Stock material or miscellaneous articles – Composite – Of epoxy ether
Reexamination Certificate
2000-04-24
2001-08-07
Lam, Cathy (Department: 1775)
Stock material or miscellaneous articles
Composite
Of epoxy ether
C428S209000, C428S411100, C428S413000, C428S418000
Reexamination Certificate
active
06270900
ABSTRACT:
TECHNICAL FIELD
The present invention relates to composite films and more particularly to composite films of a multi-layer structure having a film of a polymer containing a specific ring structure and a film of a polycondensation polymer. The composite films according to the present invention are highly balanced among dielectric properties, low water absorption property, mechanical properties, flame retardancy, etc. and are hence particularly suitable for use as, for example, films for various kinds of wiring boards such as wiring films for semiconductor packages, films for flexible printed wiring boards and wiring films for semiconductor mounting.
BACKGROUND ART
With the rapid advancement of advanced information-oriented society in recent years, development of information processing apparatus such as computers and communication apparatus, and image processing apparatus such as camcoders and digital cameras is being rapidly advanced. In the field of these electronic apparatus, there is a strong demand for the enhancement of throughput capacity, i.e., the speeding up, and miniaturization and weight saving thereof. In this field, mounting parts such as semiconductor chips such as LSI, circuit parts and functional parts are mounted on a wiring board (substrate), and this wiring board is incorporated into an electronic apparatus. It is effective for the speeding up of information processing, image processing and the like to make the interconnected wiring of these mounting parts as short as possible so as to make the density of the parts high. This technique is also effective for the miniaturization and weight saving of electronic apparatus.
The use of a flexible substrate made of a synthetic resin film as a wiring board itself is effective to realize high-density assembly and the miniaturization and weight saving of electronic apparatus. Therefore, thin and freely flexible substrates are used in circuit boards such as printed wiring boards.
Even in a mounting system for electronic parts such as semiconductor chips, a system that semiconductor chips are mounted on a wiring board as bare chips is being developed in place of the conventional mounting system by transfer molding. In this mounting system, for example, TAB (tape automated bonding) in which a package itself for LSI is a plastic film (including a sheet) is known. TAB is generally formed from a tape-like carrier film, bumps (metallic projections) and a semiconductor chip. In such a mounting system, a flexible synthetic resin film having a wiring pattern is often used as the carrier film.
Polyimide has heretofore been used as a material for substrates of flexible printed wiring boards and films having a wiring pattern. However, a polyimide film is excellent in mechanical properties and flame retardant, but involves a problem that water absorptivity is high. Therefore, the use of the polyimide film as a substrate for high-density assembly has involved a problem that reliability on insulation is lowered due to water absorption, and the dielectric constant of the substrate is lowered due to moisture absorption. Accordingly, the polyimide film cannot be said to be a substrate material sufficiently satisfying recent high requirements.
On the other hand, ring structure-containing polymers such as ring-opening polymers and addition polymers of norbornene monomers such as tetracyclododecene are publicly known as insulating materials excellent in low water absorption property and dielectric properties, and techniques that glass cloth and the like are impregnated with these polymers to use them as substrates for printed wiring boards and that they are used in the form of a sheet as insulating films have been proposed (for example, Japanese Patent Application Laid-Open No. 248164/1994). However, these ring structure-containing polymers are generally insufficient in mechanical strength and flexibility and also poor in flame retardant, and so it has been difficult to use them singly as wiring boards and wiring films.
As described above, there has not been yet found any synthetic resin film which has sufficient mechanical strength and flame retardant as a film for flexible wiring boards and is excellent in low water absorption property and dielectric properties. There is a demand for development of novel films highly balanced among these various properties as materials for high-density assembly for realizing the speeding up of processing and the miniaturization and weight saving of apparatus.
DISCLOSURE OF THE INVENTION
It is an object of the present invention to provide a composite film having excellent low water absorption property, dielectric properties, mechanical properties and flame retardant and highly balanced among these various properties.
Another object of the present invention is to provide a film for wiring boards, which serves for the speeding up of processing and the miniaturization and weight saving of apparatus and has high reliability.
The present inventors have carried out an extensive investigation with a view toward overcoming the above-described problems involved in the prior art, resulting in conceiving composite films having a layer structure of at least two layers, in which a film (A) formed from a ring structure-containing polymer such as a thermoplastic norbornene resin and a film (B) formed from a polycondensation polymer such as polyimide adjoin each other directly or through an adhesive layer. When these two kinds of films are combined to form a multi-layer film, a composite film making the best use of their merits can be obtained.
More specifically, when these two kinds of films are combined to form a multi-layer film, a composite film highly balanced between various properties such as excellent low water absorption property and dielectric properties that the ring structure-containing polymer film (A) has, and various properties such as excellent mechanical properties and flame retardant that the polycondensation polymer film (B) has can be obtained. When the layer structure is devised, a composite film that a desired property among these various properties is made far excellent can be obtained.
When it is attempted to form a film of a blend of these two kinds of synthetic resins to improve the balance among the above-described various properties, it is necessary to solve a problem that compatibility between both resins is poor. In contrast, when films respectively formed from these two kinds of synthetic resins are combined to form a multi-layer film, the improvement in the various properties can be achieved without causing the problem of compatibility.
Upon the formation of the multi-layer film, a composite film can be formed with ease by using a film of one synthetic resin as a support and applying a solution of the other synthetic resin on to the support to form a film. When the polycondensation polymer is a thermosetting resin, a composite film can be formed by applying a solution of a precursor of such a resin on to the ring structure-containing polymer film (A), and then heat-treating it to be cured. When the ring structure-containing polymer contains a hardening agent, a solution containing the ring structure-containing polymer and the hardening agent can be applied on to a film of the polycondensation polymer and cured. It goes without saying that films of the respective resins may be laminated on each other to form a composite film. Further, the composite films according to the present invention can be used as films for wiring boards such as wiring boards for semiconductor packages, flexible printed wiring boards and wiring boards for semiconductor chip mounting, since a conductive layer can be formed on the surfaces thereof.
The present invention has be led to completion on the basis of these findings.
According to the present invention, there is thus provided a composite film having a layer structure of at least two layers, wherein a film (A) formed from a ring structure-containing polymer comprising a repeating unit derived from ring-opening or addition polymerization of a monomer having a ring
Sakamoto Kei
Wakizaka Yasuhiro
Dinsmore & Shohl LLP
Lam Cathy
Nippon Zeon Co. Ltd.
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