Stock material or miscellaneous articles – Structurally defined web or sheet – Discontinuous or differential coating – impregnation or bond
Reexamination Certificate
2001-02-21
2002-12-03
Lam, Cathy (Department: 1775)
Stock material or miscellaneous articles
Structurally defined web or sheet
Discontinuous or differential coating, impregnation or bond
C528S038000, C525S474000, C525S403000, C525S476000, C524S837000, C524S743000, C524S744000, C524S753000, C524S770000, C556S413000
Reexamination Certificate
active
06489013
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a resin compound and to an adhesive film with excellent heat resistance, electrical properties, adhesion to metal and, at the same time, low elastic modulus; and the invention also relates to a circuit board and an assembly structure using these elements. The resin compound and adhesive film of the invention are applicable widely to the surface circuit layer and/or stress compliance layer of a circuit board. Because the circuit board of the invention has a low modulus of elasticity, it is most suitable for flip chip technology.
The latest technical innovations are remarkable in providing electronic devices, such as personal mobile data terminals, that are smaller in size, lighter in weight and higher in performance. As an assembly of these electronic devices, flip chip technology or a chip scale package (CSP) structure that makes it possible to realize high-density and compact packaging has come to be employed instead of conventional resin encapsulated semiconductor packaging using a resin compound made of epoxy resin and an inorganic filler.
As indicated above, a high-density compact package is frequently made of a grid array structure because, when the package is mounted on a circuit board, a number of pins must be arranged in a small area as external terminals for the package. Since there is a technical limitation to high-density packaging on a conventional circuit board for the above reason, a board with a surface laminate wiring circuit that has no through-hole, but comprises via-holes only, has been in use. As a material for forming a fine wiring circuit on a board surface, there are available a photo-via material, on which a wiring circuit is formed by exposure and development processes, and a laser-via material, on which holes are machined by laser beam or the like. Brief technology of the above type has been disclosed, for example, in “Printed Circuit Board Applicable to High-Density Packaging—Present Status and Problems of Build-up Circuit Board Technology” of “Electronic Material” issued by Industrial Research Association, October 1998 issue.
Generally speaking, a material with high heat resistance, typically such as a polyimide, has a high modulus of elasticity. For this reason, if a packaging device with low coefficient of thermal expansion and high modulus of elasticity, such as a flip chip, is mounted on a polyimide circuit board, a question as to its reliability arises because of possible disconnection due to the thermal stress caused between the board and the device.
On the other hand, because the heat resistance of a rubber-added material with a low modulus of elasticity is generally lower, a question arises concerning the heat resistance against high-temperature bath solder (lead free solder) at about 300° C.
The present invention provides a resin compound, which causes very little thermal stress even when a flip chip is mounted, which has a low modulus of elasticity, and which has a high heat resistance sufficient for solder floating at 300° C., and the present invention also provides an adhesive film, a circuit board, and an assembly structure using the resin compound.
SUMMARY OF THE INVENTION
The means of solving the above problems in accordance with the present invention are as follows.
The first aspect of the invention involves a resin compound containing (A) a polyamide imide with siloxane bond, (B) an acrylic polymer with weight-average molecular weight of 500,000 or more, (C) a thermoset resin, and (D) a solvent.
The second aspect of the invention involves an adhesive film having the above-mentioned resin compound. This adhesive film provides an adhesive material that has both a low modulus of elasticity and high heat resistance, and also provides excellent adhesion to metal and electrical properties.
The use of (A) a polyamide imide with siloxane bond as an essential component in accordance with the invention makes it possible to maintain a low modulus of elasticity without lowering the heat resistance. The polyamide imide with a siloxane bond has superior solubility to solvent, as compared to the polyimides having a similar heat resistance, and it also has excellent miscibility with other polymers. It is a suitable component for realizing the effect of the resin compound of the present invention.
In addition, since the component (A) above has a siloxane bond, it has a higher miscibility with other components of the invention, including acrylic polymer and epoxy resin. As a result, a uniform film with no layer separation can be provided in a broad range of composition (mixture).
Particularly, in combining with a high molecular-weight acrylic polymer, the miscibility is an important issue. The siloxane bond content in the acrylic polymer structure is preferred to be 20 to 80 weight %. If it is less than 20 weight %, the miscibility decreases and a uniform resin compound with acrylic polymer cannot be obtained. If it exceeds 80 weight %, the adhesion to metal decreases, and, when a fine wiring circuit is formed, a lower reliability.
In accordance with the present invention, by using a polyamide imide containing a siloxane bond, it is possible to realize excellent miscibility with a high molecular-weight acrylic polymer, and, at the same time, to drastically lower the modulus of elasticity relative to that of conventional polyamide imide.
In accordance with the invention, (A) a polyamide imide with a siloxane bond represents a condition where, for example, an amide bond or an imide bond is bonded with the siloxane bond.
To be specific, a polymer that at least contains an amide bond, an amide bond as the main chain of an imide precursor, and the following bond unit is preferred:
—NH—CO—X—Z— or —NH—CO—X—CO—NH—Y—Z—
(X and Y in the above formula are an organic group including an aliphatic or aromatic group, and can be equal or different. Z is a siloxane bond.)
Besides, a polymer that contains a siloxane bond as the end group of an amide bond and an amide bond as the main chain of an imide precursor as follows, for example, is also effective:
—NH—CO—X—Z or —NH—CO—X—CO—NH—Y—Z
(X and Y in the above formula are an organic group including an aliphatic or aromatic group, and can be equal or different. Z is a siloxane bond.)
In accordance with the present invention, by using (B) a acrylic polymer with a weight-average molecular weight of 500,000 or more, it is possible to realize a low modulus of elasticity without lowering the heat resistance. If an acrylic polymer with a weight-average molecular weight of less than 500,000 is used, sufficient properties, including heat resistance and electrical properties, cannot be attained. The use of a high molecular-weight polymer with weight-average molecular weight of 500,000 or more makes it possible to attain stable properties.
The mix ratio of the above component (A) to component (B) is preferably 3:1 to 1:5 by weight. In mixing the two, from the point of view of lowering the modulus of elasticity, increasing the mix ratio of the component (B), i.e. the acrylic polymer, is preferable so as to increase the resolution in film forming and the adhesion to metal. However, increasing the component (B), i.e. the acrylic polymer, in excess of the mix ratio 1:5 results in insufficient properties, including heat resistance and electrical properties.
It is also preferable when the glass transition temperature of the acrylic polymer is 0° C. or less. Because of this, the modulus of elasticity under a range of 0 to 150° C., a normal operating environment, can be maintained low.
Since use of a combination of the above components (A) and (B) in accordance with the present invention is not sufficient enough to maintain the properties at high temperature, it is preferred to utilize a component that forms a cross-linked structure so as to maintain the solder heat resistance at 300° C. or above.
A thermoset resin is a component that forms a cross-linked structure. It is available in the form of, for example, an epoxy resin, a maleimide resin, a cyanate resin, an isocyanate res
Nagai Akira
Noda Masayuki
Antonelli Terry Stout & Kraus LLP
Hitachi , Ltd.
Lam Cathy
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