressure from the atmospheric pressure down to a predetermined pressure over a predetermined period of time by the pressure reduction unit of the resin sealing apparatus. 
     The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a sectional view of a semiconductor device fabricated according to a resin sealing method and resin sealing apparatus of the present invention. 
     FIG. 2A is a plan view of a semiconductor device during a fabrication step employing the resin sealing method of the present invention; FIG. 2B is a sectional view taken along line II B -II B  of FIG. 2A; and FIGS. 2C and 2D are sectional views of the semiconductor device at respective fabrication steps. 
     FIGS. 3A and 3B are plan views of a semiconductor device during a fabrication step employing a modification of the resin sealing method of the present invention. 
     FIG. 4 is a diagram to describe the relationship between exhaust time t and air pressure P as to exhaust in the resin sealing method of the present invention. 
     FIGS. 5A-5D are plan views of a semiconductor device at respective steps corresponding to a conventional resin sealing method. 
     FIGS. 6A-6D are plan views of a semiconductor device at respective steps indicating problems encountered in the conventional resin sealing method. 
     FIG. 7 schematically shows a structure of a resin sealing apparatus of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Embodiments of the present invention will be described hereinafter with reference to the drawings. 
     The semiconductor device of FIG. 1 includes a semiconductor chip  1  where semiconductor elements are formed, a pad  2  which is an electrode of semiconductor chip  1 , a substrate  3  formed of, for example ceramic or organic material, an electrode  4 A for connection with substrate  3 , an external electrode  4 B of substrate  3 , a bump  5  formed of solder, for example, and resin  6  covering at least a portion of the side face of semiconductor chip  1  and filled in the gap between semiconductor chip  1  and substrate  3 . 
     As shown in FIG. 1, pad  2  of semiconductor chip  1  and electrode  4 A of substrate  3  are electrically connected by bump  5 . A gap of 20-200 μm, for example, is formed between semiconductor chip  1  and substrate  3 . This gap is filled with resin  6  such as epoxy resin which is then cured. This resin  6  covers pad  2 , connection electrode  4 A and bump  5  to prevent exposure thereof, and allows semiconductor chip  1  and substrate  3  to be fixed so as to absorb any difference in thermal stress therebetween. 
     An embodiment of the resin sealing method of the present invention will be described with reference to FIGS. 2A-2D. 
     Respective steps carried out in fabricating the semiconductor device of FIG. 1 before the resin sealing method of the present invention is employed will be first described. Bump  5  formed of solder, for example, is provided on pad  2  of semiconductor chip  1 . Semiconductor chip  1  is turned over, and positioning of pad  2  and connection electrode  4 A of substrate  3  is effected. Then, substrate  3  is mounted with semiconductor chip  1 . Bump  5  is heated to melt, whereby pad  2  of semiconductor chip  1  is electrically connected to connection electrode  4 A of substrate  3 . 
     According to the resin sealing method of the present invention, resin  6  is to be inserted or filled into the gap between semiconductor chip  1  and substrate  3  and is thereafter to be cured. As shown in FIGS. 2A and 2B, liquid resin  6  such as epoxy resin is applied to completely surround the circumference of semiconductor chip  1  with an exposed portion or predetermined space  7  above substrate  3 , between the resin  6  and the side face  1 A of the chip  1 . In other words, resin  6  is applied at the circumferential position of semiconductor chip  1  with a predetermined void or space  7  relative to the side face of semiconductor chip  1 . 
     Then, the atmosphere around substrate  3  is reduced in pressure. Accordingly, the air present in gap  8  between the semiconductor chip  1  and substrate  3  is discharged as exhaust  9  passing above exposed portion  7 , i.e. out through the predetermined space surrounding semiconductor chip  1 . 
     As shown in FIG. 2C, viscosity of the applied liquid resin  6  is reduced by applying heat, for example, under the state where the atmosphere around substrate  3  is reduced in pressure. Accordingly, resin  6  reduced in viscosity comes into contact with the side face and bottom face of semiconductor chip  1 , and further intrudes into gap  8  between substrate  3  and semiconductor chip  1  by the capillary action. Thus, gap  18  is filled with liquid resin  6  leaving a closed cavity  10  reduced in pressure. 
     As shown in FIG. 2D, the atmosphere around substrate  3  is pressurized to a predetermined pressure, for example, to the atmospheric pressure. Accordingly, closed cavity  10  reduced in pressure in gap  8  between substrate  3  and semiconductor chip  1  is compressed by the pressure difference from the ambient air to be eliminated under atmospheric pressure. As a result, gap  8  is completely filled with resin  6 . Then, a heating step is applied to cure liquid resin  6 . By the foregoing steps, cured seal resin is formed at gap  8  between substrate  3  and semiconductor chip; and also at the circumference of semiconductor chip  1 . Pressurization of the atmosphere around substrate  3  can be effected by using, for example, a valve provided in the exhaust path and releasing the atmosphere to the open air. 
     According to the resin sealing method of the present embodiment, liquid resin is applied with an exposed portion  7  provided above substrate  3  completely surrounding semiconductor chip  1 . When the atmosphere around substrate  3  is to be reduced in pressure, the air present in gap  8  between semiconductor chip  1  and substrate  3  is discharged as exhaust  9  passing above exposed portion  7  completely surrounding semiconductor chip  1 . By providing an exhaust path of exhaust  9  surrounding semiconductor chip  1  and having a large area of cross section of the exhaust path, exhaust  9  can be discharged in stability. Thus, generation of a resin covering can be prevented. 
     The modifications shown in FIGS. 3A and 3B aim for stabilizing exhaust at the lower area of each corner of semiconductor chip  1 , i.e. below the four corners when viewed in plane, in discharging the air present at the gap between semiconductor chip  1  and substrate  3 . 
     According to the modification of the resin sealing method of the present invention shown in FIG. 3A, liquid resin  6  is applied completely surrounding semiconductor chip  1  with exposed portion  7  provided above substrate  3 , as in the above-described embodiment. A particular region  11  is provided in the proximity of each corner of semiconductor chip  1  where the amount of resin applied is less than that of other regions. 
     According to another modification of the resin sealing method of the present invention shown in FIG. 3B, resin  6  is applied to surround semiconductor chip  1  with exposed portion  7  above substrate  3 . Furthermore, a particular region  12  absent of resin  6  is provided in the proximity of each corner of semiconductor chip  1 . 
     According to the above two modifications, resin  6  compressed towards the closed cavity due to pressure difference from the ambient space during pressurization of the atmosphere around substrate  3  will not be concentrated at the corner of semiconductor chip  1 , i.e. not blocked in flow. As a result, rise of resin  6  over the top surface of semiconductor chip  1  at the corner of semiconductor chip  1  is suppressed. The air present in the gap between semiconductor chip  1  and substrate  3  can be exhausted in stability from the entire circumference of semiconductor chip  1 , as in the above embodiment. Also, the rise of resin  6  at the corner of semiconductor chip  1  can be suppressed when the atmosphere around substrate  3  is pressurized. Thus, generation of a resin covering can be reliably prevented. 
     Referring to FIG. 4, Patm is the atmospheric pressure and takes the value of 900-1060 hPa whereas the achievable pressure PL is the pressure around the substrate after the pressure-reduction step. As shown in FIG. 4, the atmosphere around the substrate is gradually reduced to achievable pressure PL over a period of time in order to prevent generation of a resin covering. With achievable pressure PL set to 20 Pa, for example, the pressure is reduced from atmospheric pressure Patm down to achievable pressure PL (=20 Pa) over a period of 5 seconds starting from pressure-reduction start time T 1  to pressure-reduction end time T 3 . In order to reliably prevent generation of a resin covering, the pressure is reduced from atmospheric pressure Patm down to achievable pressure PL (=20 Pa) over a period of 7-10 seconds, for example. The resin is then heated to have the viscosity reduced under the pressure-reduced state. Then, pressure is applied up to a predetermined pressure, for example, up to atmospheric pressure Patm. 
     The pressure can be reduced gradually from pressure-reduction start time T 1  to a predetermined time T 2 , and then the pressure can be reduced rapidly from time T 2  to pressure-reduction end time T 3 , as shown in FIG.  4 . Furthermore, the pressure can be reduced continuously as shown by the broken line in FIG.  4 . Since exhaust is gradually effected from the high pressure state to lower the pressure, followed by rapid exhaust, the discharge operation can be effected more stably to reliably prevent generation of a resin covering. 
     Resin covering can be reliably prevented by the combination of the exhaust of FIG. 4 with the application of resin shown in FIGS. 2A-3B. 
     The resin sealing apparatus of the present invention will be described with reference to FIG.  7 . The resin sealing apparatus includes a stage on which is arranged a carrying body such as a tray  21  which carries thereon the substrate  3  with the semiconductor chip  1  attached thereon, a syringe (not shown) storing liquid resin, a dispenser nozzle  23  to emit resin by air pressure or the like, a heating stage  24  for heating the substrate  3 , a mechanism (not shown) for moving the tray  21  for supplying the substrate  3  having the resin applied thereon, to the heating stage  24  and taking out the substrate  3  from the heating stage  24 , a hermetic vessel  25  to seal up the substrate  3  supplied to the heating stage  24 , tubes  26   a,    26   b  adapted for pressuring or reducing pressure from the interior of hermetic vessel  25 , flow rate adjust valves  28   a,    28   b  provided respectively in the passage of tubes  26   a,    26   b,  and a vacuum pump  29  functioning through tube  26   a.    
     One end of tube  26   b  is opened to the atmosphere and the inner pressure of hermetic vessel  25  is returned to the atmospheric pressure by opening flow rate adjust valve  28   b.  Dispenser nozzle  23  is mounted to a XYZ robot  27  together with a camera  31  for image recognition used for adjusting the positional relation between the tip of the dispenser nozzle  23  and the substrate  3 . Vacuum pump  29  reduces the pressure of the interior of the hermetic vessel  25 . Compressor  30  is optionally connected to the tube  26   b  for pressurizing the interior of hermetic vessel  25 . 
     Using this resin sealing apparatus, resin is emitted from the dispenser nozzle  23  at an appropriate timing while moving the dispenser nozzle  23  by means of the XYZ robot  27 . Accordingly, liquid resin is applied on the substrate  3  as shown in FIGS. 2A-3B. After a shutter  32  attached to hermetic vessel  25  is opened, the carrying body  21  with the substrate  3  having the resin applied thereto being carried thereon, is introduced into hermetic vessel  25  along guide rails  30   a,    30   b  through the mechanism for supplying substrate  3 . Then, shutter  32  is closed and exhaust shown in FIG. 4 is effected by means of the flow rate adjust valve  28   a  and the vacuum pump  29 . The resin is heated by the heating stage  24  through the substrate  3 , whereby the viscosity of the resin is reduced. 
     The interior of hermetic vessel  25  is pressurized to a predetermined pressure, for example the atmospheric pressure, by means of flow rate adjust valve  28   b.  Then, resin is further heated by heating stage  24  to be cured. By the foregoing operation, the semiconductor device shown in FIG. 1 can be fabricated using the resin sealing apparatus of the present invention. 
     The resin sealing apparatus of the present invention is not limited to the above-described structure. The usage of flow rate adjust valve  28   a,   28   b  and vacuum pump  29  in reducing or applying pressure is only a way of example. Also, other heating means such as an infrared lamp can be used instead of heating stage  24 . 
     The embodiments are described in which epoxy resin is used as resin. However, thermosetting resin such as silicone resin, vinyl polymerization resin, phenol resin, unsaturated polyester resin, diallyl phthalate resin, or super engineering plastic such as PPS and aromatic polyamide, general-purpose engineering plastic such as nylon resin and ultrahigh molecular weight polyethylene, or thermal plastic resin such as thermoplastic elastomer using olefin or amide can be also used. 
     The bump is not limited to that formed of solder, and may be formed of Au, Ag/Sn and the like, or another conductive material such as conductive resin. 
     Although exposed portion  7  is provided completely surrounding the circumference of semiconductor chip  1  in the above embodiments, resin can be applied to come into contact with a portion of the side face of semiconductor chip  1  as long as a resin covering is not generated. Accordingly, resin can flow smoothly downwards of semiconductor chip  1  from the region in contact with the side face of semiconductor chip  1  under the state where the viscosity of resin is reduced. 
     As to the predetermined pressure, pressure is reduced down to 20 Pa and pressurized up to the atmospheric pressure in the above embodiments. However, the pressure can be reduced to less than 20 Pa or higher than 20 Pa. Also, the pressure can be increased up to below the atmospheric pressure or higher than the atmospheric pressure. 
     Although the present invention has been described and illustrated in detail, it is clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation, the spirit and scope of the present invention being limited only by the terms of the appended claims.