Semiconductor device manufacturing: process – Packaging or treatment of packaged semiconductor – Insulative housing or support
Reexamination Certificate
2002-06-14
2003-12-16
Nelms, David (Department: 2818)
Semiconductor device manufacturing: process
Packaging or treatment of packaged semiconductor
Insulative housing or support
C438S107000, C438S127000, C257S773000, C257S778000
Reexamination Certificate
active
06664138
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for fabricating a circuit device, and in particular, a method for fabricating a circuit device, which is able to achieve thinning of the circuit device using two sheets of conductive layer.
2. Description of the Prior Arts
Recently, IC packages have been actively employed in portable devices, and small-sized and high density assembly devices. Conventional IC packages and assembly concepts tend to greatly change. For example, this is described in, for example, Japanese Laid-Open Patent Publication No. 2000-133678. This pertains to a technology regarding a semiconductor apparatus in which a polyimide resin sheet being a flexible sheet is employed as one example of insulation resin sheets.
FIG.
9
through
FIGS. 11A
,
11
B and
11
C show a case where a flexible sheet
50
is employed as an interposer substrate. Also, the views illustrated upside of the respective drawings are plan views, and the views illustrated downside thereof are longitudinally sectional views taken along the lines A—A of the respective drawings.
First, copper foil patterns
51
are prepared to be adhered to each other via an adhesive resin on the flexible sheet
50
illustrated in FIG.
9
. These copper foil patterns
51
have different patterns, depending upon cases where a semiconductor element to be assembled is a transistor or an IC. Generally speaking, a bonding pad
51
A and an island
51
B are formed. Also, an opening
52
is provided to take out an electrode from the rear side of the flexible sheet
50
, from which the above-described copper foil pattern
51
is exposed.
Subsequently, the flexible sheet
50
is transferred onto a die bonder, and as shown in
FIG. 10
, a semiconductor element
53
is assembled or mounted. After that, the flexible sheet
50
is transferred onto a wire bonder, wherein the bonding pads
51
A are electrically connected to the pads of the semiconductor elements
53
by thin metal wires
54
.
Finally, as shown in
FIG. 11A
, sealing resin
55
is provided on the surface of the flexible sheet
50
, and the surface thereof is completely sealed with the sealing resin
55
. Herein, the bonding pads
51
A, island
51
B, semiconductor elements
53
and thin metal wires
54
are transfer-molded so as to be completely overcoated.
After that, as shown in
FIG. 11B
, connecting means
56
such as solder and a soldering ball is provided, wherein spherical solder
56
deposited to the bonding pad
51
A is formed via the opening
52
by passing through a solder reflow furnace. Further, since semiconductor elements
53
are formed in the form of a matrix on the flexible sheet
50
, these are diced to be separated from each other as shown in FIG.
11
.
In addition, the sectional view of
FIG. 11C
shows electrodes
51
A and
51
D on both sides of the flexible sheet
50
as the electrodes. The flexible sheet
50
is generally supplied from a maker after both sides thereof are patterned.
In prior art methods for fabricating circuit devices, a flexible sheet
50
is transferred in the above-described fabrication apparatus, for example, a die bonder, a wire bonder, a transfer molding apparatus, a reflow furnace, etc., and is mounted on a portion called a “stage” or a “table”.
The thickness of insulation resin, which becomes the base of a flexible sheet
50
, is made thin at approx. 50 &mgr;m, and where the thickness of a copper foil pattern
51
formed on the surface thereof is thin at 9 through 35 &mgr;m, there is a shortcoming by which the insulation resin is warped as shown in
FIG. 12
to cause its transfer performance to be worsened, and mountability thereof on the above-described stage or table is also worsened. It is considered that this is because the insulation resin itself is thin to be warped, and warping occurs due to a difference in the thermal expansion coefficient between the copper foil pattern
51
and the insulation resin. In particular, there is another problem in that, if a hard insulation material not using any core material of glass cloth fibers is warped as shown in
FIG. 12
, the insulation material is easily collapsed by compression from above.
Since the portion of the opening
52
is compressed from above when being molded, a force by which the periphery of the bonding pad
51
A is warped upward is brought about, the adhesion of the bonding pad
51
A is worsened.
Also, the resin material that constitutes a flexible sheet
50
has less flexibility, or if a filler to increase the thermal conductivity is blended, the flexible sheet
50
is made hard. In such a case, where bonding is carried out by a wire bonder, there may be a case where the bonded portion is cracked. Also, when performing transfer molding, there is a case where the portion with which a metal die is brought into contact is cracked. This remarkably occurs if any warping shown in
FIG. 12
is provided.
Although the flexible sheet
50
described above is such a type that no electrode is formed on the rear side thereof, there are cases where an electrode
51
D is formed on the rear side of the flexible sheet
50
as shown in FIG.
11
C. At this time, since the electrode
51
D is brought into contact with the above-described fabrication apparatus or is brought into contact with the transfer plane of transfer means between the fabrication apparatuses, another problem occurs in that damage and scratches arise on the rear side of the electrode
51
D, wherein the electrode is established with such damage and scratches retained, the electrode
51
itself may be cracked due to application of heat later on.
Also, if an electrode
51
D is provided on the rear side of the flexible sheet
50
, a problem occurs in that, when carrying out transfer molding, no facial contact with the stage can be secured. In this case, if the flexible sheet
50
is composed of a hard material as described above, the electrode
51
D becomes a fulcrum and the periphery of the electrode
51
D is compressed downward, wherein the flexible sheet
50
is cracked.
SUMMARY OF THE INVENTION
A method for fabricating a circuit device according to the invention is comprised of the steps of: preparing an insulation resin sheet having a first conductive layer and a second conductive layer adhered together by insulation resin; forming a conductive path layer by etching the above-described first conductive layer to an appointed pattern; adhering and fixing semiconductor elements on the above-described conductive path layer with the same electrically insulated therefrom; overcoating the above-described conductive path layer and the above-described semiconductor elements with a sealing resin layer; removing the above-described second conductive layer by etching the same; and providing through holes in the above-described insulation resin that covers the rear side of the above-described conductive path layer, and forming external electrodes on the above-described conductive path layer, whereby the above-described problems can be solved.
Since the flexible sheet is formed to be thick by the first conductive layer and the second conductive layer, flatness of a sheet-like circuit device can be maintained even if the insulation resin is thin.
Also, mechanical strength is retained by the second conductive layer until the step of overcoating the first conductive path layer and semiconductor elements with a sealing resin layer is finished, and the sealing resin layer retains the mechanical strength thereafter. Therefore, the second conductive layer can be easily removed. As a result, the insulation resin does not require any mechanical strength, wherein the insulation resin can be made sufficiently thin to retain only an electrical insulation property.
Further, since the lower die mold and planes of a transfer molding apparatus are brought into contact with the entirety of the second conductive layer, no local compression is brought about, and it is possible to prevent the insulation resin from being cracked.
The method according to the invention has the following ad
Igarashi Yusuke
Kobayashi Yoshiyuki
Nakamura Takeshi
Sakamoto Noriaki
Berry Renee R.
Fish & Richardson P.C.
Sanyo Electric Co,. Ltd.
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