Background Information
In copper wire bonding (e.g., using the Kulicke & Soffa Copper Kit), forming gas (e.g., 5% Hydrogen/95%
Nitrogen) is typically used to facilitate the proper and robust wire bonding process and prevent oxidation of the
heated copper wire. Extensive experimentation and testing have shown that the small percentage of hydrogen
mixed with nitrogen performs better than pure nitrogen alone. This note is provided in response to customer
questions on the subject; however, it provides general guidance only. Before designing an actual production
environment for wire bonding using forming gas (e.g., copper wire bonding), appropriate environmental
engineers or other experts in air quality should be consulted.
Hydrogen is widely and safely used in many material and food processing applications. Mixtures of hydrogen
in nitrogen are generally non-flammable for hydrogen concentrations below 5.7%1. Nitrogen makes up
approximately 78%, by volume, of the earth’s atmosphere and is the largest component of breathable air.
The forming gas recommended for use with the K&S Copper Kit is a non-flammable mixture of 5+/-
0.5% Hydrogen and 95% Nitrogen. However, because the forming gas displaces air, considerations must be
given in both the use and handling of the forming gas mixture during facilities planning and on-going use.
In a normal set up for copper wire bonding, the forming gas dissipates from the wire bonder and mixes with
the air in the clean room. Since mixtures of hydrogen in nitrogen are generally considered to be nonflammable
for hydrogen concentrations below 5.7%1, this type of forming gas can generally be mixed in any
proportion with air without causing a fire hazard. However, a potential health hazard would occur if so much
air in the room is displaced with forming gas that there is not enough air left for occupants in the room to