Abstract:
A mold includes a pot for accommodating resin, a cavity for accommodating a semiconductor chip to be resin-molded and a runner as a resin passage for transporting the resin accommodated in the pot to the cavity. A foreign matter retention pocket is disposed which is a recess formed by digging further a partial inner surface of the runner. A runner magnet attracts and attaches a metallic foreign matter contained in fluid transported in the runner to the inner surface of the foreign matter retention pocket.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application is based on and claims priority of Japanese Patent Application No. 2006-094703 filed on Mar. 30, 2006, the entire contents of which are incorporated herein by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    A) Field of the Invention 
         [0003]    The present invention relates to a mold for resin molding, a resin molding apparatus and a semiconductor device manufacture method, and more particularly to a mold and a resin molding apparatus for resin-molding a semiconductor element, and a semiconductor device manufacture method. 
         [0004]    B) Description of the Related Art 
         [0005]    There are many types of semiconductor packages, such as a quad flat package (QFP) type using a metal lead frame, a small outline package (SOP) type, a ball grid array (BGA) type using a printed circuit board, a system in package (SIP) type electrically connecting semiconductor elements (semiconductor chips). 
         [0006]    These semiconductor packages are generally molded with thermosetting resin after lead wires are connected, in order to improve impact resistance, contamination resistance and the like. 
         [0007]    As molding resin, main resin agent such as epoxy resin is used which contains curing agent, filler such as melted silica, catalyst, coloring agent and fire retarding agent, at a proper mixture ratio considering a package shape, heat resistance, molding property and the like. 
         [0008]    If metallic foreign matters are contained in molding resin, these metallic foreign matters may contact bonding wires, with which a semiconductor chip and a lead frame are connected, to short-circuit bonding wires. 
         [0009]    JP-B-HEI-6-53369 discloses the technique of burying a magnet in a mold for resin molding and making the magnet attract metallic foreign matters mixed in resin to remove them. JP-A-2002-313824 discloses the technique of supplying liquid resin on a substrate and disposing a magnet above the substrate to attract foreign matters mixed in the liquid resin. 
       SUMMARY OF THE INVENTION 
       [0010]    From the viewpoint of environment conservation, bonding material not containing lead such as Sn—Ag—Cu based paste is widely used in recent years in place of conventional solder which contains lead. Many bonding materials not containing lead have a higher melting point than that of bonding material containing lead. High heat resistance of a semiconductor package is therefore desired. 
         [0011]    One solving method for this is a method of raising a heat resistance temperature of thermosetting resin. Specifically, the amount of filler contained in resin is increased so that molding resin can be manufactured which has a low moisture absorption ratio, a high elastic modulus and a low thermal expansion coefficient. However, as the amount of filler is increased, metallic foreign matters such as chips of a metallic grinder blade are likely to be mixed in resin during a process of pulverizing the resin. Although metallic foreign matters in resin are removed by using a magnet during a resin manufacture process, it is difficult to remove all metallic foreign matters. 
         [0012]    Recent requirements for high functionality and high integration of semiconductor elements (semiconductor chips) are increasing further, and a pitch (pad pitch) between electrode pads is becoming narrower. Mass production is now under operation for semiconductor chips having a pad pitch of, e.g., 50 μm or narrower. 
         [0013]    As the pad pitch becomes narrower, a diameter of a bonding wire or a size of a solder bump becomes smaller correspondingly. 
         [0014]    As the pad pitch becomes narrow, metallic foreign matters contained in molding resin are likely to contact conductive members such as bonding wires and solder bumps, resulting in electric short circuits. A semiconductor device particularly of a SIP type requiring high functionality has an increased number of electric connection points more than a conventional semiconductor device, resulting in a large possibility of an electric short circuit. 
         [0015]    Conventionally proposed methods of removing metallic foreign matters mixed in molding resin are insufficient to remove the metallic foreign matters. Resin molding techniques have been desired which suppress electric short circuits to be caused by metallic foreign matters. 
         [0016]    An object of the present invention is to provide resin molding techniques capable of suppressing electric short circuits to be caused by metallic foreign matters mixed in molding resin. 
         [0017]    According to one aspect of the present invention, there is provided a mold for resin molding comprising: 
         [0018]    a mold comprising a pot for accommodating resin, a cavity for accommodating a semiconductor chip to be resin-molded and a runner as a resin passage for transporting the resin accommodated in the pot to the cavity; 
         [0019]    a foreign matter retention pocket consisting of a recess formed by digging further a partial inner surface of the runner; and 
         [0020]    a runner magnet for attracting and attaching a metallic foreign matter contained in fluid transported through the runner to the inner surface of the foreign matter retention pocket. 
         [0021]    According to another aspect of the present invention, there is provided a resin molding apparatus comprising: 
         [0022]    a platen for placing thereon a mold and heating the mold, the mold comprising a pot for accommodating resin, a cavity for accommodating a semiconductor chip to be resin-molded and a runner as a resin passage for transporting the resin accommodated in the pot to the cavity; 
         [0023]    a plunger for applying a pressure to the resin accommodated in the pot in the state that the mold is placed on the platen to inject the resin into the cavity; and 
         [0024]    a plunger magnet disposed in the plunger for attracting and attaching a metallic foreign matter in liquid resin accommodated in the pot. 
         [0025]    While molding resin is melted in the pot, metallic foreign matters mixed in the resin are attracted to the plunger magnet and attached to the surface of the plunger. Metallic foreign matters are therefore hard to be transported to the cavity. The plunger is used in common for various molding dies so that the magnet is not required to be changed for each mold. 
         [0026]    Further, while the melted molding resin flows in the runner, the metallic foreign matters mixed in the resin are attracted to the runner magnet and attached to the surface of the foreign matter retention pocket to be captured. The metallic foreign matters captured by the foreign matters are hard to be swept away by a flow of the resin in the runner. The metallic foreign matters in the resin can therefore be captured efficiently, and transportation of the metallic foreign matters to the cavity is suppressed considerably. 
         [0027]    Furthermore, while the molding resin is injected into the cavity of the mold, the metallic foreign matters mixed in the resin are attracted to the magnet of the ejector pin and collected to the resin surface near the ejector pin. The metallic foreign matters can therefore be captured efficiently, and existence of the metallic foreign matters near semiconductor elements and bonding wires is suppressed greatly. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0028]      FIG. 1  is a cross sectional view of a resin molding apparatus according to a first embodiment. 
           [0029]      FIG. 2A  is a plan view of a lower mold and  FIG. 2B  is a bottom view of an upper mold of the resin molding apparatus according to the first embodiment. 
           [0030]      FIG. 3A  is a cross sectional view of a runner and a runner magnet disposed in the lower mold of the resin molding apparatus of the first embodiment, this view being perpendicular to the longitudinal direction of the runner,  FIG. 3B  is a cross sectional view showing an example of another structure, and  FIG. 3C  is a cross sectional view of the runner and runner magnet as viewed along the longitudinal direction. 
           [0031]      FIG. 4A  is a cross sectional plan view of a plunger of the resin molding apparatus of the first embodiment, and  FIG. 4B  is a cross sectional plan view showing an example of another structure. 
           [0032]      FIGS. 5 to 8  are cross sectional views of the resin molding apparatus of the first embodiment illustrating a resin molding procedure. 
           [0033]      FIG. 9  is a cross sectional view showing a characteristic portion of a resin molding apparatus according to a second embodiment. 
           [0034]      FIG. 10  is a cross sectional view of a resin molding apparatus according to a third embodiment. 
           [0035]      FIGS. 11A and 11B  are cross sectional views showing characteristic portions of a resin molding apparatus according to a fourth embodiment. 
           [0036]      FIGS. 12A and 12B  are cross sectional views showing an example of another structure of characteristic portions of the resin molding apparatus according to the fourth embodiment. 
           [0037]      FIG. 13A  is a plan view of a lower mold and  FIG. 13B  is a bottom view of an upper mold of a resin molding apparatus according to a fifth embodiment. 
           [0038]      FIG. 14A  is a plan view of a lower mold and  FIG. 14B  is a bottom view of an upper mold of a resin molding apparatus according to a sixth embodiment. 
           [0039]      FIG. 15  is a cross sectional view of a resin molding apparatus according to a seventh embodiment. 
           [0040]      FIG. 16A  is a plan view of a lower mold and  FIG. 16B  is a bottom view of an upper mold of the resin molding apparatus according to the seventh embodiment. 
           [0041]      FIG. 17A  is a plan view of a lower mold and  FIG. 17B  is a bottom view of an upper mold of a resin molding apparatus according to an eighth embodiment. 
           [0042]      FIG. 18A  is a plan view of a lower mold and  FIG. 18B  is a bottom view of an upper mold of a resin molding apparatus according to a ninth embodiment. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0043]    The invention will be described in detail with preferred embodiments. 
       First Embodiment 
       [0044]      FIG. 1  is a partial cross sectional view of a resin molding apparatus and molds according to the first embodiment of the present invention. 
         [0045]    As shown in  FIG. 1 , a lower mold  10  is held by a lower platen  70  and an upper mold  30  is held by an upper platen  71 . 
         [0046]    Surfaces of the lower mold  10  and upper mold  30  facing each other are called “facing surfaces”, and surfaces on the opposite side (planes contacting the platens) are called “back surfaces”. The lower platen  70  and upper platen  71  heat the lower mold  10  and upper mold  30 , respectively. 
         [0047]    A pot  11  is formed through the lower mold  10  from the back surface to the facing surface. A plunger  14  is disposed in the lower platen  70  and can move up and down communicating with the lower mold  10 . The plunger  14  can be moved up and down by a drive mechanism  72 , and as the plunger is moved up, it is inserted into the pot  11  of the lower mold  10 . A recess (cull)  31  is formed in the upper mold  30  in an area facing the pot  11 . 
         [0048]    Recesses (cavities)  19  and  39  are formed in areas facing each other on the facing surfaces of the lower mold  10  and upper mold  30 , respectively. In  FIG. 1 , although the cavities  19  and  39  are shown disposed to the right of the pot  11 , cavities of a similar structure are also disposed to the left of the pot  11 . In the state that a lead frame  50  is squeezed between the lower mold  10  and upper mold  30 , a semiconductor chip  51  mounted on the lead frame  50  is accommodated in a space defined by the cavities  19  and  39 . 
         [0049]    A groove (runner)  12  communicating the cavity  19  with the pot  11  is formed on the facing surface of the lower mold  10 . Molding resin is accommodated in the pot  11  and melted and the plunger  14  is moved up. Resin in the pot  11  passes through the runner  12  and injected into the empty space defined by the cavities  19  and  39 . In this embodiment, a foreign matter retention pocket  13  is formed deeper on the bottom of the runner  12  at a position near the pot  11 . 
         [0050]    An ejector pin  15  is inserted into each of through holes formed through the lower mold  10  from the back surface to a bottom of the cavity  19 . A plurality of ejector pins  15  are disposed with respect to one cavity  19 . A top end of the ejector pin  15  is exposed in the cavity  19 . By protruding the ejector pin  15  into the cavity  19 , resin cured and adhered to the lower mold  10  can be easily released (demolded) from the lower mold  10 . Ejector pins  35  of a similar structure are also disposed in the upper mold  30 . 
         [0051]    In this embodiment, a magnet (hereinafter called a plunger magnet) is disposed on a surface of the plunger  14  facing the pot  11 . The plunger magnet  22  consists of an electromagnet, and exciting current is supplied from a power supply  27 . This electromagnet may be exposed in the pot  11  or may be buried at a position slightly deeper than the surface of the plunger  14 . 
         [0052]    A magnet (hereinafter called a runner magnet)  20  is disposed on the wall surface of the foreign matter retention pocket  13  of the runner  12 . The runner magnet  20  includes, for example, three electromagnets disposed along a longitudinal direction of the foreign matter retention pocket  13 , and exciting current is supplied from a power supply  25  to each electromagnet. Each electromagnet may be exposed on the surface of the foreign matter retention pocket  13  or may be buried at a position slightly deeper than the surface. 
         [0053]    Magnets (hereinafter called ejector pin magnets)  21  and  41  are loaded in the ejector pins  15  of the lower mold  10  and in the ejector pins  35  of the upper mold  30 . Each of the ejector pin magnets  21  and  41  consists of an electromagnet, and exciting current is supplied to the ejector pin magnets  21  and  41  from power supplies  26  and  46 , respectively. 
         [0054]      FIG. 2A  shows a plan shape of the lower mold  10 . A cross section taken along on-dot chain line A 1 -A 1  shown in  FIG. 2A  corresponds to the cross sectional view of  FIG. 1 . 
         [0055]    As shown in  FIG. 2A , six pots  11  are disposed along a vertical direction at an equal pitch. The plan shape of each of the pots  11  is circular. 
         [0056]    The plunger  14  is disposed inside each pot  11 . Cavities  19  are disposed on both sides of each pot  11 . Each cavity  19  has a plan shape obtained by cutting four corners of a square obliquely or in circular arc shape, and the ejector pins  15  are disposed at positions near four corners. 
         [0057]    The runner  12  extends on both sides of the pot  11  along a virtual straight line extending laterally in  FIG. 2A  and passing through the center of each pot  11 . The runner  12  changes its direction intermediately and reaches a position near the corner of the corresponding cavity  19 . The runner  12  becomes narrower and shallower toward the cavity  19 . The foreign matter retention pocket  13  is disposed in a partial area of the runner  12  near the pot  11 . 
         [0058]      FIG. 2B  shows a bottom shape of the upper mold  30 . A cross sectional view taken along one-dot chain line A 1 -A 1  shown in  FIG. 2B  corresponds to the cross sectional view shown in  FIG. 1 . 
         [0059]    As shown in  FIG. 2B , the cull  31  is formed at the position corresponding to the pot  11  of the lower mold  10 . The cull  31  has the same plan shape as that of the pod  11 . 
         [0060]    The cavity  39  is disposed at the position corresponding to the cavity  19  of the lower mold  10 . The cavity  39  has the same plan shape as that of the cavity  19  formed on the lower mold  10 . The ejector pins  35  are disposed at positions near four corners of the cavity  39 . 
         [0061]      FIG. 3A  shows a cross section perpendicular to the longitudinal direction of the foreign matter retention pocket  13  shown in  FIG. 1 . 
         [0062]    The runner  12  is formed on the facing surface of the lower mold  10 , and the bottom is dug deeper to form the foreign matter retention pocket  13 . The runner magnet  20  is buried at the position deeper than the bottom of the foreign matter retention pocket  13 . The runner magnets  20  are buried on both sides of the runner  12 . As shown in  FIG. 3B , the runner magnet  20  may have a U-character cross sectional shape extending along the surface of the runner  12  and foreign matter retention pocket  13 . 
         [0063]      FIG. 3C  shows another example of the structure of the runner magnet  20 . 
         [0064]    In the structure shown in  FIG. 1 , the runner magnet  20  includes three electromagnets disposed along the longitudinal direction of the foreign matter retention pocket  13 . As shown in  FIG. 3C , the runner magnet may be one long electromagnet extending along the longitudinal direction of the foreign matter retention pocket  13 . 
         [0065]      FIG. 4A  shows a cross sectional plan view of the plunger  14 . 
         [0066]    The plunger magnet  22  is disposed in the plunger  14  having a circular plan shape. The plunger magnet  22  has a circular plan shape having an outer circumferential line at a position slightly inside the outer circumference of the plunger  14 . 
         [0067]      FIG. 4B  shows an example of the other structure of the plunger magnet  22 . The plunger magnet  22  shown in  FIG. 4B  has a shape that a cylindrical member having the central axis shared by the plunger  14  is cut by a plurality of virtual flat planes passing through the central axis. The cylindrical member is divided in eight-fold rotation symmetry with respect to the central axis. 
         [0068]    Next, with reference to  FIGS. 5 to 8 , description will be made on a resin molding method using the resin molding apparatus of the first embodiment. 
         [0069]    As shown in  FIG. 5 , in the state that the distance between the lower mold  10  and upper mold  30  is elongated, the lead frame  50  mounting the semiconductor chip  51  as a molding target is placed on the facing surface of the lower mold  10 . Electrodes of the semiconductor chip  51  are connected to corresponding lead portions by bonding wires  52 . 
         [0070]    A solid piece  60  of molding resin is loaded in the pot  11 . At this stage, the power supply  25  for the runner magnet  20 , the power supplies  26  and  46  for the ejector magnets  21  and  41  and the power supply  27  for the plunger magnet  22  are all in an off-state. 
         [0071]    Next, as shown in  FIG. 6 , the upper mold  30  is moved down to squeeze the lead frame  50  between the lower mold  10  and upper mold  30 . 
         [0072]    Thereafter, the lower mold  10  and upper mold  30  are heated to melt the resin  60  loaded in the pot  11 . After the resin  60  is loaded, e.g., at the same time when heating starts, the power supply  27  for the plunger magnet  22  is turned on to excite the plunger magnet  22 . 
         [0073]    Upon excitation of the plunger magnet  22 , metallic foreign matters already mixed in the melted resin  60 , particularly, metallic powders and fine particles of iron (Fe) and its alloy capable of being magnetized, are attracted to the plunger magnet  22  and collected in a region of the melted resin  60  near the upper surface of the plunger  14 . A high density region  61  of the metallic foreign matters is therefore generated. 
         [0074]    A density of foreign matters in the other region of the melted resin  60  is therefore lowered. 
         [0075]    As shown in  FIG. 7 , after the resin  60  is melted, the plunger  14  is moved up to inject the resin  60  loaded in the pot  11  into the cavities  19  and  39  via the runner  12 . At this stage, the power supply  25  for the runner magnet  20  and the power supplies  26  and  46  for the ejector pin magnets  21  and  41  are turned on. 
         [0076]    Upon excitation of the runner magnet  20 , while the resin  60  passes in the runner  12 , metallic foreign matters mixed in the resin  60  are attracted to the runner magnet  20  and are brought in the foreign matter retention pocket  13 . A high density region  62  of metallic foreign matters is therefore generated in the foreign matter retention pocket  13 . As described above, the foreign matter retention pocket  13  is dug deeper than the sidewall of the runner  12 . Therefore, metallic foreign matters brought in the foreign matter retention pocket  13  stay in the foreign matter retention pocket  13  without being swept away by a flow of resin in the runner  12 . 
         [0077]    The resin  60  passing through the runner  12  and injected into the cavities  19  and  39  fills the cavities  19  and  39  to resin-mold the semiconductor chip  51 , the bonding wires  52  and a part of the lead frame  50 . 
         [0078]    At this stage, metallic foreign matters mixed in the resin  60  are attracted to the top ends of the ejector pins  15  and  35  to generate high density regions  63  of metallic foreign matters near the top ends. The high density region  63  of metallic foreign matters is positioned near the surface of the resin and remote from the semiconductor chip  51 , bonding wires  52  and the like so that a possibility of contact with these conductive members is very low. 
         [0079]    After the cavities  19  and  39  are completely filled with resin  60 , heat is applied to the resin  60  for a predetermined time to cure the resin  60 . 
         [0080]    After the resin  60  is cured, the power supplies  25  to  27  and  46  are turned off to terminate excitation of the runner magnet  20 , ejector pin magnets  21  and  41  and plunger magnet  22 . 
         [0081]    As shown in  FIG. 8 , after the resin is cured, the upper mold  30  is detached from the lower mold  10  and the ejector pins  15  and  35  are protruded to thereby demold the lead frame  50  including the semiconductor device molded by cured resin  60 A. 
         [0082]    Resin  60 B left in the pot  11 , cull  31  and runner  12  is removed from the lower mold  10  and upper mold  30 . 
         [0083]    In this manner, the high density region  60  concentrating metallic foreign matters mixed in the resin  60  is generated near the upper surface of the plunger  14  in the process shown in  FIG. 6 , and the high density region  62  concentrating metallic foreign matters is generated in the foreign matter retention pocket  13  of the runner  12  in the process shown in  FIG. 7 . 
         [0084]    It is therefore possible to considerably reduce the amount of metallic foreign matters reaching the cavities  19  and  39 . 
         [0085]    The high density regions  63  concentrating metallic foreign matters transported to top end portions of the ejector pins  15  and  35  are also generated in the cavities  19  and  39 . 
         [0086]    It is therefore possible to lower a density of metallic foreign matters in resin near the lead frame  50 , semiconductor chip  51  and bonding wires  52  interconnecting the lead frame  50  and semiconductor chip  51 . Therefore, it is possible to prevent and suppress generation of electric short circuits among the bonding wires  52 . 
         [0087]    In order to efficiently capture metallic foreign matters, it is preferable to set a magnetic force of each of the runner magnet  20 , ejector pin magnets  21  and  41  and plunger magnet  22  to  10000  gausses or higher. 
         [0088]    The plunger magnet  22  is excited only while the resin  60  in the pot  11  is melted. The runner magnet  20  is excited only while the resin  60  flows in the runner  12 . The ejector pin magnets  21  and  41  are excited only while the resin  60  in the cavities  19  and  39  is melted. 
         [0089]    A power consumption can be suppressed by selecting an excitation period in this manner. 
         [0090]    In the first embodiment described above, advantages may be expected to some extent even if one of the runner magnet  20 , ejector magnets  21  and  41  and plunger magnet  22  is disposed. 
         [0091]    Since the plunger  14  is disposed in the lower platen  70 , advantages of the magnet can be expected for various types of molds without placing the magnet in each mold. 
         [0092]    The ejector pin magnets  21  and  41  can be mounted by replacing them with other ejector pins with magnets, without machining the lower mold  10  and upper mold  30 . Therefore, magnets can be mounted easily on conventional molds. If the size of the ejector pin is standardized, the same ejector pin can be used for various types of molds. 
       Second Embodiment 
       [0093]      FIG. 9  is a cross sectional view of a characteristic portion of a resin molding apparatus according to the second embodiment of the present invention. 
         [0094]    Description will be made by paying attention to different points from the resin molding apparatus of the first embodiment, and the description of the components having the same structure is omitted. 
         [0095]    In this embodiment, a meshed member  23  made of magnetic material is disposed perpendicularly to a flow direction of resin in the runner  12 . 
         [0096]    Resin flowing in the runner  12  passes through openings of the meshed member  23 . The meshed member  23  is magnetically coupled to the runner magnet  20 . As the runner magnet  20  is excited, the meshed member  23  is magnetized. 
         [0097]    As the meshed member  23  is magnetized, metallic foreign matters mixed in resin can be attracted and attached to the meshed member  23  efficiently. Especially, it is possible to efficiently attach metallic foreign matters flowing in a region remote from the surface of the runner  12 . 
       Third Embodiment 
       [0098]      FIG. 10  is a cross sectional view of a resin molding apparatus according to the third embodiment of the present invention. 
         [0099]    Description will be made by paying attention to different points from the resin molding apparatus of the first embodiment, and the description of the components having the same structure is omitted. 
         [0100]    In the first embodiment described above, the ejector pin magnets  21  and  41  are disposed in the ejector pins  15  and  35 , respectively. 
         [0101]    In the third embodiment, ejector pins  15  and  35  are made of magnetic material such as iron. The ends of two ejector pins  15  on the back side are coupled with each other by an ejector pin magnet  80 . The ejector pin magnet  80  consists of an electromagnet, and excitation current is supplied from a power supply  82  to the ejector pin magnet  80 . 
         [0102]    Similarly, ejector pin magnets  81  and a power supply  83  are disposed for ejector pins  35  of the upper mold  30 . 
         [0103]    As the ejector pin magnets  80  and  81  are excited, the ejector pins  15  and  35  are magnetized. Therefore, metallic foreign matters can be attracted and attached to the top ends of the ejector pins  15  and  35  exposed in the cavities  19  and  39 . 
         [0104]    In the structure shown in  FIG. 10 , although one ejector pin magnet is magnetically coupled to a plurality of ejector pins, an independent ejector pin magnet may be disposed for each ejector pin. 
       Fourth Embodiment 
       [0105]      FIGS. 11A and 11B  are cross sectional views showing a characteristic portion of a resin molding apparatus according to the fourth embodiment of the present invention. 
         [0106]    Description will be made by paying attention to different points from the resin molding apparatus of the first embodiment, and the description of the components having the same structure is omitted. 
         [0107]      FIG. 11A  is a cross sectional view of the resin molding apparatus along the longitudinal direction of a runner  12  according to the fourth embodiment, and  FIG. 11B  is a cross sectional view thereof along a direction perpendicular to the longitudinal direction of the runner  12 . 
         [0108]    In the first embodiment, although the runner  12  is disposed only in the lower mold  10 , in the fourth embodiment, a runner  32  is also formed in the upper mold  30 . The runner  32  formed in the upper mold  30  is disposed at the position facing the runner  12  formed in the lower mold  10 . 
         [0109]    The runner  32  becomes shallower toward the cavity  39 . Runner magnets  40  are buried at a position slightly deeper than the both side surfaces and bottom surface of the runner  32 . The runner magnet  40  has an elongated shape along the longitudinal direction of the runner  32 . Each runner magnet  40  consists of an electromagnet, similar to the runner magnets  20  buried in the lower mold  10 . 
         [0110]    With this arrangement, metallic foreign matters mixed in resin flowing in the runner  32  formed in the upper mold  30  can be attracted and attached to the sidewall of the runner  32  by the runner magnets  40 . It is therefore possible to enhance the advantages of preventing and suppressing metallic foreign matters from entering the cavities  19  and  39 . 
         [0111]    As shown in  FIG. 12A , a plurality of runner magnets  40 , e.g., three magnets, may be divisionally disposed along the longitudinal direction of the runner  32 . Alternately, as shown in  FIG. 11B , a cross sectional shape of the runner magnet  40  may be a U-character shape extending along the surface of the runner  32 . 
       Fifth Embodiment 
       [0112]    Next, with reference to  FIGS. 13A and 13B , description will be made on a resin molding apparatus according to the fifth embodiment of the present invention. The description will be made by paying attention to different points from the resin molding apparatus of the first embodiment, and the description of the components having the same structure is omitted. 
         [0113]      FIG. 13A  shows a plan shape of the lower mold  10  of the resin molding apparatus of the fifth embodiment. 
         [0114]    In the first embodiment, the runner magnet is disposed for each of a plurality of runners  12 . 
         [0115]    In the fifth embodiment, a runner magnet  90  is disposed overlapping with a plurality of runners  12 . 
         [0116]      FIG. 13B  shows a shape of the facing surface, facing the lower mold, of the upper mold  30  of the resin molding apparatus of the fifth embodiment. 
         [0117]    A runner magnet  91  is disposed in an area corresponding to the runner magnet  90  disposed in the lower mold  10 . 
         [0118]    Similar to the first embodiment, also with the arrangement of the fifth embodiment, metallic foreign matters can be attracted and attached in the foreign matter retention pocket  13  of the runner  12 . 
       Sixth Embodiment 
       [0119]    Next, with reference to  FIGS. 14A and 14B , description will be made on a resin molding apparatus according to the sixth embodiment of the present invention. 
         [0120]    As shown in  FIG. 14A , an area occupied by the runner magnet  90  shown in  FIG. 13A  is broadened to make the runner magnet  90  be disposed also overlapping with the cavity  19 . As shown in  FIG. 14B , an area occupied by the runner magnet  91  shown in  FIG. 13B  is broadened to make the runner magnet  91  be disposed also overlapping with the cavity  39 . 
         [0121]    In the sixth embodiment, metallic foreign matters can be attracted and attached also to the inner surfaces of the cavities  19  and  39 . 
       Seventh Embodiment 
       [0122]    Next, with reference to  FIGS. 15 to 16B , description will be made on a resin molding apparatus according to the seventh embodiment. The description will be made by paying attention to different points from the resin molding apparatus of the first embodiment, and the description of the components having the same structure is omitted. 
         [0123]      FIG. 15  is a cross sectional view of the resin molding apparatus of the seventh embodiment. 
         [0124]    In the first embodiment, a semiconductor chip mounted on a lead frame is molded being covered with resin on both sides thereof. 
         [0125]    In the seventh embodiment, a resin molding target is a BGA type package and semiconductor chips mounted on one principal surface of a support substrate  100  are molded with resin on the support substrate  100 . 
         [0126]    As shown in  FIG. 15 , a plurality of semiconductor chips  101  are mounted on one principal surface of the support substrate  100 , and electrodes of the semiconductor chips  101  are connected to electrodes formed on the support substrate  101  by bonding wires. 
         [0127]    A substrate housing recess  39 A is formed in the upper mold  30 , the recess  39 A having a shape and depth generally equal to the shape and thickness of the support substrate  100 . 
         [0128]    The cavity  19  formed in the lower mold  10  has an area covering the semiconductor chips together. 
         [0129]    The support substrate  100  is held on the facing surface of the lower mold  10  in such a manner that the surface of the support substrate  100 , on which the semiconductor chips  101  are mounted, faces the lower mold  10 . All the semiconductor chips  101  are accommodated in one cavity  19 . The inner surface of the substrate housing recess  39 A formed in the upper mold  30  becomes in contact with the surface of the support substrate  100  opposite to the surface on which the semiconductor chips  101  are mounted. 
         [0130]      FIGS. 16A and 16B  show a plan shape of the lower mold  10  and a shape of the facing surface of the upper mold  30  facing the lower mold, respectively of the resin molding apparatus of the seventh embodiment. A cross sectional view taken along one-dot chain lines in  FIGS. 16A and 16B  corresponds to  FIG. 15 . 
         [0131]    As shown in  FIG. 16A , five pots  11  are disposed along a vertical direction at an equal pitch. A plan shape of each pot  11  is circular. 
         [0132]    A plunger  14  is disposed in each pot  11 . A rectangular cavity  19  is disposed on the right of each pot  11 . A runner  12  extends from each pot  11  toward the right side and branches intermediately into two runners which reach the cavity  19 . 
         [0133]    A foreign matter retention pocket  13  is formed in the runner  12  in a partial area thereof near the pot  11 . A runner magnet  20  is disposed in correspondence with each foreign matter retention pocket  13 . 
         [0134]    As shown in  FIG. 16B , a cull  31  is disposed in the upper mold  30  at a position corresponding to the pot  11 . A substrate housing recess  39 A having a plan shape larger than that of the cavity  19  is disposed in an area corresponding to the cavity  19 . A plan shape of the substrate housing recess  39 A is generally equal to the plan shape of the support substrate  100 . 
         [0135]    Also in resin molding for a BGA type package as in the seventh embodiment, the runner magnet  20  is disposed under the foreign matter retention pocket  13  formed in the runner  12  so that invasion of metallic foreign matters into the cavity  19  can be suppressed. 
         [0136]    By disposing the plunger magnet  22  in the plunger  14 , invasion of metallic foreign matters can be suppressed further. 
       Eighth Embodiment 
       [0137]      FIGS. 17A and 17B  show a plan shape of the lower mold  10  and a shape of the facing surface of the upper mold  30  relative to the lower mold, respectively of a resin molding apparatus of the eighth embodiment. 
         [0138]    The description will be made by paying attention to different points from the resin molding apparatus of the seventh embodiment, and the description of the components having the same structure is omitted. 
         [0139]    As shown in  FIG. 17A , in the eighth embodiment, one magnet  110  is disposed instead of the runner magnets  20  of the seventh embodiment. The magnet  110  is disposed overlapping with all runners  12  extending from a plurality of pots  11 , namely covers all runners together. 
         [0140]    As shown in  FIG. 17B , a magnet  111  is disposed for the upper mold  30  in an area corresponding to the magnet  110  of the lower mold. 
         [0141]    Also in the eighth embodiment, similar to the seventh embodiment, metallic foreign matters can be attracted to the foreign matter retention pocket  13  of the runner  12 . 
       Ninth Embodiment 
       [0142]      FIGS. 18A and 18B  show a plan view of the lower mold  10  and the facing surface of the upper mold  30  facing the lower mold, respectively of a resin molding apparatus according to the ninth embodiment of the present invention. 
         [0143]    In the ninth embodiment, the area occupied by the magnet  110  of the eighth embodiment is broadened to make the magnet  110  cover also the cavity  19 . The magnet  110  of the upper mold  30  has a size equal to the magnet of the eighth embodiment shown in  FIG. 17B . 
         [0144]    In the ninth embodiment, metallic foreign matters entered the cavity  19  are attracted and attached to the inner surface of the cavity  19 . It is therefore possible to prevent electric short circuits among bonding wires connected to the semiconductor chips  101 . 
         [0145]    In the embodiments shown in  FIGS. 14A ,  14 B,  18 A and  18 B, metallic foreign matters are captured by disposing a magnet overlapping with the whole inner surfaces of the cavities. The magnet may be disposed in a specified area not influencing the operation of semiconductor chips even if metallic foreign matters are concentrated on this area. Namely, the magnet may be disposed so as to concentrate metallic foreign matters on an area remote from semiconductor chips and bonding wires. 
         [0146]    The present invention has been described in connection with the preferred embodiments. The invention is not limited only to the above embodiments. It will be apparent to those skilled in the art that other various modifications, improvements, combinations, and the like can be made.