Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Adhesive outermost layer
Reexamination Certificate
1997-12-01
2001-10-16
Zirker, Daniel (Department: 1771)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Adhesive outermost layer
C428S3550EP
Reexamination Certificate
active
06303219
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an adhesive sheet suitable as an adhesive layer for a semiconductor connecting substrate used for mounting a semiconductor integrated circuit, an adhesive-backed tape used for tape automated bonding (TAB) (hereinafter called “a tape for TAB”), an adhesive-backed tape used for wire bonding connection (hereinafter called “a tape for WB”), and a semiconductor connecting substrate and a semiconductor device using any of the foregoing.
BACKGROUND ARTS
Conventional semiconductor integrated circuit (IC) mounting techniques include the following.
For mounting an IC, a method in which the electrodes of the IC are wire-bonded to metallic lead frames and sealed by a resin is most popularly used. IC packages produced in this manner are usually provided in such forms as the small outline package (SOP) and the quad flat package (QFP). In contrast to these, as smaller-sized and lighter-weight electronic apparatuses, a ball grid array (BGA), in which connection terminals are arranged on the surface of a package, are being used (FIG.
1
).
The BGA method is characterized in that solder balls (almost as many as the pins of the corresponding IC) are provided in a grid-like form as external connectors of the IC connecting substrate. For connecting an apparatus onto a printing wire board, the apparatus is placed on the board in such a manner that the solder ball faces conform with the conductor pattern of an already printed solder, and the solder is rendered molten by reflow to achieve the desired connection. The most important feature is that although the conventional QFP, etc. allows only the surrounding edges to be used for arranging connection terminals, BGA allows the surface of the connecting substrate to be used, so that more connection terminals can be arranged in a small space. This size reducing effect is more intensified in the chip scale package (CSP), and it may be called a &mgr;-BGA (micro BGA) in view of its similarity (FIG.
2
).
In the BGA method, for the necessity of keeping the solder ball faces flat for better radiation, a method comprising the steps of laminating a material such as a metallic sheet for reinforcement, radiation, electromagnetic shielding, etc., to the wiring board layer for connecting an IC, using an adhesive sheet, and curing by heating is generally adopted for producing a connecting substrate.
A connecting substrate for BGA is described below with reference to
FIG. 4. A
connecting substrate for BGA consists of at least one wiring board layer (being constituted by an insulator layer
26
and a conductor pattern
27
for connecting an IC, at least one layer
29
without any conductor pattern formed (functioning as a reinforcing sheet, radiation sheet or shielding sheet, etc.), and at least one adhesive layer
28
for laminating them. In
FIG. 4
, symbol
25
denotes an organic insulation film;
27
, an inner lead; and
30
, a solder resist.
For the adhesive layer (adhesive sheet) referred to here, a thermoplastic resin or silicone elastomer (Japanese Patent Publication (Kokoku) No. 6-50448), etc. is proposed for obtaining the effect of easing the thermal stress caused by the difference in thermal expansion coefficient of different materials such as the printed wiring board, solder balls, wiring board layer and the layer without any conductor pattern formed, during temperature cycles and reflow.
On the other hand, as the wiring board layer, a glass epoxy laminated sheet (rigid sheet) had been used, but in recent years, the use of a semiconductor connecting substrate in which a conductor pattern for connecting an IC is formed on an organic insulating film of a polyimide, etc. is increasing. A package using such a tape-like connecting substrate (pattern tape) is generally called a TCP (tape carrier package), and the TCP of a BGA method in particular is called a TAB-BGA or T-BGA.
A TCP has an advantage in that low cost packages can be mass-produced by continuously mounting using a long pattern tape. As for the IC connection method, the tape automated bonding (TAB) method in which bump electrodes of an IC are thermally pressure-bonded to the inner leads of a connecting substrate (by gang bonding or single point bonding) is typical, but a method in which the conductor pads of a connecting substrate and the electrodes of an IC are wire-bonded to each other (hereinafter called “WB method”) is also used.
As the pattern tape for a TAB method, a tape for TAB is generally used. A tape for TAB has a three-layer structure in which an adhesive layer and a releasable polyester film, etc. used as a protective film layer are laminated onto a flexible organic insulating film such as a polyimide film.
Usually since the adhesive layer is arranged to be more narrow than the organic insulating film, the tape for TAB is generally produced by once producing an adhesive sheet and laminating it onto the organic insulating film.
The tape for TAB thus obtained undergoes (1) perforation to form sprocket and device holes, (2) thermal lamination with a copper foil and heating for curing the adhesive, (3) back treatment of the copper foil for forming inner leads, (4) pattern forming (resist coating, etching, resist removal, removal of copper foil back treating agent), (5) tin or gold plating, etc., to be processed into a connecting substrate (pattern tape).
FIG. 3
shows the form of a pattern tape.
FIG. 1
is a sectional view showing an embodiment of the TCP type semiconductor device of the present invention. The inner leads
5
of a pattern tape are thermally pressure-bonded to the gold bumps
2
of IC
1
(inner lead bonding), to mount the IC. Then, a sealing resin
10
is applied for sealing, to prepare a semiconductor device. In the case of TAB-BGA, the tape further undergoes a step of laminating a layer functioning as a reinforcing sheet, radiation sheet or shielding sheet, etc. using an adhesive sheet, and a step of installing solder balls.
For the WB method, a tape for WB suitable for wire bonding connection in adhesive properties is used, though the tape form and the production method are the same as those of the tape for TAB.
A tape for WB undergoes (1) perforation of sprocket and device holes, .(2) thermal lamination with a copper foil and heating for curing the adhesive, (3) pattern forming (resist coating, etching, resist removal), (4) tin or gold plating, etc., to be processed into a connecting substrate (pattern tape) (FIG.
5
). The pattern tape does not have inner leads, and the conductors of the pattern tape and the gold bumps of a semiconductor integrated circuit are wire-bonded to each other. Finally, as in the case of TAB method, a sealing resin is applied for sealing, to obtain a semiconductor device (FIG.
6
).
The above TCP type semiconductor device is connected with a circuit board, etc. on which other parts are mounted, through outer leads or solder balls
9
, to be mounted on an electronic apparatus.
DISCLOSURE OF THE INVENTION
The adhesive sheet for a semiconductor connecting substrate is required to have the following properties:
(a) High adhesive strength not allowing peeling even at a reflow temperature of 230° C. or higher.
(b) Moderate elastic modulus and moderate coefficient of linear expansion to ease the thermal stress acting on the different materials forming the connecting substrate due to temperature cycles and reflow.
(c) Processability to allow sticking together and low temperature short time thermal cure.
(d) Insulatability in lamination on wiring.
Of the above properties, it has been especially difficult to achieve a balance between adhesive strength on the one hand and moderate elastic modulus and coefficient of linear expansion on the other hand. In the conventional adhesive compositions, if the adhesive strength is attempted to be improved, the elastic modulus at high temperature drops to pose a problem that totally satisfactory properties cannot be obtained.
In general, the adhesive strength of an adhesive can be enhanced by lowering the elastic modulus to increase the breaking energy, but this
Ando Yoshio
Hatano Taku
Kigoshi Shoji
Konishi Yukitsuna
Sawamura Yasushi
Birch & Stewart Kolasch & Birch, LLP
Toray Industries Inc.
Zirker Daniel
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