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 Posted: Sun Jun 22, 2026 11:22 pm Post subject: |
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Reposted from SFE's old Assembly Forum
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Date: 20 Feb 2026
Time: 01:52:53
Remote Name: 137.71.23.54
Remote User:
Hello Sudha Rao,
Selecting the right bondwire for semiconductor assembly, or any material for that matter, is always a balancing act between cost and the quality/reliability objectives of your organization. Cost can not be ignored-many a companies have folded up because they could not compete in terms of cost. Thus, in the real world out there, the role of the process engineer is to select the cheapest wire that meets the minimum desired quality/reliability level.
Anyway, your first decision to make is to choose what package you want to assemble in. If you will use a hermetic package, then you can't use gold wire because it won't be able to withstand the high temperature of hermetic sealing. You'll have to use aluminum wire for hermetic assembly. If you intend to assemble plastic packages, then gold wire should be your choice because it is faster, more manufacturable, and therefore more cost-effective.
Your next consideration after this is the diameter of your wire. If you intend to use it on dice that have small bond pads, then you may have to go with thinner wires, e.g., 1-mil wire. If your dice have large bond pads (say, 4 mils by 4 mils), then larger (1.3-mil) wires might be better, because they can carry more current and will be more robust against thermomechanical stresses.
Your next consideration would be the tensile strength of the wire. The wire will be subjected to a lot of tensile stresses throughout its lifetime, e.g., during bonding itself, during encapsulation, during board mounting, during usage. Needless to say, the higher the tensile strength the better. The wire manufacturer should have this info for you.
The next consideration is the elongation property of your wire. Wires with higher elongation are more difficult to control during loop formation at wirebonding. Thus, it is better to choose a wire that doesn't elongate much during the bonding process.
The last major consideration is the length of the heat-affected zone of your wire. When the end of the wire is melted by flame-off to form the free air ball prior to bonding, the high temperature enlarges the grain structures of the zone closest to the ball. These larger grain structures are more vulnerable to shearing stresses that cut across the wires. Wires with a longer heat-affected zone can not be used in low-loop wirebonding because the heat affected zone may be subjected to the shearing stresses of loop formation. Normally the wire manufacturer will indicate whether the wire is for low-loop or for high-loop applications.
Thanks for your interest and keep on posting!
Best regards,
EE
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