Abstract:
A semiconductor package including a sealing resin between a substrate and a semiconductor chip, wherein a concavity portion is defined in the surface of the substrate. The concavity facilitates spreading of the resin when the latter is injected between the substrate and the chip to connect them in a sealed manner.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a semiconductor package and a method of injecting a resin into the semiconductor package. This invention relates particularly to a flip chip type semiconductor package wherein a semiconductor chip is implemented on a substrate in face-down form. 
     2. Description of the Related Art 
     A semiconductor package of a type wherein a semiconductor chip is implemented on the surface of a circuit substrate and a connecting portion between the two is sealed with a resin or the like, has been disclosed in Japanese Patent Application Laid-Open No. Hei 7-302858 which was opened to the public by Japanese Patent Office in Nov. 14, 1995. 
     In this type of semiconductor package, a sealing resin is injected or poured between a circuit substrate and a semiconductor chip through the use of by capillary action so as to seal between the substrate and the chip as has been described in the paragraph [0023] on page 4 in the aforementioned publication. 
     Since the clearance or gap between the circuit substrate and the semiconductor chip is normally very narrow as in a range of 40 to 60 μm, the injected resin is hard to spread. 
     Since there has recently been a growing demand for a reduction in the thickness of this type of semiconductor package, such a clearance has the potential for becoming narrower. In such a case, it is considered that the resin will be increasingly harder to spread and a long time will be required for the resin to spread through the entire gap between the substrate and the chip. 
     SUMMARY OF THE INVENTION 
     With the foregoing in view, it is therefore an object of the present invention to provide a semiconductor package which makes it possible to facilitate spreading of a sealing resin when the sealing resin is formed between a substrate and a semiconductor chip. 
     It is another object of the present invention to provide a method of injecting a sealing resin, which is capable of forming the sealing resin between a substrate and a semiconductor chip uniformly. 
     In order to achieve the above objects, a typical invention of the present application provides a structure of a semiconductor package comprising a substrate, a semiconductor chip and a resin for sealing between the substrate and the semiconductor chip and wherein a concave portion is defined in the surface of the substrate. 
     Further, another typical invention provides a resin injecting method suitable for use in a semiconductor package, comprising the steps of placing a square semiconductor chip above the substrate and thereafter injecting the resin between the semiconductor chip and the substrate simultaneously from substantially the centers of each of three sides of the semiconductor chip. 
     According to the semiconductor package structure of the present invention, since a sufficient clearance can be ensured between the substrate and the semiconductor chip because the concave portion is defined in the surface of the substrate, the injected resin is easily spread. 
     According to the resin injecting method of the present invention, since the resin is injected substantially simultaneously substantially from the centers of the three sides of the square semiconductor chip, the resin can be injected between the substrate and the semiconductor chip uniformly and within a short time. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     While the specification concludes with claims particularly pointing out and distinctly claiming the subject matter which is regarded as the invention, it is believed that the invention, the objects and features of the invention and further objects, features and advantages thereof will be better understood from the following description taken in connection with the accompanying drawings in which: 
     FIG. 1 is a plan view showing a first embodiment of the present invention; 
     FIG. 2 is a cross-sectional view illustrating the first embodiment; 
     FIG. 3 is a plan view depicting a second embodiment of the present invention; 
     FIG. 4 is a plan view of a substrate  10 A employed in the second embodiment; 
     FIG. 5 is a cross-sectional view showing another example of a substrate having a concave form; 
     FIG. 6 is a plan view illustrating another example shown in FIG. 5; 
     FIG. 7 is a cross-sectional view depicting a third embodiment of the present invention; 
     FIG. 8 is a plan view showing the third embodiment; and 
     FIG. 9 is a cross-sectional view illustrating a further example of a substrate having a concave shape. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Preferred embodiments of the present invention will hereinafter be described with reference to the accompanying drawings. In the following description, portions of the embodiments directly associated with the present invention will be A first embodiment will first be explained with reference to FIGS. 1 and 2. 
     FIG. 1 is a plan view of the first embodiment of the present invention. Hidden portions are also shown by dotted lines or light lines to provide easy understanding of their description. FIG. 2 is a cross-sectional view taken along line X-X′ in FIG.  1 . 
     In the first embodiment, a semiconductor chip  20  is mounted on a package substrate  10 . The two are electrically connected to each other through electrodes  30 . The connected portions are sealed with a sealing resin  40 . 
     A plurality of the electrodes  30  are formed on a circuit forming surface of the semiconductor chip  20 . An electrical signal generated within the semiconductor chip  20  from a predetermined electrode of these electrodes  30 , is outputted to the outside. An externally-derived electrical signal is supplied to other electrodes. The electrodes  30  are typically formed of solder. Although the electrodes formed by ball-shaped solder are illustrated in the present embodiment, the shape and material are not necessarily limited to this. It is also considered that for example, flat electrodes other than the illustrated ball-shaped ones are utilized as the electrodes or other metal conductors are used as the electrodes without being limited to the solder. 
     In the package substrate  10  (which is formed with ceramic or an organic substance as a principal material), a plurality of pads  12  are provided at positions respectively corresponding to the electrodes  30 . The electrodes  30  and the corresponding pads  12  are respectively electrically connected to one another. 
     Methods of connecting them include forming a compound between metals, using organic conductive paste, using solder, etc. 
     Their connecting portions are sealed with a sealing resin  40 . This sealing can prevent corrosion of connecting portions and wires or interconnections, which is caused by the entry of moisture from the outside. The pads  12  are respectively electrically connected to a plurality of ball-shaped connecting portions  11  formed by solder on the back of the substrate  10 , through interconnections or circuits formed on and in the substrate  10 . The ball-shaped connecting portions  11  are used for connection to a device such as an external substrate or the like. 
     While the ball-shaped connecting portions can be confirmed illustrated only with the cross-sectional view of FIG. 2 to provide easy understanding of description herein, a large number of ball-shaped connecting portions are actually placed over the back of the substrate  10  in array form. 
     In the present embodiment, the pads  12  placed on the surface of the package substrate  10  and the pads  14  placed on the back of the package substrate  10  are respectively electrically connected to one another via through holes  13 . The ball-shaped connecting portions  11  are electrically connected to the pads  14 . 
     The through holes  13  are configured so as to have conductivity. For example, metal layers are respectively formed on the inner surfaces of the through holes  13  by plating or the like so as to provide their conductivity. If the through holes are defined so as to have conductivity by a process other than the plating, then they perform their conductive functions. Namely, a designer may suitably select a configuration wherein the interconnections formed on the surface of the substrate and the interconnections formed on the back thereof are electrically connected to one another. 
     In the first embodiment of the present invention, a concavity  50  is defined in the central portion of the package substrate  10 . The concavity  50  is defined in the surface of the substrate  10  on the inner side as viewed from an area in which the pads  12  are formed. Although a the concavity  50  is square in the view shown in FIG. 1 for the first embodiment, the shape of the concavity may be suitably selected by the designer according to the placement of the electrodes  30  of the semiconductor chip  20 . 
     It is considered that the position where the concavity  50  is defined, can be diversely changed according to the placement of the electrodes of the semiconductor chip. When the electrodes of the semiconductor chip are placed as in the present embodiment, it is optimal that the concavity be defined in the central portion of the substrate on the inner side as viewed from a peripheral area in which the electrodes are placed. 
     The concavity  50  is defined by a known engraving technique. The designer can arbitrarily set the depth of the concavity  50  according to the thickness of the substrate. Since the concavity  50  is defined in the central portion of the package substrate  10 , the distance to the chip from the base or bottom of the concavity  50  is greater than the distance between the semiconductor chip  20  and the substrate  10  in the substrate&#39;s peripheral area in which the electrodes  30  of the semiconductor chip  20  and the pads  12  are connected to one another. 
     A method of injecting the sealing resin  40  between the semiconductor chip  20  and the package substrate  10  will now be described. 
     When the sealing resin  40  is injected therebetween, an epoxy resin having low viscosity is dropped onto the package substrate  10  at the peripheral portion of the semiconductor chip  20 . At this time, the package substrate  10  is heated at 60-100° C. The dropped resin is charged between the semiconductor chip  20  and the package substrate  10  by capillary action. 
     In this case, the resin is charged between the semiconductor chip  20  and the package substrate  10  and the resin is formed even under the periphery of the semiconductor chip  20  so as to protrude from its periphery. 
     Thereafter, the charged resin is cured (solidified) under heat to thereby obtain such a resin or plastic molded structure as shown in FIGS. 1 and 2. 
     Since the concavity  50  is provided in the present embodiment, the gap or clearance between the substrate  10  and the semiconductor chip  20  becomes large so that the injected resin is easy to expand or spread. Since the resin is easily spread, a resin sealing process can be realized in a short time as compared with the prior process. This will bring about a very large effect for a manufacturer for fabricating this type of semiconductor device in mass production. 
     Further, since the concavity  50  is provided in the central portion of the substrate  10 , the resin is smoothly spread even in the substrate&#39;s central portion wherein, until the present invention the resin was hard to spread up to now. The smooth charging of the resin is considered to suppress problems about non-charging of the resin, etc., with the result that the invention is considered to be able to contribute to an improvement in device&#39;s reliability. 
     The aforementioned embodiment is an example in which the concavity  50  is defined by engraving the package substrate  10 . A second embodiment of the present invention wherein this package substrate is formed by bonding two substrates together, will next be explained. 
     FIG. 3 shows an example in which a substrate  10 ′ is comprised of a substrate  10 A and a substrate  10 B. The substrate  10 A is one whose central portion is hollow, as shown in FIG.  4 . The bonding of such substrates  10 A and  10 B together allows implementation of a structure in which a concave portion  50 ′ is provided in the central portion of the substrate  10 ′ in a manner similar to the first embodiment. 
     Pads  12 , electrically connected to electrodes  30  of a semiconductor chip  20 , are formed in the substrate  10 A. The pads  12  are respectively electrically connected to wires or interconnections  15  formed on the substrate  10 B via such through holes as mentioned above or interconnections formed in the substrate  10 A. The interconnections  15  are electrically connected to ball-shaped connecting portions  11  via through holes  13 ′ defined in the substrate  10 B. 
     An advantageous effect similar to that obtained by the first embodiment can be brought about in that if the sealing resin  40  is injected into such a structure by a method similar to the above, then the sealing resin  40  is easily spread between the substrate  10 ′ and the semiconductor chip  20  in a manner similar to the first embodiment. 
     Further, the a present embodiment can implement the substrate having a function similar to the substrate employed in the first embodiment by the method of simply bonding the two substrates together. 
     In the concavities  50  and  50 ′ employed in the first and second embodiments, the bottoms of the concavities are vertically shaped. However, if a concavity  51  whose bottom is shaped in the form of a gentle taper, is used as shown in FIGS. 5 and 6, then the resin is smoothly charged even into the corners of the concavity  51  upon injection of the resin. FIG. 5 is an enlarged cross-sectional view of the concavity  51 , and FIG. 6 is a plan view. 
     A third embodiment of the present invention will next be described with reference to FIGS. 7 and 8. The present embodiment is identical in basic structure to the first embodiment. The same parts as those illustrated in the first embodiment are identified by the same reference numerals and their description will therefore be omitted. 
     The present embodiment has a configuration characterized by a bottom portion of a concave portion  53  having a slope or inclination of an angle θ. A designer can selectively set the angle θ from the thickness of a substrate  10 , the depth of the deepest portion of the concave portion  53 , and the viscosity of a resin. This inclination is formed using a known engraving technique. 
     If the sealing resin  40  is injected from an X direction above the inclination where the sealing resin  40  is injected into this structure, then the resin is easily spread from above to below the inclination, i.e., over the entire surface between the substrate  10  and a chip. This is considered to result from the fact that pressure is applied to the resin through the slope so that the resin becomes easy to flow. It is desirable in this case that the resin injected from the X direction is injected from the central portion of the side of the semiconductor chip. 
     Further, if the resin is injected from the central portions (Y and Z directions) of the two adjacent sides of the semiconductor chip as well as from the X direction above the inclination as shown in FIG. 8, then the resin can spread out faster. 
     In addition, the inclination may be shaped in stepwise form as shown in FIG.  9 . Namely, such a structure with a concavity  54  has bottom sides such as bottom sides  54 - 1  and  54 - 2 , which stand on different levels or are offset. 
     If a resin is injected from an X direction above an inclination even in this case, then the resin is easy to spread from above to below the inclination, i.e., over the entire surface between a substrate and a chip. 
     According to the various embodiments of the present invention, as has been described above, a package structure in which a resin is easy to spread, can be implemented, and the resin can be also injected in a short time. 
     While the present invention has been described with reference to the illustrative embodiments, this description is not intended to be construed in a limiting sense. Various modifications of the illustrative embodiments, as well as other embodiments of the invention, will be apparent to those skilled in the art on reference to this description. It is therefore contemplated that the appended claims will cover any such modifications or embodiments as fall within the true scope of the invention.