Thermosonic Bonding
Encyclopedia
Thermosonic bonding is widely used to permanently interconnect metallized silicon integrated circuits (also known as the “chip”) and other components into computers as well as into a myriad of other electronic equipment.
Thermosonic bonding is generally used to form solid-state bonds well below the melting point of the mating metals such as gold wires to gold metallized pads deposited on silicon integrated circuits. It is formed by using a combination of heat, ultrasonic energy and pressure which is generally applied by a bonding tool. Since relatively low bonding parameters are required to form acceptable bonds, the integrity of devices, such as integrated circuits, are further assured throughout their intended lifetimes.
Thermocompression bonding: In the mid 1950s, solid state wire bonds were made using heat and pressure and was referred to as Thermocompression bonding. The process was generally limited to bonding pre-cleaned oxide-free gold-to-gold since the desired shearing action at the bonding interface was limited. Orson L. Anderson, a coauthor of the thermocompression bonding paper, later described the importance of interfacial shear in forming reliable solid-state bonds.
Ultrasonic bonding
: In the early 1960s commercial ultrasonic wire bonders were introduced which used vibratory energy and pressure to form solid-state bonds without a provision to add heat. The vibratory action enhanced the shearing action at the bonding interface which enhanced the reliability of forming gold-to-gold solid state bonds and also extended the range of mating metals to aluminum and copper.
THERMOSONIC BONDING: In the mid 1960s, Alexander Coucoulas reported the first Thermosonic wire bonds using a combination of heat, ultrasonic vibrations and pressure. He used a commercial ultrasonic wire bonder to investigate the attachment of aluminum wires to tantalum thin films deposited on glass substrates. He observed that the ultrasonic energy and pressures levels needed to sufficiently deform the wire and form the required contact areas significantly increased the incidences of cracks in the glass substrates. A means of heating the bond region was then added to the ultrasonic bonder. The bond region was then heated during the ultrasonic bonding cycle which virtually eliminated the glass failure mode since the required contact area was achieved with lower ultrasonic energy and pressure levels. The enhanced wire deformation during the ultrasonic bonding cycle was attributed to the transition from cold working (or strain hardening of the wire) to hot working where its softness was largely maintained due to the onset of recrystallization. Christian Hagar and George Harman stated that in 1970 Alexander Coucoulas, reported additional work in forming thermosonic-type bonds which he initially called hot work ultrasonic bonding. In this case, copper wires were bonded to palladium thin films deposited on aluminum oxide substrates.
At present, the majority of connections to integrated circuits are made using Thermosonic Bonding . Thermosonic bonding is the process of choice because it employs lower bonding temperatures, forces and dwell times than thermocompression bonding as well as lower vibratory energy levels than Ultrasonic bonding to form the required bond area and, therefore, eliminates damaging the relative fragile silicon integrated circuit “chip”. Such potential failure modes could be costly whether they occur during the manufacturing stage or later, during an operational failure in the field.
In summary, the use of the Thermosonic Bonding process, which was introduced by Alexander Coucoulas in the mid 1960's, has ensured the operational integrity of interconnected silicon integrated circuits which are used in computers and other solid-state electronic packages throughout the world.
https://sites.google.com/site/coucoulasthermosonicbondalta/
Coucoulas, A., “Hot Work Ultrasonic Bonding – A Method Of Facilitating Metal Flow By Restoration Processes”, Proc. 20th IEEE Electronic Components Conf. Washington, D.C., May 1970, pp. 549-556. (Thermosonic Bonding)
https://sites.google.com/site/hotworkultrasonicbonding/
Thermosonic bonding is generally used to form solid-state bonds well below the melting point of the mating metals such as gold wires to gold metallized pads deposited on silicon integrated circuits. It is formed by using a combination of heat, ultrasonic energy and pressure which is generally applied by a bonding tool. Since relatively low bonding parameters are required to form acceptable bonds, the integrity of devices, such as integrated circuits, are further assured throughout their intended lifetimes.
History
Three methods of solid state wire bonding were sequentially developed to improve the permanent interconnections between the silicon integrated circuits (ICs) to the outside circuitry.Thermocompression bonding: In the mid 1950s, solid state wire bonds were made using heat and pressure and was referred to as Thermocompression bonding. The process was generally limited to bonding pre-cleaned oxide-free gold-to-gold since the desired shearing action at the bonding interface was limited. Orson L. Anderson, a coauthor of the thermocompression bonding paper, later described the importance of interfacial shear in forming reliable solid-state bonds.
Ultrasonic bonding
Ultrasonic welding
Ultrasonic welding is an industrial technique whereby high-frequency ultrasonic acoustic vibrations are locally applied to workpieces being held together under pressure to create a solid-state weld. It is commonly used for plastics, and especially for joining dissimilar materials...
: In the early 1960s commercial ultrasonic wire bonders were introduced which used vibratory energy and pressure to form solid-state bonds without a provision to add heat. The vibratory action enhanced the shearing action at the bonding interface which enhanced the reliability of forming gold-to-gold solid state bonds and also extended the range of mating metals to aluminum and copper.
THERMOSONIC BONDING: In the mid 1960s, Alexander Coucoulas reported the first Thermosonic wire bonds using a combination of heat, ultrasonic vibrations and pressure. He used a commercial ultrasonic wire bonder to investigate the attachment of aluminum wires to tantalum thin films deposited on glass substrates. He observed that the ultrasonic energy and pressures levels needed to sufficiently deform the wire and form the required contact areas significantly increased the incidences of cracks in the glass substrates. A means of heating the bond region was then added to the ultrasonic bonder. The bond region was then heated during the ultrasonic bonding cycle which virtually eliminated the glass failure mode since the required contact area was achieved with lower ultrasonic energy and pressure levels. The enhanced wire deformation during the ultrasonic bonding cycle was attributed to the transition from cold working (or strain hardening of the wire) to hot working where its softness was largely maintained due to the onset of recrystallization. Christian Hagar and George Harman stated that in 1970 Alexander Coucoulas, reported additional work in forming thermosonic-type bonds which he initially called hot work ultrasonic bonding. In this case, copper wires were bonded to palladium thin films deposited on aluminum oxide substrates.
Summary
In the 1980s, commercial Thermosonic Bonders began to emerge for wire bonding to metallized silicon integrated circuits, flip chip-IC bonding as well for attaching many other components included in today's electronic packages.At present, the majority of connections to integrated circuits are made using Thermosonic Bonding . Thermosonic bonding is the process of choice because it employs lower bonding temperatures, forces and dwell times than thermocompression bonding as well as lower vibratory energy levels than Ultrasonic bonding to form the required bond area and, therefore, eliminates damaging the relative fragile silicon integrated circuit “chip”. Such potential failure modes could be costly whether they occur during the manufacturing stage or later, during an operational failure in the field.
In summary, the use of the Thermosonic Bonding process, which was introduced by Alexander Coucoulas in the mid 1960's, has ensured the operational integrity of interconnected silicon integrated circuits which are used in computers and other solid-state electronic packages throughout the world.
See also
Coucoulas, A., Trans. Metallurgical Society Of AIME, “Ultrasonic Welding of Aluminum Leads to Tantalum Thin Films”, 1966, pp. 587-589 (Thermosonic bonding)https://sites.google.com/site/coucoulasthermosonicbondalta/
Coucoulas, A., “Hot Work Ultrasonic Bonding – A Method Of Facilitating Metal Flow By Restoration Processes”, Proc. 20th IEEE Electronic Components Conf. Washington, D.C., May 1970, pp. 549-556. (Thermosonic Bonding)
https://sites.google.com/site/hotworkultrasonicbonding/
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