JPH04228553A - Bending resisting rolled copper foil - Google Patents

Abstract

PURPOSE:To obtain a rolled copper foil excellent in bending fatigue life and reduced in softening temp. CONSTITUTION:This copper foil is a bending resisting rolled copper foil characterized by having a draft of >= at least 90% (further preferably, >=93%) at the time of subjecting an annealed intermediate stock consisting of tough pitch copper or oxygen-free copper to final cold rolling to the prescribed thickness. Moreover, it is desirable to form a roughed surface (ruggedness) to a height of <=2mum on the surface of the cold rolled copper foil or further to form an oxide film by means of chemical conversion treatment on this roughed surface.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flex-resistant rolled copper foil, particularly to a flex-resistant rolled copper foil suitable for use in flexible printed wiring boards and other flexible wiring members.

0002

[Prior art] Flexible printed wiring board (Flexib)
Due to its high degree of freedom in mounting form, printed circuits are widely used in places where wiring to movable parts is required, such as printer units of office automation equipment and drive units of hard disk devices. This type of wiring board is made by bonding a copper foil onto an insulating film made of polyimide or the like via an adhesive made of a thermosetting resin such as epoxy, and then heating the entire board at a temperature of 130°C to 170°C for 1 to 24 hours.
It is manufactured by curing the adhesive by heating for a period of time and then etching the copper foil to form a predetermined wiring pattern. In addition, in order to increase the adhesive strength of the copper foil to the insulating film, roughening treatment is performed by electrolysis or other means.
It is common to form fine irregularities on the surface of copper foil.

[0003] Flexible printed wiring boards are required to have extremely high bending resistance (flexural fatigue strength) due to their special purpose of use, and especially in recent years, there has been a trend toward smaller devices and higher standards. Accordingly, when performing a bending test with a radius of curvature of 10 to 15 mm, it is strongly required to withstand bending 108 to 109 times under the conditions of a vibration stroke of 10 mm and a vibration frequency of 25 Hz.

[0004] The copper foil used for flexible printed wiring boards is, for example, tough pitch copper (with an oxygen content of 200 to 300 p).
A raw material (ingot) made of oxygen-free copper (high-purity electrolytic copper whose oxygen content is controlled to 50 ppm or less) or oxygen-free copper (high-purity electrolytic copper whose oxygen content is controlled to 50 ppm or less) is hot-rolled in advance, and then subjected to predetermined cold rolling. It is manufactured by repeatedly applying the necessary intermediate annealing. Since the copper foil manufactured in this manner has been work hardened due to cold rolling, it is necessary to perform an appropriate annealing treatment to improve its flexibility. The annealing treatment of copper foil is normally carried out using heat to heat and harden the resin adhesive.

[0005] Tough pitch copper rolled foil has a relatively low softening temperature, so the thermosetting temperature of the resin adhesive (usually 130°C to 100°C)
It has the property of being easily annealed at 70°C to improve its flexibility. Therefore, tough-pitch rolled copper foil is an extremely easy-to-use material in terms of manufacturing flexible printed wiring boards, but it has a problem in that its bending resistance (flexural fatigue life) is not very good. On the other hand, although oxygen-free rolled copper foil has better bending resistance than tough-pitch rolled copper foil, it is still insufficient to meet the above-mentioned strict requirements and has a relatively high softening temperature. There is a problem in that resin adhesives cannot be easily annealed at their curing temperatures. Furthermore, the surface of both types of rolled copper foil needs to be roughened to improve the adhesive strength with the insulating film, but the unevenness of the surface caused by the roughening process reduces the bending resistance. There is another troubling problem in that it actually declines.

[0006]

[Problems to be Solved by the Invention] The main object of the present invention is to provide a rolled copper foil that can be easily annealed at the curing temperature of a resin adhesive and has extremely good bending resistance (flexural fatigue life) after annealing. It's about doing.

Another object of the present invention is to propose a roughening treatment method or means that has relatively little influence on the bending resistance of rolled copper foil.

[0008]

[Means for solving the problem] Radius of curvature 10 to 15 mm
In order to realize a flexible printed wiring board that can withstand severe bending of 108 times or more under the conditions of a vibration stroke of 10 mm and a vibration frequency of 25 Hz, the rolled copper foil itself must have the appropriate bending resistance. It is necessary to That is, when a rolled copper foil is subjected to a bending test with a radius of curvature of 5 mm, which is stricter than that of a flexible printed wiring board, it is necessary that the rolled copper foil has a bending fatigue life of at least 106 times or more under similar vibration conditions.

[0009] For this reason, the inventors of the present invention have conducted numerous experiments and carefully considered the manufacturing conditions for rolled copper foil.
It has been found that there is an extremely close relationship between the degree of work during final cold rolling and the bending resistance of copper foil after rolling. That is,
Copper foil is manufactured by, for example, hot-rolling a raw material (ingot) of tough pitch copper or oxygen-free copper, and then repeating cold rolling and intermediate annealing. In either case, the greater the degree of final cold working, the better the bending strength of the copper foil after annealing. In addition, we also considered the correlation between the final cold working degree and the softening temperature, and found that in both tough pitch copper and oxygen-free copper, increasing the final cold working degree lowers the softening temperature. I found out that it can be done.

[0010] The term "final cold working degree" used in this specification refers to the final cold working degree of the rolling and annealing process repeated several times from the ingot to the completion of the copper foil. In this specification, it refers to the degree of working when an annealed intermediate material is finally cold rolled to a desired thickness, and in this specification,
The value obtained by the following formula is used exclusively.

[Equation 1] Final degree of cold working (%) = [(T-t)/T]×
100...(1)
However, T: Thickness of annealed intermediate material before final cold rolling t: Thickness of copper foil after final cold rolling

[0011] Conventionally, the final degree of cold work has remained at a level exceeding 85% at most in both tough pitch copper and oxygen-free copper. However, in order to give rolled copper foil good bending resistance and the desired softening temperature, it is absolutely necessary to roll it with a final degree of cold working of at least 90%. In order to have copper foil, it is desirable to roll it with a final degree of cold working of 93% or more.

[0012] The bending resistance and softening temperature of rolled copper foil are also affected by the oxygen content. In particular, the reason why the softening temperature of tough pitch copper is lower than that of oxygen-free copper is because the influence of oxygen is large. However, the final degree of cold working is 90
% or more (especially the effect on improving flex fatigue life), not only in the case of oxygen-free copper with extremely low oxygen content, but also in the case of tough pitch copper with relatively high oxygen content. We were able to come to a common recognition.

[0013] In the case of oxygen-free copper, it is desirable that the phosphorus content be as low as possible. Phosphorus is an element often used as an oxygen scavenger, but if too much is added,
This is because it not only increases the softening temperature of the rolled copper foil, but also causes undesirable side effects of deteriorating the inherent bending resistance of the copper foil. According to the experimental results of the present inventors, the acceptable phosphorus content was at most 1 ppm. Note that in the case of tough pitch copper, which has a relatively high oxygen content, no particular side effects were observed due to the addition of phosphorus.

[0014] If the thickness of the copper foil after cold rolling is too thick, the flexibility, which is a characteristic of flexible printed wiring boards, will deteriorate, especially 1.
This results in a loss of flexibility (flexibility within the elastic limit) at a radius of curvature of 0 to 15 mm, which is disadvantageous, and the flexural fatigue life is accordingly reduced. For this reason, it is desirable that the thickness of the rolled copper foil be at most 100 μm (0.1 mm) or less, and the preferred thickness of the rolled copper foil assuming normal usage is, for example, 0.035 mm or 0.07 mm. or 0
．． It is 018mm.

[0015] Rolled copper foil must be used with its surface roughened in order to increase the adhesive strength with the insulating film, but if the roughening treatment exceeds the specified limit, the surface of the copper foil may become rough. As a result of the increase in the unevenness, the unevenness causes a stress concentration area to occur inside the copper foil, which actually shortens the bending fatigue life of the copper foil. For this reason, it is desirable to limit the roughening treatment of the surface of the copper foil to such an extent that the height of the unevenness (thickness of the roughened cross section) due to roughening is at most 2 μm or less. In addition, by further applying chemical conversion treatment to the roughened surface,
It is also a preferable measure to form a velvet-like oxide film on the roughened surface. This type of coating not only has the effect of improving the adhesion of the adhesive resin, but also has the effect of minimizing the reduction in flexural fatigue life due to the formation of a roughened surface.

[0016]

EXAMPLES The present invention will be explained in more detail below with reference to some examples. In the following examples, the flexural fatigue life was measured using the testing apparatus shown in FIG. This device has a structure in which a vibration transmission member 3 is coupled to an oscillation driving body 4, and the copper foil 1 to be tested is loaded by fixing both ends thereof to a fixing plate 2 via screws 2a. The intermediate portion of the copper foil 1 is bent into a hairpin shape with a predetermined radius of curvature R, and connected to the tip of the vibration transmission member 3 in this state. The bending life test of copper foil was conducted using a copper foil to be tested with a width of 10 mm, setting the radius of curvature R to 5 mm, the vibration stroke to 10 mm, and the vibration frequency to 25 Hz. The average value of the results measured under the same conditions was taken as the bending fatigue life of the copper foil.

[0017]

EXAMPLES The present invention will be explained in more detail below with reference to some examples. In the following examples, the flexural fatigue life was measured using the testing apparatus shown in FIG. This apparatus has a structure in which a vibration transmitting member 3 is coupled to an oscillation driving body 4, and the copper foil 1 to be tested is loaded by fixing both ends to a fixing plate 2 via screws 2a. The intermediate portion of the copper foil 1 is bent into a hairpin shape with a predetermined radius of curvature R, and connected to the tip of the vibration transmission member 3 in this state. The bending life test uses a copper foil to be tested with a width of 10 mm, a radius of curvature R of 5 mm, and a vibration stroke of 10 m.
m, the vibration frequency was set to 25Hz, and 6
The bending fatigue life of the copper foil was defined as the average value of the results of measuring each copper foil under the same conditions.

Example 1 High-purity electrolytic copper was melted to produce an ingot (raw material) of tough pitch copper (oxygen content: 250 ppm) with a thickness of 200 mm and a width of 650 mm. After hot rolling this ingot to a thickness of approximately 10 mm, cold rolling and intermediate annealing were repeated until each thickness was 0.1 mm.
, 0.18mm, 0.35mm, 0.5mm, 0.8m
Annealed intermediate materials of 2 mm and 2 mm were produced. These intermediate materials were finally cold rolled to a thickness of 0.035 mm, and the respective final cold working degrees were 65%, 81%, 90%,
93%, 96% and 98% rolled copper foil (Samples 1 to 6)
) was produced. In addition, as a sample for comparison, a sample with a thickness of 0
．． A commercially available tough pitch copper rolled foil (sample 7) of 0.035 mm was prepared. After annealing these sample copper foils at a temperature of 160° C. for 1 hour, the bending fatigue life of each was measured using the apparatus shown in FIG. The measurement results are shown in Table 1.

[0019]

[Table 1]

As is clear from Table 1, the effect of improving the flexural fatigue life was greater in sample 3, in which the degree of final cold work was 90% or more.
- Sample 6, and among them, Samples 4 to 6, in which the final degree of cold working is 93% or more, have a particularly remarkable effect of improving the flexural fatigue life. On the other hand, Samples 1 and 2 with a final degree of cold working of less than 90% and commercially available tough pitch rolled foil (Sample 7) all have a bending fatigue life of 106 cycles or less. The value is the bending fatigue life required for flexible printed wiring boards (
108 times or more with a radius of curvature of 10 to 15 mm) cannot be satisfied.

Example 2 High-purity electrolytic copper was heated and melted in a vacuum to produce an ingot (raw material) of oxygen-free copper (oxygen content: 2 ppm) with a thickness of 200 mm and a width of 650 mm. After hot rolling this ingot to a thickness of approximately 10 mm, intermediate annealing and cold rolling were repeated to obtain thicknesses of 0.1 mm, 0.18 mm, 0.35 mm, and 0.5 mm, respectively.
, 0.8 mm and 2 mm intermediate materials were produced. These intermediate materials were finally cold rolled to a thickness of 0.035 mm, and the final working ratio was 65%, 81%, 90%, and 9, respectively.
3%, 96% and 98% rolled copper foil (Samples 8 to 13)
) was produced. As a sample for comparison, an annealed intermediate material of tough pitch copper with an oxygen content of 250 ppm was separately prepared, and the intermediate material was also processed at a working degree of 93.
% final cold rolling to the same thickness (0.0
A rolled copper foil (sample 14) with a thickness of 35 mm was manufactured. After annealing these samples at a temperature of 160° for 1 hour, the flexural fatigue life was measured using the apparatus shown in FIG. The measurement results are shown in Table 2.

[0022]

[Table 2]

[0023] As is clear from Table 2, even in the case of oxygen-free copper, the effect of improving the flexural fatigue life is greater when the degree of final cold work is 9.
It appears in all of Samples 10 to 13 where the degree of final cold work is 0% or more, and especially in Samples 11 to 13 where the final degree of cold work is 93% or more, the effect of improving the flexural fatigue life is particularly remarkable. On the other hand, Samples 8 and 9, in which the final degree of cold working was less than 90%, could not significantly improve the bending fatigue life. Although the bending fatigue life of the tough-pitch rolled copper foil of Sample 14 (corresponding to Sample 4 of Example 1) for comparison exceeds 106 cycles, the bending fatigue life of Sample 11 with the same working degree (93%) It is slightly inferior to the lifespan.

<Example 3> By heating and melting high-purity electrolytic copper in a vacuum, and adding a very small amount of phosphorus to the molten metal, an oxygen-free mold with a thickness of 200 mm and a width of 650 mm is produced. Copper (oxygen content: 2 ppm, phosphorus content: 0.4 ppm
An ingot (raw material) of m) was produced. Approximately 10 pieces of this ingot
After hot rolling to a thickness of mm, intermediate annealing and cold rolling were repeated until the thickness was 0.1 mm and 0.18 mm, respectively.
, 0.35 mm, 0.5 mm, 0.8 mm and 2 mm intermediate materials were manufactured. 0.035m of these intermediate materials
The copper foils were finally cold rolled to a thickness of m to produce rolled copper foils (Samples 15 to 20) with final workability of 65%, 81%, 90%, 93%, 96%, and 98%, respectively. As comparative samples, we separately prepared an annealed intermediate material of oxygen-free copper with a phosphorus content of 3 ppm and an annealed intermediate material of tough pitch copper with an added amount of phosphorus of 0.2 ppm and an oxygen content of 250 ppm. However, these intermediate materials were also subjected to final cold rolling with a processing degree of 93% to obtain the same thickness as the above sample (
0.035 mm) rolled copper foil (Sample 21 and Sample 22)
was produced. After annealing these samples at a temperature of 160° for 1 hour, the flexural fatigue life was measured using the apparatus shown in FIG. Table 3 shows the semi-softening temperature and flexural fatigue life of each sample.

[0025]

[Table 3]

[0026] As is clear from Table 3, in the case of this example as well, the effect of improving the flexural fatigue life is significant when the final degree of cold work is 90.
It appears in all cases of Samples 17 to 20 where the degree of final cold working is 93% or more, and the effect of improving the flexural fatigue life is particularly remarkable in Samples 18 to 20 where the final degree of cold work is 93% or more. . Even at semi-softening temperature, the final degree of cold working is 90%.
Samples 17 to 20 as described above were able to achieve a very preferable value of 140° C. or lower. In contrast, samples 15 and 16 whose final degree of cold work is less than 90%
Not only is the effect of improving flexural fatigue life not so significant, but also the semi-softening temperature exceeds 140℃,
Unsuitable for use for the purposes of the present invention.

Note that the oxygen-free rolled copper foil of Sample 21, which is a comparative example, has a large amount of phosphorus added at 3.0%, so even though it was subjected to a final cold working of 93%, its effect was As a result, the semi-softening temperature exceeds 140° C., and the effect of improving the flexural fatigue life is not so significant. On the other hand, the tough pitch copper rolled foil of Sample 22 (corresponding to Sample 4 of Example 1 and Sample 14 of Example 2), which is another comparative example, has a semi-softening temperature of 140°C or lower due to the small amount of phosphorus added. This is a preferable value, and the flexural fatigue life is also comparable to that of Sample 17. However, as in the case of Example 2, the flexural fatigue life of the same sample is slightly inferior to that of sample 18 with the same working degree (93%).

<Example 4> Tough pitch copper rolled foil with a final cold working degree of 93% produced by the method of Example 1 (sample 4 of the present invention) and the same final cold rolled foil produced by the methods of Examples 2 and 3. Oxygen-free copper rolled foils (invention samples 11 and 18) with a machining degree of 93% were used, and these samples were heated to a copper concentration of 20 g.
/l, plating solution consisting of sulfuric acid concentration 100g/l (solution temperature 2
5° C.) and copper plating was applied to one side of each sample by changing the current density to form a roughened surface. Tables 4 to 6 show the results of measuring the height of precipitates (height of unevenness) and flexural fatigue life.
Shown below. Note that the sample copper foil was annealed by heating at a temperature of 160° C. for 1 hour, as in Examples 1 to 3.

[0029]

[Table 4]

[0030]

[Table 5]

[0031]

[Table 6]

As is clear from Tables 4 to 6, when roughening treatment is applied to both tough pitch copper and oxygen-free copper, the inherent bending fatigue life of the rolled copper foil tends to decrease. However, when the current density during plating is low, the irregularities on the roughened surface tend to become finer, so especially Samples 23 and 24 (tough pitch copper) and Sample 27 where the height of the precipitates is 2 μm or less. , 28, 31, and 32 (oxygen-free copper) have relatively little decrease in bending fatigue density. In this example, the shape of the roughened surface was adjusted by changing the current density, but it is also possible to adjust the shape of the roughened surface by changing the temperature of the plating solution, copper concentration, sulfuric acid concentration, etc. be.

<Example 5> Of the rolled copper foils on which a roughened surface was formed by the method of Example 4, the copper foils with precipitate heights of 2 μm or less (tough pitch copper samples 23 and 24 and no Using oxygenated copper samples 27, 28, 31, 32), these copper foils were bonded onto a polyimide insulating film using an epoxy resin adhesive, and heated in a known manner (heating temperature 130°C).
After curing the adhesive at a temperature of 1 to 24 hours at a temperature of 1 to 170 degrees Celsius, a predetermined wiring pattern was formed by etching to produce a flexible printed wiring board. Figure 2 shows the cross-sectional structure of the completed wiring board. In the figure, 10 is a rolled copper foil, 10a is a precipitate (unevenness) formed on the copper foil, 12 is an insulating film, and 14 is a resin adhesive.

[0034] For each of the flexible printed wiring boards thus manufactured, a bending life test was conducted using the testing apparatus shown in Fig. 1 at a radius of curvature of 10 mm. Compared to the measurement results at the copper foil stage, the length was more than two orders of magnitude longer, and it was confirmed that each wiring board could sufficiently withstand bending of 108 times or more.

<Example 6> Of the rolled copper foils on which a roughened surface was formed by the method of Example 4, the copper foil of sample 32 was used, and the copper foil was subjected to a chemical conversion treatment to make the surface rough. A velvet-like black oxide film was layered on the surface. To form an oxide film, after degreasing and cleaning the surface, use NaCl2 and NaOH.
10 in a mixed solution (concentration 185 g/l, temperature 90°C) with
This was done by soaking for a minute. Table 7 shows the results of measuring the effect of this chemical conversion treatment on the flexural fatigue life. Note that the sample copper foil was annealed in the same manner as in the above example.
This was done by heating at a temperature of 60°C for 1 hour.

[0036]

[Table 7]

As is clear from Table 7, when a black oxide film by chemical conversion treatment is formed on the roughened surface, the bending fatigue life shortened by the roughening surface treatment is recovered to some extent. In addition,
Using the copper foil chemically treated by the method of this example, flexible printed wiring boards were manufactured by the method of Example 5, and a bending life test was conducted.
It was confirmed that it could sufficiently withstand bending of 108 times or more at 0 mm.

[0038]

[Effects of the Invention] According to the present invention, a rolled copper foil having a good bending fatigue life and a low softening temperature can be obtained. Although the rolled copper foil of the present invention is extremely suitable for use in flexible printed wiring boards, it can also be used for various other wiring members that require flexibility, such as the TAB mounting method (Tape A).
It can also be widely used as a tape carrier in automated bonding.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of a test device used to measure the bending fatigue life of rolled copper foil.

FIG. 2 is a cross-sectional view of a flexible printed wiring board manufactured using the copper foil of the present invention.

[Explanation of symbols]

1...Sample copper foil
10...Rolled copper foil 2...Fixing plate
10a... Roughening precipitate 3... Vibration transmission member
12... Insulating film 4... Oscillation driver
14...Resin adhesive.

Claims (8)

[Claims] Claim 1: A rolled copper foil obtained by subjecting a copper raw material to predetermined rolling and necessary annealing, and subjecting an annealed intermediate material to final cold rolling, wherein A bend-resistant rolled copper foil characterized by a degree of processing of at least 90% or more. 2. The bend-resistant rolled copper foil according to claim 1, wherein the final cold rolling has a workability of 93% or more. 3. The flex-resistant rolled copper foil according to claim 1 or 2, wherein tough pitch copper is used as a raw material for the copper. 4. The bend-resistant rolled copper foil according to claim 1 or 2, characterized in that oxygen-free copper is used as the copper raw material. Claim 5: The content of phosphorus in the copper raw material is at most 1
The bend-resistant rolled copper foil according to claim 4, characterized in that the bending-resistant rolled copper foil has a content of ppm or less. 6. The flex-resistant rolled copper foil according to claim 1, wherein the copper foil is subjected to a surface roughening treatment after final cold rolling. Claim 7: The height of the unevenness on the copper foil surface due to roughening treatment is 2
The bend-resistant rolled copper foil according to claim 6, characterized in that the bending-resistant rolled copper foil has a thickness of μm or less. 8. The method for producing rolled copper foil according to claim 6 or 7, further comprising forming an oxide film by chemical conversion treatment on the surface of the copper foil that has been subjected to the roughening treatment.