Page 262 - Fiber Fracture

FRACTURE OF SUPERFINE METALLIC WIRES 245

Fig. 3. Use of superfine wire in the fields of precision equipment and semiconductors. Left: bonding wire.
Right: magnet wire for wristwatch (courtesy of SEIKO Corp.)

electronic components and electrode wires for electrical-discharge processing (Fig. 3).
Recently, the precision of electronic equipment, wearable equipment, micromachines,
precision equipment and precision printing machines has been improved significantly,
thus the development of superfine wires is greatly anticipated in a wide range of
industrial fields.
However, a number of problems exist in the drawing of fine wires, such as the
occurrence of wire breaks due to the presence of inclusions during the drawing process,
leading to low productivity and high production cost.

Product Price and Quality Required for Superfine Wires

Processing superfine wires requires a large number of passes (drawings) and inter-
mediate softening heat treatments; however, in rare cases, the breakage of wires occurs,
resulting in high processing costs. In particular, for wires with diameters of 0.1 mm
or less, the product price increases exponentially with the decrease of wire diameter
(Yoshida, 2000a).
The quality required for wires may differ depending, to some extent, on their
use; however, the following main characteristics are required: (1) high accuracy of
dimensions (uniformity of diameter and circularity); (2) good mechanical properties
(proof stress, strength, elongation and torsion strength); (3) good electrical properties;
(4) lustrous surface of wires without flaws; (5) good rewinding performance (little wire
deformation) from a spool.

BACKGROUND OF RESEARCH ON WIRE BREAKAGE AND INTERNAL
FRACTURE

There are two methods of manufacturing extrafine wires: one is to use a wire rod as
the raw material and repeatedly subject the wire rod to wiredrawing and heat treatment,