Semiconductor package

Abstract: The first semiconductor package comprises a board (6) equipped with a wiring circuit (6b) including a connection (6a) on a main surface, a semiconductor chip (9) mounted face down having input/output terminal (9a) corresponding to the connection of the board, flat external connector terminals (8) leading to and are exposed on the other main surface of the board, and filled via hole (7) connection to be electrically connected to the wiring circuit through a filled via hole installed right above each external connector terminal (8). Further, the second semiconductor package utilizes the above-described construction but the flat external connector terminals are led to and exposed on the other main surface of the board in a constant-pitch lattice-array.

Description: This invention relates to a semiconductor package. More specifically, this invention relates to a compact and thin semiconductor package suitable for card-type external memory media. Since the construction of a memory card is restricted by such factors as its size and thickness, thinness in semiconductor packages is called for. At the same time, it is also desirable for the semiconductor package to be just as big as the semiconductor chip, and to be as compact as possible. Some well-known methods used to meet the demand for compact mounting on such card structures, for instance, the need to mount against the thickness of the board in a space no more than 1 millimeter deep, are the conventional flip chip mounting method and the COB (Chip on Board) method. Further, a well-known construction of thin semiconductor packages is shown in Fig. 1 which is a cross sectional view of the principal mechanism. In Fig. 1, reference numeral 1 represents a board equipped with wiring circuit 1a including a connection on a main surface thereof; reference numeral 2 indicates a semiconductor chip (flip chip) mounted on a main surface of the board. Reference numeral 4 indicates external connector terminals leading to the other main surface of the board 1 via a through-hole (through-hole connection) 3 while reference numeral 5 indicates a resin layer which seals the region between the semiconductor chip 2 and a main surface of the board 1. In this example, the board 1 uses alumina, aluminum nitride, or glass/epoxy resins as insulators. Moreover, reference numeral 1b in Fig. 1 represents a silver paste connector pad on the connecting surface of the wiring circuit 1a whereas 2a indicates a connector bump installed on the electrode terminal surface of the semiconductor chip 2. However, said flip chip mounted type semiconductor package has several disadvantages: Firstly, acquiring KGD (Known Good Die) is a problem with said flip chip mounting and COB methods. That is, burn-in is difficult to develop in chip state and since burn-in for the semiconductor chip to be used is usually not possible to conduct beforehand, there will be problems in terms of reliability. In other words, it is not possible to perform burn-in on this type of minute semiconductor chip, although in the near future it may be possible for the chip itself to detect defects on its own. As such, at the practical initial stage after mounting and modularization, the possibility of trouble is hidden and reliability becomes questionable. Furthermore, in terms of compacting, the COB method requires a larger mounting area compared to the flip chip mounting method thereby hindering attempts at compacting. Secondly, in the case of said semiconductor packages wherein one face is molded, for instance, when mounting on a base board, there is also danger of unwanted shorting between the wiring patterns in the external connector terminals 4 which lead to the other main surface (back side). To explain further, in a construction wherein the external connector terminals 4 lead to the other main surface (back side) via the through-hole 3, electrical connections to the external connector terminals 4 are established at the periphery of the opening of said through-hole 3. Owing to this, indentions may easily form in the vicinity of the through-hole opening of each external connector terminal 4 (i.e., the center of the external connector terminal 4) such that a level surface may not be fully achieved. Accordingly, when mounting on card-type base boards, reliability of electrical connections may be compromised. Considering these matters, a construction wherein the through-hole 3 connections are formed by adjoining (and shifting the positions of) the external connector terminals 4 to ensure a flat surface is being employed. This construction not only restricts the design and layout of the external connector terminals 4 because wiring for connections is done at the back side, but also poses a problem in terms of reliability because ensuring insulation among the external connector terminals is difficult. EP-A-0520841 describes a flip chip semiconductor device comprising a board and an interposer fixed to a surface of the board by means of a layer of underfill material. Electrical connectors are provided on the interposer, and a semiconductor die is electrically connected thereto via solder bumps. Filled vias are provided to connect the connectors to the board. EP-A-0159443 describes a semiconductor device comprising a substrate in which IC chips are buried. A plurality of connecting terminals are provided on the chips, and covered by a layer of insulating composition. A conductor path is provided between each set of connecting terminals. The connecting terminals, IC chips and insulating composition layer are all provided on the same surface of the substrate. EP-A-644587, which forms part of the prior art according to Article 54(3) EPC, describes a semiconductor package comprising a circuit board on which a semiconductor chip is mounted. The device is provided with connection terminals on two opposing sides of the circuits board, each set of connection terminals being connected together via a through hole. The semiconductor chip is connected to the connection terminals via an electrode terminal portion which is press fitted to a set of connection terminals. Accordingly, it is an object of this invention to provide a semiconductor package wherein compacting is possible and highly reliability may be ensured. It is a further object of this invention to provide a semiconductor package which can be produced at low cost and wherein high reliability may be ensured. It is yet another object of this invention to provide a semiconductor package which is compact, highly reliable and suitable for mounting or attaching to cards. The first semiconductor package related to this invention comprises: a board having first and second opposing surfaces; a wiring circuit having connections and formed on the first surface; a semiconductor chip mounted face down having input/output terminals adapted to the connections of said wiring circuit; flat external connector terminals formed on the second opposing surface; and filled via holes formed through the board and electrically connected to each of said connections and to corresponding flat external connector terminals; characterised in that: said wiring circuit and said connections are inlaid in said first surface of the board such that the outer surface of said connection and said wiring circuit are almost level with said first surface of the board; and said flat external connector terminals are inlaid in the second surface of the board such that the outer surface of the terminals are almost level with said second surface of the board and are exposed in constant-pitch lattice-array on said second surface of said board. To wit, this invention employs the following basic construction: (a) A main surface of the board is not merely used as a face down mounting region for the semiconductor chip but the available space aside from the connection to which the input/output terminals of the semiconductor chip are connected is utilized for installing wiring circuits. (b) Only flat external connector terminals are led to and exposed on the other main surface (back side) of said board, that is, in a constant-pitch lattice-array. (c) The wiring circuit on a main surface is connected to said external connector terminals through the filled via hole which is installed directly above each external connector terminal. (d) Further, the surface of the wiring circuit on a main surface of said board is formed and laid out to be as uniformly level as the board surface thereby making it easier to form and place the fine sealing resin layer between the semiconductor chip and the board surface, and while aiming for compactness and thinness in the semiconductor package, improvement in reliability is the key point. For the purposes of this invention, resin type or ceramic type boards equipped with wiring circuit including a connection on a main surface are used. The boards, for instance, as shown in the plan view of the form of a main surface of board 6 in Fig. 2, are provided with a connection 6a adapted to the input/output terminals of the semiconductor chip to be mounted. There is also a wiring circuit 6b, one edge of which is electrically connected to said connection 6a; the other edge of this wiring circuit 6b is connected to the back side (other main surface) of the circuit board 6 through the filled via hole (filled via hole connection) 7 installed right above the flat external connector terminals brought out and laid out preferably in a constant-pitch lattice-array. Fig. 3 is a plan view of the form of the back side of the board 6 wherein only external connector terminals 8 are brought out and laid out in a constant-pitch lattice-array. Here, the arrangement of flat external connector terminals 8 leading to and are exposed on the back side of the board 6 is not particularly limited; however, when arranged in said constant-pitch lattice-array, this type of semiconductor package can be standardized. Further, when the arrangement of said external connector terminals 8 is unbalanced, by installing dummy connector terminals 8' on a corner as shown in Fig. 4, planar installation of semiconductor packages will be easier to perform. It must be noted that since only flat external connector terminals 8 are led to and exposed on the back side of board 6, i.e., there is no through-hole connection nor wiring circuit, it is not only easier to ensure insulation among the flat external connector terminals 8 but also easier to select the arrangement of flat external connector terminals 8. In the present invention, when installing (by burying) the wiring circuit 6b including the connection 6a of the board surface of the semiconductor to be mounted such that it is on the same level (flat) as the surface of circuit board 6, the flatness (level) is not necessarily precise; generally, if the thickness of wiring circuit 6b is about 35/um, +/- 10/um is tolerated. Further, when ceramic type insulating material is used, said board 6 may be fabricated with the green sheet method whereas if the insulating material is resin type, the prepreg method may be used. Further, in constructing said board 6, aside from the wiring circuit 6b including the connection 6a formed on a main surface of the board 6 and/or the in-layer wiring circuit in board 6, a dummy wiring pattern (say at least 0.5 mm in width) may be installed in the non-circuited region in the outer edges by enclosing said wiring circuits and electrically insulating and isolating them. In other words, installing a dummy wiring pattern will suppress and prevent the formation of warps and at the same time allow for noise control. This dummy wiring pattern should be positioned in a region no more than 2 mm away from the outer edges, i.e., as close as possible to the outer edges. The first semiconductor package related to this invention is equipped with wiring circuit 6b including a connection 6a on a main surface of the board 6. Not only does a main surface of the board 6 function as connection for the input/output terminals of the semiconductor chip but the region which will not interfere with the mounting of the semiconductor chip may also function as pulling wiring part 6b for the flat external connector terminals 8 leading to and are exposed on the back side. As described above, said flat external connector terminals 8 and the wiring part 6b on a main surface of the board are connected together through filled via hole 7 which are installed right on top of each external connector terminal 8 such that wiring at the back side is eliminated. Consequently, while the arrangement and installation of flat external connector terminals 8 are simplified, in-layer wiring can also be omitted Further, a main surface of this wiring circuit 6b is buried, and since the surface of wiring circuit 6b is practically on the same level as the surface of other boards such that flatness is maintained, the fineness of the filling/sealing resin layer is ensured in this region. In other words, since the space between the semiconductor chip and board surfaces is flat and can also be easily filled with resin, a fine sealing layer without void is formed and maintained thereby forming a highly reliable junction. Yet further, in the case of the second semiconductor package related to this invention, if the construction of said first semiconductor package were designed such that when flat external connector terminals 8 lead to and are exposed on the other main surface of board 6 in a constant-pitch lattice-array, the connection of semiconductor sockets or mounting circuit boards can be standardized. Consequently, mounting productivity can be improved and cost can be lowered for mounting circuit boards; moreover, installing dummy connector terminals 8' will not only make level alignment/attachment easier but also ensure electrical connection. The foregoing and other objects, features, and advantages of this invention will become apparent from the following detailed description of preferred embodiments of this invention, as illustrated in the accompanying drawings. A better understanding of the invention may be had from a consideration of the detailed description hereinafter taken in conjunction with the following drawings. Fig. 1 shows a cross section of a sample principal construction of a conventional compact semiconductor package. Fig. 2 is a plan view of a sample wiring circuit on a main surface of a board used in the construction of the semiconductor package related to the present invention. Fig. 3 is a plan view of a sample arrangement of external connector terminals on the other main surface of a board used in the construction of the semiconductor package related to the present invention. Fig. 4 is a plan view of a sample arrangement of external connector terminals of other boards used in the construction of the semiconductor package related to the present invention. Fig. 5 is a cross section of a sample principal construction of the semiconductor package related to the present invention. Fig. 6 is a cross section of another example of principal construction of the semiconductor package related to the present invention. Fig. 7 is a cross section of yet another example of principal construction of the semiconductor package related to the present invention. By way of introduction of the illustrated embodiment, the components shown in figures have been assigned general reference numerals and a description of each such component is given in the following detailed description. Two preferred embodiments of the present invention are described in detail hereinafter. Preferred Embodiment 1 Fig. 5 is a cross section of a sample principal construction of the semiconductor package related to the present invention. In Fig. 5, reference numeral 6 represents a 15 mm long, 15 mm wide and 0.2 - 0.3 mm thick board equipped with wiring circuit 6b including a connection 6a on a main surface while reference numeral 9 indicates a 13 mm long, 13 mm wide and 0.3 mm thick semiconductor chip (e.g., IC chip). In this figure, a buried type of construction is employed wherein the wiring circuit 6b formed on a main surface of said board is on the same level as the main surface of board 6. Further, on the surface of the connection 6a of said board 6, a connecting pad 6c made from silver paste is installed to accommodate the connector bump 9a which is positioned on the electrode terminal of semiconductor chip 9. Still further, flat external connector terminals 8 lead to and are exposed on the back side (other main surface) right below the filled via hole, through the filled via hole connection 7 which is electrically connected to the wiring circuit 6b on a main surface of said board 6. External connector terminals 8 are arranged in a constant-pitch lattice-array as shown in Fig. 3. The board 6 having this type of construction may be manufactured in the following manner. Prepare an alumina type green sheet and instal filled via hole connecting holes in the position of said green sheet. On a main surface of the green sheet, mold the conductive paste by printing and drying the required wiring circuit 6b including connection 6a. Meanwhile, on the other main surface of said green sheet, mold the conductive paste by printing and drying the external connector terminals to which the filled via hole connecting holes are to be directly coupled. Note that in the printing process for said wiring circuit 6b or external connector terminals, the filled via hole connecting holes are filled inside with conductive paste to electrically connect the corresponding wiring circuit and external connector terminals. Alumina type board 6 is then produced by molding into the required dimensions after baking the compressed alumina type green sheet to which said printing and wiring have been done. Still further, reference numeral 10 indicates the resin layer which fills and seals the gap between semiconductor chip 9 (which has been mounted on a main surface of board 6) and the surface of board 6. It must be noted that aside from said alumina type board, other types such as aluminum nitride, glass/epoxy resin, or butylene terephthalate resin type of boards are generally used. Further, as shown in Fig. 6 which is a cross section of the principal construction of board 6, a beta-type patterned dummy wiring pattern 11 may be installed in the outer edges (preferably within approximately 2 mm from the outer edge surface) of the main surface of board 6. A manufacturing example of a semiconductor having said construction is described below. First, prepare an alumina type board 6 which has a wiring circuit 6b including connection 6a for flip chip mounting on one surface (a main surface) and a solid type wiring pattern 11 to the surrounding part, and wherein flat external connector terminals 8 lead to and are exposed in a constant-pitch lattice array fashion on the back side (other main surface), right below the filled via holes 7 which are to be connected to said wiring circuit 6b. The alumina type board 6 described here is made with the green sheet technique. Wiring circuit 6b including said connection 6a, and flat external connectors 8 are buried such that they are as flat (of the same level) as the alumina type board 6 surface. The diameter of the external connector terminal 8 is 0.5 mm, the pitch between electrode terminals 8 is 1 mm, the diameter of the filled via hole 7 is 50-150/um, while the width and pitch of wiring circuit 6b is 50-100/um and 100-200/um, respectively. Moreover, this alumina type board 6 is 15 mm long, 15 mm wide, and 0.2-0.3 mm thick; it is for face down mounting of a 13 mm long, 0.3 mm wide, and 0.3 mm thick semiconductor chip 9. The alumina type board 6 may then be fixed on the stage of a screen printer which has a vacuum suction mechanism; connecting pad 6c may be formed on the connection of alumina type board 6 which corresponds to the electrode (connecting) pad of said semiconductor chip 9. For example, using a metal mask with say, 150 x 150/um opening to accommodate the electrode pad (e.g., 100 x 100/um) 9a of semiconductor chip 9, silver paste (e.g., silver particle diameter 1 um and paste viscosity 100 ps) is screen printed on a main surface of alumina type board 6 to mold, on the surface for connection, a connecting pad 6c which has a diameter of 150 um and is approximately 80/um high. On the other hand, for the semiconductor chip 9, use a connecting gold bump 9a formed through electric plating on the electrode terminal surface or a gold ball bump (e.g., 30/um high, 100 x 100/um) 9a formed through ball bonding method. Next, on a main surface of said alumina type board 6, align and position the connecting pad 6c and connecting gold bump 9a which mutually accommodates said semiconductor chip 9, and by pressurizing the connecting parts together, fix (by burying and applying pressure) and connect at least the tip of the connector bump 9a to the connecting pad 6c to assemble a semiconductor package. In this condition, flip chip bonding is done by heat curing the silver paste comprising said connecting pad 6c. The process using the sealing resin then follows. In other words, after dropping some sealing resin (e.g., low viscosity epoxy resin) on one edge of the exposed region of the surrounding area of said alumina type board 6, the resin is warmed at 60-80°C; the gap between the lower surface of semiconductor chip 9 and upper surface of the alumina type board 6 is poured and filled with sealing resin, utilizing the capillary phenomenon from one edge of the gap. In this resin process, it is advisable that the gap be sufficiently filled with resin 10 and that some resin be allowed to flow along the sides of semiconductor 9. As such, after conducting the necessary resin process, by thermally hardening said resin used to fill the gap, a semiconductor package which employs a construction such as the one cross-sectionally shown in said Fig. 5 is achieved. Here, fixing of the semiconductor chip 9 against the alumina type board 6 is not only improved by filling with said resin layer 10 but it is also insulated and protected against the surface of the alumina type board 6. On the other hand, although the top of semiconductor chip 9 is exposed, the surface is protected because the silicon material of the exposed surface is fine and hard, thereby confirming also that there will be no problems on reliability concerning this matter. Further, since the surrounding part of said semiconductor chip 9 is surely and finely resin-sealed, strong coupling with alumina type board 6 is also assured, and the structure functions as a highly reliable semiconductor package. Moreover, it has been recognized that when the solid type dummy wiring pattern 11 is formed and placed on the outer edges of a main surface of board 6, this semiconductor package had the following effects. Through the reinforcing action of dummy wiring pattern 11, formation of breaks and warps is effectively controlled in spite of the fact that the board is merely 0.2 mm thin; while increasing yield, handling work was also simple. In addition, it was also confirmed that when this semiconductor package was used as a functioning part of a memory card, noise control is also good. Note that although the above-described construction uses a square alumina type board, a rectangular one will also do. Preferred Embodiment 2. A circuit board 6' the construction of which is cross-sectionally shown in Fig. 7 was prepared. On a main surface, it has a wiring circuit 6b' to which connection 6a' for flip chip mounting has been installed; through the via hole 7' between the wiring circuit 6b', flat external connector terminals 8 lead to and positioned in a constant-pitch lattice-array at the back side (other main surface). In other words, this time the construction is such that the alumina type board 6' has an additional in-layer wiring layer 6b" and filled via hole 7' passes through this in-layer wiring layer 6" before it is connected. However, this board 6' also employs a construction wherein wiring circuit 6b' including connection 6a' and flat external connector terminals 8 are buried so that they are almost in the same level as the surface of the circuit board 6'. On the other hand, as for the semiconductor chip (flip chip) 9, a connecting gold bump (30/um high, 100 x 100/um big) for the electrode terminal surface is installed on the electrode pad surface using electric plating method (or ball bonding method). The alumina type board 6' and flip chip 9 are aligned and positioned on the stage surface of the flip chip bonder. In other words, the alumina type board 6'is vacuum suctioned and then,after aligning and positioning the gold bump 9a (which was formed on the electrode surface of flip chip 9) on the gold connecting pad of alumina board 6', in order to glue the connecting parts of connecting pad 6c and gold bump 9a, they are heated to about 350-450°C from the top of flip chip 9 and/or the alumina type board 6', thereby coupling and integrating said connecting pad 6c' and gold pad through mutual dispersion. The space between alumina type board 6' and flip chip 9 was then filled with sealing resin 10 under the same conditions described in the above Preferred Embodiment 1. During said resin-filling process, capillary action was promoted when the temperature was suitably raised, making the filling process easier to perform. After conducting the necessary resin-filling process, the heating process was done to harden said resin filling thereby completing a semiconductor package wherein flip chip 9 has been fixed and secured on the alumina type board 6'. However, in the above-described construction, the flat external connector terminals 8 brought out and positioned at the back side of board 6' may be in a random arrangement but a constant-pitch lattice-array arrangement is desirable in terms of standardization; further, in the case of a construction with a comparatively big outer margin, dummy external terminals may be installed outside, on each corner of the required flat external connector terminals 8. From the above description it will be apparent that there is thus provided a device of the character described possessing the particular features of advantage before enumerated as desirable, but which obviously is susceptible to modifications such as in its form, method, mechanization, operation, detailed construction, and arrangements of parts. As has been explained above, the semiconductor package related to this invention is not only utilized as connecting face for the semiconductor chip to be mounted on the board; it is also utilized as wiring circuit face for connecting to the external connector terminals leading to and are exposed on the back side. By employing a construction which utilizes the board face more effectively, compacting of semiconductor packages is made easier while at the same time, when said connection including a wiring circuit is buried in the board to maintain flatness, the fineness of the sealing resin layer that fills and seals this region is also ensured. Particularly, since only external connector terminals lead to and are exposed on the back side, the required insulation can easily be established even when mounting on a base board. In other words, on the back surface of the board, without the wiring pattern, a mutually insulated condition is established and only external connector terminals lead to and are exposed. Because of this, electrical insulation between the external connector terminals as well as between the external connector terminals and the base board can surely be established thereby making it possible to form a highly reliable mounting circuit. Since reliability is easy to establish and compacting is also possible with the semiconductor package related to this invention, when coupled with features such as detachability, it can be said to be quite suitable for use in memory cards. While in order to comply with the statute, the invention has been described in language more or less specific as to structural features shown, but the means, method and construction herein disclosed comprise the preferred form of several modes of putting the invention into effect and the invention is therefore claimed in any of its forms or modifications within the legitimate and valid scope of the appended claims.

Claims: A semiconductor package comprising: a board (6) having first and second opposing surfaces; a wiring circuit (6b) having connections (6a) and formed on the first surface; a semiconductor chip (9) mounted face down having input/output terminals (9a) adapted to the connections (6a) of said wiring circuit (6b); flat external connector terminals (8) formed on the second opposing surface; and filled via holes (7) formed through the board (6) and electrically connected to each of said connections (6a) and to corresponding flat external connector terminals (8); characterised in that : said wiring circuit (6b) and said connections (6a) are inlaid in said first surface of the board (6) such that the outer surface of said connection (6a) and said wiring circuit (6b) are almost level with said first surface of the board (6); and said flat external connector terminals (8) are inlaid in the second surface of the board (6) such that the outer surface of the terminals (8) are almost level with said second surface of the board (6) and are exposed in constant-pitch lattice-array on said second surface of said board (6). A semiconductor package as set forth in claim 1, wherein the board (6) is installed with a reinforcing dummy pattern on the edges of the board by enclosing said wiring circuit region on the first surface of the board (6). A semiconductor package as set forth in claim 1 or 2, wherein the board (6) is installed with dummy connector terminals formed on comer portions of the second surface of said board (6) in addition to said external connector terminals (8). A semiconductor package according to any one of the preceding claims wherein each of said filled via holes (7) connects substantially in a straight line between each of said connections (6a) and corresponding flat external connector terminal and is installed perpendicular to the first and second surfaces of the board (6).

Inventors: IWASAKI HIROSHI, IWASAKI,HIROSHI, IWASAKI,HIROSHI, C/O INTELL. PROP. DIV. KK TOSHIBA
Applicants: TOSHIBA KK, KABUSHIKI KAISHA TOSHIBA
Application year: 1995
Main classification: H01L23
IPC codes: H01L23, H01L21