JPH02225638A - Copper alloy rolled foil for flexible print - Google Patents

Abstract

PURPOSE:To manufacture the copper alloy rolled foil for a flexible print having excellent characteristics which is used to a wiring circuit such as a printed circuit by adding specified trace amounts of Fe, P and Zn to Cu, drastically reducing the contents of impurities such as S and O2 and rolling the alloy into the shape of thin foil. CONSTITUTION:A Cu alloy constituted of, by weight, 0.05 to 0.20% Fe, 0.02 to 0.05% P, >1.0 to 5.0% Zn and <10ppm S and having <=50ppm total content of other impurities and oxygen is refined. The molten metal of the Cu alloy is east in die to face the surface and back faces of the ingot, is thereafter hot-rolled and is water-cooled from >=600 deg.C. After removing the scales on the surface of the hot-rolled Cu alloy sheet material, cold rolling, process annealing, pickling and cold rolling are repeated to manufacture the Cu alloy foil having <=40mum thickness. The Cu alloy rolled foil for a flexible print having excellent whisker resistance at the time of Sn plating and having excellent heat resistance and electrical conductivity can be manufactured.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a rolled steel alloy foil for flexible printing, and in particular, for flexible printing used for wiring circuits such as printed circuits and tape carriers. This invention relates to copper alloy rolled foil. More specifically, the present invention relates to a rolled copper alloy foil for flexible printing that has excellent ultrafine workability, whisker resistance when coated with Sn plating, heat resistance, and electrical conductivity.

[Prior Art] Copper foil with a thickness of 5 to 40 μl is often used in electrical circuits such as printed circuits. Such copper foils include electrolytic steel foil and rolled copper foil.

Printed circuit boards can be made by cladding copper foil on a substrate made of glass epoxy or paper phenol, and then forming the desired circuit pattern using a resist etching method, or by laminating copper foil onto a film such as polyimide. There are also flexible circuit boards. Some of these are tape carriers, TAB (Tape Automated B
(onding) Used as a lead in mounting semiconductor chips. Rolled foil, which is superior in flexibility, is used for flexible circuit boards.

In recent years, with the miniaturization, higher density, and multifunctionality of electrical equipment, there has been a strong demand for higher density printed circuit boards, and for this reason, surface mounting methods that can mount small chip components at high density are gradually being adopted. I started.

Recently, the pitch distance of tape carriers and TAB leads has become closer to each other, with a pitch distance of 80 g or less.

[Problems to be Solved by the Invention] Tough pitch steel and oxygen-free steel are usually used as rolled foils, but when both are used as leads, the part to be bonded to an electronic device is coated with a 5μ thick Ni underplating. , and furthermore, a ^U eyepiece with a thickness of 1 μm is formed on it.

It was common knowledge that the above-mentioned base plating and Au plating were used for connection parts where the lead-to-lead pitch of wiring was as narrow as 80 μm.

Although Au plating on the old base plating is highly reliable, it is expensive, so attempts are being made to replace it with inexpensive Sn plating. However, in the case of Sn mesh, there is a problem in that short circuits between wirings occur due to the generation of whiskers in a short period of time. On the other hand, solder plating is being considered in place of Sn plating to prevent whiskers. However, this concept has not been put into practical use because solder plating causes problems such as poor solder adhesion.

The present invention relates to a copper alloy rolled foil, and instead of the conventional Cu rolled foil, the plating at the joint and its vicinity can be changed from two-layer plating of Ml plating and ^U plating to Sn plating or solder plating. Moreover, the Sn plating layer does not generate whiskers at all, and the base material does not soften even when heated at 280°C during solder bonding, making it possible to replace tin and solder! Jl growth does not occur even after holding at 150℃ x 10σOHr, and the foil has high strength and conductivity.Moreover, even when resist etching is performed at a pitch of about 80μ■ with a thickness of 5μm, it etches very cleanly as per the target. The purpose of the present invention is to provide a rolled copper alloy foil for flexible printing.

[Means for solving the problem] The gist of N1 of the present invention is %Fe: 0.05 to 0.201
(Same for weight and below), P: 0.02-0.201
, Zn:1. O ~ 5.0k (However!, excluding seagulls)
, 10 ppm or less of S, with the remainder consisting of Cu and impurities.

The second gist of the present invention is that Fa: 0.05 to 0.201
, P: 0.02-0.201, Zn: 1.0-5
．． 0X (excluding 1.0'4), 10p
Contains S of pm or less, and the total of impurities and oxygen is 50p
It exists in a copper alloy foil for flexible printing characterized in that the balance is Cu or less.

The third gist of the present invention is a claim characterized in that the thickness of the foil is 40 μm or less! Or it exists in the copper alloy rolled foil for flexible printing according to claim 2.

[Function] The effects and reasons for limitations of the contained elements of the present invention will be explained.

Zn suppresses the generation of whiskers in the SRAM material, improves the adhesion of Sn plating or solder plating, and increases electrical conductivity. For that purpose, it is necessary to contain more than 19 g of Zn. .

When zn is contained in an amount exceeding 1 zero, the formation of an intermetallic compound (Cu3Sn) phase that deteriorates adhesion can be suppressed, and Cu,
It is thought that the formation of Kirkendahloid on the base metal side of the Sn phase can be suppressed, and the adhesion can be improved.

In addition, a small amount of Zn diffuses into the Sn mesh and relieves the internal stress of Sn, which seems to suppress whisker growth.

However, if the Zn content exceeds 5 zero, although there is no problem with whisker resistance, disadvantages such as electrical conductivity becoming less than l1OkIAC5 and the tendency to cause stress corrosion cracking peculiar to brass will appear. , zn shall be 5 zero or less.

Next, the reason for setting the upper limit of the S content will be described.

In conventional copper alloys, S is mostly Cu in copper alloys.
It exists as S, and if Mn or Mg is contained as an inert substance, it exists as MnS. It has been found that all of them arrive in the middle of the grain, which causes problems during etching. In conventional copper alloys, in particular, 5
When the foil is ~40 μl thick, it repels the etching solution during resist etching, causing problems such as uneven etching.The present inventor investigated the cause of this problem. As a result, it was found that the cause of the problem was found in S. Therefore, to prevent problems from occurring,
Although it is desirable to completely remove S, it is difficult to avoid contamination from raw materials, furnace materials, coated charcoal, fuel, etc., and it is set at ID ppm or less.

Regarding oxygen and impurities, it has been found that if impurities exist in the form of oxides, microfabrication during etching will be inhibited in foils with a thickness of 5 to 40 μm, similar to the above S, It was determined that

S, oxygen, and impurities may appear on the surface of plates or strips with a thickness of 0.1 am or more, but due to the size and size of these compounds.
The number and amount is small, and there is usually no need to limit the amount mixed in, but when the foil is 5 to 40μ thick, pinholes occur during rolling, rolling breaks, and the aforementioned resist adhesion occurs. The inventor Hiroki is aware that defects, etching defects, etc. occur, and has set the above-mentioned upper limit.

Fe forms iron phosphide with P, and is an essential element for improving strength and preventing softening under temperature conditions for soldering. However, if it is less than 0.05 zero, P (content 0.02 to 0.G
Even if it is combined with a part of 50) to form iron phosphide, the effect of improving strength is not expected, and the Fa content is 0.15
When it exceeds 1, solid solution Fa that cannot form iron phosphide increases, which acts to lower the electrical conductivity. Therefore, the content of Fa is [1,05 to Q,15 zero.

P is an element that forms iron phosphide with Fe and contributes to improving strength and softening temperature, but when the content is 0.02, it is not enough to contribute to improving strength, etc. o, o
When sx is exceeded, solid solution P that cannot form iron phosphide increases,
It begins to reduce the conductivity. Therefore, the P content is 0
．． 02 to 0.05.

〔Example〕

Hereinafter, the present invention will be explained by examples.

Various alloys shown in Table 1 were melted in graphite pots and cast in molds. The front and back sides of the ingot were milled by 2.5mm each using machine machining to obtain 50s+a+t x 70mmw x 20(1+
u+Il, hot rolled to a thickness of 10 mm at a temperature of 900°C, water-cooled from a temperature of aOO°C or higher, and after removing scale, cold rolled to a thickness of 0.2 mm, then 500°C x I
First, intermediate annealing was performed on the foil, followed by careful pickling and repeated rough cold rolling to produce a foil with a thickness of 35 μm, and pinholes and rolling breaks were observed.

In addition, 5 μm and 65 μm thick seaweed foils were produced using the same procedure.

(Etching properties) On these foils, 50 resists were baked with a width of 100 μm, an interval of 80 μm, and a length of 20 μm, and chemical milling was performed with 40% ferric chloride solution to produce 50 wood leads. investigated.

(Extent of whisker generation) After electric field degreasing in alkaline, current density 3A/da in sulfuric acid.
', then apply Sn plating to a thickness of 1.5μ, and use epoxy resin adhesive to cover the side opposite to the Sn plating for 0.2m.
Approximately 4kg/l1m by pasting with a copper alloy plate and bending
After applying a compressive stress of 2 and leaving it at room temperature for 1 year, the presence or absence of whiskers was investigated.

(Softening properties, electrical conductivity) Regarding the softening properties, IHr in an electric furnace while covered with charcoal was used.
The temperature at which 60% of the tensile strength was maintained was determined.

The conductivity was based on JISHO5Q5.

The above test results are summarized in Table 1.

Alloys containing 1 to 5 Zn do not generate whiskers even when Sn plating is applied to the surface, and by controlling S, oxygen, and other impurities, the thickness can be reduced to 5.
Even in the case of ~40 .mu.l of foil, the defect rate after resist etching was good at 2 or less.

In particular, with other alloy foils, when the thickness becomes as thin as 5 to 40 microns, the etching performance decreases significantly, but with the alloy of the present invention, there is almost no decrease.

Further, the softening temperature is 2H° C. or higher even when heated by soldering or the like, and even when heated for 1 hr. In addition, tough pitch steel (No. 8) is also listed in the table as a conventional alloy.

[Effects of the Invention] According to the present invention, even if Sn plating is performed in place of the conventional Ni and U plating, no whiskers occur at all.

Furthermore, the yield after ultra-fine processing is also improved.

Furthermore, it has a tensile strength that is significantly superior to conventional materials.

As described above, the present invention has excellent properties as a copper alloy foil for flexible printing, and has excellent properties as a material for miniaturization, high-density packaging, and multifunctionalization of electronic devices. .

Claims (3)

[Claims] (1) Fe: 0.05-0.20% (same below weight%)
, P: 0.02-0.05%, Zn: 1.0-5.0%
A copper alloy foil for flexible printing, characterized in that it contains 10 ppm or less of S (excluding 1.0%), and the remainder consists of Cu and impurities. (2) Fe: 0.05-0.20%, P: 0.02-0
．． 05%, Zn: 1.0 to 5.0% (however, 1.0%
A copper alloy foil for flexible printing, characterized in that it contains S of 10 ppm or less, the total amount of impurities and oxygen is 50 ppm or less, and the balance is Cu. (3) The rolled copper alloy foil for flexible printing according to claim 1 or 2, wherein the thickness of the foil is 40 μm or less.