JPS6380412A - Cu based substrate for electric circuit board and manufacture thereof - Google Patents

Abstract

(57) [Abstract] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a Cu-based substrate for conductive circuits used in electric circuit boards, and particularly to a Cu-based substrate used for printed circuits, tape carriers, busbars for wired circuits, etc. It is.

[Conventional technology]

A large amount of Cu foil with a thickness of about 7 to 70 μm is used in printed circuits, which have been in increasing demand in the electronics field in recent years. In addition to electrolytic Cu foil, rolled Cu foil with excellent surface quality has recently been used as the above-mentioned Cu foil. After these Cu foils are bonded to one or both sides of an insulating plate,
A desired circuit is formed by etching. In addition to the pure Cu foil, the rolled Cu foil may also contain Ag, Ag, or Ag to improve heat resistance within a range that does not reduce the electrical conductivity.
A Cu alloy foil to which P%Fe, Cd, etc. are added is also used.

In addition to rigid boards, flexible boards are also widely used as printed circuit boards, and one type of flexible circuit board is a tape carrier for semiconductor chip mounting, TAB (Tape-AutomatedBon).
ding) tape etc. are used.

Further, in fuse boxes and joint boxes used for wiring inside automobiles and various devices, busbar-shaped circuits formed by punching or the like from Cu or Cu alloy plates are wired in multiple layers via insulating plates. Although the width and thickness of this circuit are larger than those of the printed circuit, it can be considered to have a similar structure as an electric circuit board.

Recently, as electronic devices have become smaller, more dense, and more multifunctional,
There is a strong demand for higher density electrical circuit boards, and surface mounting, which allows small chip components to be mounted at high density, is becoming more widely used in printed circuit boards.

[Problem that the invention seeks to solve]

With the increase in the density of circuit boards such as the aforementioned printed circuit boards, the circuit space, which is the gap between conductors, has become 05 to 805 cm or more, and this trend is particularly noticeable in multilayer printed circuit boards and tape carriers. is remarkable.

When the circuit space is reduced in this way, Cu migration (dendritic growth occurring from the cathode side toward the anode) tends to occur, which causes a decrease in insulation, generation of leakage current, short circuit, etc. That is, although the migration depends on environmental conditions such as moisture and contaminants in the outside air, it is mainly caused by the potential difference within the circuit, and thus migration becomes more likely to occur as the density increases.

Another problem associated with higher density circuit boards is a decrease in solder joint strength. That is, as the density increases, the solder joint area decreases, resulting in a decrease in the above-mentioned joint strength, and this tendency is particularly severe in surface mounting, which has been widely adopted as an alternative to conventional hole mounting.

Further, Cu and solder (Sn--Pb alloy) undergo a diffusion reaction over time to generate a brittle intermetallic compound phase of Cu--Sn, thereby reducing the bonding strength.

The above-mentioned problems have a serious effect on the reliability of electronic equipment, and there is a strong demand for the development of base materials for circuit boards that can solve these problems.

[Means for solving problems]

The present invention was obtained as a result of intensive research to solve these problems, and provides an electric circuit characterized in that a Zn or Zn alloy layer is provided on a small portion of the surface of a Cu base material. This is a method for producing a Cu-based substrate for an electric circuit board, characterized in that the Cu-based substrate for use as well as the Cu-based substrate described above is subjected to a heat-diffusion treatment.

[For production]

The Cu-based base material according to the present invention maintains high conductivity by containing a high concentration of Zn in a small portion of the surface, and improves various properties that were problematic with conventional Cu-based base materials. It is possible to do so.

That is, it is thought that Zn is a metal less noble than Cu and has high diffusivity, which solves the problems that conventional Cu-based base materials have. First, regarding Cu migration, the above phenomenon is an electrochemical phenomenon consisting of Cu anodic elution, iontophoresis, and cand precipitation.
Zn is effective in suppressing anode elution of Cu.

Further, the coexistence of Zn is effective in suppressing the formation of a brittle layer due to diffusion reaction at the solder interface.

In the present invention, the Zn or Zn alloy layer must be present on at least a part of the surface of the Cu base material, and in the case of foil, it must be present on at least one side (in the case of a printed circuit board, the side exposed to the surface). It is necessary.

In addition to pure Cu, the Cu-based base material in the present invention includes Cu-A
g.

Cu-P, Cu-Fe, Cu-Mg, Cu-T
h, is a Cu alloy such as Cu-Zr, and the Zn or Z feeding layer is not only Zn and Cu-Zn but also Cu-Zn-3n,
Zn-8n, Zn-N1, Zn-Ag%Zn-C
d1Zn-Cd-Cu, etc. These Zn or Zn
The thickness of the alloy layer is preferably 0.1 to 10 μm, and a particularly desirable Zn or Zn alloy layer has a Zn content of 1 to 60%.
The above particularly desirable Zn or Zn alloy layer is obtained by providing a Zn or Zn alloy layer on at least a part of the surface of a Cu base material having a Zn or Zn alloy layer on the surface, and subjecting the base material to a heat diffusion treatment. It can be obtained by diffusing Zn. In addition, it is possible to perform processing such as rolling before and after the heat diffusion treatment to make the surface smooth and to have desired dimensions. The method for forming this Zn or Zn alloy layer is arbitrary, and any of plating, vapor deposition, sputtering, thermal spraying, cladding, composite casting, etc. may be used.

Next, the reasons for limitations in claims 2 to 4 of the present invention will be explained. First, Zn or Z on the surface
The thickness of the n-alloy layer is preferably 0.1 to 10 μm. The reason for this is that if α is less than 1 μm, it is difficult to obtain the above-mentioned Zn effect in practice, and if it exceeds 10 μm, the conductivity may be poor, although it depends on the application and dimensions. This is because the performance may be lowered and the practicality may be lower.

Second, the Zn or Zn alloy has a Zn content of 1 to 6
The reason why 0% Cu-Zn alloy is most useful is as follows. (1) Pure Zni is easily corroded and has poor solder wettability, which is disadvantageous for mounting work on printed circuit boards.

(2) Considering the characteristics of the base material, productivity, economic efficiency, etc.
The most useful alloy is Ou-Zn alloy. Furthermore, since the Cu--Zn alloy is more difficult to oxidize than Cu, it is also advantageous in that there is less oxidative discoloration during the heating process. (3) Cu
- In the Zn alloy, if the amount of Zn is less than 1%, it is difficult to obtain the effect of Zn, and if the amount of Zni exceeds 60%, the solder wettability is deteriorated.

Thirdly, in the present invention, a Cu--Zn alloy layer having a concentration distribution in which the amount of Zn decreases from the surface toward the inside is particularly desirable for the following reason. (1) The effect of the present invention can be maximized with a small amount of Zn, thus minimizing the decrease in conductivity. (2) Efficiently coating a small amount of Zn to coat Cu
Since it can be manufactured by diffusing it into the inside, it is also excellent in productivity. (3) Since the surface side with a high Zn concentration is base, corrosion progresses evenly and is particularly effective in preventing migration.

Fourthly, in the Cu-Zn alloy layer having the above concentration distribution, the thickness of the Zn content of 1% or more is 1 μm or more.
This is because if the thickness is less than μm, it is difficult to practically obtain the effect of Zn.

[Example 1] The present invention will be explained in more detail below with reference to Examples.

The first layer was applied to both surfaces of the tough pitch copper rolled copper foil with a thickness of 55 μm.
The Zn and Zn alloy layers shown in Table 2 were provided by plating under the plating conditions shown in the table. That is, Zn plating is Zn (ON
) l bath, Cu-Zn alloy was prepared using CuCN and Zn (
ON).

The test was carried out using a mixed bath.

Table 1 Table 2 Next, these copper foils were clad with a glass epoxy plate, and the wetted area and solder joint strength during soldering were determined by the methods described below, as well as the leakage current was measured.

, (A) After coating with preflux (Tamura Kaken/Solderite BIIIR), 85°C x 85% R
After being kept in a constant temperature and humidity chamber of I asked for

(B) A lead wire was soldered to a 3×5 mm portion, and after aging at 120° C. for 1000 hours, a tensile test was conducted to determine the solder joint strength.

(C) A circuit with LO ■ intervals was formed by etching, and after applying 25 V (DC) and maintaining it in a constant temperature and humidity chamber at 85° C. and 85% RH for 168 hr, leakage current was measured.

The above results are summarized in Table 2. Invention example Nal~
No. 5 should satisfy all properties such as solder wettability, solder joint strength, and leakage current, but conventional example N11ll has poor solder joint strength, Cu migration tends to occur, and leakage current increases. There is. Mata Z
Comparative example Nl112 in which the thickness of the n alloy layer is less than 01 μm is
Under these test conditions, no sufficient improvement was observed in terms of solder joint strength, leakage current, etc. In addition, the present invention example Nll~5
NULL, 2 where the Zn or Zn alloy layer is pure Zn
The solder wettability is inferior to NCL3-5 which are Zn alloys.

[Example 2] Zn layers were provided on both surfaces of a Cu-0.05%Ag alloy plate with a thickness of 012 mm by plating, followed by heat diffusion treatment, and then rolled to a thickness of 55 μm. Regarding the above copper alloy foil, the surface and 1
The Zn concentration at a depth of μm was analyzed and the electrical conductivity was measured. Furthermore, these copper alloy foils were clad with a glass epoxy plate, and in the same manner as described in Example 1, the wetted area and solder joint strength during soldering were determined, and the leakage current was also measured. These results are summarized in Table 3.

As is clear from Table 3, Examples 6 to 8 of the present invention have satisfactory characteristics in terms of electrical conductivity, solder wettability, solder joint strength, leakage current, etc. Na6, Sui7
Although the coating amounts of Zn are similar to those of N11L1 and No. 2, respectively, better properties are obtained in terms of wetted area and the like. In addition, Comparative Example Nα13 had an insufficient amount of Zn, with a thickness of 1 μm.
Since the depth is only about α1%, no sufficient improvement is observed in terms of solder joint strength, leakage current, etc. under the present test conditions.

〔Effect of the invention〕

The present invention greatly improves the properties of the base material for electric circuit boards, and provides an improved circuit board that is indispensable for meeting the strong demands for smaller size, higher density, and improved reliability for electronic devices. is realized. The Cu-based base material according to the present invention can be expected to be used in a wide range of applications such as tape carriers and busbars for wiring circuits, as well as various printed circuit boards, and has a remarkable industrial effect.

Claims (5)

[Claims] (1) A Cu base material for an electric circuit board, characterized in that a Zn or Zn alloy layer is provided on at least a common portion of the surface of the Cu base material. (2) The Cu base material for an electric circuit board according to claim 1, wherein the Zn or Zn alloy layer has a thickness of 0.1 to 10 μm. (3) The Cu base material for an electric circuit board according to claim 1, wherein the Zn alloy is a Cu-Zn alloy with a Zn content of 1 to 60%. (4) An electric circuit board according to claim 3, characterized in that the Zn concentration has a distribution that decreases from the surface toward the inside, and the thickness of the Zn content of 1% or more is at least 1 μm or more. Cu base material. (5) A method for manufacturing a Cu base material for an electric circuit board, which comprises providing a Zn or Zn alloy layer on a small portion of the surface of the Cu base material, and subjecting the base material to a heat diffusion treatment.