Alexander Coucoulas

In the mid-1960s, Coucoulas[2][3] reported the first thermosonic wire bonds using a combination of heat, ultrasonic vibrations and pressure which led to his first invention. He first set up a commercial ultrasonic wire bonder (capable of transmitting vibratory energy and pressure) in order to investigate the attachment of aluminum wires to tantalum thin films deposited on glass substrates which simulated bonding a lead wire to the fragile metallized silicon integrated circuit "chip". He observed that the ultrasonic energy and pressures levels needed to sufficiently deform the wire and form the required contact areas significantly increased the incidents of cracks in the glass or silicon chip 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 wire dramatically deformed to form the required contact area while using significantly 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 near hot working conditions where its softness was enhanced. As the bonding temperature was increased the onset of recrystallization (softening mechanism) occurs where the strain hardening is most extensive. Thus the dual mechanisms of thermal softening and ultrasonic softening which is caused by vibratory energy interacting at the atomic lattice level,[13] facilitated the desired wire deformation. Christian Hagar[14] and George Harman[4] stated that in 1970 Alexander Coucoulas[3] 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. As a result of these earliest reported thermosonic wire bonds, G.Harman[4] stated "as such, Alexander Coucoulas is the Father of Thermosonic Bonding". At present, the majority of connections to silicon integrated circuits are made using thermosonic bonding 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. As a result of using lower bonding parameters to form the required contact area, Thermosonic Bonding largely eliminates damaging the relatively fragile silicon integrated circuit micro-chip during the bonding cycle. The proven reliability of thermosonic bonding has made it the process of choice, since such potential failure modes could be costly whether they occur during the manufacturing stage or detected later, during an operational field-failure of a micro-chip which had been permanently connected inside a computer or a myriad of other electronic devices.

Burmeister et al., of Hamburg University, Germany, reported that using solely ultrasonic power to bond gold wires to YBa2Cu3O7 microstructures, such as microbridges, Josephson junctions and superconducting interference devices (DC SQUIDS) can degrade them. The researchers further found that the problem was overcome by using Coucoulas' thermosonic bonding process where it left the microstructure device intact so they could be employed.[15]

The majority of connections to the silicon integrated circuit chip are made using thermosonic bonding[16] because it employs lower bonding temperatures, forces and dwell times than thermocompression bonding, as well as lower vibratory energy levels and forces than ultrasonic bonding to form the required bond area. Therefore, the use of thermosonic bonding eliminates damaging the relatively fragile silicon integrated circuit chip during the bonding cycle. The proven reliability of thermosonic bonding has made it the process of choice, since such potential failure modes could be costly whether they occur during the manufacturing stage or detected later, during an operational field-failure of a chip which had been connected inside a computer or a myriad of other microelectronic devices.

Thermosonic bonding is also used in the flip chip process which is an alternate method of electrically connecting silicon integrated circuits.

Josephson effect and superconducting interference (DC SQUID) devices use the thermosonic bonding process as well. In this case, other bonding methods would degrade or even destroy YBaCuO₇ microstructures, such as microbridges, Josephson junctions and superconducting interference devices[17] (DC SQUID).

When electrically connecting light-emitting diodes with thermosonic bonding techniques, an improved performance of the device has been shown.[18]

"Compliant bonding" was awarded best paper presentation and publication at the 1970 IEEE Electronic Components Conf. Click photo to read original file resolution.

"Compliant Bonding" Patent. Click above to read Original File

Following his pioneering of thermosonic bonding, Coucoulas invents "Compliant Bonding[19] which was a means of solid-state bonding the extended electroformed leads of a "beam leaded chip" to the outside world. It was a unique method of solid state bonding in that the bonding energy (heat and pressure) was transmitted through a compliant aluminum tape. The compliant tape overcame the thickness variations of the beam leads and also acted as a chip carrier to the bonding site. In 1971, he was awarded best paper-presentation for "Compliant Bonding"[6] which was among more than 90 papers presented at the 20th IEEE Electronic Components Conference in 1970 by engineers and research scientists from around the world.

Click pictures to enlarge view

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  Stages of compliant bonding gold wires to a gold metallized surface Click picture to enlarge
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  Silicon integrated circuits showing attached and extended electroformed beam leads around the silicon chip
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  Wires solid state bonded directly to the metallized pads of a silicon integrated circuit chip
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  Hard faced bonding tool simultaneously bonding all of the extended beam leads
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  Compliant bonding a beam leaded silicon integrated circuit showing the indented compliant member after bonding the "chip"

AlO bonding patent

Twenty-three years after being awarded best paper for compliant bonding, Coucoulas was again awarded "outstanding paper" at the 43rd Electronic Components and Technology Conference in 1993. It was titled, "AlO Bonding: A Method of Joining Oxide Optical Components to Aluminum Coated Substrates."[20] He also was awarded a U.S. patent for inventing AlO bonding.[9]

Coucoulas' first industrial research position was at air reduction central research facility in New Jersey where he investigated and coauthored a paper on in the transactions of the Metallurgical Society of AIME entitled, "Some Observations on the Microstructure and Fragmentation of Solid Carbon Dioxide"[21] with the following abstract:

Solid carbon dioxide (dry ice), which exists metastably as a constantly subliming molecular solid in a normal room temperature environment, was shown to exhibit many microstructural features which are similar to those observed in metals and ceramics at temperatures approaching their melting points. An investigation was made of factors affecting a costly brittleness condition known as "sandiness" which occurred in manufactured blocks of dry ice (polycrystalline solid carbon dioxide). The sandiness was found to be highly dependent on specific manufacturing and storage conditions that cause excessive grain growth which leads to a concentration of gas filled pores in the decreasing grain boundary regions.