Metal fusion bonding – Process – Using high frequency vibratory energy
Reexamination Certificate
2000-08-03
2001-08-07
Dunn, Tom (Department: 1725)
Metal fusion bonding
Process
Using high frequency vibratory energy
C228S106000, C228S262000, C438S120000
Reexamination Certificate
active
06269999
ABSTRACT:
FIELD OF THE INVENTION
The present invention pertains to a method for mounting a semiconductor chip onto a substrate utilizing ultrasonic vibrations.
BACKGROUND OF THE INVENTION
As a method for mounting a semiconductor chip onto a substrate, a method referred to as flip-chip mounting has been widely adopted. In the case of flip-chip mounting, a body provided with several conductive bumps, that is, bumps usually made of gold, serving as connecting terminals is placed face down onto the surface (referred to as main surface, hereinafter) where circuits are formed on a semiconductor chip, that is, with the main surface facing the substrate, in order to bond said conductive bumps directly to the wires on the substrate. In flip-chip mounting, a method referred to as ultrasonic thermocompression bonding has long been well known as a method for bonding said conductive bumps to the wires on the substrate.
In the ultrasonic thermocompression bonding method, a semiconductor chip is held by suction using a vacuum suction tool and placed over the area where the bumps are to be mounted onto the wires formed on the substrate. When bonding the gold bumps onto the wires, a fixed amount of pressure is applied to the semiconductor chip using a suction tool, and the substrate is heated at the same time. Under said conditions, ultrasonic vibrations of a prescribed frequency are applied to the semiconductor chip via said suction tool. The gold bumps on the semiconductor chip are well bonded to lands on the substrate by said pressure, heat, and ultrasonic vibrations.
In order to transmit the energy of the ultrasonic vibrations applied via said suction tool to the conductive bumps efficiently, it is important to bring the suction tool and the semiconductor chip into close contact by means of vacuum suction. However, a minute gap may be created between the suction surface of the suction tool and the back of the semiconductor chip placed against the suction surface, resulting in a drop in suction power. This drop in suction power not only reduces the energy of the ultrasonic vibrations applied to the gold bumps but also creates another problem.
That is, when the suction power of the suction tool drops, the semiconductor chip can no longer follow the ultrasonic vibrations applied to the tool, resulting in the problem that tip of the suction tool ends up abrading the surface of the semiconductor chip due to friction. Some of the scraped-off fine silicon particles stick to the back of the semiconductor chip, land on the substrate, and may even be incorporated into a device eventually.
In addition, even when the aforementioned drop in the suction power is not present, the semiconductor chip stops following the vibrations of the suction tool when or immediately before the conductive bumps become fixed to the wires on the substrate. In such case, also, the aforementioned problem of chip abrading occurs.
The particles stuck to the semiconductor chip have potential for causing serious problems depending on the ultimate use of the semiconductor chip. For example, a preamplifier bare chip to be mounted on an actuator in a hard disk device may be mentioned. Said scraped-off particles (they are 0.1-5 &mgr;m or so in size) stuck to the semiconductor chip come loose inside the device due to vibrations caused by revolution of the magnetic disk and ultimately fall onto the disk. Because the magnetic head floats at a distance of 50 &mgr;m or less from the disk surface, said scraped-off particles on the disk seriously affect the function of the hard disk drive.
Therefore, the purpose of the present invention is to prevent said problems caused by said abraded particles when mounting said semiconductor chip, by preventing creation of the particles by abrasion of the chip while it is being mounted onto the substrate using the ultrasonic thermocompression bonding method.
SUMMARY OF THE INVENTION
The semiconductor chip mounting method utilizing ultrasonic vibrations of the present invention involves a step in which a semiconductor chip having conductive bumps serving as connecting terminals on its main surface is held by its back via an elastic film using a suction tool having a suction hole; a step in which said semiconductor chip is positioned against a substrate provided with connection wires corresponding to said conductive bumps, and said semiconductor chip is mounted onto said substrate in such a manner that said conductive bumps connect to said connection wires; and a step in which ultrasonic vibrations are applied from said suction tool to said semiconductor chip via said film while said semiconductor chip is being pressed against said substrate in order to bond said conductive bumps with said connection wires.
In addition, the aforementioned mounting method may also involve a step in which a hole is created on said film at the position corresponding to the suction hole of said suction tool when holding said semiconductor chip by suction via said film using said suction tool.
In addition, the semiconductor chip mounting method utilizing ultrasonic vibrations of the present invention involves a step in which a semiconductor chip having conductive bumps serving as connecting terminals on its main surface is positioned against a substrate provided with connection wires corresponding to said conductive bumps, and said semiconductor chip is mounted onto said substrate in such a manner that said conductive bumps connect to said connection wires and a step in which ultrasonic vibrations are applied to said semiconductor chip from a pressing member via an elastic film while said semiconductor chip is being pressed against said substrate from the back of said semiconductor chip via said elastic film using said pressing member in order to bond said conductive bumps with said connection wires.
In the respective mounting method above, it is desirable that said film be shaped like a long tape, and an unused area of said film is fed into the space between said suction tool and the back of said semiconductor chip every time a new semiconductor chip is mounted.
In addition, it is desirable that the step for bonding said conductive bumps with said connection wires be carried out while applying a fixed level of tension to said film. Said tension improves the oneness of the suction tool (pressing member) with the semiconductor chip, so that the energy of the ultrasonic vibrations can be transmitted more efficiently.
In addition, it is desirable that the step for bonding said conductive bumps with said connection wires be carried out while applying heat to said substrate.
Furthermore, it is desirable that said film be a 10-50 &mgr;m thick resin film, and that fluororesin or straight chain type polyimide resin be utilized as the material of said film.
An embodiment of the present invention will be explained below along with figures. In the semiconductor chip mounting method pertaining to the present embodiment, a suction tool of the kind shown in
FIG. 1
is utilized. The suction tool
10
is one of the constituents of a device, such as a flip-chip bonding device, used to mount a semiconductor chip onto a substrate.
The suction tool
10
has a suction nozzle
11
whose tip constitutes a suction surface
11
a
for the semiconductor chip. The semiconductor chip is held onto said suction surface
11
a
by means of vacuum suction achieved by the suction power obtained through a suction hole at the tip of the suction nozzle. An ultrasonic horn
12
for supplying ultrasonic vibrations is connected halfway up the suction nozzle
11
. The ultrasonic horn
12
supplies lateral vibrations of a specific frequency to the suction nozzle
11
for a prescribed period of time. The tip of the suction nozzle
11
and ultimately the semiconductor chip held there by means of vacuum suction are vibrated microscopically in the lateral direction by said vibrations. As will be described later, the semiconductor chip is bonded to the substrate by said vibrations, pressure, and heat.
Although it is not shown in
FIG. 1
, the present invention further utilizes an
Masumoto Kenji
Masumoto Mutsumi
Okazaki Tomohiro
Yamaguchi Katsumi
Cooke Colleen P.
Dunn Tom
Petersen Bret J.
Telecky , Jr. Frederick J.
Texas Instruments Incorporated
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