Semiconductor device manufacturing: process – Coating with electrically or thermally conductive material – To form ohmic contact to semiconductive material
Utility Patent
1998-10-09
2001-01-02
Niebling, John F. (Department: 2812)
Semiconductor device manufacturing: process
Coating with electrically or thermally conductive material
To form ohmic contact to semiconductive material
C438S666000
Utility Patent
active
06169022
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to a method of forming projection electrodes, and more particularly to a method of forming projection electrodes which includes a step of placing resin near positions at which the projection electrodes should be formed.
In general, as the method of forming the projection electrodes on a semiconductor device or a circuit board, a method using plating, a method using soldering paste and a method using solder balls have been known. For example, to form projection electrodes each of which has a thickness of several hundreds micrometers (&mgr;m), the method using the solder balls is used.
In recent years, circuit elements have been miniaturized, so that the projection electrodes are miniaturized and a space between the projection electrodes becomes narrow. In addition, for cost reduction, it is necessary to simplify the method for forming the projection electrodes. Thus, a method of easily forming miniaturized projection electrodes with a high reliability is desired.
2. Description of the Related Art
A description will be given, with reference to
FIGS. 1 through 6
, of a conventional method of forming projection electrodes using solder balls.
FIG. 1
shows a semiconductor device which is in an initial state before forming projection electrodes. The semiconductor device in this state has a so-called LGA (Land Grid Array) structure in which only a plurality of pad portions
10
are arranged in a mounting surface of a package
2
.
Referring to
FIG. 1
, the package
2
has a multi-layer structure made of ceramic or resin. A cavity
12
is formed in the package
2
. In the cavity
12
, a semiconductor chip
4
is mounted and a part of an internal wiring pattern
6
is formed so as to be exposed.
The internal wiring pattern
6
is electrically connected to the pad portions
10
via an internal wiring portion (not shown) which is formed inside the package
2
. The semiconductor chip
4
is connected to the internal wiring pattern by wires
8
. Thus, the semiconductor chip
4
is electrically connected to the pad portions
10
via the wires
8
, the internal wiring pattern
6
and the internal wiring portion.
To form projection electrodes
22
on the semiconductor device having the above structure, firsts as shown in
FIG. 2
, a metal mask
14
is set on the surface of the package
2
on which the pad portions
10
are formed (a mask setting step). The metal mask
14
has positioning openings
16
arranged at intervals equal to those at which the part portions
10
are arranged. The metal mask
14
is set so that the positioning openings
16
corresponds to the pad portions
10
.
After the metal mask
14
is set on the package
2
as described above, paste
18
(flux) is provided in each of the positioning openings
16
of the metal mask
14
(a paste setting step) as shown in FIG.
3
. As a method of providing the paste
18
in each of the positioning openings
16
, for example, a screen printing method can be used. Due to providing the paste
18
in each of the positioning openings
16
of the metal mask
14
, each of the pad portions
10
is covered with the paste
18
.
Next, as shown in
FIG. 4
, solder balls
20
are set on the pad portions
10
(a projection electrode setting step). In this case, since solder balls
20
are positioned by the positioning openings
16
of the metal mask
14
, the solder balls
20
can be accurately set on the pad portions
10
. In addition, the paste
18
has a predetermined viscosity, so that the paste
18
functions as an adhesive. Thus, the solder balls
20
are in a temporary fixing state on the pad portions
10
.
After the solder balls
20
are set on the pad portions
10
as described above, the metal mask
14
is removed from the package
2
as shown in FIG.
5
. The package
2
is caused to pass through a reflow furnace so that a heating process is carried out. As a result, the solder balls
20
are melted so as to be joined to the pad portions
10
. Projection electrodes
22
are thus formed on the pad portions
10
as shown in FIG.
6
. That is, conventionally, the semiconductor device
24
having the projection electrodes
22
as shown in
FIG. 6
is manufactured in accordance with the steps as described above.
In addition,
FIGS. 23 through 26
show a method of forming projection electrodes on a BGA (Ball Grid Array) type semiconductor device.
FIGS. 23 and 24
show semiconductor devices in a state in which the projection electrodes have not yet been formed. The semiconductor device in such a state has the so-called LGA structure. Only a plurality of pad portions
10
are formed on mounting surfaces of bases
26
A and
26
B. In
FIG. 23
, the base
26
A is covered with an insulation film
27
in a state where the pad portions
10
are exposed.
In
FIG. 23
, the base
26
A on which the pad portions
10
are formed has a structure using a so-called printed circuit board. In
FIG. 24
, the base
26
B has a structure using a tape in which copper is applied on a single surface. An opposite surface of each of the mounting surfaces of the bases
26
A and
26
B are provided with a resin package
3
, the semiconductor chip
4
, the wires
8
and bonding pads
29
.
The semiconductor chip
4
is connected to the base
26
A (
26
B) by a die pad
5
and connected to the bonding pads
29
by the wires
8
. The bonding pads
29
are connected to the pad portions
10
by using through holes
28
in a case shown in FIG.
23
and directly connected to the pad portions
10
in a case shown in FIG.
24
. To protect the semiconductor
4
, the wires
8
and the bonding pads
29
, they are encapsulated in the resin package
3
.
FIG. 25
shows a state in which solder balls
20
used for projection electrodes are provided on the semiconductor device shown in FIG.
23
. In this state, the solder balls
20
are temporarily fixed on the pad portions
10
by solder paste (or flux) (a projection electrode providing step).
After the solder balls
20
are temporarily fixed on the pad portions
10
, a heating process is carried out.
FIG. 26
shows the semiconductor device in which the heating process is completed. Due to the heating process, the solder paste
18
is vaporized and the solder balls
20
are melted, so that the projection electrodes are formed.
In the conventional method of forming the projection electrodes, after the metal mask
14
is removed from the package
2
as shown in
FIG. 5
, or after the solder balls
20
are set on the pad portions
10
by using the solder paste
18
, the solder balls
20
are supported by only the solder paste
18
. In this state, the solder balls
20
are not sufficiently maintained on the pad portions
10
.
In addition, in a state where the heating process is completed as shown in
FIGS. 6 and 26
, the projection electrodes
22
are maintained by only connecting forces between the projection electrodes
22
and the pad portions
10
. Thus, the projection electrodes are not sufficiently maintained on the pad portions
10
.
In the step of forming the projection electrodes
22
and while the semiconductor device
24
is being transported, the solder balls
20
or the projection electrodes
22
may be removed. Thus, a sufficient reliability of the fixation of the projection electrodes
22
is not obtained.
SUMMARY OF THE INVENTION
Accordingly, a general object of the present invention is to provide a novel and useful method of forming projection electrodes in which the disadvantages of the aforementioned prior art are eliminated.
A specific object of the present invention is to provide a method of forming projection electrodes with a high reliability.
The above objects of the present invention are achieved by a method of forming projection electrodes, comprising the steps of: (a) mounting a resin mask on a base having pad portions on which projection electrodes should be formed, the resin mask having openings used to position the projection electrodes; (b) providing paste on the pad portions of the base via the resin mask; (c) mountin
Armstrong, Westerman Hattori, McLeland & Naughton
Fujitsu Limited
Jones Josetta
Niebling John F.
LandOfFree
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