JPH06300714A - Evaluation of copper foil - Google Patents

Abstract

PURPOSE:To establish a method in which information on the inside texture of a copper foil is obtained. CONSTITUTION:A thin-film region in the central part in the thickness direction of s sample as a copper foil and in a cross section parallel to the plane of the sample as the copper foil is transmission-inspected by an electron microscope, information on the inside texture of the copper foil is obtained directly, and the copper foil is evaluated. In the case of the sample as the copper foil which is provided with a roughened face M having a roughened and treated layer 10 is removed, the sample as the copper foil is electrolytically polished, the central part of the copper foil can be changed into a thin film, and the sample which precisely reflects the inside center of the copper foil can be obtained. A grain boundary, a dislocation and a flaw as well as the occurrence situation and the state of the size, the shape (the form), the distribution and the like of a twin crystal are observed directly in individual regions in the inside center of the copper foil, and an index to the improvement of the texture of the copper foil is obtained on the basis of their evaluation.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for evaluating a copper foil, and more particularly to a method for evaluating the thickness of a copper foil prepared by electrolytic polishing in order to obtain an index for improving the structural characteristics of the copper foil for printed circuits. The present invention relates to a method for evaluating a copper foil by obtaining structure information such as crystal growth by conducting a transmission inspection of the central cross-section area with an electron microscope.

[0002]

2. Description of the Related Art Copper and copper alloy foils (hereinafter referred to as copper foils)
Contributes greatly to the development of the electrical and electronic related industries,
In particular, it is indispensable as a printed circuit material. Copper foil for printed circuits is generally laminated and bonded to a thermoplastic resin substrate under high temperature and high pressure with or without an adhesive to a substrate such as a synthetic resin board or a film, and then the target circuit. After printing the circuit necessary to form the film, an etching process for removing unnecessary portions is performed. Finally, the required elements are soldered to form various printed circuit boards for electronic devices.

Quality requirements for copper foil for printed wiring boards are a surface (roughened surface) bonded to a resin substrate and a non-bonded surface (glossy surface).
And is different. The requirements for the roughened surface are mainly
No oxidative discoloration during storage, sufficient peeling strength from the base material even after high temperature heating, wet treatment, soldering, chemical treatment, etc. There is no such thing. On the other hand,
Good appearance on glossy surface, no oxidative discoloration during storage, good solder wettability,
It is required that there be no oxidative discoloration during heating at high temperature and that the adhesiveness with the resist be good. In order to meet such demands, various surface treatments have been proposed for the roughened surface and the glossy surface.

Apart from such surface characteristics, quality control of the internal structure of the copper foil itself has also become important. So far
X-ray diffraction and SEM are available as means for obtaining the structural information of the copper foil.
Although (scanning electron microscope) has been mainly used, X-ray diffraction gives only average information of crystal grains and orientations, and S
The EM only provided information on defects such as pits on the copper foil surface and crystal grains.

[0005]

By the way, with the recent miniaturization of printed circuit wiring, finer and finer etching is required than before, and the internal crystal structure of the copper foil, which has a great influence on the etching, is important. Has become a concern.
In addition, as the range of applications of printed circuit boards expands, mechanical properties such as flexibility and strength of copper foils are becoming important considerations, and from this point it is necessary to control the internal crystal structure of copper foils. Has become. For that purpose, we will go further from the conventional evaluation method of copper foil, and determine the grain boundaries, dislocations, defects, twin size, shape (morphology), and distribution in individual regions in the inner center that is the substantial part of the copper foil. It is necessary to directly observe the occurrence situation and state of such as and to obtain an index for improvement of the copper foil based on the observed information. An object of the present invention is to establish a method for obtaining internal organization information that reflects the actual condition of copper foil.

[0006]

According to the present invention, the thickness of a copper foil sample is determined based on the judgment that the transmission inspection by an electron microscope of the inner center portion of the copper foil is optimum for obtaining the correct internal structure information of the copper foil. Provided is a method for evaluating a copper foil, characterized in that a thinned region in a cross section parallel to a plane of a copper foil sample at a central portion in the depth direction is subjected to a transmission inspection with an electron microscope to obtain internal texture information of the copper foil.

Electropolishing can first be considered as a method of exposing the inner central cross section of a copper foil sample. The surface of the copper foil to be adhered to the base material is usually subjected to electrodepositioning of, for example, copper humps on the surface of the copper foil after degreasing for the purpose of improving the peel strength of the copper foil after lamination. Copper roughening treatment is applied. Such copper kinky electrodeposition is easily brought about by so-called burn electrodeposition. When roughening treatment is applied to the electrolytic copper foil raw foil, the raw foil itself already has a convex portion, and a large number of protruding copper electrodeposits are electrodeposited near the top of the convex portion to form a convex shape. The department will be further strengthened. In order to prevent the electrodeposits from falling off, thin copper plating or the like is often performed as a finishing treatment after roughening. If such a roughening treatment layer is still present, electrolytic polishing of the copper foil sample does not progress electrolytic polishing from the roughened surface side, but electrolytic polishing progresses only from the glossy surface side. It was found that the copper foil portion in the vicinity of the layer was left, and the inner central portion of the copper foil could not be exposed in a thin film state. In order to correctly obtain the internal texture information of the copper foil, the copper foil sample observed by the electron microscope needs to be obtained from the center inside the copper foil. Under such considerations, the present invention also removes the roughened layer of the roughened surface of the copper foil sample having the roughened surface having the roughened layer and the glossy surface, and then electropolishing the copper foil sample. To expose a thinned region in a central portion in the thickness direction of the copper foil sample and in a cross section parallel to the plane of the copper foil sample, and to inspect the exposed thinned region with an electron microscope to inspect the internal structure information of the copper foil. A method for evaluating a copper foil is provided.

[0008]

[Function] The individual regions at the inner center of the copper foil are examined by the transmission inspection of the thinned region in the center portion of the copper foil sample in the thickness direction of the copper foil sample and in the cross section parallel to the plane of the copper foil sample. In order to obtain the index of copper foil improvement based on the observed information, it is possible to directly observe the occurrence state and state of grain boundaries, dislocations, defects, twin crystal size, shape (morphology), distribution, etc. Can be evaluated correctly. By removing the roughening treatment layer on the roughened surface of the copper foil sample and electrolytically polishing the copper foil sample, the inner central portion of the copper foil can be reliably thinned, and the reliability of information is increased.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention is directed to copper foils, especially copper foils for printed circuits. The copper foil includes both electrolytic copper foil and rolled copper foil. Taking electrolytic copper foil as an example, copper foil is electrodeposited with copper around a rotating drum immersed in an electrolytic solution, and the amount of electrodeposition is increased as the drum rotates, resulting in a certain thickness of electrodeposited copper. Is manufactured by peeling the tape from the drum. afterwards,
As the minimum treatment, for the purpose of improving the peeling strength of the copper foil after lamination on the surface to be bonded to the resin base material, for example, the electrodeposition of copper pistil-like electrodeposition on the surface of the copper foil after degreasing Copper roughening treatment is performed. Such copper kinky electrodeposition is easily brought about by so-called burn electrodeposition. In order to prevent the lumpy electrodeposits from falling off, thin copper plating or the like is often applied to cover them.
Such electrolytic copper foil has various internal structures depending on its forming conditions. The rolled copper foil also undergoes many heat treatments and processing steps from a copper ingot to a copper foil, and has various internal structures depending on the conditions.
The copper foil is then subjected to various treatments in order to give the initially mentioned requirements on the roughened surface and the glossy surface, respectively, but prior to that, the copper foil itself must have a predetermined internal structure. It is essential.

According to the present invention, for the purpose of obtaining an index for directing the improvement of the internal structure of the copper foil, thinning of the copper foil sample in a central portion in the thickness direction and in a cross section parallel to the plane of the copper foil sample is performed. The copper foil is evaluated by inspecting the area with an electron microscope to obtain information on the internal structure of the copper foil.

Transmission inspection by electron microscope (TEM inspection)
In order to carry out, it is necessary to prepare a thin sample suitable for it, and this is conveniently carried out by electropolishing. The copper foil sample is cut out from the copper foil as, for example, a circular sample having a diameter of about 3 mm, a hexagon, or another shape. The automatic electropolishing apparatus itself for metal thin films is commercially available (for example, the automatic electropolishing apparatus sold under the trade name “Tennepol-3” manufactured by Struers, Denmark), and such an apparatus is also used in the present invention. be able to.

FIG. 1 shows a cross-sectional appearance of the electrolytically polished portion of the above-mentioned "Tenupole-3". An electrolysis cell 3 having an electrolysis chamber 2 therein is mounted on a tank 1 containing an electrolytic solution. The tank 1 and the electrolytic cell 3 are connected to each other by a suction pipe 4 for sucking the electrolytic solution to feed the electrolytic solution to the electrolytic chamber 2 and a discharge pipe 5 for returning the electrolytic solution circulated through the electrolytic chamber to the tank. The sample cut out from the copper foil is fixed to, for example, an annular copper grid with an adhesive, and then mounted on the sample fixture 6 such that the center of the grid is aligned with the longitudinal axis of the electrolytic cell. The sample fixture 6 is suitably supported within the electrolysis chamber by a support 7 having a central through hole aligned with the longitudinal axis of the electrolysis cell and forming the electrolyte flow path. The sample is connected to the (+) pole via the sample fixture and the support 7 is connected to the (-) pole. The electrolytic solution is sucked up from the tank 1 through the suction pipe 4 by an appropriate pump means (not shown), enters the electrolytic chamber through the central conducting hole, and enters between the sample fixture 6 and the support 7. It overflows through the gap and is returned to the tank through the discharge pipe 5. In this way, electrolytic polishing can be performed at high speed while circulating the electrolytic solution. An infrared transmitter 8 and a receiver 9 are arranged in the apparatus in alignment with the longitudinal axis so that the sample is gradually thinned by electropolishing and the power is turned off at the moment when a hole is formed. As the electrolytic solution for electrolytic polishing, for example, phosphoric acid: 250 ml, distilled water: 500 ml,
An electrolyte consisting of ethanol: 250 ml, propanol: 50 ml and urea: 5 g can be used.

The sample thus electropolished is thin enough to undergo transmission inspection by electron microscopy at the perimeter of the hole. After washing and drying, the thin film area of the sample is inspected with an electron microscope to examine the grain boundaries, dislocations, defects, twin crystal size, shape (morphology), distribution, etc. in the individual areas in the center of the copper foil. Directly observe the occurrence situation and condition, and take and photograph. An evaluation is made to obtain an index of future improvement of the copper foil based on the observed information.

As described above, one surface of the copper foil is often roughened. When the copper foil sample having such a roughening treatment layer is electropolished as it is, the copper foil sample is unilaterally electropolished from the glossy surface S side, as shown in FIG.
The roughened surface M having the roughened layer 10 is not electropolished, and as a result, the copper foil portion in the immediate vicinity of the roughened layer is thinned. Even if you observe these samples with an electron microscope,
The information obtained is not representative of the inner center of the copper foil and will, at times, result in incorrect evaluations.

Therefore, as shown in FIG. 3, it is necessary to remove the central portion of the roughened layer of the sample and then perform electrolytic polishing. By doing so, the sample is electrolytically polished from the glossy surface S and the roughened surface M at the same time, and the inner central portion in the thickness direction of the copper foil sample is thinned. Such a roughening treatment layer can be removed by first masking the glossy surface by, for example, disposing another copper foil material with the roughened surface outside, and electrolytically polishing only the roughened surface. After that, electrolytic polishing is performed from both sides. In this way, it is possible to obtain a sample reflecting the inner center which is the substantial part of the copper foil.

(Example) A thickness 35 of which one surface is roughened
A hexagonal sample having a facing side length of 2.5 mm was cut out from an electrolytic copper foil of μm. The sample was fixed concentrically with an adhesive on an annular copper grid having an outer diameter of 3 mm. By electropolishing this sample with a copper foil placed on the glossy side, only the roughened surface was first electropolished, and the roughening-treated layer was removed. After that, electrolytic polishing was performed from both sides using an automatic electrolytic polishing apparatus manufactured by Struers under the trade name "Tenupole-3". There was a hole where the cell voltage increased to 2.5 V and the current density increased to 15 A / dm ² . As shown in FIG. 3, this sample was thinned in the central portion in a substantially symmetrical manner from both sides. Grain boundaries,
It was possible to directly observe the generation state and state of dislocations, defects, twin size, shape (morphology), and distribution. The copper foil could be evaluated usefully based on the observation information taken and photographed.

[0017]

In order to improve the mechanical properties and etching characteristics of the copper foil, the thinned region of the copper foil in the central portion in the thickness direction of the copper foil sample and in the cross section parallel to the plane of the copper foil sample is electronically changed. The size of the grain boundaries, dislocations, defects, and twins in the individual regions at the center of the inside of the copper foil are examined by transmission inspection with a microscope.
Directly observe the state of occurrence such as shape (form) and distribution,
An index for improvement can be obtained based on the observed information.

[Brief description of drawings]

FIG. 1 is a sectional view of an electrolytic polishing section of a commercially available automatic electrolytic polishing apparatus.

FIG. 2 is an explanatory diagram showing a state in which electrolytic polishing progresses only from a glossy surface when electrolytic polishing is performed with a roughening treatment layer.

FIG. 3 is an explanatory diagram showing a state in which electrolytic polishing proceeds from both the glossy surface and the roughened surface when electrolytic polishing is performed after removing the roughening treatment layer.

[Explanation of symbols]

 1 Tank 2 Electrolysis Chamber 3 Electrolysis Cell 4 Suction Tube 5 Emission Tube 6 Specimen Fixture 7 Support 8 Infrared Transmitter 9 Receiver 10 Roughening Layer M Roughened Surface S Glossy Surface

Claims (2)

[Claims] 1. A thin film-forming region in a cross section parallel to the plane of the copper foil sample at the central portion in the thickness direction of the copper foil sample is inspected by an electron microscope to obtain an internal structure information of the copper foil. Evaluation method for copper foil. 2. The thickness of the copper foil sample is obtained by electrolytically polishing the copper foil sample after removing the roughening treatment layer on the roughened surface of the copper foil sample having the roughened surface having the roughened surface and the glossy surface. A thin film region in a cross section parallel to the plane of the copper foil sample at the center in the vertical direction is exposed, and the exposed thin film region is inspected by an electron microscope to obtain internal texture information of the copper foil. Evaluation method for copper foil.