JP3502502B2 - Circuit board and circuit board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To meet the major requirements for putting a product to practical use, which are low cost, high density and high reliability, allow almost no warpage of a substrate, provide excellent following performance of a polyimicle resin layer at a bent part, even when bending process which applies strong stress to bend nearly 90 degrees is performed, and prevent insulation failure. SOLUTION: On one side or both sides of a long-size stainless foil 1, a polyimide resin layer 2, which has a specific structure unit in the molecule, is formed on the whole or partial area so as to manufacture a board for making a circuit. As a board for making a circuit, the board can be compounded by forming a conductor layer 3 on the polyimide resin layer, and a circuit board is obtained by making a fine pattern by etching the conductor layer 3. The circuit board is preferably used for the suspension for a hard disc, and when photosensitive polyimide resin is used for the polyimide resin, the board is permitted to excel in fine processability.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a circuit forming board and a circuit board, and more particularly to various mounting circuit forming boards and circuit boards, and in particular, a suspension for a hard disk, which has been urgently required to have a higher capacity and a smaller size in recent years. The present invention relates to a circuit forming substrate and a circuit substrate as a component for directly forming an electric signal line on the substrate.

[0002]

2. Description of the Related Art In recent years, thin-film multilayer substrates for high-density mounting of semiconductors and high-speed signal processing have attracted attention, and generally, a substrate in which a copper foil as a conductive layer and a polyimide resin layer as a supporting layer are laminated. Is used. A device is mounted on such a substrate, but it is desired to use a substrate material having a high heat dissipation effect so that heat is not stored inside a system incorporating the device in order to generate heat due to the characteristics of the device.

Various types of circuit boards with a heat spreader have been proposed as such a board. Usually, a single-wafer board is used to manufacture these boards, and a liquid resin is formed on a metal board having a high heat dissipation effect. A so-called sequential lamination method of coating and drying and then forming a conductor layer, a press lamination method of pressing a copper clad laminate and a metal plate having a large heat dissipation effect, and the like have been proposed.

However, the former method has a problem that the number of steps for processing is large and thus the cost is high, and the latter method has a problem in that it is difficult to form a fine line because the alignment accuracy is rough. Since such problems are essential problems in practical application, the reality is that they have not yet achieved high reliability, high density, and low price.

On the other hand, from the viewpoint of increasing the storage capacity and speed of a hard disk, a conventional MIG is used as a magnetic head.
In place of the (metal-in-gap) or magnetic induction type thin film, a so-called MR-thin film composite type head, in which a magnetoresistive MR element and a thin film are integrated, is drawing attention. Whereas the conventional head uses one head for both reading and writing of magnetic signals, the MR head has twice the number of terminals (additional ground terminal is added if necessary) in order to divide the work for reading and writing within one head. Therefore, it is necessary to thin the wire that connects the head and the disk body. However, if the wire is thinned, the wire is likely to corrode, impedance matching is difficult to obtain, and head mounting becomes difficult.

As a method for solving such a new problem, a method for directly forming a circuit on a suspension for mounting a head has been proposed (Japanese Patent Laid-Open No. 48-1).
6620 gazette).

However, if the materials constituting these substrates have different thermal expansion coefficients (linear expansion coefficients), the substrates will warp due to heat generation. Further, if the water absorption of the polyimide resin layer used for the circuit-forming substrate as described above is high, for example, when such a substrate is incorporated as a suspension in the hard disk body, the dimensions accompanying absorption and desorption of water to the polyimide resin layer There is a possibility that the change becomes large and the suspension itself is warped, the alignment accuracy is lowered, and the gap between the disk and the main body is changed, resulting in poor device performance.

Further, the circuit forming substrate and the circuit substrate according to the present invention include a polyimide resin layer on a long stainless steel foil,
Although it is manufactured by a single-wafer process of sequentially forming conductor layers, the number of manufacturing processes increases and the process becomes complicated, resulting in high cost.

Further, even if a three-layer substrate of a copper-clad laminate (for example, a two-layer substrate of a polyimide resin layer and a copper foil) and a long stainless steel foil is available, a plasma is used for patterning the polyimide resin layer. It is necessary to perform dry etching such as etching or laser ablation. As a result, the stainless steel foil and other wiring circuits may be damaged, and the cost may be increased due to poor throughput. On the other hand, processing of the polyimide resin layer by wet etching is also conceivable, but harmful chemicals such as hydrazine have to be used as a processing liquid, which is not good in environmental hygiene.

Further, the circuit-forming board is not always used in a flat plate state, and in some cases, after forming a circuit to form a circuit board, the circuit-forming board may be partially bent to approximately 90 degrees. When such a processing is applied, stress is applied to the bent portion, so that a crack may occur in the polyimide resin layer forming the substrate and an insulation failure may occur.

[0011]

SUMMARY OF THE INVENTION Therefore, the object of the present invention is to solve the above-mentioned problems of the prior art and to sufficiently realize practically important low cost, high density and high reliability in forming various circuit boards. Satisfactory, almost no warpage of the substrate itself occurs, and even if a bending process with a strong stress of about 90 degrees is applied, the polyimide resin layer follows the bent part well and causes insulation failure. An object of the present invention is to provide a circuit-forming substrate excellent in processability and a circuit substrate using the same.

[0012]

That is, the circuit-forming substrate of the present invention is characterized in that a polyimide resin layer is formed wholly or partially on one surface or both surfaces of a long stainless steel foil. is there.

Particularly, the difference (n) between the average linear expansion coefficient (α1) of the polyimide resin layer and the average linear expansion coefficient (α2) of the long stainless steel foil in the temperature range of 5 to 200 ° C. is −5.
From the viewpoint of preventing warpage, it is preferable to adjust the concentration between 5 ppm and 5 ppm.

The circuit-forming substrate of the present invention has a polyimide resin layer formed on the entire surface or a partially formed polyimide resin layer and exposed stainless steel foil, with a chromium layer or a titanium layer interposed therebetween, or A conductor layer is formed by laminating copper layers without any interposition.

Particularly, in the circuit-forming substrate of the present invention, it is preferable to form the polyimide resin layer from a photosensitive polyimide resin containing a photosensitizer in order to pattern it into a desired shape. It is preferable to use these circuit-forming substrates as a suspension for a hard disk in order to fully exhibit the characteristics of the product of the present invention.

Also, the difference (n) between the average linear expansion coefficient (α1) of the polyimide resin layer and the average linear expansion coefficient (α2) of the long stainless steel foil in the temperature range of 5 to 200 ° C., and between α1 and the conductor layer. It is a preferred embodiment from the viewpoint of preventing warpage that the difference (m) between the average linear expansion coefficients (α3) is adjusted to be between −5 ppm and 5 ppm.

Further, the present invention is a circuit board formed by using the above-mentioned circuit-forming board, wherein the conductor layer is finely patterned in the circuit-forming board.

By producing the circuit-forming board and the circuit board as described above, it is possible to inexpensively produce a fine pattern having excellent dimensional stability, and to select the substrate material without selecting the type of constituent material for each layer. It is possible to obtain an excellent circuit board that does not cause warpage or cracks in the polyimide resin layer.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION The circuit-forming substrate and the polyimide resin used for the circuit substrate of the present invention are so-called wholly aromatic polyimides having a structural unit represented by the following [Chemical Formula 7] in the molecule. is there.

[0020]

[Chemical 7]

When the polyimide resin is formed into a layer on a long stainless foil, its water absorption is 0.7% by weight.
In order to obtain a low water absorption rate of preferably 0.5% by weight or less, it is preferable to use a so-called wholly aromatic polyimide having a structural unit represented by the following [Chemical Formula 8] in the molecule. .

[0022]

[Chemical 8]

That is, when the polyimide resin layer having a water absorption rate of 0.7% by weight or less is formed on the long stainless steel foil, it serves as an insulating layer between the upper conductive layer and the electric signal line. It is possible to sufficiently design a circuit, and it is possible to obtain a substrate whose warp is less likely to vary with ambient temperature even with a flexible stainless steel foil.
On the other hand, a polyimide resin conventionally used for a circuit-forming substrate or a circuit board, particularly a polyimide resin conventionally used as a suspension for a hard disk, has a water absorption rate of more than 0.7% by weight, and usually 1. 0% by weight
Because of the above, the effects of the present invention cannot be exhibited. In the present invention, the water absorption rate is 85 ° C. × 8.
5% R. H. It is a value when measured by the Karl Fischer method after being left for 100 hours under the high temperature humidification condition.

Among the polyimide resins having a low water absorption having the structural unit represented by the above [Chemical formula 8] in the molecule, a particularly preferable structure is that R ₁ is 5,5 ′-[2,2,2-tri Fluoro-1- (trifluoromethyl) ethylidene] bis-1,3-isobenzofurandione and a polyimide resin in which R ₂ is 4,4′-dimethyl-3,3′-diaminodiphenylhexafluoropropane.

When the polyimide resin is formed into a layer on a long stainless foil, its elongation is 20% or more,
To obtain a high elongation of 25% or more, it is preferable to use a so-called wholly aromatic polyimide having a structural unit represented by the following [Chemical Formula 9] in the molecule.

[0026]

[Chemical 9]

That is, when the polyimide resin layer having an elongation of 20% or more is formed on a long stainless steel foil, it serves as an insulating layer between the upper conductive layer and the polyimide resin layer, so that the electric signal line can be freely designed. It is possible to do so sufficiently, and it is possible to freely bend the terminal portion of the signal line and connect it to another circuit. On the other hand, in the polyimide resin conventionally used for a circuit forming substrate or a circuit board, particularly a polyimide resin conventionally used as a suspension for a hard disk, a photopolymerizable group is used to form a fine pattern in the polyimide resin layer. Although the photosensitive polyimide resin introduced is used, the elongation rate is less than 20%,
Usually, since it is 10% or less, cracks are generated during bending, and the effects of the present invention cannot be exhibited. In the present invention, the term "elongation rate" means a tensilon tensile tester (manufactured by Toyo Baldwin Co., Ltd.) at a temperature of 24 to 26 ° C.
Is a value measured under the conditions of a test piece width of 2 mm, a chuck distance of 5 mm, and a pulling speed of 5 mm / min, and is a value obtained by dividing the elongation until break (break elongation) by the initial length.

Among the high-elongation polyimide resins having the structural unit represented by the above [Chemical Formula 9] in the molecule, a particularly preferred structure is where R ₁ is a biphenyl group and R ₂ is 1,4-bis. (Phenoxy) A polyimide resin having a phenylene group.

The above-mentioned polyimide resin used in the present invention has the structural unit shown in [Chemical formula 7], [Chemical formula 8] or [Chemical formula 9] in the molecule and has a relatively small coefficient of linear expansion or water absorption. Or other structural unit having a relatively high elongation, but within a range that does not significantly change the physical properties of the linear expansion coefficient, the water absorption rate or the elongation rate, specifically, a group other than R ₁ and R ₂ described above. It goes without saying that a polyimide resin having a can be copolymerized or mixed.

In the present invention, the polyimide resin layer is
It is formed on one side or both sides of a long stainless steel foil.
Normally, N-methyl-2 is used in the synthesis of polyimide resins.
-Pyrrolidone, N, N-dimethylacetamide, N, N
-Dimethylformamide, 1,3-dimethyl-2-imidazolidinone, dimethyl sulfoxide, dimethyl sulfide, dimethyl sulfone, pyridine, tetramethylurea, diglyme, triglyme, tetrahydrofuran,
An organic solvent such as dioxane, cyclohexanone or hexamethylphosphoramide is used to obtain a polyimide precursor solution. Next, this is applied and dried on a long stainless steel foil,
By imidizing, a polyimide resin layer having a thickness of 3 to 25 μm, preferably 5 to 20 μm can be formed to obtain the circuit-forming substrate of the present invention (see FIG. 1A). When the thickness of the polyimide resin layer is less than 3 μm, the withstand voltage is low and the insulation reliability of the insulating film is lowered, or the capacitance value is increased. When the thickness exceeds 25 μm, the residual stress becomes large and the warp becomes large even when the water absorption is 0.7% by weight or less or the elongation is 20% or more, and the desired effect is exhibited. You may not get it.

Ferrite-based stainless steel foil,
A martensite-based material, an austenitic-based material, or the like can be used, but an austenitic-based material that is excellent in corrosion resistance, flexibility, and weldability is preferably used. The long stainless steel foil used in the present invention has a thickness of 10 to 75 μm.
m, preferably 10 to 40 μm in thickness, more preferably about 20 to 30 μm in thickness and 100 to 300 m in width.
m, preferably about 110 to 250 mm in width and 10 m in length
The above foil-like thing is shown. If the thickness is less than 10 μm, it is susceptible to mechanical damage.
When it exceeds 0 μm, when it is used as a spring material for a suspension for a hard disk, a problem may occur in the floating characteristics and sufficient characteristics may not be obtained, which is not preferable.

The polyimide resin layer in the circuit-forming substrate of the present invention thus obtained is subjected to patterning as required (see FIG. 2 (a)). To perform pattern processing, a non-photosensitive polyimide resin and photoresist are used together, wet etching with hydrazine or the like, or a method of forming a pattern by performing dry etching such as plasma etching or laser etching, or a positive type Alternatively, a method of directly patterning with a negative photosensitive polyimide resin may be used.
Among these methods, it is preferable to use a photosensitive polyimide resin from the viewpoint of work environment and low throughput for processing long objects.

Then, a conductor layer is formed by laminating a copper layer on the polyimide resin layer with or without a chromium layer or titanium layer interposed therebetween (FIGS. 1B and 2B).
reference). That is, the conductor layer is metallized by forming one of a chromium / copper layer, a titanium / copper layer, and a copper layer on the polyimide resin layer. The conductor layer thus formed has a thickness of 2 to 20 μm, preferably 5 to 15 μm from the viewpoint of impedance matching. As a method of forming the conductor layer, a chromium / copper layer or a titanium / copper layer is formed on the polyimide resin layer by a continuous sputtering method.
A copper layer and a copper layer are formed so as to have a thickness of several hundred to several thousand Å, and copper is subsequently electrolytically plated so that the thickness is within the above range (FIG. 1 (c) and FIG. 2 (c). )
reference). Other than the sputtering method, for example, the conductor layer can be formed only by the EB vapor deposition method without performing the electrolytic plating treatment. From the viewpoint of adhesion reliability, a chromium layer or a nickel layer may be provided on the conductor layer, if necessary.

When the polyimide resin layer is partially formed on the stainless steel foil as shown in FIG. 3A, the conductor layer is formed on the exposed long stainless steel foil and the polyimide resin layer. It is formed as shown in FIG.

An example of the circuit-forming substrate and the method of manufacturing the circuit substrate of the present invention will be specifically described below.

First, a polyimide precursor used for forming a polyimide resin layer is prepared by a known method,
A solution of a polyamic acid that is a precursor of a polyimide resin containing the structural unit described in any of [Chemical Formula 7] to [Chemical Formula 9] is obtained.

Next, this polyimide precursor (polyamic acid) solution is applied and dried on a long stainless steel foil using a roll coater, comma coater, knife coater, doctor blade or the like. In this case, the drying temperature is 60 to 120.
At a temperature of about 0 ° C., only the organic solvent that is a solvent is removed to form a polyimide precursor layer.

When the formed polyimide precursor layer is patterned into a desired shape, diethylaminoethyl methacrylate, Michler's ketone, or the like is added to the solution before applying the polyimide precursor solution to form a polyimide precursor solution. It imparts photosensitivity. When diethylaminoethyl methacrylate is added, it is blended so as to be contained in the range of 5 to 20 parts by weight, preferably 10 to 15 parts by weight, based on 100 parts by weight of the solid content of the polyimide precursor,
When Michler's ketone is added, it should be blended so as to be contained in the range of 2 to 10 parts by weight, preferably 2.5 to 5 parts by weight, based on 100 parts by weight of the solid content of the polyimide precursor. It is preferable from the viewpoint of sex. If the blending amount exceeds the upper limit, the deposition of the photosensitizer and the reduction of the film thickness during imidization may be large.

The polyimide precursor layer thus formed is irradiated with light through a photomask having a desired pattern. In the present invention, since a long product is used, a continuous long exposure machine is used. Next, continuous development processing is performed using a developing solution containing N-methyl-2-pyrrolidone as a main component, which is usually used as a developing solution. In consideration of the working environment such as environmental hygiene and explosion proof, it is preferable to use an aqueous solution as the developing solution instead of the organic solvent.

As a photosensitizer capable of using such an aqueous solution as a developer, it is preferable to use a 1,4-dihydropyridine derivative described in JP-A- 6-75376 as a photosensitizer, and if necessary. Known sensitizers may be added. Specific examples of such sensitizers that can be suitably used include, for example, 2,
6-dimethyl-3,5-dicyano-4- (2'-nitrophenyl) -1,4-dihydropyridine, 2,6-dimethyl-3,5-diacetyl-4- (2'-nitrophenyl) -1, 4-dihydropyridine, 2,6-dimethyl-
3,5-Diacetyl-4- (2 ', 4'-dinitrophenyl) -1,4-dihydropyridine, 4- (2'-nitrophenyl) -2,6-dimethyl-3,5-dicarbomethoxy-1 , 4-dihydropyridine and the like. In such a 1,4-dihydropyridine-based photosensitizer, the molecular structure exposed to actinic rays such as ultraviolet rays changes to a pyridine skeleton and becomes basic. Then, after the exposure, a heat treatment at about 150 to 190 ° C., preferably 160 to 180 ° C. further advances a chemical reaction to cause some interaction with the polyimide precursor to lower the solubility in an alkaline aqueous solution, A negative pattern having a good contrast can be obtained by the development processing. As the alkaline aqueous solution as a developing solution, an aqueous solution of an inorganic alkaline such as sodium hydroxide or potassium hydroxide, or propylamine, butylamine, monoethanolamine,
Aqueous solutions of organic alkalis such as tetramethylammonium hydroxide and choline can be used alone or in admixture of two or more. From the viewpoint of high purity and versatility, it is preferable to use an aqueous solution containing tetramethylammonium hydroxide as a main component as the developing solution. Further, this alkaline aqueous solution (developing solution) may contain alcohols and surfactants, if necessary.

When such a photosensitizer is used, the compounding amount is 5 to 70 parts by weight, preferably 15 to 55 parts by weight, relative to 100 parts by weight of the solid content of the polyimide precursor in the formed polyimide precursor layer. It is blended so as to be within the range of parts.
When the compounding amount is small, the dissolution inhibiting ability of the exposed area becomes poor, and the solubility contrast is liable to be unclear.
If the blending amount is too large, the photosensitizer may be precipitated during storage in a solution state or the film thickness may be greatly reduced during the heat treatment after pattern formation.

Then, the substrate having the polyimide precursor layer formed on the long stainless steel foil as described above is heated to about 300.degree.
As described above, the polyimide precursor is heated to preferably 350 ° C. or higher to dehydrate and ring-close the polyimide precursor to imidize it to form a polyimide resin layer. A device such as a hot air circulation type heating furnace or a far infrared heating furnace can be used for heating at this time, and in order to prevent the oxidation deterioration of the resin layer and the surface oxidation of the stainless steel foil, a gas such as argon or nitrogen gas is used. Heat treatment is performed in an active gas atmosphere or in a vacuum. Usually, the heat treatment is performed so that the oxygen concentration is 1% by volume or less, preferably 0.1% by volume or less.

Although the polyimide resin layer can be formed on one surface of the stainless steel foil as described above, when the polyimide resin layer is formed on both surfaces of the stainless steel foil, the same operation is performed on the other surface side after the above operation. Perform the operation. In addition,
When the polyimide resin layer is formed on both sides and the polyimide resin layer is patterned, it is possible to prevent the warp and twist of the substrate by making the polyimide resin patterns formed on both sides face each other via the stainless steel foil. It is preferable from the point.

The circuit-forming substrate of the present invention is obtained as described above, and has an average linear expansion coefficient (α1) of the polyimide resin layer at 5 to 200 ° C. and an average linear expansion coefficient (α2) of the long stainless steel foil. (N) is about 10 to 60 ppm, but in the case of the product of the present invention,
By adjusting so as to be in the range of 5 ppm to 5 ppm, it is possible to prevent the deviation of the circuit pattern and the warp of the base material itself due to thermal contraction. 1ppm means 1
It means ^{x10 -6} , that is, 1x10 ^-4 %, and the average linear expansion coefficient in the present invention can be measured by a thermal mechanical analysis method (TMA method).

The circuit-forming board of the present invention can be obtained as described above. A circuit-forming board is prepared by further forming a conductive layer on the formed polyimide resin layer.
The method of forming the conductive layer is as described above.

The circuit-forming substrate having the conductive layer thus obtained has an average linear expansion coefficient (α1) of the polyimide resin layer at 5 to 200 ° C. and an average linear expansion coefficient (α2) of the long stainless steel foil. ), And the difference (m) between α1 and the average linear expansion coefficient (α3) of the conductor layer are both −
It is preferable to adjust it to be between 5 ppm and 5 ppm. When the difference (n) and the difference (m) are out of the above ranges, it is difficult to prevent the warp of the circuit board, which is not preferable.

The circuit board of the present invention can be obtained by etching the circuit-forming board having the conductive layer thus obtained into a desired fine line pattern. In particular, by processing a long stainless steel foil into a suspension for a hard disk, a wireless circuit board for a magnetic head can be obtained.

[0048]

As described above, the circuit-forming substrate of the present invention has a polyimide resin layer formed entirely or partially on one or both sides of a long stainless steel foil, and further has a specific conductor on the polyimide resin layer. Forming layers.

In particular, by using a polyimide resin having a specific structural unit, it is possible to approximate the linear expansion coefficient between the stainless steel foil and the polyimide resin layer or to reduce the water absorption, and suppress the warpage phenomenon as much as possible. Is possible. Furthermore, even if various bending processes are performed, the polyimide resin layer as an insulating layer is free from cracks and the like, and the followability is excellent.

Therefore, even when the conductor layer is processed into a fine line pattern or the like to be used for suspension of a hard disk and the like, the dimensional accuracy can be kept high, and the circuit forming substrate having high density and high reliability for practical use can be obtained. This has the effect of providing a circuit board.

[0051]

EXAMPLES Examples of the present invention will be shown below and will be described more specifically. In the following text, "parts" means "parts by weight".

Example 1 Pyromellitic dianhydride and approximately equimolar amounts of 4,4'-diaminodiphenyl ether were polymerized in N-methyl-2-pyrrolidone to prepare a polyimide precursor solution, which was prepared for a long time. Using a comma coater, the cast stainless steel foil (SUS304, 25 μm thick) was uniformly cast on one side and dried at about 80 ° C.

Next, this was placed in a continuous heating furnace having an oxygen concentration of 0.1% by volume or less by nitrogen gas substitution, and heated so that the maximum temperature reached was 400 ° C. to imidize the polyimide precursor layer. A circuit-forming substrate having a polyimide resin layer on one surface of a long stainless foil was produced.

Then, a polyimide resin layer is formed on the other surface side of the obtained circuit forming substrate in the same manner as described above, and the circuit forming substrate of the present invention having a polyimide resin layer on both surfaces of a long stainless foil. Was produced.

When the cross section of the obtained circuit-forming substrate was observed with a scanning electron microscope, the thickness of the formed polyimide resin layer was about 5 μm on both sides. Further, this substrate showed no warp phenomenon even in an atmosphere of 60 ° C., which was equivalent to that at room temperature.

Example 2 Diethylaminoethyl methacrylate was added to the polyimide precursor solution prepared in Example 1 to obtain a precursor solid content of 100.
After adding 15 parts to each part and 3 parts of Michler's ketone to impart photosensitivity, the solution was uniformly cast onto a stainless steel foil (SUS304, 25 μm thick) by the same method as in Example 1 and dried.

Next, light irradiation (light having a wavelength of 400 nm or more is performed through a photomask having a desired pattern, 1000
mJ / cm ² ) and then development treatment using N-methyl-2-pyrrolidone to form a polyimide precursor layer having a desired pattern.

Then, this was imidized in the same manner as in Example 1 to prepare a circuit-forming substrate having a patterned polyimide resin layer on one surface of a long stainless steel foil.

On the other surface side of the circuit-forming substrate thus obtained, a patterned polyimide resin layer was formed in the same manner as above, and the patterned polyimide resin layer was formed on both surfaces of the long stainless steel foil. A circuit-forming substrate of the present invention having a layer was produced. In addition, in order to form the polyimide resin patterns formed on both sides via the stainless steel foil at the opposite positions, a hole for alignment was previously formed in a part of the stainless steel foil, and the alignment was accurately performed.

When the cross section of the obtained circuit-forming substrate was observed with a scanning electron microscope, the thickness of the formed polyimide resin layer was about 5 μm on both sides, and the positional deviation of the patterns on both sides was 10 cm. It was ± 10 μm. Further, this substrate showed no warp phenomenon even in an atmosphere of 60 ° C., which was equivalent to that at room temperature.

Example 3 Instead of the pyromellitic dianhydride in Example 1,
A circuit-forming substrate of the present invention having a polyimide resin layer on both surfaces of a long stainless steel foil was prepared in the same manner as in Example 1 except that 3,3 ′, 4,4′-benzophenonetetracarboxylic dianhydride was used. It was made.

When the cross section of this substrate was observed by a scanning electron microscope in the same manner as in Example 1, the thickness of the polyimide resin layer formed was about 5 μm on both sides, and the thickness was 60 ° C. as in Example 1. No warp phenomenon was observed even in the atmosphere. That is, the circuit-forming substrate having the structure of the present invention does not exhibit the phenomenon of warpage even if the type of polyimide resin is different, and thus it has been found that there is no material selectivity.

Example 4 The polyimide precursor solution prepared in Example 1 was treated with 4-
(2'-nitrophenyl) -2,6, -dimethyl-3,
30 parts of 5-dicarbomethoxy-1,4-dihydropyridine (conventional name: nifedipine) was added to 100 parts of the precursor solid content to impart photosensitivity, and then long-sized was prepared in the same manner as in Example 1. Stainless foil (SUS304, 30 μm
(Thickness) was uniformly cast and applied, and dried at 80 ° C.

Next, light irradiation (wavelength 360 to 440 nm, irradiation energy 500 mJ / cm ² ) was performed through a photomask having a desired pattern, and then 1 more.
Heat treatment was performed at 60 ° C. Then, a mixed solution of a 5% by weight tetramethylammonium hydroxide aqueous solution / ethyl alcohol (2/1 volume ratio) is used as a developing solution, and development processing is performed at 40 ° C., followed by washing with water and drying to obtain a polyimide precursor layer having a desired pattern. Was formed.

Next, this was heated in a batch atmosphere heating furnace in a vacuum state (0.1 torr) so that the maximum temperature reached was 380 ° C. to imidize the polyimide precursor layer,
A circuit-forming substrate of the present invention having a polyimide resin layer (about 5 μm thick) patterned on one surface of a long stainless foil was prepared.

The obtained pattern had a good positive taper shape, and no warpage phenomenon was observed even when the polyimide resin layers having the same pattern were formed on both surfaces as in Example 2.

Example 5 A circuit-forming substrate having a patterned polyimide resin layer (thickness of about 5 μm) on one surface of the long stainless steel foil obtained in the above-mentioned Example 4 was placed on a long sputtering apparatus to form chromium,
Copper was continuously metallized in the same batch.
Then, the other stainless steel surface on which the polyimide resin layer was not formed was similarly metalized. At this time, when a cross-section was observed with a scanning electron microscope, it was found that the chromium layer was 500Å and the copper layer was 1000Å on both surfaces.

Next, in order to prevent the activity of the sputtering film from decreasing, electrolytic plating treatment was carried out within 1 hour after the sputtering treatment to further form a copper layer to prepare a circuit-forming substrate having a conductor layer. The obtained plating film was measured with a stylus type surface roughness meter, and as a result, it was 9 to 1 with a 10 cm square width.
It had a thickness of 0 μm and a film thickness accuracy of 9 μm ± 10%. Further, since the phenomenon of warpage is hardly seen in this substrate, it has been found that high dimensional accuracy is ensured when the conductor layer is processed to produce a circuit board.

Example 6 Pyromellitic dianhydride and approximately equimolar amounts of 4,4'-diaminodiphenyl ether / paramine (15/85 mol%) were polymerized in N-methyl-2-pyrrolidone to prepare a polyimide precursor. Body solution is prepared, and diethylaminoethyl methacrylate is added to this polyimide precursor solution as a precursor solid content 1
After blending 15 parts with respect to 00 parts and further 3 parts of Michler's ketone to impart photosensitivity, the solution was uniformly cast-coated on a stainless steel foil (SUS304, 25 μm thick) by the same method as in Example 1 and dried. .

Next, light is irradiated through a photomask having a desired pattern (1000 with light having a wavelength of 400 nm or more.
mJ / cm ² ) and then development using N-methyl-2-pyrrolidone to form a polyimide precursor layer having a desired pattern only on a necessary portion on the stainless steel foil.

Then, this was imidized in the same manner as in Example 1 to prepare a circuit-forming substrate having a patterned polyimide resin layer on one surface of a long stainless steel foil.

When a cross section of the obtained circuit-forming substrate was observed with a scanning electron microscope, the thickness of the formed polyimide resin layer was about 5 μm. Further, this substrate showed no warp phenomenon even in an atmosphere of 60 ° C., which was equivalent to that at room temperature.

Example 7 Instead of pyromellitic dianhydride in Example 6,
A polyimide precursor solution was prepared using 3,3 ′, 4,4′-benzophenone tetracarboxylic acid dianhydride, and the same as in Example 6 except that the compounding amount of Michler's ketone as a photosensitizer was changed to 10 parts. As a result, a circuit-forming substrate of the present invention having a polyimide resin layer on one surface of a long stainless foil was produced.

When the cross section of this substrate was observed with a scanning electron microscope in the same manner as in Example 1, the thickness of the polyimide resin layer formed was about 5 μm. No warp phenomenon was observed even in. That is, it is clear that the circuit-forming substrate having the structure of the present invention does not show the warp phenomenon even if the kind of the polyimide resin is different, and therefore has no material selectivity.

Example 8 The polyimide precursor solution prepared in Example 6 was treated with 4-
(2'-nitrophenyl) -2,6, -dimethyl-3,
30 parts of 5-dicarbomethoxy-1,4-dihydropyridine (conventional name: nifedipine) was added to 100 parts of the precursor solid content to impart photosensitivity, and then long-sized was prepared in the same manner as in Example 1. Stainless foil (SUS304, 30 μm
(Thickness) was uniformly cast and applied, and dried at 80 ° C.

Next, light irradiation (wavelength 360 to 440 nm, irradiation energy 500 mJ / cm ² ) was performed through a photomask having a desired pattern, and then 1 more.
Heat treatment was performed at 60 ° C. Then, a mixed solution of a 5% by weight tetramethylammonium hydroxide aqueous solution / ethyl alcohol (2/1 volume ratio) is used as a developing solution, and development processing is performed at 40 ° C., followed by washing with water and drying to obtain a polyimide precursor layer having a desired pattern. Was formed.

Then, this was heated in a batch atmosphere heating furnace in a vacuum state (0.1 torr) so that the maximum temperature reached was 380 ° C. to imidize the polyimide precursor layer,
A circuit-forming substrate of the present invention having a polyimide resin layer (about 5 μm thick) patterned on one surface of a long stainless foil was prepared.

The obtained pattern had a good positive taper shape, and no warp phenomenon was observed on the substrate.

Example 9 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride was used in place of the pyromellitic dianhydride in the above Example 6, and the diamine component was 4,4 ′. A polyimide precursor solution was prepared by substituting a mixture of 20 mol% of diaminodiphenyl ether and 80 mol% of paramine.

The maximum attainable temperature in curing (imidization) after pattern formation of this polyimide precursor solution was 42.
In the same manner as in Example 8 except that the temperature was 0 ° C., a patterned polyimide resin layer (about 5
A circuit-forming substrate of the present invention having a thickness of μm) was produced.

Α1 in the obtained circuit-forming substrate is 1
8 ppm and α2 were 17.3 ppm, and the difference (n) between them was 0.7 ppm.

Example 10 A circuit forming substrate having a patterned polyimide resin layer (thickness of about 5 μm) on one surface of the long stainless steel foil obtained in the above-mentioned Example 9 was placed on a long sputtering apparatus to form chromium,
Copper was continuously metallized in the same batch.
Then, the other stainless steel surface on which the polyimide resin layer was not formed was similarly metalized. At this time, when a cross-section was observed with a scanning electron microscope, the chromium layer was 500Å and the copper layer was 1000Å on both sides.
Met.

Next, in order to prevent the activity of the sputtering film from decreasing, electrolytic plating treatment was performed within 1 hour after the sputtering treatment to further form a copper layer, and a circuit-forming substrate having a conductor layer was prepared. The obtained plating film was measured with a stylus type surface roughness meter, and as a result, it was 9 to 1 with a 10 cm square width.
It had a thickness of 0 μm and a film thickness accuracy of 9 μm ± 10%. Further, since the phenomenon of warpage is hardly seen in this substrate, it has been found that high dimensional accuracy is ensured when the conductor layer is processed to produce a circuit board. Note that α1 is 18 ppm, α2 is 17.3 ppm,
α3 is 18 ppm, and the difference (n) between them is 0.7 p
The pm and difference (m) were 0 ppm.

Comparative Example 1 A circuit-forming substrate was prepared in the same manner as in Example 6 except that all of the paramine used in Example 6 was replaced with 4,4'-diaminodiphenyl ether.

As a result, the shape of the polyimide resin layer on the back surface of the stainless steel foil clearly appeared, and it was revealed that a large stress existed between the polyimide resin layer and the stainless steel foil. At this time, α1 is 35 pp
m and α2 were 17.3 ppm, and the difference (n) between them was 17.7 ppm.

Comparative Example 2 The amine component in Example 6 was replaced with the aromatic group (trifluoromethyl group at the 2,2'-position of the diphenyl group) located at the third position from the left in the upper row of R ₂ in the above [Chemical formula 7]. A circuit-forming substrate was produced in the same manner as in Example 6, except that all of the aromatic groups having

As a result, the substrate was warped on the stainless steel foil side. At this time, α1 is -7 ppm and α2 is 17.
3 ppm, and the difference (n) between them is −24.3 ppm
Met.

Example 11 Pyromellitic dianhydride / 5,5 '-[2,2,2-trifluoro-1- (trifluoromethyl) ethylidene]
Bis-1,3-isobenzofurandione and 4,4'-
Diaminodiphenyl ether / 4,4'-dimethyl-
An approximately equimolar amount of 3,3′-diaminodiphenylhexafluoropropane was polymerized in N-methyl-2-pyrrolidone to prepare a polyimide precursor solution, and diethylaminoethyl methacrylate was added to 100 parts of the precursor solid content. 15 parts, and further 3 parts of Michler's ketone were blended to prepare a photosensitive solution.

The photosensitive solution thus obtained was uniformly cast-coated on one surface of a long stainless steel foil (SUS304, 25 μm thick) using a comma coater and dried at about 80 ° C. to obtain a photosensitive polyimide precursor. A body layer was formed.

Next, light irradiation (wavelength: 36) from the polyimide precursor layer side is performed through a photomask having a desired pattern.
After performing 1000 mJ / cm ² ) with light of 5 nm or more, development processing was performed using N-methyl-2-pyrrolidone to form a polyimide precursor layer having a desired pattern on a long stainless steel foil.

Next, this was placed in a continuous heating furnace having an oxygen concentration of 0.1% by volume or less by nitrogen gas substitution, and heated so that the maximum temperature reached was 400 ° C. to imidize the polyimide precursor layer. A circuit-forming substrate having a polyimide resin layer on one surface of a long stainless foil was produced.

When the cross section of the obtained circuit-forming substrate was observed with a scanning electron microscope, the thickness of the formed polyimide resin layer was about 5 μm. Further, this substrate was subjected to 85 ° C. × 85% R. H. The water absorption of the polyimide resin layer when left in the atmosphere for 100 hours was about 0.5% by weight. The elongation of the polyimide resin layer at this time is about 0.1%
No substantial elongation, no change in shape before and after water absorption,
No warpage phenomenon was observed.

Example 12 In place of the pyromellitic dianhydride in Example 11, 3,3 ', 4,4'-benzophenonetetracarboxylic dianhydride was used, and the compounding amount of Michler's ketone was 10%.
A circuit-forming substrate of the present invention having a polyimide resin layer on one surface of a long stainless foil was produced in the same manner as in Example 11 except that the parts were formed.

The polyimide resin layer of this substrate had a water absorption of about 0.5% by weight and an elongation of about 10%. Further, almost no change in shape (warpage phenomenon) was observed before and after water absorption. That is, the circuit-forming substrate having the structure of the present invention does not exhibit a warp phenomenon even if the type of the polyimide resin is different, and thus it has been proved that there is no material selectivity.

Example 13 To the polyimide precursor solution prepared in Example 11, 4- (2'-nitrophenyl) -2,6-dimethyl-3,5 as a photosensitizer was used instead of diethylaminoethyl methacrylate and Michler's ketone. -Dicarbomethoxy-
1,4-dihydropyridine (conventional name: nifedipine)
Was blended with 30 parts per 100 parts of the precursor solid content to impart photosensitivity, and then uniformly cast onto a long stainless steel foil (SUS304, 30 μm thick) in the same manner as in Example 11. It was dried at 80 ° C.

Next, light irradiation (wavelength 360 to 440 nm, irradiation energy 500 mJ / cm ² ) was performed through a photomask having a desired pattern, and then 16 more.
Heat treatment was performed at 0 ° C. After that, a mixed solution of 5% by weight tetramethylammonium hydroxide aqueous solution / ethyl alcohol (2/1 volume ratio) was used as a developing solution to prepare 4
A development treatment was performed at 0 ° C., followed by washing with water and drying to form a polyimide precursor layer having a desired pattern.

Then, this was heated in a batch atmosphere heating furnace in a vacuum state (0.1 torr) so that the maximum temperature reached was 380 ° C. to imidize the polyimide precursor layer,
A circuit-forming substrate of the present invention having a polyimide resin layer (about 5 μm thick) patterned on one surface of a long stainless foil was prepared.

The obtained pattern had a good shape with a positive taper, the water absorption rate was 0.6% by weight, and the shape change (warp phenomenon) before and after water absorption was observed as in each of the above Examples. Was not done.

Example 14 A circuit forming substrate having a patterned polyimide resin layer (thickness of about 5 μm) on one surface of the long stainless steel foil obtained in the above-mentioned Example 13 was placed on a long sputtering apparatus to obtain chromium and copper. Were continuously metallized in the same batch. At this time, when a cross-section was observed with a scanning electron microscope, the chromium layer was 500Å and the copper layer was 1000Å.

Next, in order to prevent the activity of the sputtering film from decreasing, continuous copper electrolytic plating treatment was performed within 1 hour after the sputtering treatment to further form a copper layer, and a circuit forming substrate having a conductor layer was prepared. The obtained plated film was measured with a stylus type surface roughness meter, and as a result, it was 9 cm in 10 cm square width.
It had a thickness of 10 μm and a film thickness accuracy of 9 μm ± 10%.

Since the obtained board hardly shows a warp phenomenon even under the condition of pressure cooker test (121 ° C./2 atmosphere), when the conductor layer is processed to produce a circuit board, high dimensional accuracy is obtained. It was found that

Comparative Example 3 A polyimide precursor solution was prepared by using pyromellitic dianhydride and 4,4′-diaminodiphenyl ether as the monomers used in the synthesis of the polyimide precursor in Example 11. Except for this, the photosensitive liquid was prepared in the same manner as in Example 11 to prepare a circuit-forming substrate.

The water absorption of the polyimide resin layer in the obtained substrate was 1.5% by weight, and the dimensional change (elongation) before and after water absorption was 1% or more. In addition, the warp of these substrates was warped to the polyimide resin layer side before water absorption, but it was flattened after water absorption, and it was found that a large shape change (change in warp) occurs due to water absorption. did.

Example 15 Pyromellitic dianhydride and approximately equimolar amounts of 4,4'-diaminodiphenyl ether were polymerized in N-methyl-2-pyrrolidone to prepare a polyimide precursor solution, which was prepared with diethylamino. Ethyl methacrylate as precursor solid content 1
15 parts with respect to 00 parts and 3 parts of Michler's ketone were further mixed to prepare a photosensitive solution.

The photosensitive solution thus obtained was uniformly cast-coated on one surface of a long stainless steel foil (SUS304, 25 μm thick) using a comma coater and dried at about 80 ° C. to obtain a photosensitive polyimide precursor. A body layer was formed.

Next, light irradiation (wavelength: 36) from the polyimide precursor layer side is performed through a photomask having a desired pattern.
After performing 1000 mJ / cm ² ) with light of 5 nm or more, development processing was performed using N-methyl-2-pyrrolidone to form a polyimide precursor layer having a desired pattern on a long stainless steel foil.

Next, this was placed in a continuous heating furnace having an oxygen concentration of 0.1% by volume or less by nitrogen gas substitution, and heated so that the maximum temperature reached was 400 ° C. to imidize the polyimide precursor layer. A circuit-forming substrate having a polyimide resin layer on one surface of a long stainless foil was produced.

When the cross section of the obtained circuit-forming substrate was observed with a scanning electron microscope, the thickness of the formed polyimide resin layer was about 5 μm. When this substrate was bent at an angle of 90 degrees so that the polyimide resin layer was on the outside, no cracks were generated in the polyimide resin layer.

Further, the stainless steel foil of this substrate was removed by etching with ferric chloride to leave only the polyimide resin layer,
When this elongation was measured, it had an elongation of 48%.

Example 16 In place of the pyromellitic dianhydride in Example 15, 3,3 ', 4,4'-benzophenonetetracarboxylic dianhydride was used, and the compounding amount of Michler's ketone was 10%.
A circuit-forming substrate of the present invention having a polyimide resin layer on one surface of a long stainless steel foil was produced in the same manner as in Example 15 except that the parts were formed.

The elongation percentage of the polyimide resin layer of this substrate is 3
When a bending test was conducted in the same manner as in Example 15 at 5%, no cracks were observed in the polyimide resin layer.

Example 17 The polyimide precursor solution prepared in Example 15 was mixed with 4- (2'-nitrophenyl) -2,6-dimethyl-3,5 as a photosensitizer instead of diethylaminoethyl methacrylate and Michler's ketone. -Dicarbomethoxy-
1,4-dihydropyridine (conventional name: nifedipine)
Was added to 30 parts with respect to 100 parts of the precursor solid content to impart photosensitivity, and then uniformly cast onto a long stainless steel foil (SUS304, 30 μm thick) in the same manner as in Example 15, It was dried at 80 ° C.

Next, light irradiation (wavelength 360 to 440 nm, irradiation energy 500 mJ / cm ² ) was performed through a photomask having a desired pattern, and then 16 more.
Heat treatment was performed at 0 ° C. After that, a mixed solution of 5% by weight tetramethylammonium hydroxide aqueous solution / ethyl alcohol (2/1 volume ratio) was used as a developing solution to prepare 4
A development treatment was performed at 0 ° C., followed by washing with water and drying to form a polyimide precursor layer having a desired pattern.

Then, this was heated in a batch atmosphere heating furnace in a vacuum state (0.1 torr) so that the maximum temperature reached was 380 ° C. to imidize the polyimide precursor layer,
A circuit-forming substrate of the present invention having a polyimide resin layer (about 5 μm thick) patterned on one surface of a long stainless foil was prepared.

The elongation percentage of the polyimide resin layer in the obtained substrate was 39%, and when a bending test was conducted in the same manner as in Example 15, no cracks were observed in the polyimide resin layer.

Example 18 A circuit-forming substrate having a patterned polyimide resin layer (thickness of about 5 μm) on one surface of the long stainless steel foil obtained in the above-mentioned Example 17 was placed on a long sputtering apparatus to obtain chromium and copper. Were continuously metallized in the same batch. At this time, when a cross-section was observed with a scanning electron microscope, the chromium layer was 500 Å and the copper layer was 1000 Å.

Next, in order to prevent the activity of the sputtering film from decreasing, continuous copper electrolytic plating treatment was performed within 1 hour after the sputtering treatment to further form a copper layer, and a circuit forming substrate having a conductor layer was produced. As a result of measuring the obtained plated film with a stylus type surface roughness meter, it was found to have a 10 cm square width, a thickness of 9 to 10 μm, and a film thickness accuracy of 9 μm ± 10%.

When the obtained substrate was subjected to the same bending test as in Example 15, no cracks were observed in the polyimide resin layer.

Comparative Example 4 A polyimide precursor solution was prepared using paramine instead of the monomer 4,4′-diaminodiphenyl ether used in the synthesis of the polyimide precursor in Example 15. Except for this, the photosensitive liquid was prepared in the same manner as in Example 15 to prepare a circuit-forming substrate.

The elongation percentage of the polyimide resin layer in the obtained substrate was 16%, and when a bending test was carried out in the same manner as in Example 15, a large crack that would cause insulation failure was generated in the polyimide resin layer.

[Brief description of drawings]

1A to 1C are cross-sectional views showing respective steps for obtaining a circuit-forming substrate of the present invention.

2A to 2C are cross-sectional views showing respective steps for obtaining another circuit-forming substrate of the present invention.

3A and 3B are cross-sectional views showing respective steps for obtaining another circuit-forming substrate of the present invention.

FIG. 4 is a perspective view showing a state where the long substrate of FIG. 3 (a) is wound into a roll.

[Explanation of symbols]

1 Long stainless steel foil 2 Polyimide resin layer 3 Conductor layer (metalizing film) 4 Conductor layer (after electrolytic plating)

─────────────────────────────────────────────────── ─── Continuation of the front page (31) Priority claim number Japanese Patent Application No. 7-196438 (32) Priority date August 1, 1995 (August 1, 1995) (33) Priority claim country Japan (JP) Application for accelerated examination (72) Inventor Kazumasa Igarashi 1-2 1-2 Shimohozumi, Ibaraki City, Osaka Prefecture Nitto Denko Corporation (56) Reference JP-A-2-172109 (JP, A) JP-A-3 -142991 (JP, A) JP 4-188792 (JP, A) JP 7-74443 (JP, A) JP 2-81495 (JP, A) JP 6-29634 (JP, A) ) JP-A-6-237056 (JP, A) JP-A-5-347461 (JP, A) JP-A-60-157286 (JP, A) JP-A-6-132652 (JP, A) JP-B 7- 19945 (JP, B2) (58) Fields investigated (Int.Cl. ⁷ , DB name) H05K 1/05 H05K 1/03

Claims (14)

(57) [Claims] 1. A circuit-forming substrate comprising a polyimide resin layer formed on all or part of one surface or both surfaces of a long stainless foil , wherein the long stainless foil is a suspension for a hard disk.
And the thickness of the long stainless steel foil is 10 to 30 μm,
And the average linear expansion coefficient of the polyimide resin layer at 5 to 200 ° C.
Number (α1) and the average linear expansion coefficient (α
The difference (n) with 2) is between -5ppm and 5ppm.
A substrate for forming a circuit. 2. The thickness of the polyimide resin layer is 3 to 25 μm.
Circuit-forming board according to claim 1, wherein it is. 3. The water absorption of the polyimide resin layer is 0.7% by weight.
The circuit-forming substrate according to claim 1, which is at most% . 4. The elongation percentage of the polyimide resin layer is 20% or more.
Circuit-forming board according to claim 1, wherein it is. 5. A polyimide resin is represented by the following general formula:
At least one selected from [Chemical Formula 2] and [Chemical Formula 3]
The circuit-forming substrate according to claim 1 , which has a structural unit selected from the inside . [Chemical 1] [Chemical 2] [Chemical 3] 6. A long stainless steel foil and a polyimide resin
Layer or polyimide resin layer, and then a chromium layer.
Or a copper layer with or without a titanium layer
The circuit-forming board according to claim 1, further comprising a conductor layer formed of: 7. A polyimide resin layer containing a photosensitizer.
It is formed from a light-sensitive polyimide resin, or
6. The circuit-forming substrate according to item 6 . 8. A polyimide resin layer at 5 to 200 ° C.
Coefficient of linear expansion (α1) and average coefficient of linear expansion of conductor layer
The difference (m) of (α3) is between -5ppm and 5ppm
The circuit-forming substrate according to claim 6, wherein the circuit-forming substrate is provided. 9. One or both sides of a long stainless steel foil
Then, a polyimide resin layer is formed on all or part of
Long stainless steel foil and polyimi
On top of the resin layer or polyimide resin layer.
A copper layer with or without a copper or titanium layer
7. The circuit according to claim 6, wherein a laminated conductor layer is formed.
In the substrate for forming the path, the conductor layer is finely patterned.
The long stainless steel foil is a suspension for hard disks.
And the thickness of the long stainless steel foil is 10 to 30 μm,
And the average linear expansion coefficient of the polyimide resin layer at 5 to 200 ° C.
Number (α1) and the average linear expansion coefficient (α
The difference (n) with 2) is between -5ppm and 5ppm.
A circuit board characterized by the following . 10. A polyimide resin at 5 to 200 ° C.
Average linear expansion coefficient (α1) of layers and average linear expansion coefficient of conductor layers
The difference (m) of (α3) is between -5ppm and 5ppm
The circuit board according to claim 9, wherein the circuit board is provided. 11. The water absorption of the polyimide resin layer is 0.7
The circuit board according to claim 9, wherein the amount is less than or equal to%. 12. The elongation percentage of the polyimide resin layer is 20% or less.
The circuit board according to claim 9, which is above . 13. A polyimide resin represented by the general formula
4], [Chemical formula 5] and [Chemical formula 6]
10. The structure having a structural unit selected from one type in the molecule.
On-board circuit board. [Chemical 4] [Chemical 5] [Chemical 6] 14. The polyimide resin layer contains a photosensitizer.
10. Formed from a photosensitive polyimide resin.
Circuit board.