Tomohiro Uno

Surface-enhanced copper bonding wire for LSI

There is growing interest in Cu wire bonding for LSI interconnection due to cost savings and better electrical and mechanical properties. Cu bonding wires, in general, are severely limited in their use compared to Au wires; such as wire oxidation, lower bondability, forming gas of N2+5%H2, and lower reliability. It is difficult for conventional bare Cu wires to achieve the target of LSI application. A surface-enhanced Cu wire (EX1) has been developed. It is a Pd-coated Cu wire and has many advantages compared to bare Cu wires. Stitch strength was much better under fresh conditions and maintained without any deterioration after being stored in air for a prolonged period of time. EX1 had a lifetime of over 90 days in air, although it was 7days for the bare Cu wire. Spherical balls were formed with pure N2 (hydrogen-free), whereas the bare Cu produced off-center balls. Cost-effective and secure gas, pure N2 was only available for EX1. The reliability for Cu wire bonding under conditions of high humidity was investigated in pressure cooker test (PCT). The lifetime for EX1 and the bare Cu was over 800h and 250h, respectively. Humidity reliability was significantly greater for EX1. Continuous cracking was formed at the bond interface for the bare Cu wire, although there was no cracking for EX1. Corrosion-induced deterioration would be the root cause of failure for bare Cu wires in PCT. EX1 improves the bond reliability by controlling diffusion at the bond interface. The excellent performance of Pd-coated Cu wire, EX1 is comparable with Au wires and suitable for LSI packaging.

Improving humidity bond reliability of copper bonding wires

There is growing interest in Cu wire bonding for LSI interconnection due to cost savings and better electrical and mechanical properties. Conventional bare Cu bonding wires, in general, are severely limited in their use compared to Au wires. A coated Cu bonding wire (EX1) has been developed for LSI application. EX1 is a Pd-coated Cu wire to enhance the bondability. Bond reliability at a Cu wire bond under a humid environment is a major concern in replacing Au wires. The bond reliability of EX1 and bare Cu was compared in the reliability testing of PCT and uHAST (unbiased HAST). The lifetimes for EX1 and the bare Cu in PCT testing were over 800 h and 250 h, respectively. Humidity reliability was significantly greater for EX1. Continuous cracking was formed at the bond interface for the bare Cu wire. Corrosion-induced deterioration would be the root cause of failure for bare Cu wires. The corrosion was a chemical reaction of CuAl IMC (Intermetallic Compound) and halogens (Cl, Br) from molding resins. EX1 improves the bond reliability by controlling diffusion and IMC formation at the bond interface. The excellent humidity reliability of the coated Cu wire, EX1 is suitable for LSI application.

Thermal reliability of gold–aluminum bonds encapsulated in bi-phenyl epoxy resin

Abstract Bond degradation of Au wire/Al pad has become a major problem, because of the use of molding resin with low thermal stability (e.g. bi-phenyl epoxy resin) and the use of the IC devices under high thermal environments. It is therefore important to insure the thermal reliability at Au/Al bonds. The lifetime to bond failure of bi-phenyl epoxy molding became shorter than that for cresol novolac epoxy. The failures were caused by the corrosion reaction of Au–Al intermetallics with bromine (Br) contained in the resin compounds. It was clarified that the reactive intermetallic was Au4Al phase formed in the bond interface. The governing factors of the bond corrosion were investigated such as resin compound and gold wire material. Especially some impurities in gold wire could affect the Au–Al intermetallic growing and therefore retard the corrosion. The use of the alloyed wire was effective in improving the bond reliability.

Significant reduction of wire sweep using Ni plating to realise ultra fine pitch wire bonding

Significant reduction of the wire sweep in molding is proposed because the wire sweep is considered to be the major problem to realise wire bonding with ultra fine pitches of under 30 micrometers. In the present proposal, Ni was plated for several micrometers before molding on bonded Au wires. Ni plating was carried out by means of electroless plating for several minutes in the aqueous solution kept at 358 K containing Ni and P. The wire sweep ratio for Ni plated wire (total diameter was 21 micrometers) was almost half of that for Au wire with the diameter of 15 micrometers except Ni plate, and was slightly smaller than that for Au wire with the diameter of 25 micrometers except Ni plate even the total diameter was smaller. It is considered that wire sweep suppression by this technique was due to the enhancement of both elastic and plastic properties.

Development of ultra-fine pitch ball bonding technology

While the environment surrounding wire bonding, i.e., wire, lead frame, wire bonder, and capillary, is being developed more eagerly than ever, wire bonding technology which can better meet the more compact and higher density chips without modifying the existing assembly process is desired. This paper discusses reduction of the diameter of a ball to be formed at the tip of the wire, the required wire diameter reduction, capillary tip diameter reduction, and attainment of a higher Youngs modulus for the wire which can suppress wire sweep in transfer molding, and indicates that wire bonding for a pitch of 70 /spl mu/m or less can be performed with no problem in reliability of the bonded zone.

Thermal Bond Reliability of High Reliability New Palladium-Coated Copper Wire

Pd coated copper (PCC) wire and Au-Pd coated copper (APC) wire have been widely used in the field of LSI device. Recently, higher bond reliability at high temperature becomes increasingly important for on-vehicle devices. However, it has been reported that conventional PCC wire caused a bond failure at elevated temperatures. On the other hand, new-APC wire had higher reliability at higher temperature than conventional APC wire. New-APC wire has higher concentration of added element than conventional APC wire. In this paper, failure mechanism of conventional APC wire and improved mechanism of new-APC wire at high temperature were shown. New-APC wire is suitable for onvehicle devices.

High-Performance Silver Alloy Bonding Wire for Memory Devices

For memory devices, focus has been on Ag alloybonding wire as a low-cost alternative to Au bonding wire. However, Ag bonding wire has lower long-term bond reliabilitythan Au bonding wire under high temperature and humidityconditions. Past research has mainly been concerned withenhancing the bond reliability by Pd doping into the Agbonding wire. On the other hand, Ag-Pd alloy bonding wire haspractical issues such as high electrical resistance and high freeair-ball (FAB) hardness. A new type of Ag alloy wire (2N Agalloy) was developed to achieve enhanced bond reliability, lowelectrical resistance and low FAB hardness compared toconventional one. Moreover, the 2N Ag alloy wire has goodFAB formability and bond properties. This new Ag alloy wire isconsidered to be preferable for advanced memory devices.