JP2913420B2 - Manufacturing method of flexible printed circuit board - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a method for manufacturing a flexible printed circuit board (hereinafter referred to as FPC), and more particularly, to a method for manufacturing a flexible printed circuit board adapted to various physical properties of a film. About.

[Conventional technology]

In the technical field of electronics, the demand for high-density mounting is increasing, and accordingly, the demand for high-density mounting is also increasing in the field of FPC. In the manufacturing process of the FPC, a process having a large dimensional change is before and after the etching process, and a small dimensional change of the FPC before and after this process is required as an indispensable condition for high-density mounting.

FPC production is performed on a roll-to-roll basis.
As shown in the figure, the FPC base film 1 and the copper foil 2 wound on the rolls are respectively drawn out and pressed and heated between the laminating roll 3 and the receiving roll 4 to be laminated. For this reason, tension is applied to the base film 1 and the copper foil 2 in a feed direction in which the base film 1 and the copper foil 2 are fed by a roll, that is, a mechanical feed direction (hereinafter, referred to as an MD direction), and the FPC 5 is manufactured in that state. I have.

Considering the base film 1, in the MD direction, the base film 1 is provided with an elongation of the film due to tension, an elongation of thermal expansion due to heat applied during lamination, and an elongation due to the pressure of the laminating roll 3. It is fixed to the copper foil 2. Next, a phenomenon occurs in which the film 1 shrinks in a direction perpendicular to the mechanical feed direction of the film 1 (hereinafter referred to as TD direction) by the amount that the film 1 is stretched in the MD direction by this tension. Elongation of thermal expansion is given by heat applied at the time of lamination, and in that state, it is fixed to the copper foil 2 by an adhesive.

On the other hand, when examining the copper foil 2, the copper foil 2 has a very large elastic modulus, so that the copper foil 2 is hardly deformed by the tension applied in the normal manufacturing process of the FPC 5. The copper foil 2 is deformed only by the thermal expansion caused by the heat applied during lamination. The copper foil 2 is given elongation due to the thermal expansion in the MD and TD directions.
And glued.

Therefore, in the MD direction, if the sum of the elongation of the film 1 due to the tension, the elongation due to the thermal expansion of the film 1 and the elongation due to the pressure of the laminating roll 3 is equal to the elongation of the copper foil 2 due to the thermal expansion, the strain is offset. become.
In the TD direction, if the sum of the contraction of the film 1 due to stretching in the MD direction by tension and the elongation due to thermal expansion is equal to the elongation due to the thermal expansion of the copper foil 2, the strain is canceled.

However, the base film 1 and the copper foil 2 are isotropically manufactured, and the FPC 5 on which the base film 1 and the copper foil 2 are laminated is fixed when the copper foil is removed by etching to form a predetermined pattern. The distorted distortion is released. Therefore, regarding the MD direction,
The difference between the elongation of the film 1 due to the tension, the sum of the elongation due to the thermal expansion of the film 1 and the elongation due to the pressure of the laminating roll 3, and the elongation due to the thermal expansion of the copper foil 2 appears as a dimensional change. In the TD direction, the difference between the sum of the elongation due to the thermal expansion and the shrinkage of the film 1 caused by stretching in the MD due to the tension and the difference between the elongation due to the thermal expansion of the copper foil 2 appears as a dimensional change. Become.

For this reason, the method of determining the manufacturing conditions in the actual manufacturing process of the FPC5 is to manufacture the FPC5 by changing various manufacturing conditions such as the tension for attaching the film 1, the pressure of the laminating roll 3, the laminating temperature, and the like. The conditions were determined. In this method, it took a lot of time to find manufacturing conditions suitable for the characteristics of the film 1 used.

Therefore, the present inventors have eagerly determined the manufacturing conditions (tension, nip pressure, lamination temperature) suitable for the characteristics of the film used, and obtained a method for immediately manufacturing an FPC under the optimum conditions. As a result of the research, the present invention was reached.

[Means for solving the problem]

The gist of the method for manufacturing a flexible printed circuit board according to the present invention is that an equation for determining a dimensional change rate generated during the manufacturing of the flexible printed circuit board is provided. (However, in the formula, the elastic modulus ₁ of the film is the elastic modulus of the film at the temperature of the B stage, and the elastic modulus ₂ of the film is the elastic modulus of the film at the laminating temperature). It is to determine the tension, the nip pressure and the lamination temperature so as to be as follows, and to manufacture.

〔Example〕

Hereinafter, embodiments of the present invention will be described in detail. In the description, the portions described above are omitted.

As shown in FIG. 1, a film 1 and a metal foil 2 are bonded to each other to manufacture an FPC 5. As the film 1, for example, a resin film having particularly excellent heat resistance, such as polyimide or polyamide, is selected. Further, as the metal foil 2, for example, a material that is particularly an electrically good conductor and can be made into a thin film, such as copper, a copper alloy, aluminum, or an aluminum alloy, is selected.

As mentioned above, FPC (Flexible Printed Circuit Board)
The step in which a large dimensional change occurs in the manufacturing process 5 is an etching step. Before and after the etching step, the following conditions must be satisfied in order to make the dimensional change of the FPC 5 extremely small. That is, in the MD direction, the sum of the elongation of the film 1 due to the tension, the elongation of the film 1 due to the thermal expansion, and the elongation of the laminate roll 3 due to the pressure is equal to the elongation of the metal foil 2 due to the thermal expansion. With respect to (1), it is necessary that the sum of the contraction of the film 1 due to stretching in the MD direction by tension and the elongation due to thermal expansion is equal to the elongation of the metal foil 2 due to thermal expansion. That is, it is necessary to satisfy the following equation.

MD direction: (elongation of film due to tension) + (elongation due to thermal expansion of film) + (elongation due to pressure of laminating roll) = (elongation due to thermal expansion of metal foil) TD direction: (stretched in MD direction by tension) (Expansion due to thermal expansion) = (elongation due to thermal expansion of metal foil) Expressing this relational expression using Hooke's law, definition of linear expansion coefficient, and definition of Poisson's ratio, before and after the etching process The dimensional change at It is represented by

Here, the coefficient of linear expansion of the film 1 refers to the coefficient of linear expansion from room temperature to the laminating temperature in the case where the adhesive to be used is applied to the film 1 and dried (B-stage). The coefficient refers to a coefficient of linear expansion from room temperature to lamination temperature. The tension is a force for pulling the film 1, and the nip pressure is a pressure for the laminating roll 3 to press the receiving roll 4, and the unit is a pressing force per 1 cm (kg / cm), which is expressed by a linear pressure. The proportional constant is a constant determined by the machine used, and is determined by a method described later. The width and thickness refers to the width and thickness of the film 1 to be used, respectively, the elastic modulus ₁ l of film 1 FPC
The elastic modulus of the film 1 measured in a state where the adhesive is applied at a temperature at which the adhesive is dried in the manufacturing process of 5 (B-stage temperature), and the elastic modulus _{2 of the} film 1 is a laminating temperature. Means the elastic modulus of the film. Poisson's ratio is when film 1 is pulled in one direction Say.

Since the value obtained by the above equation is of the order of 10 ^-4 , which is too small, the following equation, which is multiplied by 100 to obtain an order of%, was employed.

Next, a method of obtaining a proportional constant in the MD direction nip pressure × proportional constant will be described.

FPC5 is created by changing the conditions other than the nip pressure, such as tension, adhesive drying temperature (B-stage temperature) and line speed, and changing only the nip pressure within the range of 0 to 20 kg / cm. IPC-TM650, 2.2.4 Met
Measured according to hod B. As an example, width 254mm, thickness
An experiment was performed using a 25 μm polyimide film, and the relationship between the nip pressure and the dimensional change before and after etching was examined. The result is shown in FIG. The laminating roll 3 used was made of stainless steel, and the receiving roll 4 was a roll coated with silicone rubber.

From the figure, the relationship between the dimensional change rate (%) in the MD direction and the nip pressure is found to be proportionally open: y = −0.016x−0.092 (where x is the nip pressure and y is the dimensional change rate in the MD direction). Represents the laminating roll 3 at an arbitrary nip pressure.
The elongation by pressure is determined by the difference between the dimensional change at a nip pressure of 0 and the dimensional change at a given nip pressure. That is, the elongation (%) of the laminating roll 3 due to the pressure = −0.09
2 − (− 0.016x−0.092) = 0.016x The force required to cause a dimensional change in the film 1 by the elongation due to the pressure of the laminating roll 3 is: However, the elastic modulus (kg / mm ² ) of the used film 1 is 430 at room temperature, 280 at 120 ° C., and 245 at 180 ° C.

Therefore, the formula for determining the dimensional change rate that occurs during the manufacture of a flexible printed circuit board is: Becomes

Next, in this formula, when the type of the adhesive for bonding the film 1 and the metal foil 2 is determined, the drying temperature (B-stage temperature) of the adhesive is determined, and the elastic modulus of the film 1 at that time is determined. I do. On the other hand, film 1 or metal foil 2
Since the coefficient of linear expansion and Poisson's ratio are constant, the tension, nip pressure, and lamination temperature can be easily changed under the manufacturing conditions of the flexible blind substrate 5. However, in terms of tension, the condition is that the film 1 can be uniformly applied to the metal foil 2 and the adhesive can be applied uniformly, so that the tension is practically about 0.2 kg / m or more. It is preferred that Further, the laminating temperature is set in a range from room temperature or higher to a heat-resistant temperature of the receiving roll 4 covered with silicon rubber or the like. Furthermore, the nip pressure is 0 to 20 kg for normal laminating
/ cm.

Therefore, the absolute value of the expression for calculating the dimensional change rate in the MD direction and the TD direction is 0.15 or less, preferably, in order to minimize the dimensional change occurring at the time of manufacturing the flexible printed circuit board 5, that is, to minimize it as much as possible. 0.
Tens or less, more preferably 0.05 or less, the tension, nip pressure and laminating temperature are respectively set by the above formulas, and the manufacturing conditions are set based on the set values to manufacture a flexible printed circuit board. .

Example 1 A flexible printed circuit board (FPC) was manufactured by using a polyimide film as a film and bonding the film and a copper foil with a modified phenol-based adhesive. The drying condition of the adhesive (B-stage temperature) is 120 ° C. for 1 minute, and the laminator line speed is 2 m / min.

The coefficient of thermal expansion (° C ^-1 ) of the film used was 1.00 in the MD direction and 0.53 in the TD direction from room temperature to 120 ° C, and 1.20 in the MD direction and 0.60 in the TD direction from room temperature to 180 ° C. . The coefficient of thermal expansion (° C ^-1 ) of the copper foil is 120
At ℃, it was 1.42 in MD direction and 1.29 in TD direction. From room temperature to 180 ° C, it was 1.56 in MD direction and 1.47 in TD direction.

The tension is 2kg / cm, the nip pressure is 3kg / cm, and the laminate is so that the dimensional change rate of the FPC is -0.12% in the MD direction and + 0.11% in the TD direction, where the absolute value of the calculated value is 0.15% or less in the calculated value. The temperature was set to 120 ° C., and an FPC was manufactured under these conditions. The dimensions of the resulting FPC as a reference dimension L ₀ and after etching the bonded copper foil, dried, the size of the resulting film as L _1, were examined dimensional change in the MD and TD directions. The dimensional change rate (%) in the MD and TD directions is Asked by. Table 1 shows the results.

Example 2 After an FPC was manufactured using the same materials and equipment as in Example 1, the copper foil was removed by etching and the dimensional change was examined. However, as a manufacturing condition of the FPC, the dimensional change rate of the FPC is −0.06 in the MD direction where the absolute value in the calculated value is 0.15% or less.
%, + 0.05% in the TD direction, the tension was set to 1 kg / cm, the nip pressure was set to 3 kg / cm, and the lamination temperature was set to 120 ° C., and an FPC was manufactured under these conditions.

 The results are shown in Table 1.

Example 3 After an FPC was manufactured using the same materials and equipment as in Example 1, the foil was removed by etching and the dimensional change was examined. However, as a manufacturing condition of the FPC, the dimensional change rate of the FPC is −0.03 in the MD direction where the absolute value in the calculated value is 0.15% or less.
%, + 0.05% in the TD direction, the tension was set at 1 kg / cm, the nip pressure was set at 1 kg / cm, and the lamination temperature was set at 120 ° C., and an FPC was manufactured under these conditions.

 The results are shown in Table 1.

Example 4 After an FPC was manufactured using the same materials and equipment as in Example 1, the copper foil was removed by etching and the dimensional change was examined. However, as a manufacturing condition of the FPC, the dimensional change rate of the FPC is −0.03 in the MD direction where the absolute value in the calculated value is 0.15% or less.
%, The tension is 0.5kg / cm so that it becomes + 0.10% in the TD direction.
The nip pressure was set to 0.5 kg / cm and the lamination temperature was set to 180 ° C., and an FPC was manufactured under these conditions.

 The results are shown in Table 1.

Example 5 After an FPC was manufactured using the same materials and equipment as in Example 1, the copper foil was removed by etching and the dimensional change was examined. However, as a manufacturing condition of the FPC, the dimensional change rate of the FPC is −0.03 in the MD direction where the absolute value in the calculated value is 0.15% or less.
%, The tension is 0.5kg / cm so that it becomes + 0.01% in the TD direction.
The nip pressure was set to 0.5 kg / cm and the lamination temperature was set to room temperature, and an FPC was manufactured under these conditions.

 The results are shown in Table 1.

Comparative Example After an FPC was manufactured using the same materials and equipment as in Example 1, the copper foil was removed by etching, and the dimensional change was examined. However, as a manufacturing condition of the FPC, the tension is set to 5 k so that the dimensional change rate of the FPC exceeds 0.15% as an absolute value in the calculated value.
g / cm, a nip pressure of 5 kg / cm, and a lamination temperature of 180 ° C. The dimensional change rate in the calculated value at that time is
It was -0.34% in the MD direction and + 0.11% in the TD direction. An FPC was manufactured under these conditions, and the dimensional change was examined.

 The results are shown in Table 1.

As mentioned above, although Examples and Comparative Examples of the present invention have been described, the types of films and metal foils are not limited at all,
The film or metal foil, in particular, it is possible to set manufacturing conditions adapted to the characteristics of the film, and the present invention does not depart from the gist of the present invention, and various improvements, corrections, and modifications based on the knowledge of those skilled in the art. Can be implemented.

〔The invention's effect〕

In the present invention, in advance, a calculation formula for determining a dimensional change rate caused by bonding a film and a metal foil is obtained,
Set the manufacturing conditions suitable for the characteristics of the film and metal foil, especially the characteristics of the film with large changes, on the desk, and immediately set the flexible printed circuit board (FP) under the set manufacturing conditions.
Since C) can be manufactured, the productivity of FPC has been dramatically improved. In addition, since there is no need to manufacture FPCs on a trial basis and check the dimensional change rate,
The present invention has excellent effects, such as not only requiring a time loss but also not requiring various kinds of loss accompanying a test, and reducing manufacturing costs.

[Brief description of the drawings]

FIG. 1 is an explanatory view schematically showing a method of manufacturing a flexible printed circuit board to which the present invention is applied. FIG. 2 is a diagram showing the relationship between the nip pressure and the dimensional change rate. 1; film 2; metal foil 3; laminating roll 4; receiving roll 5; flexible printed circuit (FPC)

Claims (1)

(57) [Claims] 1. An equation for determining a dimensional change rate occurring during manufacturing of a flexible printed circuit board. (However, in the formula, the elastic modulus ₁ of the film is the elastic modulus of the film at the temperature of the B stage, and the elastic modulus ₂ of the film is the elastic modulus of the film at the laminating temperature). A method of manufacturing a flexible printed circuit board, wherein the manufacturing is performed by determining a tension, a nip pressure, and a lamination temperature as follows.