Electrodeposition of Near-Eutectic SnAg Solders for Wafer-Level Packaging

Abstract

The electrodeposition of near-eutectic SnAg solders for wafer level packaging was investigated with Shipley-Ronal’s EXP-0700 SnAg bath. Fundamental studies including polarization behavior, morphological transition, and compositional change were performed to investigate the alloy deposition mechanism. It was proven that the mass transfer limitation of silver ions at low potential drove the drastic change of morphology and composition with increasing current density. The morphological transition occurred through four stages (dendrites, suppression of dendrites, facets, and dendrites) and the content of silver in the deposit dropped with increasing current density. The deposition mechanism of SnAg alloys with this bath looks similar to that of SnAgCu alloys with an alkaline bath due to a similar polarization behavior. Pattern plating results including studs, mushrooms, and stacks can be summarized as fine-grained surface, high deposition rate, good uniformity, and repeatability. Two types of in situ stack plating, Cu/SnAg and Ni/SnAg, were successfully performed with no defects between two layers. Reflow tests conducted with near-eutectic SnAg solders on copper studs showed spherical shapes with smooth surfaces, where the average melting point of whole bumps in a wafer was 223.7°C, which is close to the melting point (221°C) of the eutectic composition. © 2003 The Electrochemical Society. All rights reserved.

Non-PR Sn-3.5Ag Bumping on a Fast Filled Cu-Plug by PPR Current

“…4 demonstrates the Ag content in the Sn-Ag bumps plated for 20 min, where the current density was changed from −40 to −60 mA/cm 2 . The Ag content decreased with increasing current density because the deposition potential of Ag is higher than that of Sn, and more Ag was deposited at a lower current density [16], [29]. In addition, Joseph et al [30] and Jang et al [31] reported that when the current density was higher, the fluxes of Sn ions were stronger than that of the noble ion, which resulted in a lower Ag content of the deposits.…”

“…The Sn-Ag-Cu alloy [13], [14] has reliable mechanical properties, but producing a ternary alloy with a desired composition is relatively difficult to achieve by electroplating. Among the bumping materials, Sn-Ag [15]- [22] is popular compared to other metal alloys owing to its good creep resistance, thermomechanical fatigue behavior [16], comparable shear strength to that of conventional Sn-Pb [20], and greater connection reliability [17], [21].…”

Tin and Tin Alloys for Lead‐Free Solder

“…Its higher melting temperature and superior thermal fatigue property make it a good candidate for automotive and flip-chip applications. This realization motivated researchers in industrial laboratories as well as academia to develop a number of commercially viable tin-silver plating processes [92,93,[99][100][101][102][103][104][105][106][107].…”

New process of electroplate Sn bumping on TSV without a PR mould for 3D-chip stacking

“…Among these methods, electroplating is the most popular. Many prior studies related to this method have been conducted [5,6,[9][10][11][12][13]. Much interest has been generated by lead-free Sn-based alloys as bumping materials, and Sn-Ag [5,10,[12][13][14][15][16][17], Sn-Cu [11], and Sn-Ag-Cu [18,19] electroplating approaches have been investigated.…”