JPH0484488A - Manufacture of board for flexible printed wiring board - Google Patents

Abstract

PURPOSE:To improve the adhesive strength at high temperature by winding a flexible board, which is made by applying polyimide precursor resin solution on a conductor and drying it, and a sheet-shaped material, whose surface roughness is above specified, together into a cylindrical shape, and then heating it. CONSTITUTION:A product lined with copper is attached to a shaft 1, and the product 2 lined with copper veered out of this shaft 1 is supplied to a roll 4 via each roll. At this roll 4, the product 2 lined with copper and the aromatic polyamide unwoven fabric of Ra=1.5mum veered out of a shaft 3 are put on the other, and those are wound together on the pipe attached to a shaft 5 so that the resin side of the product 2 lined with copper may turn outside and that the lustrous metallic face may turn inside, thus a together wound product can be gotten. The together wound product is loaded in a vacuum furnace horizontally and it is vacuumized and the temperature is raised gradually, and the solvent is discharged enough, and again it is adjusted to be 330-340 deg.C. Next, with the inside of the furnace decompressed, the temperature is lowered, and the together wound product is taken out, and rewinding is performed.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention improves adhesion, heat resistance, and
The present invention relates to a method for manufacturing a curl-free flexible printed wiring board substrate with excellent dimensional stability.

[Conventional technology]

Conventionally, methods for producing substrates for flexible printed wiring boards include (1) a method of laminating a polyimide film and a metal foil via an adhesive layer; (2) a method of laminating a polyimide film and a metal foil through an adhesive layer; and (2) a method of manufacturing a substrate for a flexible printed wiring board.
As disclosed in Japanese Patent No. 40, a method is known in which a polyimide precursor resin solution is directly applied onto a metal foil, dried, and then imidized to form a polyimide layer on the metal foil.

However, in the case of (1) above, the heat resistance of the adhesive layer is not sufficient and the inherent heat resistance of the polyimide film is not utilized, and the resulting flexible printed wiring board has poor bending resistance and is prone to curling and distortion. There are problems that occur. In addition, the method (2) above has advantages such as high dimensional stability and improved heat resistance because it does not use adhesive, but it requires heat treatment at high temperature for a long time in order to obtain sufficient characteristics. It requires expensive equipment and has low productivity.

In order to solve this problem, Japanese Unexamined Patent Publication No. 61-307
, No. 789, a method has been proposed in which after coating and drying, the cylindrical shape is heated and cured. However, in this method, the coated surface comes into contact with the uncoated metal part, so when the temperature rises, During this time, adhesion occurs, leading to problems such as promoting deterioration such as surface oxidation of the metal foil and deteriorating various properties of the resin.

[Problem to be solved by the invention]

Therefore, as a result of intensive research in order to solve the above problem, the present inventors have succeeded in applying a polyimide precursor resin solution directly onto the conductor, drying it, and then employing a specific heat curing method. The present inventors have discovered that a substrate for a flexible printed wiring board having such characteristics can be manufactured with high productivity, and have completed the present invention.

Therefore, an object of the present invention is to provide a flexible printed wiring board that has excellent adhesive strength between a polyimide film and metal foil, especially at high temperatures, has high dimensional stability and heat resistance, and is free from curling and oxidation. The purpose is to provide the substrate.

[Means to solve the problem]

That is, the present invention involves winding a flexible substrate formed by applying and drying a polyimide precursor resin solution onto a conductor and a sheet material having an average surface roughness Ra of 0.5 or more into a cylindrical shape. This is a method for manufacturing a substrate for a flexible printed wiring board, which is then heated and cured.

In the present invention, metal foils such as copper, nickel, and aluminum can be used as the conductor used to manufacture the flexible substrate, but copper foil with a thickness of 5 to 150 mm is preferable.

Further, the polyimide precursor resin used for manufacturing this flexible substrate is one that forms imide bonds by heating and curing, and is typically polyamic acid. In order to prevent curling after curing, it is preferable to provide a resin with a linear expansion coefficient of 3 x 10-5 (1/K) or less, and more preferably, the structural formula after curing is the following general formula [1] (however, In the formula, R1 to Rs are hydrogen, halogen,
A polyamide containing a structural unit which is any group selected from a lower alkyl group and a lower alkoxy group, among which at least one of R3-R6 is a lower alkoxy group, and Ar represents one of the following. Imide resin or the following general formula [2] (in the formula R9 to R
1□ is a polyimide resin containing a structural unit represented by hydrogen, halogen, a lower alkyl group, a lower alkoxy group, a nitro group, and a nitrile group.

Further, it is also possible to add other resins, fillers, or additives such as antifoaming agents and leveling agents to the polyimide precursor resin for the purpose of imparting flexibility and improving fluidity.

When applying the polyimide precursor resin onto the conductor, any coating machine can be used, preferably a gravure coater, reverse roll coater, bar reverse roll coater, bar coater, doctor blade coater,
die coater and multilayer die coater. Furthermore, using these materials, 1.
Two or more layers of seeds or resin solutions of two or more types may be applied.

Any device can be used for drying. Drying is usually 150°C or less, preferably 90°C or less.
Although the coating is carried out at 130° C., it is preferable to remove the solvent in the polyimide precursor resin solution to 50 parts by weight or less based on the resin at the time of coating.

If more than 50 parts by weight of the solvent remains, tackiness remains on the resin surface and the resin adheres closely to the sheet-like material when wound into a cylindrical shape, resulting in deterioration of the resin after heating.

In addition, the sheet-like material used in the present invention has at least one surface with a surface roughness of Ra=0.5Iim or more, and has a heat shrinkage rate of 350°C in order to smoothly remove volatile components generated when the temperature is increased. Preferably, it has a high thermal stability of 1% or less. Such sheet-like materials include, for example, woven or nonwoven fabrics made of aromatic polyamide fibers, and in this case Ra is preferably in the range of 0.5 to 5.

If Ra is less than 0°5, volatile matter cannot be removed sufficiently, causing clouding or adhesion on the resin surface, causing resin deterioration. Furthermore, if Ra exceeds 5, fibers will partially adhere to the resin surface, causing variations in quality.

Other preferable sheet materials include transmission accuracy of 200~
Stainless steel wire mesh in the 350 mesh range is included. In this case, if the transmission accuracy is less than 200 meshes, traces of wire mesh will be transferred onto the resin surface, resulting in uneven film thickness, and if it exceeds 350 meshes, adhesion with the resin surface will occur. In addition, the R of the 200 mesh stainless steel wire mesh
a is 8.0 trend, and the same <350jt is Ra=4
．． Corresponds to 8 trends.

When the flexible substrate, which has been hand-formed by applying a resin solution onto the metal foil and drying it, and the sheet-like material are rolled together, it is preferable to roll them so that no wrinkles or twists occur. This may cause wrinkles or twists on the applied surface to be transferred, or
This is to prevent the solvent from interfering with volatilization. In addition, when trail-winding, it is not necessary to cover the entire coated surface with the sheet-like material, and the part near the outer periphery of the roll has relatively good thermal conductivity, so there is no problem even if it is not trail-wound with the sheet-like material. do not have. Further, in order to alleviate residual stress in the polyimide film when the temperature rises, it is preferable to tail-wrap the polyimide film so that the metal part faces inside and the resin surface faces outside.

Curing of the resin after coating and drying is preferably carried out under an inert gas atmosphere or under reduced pressure of 100 Torr or less,
It is more preferable to carry out the reaction continuously under reduced pressure of 5 Torr or less. This is to completely remove the organic solvent generated from the applied resin and the moisture generated during the imidization ring-closing reaction. If moisture remains in the atmosphere, hydrolysis of the resin will occur, resulting in a decrease in the degree of polymerization of the resin, which may result in deterioration of the physical properties of the polyimide film.

The temperature raising procedure in the vacuum furnace during the heat curing process is as follows:
It is preferable to carry out the process in two main stages: a stage in which sufficient deaeration and solvent removal are carried out, and a stage in which the curing reaction is completed. That is, first, the temperature is gradually or stepwise raised to around 150°C, preferably around the boiling point of the organic solvent, and after the residual solvent in the resin is sufficiently volatilized, the temperature is gradually or stepwise raised to 150 to 330°C. Preferably, the temperature is raised. More preferably, the heating rate is 0.75 to 12°C/min. When the temperature increase rate exceeds 12° C./n+in, the solvent is removed rapidly and foaming occurs in the resin.

Moreover, if it is smaller than 0.75°C/min, it will take a long time to reach the maximum temperature, and the resin will be exposed to high temperature for a long time, causing deterioration of the resin. Further, when cooling to room temperature after heat curing, it is preferable to perform the cooling under an inert gas atmosphere or under a vacuum of 100 Torr or less, more preferably under a vacuum of 10 Torr or less. As a cooling means, it is possible to simply leave it alone, but in consideration of production efficiency, it is preferable to use forced cooling means such as flowing cooling water.

In the above, a case has been described in which a substrate for a flexible printed wiring board is manufactured using a conductor-clad laminate on one side, but it is also possible to manufacture a double-sided copper-clad laminate using the method of the present invention as disclosed in Japanese Patent Application Laid-Open No. 1-244.841. It is also possible to manufacture plates.

〔Example〕

Examples of the present invention will be shown below to explain the present invention in more detail.

In the following examples, the average surface roughness was measured by tracing the measurement surface with a high-precision differential transformer type pick-up using an average surface roughness profile measuring device (Tokyo Seimitsu Co., Ltd., manufactured by Kiki, Surfcom 110B). I asked for it.

The coefficient of linear expansion is determined using a thermomechanical analyzer (TMA) using a sample that has undergone sufficient imidization reaction.
After heating to 250°C, cool at 10°C/min to 240°C.
The average linear expansion coefficient from 100°C to 100°C was calculated.

Adhesive strength is determined by using a tension tester to fix the resin side of a 10 m wide copper-clad product to an aluminum plate with double-sided tape, and peeling off the copper foil at an angle of 180°C at a speed of 5 m/min. I asked for it from.

The heat shrinkage rate was determined by using a film after etching a conductor with a width of 10 mm and a length of 200 mm, heat treating it in a hot air oven at 2508C for 30 minutes, and determining the dimensional change rate before and after that.

The curl of the film after etching is determined by etching the entire surface of the conductor with a ferric chloride aqueous solution,
After drying a film with a size of 25 m×thickness for 10 minutes at 100° C., the bending radius of the curl that occurred was determined and quantified.

The strength and elastic modulus of the film after etching are JIS
Ivy according to Z-1702, ASTM D-882-67.

In the solder heat resistance test, after the curing was sufficiently completed, the sample was immersed in a solder bath at 400° C. for 1 minute, and judgment was made based on the presence or absence of abnormalities such as blistering and peeling.

Example 1 A polyamide-imide precursor resin solution was applied to the roughened surface of a 35A thick electrolytic copper foil having a roughened surface and a glossy surface so as to have a thickness of 25 mm, and dried at 130° C. for 12 minutes to form polyimide. A copper-clad product made of resin and copper foil was obtained. At this time, the amount of solvent remaining in the resin was 0.78 parts by weight, the resin was dried to solidity, and no tackiness was observed.

Next, attach the copper-clad product to the shaft 1 in FIG.
The copper-clad product 2 fed out from the shaft 1 was supplied to the roll 4 via each roll.

In this roll 4, Ra = 1.51i! drawn out from the copper-clad product 2 and the shaft 3! 11 and an aromatic polyamide nonwoven fabric with a thickness of 40 mm, and the resin surface of the copper-clad product 2 is placed on the outside of a polished metal aluminum pipe with an outer diameter of 90 mm, which is attached to the shaft 5. The pieces were wrapped together so that the shiny metal surfaces faced inward to obtain a rolled product.

The above-mentioned trailing product was loaded horizontally into a vacuum drying oven, the pressure inside the furnace was reduced to IO-'Torr, and the temperature of the trailing product was gradually raised to uniformly reach 150°C. After holding for 2 hours and sufficiently removing the solvent, the temperature was adjusted to 330 to 340°C again over 2 hours. Next, cooling water was poured over the furnace walls to cool down the temperature while the pressure inside the furnace was kept reduced, and then the trailing product was taken out of the furnace and rewound in the exact opposite manner to the trailing winding procedure described above.

The thus obtained flexible printed wiring board substrate has no curls and has an adhesive strength of 2.0kg7c.
m, the heat shrinkage rate was 0.05%, the linear expansion coefficient was 11 x 10-6 (1/K), and no abnormality was observed in the soldering heat resistance test. Further, there was no oxidation of the shiny surface of the copper foil, and the desired circuit pattern could be easily formed.

Example 2 As in Example 1, the thickness was 18. After applying a polyimide precursor resin solution to a thickness of 25 mm on the roughened surface of rolled copper foil and drying it, the shaft 3 was coated with a transmission accuracy of 325 j.
A stainless steel wire mesh with a thickness of 70 mm was rolled out from the bush and both were wrapped together. Next, solvent removal and heat curing were performed in a vacuum furnace under reduced pressure of 10-' Torr. The obtained flexible printed wiring board was flat with no foreign matter observed on the resin, had an adhesive strength of 1.8 kg/cm, and a heat shrinkage rate of 0.
．． 05%, linear expansion coefficient 1. OX 10-' (1/K)
No abnormality was observed in the solder resistance test.

Comparative Example 1 A test was conducted in exactly the same manner as in Example 1 except that the trailing sheet material was not used, and the resulting flexible printed wiring board substrate showed severe adhesion.
The resin had clearly deteriorated.

Comparative Example 2 In Example 1, the Ra of the polyamide nonwoven fabric to be wrapped
When the test was carried out in exactly the same manner except that one with 0 and 1 was used, cloudiness and adhesion were observed on the resin surface of the obtained flexible printed wiring board substrate, and the film strength was 1.
It was less than 5kg/emu.

Comparative Example 3 In Example 1, the Ra of the trailing polyamide nonwoven fabric
The test was conducted in exactly the same manner except that 60 parts by weight of the solvent remained after coating and drying the polyamide-imide precursor, and the adhesive between the sheet material and the resin surface was 1.5. The resin clearly deteriorated after being heated and cured.

Comparative Example 4 In Example 1, the Ra of the polyamide nonwoven fabric to be wrapped
When a test was conducted in exactly the same manner except that a substrate with a diameter of 10 was used, it was found that fibers were partially attached to the obtained flexible printed wiring board substrate.

Comparative Example 5 A test was conducted in exactly the same manner as in Example 2, except that the trailing stainless steel wire mesh had a transmission accuracy of 400, and adhesion was observed between the sheet material and the resin surface. Ta.

Comparative Example 6 A test was carried out in exactly the same manner as in Example 2, except that the trailing stainless steel wire mesh had a transmission accuracy of 165, and the surface shape of the sheet material was transferred to the resin surface. .

〔Effect of the invention〕

According to the method of the present invention, it is possible to easily produce a substrate for a flexible printed wiring board that has high dimensional stability, low thermal expansion, and excellent heat resistance, and is free from curling and oxidation.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing an outline of the lines used for trail winding in the examples and comparative examples of the present invention. Explanation of symbols

Claims (5)

[Claims] (1) A flexible substrate formed by coating a polyimide precursor resin solution on a conductor and drying it, and an average surface roughness Ra of 0.
．． A method for producing a substrate for a flexible printed wiring board, which comprises rolling a sheet material of 5 μm or more into a cylindrical shape and then heating and curing the material. (2) The method for manufacturing a flexible printed wiring board substrate according to claim 1, wherein the sheet material is an aromatic polyamide nonwoven fabric. (3) Claim 1, wherein the sheet-like material is a stainless steel wire mesh.
The method for manufacturing the flexible printed wiring board substrate described above. (4) The method for manufacturing a flexible printed wiring board substrate according to any one of claims 1 to 3, wherein the heat curing is performed under vacuum. (5) As a polyimide precursor resin, the structural formula after curing is the following general formula [1] ▲ There are mathematical formulas, chemical formulas, tables, etc. ▼ (However, in the formula, R_1 to R_8 are hydrogen, halogen, lower alkyl group, lower Any group selected from alkoxy groups, of which at least one of R_3 to R_6 is a lower alkoxy group, and Ar has ▲a mathematical formula, a chemical formula, a table, etc.▼ or ▲a mathematical formula, a chemical formula, a table, etc. ▼) or the following general formula [2] ▲ Numerical formula, chemical formula, table, etc. ▼ [2] (In the formula, R_9 to R_1_2 are hydrogen, halogen , a lower alkyl group, a lower alkoxy group, a nitro group, and a nitrile group).
The method for manufacturing the flexible printed wiring board described above.