Carboxylate-Passivated Silver Nanoparticles and Their Application to Sintered Interconnection: A Replacement for High Temperature Lead-Rich Solders

Abstract

Lead-free silver nanoparticle pastes have been tested as a replacement for high temperature lead-rich solders used in electronic manufacturing. The pastes contain a small amount of solvent, and primarily consist of submicronsilver powder and passivated silver nanoparticles. The nanoparticles were synthesized from Ag 2 CO 3 and a long-chain alcohol by a method that produced a passivating layer consisting almost exclusively of the carboxylate of the reactant alcohol. The pastes were used to connect a silicon diode chip to copper bases without applied pressure when sintered at 350°C under nitrogen. Diode packages made with sintered silver interconnects had electrical and thermal properties equal to those with lead-soldered interconnects, even after 3000 thermal cycles between À55°C and +150°C. The mechanical strength was half that of lead-rich solder joints, but still strong enough for practical use.

Are Sintered Silver Joints Ready for Use as Interconnect Material in Microelectronic Packaging?

“…The following parameters have been used to evaluate the effects of fatigue stress on the integrity of sintered Ag joints: die shear strength, 65-69 thermal and electrical resistance 60,70 and ''life cycle to failure'' (N f ). In the case of ''life cycle to failure'' (N f ), the criterion for failure differs from one work to another; some researchers have used the loss of 20 % of the die-bonded area the failure criterion, while others have used 10 % of the die-bonded area.…”

“…In one thermal-cycling study that used bare copper as a substrate, air-sintered Ag joints exhibited higher thermal and electrical resistance than Ag joints formed in a nitrogen atmosphere. 70 These reduced properties of the air-sintered Ag joints were caused by the delamination of the copper oxide at the interface. It has also been reported elsewhere that Ag nanoparticles exhibit reduced adhesion on copper oxides compared to bare copper because of the reduced deformation and contact surface area on hard copper oxides compared to bare copper.…”

“…66 The ''threshold stress'' must be exceeded to achieve a significant increase in the density and strength of a sintered Ag joint. Such ''low-pressure'' formulations of Ag pastes typically exploit the shapes of Ag fillers 66 with a mixture of micron-sized particles (>1,000 nm), sub-micron-sized particles (100-1,000 nm) and nanoparticles (<100 nm), 67,70 and other strategies that have been described earlier in '''Pressureless'' Micron-Ag Paste' and '''Pressureless'' Nano-Ag Paste'. Another advantage of using sub-micron-and micron-sized Ag fillers is their smaller surface areas compared to Ag nanoparticles, which translates into a lower volume of capping agent or dispersant in the Ag pastes.…”

Metal&ndash;Metal Bonding Process Using Cu+Ag Mixed Nanoparticles

“…The high temperature solders containing 90 95 mass% Pb are still widely used in various applications. 4) Recently, there has been an increasing focus on low temperature interconnect technologies with metal nanoparticles (Ag nanoparticles, Cu nanoparticles. etc.)…”

Mechanism of Low Temperature Sintering-Bonding through <i>In-Situ</i> Formation of Silver Nanoparticles Using Silver Oxide Microparticles

“…In the case of the lack of suitable non-Pb alternatives, European RoHS regulations temporarily exempt high-Pb solders used as component solders and die attachment for automotive and other high temperature applications. 3,4) It is necessary to find Pb-free alternatives for high temperature applications.…”