JP5505349B2 - Metal-coated polyimide film, flexible wiring board, and production method thereof - Google Patents

Description

  The present invention relates to a metal-coated polyimide film, a flexible wiring board, and a method for producing the same, and more specifically, a metal-coated polyimide film having high adhesion strength and excellent bending resistance, a method for producing the same, and a poor connection. The present invention relates to a reduced flexible wiring board and a manufacturing method thereof.

  The board on which these electronic components are formed by forming an electronic circuit is a rigid plate-like “rigid wiring board” and a film-like, flexible “flexible wiring board” (hereinafter referred to as FPC). May be called). Of these, FPCs can be used in flexible parts such as LCD driver wiring plates, hard disk drives (HDD), digital versatile disk (DVD) modules, and mobile phone hinges, taking advantage of their flexibility. Therefore, the demand is increasing more and more.

By the way, such a flexible wiring board uses a base material provided with a metal layer on the surface of a polyimide film, and wiring is obtained by processing the metal layer by a subtractive method or a semi-additive method. Incidentally, when obtaining a flexible wiring board by the subtractive method, first, a resist layer is provided on the surface of the metal layer of the base material, a mask having a predetermined wiring pattern is provided on the resist layer, and ultraviolet rays are irradiated from above. Then, exposure and development are performed to obtain an etching mask for etching the metal layer, and then the exposed metal portion is removed by etching, then the remaining resist layer is removed, washed with water, and wiring if necessary. This is obtained by applying predetermined plating to the lead terminal portion and the like.
On the other hand, in the case of the semi-additive method, a resist layer is provided on the metal surface of the substrate, a mask having a predetermined wiring pattern is provided on the resist layer, and ultraviolet rays are irradiated from above to be exposed and developed. A plating mask for electrodepositing copper on the surface of the metal layer is obtained, and the wiring layer is formed by electroplating using the metal layer exposed in the opening as a cathode, and then the resist layer is removed and soft etching is performed. Then, the metal layer on the surface of the base material other than the wiring portion is removed to complete the wiring portion, washed with water, and if necessary, obtained by performing predetermined plating on the lead terminal portion of the wiring.

Currently, liquid crystal displays (hereinafter sometimes referred to as LCDs), mobile phones, digital cameras, and various electrical devices are required to be thin, small, light, and low in cost, and electronic components mounted on them. Of course, the trend toward miniaturization is progressing, and the wiring pitch of the flexible wiring board used is required to be 25 μm or less.
In order to meet this requirement, when trying to obtain a flexible wiring board with a wiring pitch of 25 μm, when wiring is provided by the subtractive method, the influence of side etching at the time of wiring creation is eliminated, and the cross section is rectangular. In order to obtain good wiring, the thickness of the metal layer provided on the substrate must be 20 μm or less.
In order to obtain such a substrate, a metal thin film is provided on the edge resin film surface by a dry plating method, a copper thin film is provided thereon by a dry plating method, and a copper layer is provided thereon by a wet plating method. A method of obtaining a metal layer is recommended. This is because the thickness of the metal layer can be arbitrarily controlled in this base material because all the constituent films are provided by plating.

In addition, as the wiring pitch becomes finer, the improvement in the adhesion between the metal layer and the insulating film is also required. For example, when a semiconductor element is mounted on a flexible wiring board, the electrode on the surface of the semiconductor element and the inner lead portion of the wiring are wire-bonded. In order to shorten the tact time at this time, pressure is applied at a high temperature. This is because wire bonding is performed by multiplying. For this reason, for example, it has become important to evaluate the adhesion strength (PCT adhesion strength) after a Pressure Cooker Test (hereinafter referred to as a PCT test) performed at 125 ° C., humidity 85% and 96 hours.
Further, the flexible wiring board is required to have dimensional stability and MIT folding resistance. In particular, along with the increase in the number of channels used in electronic equipment and CPU (Central Processing Unit Central Processing Unit), it is necessary to improve dimensional stability for mounting COF (Chip on Film) with a fine pitch of 25 μm or less. Therefore, in order to avoid disconnection of the lead when bent and mounted, MIT folding resistance is required. In particular, metallized polyimide films used in small electronic devices such as mobile phones, notebook personal computers, and large liquid crystal LCDs are strongly required to have excellent MIT folding resistance.

By the way, improving the adhesion strength between the polyimide film and the metal layer provided on the surface thereof has been a constant study subject since the development of such a base material, and many attempts have already been made. .
Incidentally, the present applicant, for example, has provided pyromellitic dianhydride (PMDA) as a main component in order to provide a two-layer plated copper polyimide substrate having excellent initial adhesion, heat-resistant adhesion, and adhesion after PCT. ) And 4,4′-diaminodiphenyl ether (ODA), or a component composed of pyromellitic dianhydride (PMDA) and 4,4′-diaminodiphenyl ether (ODA) as main components and biphenyltetracarboxylic acid A polyimide film containing a component consisting of non-hydrate (BPDA) and 4,4′-diaminodiphenyl ether (ODA) is used, and the surface of the polyimide film is modified by plasma treatment, corona discharge or wet treatment to make the surface hydrophilic. A functional group is introduced, the thickness of the modified layer is set to 200 mm or less, and a small amount is formed thereon by sputtering. It is proposed that a seed layer is made of a metal selected from the group consisting of at least nickel, chromium, and alloys thereof, and a copper layer having a thickness of 8 μm is formed thereon by plating (Patent Document 1 No. 1). 1 and 2).
By this method, the adhesion strength between the polyimide surface of the base material and the metal layer is improved, the initial adhesion strength, the adhesion strength after standing in the atmosphere at 150 ° C. for 168 hours, 121 ° C., 95% humidity, 100 at 2 atm. The adhesion strength after the time PCT test is 400 N / m or more (see Patent Document 1, page 5).

  Also proposed is a polyimide film with excellent dimensional stability and suitable for fine pitch circuit boards, especially for COF (Chip on Film) wired in a narrow pitch in the film width direction, and a copper-clad laminate based on it. (Patent Document 2). Here, a specific amount or more of 4,4′-diaminobenzanilide is used as the diamine component, the thermal expansion coefficient of the polyimide film is defined from the viewpoint of dimensional stability, and the thermal expansion coefficient is made equal to the thermal expansion coefficient of the metal. It is described that it is desirable. A circuit board using a metallized polyimide film requires not only dimensional stability but also adhesion strength. However, Patent Document 2 does not include a detailed description of the MIT folding resistance test, which is an index of adhesion strength and bendability.

None of the conventional metal-coated polyimide substrates can achieve 2000 times or more of the bending resistance required when the chip-on-film (COF) is bent and mounted in the MIT folding resistance test (JIS C 6471-1995).
Also, there is no known metal-coated polyimide substrate for semiconductor mounting that has excellent durability against MIT folding resistance, which is difficult to break the lead, and metal-coated polyimide that combines dimensional stability and adhesion as well as MIT folding resistance testing. A method that can stably produce a substrate has been desired.

JP 2007-318177 A (refer to pages 1, 2, and 5) JP 2009-67859 A

  An object of the present invention is to provide a metal-coated polyimide film having improved initial adhesion strength and adhesion strength after the PCT test, and improved MIT folding resistance test, which is an index of bendability, The object is to provide a flexible wiring board with reduced defects.

  As a result of various studies to solve the above problems, the inventors of the present invention contain an imide bond by biphenyltetracarboxylic acid and a diamine compound in the polyimide molecule, and the TD direction of the surface is measured by thin film X-ray diffraction measurement (Cu Kα incident). When the angle is 0.1 °), the water absorption rate is 1 to 3% when the film has a peak at a position of 2θ = 10 ° to 12 ° and a position of 2θ = 17 ° to 20 ° and has a film thickness of 35 μm. By using a polyimide film having a thermal expansion coefficient in a specific range in the TD direction, a metal-coated polyimide film provided with a metal film directly on this surface has been found to be able to reduce connection failures during wiring processing, The present invention has been completed.

That is, according to the first invention of the present invention, a metallized polyimide film in which a metal film is provided on at least one surface of the polyimide film without using an adhesive,
The polyimide film contains an imide bond by biphenyltetracarboxylic acid and a diamine compound in the polyimide molecule, and when the TD direction of the surface is measured by thin film X-ray diffraction (Cu Kα incident angle = 0.1 °), When 2θ = 10 ° to 12 ° has a peak with a half width of 1.5 ° or less, and 2θ = 17 ° to 20 ° has a peak with a half width of 1.5 ° or less, and when the film thickness is 35 μm, A metal-coated polyimide film having a water absorption of 1 to 3% and a thermal expansion coefficient in the TD direction of 4 ppm / ° C. to 6 ppm / ° C. is provided.

  According to the second invention of the present invention, in the first invention, the metal film is at least one selected from nickel, chromium, or an alloy thereof provided on the surface of the polyimide film. There is provided a metal-coated polyimide film comprising a metal thin film and a copper thin film provided on the surface of the metal thin film.

  According to the third invention of the present invention, in the first or second invention, the metal film is composed of three layers in which a copper layer is provided on the metal thin film and the copper thin film. A metal-coated polyimide film is provided.

  According to a fourth aspect of the present invention, there is provided the metal-coated polyimide film according to the second or third aspect, wherein the metal thin film and the copper thin film are both formed by a dry plating method. Is done.

  According to a fifth aspect of the present invention, there is provided the metallized polyimide film according to the third aspect, wherein the copper layer is formed by a wet plating method.

  According to a sixth aspect of the present invention, there is provided a metal-coated polyimide film according to any one of the first to fifth aspects, wherein the metal film has a thickness of 20 μm or less. .

  According to a seventh aspect of the present invention, there is provided a metallized polyimide film manufacturing method in which a metal film is provided on at least one surface of a polyimide film without using an adhesive, and the polyimide film includes biphenyltetracarboxylic acid. When the polyimide molecule contains an imide bond by a diamine compound and the TD direction of the surface is measured by thin film X-ray diffraction (Cu Kα incident angle = 0.1 °), the half value is 2θ = 10 ° to 12 °. A peak having a width of 1.5 ° or less and a peak at 2θ = 18 ° to 20 ° having a half width of 1.5 ° or less and a film thickness of 35 μm, the water absorption is 1 to 3%. A metal film having a thermal expansion coefficient of 4 ppm / ° C. to 6 ppm / ° C. in the TD direction is used, and the metal film is at least one selected from nickel, chromium, or an alloy thereof on the surface of the polyimide film. A metal thin film provided by dry plating method consisting, further method for producing a metal-coated polyimide film characterized by providing a dry plating method a copper thin film on the surface of the metal thin film is provided.

According to an eighth aspect of the present invention, in the seventh aspect, the metal film comprises a metal thin film layer provided on the surface of the polyimide film, a copper thin film provided on the surface of the metal thin film layer, and There is provided a method for producing a metal-coated polyimide film comprising a copper layer provided on the surface of the copper thin film, wherein the copper layer is provided by a wet plating method.
According to the ninth invention of the present invention, in any one of the first to sixth inventions, a flexible wiring board obtained by wiring a metal-coated polyimide film is provided.

  According to the tenth invention of the present invention, the metal-coated polyimide film obtained by the manufacturing method of the seventh invention is processed by wiring by either a semi-additive method or a subtractive method. A method for manufacturing a flexible wiring board is provided.

  The metal-coated polyimide film of the present invention is superior to conventional metal-coated polyimide films in terms of initial adhesion strength, adhesion strength after PCT test, and fold resistance specified in the MIT folding resistance test method. It can be used as a material of a flexible wiring board suitable for the above. The flexible wiring board of the present invention obtained using the metal-coated polyimide film of the present invention can reduce connection failures.

It is a chart of the thin film X-ray diffraction of the polyimide film used for Example 1 of this invention.

The metal-coated polyimide film of the present invention is a metallized polyimide film in which a metal film is provided on at least one surface of the polyimide film without using an adhesive, and the polyimide film is made of biphenyltetracarboxylic acid and a diamine compound. When an imide bond is contained in the polyimide molecule and the TD direction on the surface thereof is measured by thin film X-ray diffraction measurement (Cu Kα incident angle = 0.1 °), the half width is 1.θ from 2θ = 10 ° to 12 °. It has a peak of 5 ° or less, a peak at 2θ = 17 ° to 20 ° and a half width of 1.5 ° or less, and when the film thickness is 35 μm, the water absorption is 1 to 3% and the heat in the TD direction The expansion coefficient is 4 ppm / ° C. to 6 ppm / ° C.
Since the metal-coated polyimide film of the present invention has such characteristics, the initial adhesion strength is 900 N / m or more, the adhesion strength after the PCT test is 600 N / m or more, and the bendability defined in the MIT folding resistance test method is 2000. In order to show ~ 3000 times, when this metal-coated polyimide film is processed by a semi-additive method or a subtractive method to form a flexible wiring board, it is possible to reduce the connection failure between the lead and the polyimide film generated in the inner reed portion. .

1) Polyimide film The polyimide film used in the present invention contains an imide bond by biphenyltetracarboxylic acid and a diamine compound in the polyimide molecule, and the surface thereof is thin-film X-ray diffracted in the TD direction (width direction of the polyimide film). When measured (Cu Kα incident angle = 0.1 °), the peak at 2θ = 10 ° to 12 ° has a half width of 1.5 ° or less, and the half width at 2θ = 17 ° to 20 ° is 1 It has a peak of not more than 5 °, and its thermal expansion coefficient is 4 ppm / ° C. to 6 ppm / ° C.
In addition, since the polyimide film used in the present invention is simply subjected to X-ray diffraction measurement (Cu Kα), it is difficult to find specific peaks at 2θ = 10 ° to 12 ° and 17 ° to 20 °. However, it is not easy, and the peak can be confirmed only when the incident angle is measured by thin film X-ray diffraction measurement at 0.1 °, and the surface state can be confirmed. Some polyimide films have a peak at a half-value width of 1.5 ° or less at 2θ = 2 ° to 10 °, but the polyimide film used in the present invention has a half-value width of 1.5 ° at this position. There are no peaks below.

In the metal-coated polyimide film of the present invention, a metal thin film and a copper thin film are provided on the surface of the specific polyimide film by a dry plating method, and then a copper layer having a predetermined thickness is provided by a wet plating method.
When a copper layer is provided by a wet plating method, particularly an electroplating method, a tensile stress is formed as an electrodeposition stress in the copper layer. This tensile stress causes peeling between the metal layer and the polyimide layer.
When a copper layer is provided by a wet plating method, the polyimide film is immersed in a plating bath. The polyimide film has good water absorption, and when immersed in a plating bath, it absorbs water and expands. And since it is heat-dried after completion | finish of plating, it shrink | contracts and it returns to the state before a plating process. Therefore, if the expansion rate of the polyimide film due to water absorption is appropriate, a copper plating layer is completed on the surface of the polyimide film that has been appropriately expanded, and then the polyimide film is contracted and stretched by heating and drying. It is possible to reduce the tensile stress remaining as internal stress in the copper layer.

In the present invention, it is necessary to consider the water absorption rate as well as the expansion rate of the polyimide film due to water absorption. In the present invention, a polyimide film having a water absorption rate of 1 to 3% is used. However, if the water absorption rate is less than 1%, the amount of expansion of the polyimide film due to water absorption decreases, and the object of the present invention is not achieved. If the water absorption exceeds 3%, the amount of expansion due to water absorption of the polyimide film becomes too large, and when heated and dried, compressive stress is generated as internal stress in the copper layer, and sufficient initial adhesion strength and PCT adhesion strength are obtained. There may not be.
When a metal layer is provided directly on the surface of the polyimide film, the larger the difference in the coefficient of thermal expansion between the metal layer and the polyimide film, the greater the load on the bonding surface between the narrow wiring portion and the polyimide film due to high-temperature heating during bonding wire. Takes and becomes easy to peel off.

The reason why the polyimide film has oxygen permeability and water absorption as described above is considered as follows.
Generally, it is known that a polyimide film is easily crystallized due to its heat resistance and molding method. In the crystallized polyimide film, polyimide molecules are aligned, and moisture easily enters and exits between the molecules. That is, in the moderately crystallized polyimide, the value of oxygen permeability obtained by measuring under 1013hPa using a polyimide film having a thickness of 35 [mu] m, can the 300~500cm ³ / ^m 2/24 hours, the water absorption It can be 1 to 3%.
In order to confirm whether the polyimide film is crystallized, the polyimide film surface may be measured by thin film X-ray diffraction. When it is crystallized, a plurality of peaks are usually confirmed on the chart, although it varies depending on the degree of crystallinity. In the present invention, when a peak having a half width of 1.5 ° or less at 2θ = 10 ° to 12 ° and a peak having a half width of 1.5 ° or less at 2θ = 17 ° to 20 ° is used. Since the polyimide film is appropriately crystallized, the polyimide film has an appropriate water absorption rate.
The polyimide film having the above characteristics has high elasticity as a bulk due to its crystallinity, and contributes to improvement of the bendability of the metal-coated polyimide film.
Moreover, since the thermal expansion coefficient in the TD direction is 4 ppm / ° C. to 6 ppm / ° C., it contributes to the reduction in bonding failure between the lead and the polyimide film generated in the inner lead portion of the flexible wiring board obtained by wiring processing.

  The polyimide film used in the present invention is not particularly limited as long as it has the above characteristics, but it is preferable to use a polyimide film mainly composed of biphenyltetracarboxylic acid. This is because a polyimide film containing biphenyltetracarboxylic acid as a main component is excellent in heat resistance and dimensional stability.

  The thickness of the polyimide film used in the present invention is not particularly limited, but it is preferably 25 to 50 μm in view of ensuring bendability and yield when forming a metal film.

Moreover, a filler can also be added and used for the purpose of improving various properties of the film such as slidability and thermal conductivity. In this case, any filler may be used, but preferred examples include silica, titanium oxide, alumina, silicon nitride, boron nitride, calcium hydrogen phosphate, calcium phosphate, mica and the like.
The particle diameter of the filler is not particularly limited because it is determined by the film characteristics to be modified and the type of filler to be added, but generally the average particle diameter is 0.05 to 100 μm, preferably 0.8. It is 1 to 75 μm, more preferably 0.1 to 50 μm, and particularly preferably 0.1 to 25 μm. If the particle size is below this range, the modification effect is less likely to appear. If the particle size is above this range, the surface properties may be greatly impaired or the mechanical properties may be greatly deteriorated. Also, the amount of filler added is not particularly limited because it is determined by the film properties to be modified, the filler particle diameter, and the like. Generally, the addition amount of the filler is 0.01 to 100 parts by weight, preferably 0.01 to 90 parts by weight, and more preferably 0.02 to 80 parts by weight with respect to 100 parts by weight of the polyimide. If the amount of filler added is less than this range, the effect of modification by the filler hardly appears, and if it exceeds this range, the mechanical properties of the film may be greatly impaired.
As an example of such a polyimide film, for example, Upilex 35SGA V1 (registered trademark) commercially available from Ube Industries, Ltd. may be mentioned.

Next, the manufacturing method of a polyimide film is illustrated.
(I) Production of polyamic acid as a precursor As a method for obtaining a polyamic acid, any known method and a method combining them can be used. Typical polymerization methods include the following methods (a) to (e). That is,
(A) An aromatic diamine is dissolved in an organic polar solvent, and an equimolar amount of an aromatic tetracarboxylic dianhydride is added thereto and polymerized.
(B) An aromatic tetracarboxylic dianhydride is reacted with a small molar amount of an aromatic diamine compound in an organic polar solvent to obtain a prepolymer having acid anhydride groups at both ends. Subsequently, the aromatic diamine compound is added and polymerized so that the aromatic tetracarboxylic dianhydride and the aromatic diamine compound finally become substantially equimolar.
(C) An aromatic tetracarboxylic dianhydride and an excess molar amount of the aromatic diamine compound are reacted in an organic polar solvent to obtain a prepolymer having amino groups at both ends. Subsequently, the aromatic tetracarboxylic dianhydride is added and polymerized so that the aromatic tetracarboxylic dianhydride and the aromatic diamine compound finally become substantially equimolar.
(D) After dissolving and / or dispersing the aromatic tetracarboxylic dianhydride in an organic polar solvent, an aromatic diamine compound is added and polymerized so as to be substantially equimolar.
(E) A substantially equimolar mixture of aromatic tetracarboxylic dianhydride and aromatic diamine is reacted in an organic polar solvent for polymerization.
In order to obtain a polyamic acid, any of these methods (a) to (e) may be used, or a combination thereof may be used. The polyamic acid obtained by any method can also be used as a raw material for the polyimide film used in the present invention.

Examples of the acid dihydrate include pyromellitic dianhydride, 2,3,6,7-naphthalenetetracarboxylic dianhydride, 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride. 1,2,5,6-naphthalenetetracarboxylic dianhydride, 2,2 ′, 3,3′-biphenyltetracarboxylic dianhydride, 3,3 ′, 4,4′-benzophenonetetracarboxylic dianhydride Anhydride, 4,4′-oxyphthalic dianhydride, 2,2-bis (3,4-dicarboxyphenyl) propane dianhydride, 3,4,9,10-perylenetetracarboxylic dianhydride, bis (3,4-dicarboxyphenyl) propane dianhydride, 1,1-bis (2,3-dicarboxyphenyl) ethane dianhydride, 1,1-bis (3,4-dicarboxyphenyl) ethane dianhydride Bis (2,3-dicarboxy Phenyl) methane dianhydride, bis (3,4-dicarboxyphenyl) ethane dianhydride, oxydiphthalic dianhydride, bis (3,4-dicarboxyphenyl) sulfone dianhydride, p-phenylenebis (trimerit Acid monoester acid anhydride), ethylene bis (trimellitic acid monoester acid anhydride), bisphenol A bis (trimellitic acid monoester acid anhydride), and the like. A mixture of proportions can be preferably used.
Among these acid dianhydrides, especially pyromellitic dianhydride and / or 3,3 ′, 4,4′-benzophenone tetracarboxylic dianhydride and / or 4,4′-oxyphthalic dianhydride and It is preferable to use 3,3′4,4′-biphenyltetracarboxylic dianhydride, and further, an acid dianhydride containing 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride The use of a mixture of

  Examples of the aromatic diamine compound include 4,4′-diaminodiphenylpropane, 4,4′-diaminodiphenylmethane, benzidine, 3,3′-dichlorobenzidine, 3,3′-dimethylbenzidine, and 2,2′-dimethylbenzidine. 3,3′-dimethoxybenzidine, 2,2′-dimethoxybenzidine, 4,4′-diaminodiphenylsulfide, 3,3′-diaminodiphenylsulfone, 4,4′-diaminodiphenylsulfone, 4,4′-oxy Dianiline, 3,3′-oxydianiline, 3,4′-oxydianiline, 1,5-diaminonaphthalene, 4,4′-diaminodiphenyldiethylsilane, 4,4′-diaminodiphenylsilane, 4,4 '-Diaminodiphenylethylphosphine oxide, 4,4'-diaminodiphenyl N Methylamine, 4,4′-diaminodiphenyl N-phenylamine, 1,4-diaminobenzene (p-phenylenediamine), 1,3-diaminobenzene, 1,2-diaminobenzene, bis {4- (4-amino Phenoxy) phenyl} sulfone, bis {4- (3-aminophenoxy) phenyl} sulfone, 4,4′-bis (4-aminophenoxy) biphenyl, 4,4′-bis (3-aminophenoxy) biphenyl, 1, 3-bis (3-aminophenoxy) benzene, 1,3-bis (4-aminophenoxy) benzene, 1,3-bis (4-aminophenoxy) benzene, 1,3-bis (3-aminophenoxy) benzene, 3,3′-diaminobenzophenone, 4,4-diaminobenzophenone, and the like thereof.

The polyamic acid for polyimide film used in the present invention is obtained by selecting and polymerizing the kind and blending ratio of aromatic acid tetracarboxylic dianhydride and aromatic diamine within the above range.
As the preferred solvent for synthesizing the polyamic acid, any solvent can be used as long as it dissolves the polyamic acid, but amide solvents, that is, N, N-dimethylformamide, N, N-dimethylacetamide, N- Methyl-2-pyrrolidone and the like are preferable, and N, N-dimethylformamide and N, N-dimethylacetamide are particularly preferable.

(Ii) Conversion from polyamic acid to polyimide The polyamic acid thus obtained is then converted to polyimide. An organic solution containing polyamic acid is cast on a support such as a glass plate, an aluminum foil, a metal endless belt, or a metal drum to obtain a resin film. At this time, it is partially cured and / or dried by heating on the support. At this time, hot air or far-infrared radiation heat may be applied. Alternatively, the support itself may be heated. Furthermore, a method of applying hot air or far infrared radiation heat and a method of heating the support itself can be combined.
The resin film cast by heating becomes a self-supporting semi-cured film, a so-called gel film, and is peeled off from the support. This gel film is in the intermediate stage of curing from polyamic acid to polyimide, that is, partially imidized and has self-supporting properties, and has residual volatile components such as a solvent.
Next, the gel film is heated to dry to remove the remaining solvent, and the curing (imidization) is completed together with this, but in order to avoid shrinkage of the gel film during drying and curing, the gel film While being held by a tenter frame with a pin or a tenter clip, it is conveyed to a heating furnace and heated at 200 to 400 ° C. to obtain a polyimide film.

2) Metal-coated polyimide film The specific polyimide film thus obtained is a metal-coated polyimide film as follows.
A metal thin film made of at least one selected from nickel, chromium, and alloys thereof is provided on the surface by a dry plating method, and a copper thin film is provided thereon by a dry plating method. Depending on the method of using the metal-coated polyimide film, that is, the method of manufacturing the flexible wiring board of the present invention, a copper layer having a predetermined thickness may be provided on the surface of the copper thin film by a wet plating method.

a) Metal thin film The metal thin film is provided in order to ensure reliability such as adhesion and heat resistance between the polyimide film and the metal film. Therefore, the material of the metal thin film may be any one selected from nickel, chromium, or an alloy thereof in order to increase the adhesion between the polyimide film and the copper layer. It is preferable to use a nickel-chromium alloy because of the ease of etching. Further, in order to provide a nickel-chromium alloy concentration gradient, the metal thin film may be composed of a plurality of nickel-chromium alloy layers having different chromium concentrations. If comprised with these metals, the corrosion resistance and migration resistance of the metallized polyimide film will be improved.
Further, in order to further increase the corrosion resistance of the metal thin film, vanadium, titanium, molybdenum, cobalt, or the like may be added to the metal.
Also, in order to improve the adhesion between the polyimide film and the metal thin film before dry plating, it is preferable to subject the polyimide film surface to surface treatment by corona discharge or ion irradiation, and then to ultraviolet irradiation in an oxygen gas atmosphere. . These treatment conditions are not particularly limited, and may be conditions applied to a normal method for producing a metallized polyimide film.
The thickness of the metal thin film is preferably 3 to 50 nm. If the thickness is less than 3 nm, when the wiring is formed by etching the metal layer of the metallized polyimide film, the etching solution may erode the metal thin film, soak into the polyimide film and the metal thin film, and the wiring may float. There is not preferable. On the other hand, when the thickness exceeds 50 nm, when a wiring is formed by etching, the metal thin film is not completely removed and remains as a residue between the wirings, and there is a high possibility that an insulation failure between the wirings occurs.
The metal thin film is preferably formed by dry plating. The dry plating method includes sputtering method, magnetron sputtering method, ion plating method, cluster ion beam method, vacuum deposition method, CVD method, etc. Any of these may be used, but industrially magnetron sputtering method is used. It is done. This is because production efficiency is high.

b) Copper thin film In the present invention, the copper thin film is preferably obtained by a dry plating method. As the dry plating method to be employed, any of the above-described sputtering method, magnetron sputtering method, ion plating method, cluster ion beam method, vacuum deposition method, CVD method and the like can be used. It is also possible to provide a copper thin film by a vapor deposition method after forming the metal thin film by a magnetron sputtering method. That is, there is no reason why the metal thin film and the copper thin film must be dry-plated by the same method.
The reason why the copper thin film is provided is that when a copper layer is directly provided on the metal thin film by electroplating, the energization resistance is high and the current density of electroplating becomes unstable. By providing a copper thin film, the current resistance can be lowered and the current density during electroplating can be stabilized. The thickness of the copper thin film is preferably 10 nm to 1 μm. If the thickness is too thin, the energization resistance at the time of electroplating cannot be lowered sufficiently, and if the thickness is too thick, it takes too much time, which deteriorates productivity and impairs economy.

c) Copper layer In the present invention, the thickness of the copper layer is preferably 1.0 to 20.0 μm. If the thickness is less than 1.0 μm, sufficient conductivity may not be obtained when the wiring is formed, and if the thickness exceeds 20 μm, the internal stress of the copper layer becomes too large.
The copper layer is preferably provided by a wet plating method. This is because in the dry plating method, it takes too much time to plate up to a predetermined thickness, which deteriorates productivity and impairs economy. There are electroplating methods and electroless plating methods as wet plating methods, but any of them may be used in combination, but the electroplating method is simple and the resulting copper layer is dense. Since it becomes a thing, it is preferable. The plating conditions are known conditions.
When a copper layer is provided by electroplating, it is more preferable to use a sulfuric acid bath because an electrodeposited copper layer having an appropriate tensile stress can be obtained, and the internal stress due to expansion and expansion / contraction of the polyimide film can be easily balanced.
When a copper layer is obtained by electroplating, the internal stress of the copper layer is preferably a tensile stress of 5 to 30 MPa before the polyimide film is dried. When it is less than 5 MPa, the polyimide film stretch effect becomes too large when the polyimide film is dried, and when the tensile stress exceeds 30 MPa, the stretch effect of the polyimide film when the polyimide film is dried becomes too small. It is.
The electrolytic copper plating using a sulfuric acid bath may be performed under normal conditions. As a plating bath, a commercially available copper sulfate plating bath used for general electrolytic copper plating can be used. Moreover, it is preferable that the cathode current density sets the average cathode current density of a plating tank to 1-3 A / dm < ² >. When the average cathode current density of the cathode current density is less than 1 A / dm ² , the hardness of the obtained copper layer becomes high and it becomes difficult to ensure the bendability, and a flexible wiring board using the obtained metallized polyimide film This is because the obtained flexible wiring board does not have good flexibility. On the other hand, if the average cathode current density exceeds 3 A / dm ² , the residual stress generated in the obtained copper layer varies.
The copper electroplating equipment using the sulfuric acid bath unwinds the roll-shaped polyimide film from the unwinder installed on the entrance side of the copper electroplating equipment in the same way as the dry plating process, and sequentially passes through the plating tank while transporting it. It is preferable to use a roll-to-roll type electroplating apparatus that is performed while being wound by a winder in order to increase production efficiency and reduce manufacturing costs. In this case, it is preferable to adjust the film conveyance speed to 50 to 150 m / h. If the conveyance speed is less than 50 m / h, the productivity becomes too low, and if it exceeds 150 m / h, the energization current amount must be increased, and a large-scale power supply device must be used. There is a problem that it becomes expensive.
The metallized polyimide film of the present invention thus obtained has an initial adhesion strength of 900 N / m or more and a temperature of 125 by an evaluation of peel strength based on JIS C-6471-1995-8.1. Metal coating with adhesion strength after PCT of 600 ° C., humidity 85%, 96 hr, and foldability specified in MIT folding resistance test (JIS C 6471-1995-8.2) of 2000 to 3000 times It becomes a polyimide film.

3) Flexible wiring board The flexible wiring board of the present invention is obtained by wiring using the metal-coated polyimide film by a subtractive method or a semi-additive method.
For example, in the case of the subtractive method, a resist layer is provided on the surface of the metal film of the metal-coated polyimide film of the present invention, an exposure mask having a predetermined pattern is provided thereon, and exposure is performed by irradiating ultraviolet rays thereon. Then, development is performed to obtain an etching mask for obtaining a wiring portion. Next, the exposed metal film is removed by etching, then the remaining etching mask is removed, washed with water, and a desired plating is applied to necessary portions to obtain the flexible wiring board of the present invention.
For example, in order to obtain a flexible wiring board by the semi-additive method, a resist layer is provided on the metal film surface of the metal-coated polyimide film of the present invention, a mask having a predetermined wiring pattern is provided thereon, and ultraviolet rays are irradiated. Exposure and development to obtain a plating mask in which the wiring becomes an opening, copper is deposited on the surface of the metal film exposed to the opening by an electrolytic copper plating method, and then the plating mask is removed . Thereafter, the metal layer other than the wiring is removed by soft etching to ensure the insulation of the wiring, washed with water, and desired plating is performed on the necessary portion to obtain the flexible wiring board of the present invention.
Note that the metal-coated polyimide film used when obtaining a flexible wiring board by the semi-additive method is composed of three layers of a metal thin film, a copper thin film and a copper layer, even if the metal film is composed of two layers of a metal thin film and a copper thin film. Or either. Since the wiring is formed by depositing copper by the electrolytic copper plating method, the deposited wiring corresponds to the copper layer of the metal-coated polyimide film of the present invention.
Therefore, the wiring structure of the flexible wiring board of the present invention has a structure in which a metal thin film, a copper thin film, and a copper layer are laminated in this order from the polyimide film surface, regardless of which method is used.

Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to these examples. In addition, the measurement conditions of thin film X-ray diffraction of the polyimide film used in the Example, the water absorption, the thermal expansion coefficient, the measurement method of the adhesion strength of the obtained metal-coated polyimide film, the PCT test, the measurement method of MIT folding resistance The conditions are as follows.
(1) Thin-film X-ray diffraction measurement: As a diffractometer, a horizontal X-ray diffractometer “SmartLab” manufactured by Rigaku Corporation is used, and an incident angle (ω) is 0.1 ° in the TD direction and a sampling width is 0.1 °. The measurement angle 2θ was 2 ° to 60 °, and the scanning speed was measured at 4 ° / min.
(2) Water absorption: determined by the immersion method (Immersion) at 20 ° C. for 24 hours as defined in ASTM D570.
(3) Thermal expansion coefficient: Using a TMA (thermomechanical analysis) apparatus, the TD direction in the range of 50 ° to 200 ° was determined by a tensile method.
(4) Adhesion strength: A wiring pattern having a line width of 1 mm and a length of 50 mm was formed by a subtractive method, and was obtained by a peeling method according to JIS C-6471-1995-8.1.
(5) PCT test: Measured under conditions of a temperature of 125 ° C., a humidity of 85%, and 96 hours.
(6) MIT folding endurance: Bending until bending occurs under the conditions of R = 0.38, load 500 g, line width 1 mm according to the MIT folding endurance test method according to JIS C 6471-1995-8.2. The number of times was calculated.

Example 1
First, the water absorption is 1.8%, the thermal expansion coefficient is TD direction: 4 ppm / ° C., and as a result of thin film X-ray diffraction, as shown in FIG. 1, the half width is 1.5 at 2θ = 11 °. A long polyimide film mainly composed of biphenyltetracarboxylic acid having a thickness of 35 μm in which a peak of less than ° and a peak at 2θ = 18 ° with a half width of 1.5 ° or less can be seen (manufactured by Ube Industries, Ltd.) Upilex SGA V1) was prepared.
On one side of this polyimide film, a 20 mass% chromium-nickel alloy layer having an average thickness of 230 mm as a metal thin film is formed by a direct current sputtering method using a sputtering facility comprising an unwinder, a sputtering device, and a winder. Formed. Further, similarly, a copper thin film having an average thickness of 1000 mm was formed on the metal thin film.
Next, a copper layer having a thickness of 8 μm was provided on the copper thin film by electrolytic copper plating to obtain a metallized polyimide film. The electroplating bath used was a copper sulfate plating bath with a copper concentration of 23 g / l, and the bath temperature during plating was 27 ° C. In addition, the plating tank is a multi-structure tank in which a plurality of plating tanks are connected so that a polyimide film having a metal layer on one side is continuously immersed in each tank by an unwinder and a winder. Electroplating was performed while being conveyed. The conveyance speed was 75 m / h, and the average cathode current density of the plating tank was adjusted to 1.0 to 2.5 A / dm ² to perform copper plating.
When the initial adhesion strength of the obtained metal-coated polyimide film was determined, it was 958 N / m, and the adhesion strength after the PCT test was 692 N / m. Incidentally, the adhesion strength after holding at 150 ° C. for 168 hours was 546 N / m, and the MIT folding resistance was 2850 times.
Next, using this metal-coated polyimide film, a COF (Chip on film) with a wiring interval of 35 μm and a total wiring width of 15000 μm is prepared by a subtractive method, and an IC chip is mounted on the COF and the electrodes and wiring on the surface of the IC chip. The lead part was wire-bonded using a wire bonding apparatus at 400 ° C. under a bonding process condition of 0.5 seconds. At this time, the ratio of the bonding failure between the lead and the polyimide film generated in the inner reed portion was 0.0001%.

(Example 2)
A flexible wiring board was prepared in the same manner as in Example 1 except that the metal-coated polyimide film obtained in Example 1 was used and the wiring interval was set to 25 μm, and the proportion of bonding failure was determined in the same manner as in Example 1. The ratio of poor bonding between the inner lead and the polyimide film was 0.005%, and it was found that there was sufficient dimensional reliability even at a fine pitch.

(Comparative Example 1)
As a polyimide film, a 38 μm-thick polyimide film (manufactured by Toray DuPont Co., Ltd., Kapton 150EN) whose main component is biphenyltetracarboxylic acid having a water absorption rate of 1.7% and a thermal expansion coefficient of TD direction: 16 ppm / ° C. A metallized polyimide film was obtained in the same manner as in Example 1 except that it was used. When Kapton 150EN was subjected to thin film X-ray diffraction, large peaks at 2 ° and 10 ° and 14 ° were confirmed.
When the obtained metallized polyimide film was evaluated in the same manner as in Example 1, the initial adhesion strength was 725 N / m and the PCT adhesion strength was 412 N / m. Incidentally, the adhesion strength after holding at 150 ° C. for 168 hours was 423 N / m, and the MIT folding resistance was 113 times.
Next, a flexible wiring board having a wiring width of 35 μm was prepared in the same manner as in Example 1 except that the metallized polyimide film was used, and the proportion of defective bonding was determined in the same manner as in Example 1. The proportion of bonding failure occurring in the inner lead portion of the wiring is 0.001%, which is a bad value as compared with Example 1, and even with a wiring width of 35 μm, a product having sufficient reliability was not obtained.

(Comparative Example 2)
A flexible wiring board was prepared in the same manner as in Comparative Example 1 except that the wiring interval was set to 25 μm, and the proportion of bonding failure was determined in the same manner as in Example 1. The proportion of poor bonding that occurred in the inner lead portion of the wiring was 0.1%, and when the pitch was made fine, a product having sufficient reliability could not be obtained.

(Comparative Example 3)
As a polyimide film, a 35 μm thick polyimide film (product name, Apical 35FP manufactured by Kaneka) whose main component is biphenyltetracarboxylic acid having a water absorption rate of 1.4% and a thermal expansion coefficient of TD direction: 14 ppm / ° C. is used. A metallized polyimide film was obtained in the same manner as in Example 1 except that. When Upilex 35SGA was subjected to thin film X-ray diffraction, a large peak with a half-value width of 1.0 ° was confirmed at a position of 2θ = 14 °.
When the obtained metallized polyimide film was evaluated in the same manner as in Example 1, the initial adhesion strength was 928 N / m, and the adhesion strength after the PCT test was 692 N / m. Incidentally, the adhesion strength after holding at 150 ° C. for 168 hours was 446 N / m, and the MIT folding resistance was 150 times.
Next, a flexible wiring board having a wiring width of 35 μm was prepared in the same manner as in Example 1 except that the metallized polyimide film was used, and the proportion of defective bonding was determined in the same manner as in Example 1. The proportion of poor bonding that occurred in the inner leads of the wiring was 0.001%, which was a bad value as compared with the example.

(Comparative Example 4)
A flexible wiring board was prepared in the same manner as in Comparative Example 3 except that the wiring interval was set to 25 μm, and the proportion of bonding failure was determined in the same manner as in Example 1. It was found that the proportion of poor bonding that occurred in the electrode portion of the wiring was 0.1%, and when the pitch was made fine, a reliable one could not be obtained.
As can be seen from the above, the metal-coated polyimide film of the present invention has very high initial adhesion strength and PCT adhesion strength after the PCT test. Even when wire bonding is performed by pressing at a temperature of 400 ° C. or higher when mounting the IC on the lead, the lead is not peeled off from the polyimide film, and a highly reliable flexible wiring board can be obtained. In contrast, it can be seen that a flexible wiring board obtained by using a metal-coated polyimide film that does not meet the conditions of the present invention cannot provide a highly reliable flexible wiring board even if the wiring width is 35 μm.

  When a fine-pitch flexible wiring board is created using the metal-coated polyimide film of the present invention, even if wire bonding is performed by pressing at a temperature of 400 ° C. or higher when an IC is mounted on the wiring board, the lead is made from the polyimide film. There is no peeling and a highly reliable flexible wiring board is obtained. Therefore, the present invention can be used as a substrate for manufacturing a flexible wiring board, which has been most demanded recently.

Claims (10)

A metallized polyimide film provided with a metal film on at least one surface of the polyimide film without using an adhesive,
The polyimide film contains an imide bond by biphenyltetracarboxylic acid and a diamine compound in the polyimide molecule, and when the TD direction of the surface is measured by thin film X-ray diffraction (Cu Kα incident angle = 0.1 °), When 2θ = 10 ° to 12 ° has a peak with a half width of 1.5 ° or less, and 2θ = 17 ° to 20 ° has a peak with a half width of 1.5 ° or less, and when the film thickness is 35 μm, A metal-coated polyimide film having a water absorption rate of 1 to 3% and a thermal expansion coefficient in the TD direction of 4 ppm / ° C to 6 ppm / ° C.   The metal film has two layers of a metal thin film made of at least one selected from nickel, chromium, or an alloy thereof provided on the surface of the polyimide film, and a copper thin film provided on the surface of the metal thin film. The metal-coated polyimide film according to claim 1, comprising:   2. The metal-coated polyimide film according to claim 1, wherein the metal film is composed of three layers in which a copper layer is provided on the metal thin film and the copper thin film.   4. The metal-coated polyimide film according to claim 2, wherein both the metal thin film and the copper thin film are formed by a dry plating method.   The metallized polyimide film according to claim 3, wherein the copper layer is formed by a wet plating method.   The metal-coated polyimide film according to claim 1, wherein the metal film has a thickness of 20 μm or less. A metallized polyimide film manufacturing method in which a metal film is provided on at least one surface of a polyimide film without using an adhesive,
When the polyimide film contains an imide bond by biphenyltetracarboxylic acid and a diamine compound in the polyimide molecule, and the TD direction of the surface is measured by thin film X-ray diffraction measurement (Cu Kα incident angle = 0.1 °), 2θ = 10 ° to 12 ° having a half-value width of 1.5 ° or less peak and 2θ = 18 ° to 20 ° having a half-value width of 1.5 ° or less peak. The rate is 1 to 3%, and the thermal expansion coefficient in the TD direction is 4 ppm / ° C. to 6 ppm / ° C.
The metal film is formed by providing, on a surface of the polyimide film, a metal thin film made of at least one selected from nickel, chromium, or an alloy thereof by a dry plating method. Further, a copper thin film is dry-plated on the surface of the metal thin film. The manufacturing method of the metal-coated polyimide film characterized by providing by the method.   The metal film is composed of a metal thin film layer provided on the surface of the polyimide film, a copper thin film provided on the surface of the metal thin film layer, and a copper layer provided on the surface of the copper thin film, and the copper layer is wet-plated The method for producing a metal-coated polyimide film according to claim 7, which is provided by a method.   The flexible wiring board obtained by carrying out wiring processing of the metal-coated polyimide film in any one of Claims 1-6.   A method for producing a flexible wiring board, wherein the metal-coated polyimide film obtained by the production method according to claim 7 or 8 is subjected to wiring processing by either a semi-additive method or a subtractive method.

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