Page 79 - Wire Bonding in Microelectronics

58 Cha pte r T h ree

22
20
18 Actual
Breaking strength (g) → 14 Composite
16

12
10
8
6
?
4
2
0
0 1 2 3 4 5 6
Elongation (%) →

FIGURE 3-5 The breaking strength versus elongation for 25 µm (1 mil) diameter
1% Si Al wire. There may be variation in elongation in the intermediate range
which results in drift of that parameter during aging, as shown in Fig. 3-3 [3-1].

An annealing curve for Al, 1% Si, 25 µm (1 mil) diameter wire is
given in Fig. 3-5 [3-1]. The small-diameter silicon-doped wire is quite
different from the large wire. The exact shape of such curves for this
type of wire will vary with annealing temperature, cooling time, and
the individual manufacturer’s process. In some cases, the changes
(swings) in elongation of the wire can be several times larger than
shown in Fig. 3-5. The explanation for these elongation swings is
related to crystallographic structural change of the wire’s fiber axis
from <110>, as drawn, to <111>, during recrystallization (heat treat-
ment). Details of such crystallographic behavior is beyond the scope
of this book,∗ and the reader is referred to other general metallurgy
books [3-2] for a more complete understanding.

3.4 General Discussion of Gold Bonding Wire
Small-diameter gold bonding wires for ball bonding come in two
distinctly different types. The first was originally used for manual
wire bonders. Its breaking load is in the range of 6 to 8 g, annealed,

∗See for instance, Understanding Materials Science: History, Properties, Applications
(Hardcover), by Rolf E. Hummel Springer-Verlag; 2d ed. (May 1998). Also see,
Fundamentals of Materials Science and Engineering: An Integrated Approach, 3d ed.
William D. Callister, Jr. and David G. Rethwisch, December 2007. For data, formulas,
etc. see CRC Materials Science and Engineering Handbook, by J. F. Shackelford and
W. Alexander (eds), 3d ed., 2001.