Microstructure of a lead-free composite solder produced by an in-situ process

Abstract

A composite solder, which consisted of solder matrix and intermetallic reinforcements, was manufactured by an innovative method. The cast ingot of the Sn-6.9Cu-2.9Ag alloy has primary Cu 6 Sn 5 intermetallics in dendritic form. After rolling, the intermetallic dendrites are crushed into fine particles and distributed uniformly in the solder matrix. The crushed intermetallic particles do not melt, and they retain their shape during spheroidizing and reflow because of their high melting temperature. Coarsening and gravitational segregation of the particles was observed during reflow and analyzed theoretically.

Cu6Sn5 crystal growth mechanisms during solidification of electronic interconnections

“…Hwang et al [18] observed dendritic Cu6Sn5 in Sn-6.9Cu-2.9Ag alloy cooled at ~17-500 K/s. Liu et al [6] reported Cu6Sn5 dendrites in Sn/Cu joints held at 426C for 80ms and 120ms before cooling at >800 K/s.…”

“…Primary Cu6Sn5 has been reported to grow with various morphologies such as needles [10][11][12], hollow rods [11,13], X-shapes [9,14,15], Y-shapes [8,9], H-and M-shapes [16,17] and as dendrites [6,18]. Since many of these studies have been based on arbitrary 2D cross sections, it is not clear how many of these morphologies are separate growth forms in 3D.…”

Formation and growth of intermetallics around metallic particles in eutectic Sn-Ag solder

“…The strong role of time and temperature performance, particularly, in lead-free solders. [8][9][10][11][12] above solder liquidus during reflow, especially Such solders may contain a IMC produced either by during the heating segment, in development of sun flower morphologies into blocky morphologies has been documented in an earlier study. 13…”

“…The strong role of time and temperature performance, particularly, in lead-free solders. [8][9][10][11][12] above solder liquidus during reflow, especially Such solders may contain a IMC produced either by during the heating segment, in development of sun flower morphologies into blocky morphologies has been documented in an earlier study. 13 The goal of the present study was to compare the morphology of the IMC formed around the metallic reinforcements, Ag, Cu, and Ni, contained in the Sn-Ag solder so as to gain a better understanding of parameters that contribute to various IMC morphologies.…”

“…The amount of heat input caused no significant change in morphology of the IMCs formed around Cu and Ag particulate reinforcements. Also, the IMC morphol ogy around Ni particles was sensitive to the Cu content in the solder, whether the Cu came from the substrate during reflow or it was already present within the solder.Key words: Lead-free composite solder, intermetallic morphology, metallic particle reinforcements in-situ methods 8,9 or mechanically incorporated, INTRODUCTION metallic particles, which upon reflow completely or Intermetallic compounds (IMCs) formed both partially transform into IMCs. [10][11][12] Ternary and quaat the solder/substrate interface and within the ternary alloys being considered for enhanced service solder during reflow exhibit different morphological performance also derive their better attributes befeatures depending on the conditions employed.…”