Abstract
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.
Highlights
In the long run, the traditional lead-tin (Pb-Sn) solders have gradually been substituted with environmentally friendly Pb-free solders, which are currently employed by far in most of the electronic packaging industries
Most of the components assembled to the printed circuit boards (PCBs) in the soldering process are designed primarily for Sn-Pb soldering with a thermal tolerance up to a maximum temperature of 240°C
It can be speculated that a combination of the surfactant (PVP) and residual precursors possibly adsorbed on the surface of as-synthesiszed nanoparticles,[7] as well as the excess flux, which was not completely driven away from the joint interface due to the deficient reflowing of nanoparticles, are the main reasons for this organic residue
Summary
The traditional lead-tin (Pb-Sn) solders have gradually been substituted with environmentally friendly Pb-free solders, which are currently employed by far in most of the electronic packaging industries. Most of the components assembled to the printed circuit boards (PCBs) in the soldering process are designed primarily for Sn-Pb soldering with a thermal tolerance up to a maximum temperature of 240°C. The higher melting temperatures of the typical Pb-free solders such as Sn-Ag (SA) and Sn-Ag-Cu (SAC) require reflow temperatures at or above 240°C. That makes it more difficult to optimize the reflow process for all components on the PCB.[1,2,3,4,5] To tackle this issue in the transition process toward Pb-free solders, a (Received November 12, 2015; accepted April 25, 2016; published online May 13, 2016)
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