Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Reexamination Certificate
2000-03-27
2003-09-09
Ball, Michael W. (Department: 1733)
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
C156S164000, C428S001200, C428S001620, C174S259000
Reexamination Certificate
active
06616796
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a metal laminate for a circuit board, having a film (which film is hereinafter referred to as a thermotropic liquid crystal polymer film) made of a thermotropic polymer capable of forming an optically anisotropic melt phase (which thermotropic polymer is hereinafter referred to as a thermotropic liquid crystal polymer), and a method for producing the same. More particularly, the metal laminate for a circuit board according to the present invention has not only an excellent low moisture absorbability, heat resistance, chemical resistance, and electric properties deriving from the thermotropic liquid crystal polymer film but also an excellent dimensional stability, so that it is useful as a material for a circuit board such as a flexible wiring board or a circuit board for mounting a semiconductor.
2. Description of the Prior Art
In recent years, the demands for scale reduction and weight reduction in portable electronic devices for mobile communication and others are becoming high, and an expectation for high density mounting is becoming increasingly strong. In accordance therewith, multi-layered wiring boards, reduced wiring pitches, fine via holes, and small-size multiple-pin IC packages are being developed, and also the scale reduction and surface mounting of passive elements such as capacitors and resistors are taking place along with this. Especially, the technique of forming these passive components directly on a surface or in an inside of a printed wiring board or the like can not only achieve high density mounting but also contributes to an improvement in reliability. In accordance therewith, the level of demands for the dimensional stability of the wiring boards. i.e. small variation in the dimension after the formation of a conductor circuit, are becoming high, and further there is a demand for eliminating its anisotropy.
In the meantime, thermotropic liquid crystal polymer films having an excellent low moisture absorbability, heat resistance, chemical resistance, and electric properties are rapidly commercialized as an electrically insulating material that improves the reliability of printed wiring boards and others.
Conventionally, in producing a metal laminate for use in a circuit board such as a printed wiring board using a thermotropic liquid crystal polymer film, a thermotropic liquid crystal polymer film cut to a predetermined size and a metal foil are placed in superposition between two hot platens with the use of a vacuum hot press device, and thermally press-bonded in a vacuum state (batch type vacuum hot press lamination). At this time, if the segment orientation ratio SOR of the thermotropic liquid crystal polymer film before press-bonding is approximately 1, then a metal laminate having a good dimensional stability is obtained. However, since the vacuum hot press lamination is a sheet-type production method, the period of time for superposing the materials, the period of time for one pressing operation, the period of time for taking out the material after pressing, and the like will be long, thereby slowing the production speed per one sheet of the metal laminate and leading to increased costs. Moreover, if the equipments are improved so that a large number of sheets can be produced at the same time for increasing the production speed, then the equipments will be large in scale, disadvantageously leading to high equipment costs. Accordingly, there is a demand for solving this problem and developing a continuous production method capable of providing metal laminates at a low cost.
Thus, there is proposed (a) a method of superposing a long thermotropic liquid crystal polymer film on a metal foil and allowing them to pass between hot rolls for press-bonding in such a manner that the press-bonding temperature is within the range from a temperature lower by 80° C. than the melting point of the thermotropic liquid crystal polymer film to a temperature lower by 5° C. than the melting point for performing continuous production of the metal laminates (Japanese Laid-open Patent Publication No. 05-42603/1993). Further, there is proposed a method of thermally treating a thermotropic liquid crystal polymer film at a predetermined temperature (Japanese Laid-open Patent Publication No. 08-90570/1996).
However, according to the methods of (a) and (b), it is difficult to continuously and stably obtain a metal laminate having a good isotropy and good dimensional stability. In other words, in the case where a thermotropic liquid crystal polymer film is press-bonded to a metal foil between hot rolls, the temperature conditions are described as shown above, but the tension imposed on the film in press-bonding is not considered at all. If this tension is applied, the movement of the molecules in the thermotropic liquid crystal polymer film is likely to occur. As a result, in accordance with heating, the change in the molecule orientation is likely to take place on the surface of the film in a metal laminate using the film. For these reasons, it has been difficult to obtain a metal laminate having a good isotropy and good dimensional stability.
Further, in the method of (a), although the conditions for improving the adhesion strength to the metal sheet and the improvement in the mechanical strength are described, the improvement in the dimensional stability is not described. In the method of (b), although the heated dimensional changing ratio of the thermotropic liquid crystal polymer film is described, the properties of the metal laminate using the thermotropic liquid crystal polymer film are not described. Therefore, in the conventional methods, continuous production of metal laminates for circuit boards having a good isotropy and a good dimensional stability has not been realized.
Accordingly, the object of the present invention is to provide a metal laminate for a circuit board and a method for producing the same by which the metal laminate for a circuit board having an excellent isotropy and an excellent dimensional stability can be produced continuously at a high productivity by using hot rolls and a heating equipment.
SUMMARY OF THE INVENTION
In order to achieve the aforesaid object, the inventors of the present invention have made studies and found a method that can continuously and stably produce metal laminates for a circuit board having an excellent isotropy and an excellent dimensional stability. The methods comprises the steps of: using a thermotropic liquid crystal polymer film whose segment orientation ratio SOR is within a specific range and; after the thermotropic liquid crystal polymer film and a metal sheet such as represented by a metal foil and a metal plate are press-bonded together between hot rolls under a specific tension condition depending on the segment orientation ratio SOR, heating the obtained laminate under a specific temperature condition. According to this method, the isotropy of a thermotropic liquid crystal polymer film in a laminated state can be obtained thereby obtaining a metal laminate for a circuit board being excellent in isotropy and dimensional stability.
The production method according to the first invention comprises a first step of using a thermotropic liquid crystal polymer film having a segment orientation ratio SOR within a range not smaller than 1.03 and smaller than 1.15 along a longitudinal direction of the film, and press-bonding a metal sheet on at least one surface of the thermotropic liquid crystal polymer film between hot rolls while said thermotropic liquid crystal polymer film is in a tense state; and a second step of heating the laminate obtained in the first step to a temperature not lower than a melting point of the thermotropic liquid crystal polymer film.
Here, the term “segment orientation ratio (SOR)” used hereinbefore and hereinafter is an index descriptive of the degree of orientation of molecules forming a segment and represents, unlike the standard MOR (molecular orientation ratio), a value in which the thickness of an o
Onodera Minoru
Sato Toshiaki
Tsudaka Takeichi
Yoshikawa Tadao
Ball Michael W.
Goff John
Kuraray Co. Ltd.
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