stack package made of chip scale packages

[0001] This application claims priority under 35 U.S.C. § 119 from Korean Patent Application 2003-281 filed Jan. 3, 2003, in the Korean Intellectual Property Office, the entire contents of which are hereby incorporated by reference.

[0002] 1. Field of the Invention

[0003] The present invention relates generally to semiconductor packages, and more particularly, to a stack package made of a plurality of area array type chip scale packages.

[0004] 2. Description of the Prior Art

[0005] The miniaturization of semiconductor packages has progressed very rapidly during the past ten years in order to keep up with the miniaturization of electronic devices. This progression of miniaturization has been especially prevalent in the field of mobile electronic devices because of the wide spread usage of chip scale packages (CSP). However, chip scale packages have a disadvantage when compared with conventional lead frame type packages because of the difficulty in using them with package stacking technology.

[0006] Stack packages, which are made by stacking a plurality of packages, have been developed and widely used to increase the installation density of chips. The stack package is different from a multi chip package (MCP), which is made by installing a plurality of chips in a package. The multi chip package has advantages in package size and package installation convenience. However, productivity of the multi chip package can be low because often chips that have not been tested for their quality are used, and if even one of the installed chips is inferior in performance, the entire multi chip package becomes inferior. On the contrary, the productivity of the stack package is usually superior to that of the multi chip package because all of the packages used for the stack package are tested. Therefore, even though both methods are available, the stack package is the preferred method to enhance chip installation density because of its reliability.

[0007] Chip scale packages are generally area array type packages, which are more inappropriate for stacking than lead frame type packages. There has been much effort to develop chip scale packages suitable for package stacking. Three examples of chip scale packages suitable for the stack package are disclosed in FIG. 1–FIG. 3.

[0008] FIG. 1 shows a well-known conventional type stack package 600 made of a plurality of chip scale packages. Each stacked chip scale package is a fan-out type ball grid array package 610. As shown in FIG. 1, a semiconductor chip 611 is installed and electrically connected to a beam lead 622 on a circuit board 620. A plurality of solder balls 637 are positioned on the peripheral area of the circuit board 620 and are connected to the semiconductor chip 611 through the beam lead 622.

[0009] One problem with the chip scale package 610 disclosed in FIG. 1, is that it is difficult to standardize the arrangement of the solder balls 637, because the arrangement of the solder balls 637 must be designed according to the size of the installed chip. For example, a 512 Mb DRAM chip cannot be installed in a package designed for a 256 Mb DRAM chip. This severely limits the versatility of this type of chip scale package stack.

[0010] FIG. 2 shows another conventional type stack package 700. Referring to FIG. 2, each stacked chip scale package 710 is made by attaching a chip 711 to a carrier tape 720 by beam lead bonding. The outer leads 737 of the stacked chip scale packages 710 are electrically connected to each other. In this kind of stack package, it is difficult to standardize each stacked package because the length of the outer leads 737 of each stacked package varies according to the stacked level. This non-standardization of lead parts results in production cost increases.

[0011] FIG. 3 shows a further conventional type stack package 800. Referring to FIG. 3, the stack package 800 comprises a plurality of fan-out type chip scale packages 810 and a conventional ball grid array (BGA) type chip scale package 805. The fan-out type chip scale packages 810 are electrically connected to each other and to the BGA chip scale package 805 with solder balls 838 formed on a lower surface of substrate 821. The BGA type chip scale package 805 is stacked at the lowest level. The solder balls 837 are formed on the entire area of the BGA type chip scale package, and function as Input/Output ports of the stack package 800. This kind of stack package has the same technical drawback, i.e., the difficulty of standardizing the solder ball arrangement, as that of the stack package 600.

[0012] A stack package according an embodiment of the present invention comprises at least two area array type chip scale packages. Each chip scale package has a substrate, a plurality of ball land pads formed on a lower surface of the substrate, a plurality of circuit patterns formed on the lower surface of the substrate and electrically connected to the ball land pads, and at least one chip installed on the upper surface of the substrate and electrically connected to the circuit patterns.

[0013] Embodiments of the present invention direct the stacked chip scale packages to be attached to one another by orienting the ball land pads of the upper stacked chip scale package so that they face in the opposite direction of those of the lower stacked chip scale package. In addition, the circuit patterns of the upper stacked chip scale package are electrically connected to those of the lower stacked chip size package by connecting boards.

[0014] Furthermore, a hole may be formed on the substrate of each chip scale package, to allow the chip to be electrically connected to the circuit patterns by bonding wires passing through the hole.

[0015] Additionally, the chip may be protected by a first encapsulating part, and the bonding pads and the bonding wires may be protected by a second encapsulating part.

[0016] When an odd number of chip scale packages need to be stacked, a single chip scale package can be stacked on and electrically connected to adjacently stacked chip packages through a plurality of solder balls.

[0017] When an even number of chip scale packages needs to be stacked, adjacently stacked chip scale packages coupled by the connecting boards may be stacked on, and electrically connected through a plurality of solder balls to the other adjacently stacked chip scale packages.

[0018] A plurality of connection pads may be further formed on the region of each substrate on which the plurality of ball land pads are formed, and electrically connected to the circuit patterns. The connecting boards may then be attached to the connection pads so that they may be electrically connected to the circuit patterns through the connection pads.

[0019] Also, each chip scale package of an adjacent pair of chip scale packages may be attached to the other by an adhesive applied on the first encapsulating part or each package.

[0027] The present invention will now be described more fully with reference to the accompanying drawings, in which embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete and will fully convey the concept of the invention to those skilled in the art. In the drawings, the shape of elements is exaggerated for clarity, and the same reference numerals in different drawings represent the same element.

[0028] An embodiment of the present invention is disclosed in FIG. 4. Referring to FIG. 4, the stack package 100 comprises two chip scale packages 110, 150. The two chip scale packages 110, 150 are ordinary area array type packages and have the same structure, except that a plurality of solder balls 137 are formed only on the lower stacked chip scale package 110. The two chip scale packages 110, 150 are stacked in a manner that the ball land pads 163 of the upper stacked chip scale package 150 face in the opposite direction to the ball land pads 123 of the lower stacked chip scale package 110.

[0029] The lower stacked chip scale package 110 will be described referring to FIG. 4. The lower stacked chip scale package 110 is a conventional ball grid array (BGA) type package. A printed circuit board (PCB) or a tape circuit board may be used as a substrate 121 of the chip scale package 110. A plurality of ball land pads 123 are formed and electrically connected to circuit patterns 125 on the lower surface of the substrate 121. A plurality of solder balls 137 may be formed on the ball land pads 123 and function as I/O ports of the stack package 100. A semiconductor chip 111 is attached to the upper surface of the substrate 121 by an adhesive 131, and electrically connected to the circuit patterns 125.

[0030] A plurality of bonding pads 112 of the semiconductor chip 111 are electrically connected to the circuit patterns 125 by bonding wires 135 passing through a hole 127 formed in the central area of the substrate 121. In this embodiment, a center pad type semiconductor chip 111, which has bonding pads formed on the central region of the chip, is preferred. The semiconductor chip 111 is protected by the first encapsulating part 141, and the bonding wires 135, bonding pads 112 and circuit patterns 125 are protected by the second encapsulating part 143.

[0031] The upper stacked chip scale package 150 has the same structure as the lower stacked chip scale package 110 except that solder balls are not formed on the ball land pads 163. That is to say, the upper stacked chip scale package 150 is a land grid array type package that includes semiconductor chip 151 attached to an upper surface of the substrate 161 with adhesive 171. A plurality of bonding pads 152 on semiconductor chip 151 are electrically connected to the circuit patterns 165 by bonding wires 175 passing through a hole 167 formed in the central area of the substrate 161. In this embodiment, a center pad type semiconductor chip 151, which has bonding pads formed on the central region of the chip, is preferred. The bonding wires 175, bonding pads 152 and circuit patterns 165 are protected by the encapsulating part 183.

[0032] On the substrates 121, 161 of the two stacked chip size packages 110, 150, connection pads 126, 166, electrically connected to the circuit patterns 125, 165, are formed outside of the area in which the ball land pads 123, 163 are formed.

[0033] The two chip scale packages 110, 150 are stacked in a manner that the ball land pads 123, 163 of each chip scale package face in opposite directions. This allows the first encapsulating parts 141, 181 of the two chip scale packages 110, 150 to be attached to each other by an adhesive layer 195.

[0034] The connection pads 166 of the upper chip scale package 150 are electrically connected to the connection pads 126 of the lower chip scale package 110 by flexible circuit boards 190. Each flexible circuit board 190 comprises a base film 191 and wiring patterns 192 formed on the base film 191. The flexible circuit boards 190 are attached to the sides of the stack package 100, and the ends of the flexible circuit boards 190 may be electrically connected to the connection pads 126, 166 by tape automated bonding (TAB). Preferably, each end of the flexible circuit boards 190 is folded to increase the connecting area between the circuit boards 190 and the connection pads 126, 166.

[0035] Although the flexible circuit boards are used in this embodiment for electrically connecting the connection pads 126, 166, it is possible to make an electrical connection between the connection pads 126, 166 by other methods, such as via holes filled with conductive materials.

[0036] As described in this embodiment, the chip scale packages 110, 150 used for the stack package 100 have ordinary area array structures. Strictly speaking, the matrix of ball land pads 163 of the upper chip scale package 150 is the same as that of the lower chip scale package 110. Additionally, each chip scale package can be tested for its functional reliability. Therefore, the reliability of the stack chip package can be improved by using tested chip scale packages. Further, an addition of a new chip scale package to the stack package is easily accommodated because each chip scale package used for the stack package is standardized.

[0037] Additions of chip scale packages to the stack package will be described referring to FIG. 5 and FIG. 6.

[0038] FIG. 5 shows another embodiment of the present invention, in which another chip scale package 210 is added to the stack package 100 disclosed previously in FIG. 4. This addition results in the stack package 200 now including three chip size packages 110, 150, and 210. Referring to FIG. 5, the ball land pads 263 of the highest stacked chip scale package 210 are electrically connected to the ball land pads 163 of the middle stacked chip scale package 150 by a plurality of solder balls 237.

[0039] FIG. 6 shows yet another embodiment of the present invention, in which the stack package 500 comprises two of the stack packages disclosed in FIG. 4. This results in the stack package 500 now including four chip size packages 310, 350, 410, and 450. Referring to FIG. 6, chip scale packages 310, 350 are stacked to form a lower stack package 300, and chip scale packages 410, 450 are also stacked to form an upper stack package 400 by the previously described method in FIG. 4. Next, the upper stack package 400 is stacked on and electrically connected to the lower stack package 300 by an electrical connection between the ball land pads 463 of the chip scale package 410 and the ball land pads 363 of the chip scale package 350 through a plurality of solder balls 437.

[0040] By using the structure of stack packages disclosed in the embodiments, any desired number of ordinary area array type chip scale packages can be stacked. Further, because of the standardized structure of the chip scale package stacks, the production costs of the components used in forming these stacks can be reduced.

[0041] Although certain embodiments of the present invention have been shown and described in detail, it should be understood that various changes and modifications may be made therein without departing from the spirit and scope of the appended claims.