Active solid-state devices (e.g. – transistors – solid-state diode – Combined with electrical contact or lead – Die bond
Reexamination Certificate
2000-01-28
2004-09-14
Zarneke, David A. (Department: 2827)
Active solid-state devices (e.g., transistors, solid-state diode
Combined with electrical contact or lead
Die bond
C257S784000
Reexamination Certificate
active
06791194
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a circuit tape, a semiconductor device, and a method of manufacturing the same, which are superior in electrical characteristics, mounting reliability, and assembling easiness, and are responsive to the requirements for high density mounting, multipins mounting, and fast transmittance.
Currently, in the continuing effort to improve electronic devices to provide high performance, the demand for high integration and high density mounting of semiconductor elements has become strong. Therefore, semiconductor elements have been improved to achieve high integration and high performance, such as in LSI, VLSI, and ULSI devices, and there has been increase in the capacity, the number of pins, the speed, and power consumption thereof. In responding to such advances, the package structure of the semiconductor device for multipins has been changed from a structure, in which connecting terminals are provided at two sides of the semiconductor element, to an advanced structure, in which the connecting terminals are provided at all four sides of the semiconductor element. Furthermore, in order to respond to increasing the number of pins, a grid array structure has come to be used in practice. The grid array structure is a structure of a semiconductor element, in which the connecting terminals are provided in a grid array over the entire mounting surface of the semiconductor element by using a multilayer carrier substrate. The grid array structure includes a ball grid array structure (BGA), which has a shortened connecting terminal length in order to make fast signal transmission possible. The ball type structure of the connecting terminal increases the width of its conductor; therefore, the ball structure is also effective in decreasing inductance. Currently, in order to respond to the requirement for fast signal transmission, organic materials haying a relatively low dielectric constant have been investigated for use in the multilayer carrier substrate. However, the organic materials have generally a larger thermal expansion coefficient than the semiconductor element, and so thermal stress generated by the difference in thermal expansion becomes a problem from the point of view of connection reliability, and so on. Recently, a structure which does not use a carrier substrate has been proposed for the BGA package.
More particularly, a new semiconductor element package structure has been disclosed (U.S. Pat. No. 5,148,265), in which the connection reliability is improved by using an elastomer material having a low modulus of elasticity for reducing the thermal stress generated by the difference in thermal expansion between the semiconductor element and the mounting substrate. The proposed package structure uses a circuit tape composed of a polyimide and the like, instead of a carrier substrate, for electrically connecting the semiconductor element and the mounting substrate. Therefore, the electrical connections between the semiconductor element and the circuit tape are effected by a wire bonding method or a bonding connection with leads, and the circuit tape and the mounting substrate are electrically connected by soldering ball terminals. As the elastomer material of the prior art, a silicone material is generally used since this is a material having a low modulus of elasticity and a superior heat resistance. As a general method for forming a stress buffer layer with a silicone material, the steps of printing an uncured liquid resin on the circuit tape using masks, and subsequently, curing the printed resin, are generally used. However, the above method has problems, such as a difficulty in maintaining the flatness of the buffer layer obtained by the printing, and the complexity of the printing process, which requires a long time for the printing, is disadvantageous. Accordingly, the above method is not suitable for a mass-production process, and so the problems which undesirably affect the assembling yield and reliability of mounting caused by the difficulty in maintaining the flatness of the buffer layer are yet to be solved.
SUMMARY OF THE INVENTION
One of the objects of the present invention is to provide a method of obtaining a stress buffer layer which is superior in flatness by using a film material as the elastomer material for reducing the thermal stress in the semiconductor devices, thereby obtaining semiconductor devices which are superior in mass productivity.
In order to realize the above object, the present invention provides the following measures.
The measures can be achieved by providing a semiconductor device comprising a circuit tape having a pattern layer connected electrically to a semiconductor element, an external terminal provided on the circuit tape for electrically connecting the circuit tape to a mounting substrate, and film material for causing the circuit tape to adhere to the semiconductor element while maintaining an insulation condition between the circuit tape and the semiconductor element, wherein the film material for effecting the adhering has a physical property such that the modulus of elasticity of the film material in the temperature range of a solder reflow condition for mounting (200-250° C.) is at least 1 MPa.
The above film material for effecting the adhering is passed through a process for forming an external terminal, such as a solder ball and the like, for connecting the mounting substrate and the circuit tape, or a solder reflow process for mounting the semiconductor element of the present invention onto a mounting substrate in the manufacturing process of the semiconductor devices. The reflow temperature is generally a high temperature in the range of 200-250° C. Therefore, if the semiconductor device contains moisture, the moisture evaporates during the heat treatment, and the film material swells due to the vapor pressure of the moisture. When the swelling exceeds a threshold value, a foaming phenomenon is generated, and defects, such as void formation, delamination, and the like, are generated. Therefore, the film material to be used is required to have as low a moisture absorption rate as possible and a high modulus of elasticity in the range of the reflow temperature. In accordance with the present invention, various film materials have been studied, and it was found that the adhesive materials having a modulus of elasticity in the temperature range of a reflow process of at least 1 MPa had superior reflow characteristics. Several examples of the temperature dependence of the modulus of elasticity of the material are shown in FIG.
1
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Furthermore, it was found that when materials, of which the modulus of elasticity in the temperature range of the mounting reflow condition was maintained at least at 1 MPa, were used, a preferable result in the anti-reflow characteristics could be obtained. The amount of swelling depends on the ratio of the vapor pressure and the modulus of elasticity, and the higher the modulus of elasticity is, the less will be the amount of swelling. The foaming phenomenon is generated when the amount of swelling exceeds the break elongation, one of the mechanical properties of the material. Furthermore, the modulus of elasticity correlates with the mechanical strength of the adhesive film material, and generally, the higher the modulus of elasticity is, the greater will be the tendency to increase the break stress and break elongation. Therefore, by using a material having a high modulus of elasticity in the range of the reflow temperature, the reflow characteristics can be improved as to both the swelling amount and the mechanical characteristics. In the above case, the adhesive film material may be either a thermosetting resin or a thermoplastic resin.
The adhesive layer is sometimes composed of either sticky adhesive agents or sticky-cohesive adhesive agents, in addition to the adhesive agents made of the above material. In order to maintain the modulus of elasticity at least at 1 MPa in the temperature range of the reflow process, the thermoplastic resin
Anjoh Ichiro
Eguchi Shuji
Hattori Rie
Ishii Toshiak
Kitano Makoto
Antonelli Terry Stout & Kraus LLP
Cruz Lourdes (Elle)
Hitachi , Ltd.
Zarneke David A.
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