JP2008294193A - Method of manufacturing substrate for flexible wiring board - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing a substrate for flexible wiring board which has no pinhole. <P>SOLUTION: When a base having a seed layer made of chromium, nickel, copper, or alloy thereof on a top surface of an insulating film by a dry plating method, namely, a thin underlayer comprising the seed layer and a copper layer provided thereupon by a dry plating method is used to manufacture the substrate for flexible wiring board by providing a copper layer on the top surface of the underlayer by an electrolytic copper plating method using the underlayer of the base as a cathode, the cathode is provided on the back side of the insulating film of the base (on the opposite side from an anode) and on an external wall surface of an electrolytic cell, and a voltage applied to the cathode is set higher than a voltage applied to the underlayer of the base. In this invention, it is effective that the underlayer is grounded to be held at 0 V. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for producing a substrate for a flexible wiring board used in fields such as electricity, electronics, and communications, and more specifically, an insulating film and a seed layer provided on the surface thereof, The present invention relates to provision of a flexible wiring board substrate having a seed layer that does not have a pinhole, in a substrate for a flexible wiring board that includes a conductive layer.

  In recent years, high integration and miniaturization of various electric and electronic parts have been demanded. In response, flexible wiring boards in which metal wiring is provided on a flexible insulating film have been widely used in electrical and electronic devices such as notebook personal computers and mobile phones that require space saving. Yes.

  Such a flexible wiring board is generally manufactured by a semi-additive method using a so-called two-layer substrate in which a conductive layer is directly provided on a polyimide film such as Kapton. In this two-layer substrate, a seed layer is formed on a polyimide film by a vacuum deposition method or a sputtering method, and a copper sputtered film is provided on the seed layer if necessary, and a conductive layer is formed thereon by an electrolytic copper plating method. In many cases, the seed layer and the conductive layer are combined and handled as a base layer.

  In the semi-additive method, first, a photoresist layer is provided on the surface of the base layer of a two-layer substrate by a coater or screen printing, exposed using a photomask having a desired circuit pattern, and developed to obtain a plating mask. .

  Next, copper is deposited by electrolytic copper plating on the base layer exposed in the opening of the mask to form a copper layer.

  Next, the plating mask is removed, and the underlying layer exposed thereby is removed to obtain a circuit pattern.

  By the way, the base layer is generally composed of only a seed layer formed by vapor deposition or sputtering using chromium, nickel or an alloy thereof as a target, or a copper layer provided on the seed layer by a similar method. It is composed of the combination. Since the seed layer has different dissolution characteristics from the copper layer, an etchant that is less susceptible to copper erosion can be selected when the seed layer is etched away. However, if the seed layer is thick, the copper circuit portion itself is also violated while the seed layer is etched away, and a good circuit pattern cannot be obtained. For this reason, the thickness of the seed layer is desired to be as thin as possible. Further, regarding the copper sputter layer provided on the seed layer, it is not preferable to obtain a too thick copper sputter layer because the production cost increases. As a result, the entire underlayer is required to be as thin as possible so as not to hinder electrolytic copper plating in the subsequent process. Such a thin underlayer cannot sufficiently eliminate pinholes because of its manufacturing method.

  When a flexible wiring board having a fine circuit pattern is prepared by a semi-additive method using a substrate for flexible wiring board obtained by electrolytic copper plating on an underlayer having such pinholes, copper is deposited in the pinhole portion. Therefore, a phenomenon that the adhesion strength of the wiring is not sufficient occurs.

As a method for obtaining such a base layer having no pinhole, the thickness of the seed layer made of chromium, nickel or an alloy thereof is set to 1 to 1000 nm, and the thickness of the copper sputtered film provided on the seed layer is set to 50 to 3000 nm. (See Patent Document 1).
JP 2007-073935 A

  Even in the method disclosed in Patent Document 1, pinholes cannot be eliminated from the base layer if an attempt is made to obtain a thin base layer substrate for obtaining a flexible wiring board having a high-density circuit pattern required in recent years. .

  An object of this invention is to provide the manufacturing method of the board | substrate for flexible wiring boards which does not have a pinhole.

  As a result of various studies by the present inventors to solve the above-mentioned problems, a substrate having a copper sputtered film formed on a seed layer made of chromium, nickel, copper, or an alloy thereof, or on the seed layer is disclosed. In a method of obtaining a flexible wiring board substrate by obtaining a copper layer having a desired thickness on the substrate by electrolytic copper plating, a pin for the underlayer is provided by providing a new electrode on the back surface of the substrate to be plated. It has been found that copper is deposited in the hole, and the present invention has been achieved.

  That is, the present invention that solves the above problems uses a base material in which a thin base layer is provided on the surface of an insulating film by a dry plating method, and the base layer surface is formed by an electrolytic copper plating method using the base layer of the base material as a cathode. When a flexible wiring board substrate is manufactured by providing a copper layer on the substrate, a cathode is provided on the outer wall surface of the electrolytic cell on the back side (opposite side of the anode) of the insulating film of the base material, and the voltage applied to the cathode is applied to the base. The voltage is higher than the voltage applied to the base layer of the material.

  In the present invention, it is also effective to ground the base layer to 0 volts.

  According to the present invention, copper can be deposited also in the pinhole of the base layer of the printed wiring board substrate. Therefore, even when a printed wiring board having a circuit pattern with a high density and a narrow wiring width is produced using the printed wiring board substrate of the present invention, the adhesion strength of the circuit pattern is sufficient.

  In the present invention, a cathode is newly provided on the outer wall surface of the electrolytic cell on the back side of the insulating film constituting the base material by attracting copper ions to the inside of the pinhole of the base material underlayer by the electromagnetic field formed by the cathode. The ions are brought into contact with the surrounding base layer to precipitate as metal in the pinhole.

  Therefore, the voltage applied to the cathode must be applied to the underlayer on the surface of the insulating film because the electric field strength at the pinhole portion needs to be stronger than the electric field strength on the surface of the underlayer. Higher than the voltage to be applied.

  The strength of the voltage to be applied is naturally different depending on the distance between the insulating film and the cathode. This interval is also affected by the structure of the electrolytic cell itself.

  Therefore, it is preferable to obtain optimum conditions in advance for implementation.

  In the present invention, a polyimide film, a polyethylene film, a polypropylene film, or the like can be used as the insulating film.

  Hereinafter, the present invention will be described using examples.

  In the electrolytic cell, the electrodes B and C were disposed so as to face each other, and the electrode A was disposed on the outer surface of the electrolytic cell on the electrode B side. A copper sulfate plating solution is placed in the electrolytic bath, and the electrode B is used as a cathode, the electrode C is used as an anode, and a normal plating voltage (1 to 2 V) is applied between B and C so that copper is plated on the electrode B. It was confirmed.

  Next, the electrode B was changed to a 35 μm thick polyimide film provided with a nickel-chromium alloy layer as a seed layer and a copper film having a pinhole of 10 μm thickness and a diameter of about 20 μm. Further, electrolytic copper plating was performed in the same manner as described above while applying a voltage of minus 100 V to the electrode A. At this time, the electrode C was grounded (0 V).

  When the obtained electrode was observed, it was found that a remarkable tendency of plating growth was observed around the pinhole, and the diameter of the pinhole was as small as 10 microns.

  A simulation was performed to analyze this phenomenon, and it was found that a high electric field leaked from the pinhole into the plating solution as shown in FIG. It can be presumed that the metal ions in the electrolytic solution are gathered by this high electric field and the ion density is increased.

It is the figure which showed the simulation result performed in the Example.

Claims (2)

A substrate for a flexible wiring board using a base material on which a thin base layer is provided by a dry plating method on the surface of an insulating film, and using the base layer of this base material as a cathode, a copper layer is provided on the base layer surface by an electrolytic copper plating method When a cathode is provided on the outer wall surface of the electrolytic cell on the back side (opposite side of the anode) of the insulating film of the base material, the voltage applied to the cathode is higher than the voltage applied to the base layer of the base material. A method for producing a flexible wiring board substrate, comprising:   A method of manufacturing a substrate for a flexible wiring board, wherein a voltage applied to the cathode is 0 volts.

Images