Page 97 - Wire Bonding in Microelectronics

76 Cha pte r T h ree

FIGURE 3B-2 A temperature cycled Cu ball bond (encapsulated) that developed
a neck crack.

There are however manufacturing facilities that currently manu-
facture copper wire products but mostly limited to power devices
where large diameter wire is used.
Small-diameter wire (<33 µm) is still a challenge not because of
bonding capability but because of reliability concerns as indicated
above.

Conclusion
There is no question copper is a cheaper material but also one that
brings new challenges to the bonding engineers. It may also be a cost-
effective process in the eyes of a product manager but when the extra
care and attention is required, it is weighed against the existing gold
process and then we should ask ourselves, are the net savings
worth?

References
3-1 Douglas, P., Custom Chip Connection, private communication. For a discussion
of some small diameter bonding wire characteristics, see also, New Bonding
Wire Developments, Microelectronic Packaging Technology: Materials and
Processes, Proc. of the 2nd ASM International Electronic Materials and Processing
Congress, Philadelphia, PA, Apr. 24–28, 1989, pp. 8902–8908.
3-2 Jones, W. K., Liu, Y. and Morrone, A., “The Effect of Thermal Exposure on the
Structure and Mechanical Properties of Al-1% Si Bonding Wire,” Proc. of the
1993 International Symposium on Microelectronics (ISHM), Nov. 9–11, Dallas, TX,
1993, pp. 445–450.
3-3 U.S. Patent 3,272,625, Sept. 13, 1966. Beryllium-Gold Alloy and Article Made
Therefrom, Brenner, Bert, assigned to Sigmund Cohn Corp.
3-4 Ohno, Y., Ohzeki, Y., et, al. “Factors Governing The Loop Profile in Au Bonding
Wire.,” Proc. 1992 Electronic Components & Technology Conf., San Diego, CA,
May 18–20, 1992, pp. 899–902.
3-5 Hu, S. J., Lim, R. K. S., and Sow, G. Y., “Gold Wire Weakening in the Thermosonic
Bonding of the First Bond”, IEEE Trans. on CPMT-Part A, Vol. 18, Mar. 1995,
pp. 230–234.
3-6 Levine, L. and Sheaffer, M., “Wire Bonding Strategies To Meet Thin Packaging
Requirements,” Part 1,Solid State Technology, Vol. 36, Mar. 1993, pp. 63–70,
Part 2 is in July 1993, pp. 103–109.