Active solid-state devices (e.g. – transistors – solid-state diode – Combined with electrical contact or lead – Flip chip
Reexamination Certificate
2000-03-09
2002-11-19
Flynn, Nathan J. (Department: 2826)
Active solid-state devices (e.g., transistors, solid-state diode
Combined with electrical contact or lead
Flip chip
C438S613000
Reexamination Certificate
active
06483195
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a transfer bump sheet for mounting bumps for flip chip interconnection to a semiconductor chip by transferring all bumps at a time to the semiconductor chip, a semiconductor flip chip having a semiconductor chip on which bumps for flip chip interconnection are formed, and a method of manufacturing the semiconductor flip chip.
BACKGROUND OF THE INVENTION
In recent years, requirements for more functionality and miniaturization of electronic equipment have been increasing, and higher-density integration design and higher-density packaging design of electronic parts have been required accordingly. Therefore, the semiconductor packages used in such electronic equipment have been increasingly miniaturized and are provided with an increasingly large number of pins to a greater extent than in the past.
Conventional semiconductor packages which use lead frames have reached their limits on miniaturization and, therefore, new package methods of area array mount, such as BGA (Ball Grid Array) and CSP (Chip Scale Package), have recently been proposed as a package in which semiconductor chips are mounted on a substrate. In these semiconductor packages, wire bonding, TAB (Tape Automated Bonding), FC (Flip Chip) bonding, etc., are known as methods of electrical connection between pads of semiconductor chip and pads of substrate, which comprises one of various insulating material such as plastics and ceramics, and circuit trace, with a function of conventional lead frame. Recently, however, structures of BGA and CSP using FC bonding, which are favorable for the miniaturization of semiconductor packages, have frequently been proposed. In this FC bonding, bumps are usually formed beforehand on the pads of a semiconductor chip, the bumps being then located in correspondence to the terminals located on an interconnect substrate, and the bonding is performed by thermo-compression.
A vacuum evaporation method, printing method, solder ball aligning method, stud bump method, electrolytic plating method, and etc., are known as methods of directly forming bumps on a semiconductor chip (direct system).
In the vacuum evaporation method, Sn and Pb are evaporated through the use of a metal mask, and solder bumps are formed by means of a wet back. It is impossible to adopt this method in a case of narrow pitches because of the use of the metal mask. In addition, because the growth speed of bumps is low, it takes long time to form bumps for providing a required height, thus posing a problem.
In the printing method, solder-paste projections are formed by methods such as screen printing and are made to reflow, thereby forming solder bumps. This method is low in cost and has high productivity. However, in this method solder paste oozes during printing and sometimes comes into contact with the solder-paste projection formed on an adjoining pad. For this reason, it is difficult to adopt this method in a case of narrow pitches. On the other hand, when a printing method can be used in the case of narrow pitches, it becomes impossible to form bumps having a required height, thus posing a problem.
In the solder ball aligning method, ready-made solder balls are adsorbed with the aid of an adsorption tool provided with holes of the same alignment as the pad alignment of a semiconductor chip, which solder balls are then positioned on the pads of the semiconductor chip and are made to reflow, thereby forming solder bumps. The bump pitch depends on the solder ball diameter. Especially when solder balls are minute, dirt and dust on solder balls and the effect of static electricity sometimes induce failure in adsorption and the adhering of excessive solder balls or cause multiple solder balls to be adsorbed in a grape-like form by one hole of the adsorption tool. Thus, this method has the problem that solder bumps cannot be surely formed.
In the stud bump method, gold bumps or solder bumps are formed by bonding gold wires or solder wires to the pads of a semiconductor chip and cutting these wires. In this method, it is possible to cope with narrow pitches. When gold wires are used, gold bumps can be formed directly on the pads (aluminum pads) of a semiconductor chip and, therefore, there is an advantage that it is unnecessary to form barrier metal. In this method, however, because bumps are formed one by one on the pads of a semiconductor chip, the manufacturing time is long. In addition, the cost of manufacturing is high because the price of gold wire is high. Besides there is a fear that damage to a semiconductor chip may occur and, therefore, this poses the problem that this method cannot be adopted in a case of the area array mount.
In the electrolytic plating method, a plating mask is formed on a semiconductor chip, openings being formed in the positions of pads by exposure and development, and bumps are then formed by electrolytic plating. Because in this method bumps are formed to a required height by plating alone, the manufacturing time is long and the cost of the manufacturing is high. Further, because in the electrolytic plating method it is difficult to make the current density distribution in a plating bath completely uniform, variations in the height of formed bumps occur. The longer the plating time, the more remarkable variations in the height of the formed bumps become and, therefore, it is difficult to solve the problem insofar as the method of forming bumps by plating alone is concerned.
As mentioned above, the direct systems have various problems, and an improvement in the yield of bump forming is the greatest interest.
On the other hand, a transfer bump method has also been developed. In this method, an improvement in yield is aimed by transferring all bumps judged to have good quality to a semiconductor chip at a time. By locating a transfer bump sheet in place, in which bumps have been formed beforehand, in correspondence to a semiconductor chip and by performing heating and pressurization, all the bumps on the transfer bump sheet are transferred to the semiconductor chip at a time.
Methods of forming bumps on a transfer bump sheet, which have hitherto been known, are the vacuum evaporation method, printing method, bump punching method, electrolytic plating method, etching method, and etc.
The vacuum evaporation method has the problem that it is difficult to cope with narrow pitches and the problem that it takes time to form bumps as in the above vacuum evaporation method.
The printing method has the problem that it is difficult to cope with narrow pitches and the problem that bumps cannot be formed to a required height although the cost is low with high productivity similarly to the above printing method.
In the bump punching method, a metal ribbon is punched in the shape of bumps by means of a die and a punch and the bumps are aligned on a base sheet. Although this method has the advantage that the material for the metal ribbon can be freely selected, it has the problem that the manufacturing time is long because bumps are formed one by one on the base sheet. Further, although narrow pitches can be coped with by reducing the punch diameter, the service life of the punch becomes short because of its small diameter, thus posing a problem.
The electrolytic plating method has the problem that the manufacturing time is long and the cost of manufacturing is high and that variations in the height of bumps occur similarly to the above electrolytic plating method.
In the etching method, bumps are formed by etching a metal foil on a base sheet. Because bumps are formed by etching the metal foil, the manufacturing time can be shortened in comparison with the method of forming bumps by electrolytic plating. In addition, this method has the advantage that the bump height can be made uniform by making use of a metal foil with a uniform thickness. As the examples of the metal foil, there are known gold foil, solder foil and copper foil. In the case of using the gold foil, because bumps are made to remain in necessary portions by etching the gold foil, almost all of g
Aoki Hitoshi
Hara Hideki
Hosomi Takeshi
Kato Masaaki
Nakamura Kensuke
Andüjer Leonardo
Flynn Nathan J.
Smith , Gambrell & Russell, LLP
Sumitomo Bakelite Company Limited
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