JP2000173364A - Tin plating applied flat conductor and flat cable using same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent generation of whisker without adding lead by applying tin plating having a crystallization particles whose a ratio between a large diameter and a short diameter is a specified value or more. SOLUTION: A flat conductor formed by the application of tin plating onto a round copper wire and then by being rolled is brought into contact with roller shaped electrodes while it is fed from one end and taken up to the other end, and between the electrodes thermal treatment to make a specified current flow into the conductor is conducted. Concretely, e.g. in the case of a distance between the electrodes 30 cm, the taking-up speed of flat conductor 60 m/min., a current flowing between the electrodes 15A, water cooling of about 500 mm until the conductor is taken up after passing through the electrodes, and subsequent water cooling of about 2 m, the tin plating layer becomes the metal layer having a ratio of 3 or more between the long diameter and the short diameter and crystallization particles whose long diameter is 10 m or more. When a flat cable of about 0.5 mm pitch is produced by using this flat conductor, no whisker is generated, resulting in that it can be used for high density wiring of electronic equipment.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flat cable used in the field of electronic equipment and a flat conductor used for the flat cable.

[0002]

2. Description of the Related Art Along with miniaturization and weight reduction of a video, a printer, and the like, a flat cable having an excellent space factor has been widely used. The flat cable has a structure in which a plurality of flat conductors are sandwiched between insulator films in a sandwich shape. Due to the demand for high-density wiring, the pitch between the flat conductors is as small as 0.5 mm or less. Are also used.

[0003]

The flat conductor is required to be hardly corroded and to have good solderability.
Therefore, tin plating is applied. However, in the case of the narrow pitch as described above, there is a fear that a short circuit between adjacent conductors occurs due to generation of a whisker-like crystal called a whisker by tin plating. It is well known that lead is added to tin to prevent whiskers. However, lead is highly toxic, and adding lead is not desirable in terms of environmental measures. Must be prevented.

[0004]

Means for Solving the Problems The present inventors have studied variously the above problems. Then, it was found that if the metal structure of tin plating is a specific structure, that is, a structure having crystal grains having a ratio of major axis / minor axis of 3 or more, it is effective in preventing whiskers without adding lead. The present invention has been completed.

[0005]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to embodiments. After performing tin plating by electroplating on a round copper wire, it is drawn and rolled to obtain a width of 0.3 mm and a thickness of 35 μm.
m, a flat conductor having a tin plating thickness of 1 μm was prepared. Using this conductor as it was, a flat cable of 0.5 mm pitch was produced, and the observation near the conductor was continued.
One week later, whiskers were observed.

Next, this flat conductor is supplied from one end,
While the film was wound around the other end, it was brought into contact with a pair of roller-shaped electrodes, and heat treatment was performed in which a predetermined current was applied to the conductor between the roller-shaped electrodes. At a distance of 30 cm between the roller-shaped electrodes and a winding speed of the flat conductor of 60 m / min, the current flowing between the roller-shaped electrodes was set at 15 A. ,continue,
As a result of air cooling of about 2 m, the tin-plated layer became a metal layer containing crystal grains having a major axis / minor axis ratio of 3 or more and a major axis of 10 μm or more, as shown in FIG.

The thus obtained tin-plated flat conductor having crystal grains having a ratio of major axis / minor axis of 3 or more, having a length of 0.5 m
An m-pitch flat cable was produced. Then, as in the case where the conductor without heat treatment was used, observation near the conductor was continued, but no whisker was observed.

[0008]

As described in the description of the embodiments, a tin-plated flat conductor having crystal grains having a major axis / minor axis ratio of 3 or more, even though there is no addition of lead to tin. No whiskers were found. Therefore, when used in a flat cable, there is no problem of whiskers being generated, and it means that a flat conductor having no environmental problems has been obtained. This can be used for high-density wiring of electronic devices.

[Brief description of the drawings]

FIG. 1 is an enlarged view of a crystal grain in a tin plating layer of the present invention.

Claims (2)

[Claims] 1. A tin-plated flat-type conductor, which is plated with tin having crystal grains having a ratio of major axis / minor axis of 3 or more. 2. A flat cable using the conductor according to claim 1.