Size effects in small scaled lead-free solder joints

Although considerable research has been dedicated to the synthesis and characterization of lead-free nanoparticle solder alloys, only very little has been reported on the reliability of the respective joints. In fact, the merit of nanoparticle solders with depressed melting temperatures close to the Sn-Pb eutectic temperature has always been challenged when compared with conventional solder joints, especially in terms of inferior solderability due to the oxide shell commonly present on the nanoparticles, as well as due to compatibility problems with common fluxing agents. Correspondingly, in the current study, Sn-Ag-Cu (SAC) nanoparticle alloys were combined with a proper fluxing vehicle to produce prototype nanosolder pastes. The reliability of the solder joints was successively investigated by means of electron microscopy and mechanical tests. As a result, the optimized condition for employing nanoparticles as a competent nanopaste and a novel procedure for surface treatment of the SAC nanoparticles to diminish the oxide shell prior to soldering are being proposed.

Section: Resultsmentioning

confidence: 99%

Sn-Ag-Cu Nanosolders: Solder Joints Integrity and Strength

Roshanghias

Khatibi

Yakymovych

et al. 2016

“…The microstructure of the Sn-3.5Ag solder joints after reflow and heat treatment at 120°C for 6 h consisted of b-Sn phase surrounded by a eutectic mixture of Sn and Ag 3 Sn. An intermetallic layer of Cu 6 Sn 5 formed at the Cu/solder interface due to the reaction between liquid Sn and Cu.…”

Section: Experimental Methodologymentioning

confidence: 99%

“…1 In a series of recent investigations on the influence of further miniaturization on the mechanical response of some lead-free model solder joints, consisting of Sn-3.5Ag (in weight percent, throughout this paper) between Cu substrates, a pronounced constraining effect was observed. 2,3 This constraining effect resulted in a remarkable increase of the tensile strength and a pronounced reduction of the ductility as a function of decreasing joint thickness following an almost hyperbolic law of the type…”

Section: Introductionmentioning

confidence: 99%

Constraining Effects of Lead-Free Solder Joints During Stress Relaxation

Zimprich

Saeed

Weiß

et al. 2008

Reliability and quality control of microelectronics depend on a detailed understanding of the complex thermomechanical properties of miniaturized lead-free solder joints. With the continuous reduction in size of modern electronic devices, including also the size of the solder joints themselves, mechanical constraint effects may become of importance for the reliability of the joints. In the present study stress relaxation tests in tensile mode were performed on model solder joints consisting of eutectic Sn-3.5Ag solder between Cu substrates. The gap size of the joints was varied between 750 lm and 150 lm in order to investigate the variation of the mechanical properties as a function of the gap size. As it turned out, stress relaxation was dramatically reduced when the solder gaps became smaller due to constraint effects already well known from earlier measurements of the tensile strength. By employing a traditional creep model, the stress exponents and the activation energies were derived and compared with available data in the literature. The consequences of these constraint effects for the case of thermomechanical fatigue are discussed.

“…[1][2][3] Consequently, the requirements for high integrity and reliability have demanded superior mechanical properties of interconnect materials, in which solder alloys play key roles. This is particularly true for lead-free solders which have poor process performance and lower integrity level compared with eutectic or near-eutectic tin-lead solders.…”

Section: Introductionmentioning

confidence: 99%

“…2,3 In addition, it is worth noticing that the performance of a solder joint is strongly dependent on its size. In contrast to the increasing concern about integrity and reliability of lead-free solder interconnections, there is not a good understanding of the effect of size on the mechanical behavior of microscale joints.…”

Section: Introductionmentioning

confidence: 99%

Size and Volume Effects on the Strength of Microscale Lead-Free Solder Joints

Yin

Zhang

2009

The fracture behavior of microscale lead-free Sn-3.0Ag-0.5Cu solder joints of different sizes was investigated under quasistatic microtension loading. The experimental results show that the ultimate tensile strength of a joint does not always increase with decreasing thickness-to-diameter ratio (d/t), which is commonly regarded as the dominant factor for mechanical constraint in the joint. A clear joint volume effect on the strength has been found, i.e., the joint's strength increases with decreasing joint volume V ¼ p 4 d 2 t À Á ; and the correlation follows an inverse proportional function reasonably well.