The present invention relates to a semiconductor device comprising a semiconductor element connected to a circuit board via an anisotropic conductive film. More particularly, the present invention relates to a semiconductor device capable of maintaining superior conductive property even when used in an environment associated with drastic temperature changes.
In general terms, semiconductor elements, such as IC, are formed in great numbers on a wafer and cut into respective chips. These chips are each connected to a circuit board. With an increasing number of ICs formed on a chip, the number of electrodes formed on the chip also increases, which in turn necessitates the shape and arrangement pattern of the electrodes to be finer and more narrow-pitched. From the aspect of a mounting technique, a chip and a circuit board are not connected by a wire (wire bonding) any more but by mating a conductor circuit (terminal) of the circuit board to an electrode part of the chip (e.g., flip chip bonding). Alternatively, a naked chip may be mounted on a substrate (bare chip mounting) in accordance with the connection method.
When mating a conductor circuit of a circuit board to an electrode of a chip as mentioned above, an anisotropic conductive film may be used between the chip and the circuit board. An anisotropic conductive film is anisotropic in terms of conductivity, because it is conductive in the direction penetrating the two sides of a film (direction of film thickness) and insulating in the direction of expansion of the film surface.
As the above-mentioned anisotropic conductive film, WO98/07216 proposes an anisotropic conductive film wherein a film substrate made from an insulating resin comprises plural conductive paths insulated from each other and passing through the substrate in the thickness direction. When this anisotropic conductive film is used, the anisotropic conductive film is inserted between the semiconductor element (chip) and the circuit board and these three members are heated with or without pressurization. As a result, the both surfaces of the film substrate of the anisotropic conductive film, which is made from an adhesive insulating resin, are adhered to the surface of the semiconductor chip and the board surface of the circuit board. The semiconductor element and the circuit board are electrically connected by the conductive path which, from among the plural conductive paths, is located such that the both ends of the path can be each connected to an electrode of the semiconductor element and a conductor circuit (terminal) of the circuit board.
When the above-mentioned semiconductor device, wherein the semiconductor element is electrically connected to the circuit board via the anisotropic conductive film, is used for a long time in an environment associated with radical temperature changes, the conductive property, which was superior at the beginning, may be degraded strikingly during the use. The present inventors have closely investigated the connection state between the semiconductor element and the circuit board of such a semiconductor device, and found that the connection interface (i.e., at least one of the interface of the connection part between the anisotropic conductive film and the circuit board, and the interface of the connection part between the anisotropic conductive film and the semiconductor element) was destroyed.
It is therefore an object of the present invention to provide a semiconductor device capable of maintaining superior conductive property without destruction of the connection interface even when placed in an environment associated with radical temperature changes.
In accordance with the present invention, the following has been clarified. A conventional semiconductor device has a structure wherein the both surfaces of a film substrate of an anisotropic conductive film are in contact (connected) with the surface of the semiconductor element and the board surface of the circuit board. As a result, the thermal expansion (contraction) of both the semiconductor element and the circuit board acts on the anisotropic conductive film, and a stress due to the difference in the coefficient of linear expansion between the semiconductor element and the circuit board is generated in the connection part between the anisotropic conductive film and the semiconductor element, and in the connection part between the anisotropic conductive film and the circuit board, thereby causing the destruction of the connection interface.
The present invention has been made based on the above finding and is characterized by the following aspects.
(1) A semiconductor device comprising a circuit board, an anisotropic conductive film and a semiconductor element electrically connected to said circuit board via said anisotropic conductive film, wherein the anisotropic conductive film comprises a film substrate made from an insulating resin and plural conductive paths insulated from each other, which paths are disposed in and through the film substrate in the thickness direction, and wherein a gap is formed between the surface on the circuit board side of the film substrate and the board surface of the circuit board.
(2) The semiconductor device of (1) above, wherein the gap has a size of 20-100 xcexcm.
(3) The semiconductor device of (1) above, wherein at least an end of the conductive path at the position corresponding to the conductor circuit formed on the board surface of the circuit board protrudes from the surface on the circuit board side of the film substrate.
(4) The semiconductor device of (1) above, wherein a solder layer is formed on the conductor circuit formed on the board surface of the circuit board, and the anisotropic conductive film and the circuit board are connected by connecting the solder layer with an end of the conductive path.
According to the semiconductor device of the present invention, the surface on the circuit board side of the film substrate of the anisotropic conductive film and the board surface of the circuit board are not connected (contacted) by the presence of a gap between them. Therefore, the anisotropic conductive film is not affected greatly by the external force caused by the thermal expansion (contraction) of the circuit board. As a result, the stress due to the difference in the coefficient of linear expansion between the semiconductor element and the circuit board decreases, that occurs in the connection part between the anisotropic conductive film and the semiconductor element, as well as the connection part between the anisotropic conductive film and the circuit board, thereby preventing the destruction of the connection interface.