JP2007214519A - Metal-coated polyimide substrate and tin plating method using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a metal-coated polyimide substrate, capable of providing COF for which peeling is not caused by a heat history for hardening a sealing resin, without forming a heterogeneous metal layer of nickel or the like on a copper plated surface, by controlling the layer thickness near final plating, to an appropriate thickness in the copper plating coating of a laminated structure formed into a desired thickness, by continuously executing plating. <P>SOLUTION: For the metal-coated polyimide substrate, the copper plating coating is executed by a plurality of electrolytic cells on the surface of a metal layer formed on a polyimide film surface by a sputtering method, and tin plating coating is executed on the surface of the copper plating coating. When tin plating of a film thickness (t) is applied to the surface of the copper plating coating, electric copper plating is applied by the same electrolytic cell to an area from the copper plating surface layer, to at least a depth 3t. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a metal-coated polyimide substrate for mounting a semiconductor for mounting a semiconductor for driving a liquid crystal screen, for example, and a tin plating method for an electronic circuit obtained using the substrate.

  COF (Chip on Film) attracts attention as a technique for mounting a driver IC chip for liquid crystal display. COF is a mounting method that allows fine pitch mounting compared to TCP (Tape Carrier Package), which is a conventional mounting method, and makes it easy to reduce the size and cost of the driver IC. COF uses a metal-coated polyimide substrate in which a polyimide film, which is a highly heat-resistant and highly insulating resin, and a copper layer, which is a good conductor, are in close contact, and the copper layer is finely patterned by a photolithography technique. Generally, it is obtained by coating with tin plating and solder resist. As the polyimide film used for the metal-coated polyimide substrate, Kapton EN (manufactured by Toray DuPont), Upilex (manufactured by Ube Industries), NPI (manufactured by Kaneka), etc. are used, and the thickness is generally 25 to 38 μm. .

  Moreover, as a method of forming a metal layer on the polyimide film surface, first, a method of forming a metal layer such as a nickel-chromium alloy by sputtering and subsequently forming a copper film in order to impart good conductivity is used. . The metal layer formed by the sputtering method is generally about 100 to 500 nm. If further thickening is necessary, it is generally performed by electroplating and using electroplating and electroless plating in combination, and the thickness is 5 when a circuit is formed by a subtractive method, for example. ˜12 μm is common.

As a method of manufacturing COF or TCP using a metal-coated polyimide substrate obtained by sputtering, plating, or a method of bonding a copper foil to a polyimide film with an adhesive, etc., a copper layer is etched. After the circuit is formed, a method of forming a solder resist on a desired portion after forming a thickness of about 0.5 μm on the surface of the circuit by an electroless tin plating method, performing a heat treatment at about 80 to 150 ° C. It is general (refer patent document 1).
The tin-plated film formed on the surface of the copper film by this method is easy to grow a needle-like crystal called whisker, and in some cases, a short circuit occurs between the adjacent circuits, and does not serve as an electronic circuit. . On the other hand, Patent Document 1 discloses a technique for suppressing generation by performing heat treatment at 80 to 150 ° C. after tin plating. Moreover, the method of suppressing generation | occurrence | production of a whisker is also disclosed by adding the salt of low melting-point metals, such as lead, to an electroless tin plating solution, and forming an alloy plating layer with tin (refer patent document 2).

  On the other hand, as a method of forming a copper film by electroplating on the surface of the sputtered film formed on the polyimide film, a plurality of plating tanks having an anode and an electrolytic solution are arranged, a sputtered film, or a polyimide film having a plated film, A general method is to successively supply these plating tanks in succession, perform electroplating while controlling the amount of current for each plating tank, and continuously form an electroplating layer on the coating surface to a desired thickness. Yes (see Patent Document 3).

By the way, the COF is sealed by applying and curing a thermosetting resin to the IC chip and its peripheral part after bonding the IC chip and the inner lead part. Under the present circumstances, although hardening of resin is performed by passing through the heat history of 3 to 4 hours at 150 to 160 degreeC, when using the metal-coated polyimide substrate obtained by the method of the said patent document 3, After the thermal history, there arises a problem of peeling from the circuit together with the tin plating film, or the tin plating film and a film such as a solder resist or a sealing resin formed on the surface thereof. This is because the heat treatment for suppressing whisker generation and the heat treatment for curing the sealing resin cause the copper tin alloy film formed at the interface between the copper tin alloy layer and the copper film to diffuse. When voids called Kirkendall voids are generated and grow, peeling occurs at the interface. In general, a method of forming a dissimilar metal layer such as nickel at the interface between copper and tin has been disclosed as a technique for suppressing this problem (see Patent Document 4).
JP 2001-144145 A JP-A-8-296050 Japanese Patent Laid-Open No. 7-022473 Japanese Patent Laying-Open No. 2005-226097

  However, when the technique of Patent Document 4 is used for the metal-coated polyimide substrate obtained by the technique of Patent Document 3, there is an economical cost for forming a dissimilar metal layer such as nickel on the copper film prior to tin plating. In addition, the stress applied to the circuit due to nickel plating increases the position of the bumps and leads due to the bonding of the IC chip, etc., especially in the case of fine pinch COF. Get higher.

  The present inventor has been made to solve the above problems, and in a copper plating film having a laminated structure formed to a desired thickness by continuous plating, the layer thickness in the vicinity of the final plating is set to an appropriate thickness. A metal-coated polyimide substrate capable of providing a COF that does not cause peeling due to a thermal history for curing the sealing resin without forming a dissimilar metal layer such as nickel on the copper plating surface by controlling It aims at providing the tin plating method using this.

  In the metal-coated polyimide substrate according to the present invention, a copper plating film is applied to the surface of the metal layer formed by sputtering on the polyimide film surface using a plurality of electrolytic baths, and a tin plating film is further applied to the surface of the copper plating film. When the tin plating with a film thickness t was applied to the surface of the copper plating film, the copper plating was applied to the region from the copper plating surface layer to a depth of 3 t in the same electrolytic cell. It is characterized by this.

  In addition, the tin plating method using the metal-coated polyimide substrate according to the present invention is a copper plating film formed by forming a metal layer on the polyimide film surface by a sputtering method and then continuously performing electroplating using a plurality of electrolytic cells. In the tin plating method using a metal-coated polyimide substrate for forming a tin plating with a film thickness t on the surface of the copper plating film, the copper plating is performed when the tin plating with a film thickness t is applied to the surface of the copper plating film. Electrolytic copper plating is applied to the region from the surface layer to at least a depth of 3 t in the same electrolytic bath, and after tin plating, heat treatment at 120 ° C. or higher is performed.

  The metal-coated polyimide substrate according to the present invention prevents the tin plating film from peeling off from the circuit portion even after undergoing a thermal history for curing the sealing resin applied in the assembly process of the COF and IC obtained using the same. Thus, electrical insulation reliability is sufficiently ensured. In addition, the metal-coated polyimide substrate of the present invention does not require the formation of a dissimilar metal layer such as nickel on the interface between the circuit surface and the tin plating film in order to eliminate the above-mentioned peeling problem. It becomes possible to realize a high density, and it is possible to supply products economically.

  In the present invention, when tin plating having a film thickness t is applied to the surface of a copper plating film having a laminated structure formed to have a desired thickness by continuous electroplating, it is applied to a region from the copper plating surface layer to a depth of at least 3 t. The reason why the copper electroplating is performed in the same electrolytic cell and the specific method thereof will be described below.

  In general, when a tin coating is formed on the copper surface and further heat treatment at 120 ° C. or more is performed, there are not a few voids called Kirkendall voids at the interface between copper and the copper-tin alloy as described above. Except when an excessive heat history of about 200 ° C. for about 24 hours or more, or when an excessive external force such as a terminal portion of the connector is applied, the use of electronic parts such as COF does not result in peeling. However, when the copper layer is continuously formed in a plurality of electrolytic baths, that is, to a desired thickness as a laminated structure, discontinuity occurs in the growth of the plated crystal in each layer. In normal applications, this discontinuity has very little risk of developing into problems such as delamination between copper layers. However, the degree of discontinuity is, for example, the plating growth stop time generated between the electrolytic cells, the plating surface state at that time, for example, the coating condition of the plating solution, washing water, etc., the exposed environment, such as temperature, humidity, etc. Since it is affected by various factors, it is extremely difficult to always realize a situation in which the discontinuity is extremely suppressed, and the copper layer interface having a relatively strong discontinuity with the generation site of the Kirkendall void. If they are coincident or very close to each other, peeling may occur.

In the present invention, even if the discontinuity exists, the risk of peeling is eliminated by adopting a structure that does not basically coincide with the site where the Kirkendall void is generated. This is based on the thickness of the tin-plated film formed on the copper surface and the degree of thermal history applied thereafter, and the generation site of Kirkendall void is estimated, and the discontinuity between this generation site and the copper plating layer, that is, the laminated interface is the same. This is done by controlling the copper plating layer thickness.
Specifically, it is performed by adjusting the electrodeposition time in the corresponding electrolytic cell, for example, the distance between the cathodes or the cathode current density. Here, when the thickness of the tin plating film formed on the copper surface is t, the heat treatment usually applied in the COF processing step is 120 ° C. for 30 to 60 minutes for tin plating whisker growth suppression. Heat treatment, 120 ° C. for solder resist curing, 2-3 hours heat treatment, 420 ° C. applied during IC bonding to COF, heat treatment for about 1-5 seconds, 150 ° C. for IC sealing resin curing, 3 The location of the Kirkendall void generated by heat treatment for ˜4 hours and heat treatment for about 1 minute at 200 ° C. for outer lead bonding to the liquid crystal panel is approximately from the surface of the copper coating immediately before the tin plating is formed. It corresponds to the position of depth 2t. Therefore, in order to avoid the encounter between the Kirkendall void generation position and the discontinuous interface position between the copper plating layers, the region from the copper plating surface layer to at least a depth of 3 t is taken into consideration when the variation of the thermal history and the variation due to the difference are taken into account. It is necessary to adjust so that there is no plating interface.
Of course, when the desired copper plating thickness is obtained in a single electrolytic cell, the above-mentioned peeling problem is solved, but when a copper coating is formed on a sputter coating by electroplating as in the present invention, it is usually Since the sputter coating is very thin, 0.1 to 0.5 μm, it is impossible to supply a large amount of current at the initial stage of plating, so it is difficult to ensure a long distance between the cathodes. A general method is to provide, that is, to perform plating while maintaining an appropriate distance between the electrodes.

Next, the form and manufacturing method of the metal-coated polyimide substrate according to the present invention will be described.
FIG. 1 is a schematic sectional view showing an embodiment of the metal-coated polyimide substrate of the present invention.
That is, the metal-coated polyimide substrate of the present invention is nickel-chromium formed by sputtering between a copper film 4 having a laminated structure in which a plating layer is continuously formed using a polyimide film 1 and a plurality of electrolytic baths. An alloy layer 2 and a copper layer 3 are provided.
The polyimide film 1 used in the present invention generally has a thickness of 25 to 50 μm, more preferably 30 to 40 μm, when viewed as a COF material, which is a mounting method for a liquid crystal display driver IC. For example, Kapton 150EN (made by Toray DuPont), Upilex 35 _S (made by Ube Industries), etc. are suitable.

  The metal layer formed by sputtering on the polyimide film surface is generally a nickel-chromium alloy layer 2 as a metal layer directly formed on the polyimide film. The first metal layer is assumed to play a role of ensuring the adhesion strength between the polyimide film and the metal layer, and its heat resistance and stability in a humidity resistant environment. The alloy composition and thickness of the nickel-chromium alloy layer 2 are closely related to the above characteristics, and in the case where an electronic circuit is formed by etching a metal layer such as COF, etching with copper which is a good conductor. However, it is inconvenient if the composition and thickness are significantly different. Therefore, the chromium concentration in the alloy layer is preferably 5 to 30%, and the thickness of the alloy layer is preferably 5 nm to 50 nm.

  After the first metal layer is formed by sputtering, before the electroplating is performed, a technique of subsequently forming the copper layer 3 by sputtering is used to ensure the conductivity of the sputtered layer. This copper layer 3 is formed in order to impart conductivity to the sputtered layer in order to perform deposition by electroplating uniformly and smoothly, and its thickness is generally 50 to 500 nm. That is, when the thickness is less than 50 nm, sufficient conductivity cannot be obtained, which may adversely affect the copper deposition uniformity by subsequent electroplating. On the other hand, when the thickness exceeds 500 nm, the conductivity is reduced. Although it is more convenient in terms of application, it is because there is a concern about adverse effects on the product obtained such as COF due to the influence of dimensional change, deformation, etc. of the substrate due to the increase of thermal history strength to the polyimide film by sputtering.

  After the sputtering treatment, the electrolytic copper plating layer 4 having a laminated structure is continuously formed on the surface of the sputter coating using a plurality of electrolytic baths. In that case, the configuration of the plating apparatus in which the electrolytic cell, the power feeding mechanism, the substrate transport mechanism, etc. are combined is not particularly limited. In general, the amount of energization is controlled for each electrolytic cell, and the conductor layer is generally a layer to be plated. In the initial stage where the thickness is thin, the energization amount is small, and the energization amount is set to increase in accordance with the electroplating sequence. In each plating tank, anodes for performing electroplating are usually arranged on both the carry-in side and the carry-out side of the object to be plated. On the other hand, there is a mechanism for supplying power to the plating film between the electrolyzers, which has a structure in which the plating surface is in contact with, for example, a stainless steel roller having excellent corrosion resistance, and power is supplied to the plating surface via the roller. Supply structure is taken. In addition, since the substrate of the power feeding mechanism is exposed to the atmosphere between the electrolytic layers, it is desirable that the plating surface be covered with an appropriate electrolyte, for example, a plating solution diluted with water. This is because the degree of discontinuity of the plating crystal growth present at the interface of the laminated structure is affected by the situation where the substrate is exposed to the atmosphere.

Although it does not specifically limit as a plating solution used by this invention, The so-called copper sulfate plating bath which has a sulfuric acid and copper as a main component is common, In this invention, sulfuric acid 180g / L, copper sulfate 80g / L, chloride ion 50mg. / L, and a solution to which an appropriate amount of an additive for obtaining the surface smoothness and electrodeposition stress relaxation property of the copper plating film is added can be used.
The anode used in the present invention is preferably made of phosphorous copper when a copper sulfate plating bath is used. Moreover, as a power feeding mechanism used in the present invention, for example, a method in which a plating surface is brought into contact with a stainless steel roller is adopted, and drying of the plating surface is suppressed by spraying ion exchange water on the plating surface before contact. .

The copper plating thickness formed in the present invention is generally a total thickness of 8 μm for COF applications, and the tin plating thickness formed on the copper surface is generally 0.6 μm. Therefore, in this invention, what is necessary is just to set it as the structure plated by the one electrolytic vessel at least 1.8 micrometers area | region from a copper plating surface layer. In order to secure a copper plating layer thickness of 1.8 μm or more, the substrate transport speed, that is, the electrolysis time in the electrolytic cell, the distance between the electrodes, and the amount of current supplied to the plating surface is obtained from the substrate width. be able to. In addition, before activating the electroless tin plating, if the copper surface is activated or partly etched to remove adhering foreign matter, the thickness of the etched structure is taken into consideration and the copper layer thickness of the laminated structure is adjusted. There is a need.
In the present invention, when a tin layer is formed on the copper surface, it can be performed by an electroless plating method, and a general fluorination bath can be used as the electroless plating solution. For example, Rim & Haas Tinposit LT-34 is used. In addition, when heat treatment at about 120 ° C. or higher, such as heat treatment for suppressing tin whisker growth, is performed after electroless tin plating, the peeling prevention effect according to the present invention is more exhibited.

[Example]
Hereinafter, the effectiveness of the present invention will be described with reference to examples, but the present invention is not limited thereto.

  Kapton 150EN (manufactured by Toray DuPont) was used as a polyimide film, and heat treatment was performed at 150 ° C. for 1 minute in a chamber maintained at a vacuum degree of 0.01 to 0.1 Pa. Subsequently, a nickel-chromium alloy target containing 20% by weight of chromium and a copper target were used to form a nickel-chromium alloy layer having a thickness of 20 nm and a copper layer having a thickness of 100 nm on the polyimide film surface. After that, 18 electrolytic tanks with a power feeding mechanism with stainless steel rollers between the electrolytic tanks, and sputtering surface activation treatment, plating surface water washing, and rust prevention treatment were arranged before and after the electrolytic cell rows in the horizontal direction. The thickness of the copper plating layer plated in each electrolytic bath was adjusted using an electrolytic copper plating line having a transport mechanism by a held roller to form a copper plating film having a total plating layer thickness of 8.1 μm. The copper plating film is shown in Table 1.

Next, using the metal-coated polyimide substrate having the copper plating film shown in Table 1, the copper plating surface activation treatment was performed by etching away 0.5 μm thick copper from the plating surface layer, and then the copper surface. Then, an etching resist layer was formed by photolithography, the exposed copper layer was dissolved and removed, and the etching resist layer was peeled off to form a circuit having inner lead portions of 35 μm pitch. Subsequently, an electroless tin plating solution (Tinposit LT-34) manufactured by Rohm and Haas was used to form a tin plating film having a thickness of 0.6 μm on the circuit surface, and heat treatment was performed at 120 ° C. for 30 minutes. Thereafter, a solder resist film was formed on a desired portion other than the inner lead portion and the outer lead portion, and a heat treatment was performed at 120 ° C. for 2 hours to obtain a COF having an inner lead portion of 35 μm pitch. The obtained COF inner lead portion and a predetermined pad portion of the IC are bonded by pressure bonding at 420 ° C. for 0.3 seconds, and then a sealing resin is applied to the IC and a desired portion around it, and 150 ° C. For 3.5 hours.
After the above treatment, the COF and the periphery of the sealing resin were observed with a microscope, but no peeling between the tin plating film and the solder resist or the tin plating film having the sealing resin formed on the surface and the circuit part was observed. It was.

In Example 1, the current in the electrolytic cell was adjusted so that the copper plating had the laminated structure shown in Table 2, a copper plating film having a total plating layer thickness of 8.1 μm was formed, and the activation process of the copper plating film was performed. A COF was produced in the same manner as in Example 1 except that it was not performed, and an IC was bonded to the obtained COF and sealed with resin.
After the above treatment, the COF and the peripheral portion of the sealing resin were observed with a microscope. In this example, the tin plating film, the solder resist, or the tin plating film having the sealing resin formed on the surface and the circuit portion No peeling was observed.

In Example 1, a COF was produced in the same manner as in Example 1 except that the current in the electrolytic cell was adjusted so that the copper plating had a laminated structure shown in Table 3 and a copper plating film having a total thickness of 8.1 μm was formed. Then, an IC was bonded to the obtained COF and sealed with resin.
After the above treatment, the COF and the peripheral portion of the sealing resin were observed with a microscope. In this example, the tin plating film, the solder resist, or the tin plating film having the sealing resin formed on the surface and the circuit portion No peeling was observed.

In Example 1, COF was produced in the same manner as in Example 1 except that the current in the electrolytic cell was adjusted so that the copper plating had a laminated structure shown in Table 4 and a copper plating film having a total thickness of 8.1 μm was formed. Then, an IC was bonded to the obtained COF and sealed with resin.
After the above treatment, the COF and the peripheral portion of the sealing resin were observed with a microscope. In this example, the tin plating film, the solder resist, or the tin plating film having the sealing resin formed on the surface and the circuit portion No peeling was observed.

〔比較例１〕

[Comparative Example 1]

In Example 1, COF was produced in the same manner as in Example 1 except that the current in the electrolytic cell was adjusted so that the copper plating had the laminated structure shown in Table 5 and a copper plating film having a total thickness of 8.1 μm was formed. Then, an IC was bonded to the obtained COF and sealed with resin.
After the above treatment, the COF and the periphery of the sealing resin were observed with a microscope. As a result, it was found that the tin plating film was peeled off with a size of 10 μm × 10 μm, and the reliability as an electronic component was lacking. It was.

  The metal-coated polyimide substrate obtained by the present invention can prevent the peeling of the tin-plated film from the circuit portion even through the thermal history applied in the assembly process of the COF and IC obtained using this, Sufficient insulation reliability. In addition, since it is not necessary to form a dissimilar metal layer such as nickel on the circuit surface and the tin plating film interface in order to eliminate the problem of peeling, the metal-coated polyimide substrate obtained by the present invention is an electronic component such as COF. This makes it possible to realize a higher density and to supply products economically.

It is a schematic sectional drawing which shows one Example of the metal-coated polyimide board | substrate of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Polyimide film 2 Nickel-chromium alloy layer 3 Copper layer by spattering 4 Electrolytic copper plating layer of laminated structure

Claims (2)

  A metal-coated polyimide substrate in which a copper plating film is applied to a surface of a metal layer formed by a sputtering method on a polyimide film surface, and a tin plating film is further applied to the surface of the copper plating film, A metal-coated polyimide substrate in which electrolytic copper plating is performed in the same electrolytic cell in a region from the copper plating surface layer to at least a depth of 3 t when tin plating having a film thickness t is applied to the surface of the copper plating film. After a metal layer is formed on the polyimide film surface by sputtering, a copper plating film is formed by continuously performing electroplating using a plurality of electrolytic baths, and tin plating with a film thickness t is further formed on the surface of the copper plating film. In the tin plating method using a metal-coated polyimide substrate to be applied, when performing tin plating with a film thickness t on the surface of the copper plating film, electrolytic copper plating is performed in the same electrolytic cell in a region from the copper plating surface layer to a depth of 3 t. A tin plating method using a metal-coated polyimide substrate, characterized by applying a heat treatment at 120 ° C. or higher after tin plating.

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