Metal fusion bonding – Process – Using a compliant cushioning medium
Reexamination Certificate
1999-08-13
2001-02-27
Ryan, Patrick (Department: 1725)
Metal fusion bonding
Process
Using a compliant cushioning medium
C228S110100, C228S112100, C228S114000, C156S073100
Reexamination Certificate
active
06193136
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field of the Invention
The present invention relates to component mounting method and apparatus wherein a component is mounted on a mounting surface by bonding their respective metallic electrical bonding interconnects. In particular, it describes the process of and apparatus for manufacturing an electronic circuit substrate wherein electronic components such as bare IC chips are mounted on substrates such as printed-wiring circuit boards.
2. Description of Prior Art
Bare IC chips are formed of a semiconductor wafer on which circuit patterns are fabricated using thin-film forming techniques and mounted on a printed board for manufacturing an electronic circuit board. As shown in
FIG. 11
, electrodes
107
are prefabricated in a circuit pattern on a bare IC chip
103
to be electrically connected to conductor lands
109
formed on a printed-wiring board
104
. For mounting such bare IC chip
103
on the circuit board
104
, a surface mount method is used wherein the bonding face
103
a
of the IC chip
103
where the electrodes
7
exist and the bonding face
104
a
of the circuit board
104
where the conductor lands
109
exist are brought to a face-to-face contact and fixed to each other for achieving electrical connection between the conductor lands
109
and electrodes
107
. Sealant
111
made of resin is then filled between the bonding faces
103
a,
104
a
as shown in
FIG. 12
for encapsulating the circuit pattern including the electrical bonding areas formed on the bonding face
103
a
of the IC chip
103
.
In a mounting method which has been used in recent years, a bare IC chip
103
, on which metal bumps
108
have been formed upon electrodes
107
as shown in
FIG. 11
by a wire bonding process or the like, is held by suction with a suction nozzle
114
and is brought opposite to a circuit board
104
at a predetermined location, where the bumps
108
are pressed onto conductor lands
109
on the circuit board
104
for bonding them in electrical connection with each other. At the same time the bumps
108
and conductor lands
109
are fixed to each other with adhesive
112
that may be supplied in advance to bumps
108
or conductor lands
109
or with solder paste that assists electrical bonding of metal interconnects. The bare IC chip
103
is thus mounted on the circuit board
104
. The circuit board
104
is then held in an inclined state as shown in
FIG. 12
, and sealant
111
is flowed between the bonding faces
103
a,
104
a
of the IC chip
103
and circuit board
104
as shown in phantom lines in the figure with the use of a dispenser
115
or the like. Sealing is completed when the sealant
111
is filled between the IC chip
103
and circuit board
104
as shown in solid lines in FIG.
12
.
In such method the equipment cost is high, since the process of mounting bare IC chips
103
on circuit boards
104
and the process of dispensing sealant
111
between the bonding faces
103
,
104
a
of IC chip
103
and circuit board
104
differ substantially from each other in the handling of circuit boards and the design of operations, and are performed separately in different apparatuses. Moreover, the sealant
111
takes time to flow into between the bonding faces
103
,
104
a,
wherefore the productivity is low. For example, in the case of mounting an IC chip
103
of 10 mm×10 mm size, the dispenser
115
is moved along the upper side of the IC chip from one end to another and returned so as to apply the sealant
111
to the entire area between the bonding faces
103
a,
104
a.
The operation is finished only when the sealant has filled between IC chip
103
and circuit board
104
to the extent that a wetted portion
113
is formed around the IC chip
103
as shown in FIG.
12
. In such method it takes about 10 seconds for the operation of mounting one IC chip
103
. Furthermore, there is not much choice of sealing materials, i.e., the sealant
111
must have a viscosity in the range 2000 to 3000 cps, since it is poured into the very small gap of about 50 &mgr;m between the bonding faces
103
a,
104
a.
Moreover, a sealant
111
having such viscosity needs to be heated at a relatively high temperature of from 40 to 60° C. to set, because of which the operation time is further increased. It is also undesirable in the interest of economy in energy since heat consumption is high.
In addition, there is a risk that fillers contained in the sealant
111
that is poured in between the bonding faces
103
a,
104
a
may be distributed in stripes, causing a sealing failure. Also, since electrical connection between bumps
108
of IC chips
103
and conductor lands
109
of circuit boards
104
is accomplished only by mutual contact, a defective bond is sometimes formed, even though the electrical bonding areas on IC chips and circuit boards are fixed with each other with adhesive
112
and sealant
111
. The yield of product is thereby decreased. The bumps
108
and lands
109
may be fixed with each other using solder paste, which will, however, result in consumption of more heat and time for heating solder paste and for letting it set.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a method and an apparatus for mounting components in which electrical bonding of components on a mounting surface is achieved without failure in a short period of time with simple equipment and low heat consumption.
To accomplish the above object, the component mounting method according to the present invention comprises the steps of: supplying a sealant to one or both of the component and mounting surface; placing the component in proximity to the mounting surface; pressing an electrical bonding area of the component tightly to an electrical bonding area of the mounting surface, whereby the sealant is compressed and filled between the component and mounting surface in a required area; and generating friction between the electrical bonding areas of the component and the mounting surface in tight contact with each other by moving the component and mounting surface relative to each other, whereby both of the electrical bonding areas are melted and welded together.
By the above method, the sealant can be forcibly and instantaneously filled in a required area between the component and mounting surface without any additional operation or time. Therefore, the bonding of both electrical bonding areas and the filling of the sealant can be achieved with one operation in a short time. There are no viscosity restrictions on the sealant as in the case of the flowing method and a sealant of high viscosity can be used, wherefore the sealant can be set in a short time at a low temperature during the above operation. The component mounting can thus be accomplished with simple operation and apparatus in a short period of time with low heat consumption. Moreover, the electrical bonding areas are securely welded together by melting metal, whereby the formation of a defective bond is prevented and the yield is improved. The production cost can be accordingly reduced.
In particular, when pressure-welding the electrical bonding areas of the component and mounting surface by friction therebetween, the metal welding can be swiftly performed if ultrasonic vibration is applied to the component thereby ultrasonically bonding the electrical bonding areas.
The sealant is supplied in advance to at least one of the bonding faces of the component and mounting surface. Since it is provided in a mass, air is hardly mixed therein. Alternatively, the sealant may be coated using a dispenser, printed, or transferred at an appropriate time. Either way, the sealant can be fed simply and swiftly during or in association with the operations for handling the component or mounting surface.
By using a bump for at least one of the electrical bonding areas of the component and the mounting surface, the ultrasonic bonding of the local electrical bonding areas of the component and mounting surface can be achieved easily and securely with a sufficient amount
Higashi Kazushi
Kanayama Shinji
Minamitani Shozo
Otani Hiroyuki
Takahashi Kenji
Matsushita Electric - Industrial Co., Ltd.
Price and Gess
Ryan Patrick
Stoner Kiley
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