Active solid-state devices (e.g. – transistors – solid-state diode – Lead frame
Reexamination Certificate
2002-01-31
2002-11-05
Cao, Phat X. (Department: 2814)
Active solid-state devices (e.g., transistors, solid-state diode
Lead frame
C257S676000
Reexamination Certificate
active
06476466
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a technique that is applied to a semiconductor device, especially to a semiconductor device having a base substrate that comprises flexible films.
As a suitable semiconductor device for a high-pin-count package, a semiconductor device having a BGA (BALL GRID ARRAY) structure has been developed. In this semiconductor device with a BGA structure, a semiconductor chip is mounted on a chip mount area of a main surface of a base substrate by using adhesive material and several bump electrodes are positioned in an array on the back side thereof that is opposite to said main surface of the base substrate.
The above-mentioned base substrate is provided in the form of the rigid resin substrate that consists of glass impregnated with, for example, an epoxy resin, a polyimide resin, a maleimide resin, etc. Electrode pads for wire connection are arranged in a peripheral area that surrounds the periphery of the chip mount area of the main surface of the base substrate, and several electrode pads for bump connection are arranged on the back of the base substrate. The bump electrodes comprise solder materials of, for example, a Pb—Sn composition, which fix and connect to the electrode pads for bump connection electrically and mechanically.
The above-described semiconductor chip comprises the structure mainly of a semiconductor substrate that includes, for example, monocrystal silicon. On the semiconductor chip, a logical circuit system, a storage circuit system or a mixture of these circuit systems are formed. And, several external terminals (bonding pads) are allocated to the main surface (element formation face) of the semiconductor chip. These external terminals are electrically connected through wires to electrode pads for wire connection arranged on the main surface of the base substrate.
The semiconductor chip, the wires, the electrode pads for wire connection, etc. are sealed in the resin sealing body formed on the main surface of the base substrate. The resin sealing body is formed by a method of transfer molding, which is suitable for mass production.
A semiconductor device of the BGA structure composed like this is mounted on the surface of a printed circuit board by melting connection of the bump electrodes onto the electrode pads formed on the surface of the printed circuit board.
NIKKEI electronics (Feb. 28, 1994, from the 111th page to the 117th page) published by NIKKEI BP, describes a semiconductor device having the above-described BGA structure.
SUMMARY OF THE INVENTION
A semiconductor device having a BGA structure and using a flexible film as a base substrate has been developed in recent years. The semiconductor device of this type can be made thinner, is able to provide a high-pin-count package and is more amenable to miniaturization in comparison with a semiconductor device using a rigid resin substrate as a base substrate. However, we have found the following problems in developing semiconductor devices using a flexible film as a base substrate.
A base substrate that comprises flexible films is generally made using the following process. First, a connection hole is formed in the bump connection area of a flexible film. Then, a metal foil, such as, for example, copper (Cu), is attached to one surface of a flexible film through an adhesive material. Then, electric conductor layers that comprise electrode pads for bump connection, an electric conductor, an electrode pad for wire connection and an electric conductor for plating etc. are formed by patterning on the metal foil. Then, an insulation layer that protects the electric conductor layer is formed. Then, plating processing to form a plating layer on the electrode pad for bump connection and wire connection is carried out. Plating processing is done by a method of electrolytic plating. This plating processing is sometimes performed in the step before forming the insulation layer. The plating layer is formed on, for example, a gold (Au)
ickel (Ni) film or a gold (Au)/palladium (Pd)
ickel (Ni) film.
The above insulation layer is formed by the following process, for example. First, a photosensitive resin film is formed on one surface of a flexible film. Then, after performing a baking processing, by using a photograph printing technique, photosensitive processing, development processing and cleaning are performed. The insulation layer is formed on all areas of the one surface of the flexible film containing the electric conductor layers, except for the electrode pads for wire connection. That is, insulation layers are formed on almost all areas of the one surface of the flexible film. Therefore, warp and distortion, etc. arise in the base substrate. This deformation of a base substrate causes a transfer problem during the manufacturing process (assembly process) of a semiconductor device. And, this deformation of a base substrate becomes a cause of a further problem in the process that mounts a semiconductor chip, in that the wetting performance of the adhesive material being used is deteriorated.
As for the cause of deformation of the above-described base substrate, it is a main factor that the thermal expansion coefficient and the hardening shrinkage rate of an insulation layer are large. But, in case an insulation layer is not formed on the flexible film, the following problems arise.
(1) Electrode pads for bump connection are arranged on the chip mount area of a main surface of a base substrate. Therefore, when mounting a semiconductor chip through the use of an adhesive insulation material to the chip mount area on a main surface of the base substrate, it is difficult to control the thickness of the adhesive material. And, if the semiconductor chip should touch the electrode pads for bump connection, a short circuit could arise between them.
(2) Electrode pads for bump connection are arranged on the chip mount area of the main surface of the base substrate. Bump electrodes arranged on the back side of the base substrate are connected to these electrode pads for bump connection through connection holes formed in the chip mount area of the base substrate. That is, bump electrodes are arranged in the area under a semiconductor chip.
The electrode pads for bump connection arranged on the chip mount area of the above-described base substrate are integrated and are electrically connected through electric conductors to the electrode pads for wire connection arranged on the peripheral area that surrounds the chip mount area of the main surface of the base substrate. That is, in the peripheral area of the main surface of the base substrate, electric conductors are arranged on the area between a semiconductor chip and the electrode pads for wire connection. Therefore, when connecting the external terminals of a semiconductor chip and pads for wire connection with wires, other electric conductors that adjoin electric conductors electrically connected to the wires and these wires sometimes cross themselves. In case there is a sufficient height for the wire connection, there is no problem. However, there is some possibility of a short circuit with wires and other electric conductors, when wires and other electric conductors are not arranged in parallel at the corner of a semiconductor chip. And, there is a possibility that, in case wires and other electric conductors cross each other on the side of electrode pads for wire connection, a short circuit with these wires and other electric conductors may also arise.
It is an object of the present invention to provide a technique which makes it possible to suppress deformation (warp and distortion) of a base substrate in a semiconductor device when the base substrate comprises flexible films.
It is another object of the present invention to provide a technique which makes it possible to suppress deformation of a base substrate in a semiconductor device when the base substrate comprises flexible films and to prevent a short circuit between electric conductors of the base substrate and the semiconductor chip.
It is another object of
Fujisawa Atsushi
Haruta Ryo
Ichitani Masahiro
Konno Takafumi
Ohsaka Shingo
Cao Phat X.
Hitachi Hokkai Semiconductor Ltd.
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