JP2006159411A - Flexible substrate and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a flexible substrate not having a curl and the curl of a polyimide film after the etching of a metal foil, including no thermoplastic polyimide having the high coefficient of linear expansion and having high adhesion strength. <P>SOLUTION: The flexible substrate is constituted by forming a polyimide layer on the metal foil and characterized in that the average coefficient of linear expansion of the polyimide layer is 5×10<SP>-6</SP>to 25×10<SP>-6</SP>(1/°C), when the cross section of the flexible substrate is confirmed in the transmitted light mode of an optical microscope, the hue in the polyimide layer is observed as a single layer and, when the polyimide layer is analyzed in a film thickness direction using Raman spectroscopy, the maximum value of an orientation parameter is present on the surface side of the metal foil from the central part of the surface on the metal foil side of the polyimide layer and the surface on the opposite of the metal foil thereof. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for manufacturing a flexible substrate and a flexible substrate widely used in the electronics industry.

  The flexible substrate is configured by laminating a metal foil layer and an insulating resin layer, and has flexibility and flexibility. This flexible substrate is widely used in electronic devices that require high-density mounting. As a typical flexible substrate, there is one in which a copper foil is used for a metal foil layer and a polyimide resin is used for an insulating resin layer, which are widely used.

  Among such flexible substrates, a “cast type” in which a polyimide resin is applied to a copper foil has been energetically studied and has been put to practical use.

  In the method of applying polyimide resin to copper foil, curling of the flexible substrate can be eliminated by matching the linear expansion coefficient after heat treatment of the polyimide resin to be applied to copper foil (see Patent Documents 1, 2, and 3). . However, the flexible substrate produced by this method is curled with the surface on which the copper foil was present inside after etching the copper foil.

  In the method of applying a polyimide resin to a copper foil, curling can be eliminated even after the copper foil of the flexible substrate is etched by a method of laminating a plurality of layers of polyimides having different linear expansion coefficients (see Patent Document 4). However, the flexible substrate produced by this method uses a thermoplastic polyimide resin having a high linear expansion coefficient. For example, the wiring sinks when bonding is performed at a high temperature due to a gold / tin eutectic formation reaction in chip-on-flex (COF). Problem arises.

As a method for solving these problems, a method of laminating a plurality of low linear expansion polyimide resins has been proposed (see Patent Document 5). However, when a low linear expansion coefficient polyimide is laminated on a low linear expansion coefficient polyimide, there is a problem that the polyimide / polyimide is separated.
JP-A-60-157286 (page 2-8) JP-A-60-210894 (page 1-2) Japanese Patent Laid-Open No. 61-111182 (page 2-6) JP-A-1-245586 (page 2-6) JP-A-4-337690 (page 2-3)

  As described above, in a flexible substrate, there is no curl in the state with a metal foil, and it is a flexible substrate that does not generate curl even after etching the metal foil, does not have a high linear expansion coefficient thermoplastic polyimide, and has high adhesion Despite the demand for flexible substrates with strength, they have not yet been achieved.

That is, this invention is a flexible substrate which has a polyimide layer formed on metal foil, Comprising: The average coefficient of linear expansion of a polyimide layer is 5 * 10 < ^-6 > or more and 25 * 10 < ^-6 > (1 / degreeC) or less. When the cross section of the flexible substrate is confirmed in the transmitted light mode of the optical microscope, the hue in the polyimide layer is observed as a single layer, and when the film thickness direction analysis is performed using Raman spectroscopy, the maximum value of the orientation parameter is A flexible substrate characterized by being on the metal foil surface side from the center of the metal foil side surface of the polyimide layer and the surface on the opposite side.

Another aspect of the present invention is a method for producing a flexible substrate having a polyimide layer formed on a metal foil,
(A) The process of apply | coating the polyamic-acid varnish used as the polyimide of 5 * 10 < ^-6 > (1 / ( ^degreeC )) or less and 25 * 10 < ^-6 > (1 / ( ^degreeC )) at a film thickness T1 to a metal foil,
(B) a step of heat-treating the polyamic acid applied in step (a) so that the imidization ratio is 15% or more and 95% or less;
(C) A polyamic acid varnish that becomes a polyimide having a linear expansion coefficient of 5 × 10 ⁻⁶ (1 / ° C.) or more and 25 × 10 ⁻⁶ (1 / ° C.) or less on the layer formed in the step (b). Is applied at a film thickness T2 (provided 1 ≦ T2 / T1 ≦ 100 is satisfied),
(D) a step of imidizing all layers by heat treatment;
It is a manufacturing method of the flexible substrate which has this.

  According to the present invention, a flexible substrate has a metal foil and a polyimide layer formed by applying a polyamic acid varnish on a metal foil and heat-treating it. Does not curl. Moreover, a very excellent flexible substrate that can be used as a substrate for gold / tin eutectic bonding requiring a temperature of 300 ° C. can be obtained.

The polyimide layer of the present invention is a polyimide having an average linear expansion coefficient of 5 × 10 ⁻⁶ or more and 25 × 10 ⁻⁶ (1 / ° C.) or less over the entire region. The average linear expansion coefficient of the polyimide layer of the present invention is 5 × 10 ⁻⁶ or more and 25 × 10 ⁻⁶ (1 / ° C.) or less. The average linear expansion coefficient in the present invention refers to the average linear expansion coefficient of polyimide from 30 ° C. to 250 ° C. When the average linear expansion coefficient is smaller than 5 × 10 ⁻⁶ (1 / ° C.), the flexible substrate curls with the metal foil inside. When the average linear expansion coefficient is larger than 25 × 10 ⁻⁶ (1 / ° C.), the flexible substrate curls with the metal foil facing outside.

In the present invention, when the cross section of the flexible substrate is observed in the transmitted light mode of the optical microscope, the hue in the polyimide layer is observed as a single layer. The case where the hue of the polyimide layer is not observed as a single layer is, for example, a state where there is an interface between the polyimide and the polyimide. Since the refractive index of light slightly changes at this interface, it is considered that the hue does not appear to be single. When the hue of the polyimide layer is not single, the normal adhesion is high, but the adhesion at the polyimide-polyimide interface is markedly reduced when placed in a high temperature and high humidity atmosphere. On the other hand, when the hue of the polyimide layer is observed singly, since there is no interface in the polyimide, the adhesion is hardly lowered even in an atmosphere of high temperature and high humidity. It is preferable that the adhesive force when peeling the polyimide and the metal foil after the high temperature and high humidity treatment (after the PCT treatment) is 10 N / cm or more.
In the present invention, the polyimide layer is analyzed for film thickness direction using Raman spectroscopy, and the maximum value of the orientation parameter obtained at that time is higher than that of the center of the metal foil side surface of the polyimide layer and the opposite surface. On the foil side.

The method for analyzing the film thickness direction of the polyimide layer according to the present invention using Raman spectroscopy will be described below. When the cross section of the flexible substrate is analyzed by Raman spectroscopy, polarized Raman spectra in the vertical direction and parallel direction of the flexible substrate are obtained. To normalize phenyl C = C stretch around 1615 cm ^-1, 725 cm around ^-1, C-N-C symmetry and inverse symmetric stretching near 1100 cm ^-1, the C = O stretching in the vicinity of 1770 cm ^-1, vertical The peak intensity in the parallel direction increases with CN stretching near 1380 cm ⁻¹ . The orientation parameters in the present invention were defined as follows.

Orientation parameter = [A _1380cm-1 / A _725cm-1 (parallel)] / [A _1380cm-1 / A _725cm-1 (vertical)]
These parameters indicate that the larger the value is, the higher the orientation is, and 1 when there is no orientation.

  In the present invention, the maximum value of the orientation parameter when the polyimide layer is analyzed in the film thickness direction using Raman spectroscopy indicates the position where the orientation is the largest in the polyimide layer. In the present invention, the maximum value of the orientation parameter is closer to the metal foil surface side than the center of the metal foil side surface of the polyimide layer and the opposite surface. It shows that there is a position with the largest orientation on the metal foil side than the center with the surface. Since there is a position having the greatest orientation at this position, a flexible substrate can be obtained that not only does not curl with the metal foil attached but also does not cause curl after the metal foil is etched.

  In the present invention, the curl evaluation method is performed as follows. After cutting the flexible substrate with all layers heat-treated to 100 mm x 100 mm, left for 24 hours at 25 ° C and 40-60% RH, and then left on a flat metal plate to increase the warp of 4 strokes. The total value of the measured thickness is defined as a curl with copper. Moreover, the copper foil of this flexible substrate was etched on the entire surface with a ferric chloride solution, and similarly, left for 24 hours at 25 ° C. and 40 to 60% RH, and then left on a flat metal plate. The total value obtained by measuring the height of the warping of the four strokes is taken as the curl after copper etching. The curl is preferably 10 mm or less, more preferably 5 mm or less.

The production method of the flexible substrate of the present invention is shown in detail below.
The present invention is a method for producing a flexible substrate having a polyimide layer formed on a metal foil,
(A) The process of apply | coating the polyamic acid varnish used as the polyimide whose average linear expansion coefficient is 5 * 10 < ^-6 > or more and 25 * 10 < ^-6 > (1 / degrees C) or less to film thickness T1;
(B) a step of heat treatment so that the imidization ratio of the polyamic acid applied in the step (a) is 15% or more and 95% or less;
(C) On the layer formed in the step (b), a polyamic acid varnish that becomes a polyimide having an average linear expansion coefficient of 5 × 10 ⁻⁶ or more and 25 × 10 ⁻⁶ (1 / ° C.) or less is obtained. Step of applying at T2 (however, 1 ≦ T2 / T1 ≦ 100 is satisfied),
(D) A method for producing a flexible substrate having a step of imidizing all layers by heat treatment.

  In the present invention, the thickness of the polyimide layer after the heat treatment (d) is usually preferably 2 μm or more and 50 μm or less.

In the step (a), a polyamic acid varnish that is a polyimide having an average linear expansion coefficient of 5 × 10 ⁻⁶ or more and 25 × 10 ⁻⁶ (1 / ° C.) or less is applied. The ratio T2 / T1 between the thickness T1 of the polyimide layer and the thickness T2 of the polyimide layer applied in the step (c) is preferably 1 ≦ T2 / T1 ≦ 100. When T2 / T1 is less than 1, the maximum value of the orientation parameter of Raman spectroscopy described below is on the opposite side of the center of the metal foil surface of the polyimide layer and the opposite surface. End up. For this reason, after etching a metal foil, curl will appear with the one with the metal foil inside. On the other hand, when T2 / T1 is larger than 100, the maximum value of the orientation parameter of the first layer portion does not become the maximum value of the orientation parameter. That is, the maximum value of the orientation parameter is shifted from the center between the copper foil surface of the polyimide layer and the opposite surface to the opposite surface side. For this reason, after etching a metal foil, curl will appear with the one with the metal foil inside. Preferably, 1.5 ≦ T2 / T1 ≦ 50. By setting it as this range, the flexible substrate with a small curl after etching metal foil can be manufactured stably.

  Next, in step (b), the polyamic acid is heat-treated so that the imidization ratio is 15% or more and 95% or less. If the imidization ratio is less than 15%, the orientation of the polyimide becomes insufficient. As a result, curling occurs after the metal foil is etched. More preferably, the imidization rate is 40% or more. When it is 40% or more, more sufficient orientation can be obtained. On the other hand, when the imidization ratio is larger than 95%, when the polyamic acid varnish is applied in the step (c) and the entire layer is heat-treated in the step (d), the hue of the polyimide layer is not observed as a single layer. As a result, the adhesion after the high temperature and high humidity treatment is reduced. More preferably, it is 90% or less. If it is 90% or less, a flexible substrate having a single hue of the polyimide layer can be obtained stably.

In addition, the imidation ratio of the (b) process can be measured by FTIR-ATR. The absorption spectral intensity ratio between the CN stretching vibration peak of the imide ring near 1360 cm ⁻¹ and the aromatic ring near 1515 cm ⁻¹ is determined by measuring each polyimide. At this time, the imidization rate is calculated by setting the imidization rate of polyimide cured at 350 ° C. for 1 hour in a nitrogen atmosphere as 100%. In step (c), a polyamic acid varnish is applied, and in step (d), the entire region is heat-treated.

The polyimide layer of the flexible substrate thus manufactured has an average linear expansion coefficient of 5 × 10 ⁻⁶ or more and 25 × 10 ⁻⁶ (1 / ° C.) or less, and the cross section of the flexible substrate is transmitted through an optical microscope. When observed in the optical mode, the hue in the polyimide layer is observed as a single layer, and when the cross section of the flexible substrate is analyzed in the film thickness direction using Raman spectroscopy, the maximum value of the orientation parameter is It appears on the metal foil surface side rather than the center of the metal foil side surface of the layer and the surface on the opposite side.

The polyimide whose average linear expansion coefficient which forms the polyimide layer used by this invention is 5 * 10 < ^-6 > or more and 25 * 10 < ^-6 > (1 / degreeC) or less is not specifically limited if the said average linear expansion coefficient is satisfy | filled, The polyamic acid varnish can be produced by curing, and the polyamic acid varnish can be obtained by polymerizing a tetracarboxylic dianhydride component and a diamine component.

In order to make the average linear expansion coefficient 5 × 10 ⁻⁶ (1 / ° C.) or more and 25 × 10 ⁻⁶ (1 / ° C.) or less, as the acid dianhydride component, pyromellitic dianhydride, 3, 3 It is preferable that at least one of ', 4,4'-biphenyltetracarboxylic dianhydride is contained in an amount of 50 mol% or more, and more preferably 70 mol% or more. Examples of the diamine component include p-phenylenediamine, 4,4′-diaminobenzanilide, 2′-methoxy-4,4′-diaminobenzanilide, 2,2′-dimethyl-4,4′-diaminobiphenyl, It is preferable that at least one of 4,4′-diaminodiphenyl ethers is contained in an amount of 50 mol% or more, and more preferably 70 mol% or more.

Other tetracarboxylic dianhydride components that can be used include 2,3 ′, 3,4′-biphenyltetracarboxylic dianhydride, 2,2 ′, 3,3′-biphenyltetracarboxylic dianhydride 3,3 ′, 4,4′-benzophenone tetracarboxylic dianhydride, 2,3 ′, 3,4′-benzophenone tetracarboxylic dianhydride, 2,2 ′, 3,3′-benzophenone tetra Carboxylic dianhydride, 3,3 ′, 4,4′-diphenyl ether tetracarboxylic dianhydride, 2,3 ′, 3,4-diphenyl ether tetracarboxylic dianhydride, 2,2 ′, 3,3 ′ -Diphenyl ether tetracarboxylic dianhydride, 3,3 ', 4,4'-diphenylsulfone tetracarboxylic dianhydride, 2,3', 3,4-diphenylsulfone tetracarboxylic dianhydride, 2,2 ' , 3,3'- Examples thereof include diphenylsulfonetetracarboxylic dianhydride and 4,4 ′-(hexafluoroisopropylidene) diphthalic dianhydride. The tetracarboxylic dianhydride may be used alone or in combination of two or more. Examples of the diamine component that can be used include m-phenylenediamine, 2,5-diaminotoluene, 2,4- Diaminotoluene, 2-methoxy-1,4-phenylenediamine, 3,4'-diaminobenzanilide, 3,3'-diaminobenzanilide, 2'-methyl-4,4'-diaminobenzanilide, benzidine, 3, 3'-dimethyl-4,4'-diaminobiphenyl, 2,2'-dimethoxy-4,4'-diaminobiphenyl, 3,3'-dimethoxy-4,4'-diaminobiphenyl, 2,2'-ditrifluoro Methyl-4,4′-diaminobiphenyl, 3,3′-ditrifluoromethyl-4,4′-diaminobiphenyl, 3,3′-diaminodiphenyl ether 3,4'-diaminodiphenyl ether, 4,4'-diaminodiphenyl sulfone, 3,3'-diaminodiphenyl sulfone, 3,4'-diaminodiphenyl sulfone, 4,4'-diaminodiphenylmethane, 3,3'- Diaminodiphenylmethane, 3,4'-diaminodiphenylmethane, 4,4'-diaminobenzophenone, 3,3'-diaminobenzophenone, 3,4'-diaminobenzophenone, 4,4'-diaminodiphenyl sulfide, 2,2-bis ( 4-aminophenyl) propane, 2,2-bis (3-aminophenyl) propane, 4,4′-bis (4-aminophenoxy) biphenyl, 2,2-bis [4- (4-aminophenoxy) phenyl] Propane, 2,2-bis [4- (3-aminophenoxy) phenyl] propane, 2,2-bis 4- (4-aminophenoxy) phenyl] methane, 2,2-bis [4- (3-aminophenoxy) phenyl] methane, bis [4- (4-aminophenoxy) phenyl] ether, bis [4- (3 -Aminophenoxy) phenyl] ether, 1,4-bis (4-aminophenoxy) benzene, 1,3-bis (4-aminophenoxy) benzene, 1,4-bis (3-aminophenoxy), 1,3- Bis (3-aminophenoxy) benzene, bis [4- (4-aminophenoxy) phenyl] sulfone, bis [4- (3-aminophenoxy) phenyl] sulfone, 2,2-bis [(4-aminophenoxy) phenyl ] Hexafluoropropane, 2,2-bis [(3-aminophenoxy) phenyl] hexafluoropropane, 2,2-bis (4-amino) Phenyl) hexafluoropropane, and 2,2-bis (3-aminophenyl) hexafluoropropane and the like. The said diamine can be used individually or in mixture of 2 or more types.

  In order to improve the adhesiveness of polyimide, it is possible to copolymerize a diamine having a siloxane bond within a range that does not lower the heat resistance. Preferable specific examples include bis (3-aminopropyl) tetramethyldisiloxane.

  Solvents of the polyamic acid varnish include amide solvents such as N-methyl-2-pyrrolidone, N, N-dimethylacetamide, N, N-dimethylformamide, lactone polar solvents such as γ-butyrolactone, and ethers such as methyl cellosolve. An ester solvent such as a system solvent or ethyl lactate is used. In addition, hydrocarbon solvents such as toluene and xylene can also be used.

  In the present invention, other resins and fillers can be added to the polyimide layer. Examples of other resins include acrylic resins, butadiene resins, urethane resins, polyester resins, polyamide resins, polyamideimide resins, epoxy resins, and phenol resins. Examples of the filler include silica, alumina, titanium oxide, quartz powder, magnesium carbonate, potassium carbonate, barium sulfate, mica, and talc.

  The polymerization method of the polyamic acid varnish used in the present invention is not particularly limited. For example, it can be obtained by reacting a tetracarboxylic dianhydride and a diamine component at a predetermined molar ratio in a predetermined solvent at a temperature range of 0 to 80 ° C. for 0.1 to 72 hours. At this time, the total number of moles of the tetracarboxylic dianhydride component and the diamine component is preferably 92/100 to 100/92. By making the ratio substantially 100/100, the molecular weight of polyimide is maximized and a tough polyimide film can be formed. If necessary, by adjusting the tetracarboxylic dianhydride component or the diamine component in excess, it is possible to adjust the polymerization viscosity and improve the adhesion. It is also possible to seal the ends with monoamines such as aniline and phthalic anhydride, and dicarboxylic anhydrides.

  The polyamic acid varnish thus obtained is applied to a metal foil. As the metal foil, any of aluminum foil, stainless steel foil, and copper foil can be used. The metal foil is patterned and used as a conductor. In the flexible substrate, a copper foil is preferably used, and an electrolytic copper foil and a rolled copper foil are used depending on the purpose, either of which may be used in the present invention. The copper foil may be roughened on the bonding surface side in order to improve the adhesion with a resin or the like. On the other hand, the copper foil may not be roughened to cope with fine pitch and improve transparency. Either can be used in the present invention. The copper foil may be rust-proofed as necessary. The antirust treatment generally forms a thin film layer of nickel, zinc, chromium compound or the like on the copper foil surface. Moreover, in order to improve adhesiveness with a resin layer, the copper foil surface may be processed with the silane coupling agent.

  The thickness of the metal foil is preferably 1 μm or more and 50 μm or less. As the conductor wiring pattern is miniaturized, the metal foil is preferably thinner. However, when the metal foil becomes thin, it becomes difficult to handle it alone. A metal foil having a thickness of 5 μm or less may be handled as a metal foil with a carrier attached to a support (carrier) such as a resin or metal foil having a thickness of about 20 to 50 μm. In this case, after laminating the resin, Used after peeling. Alternatively, after laminating a resin on a metal foil having a thickness of 10 μm or more, the metal foil is thinned by etching the entire surface of the metal foil with a known metal etching solution, and may be adjusted to a preferable thickness.

  Examples of the method for applying the polyamic acid varnish include a bar coater, a roll coater, a die coater, a gravure coater, and a knife coater. In this case, the viscosity of the polyamic acid varnish is easily handled as 10 to 100,000 mPa · s.

  After the polyamic acid varnish is applied, heat treatment is performed so that the imidization ratio of the polyamic acid is 15% or more and 95% or less in the step (b) described above. In the present invention, the heat treatment conditions for setting the imidation rate in the step (b) to 15% or more and 95% or less are the maximum temperature of 150 ° C. or more and 240 ° C. or less. In order to prevent foaming due to water generated by bumping of the solvent in the varnish or imidization, it may be dried in advance at a temperature of 60 ° C to 150 ° C. The holding time at the maximum temperature of 150 ° C. or higher and 240 ° C. or lower is preferably 10 seconds or longer and 1 hour or shorter. If it is less than 10 seconds, the target imidation rate may not be reached, and stable production cannot be achieved. Heat treatment for more than 1 hour is not problematic in terms of performance, but costs high. The heat treatment is preferably performed in an inert gas atmosphere such as nitrogen.

The polyamic acid varnish applied in the step (c) needs to be a polyamic acid varnish that becomes a polyimide having a linear expansion coefficient of 5 × 10 ⁻⁶ or more and 25 × 10 ⁻⁶ (1 / ° C.) or less. The composition of the polyamic acid varnish applied in the step (a) and the polyamic acid varnish applied in the step (c) may be the same or different. Among them, it is most preferable to use a polyamic acid varnish that is the same polyimide.

  As the pretreatment for applying the polyamic acid varnish in the step (c), a known pretreatment may be performed. A dry process such as a corona discharge process or a plasma process or a wet process such as an alkali process is preferably used.

In the step (d), it is preferable that the imidization of the entire polyimide layer formed on the metal foil is substantially imidized to 100%. In order to achieve a substantially 100% imidization rate, it is preferable to heat the glass to a glass transition temperature or higher, but the average linear expansion coefficient is 5 × 10 ⁻⁶ or more and 25 × 10 ⁻⁶ (1 / ° C.). The following polyimides often do not show a clear glass transition temperature. Even in this case, when the heat treatment is performed at 250 ° C. or higher, an imidization ratio larger than 95% is obtained. Preferably, the heat treatment is performed at 300 ° C. or higher. The holding time at the maximum temperature is preferably carried out within 1 minute to 24 hours. The heat treatment is preferably performed in a nitrogen atmosphere.

  The flexible substrate of the present invention and the flexible substrate manufactured by the manufacturing method of the present invention are used as FPC substrates used in electronic devices, and among them, for multilayer flexible substrates that have a process of pressing at high temperature, and for IC bonding. It is preferably used for COF where heat of 300 ° C. or higher is applied.

  EXAMPLES The present invention will be described below with reference to examples, but the present invention is not limited to these examples. Test methods for average linear expansion coefficient, cross-section observation method, orientation parameter by Raman spectroscopy, imidization rate, adhesion strength, adhesion strength after high temperature and high humidity treatment, curl measurement, and bonding test are described below.

(1) Average linear expansion coefficient Polyamic acid varnish was applied to a glossy surface of a copper foil having a thickness of 18 μm with a bar coater so that the thickness after heat treatment was 10 μm, and dried at 80 ° C. for 10 minutes and 120 ° C. for 10 minutes. Then, in a nitrogen atmosphere, the temperature was raised to 140 ° C. for 30 minutes, from 140 ° C. to 350 ° C. in 1 hour, and heat treatment was performed at 350 ° C. for 1 hour.

Next, the copper foil was etched with a ferric chloride solution to obtain a polyimide single film. The obtained single membrane was cut into 30 mm × 15 mm. The sample length at each temperature when a 0.5 g load was applied using a thermomechanical analyzer SS-6100 (manufactured by Seiko Instruments Inc.) Determined by measurement. First, the temperature was raised to 300 ° C., annealed, lowered to 30 ° C. or lower, then raised from 30 ° C. to 250 ° C. at a rate of 5 ° C./min, and the average linear expansion coefficient from 30 ° C. to 250 ° C. Asked. The calculation formula is as follows.
Average linear expansion coefficient = (1 / L ₃₀ ) × [(L ₂₅₀ -L ₃₀ ) / (250-30)]
Here, L ₃₀ and L ₂₅₀ are sample lengths at 30 ° C. and 250 ° C., respectively.

(2) Method for observing cross section The obtained flexible substrate was embedded in an embedding resin and polished so that the cross section could be observed. This was observed with an optical microscope. When observed in the transmitted light mode, when the hue in the polyimide layer was single, it was set to “single”, and when the hue in the polyimide layer was two layers, it was set to “two layers”.

(3) Orientation parameters by Raman spectroscopy The obtained flexible substrate was embedded in an embedding resin and polished so that the cross section could be observed. This was analyzed by Raman spectroscopy in the film thickness direction under the following conditions.

Analysis method: Laser Raman spectroscopy Device: PDP320 (manufactured by Photon Design)
Conditions: Measurement mode: Microscopic Raman, objective lens: x100, beam diameter: 1 μm, cross slit: 400 μm, light source: Nd-YAG / 1064 nm, laser power: 1 W / 45 °, diffraction grating: Spectrograph 300 gr / mm, 900 gr / mm, slit; 100 μm, detector; InGaAs / Roper Scientific 512.

Under this condition, the measured Raman spectrum was normalized with the Raman band of the phenyl group C═C stretching near 1615 cm ⁻¹ . According to this deflection spectrum, the C—N—C symmetric / inverse symmetric Raman band near 725 cm ⁻¹ tended to increase in the vertical direction. On the other hand, the CN stretched Raman band near 1380 cm ⁻¹ tended to increase in the parallel direction. The anisotropy of these Raman bands reflects molecular orientation, and the greater the difference in band intensity, the greater the anisotropy, that is, the higher the orientation.

In the present invention, the orientation parameters were set as follows.
Orientation parameter = [A _1380cm-1 / A _725cm-1 (parallel)] / [A _1380cm-1 / A _725cm-1 (vertical)]
Here, A indicates the Raman band intensity at the wave number.

(4) Imidization rate
The polyamic acid varnish was applied with a bar coater, dried, and then heat-treated at a set temperature. The imidization rate was measured by FTIR-ATR.
Analysis method: FTIR-ATR
Apparatus: FTS-55A (manufactured by Bio-Rad)
Conditions: ATR attachment (Ge45 °), light source; special ceramics, detector; MCT, resolution; 4 cm ⁻¹ , integration count: 128 times.

The absorption spectrum intensity of the CN stretch of the imide ring near 1380 cm ⁻¹ and the aromatic ring near 1515 cm ⁻¹ was measured, and the ratio was determined for each polyimide. At this time, the imidization rate was calculated by setting the imidization rate of polyimide cured at 350 ° C. for 1 hour in a nitrogen atmosphere as 100%. The calculation formula is as follows.
_Imidation ratio = [A _{1380 cm −1} / A _{1515 cm −1} (set temperature)] / [A _{1380 cm −1} / A _{1515 cm −1} (350 ° C.)].

(5) Measurement of adhesion force in normal state The copper foil of the flexible substrate was etched with a ferric chloride solution to form a 2 mm wide pattern. The metal layer having a width of 2 mm was measured with “Tensilon” UTM-4-100 (manufactured by TOYO BOLDWIN) at a pulling rate of 50 mm / min and 90 ° peeling.

(6) Measurement of adhesion after high-temperature and high-humidity treatment (after PCT treatment) The copper foil of the flexible substrate was etched with a ferric chloride solution to form a 2 mm wide pattern. This sample was placed under conditions of PCT conditions (121 ° C., 100% RH, 2 atm) for 96 hours, and then the adhesion was measured in the same manner as in (5).

(7) Curl measurement After the flexible substrate with all layers heat-treated was cut into 100 mm x 100 mm, it was allowed to stand for 24 hours under conditions of 25 ° C and 40-60% RH, and then left on a flat metal plate. The height of the image warp was measured and the total value was taken as the curl of the flexible substrate. Moreover, the copper foil of this flexible substrate was etched on the entire surface with a ferric chloride solution, and similarly, left for 24 hours at 25 ° C. and 40 to 60% RH, and then left on a flat metal plate. The height of the warp of the four strokes was measured, and the total value was defined as the curl after copper etching. Moreover, when it curled greatly and became a cylindrical shape, it showed how many times it curled. When curling with the copper foil side as the inside, the measured value was “+”, and when curling with the copper foil side as the outside, the measured value was “−”.

(8) Gold / tin eutectic bonding resistance After applying a positive resist 300RH (manufactured by Tokyo Ohka Kogyo Co., Ltd.) to the copper layer surface of the flexible substrate so that the film thickness after drying becomes 4 μm, a bonding pattern is formed. The film was exposed through the mask and developed using a developer PMER “P-1S” (manufactured by Tokyo Ohka Kogyo Co., Ltd.). This was etched with a ferric chloride aqueous solution, and the resist film was peeled off with an alkaline aqueous solution to form a copper wiring pattern with 200 bonding portions. This was degreased and soft-etched, and then tin-plated with TINPOSIT “LT-34” (manufactured by Shipley Far East Co., Ltd.).

Using a flip chip bonder FC2000 (manufactured by Toray Engineering Co., Ltd.), an IC chip having 200 gold bumps was bonded under the following conditions.
Stage temperature: 80 ° C., load: 40 N, indentation time: 3 seconds, tool temperature: 380 ° C., bonding interface temperature: 300 ° C.
The shape of the bonded portion was observed with an optical microscope and SEM.

  The names of the abbreviations of acid dianhydride, diamine, and solvent shown in the following production examples are as follows.

PMDA: pyromellitic dianhydride BPDA: 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride BTDA: 3,3 ′, 4,4′-benzophenone tetracarboxylic dianhydride PDA: p- Phenylenediamine DAE: diaminodiphenyl ether DAPE: 2′-methoxy-4,4′-diaminobenzanilide SiDA: bis (3-aminopropyl) tetramethyldisiloxane NMP: N-methyl-2-pyrrolidone.

Production Example 1
SiDA 12.4 g (0.05 mol), PDA 73.5 g (0.68 mol), DAE 54.1 g (into a reaction kettle equipped with a thermometer, dry nitrogen inlet, hot water, cold water heating / cooling device, and stirring device) 0.27 mol) and 1200 g of NMP were charged and stirred at 30 ° C. for complete dissolution. Next, 291.3 g (0.99 mol) of BPDA and 525 g of NMP were charged at 30 ° C. Reaction was performed at 60 ° C. for 4 hours to obtain 20% polyamic acid varnish A. This varnish was diluted with NMP according to the purpose and used. The linear expansion coefficient after curing of this polyamic acid was 16 × 10 ⁻⁶ (1 / ° C.).

Production Example 2
PDA 81.1 g (0.75 mol), DAE 50.1 g (0.25 mol), and NMP 1200 g were charged in a reaction kettle equipped with a thermometer, dry nitrogen inlet, hot water, cold water heating / cooling device, and stirring device. Stir at 30 ° C. to dissolve completely. Next, PMDA 163.6 g (0.75 mol), BPDA 70.6 g (0.24 mol), and NMP 266 g were charged at 30 ° C. Reaction was performed at 60 ° C. for 4 hours to obtain 20% polyamic acid varnish B. This varnish was diluted with NMP according to the purpose and used. The linear expansion coefficient after curing of this polyamic acid was 16 × 10 ⁻⁶ (1 / ° C.).

Production Example 3
A reaction kettle equipped with a thermometer, dry nitrogen inlet, hot water, cold water heating and cooling device, and a stirring device was charged with DAPE 154.4 g (0.6 mol), DAE 80.1 g (0.4 mol), and NMP 1200 g. Stir at 30 ° C. to dissolve completely. Next, PMDA 215.9 g (0.99 mol) and NMP 602 g were charged at 30 ° C. Reaction was performed at 60 ° C. for 4 hours to obtain 20% polyamic acid varnish C. This varnish was diluted with NMP according to the purpose and used. The linear expansion coefficient after curing of this polyamic acid was 13 × 10 ⁻⁶ (1 / ° C.).

Production Example 4
200.2 g (1 mol) of DAE and 1200 g of NMP were charged into a reaction kettle equipped with a thermometer, a dry nitrogen inlet, hot water, a heating / cooling device using cold water, and a stirring device, and stirred at 30 ° C. to completely dissolve. Next, PMDA 65.4 (0.3 mol), BTDA 222.3 g (0.69 mol), and NMP 752 g were charged at 30 ° C. Reaction was performed at 60 ° C. for 4 hours to obtain 20% polyamic acid varnish D. This varnish was diluted with NMP according to the purpose and used. The linear expansion coefficient after curing of this polyamic acid was 45 × 10 ⁻⁶ (1 / ° C.).

Example 1
The polyamic acid varnish A was applied by a bar coater so that the film thickness after heat treatment was 3 μm on an electrolytic copper foil SQ-VLP (made by Mitsui Mining & Smelting Co., Ltd.) having a thickness of 18 μm whose surface was roughened. This was dried at 80 ° C. for 10 minutes and 120 ° C. for 10 minutes, then heated from 80 ° C. to 200 ° C. in 30 minutes in a nitrogen atmosphere, and heat-treated at 200 ° C. for 30 minutes. The imidation ratio measured by IR at this time was 62%.

  On top of this, the polyamic acid varnish A was applied with an applicator so that the film thickness after heat treatment was 22 μm. After drying this at 80 ° C. for 10 minutes and at 120 ° C. for 10 minutes, the temperature was raised from 140 ° C. to 350 ° C. over 1 hour in a nitrogen atmosphere, and heated at 350 ° C. for 1 hour. The imidation ratio at this time was 100%.

  At this time, the normal adhesion strength was 14 N / cm, and the adhesion strength after PCT treatment was 13 N / cm. As a result of observing the cross section with an optical microscope, the hue was single. A photograph is shown in FIG. The maximum value of the orientation parameter by Raman spectroscopy was 3 μm from the copper foil surface, and the value at that time was 4.07. The relationship between the orientation parameter and the distance from the copper foil surface is shown in FIG. The curl of this flexible substrate was 1 mm when the copper foil was attached, and 1 mm after the copper foil was etched, and the curl was small. The result of the bonding test was good, and even at the temperature at which the gold / tin eutectic reaction occurred, neither copper-polyimide separation nor polyimide sinking was observed.

Comparative Example 1
The polyamic acid varnish A was applied by an applicator so that the film thickness after heat treatment was 25 μm on an electrolytic copper foil SQ-VLP (made by Mitsui Mining & Smelting Co., Ltd.) having a thickness of 18 μm whose surface was roughened. This was dried at 80 ° C. for 10 minutes, 120 ° C. for 10 minutes, then heated to 140 ° C. for 30 minutes, from 140 ° C. to 350 ° C. in 1 hour, and heat-treated at 350 ° C. for 1 hour. .

At this time, the normal adhesion strength was 14 N / cm, and the adhesion strength after PCT treatment was 13 N / cm. As a result of observing the cross section with an optical microscope, the hue was single. The maximum value of the orientation parameter by Raman spectroscopy was 24 μm from the copper foil surface, and the value at that time was 3.53. The relationship between the orientation parameter and the distance from the copper foil surface is shown in FIG. The curl of the flexible substrate was 1 mm when the copper foil was attached, but after etching the copper foil, the surface having the copper foil was made inward and curled 1.5 times. Comparative Example 2
The polyamic acid varnish A was applied to an electrolytic copper foil SQ-VLP (manufactured by Mitsui Mining & Smelting Co., Ltd.) having a thickness of 18 μm with a roughened adhesive surface with a bar coater so that the film thickness after heat treatment was 3 μm. This was dried at 80 ° C. for 10 minutes and 120 ° C. for 10 minutes, then heated from 80 ° C. to 250 ° C. in 30 minutes in a nitrogen atmosphere, and heat-treated at 250 ° C. for 30 minutes. The imidation ratio measured by IR at this time was 98%.

  On top of this, the polyamic acid varnish A was applied with an applicator so that the film thickness after heat treatment was 22 μm. After drying this at 80 ° C. for 10 minutes and at 120 ° C. for 10 minutes, the temperature was raised from 140 ° C. to 350 ° C. over 1 hour in a nitrogen atmosphere, and heated at 350 ° C. for 1 hour. The imidation ratio at this time was 100%.

  The normal adhesion strength at this time was 14 N / cm, and the adhesion strength after the PCT treatment was 1 N / cm, and peeling occurred at the polyimide / polyimide interface. As a result of observing the cross section with an optical microscope, the hue was not single, but was observed in two layers. A photograph is shown in FIG. The maximum value of the orientation parameter by Raman spectroscopy was 3 μm from the copper foil, and the value at that time was 4.22. The curl of this flexible substrate was 1 mm when the copper foil was attached, and 1 mm after the copper foil was etched, and the curl was small.

Examples 2-18, Comparative Examples 3-5
The same experiment as in Example 1 was performed except that the heat treatment temperature of the first layer polyimide, the film thickness of the first layer polyimide, the polyamic acid varnish, and the copper foil were as shown in Table 1. The copper foil used was an electrolytic copper foil F0-WS (manufactured by Furukawa Circuit Foil Co., Ltd.) having a thickness of 12 μm, the surface of which is not roughened, and NS-VLP (manufactured by Mitsui Metal Mining Co., Ltd.), bonding, 12-μm thick electrolytic copper foil F1-WS (made by Furukawa Circuit Foil Co., Ltd.) whose surface side is roughened, and 18 μm thick rolled copper foil BHY (manufactured by Nikko Materials Co., Ltd.) whose surface is roughened on the adhesive side It is.

Comparative Example 6
The polyamic acid varnish D was applied to an electrolytic copper foil SQ-VLP (manufactured by Mitsui Mining & Smelting Co., Ltd.) having a thickness of 18 μm with the adhesive side roughened by a bar coater so that the film thickness after heat treatment was 3 μm. This was carried out at 80 ° C. for 10 minutes and at 120 ° C. for 10 minutes. On top of this, the polyamic acid varnish C was applied with an applicator so that the film thickness after heat treatment was 19 μm. This was carried out at 80 ° C. for 10 minutes and at 120 ° C. for 10 minutes. On top of this, the polyamic acid varnish D was applied with a bar coater so that the film thickness after heat treatment was 3 μm. This was carried out at 80 ° C. for 10 minutes and at 120 ° C. for 10 minutes. This was heated in a nitrogen atmosphere at 140 ° C. for 30 minutes, from 140 ° C. to 350 ° C. in 1 hour, and heat-treated at 350 ° C. for 1 hour. As a result of the bonding test at this time, the polyimide layer was submerged at the temperature at which the gold / tin eutectic reaction occurred, and peeling of the tip of the pattern was observed.

Explanation of symbols

1 Copper foil 2 Polyimide layer 2a Polyimide layer (first layer)
2b Polyimide layer (second layer)

Photo showing the hue of the polyimide layer of Example 1 using an optical microscope Photo showing the hue of the polyimide layer of Comparative Example 2 using an optical microscope The figure which showed the orientation parameter of Example 1 and Comparative Example 2

Claims (2)

A flexible substrate having a polyimide layer formed on a metal foil, wherein the polyimide layer has an average linear expansion coefficient of 5 × 10 ⁻⁶ or more and 25 × 10 ⁻⁶ (1 / ° C.) or less, and a cross section of the flexible substrate Is confirmed in the transmission light mode of the optical microscope, the hue in the polyimide layer is observed as a single layer, and when the film thickness direction analysis is performed using Raman spectroscopy, the maximum value of the orientation parameter is the metal foil of the polyimide layer. A flexible substrate characterized by being on the metal foil surface side from the center of the side surface and the opposite surface. A method for producing a flexible substrate having a polyimide layer formed on a metal foil,
(A) The process of apply | coating the polyamic acid varnish used as the polyimide whose average linear expansion coefficient is 5 * 10 < ^-6 > or more and 25 * 10 < ^-6 > (1 / degrees C) or less to film thickness T1;
(B) a step of heat-treating the polyamic acid applied in step (a) so that the imidization ratio is 15% or more and 95% or less;
(C) On the layer formed in the step (b), a polyamic acid varnish that becomes a polyimide having an average linear expansion coefficient of 5 × 10 ⁻⁶ or more and 25 × 10 ⁻⁶ (1 / ° C.) or less is obtained. Step of applying at T2 (however, 1 ≦ T2 / T1 ≦ 100 is satisfied),
(D) a step of imidizing all layers by heat treatment;
The manufacturing method of the flexible substrate which has this.