Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
1999-07-06
2001-05-01
Dawson, Robert (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C523S458000
Reexamination Certificate
active
06225379
ABSTRACT:
The priority of Korean patent application 98/27292, filed Jul. 7 1998, is claimed under 35 USC 119.
BACKGROUND OF THE INVENTION
(a) Field of the Invention
The present invention relates to a die attach adhesive composition for bonding semiconductor chips to lead frames, and more particularly, to a die attach adhesive composition that has superior modulus characteristics, bonding power, adhesion strength and workability, thereby enabling use with semiconductor chips in a wide range of sizes.
(b) Description of the Prior Art
Typically, semiconductor packages comprise lead frames/substrates in which semiconductor chips are bonded onto lead frame paddles via adhesives.
FIG. 1
shows a thin quad flat package (TQFP)
1
, which is a type of surface-mounting semiconductor, in which a semiconductor chip
2
is mounted on a semiconductor chip paddle
3
a
of a lead frame
3
, by an adhesive layer
6
. A bond pad (no reference numeral given) on the mounted semiconductor chip
2
and internal leads
3
b
are electrically connected by conductive wires
4
. The semiconductor chip
2
and the conductive wires
4
are protected from the exterior by a molded encapsulating resin compound
5
, and external leads
3
c
are soldered on, for example, a circuit board, the external leads
3
c
serving as external connection terminals.
In the above, die attach adhesive compositions are used in bonding the semiconductor chip
2
on the paddle
3
a
of the lead frame
3
. Here, it is necessary for such adhesive compositions to have exceptional physical and chemical properties after the composition is cured, as well as provide a sufficient level of workability. Necessary physical properties for the die attach adhesive compositions include a low coefficient of thermal expansion, high adhesive strength, high thermal- and electroconductivity, and durability, while the required chemical properties include high chemical resistance and low impurity content. With regard to the workability of the adhesive compositions, it is necessary for the same to have a suitable level of viscosity and rate of cure.
Die attach adhesive compositions meeting the above requirements and typically used include an epoxy base resin, which may have substituents; a curing agent, containing an amine compound; a diluent, such as epoxide or butyl carbitol acetate; an adhesion promoter, such as silane or dicyandiamide; a thixotropic agent, such as colloidal magnesium silicate; and other additive agents, such as silicone. Here, depending on the required characteristics, intended use, etc., modifications can be made to the epoxy resin adhesive composition to meet varying demands.
Particularly, Ag flakes are commonly used as a filler to provide the die attach adhesive compositions with superior thermal and/or electrical conductivity. Because of good dispersion in organic resin systems, silver has the advantage of easily controlling the composition's thixotropy needed upon dispersion or die placement. However, silver does not provide sufficient adhesive strength between the semiconductor chip and the chip paddle of the lead frame, thereby reducing package reliability. For example, delamination can occur at the interface between the semiconductor chip and the chip paddle and/or cracks in the package may develop.
The above is particularly true in ‘hard’ modified die attach compositions that are high in modulus. In contrast, such problems do not occur in ‘soft’ modified compositions. However, when a wire bonding process (a high temperature process of 240° C.), subsequent to the semiconductor chip-mounting process, is performed by a bonding machine, minute vibrations are generated causing defects in the wire bonding, which the ‘soft’ composition cannot resist.
In more detail, when the capillary of the bonding machine is pressure-welded into the outside edge of the surface of the semiconductor chip, the adhesive layer beneath the semiconductor chip is slightly distorted by the pressure of the capillary load. When the capillary is released from the semiconductor chip, damped vibration occurs, causing defects in the wire bonding or a tilt in the mounting of the semiconductor chip slant. Accordingly, ‘soft’ modified adhesive compositions are unsuitable for the use in packages on which small semiconductor chips are mounted since the minute vibrations cannot be absorbed.
As with ‘hard’ modified epoxy resin compositions, ‘intermediate’ modified epoxy resin compositions, which are in modulus between ‘hard’ and ‘soft’ epoxy resin compositions, do not provide sufficient adhesive strength. As a result, the problems of interfacial delamination and/or cracking remain.
SUMMARY OF THE INVENTION
The present invention has been made in an effort to solve the above problems.
It is an object of the present invention to provide an ‘intermediate’ adhesive composition having a high level of modulus such that wire bonding defects caused by wire sticking do not arise.
It is another object of the present invention to provide a die attach adhesive composition for bonding semiconductor chips which provides substantial adhesive strength such that the occurrence of interface delamination and/or cracking is prevented.
It is yet another object of the present invention to provide a die attach adhesive composition which both can be used for semiconductor chips of a wide variety of sizes and provides for a high level of workability.
To achieve the above objects, the present invention provides a die attach adhesive resin composition for bonding semiconductor chips. The adhesive composition comprises an epoxy resin component, a curing agent, a diluent, a curing promoter and a thixotropic agent, and an inorganic filler component. The resin component is approximately 10-50% by weight, and the inorganic filler component is approximately 50-90% by weight and comprises a copper ingredient and a silver ingredient. The copper ingredient is selected from the group consisting of CuO, Cu
2
O, and mixtures thereof and amounts to approximately 0.1-50% by weight based on the total weight of said inorganic filler component; the silver ingredient amounts to approximately 50-99.0% by weight based on the total weight of the inorganic filler ingredient.
According to a feature of the present invention, the copper ingredient is approximately 5-25% by weight based on the total weight of the inorganic filler component.
According to another feature of the present invention, the resin component is 20-40% by weight and the inorganic filler component is 60-80% by weight.
According to yet another feature of the present invention, the composition has a modulus 2 to 4×10
9
Pa at 0° C., and the modulus gradually decreases at temperatures between 25 and 150° C., and decreases to 7×10
7
-3×10
9
Pa at above 150° C.
According to still yet another feature of the present invention, the composition ranges in viscosity from 8,000 to 20,000 cps at 25° C.
According to still yet another feature of the present invention, the composition gives an adhesive layer, formed between a semiconductor chip and a paddle of a lead frame, ranging in adhesive strength from 100 to 170 Kgf/cm
2
after cure.
REFERENCES:
patent: 5582772 (1996-12-01), Kwak
Kwak Jae-Sung
Moon Byung-Hoon
Aylward D.
Dawson Robert
Gennaro Jane E.
National Starch and Chemical Investment Holding Corporation
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