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Title: Massive spalling of intermetallic compounds in solder-substrate reactions due to limited supply of the active element

Abstract

Massive spalling of intermetallic compounds has been reported in the literature for several solder/substrate systems, including SnAgCu soldered on Ni substrate, SnZn on Cu, high-Pb PbSn on Cu, and high-Pb PbSn on Ni. In this work, a unified thermodynamic argument is proposed to explain this rather unusual phenomenon. According to this argument, two necessary conditions must be met. The number one condition is that at least one of the reactive constituents of the solder must be present in a limited amount, and the second condition is that the soldering reaction has to be very sensitive to its concentration. With the growth of intermetallic, more and more atoms of this constituent are extracted out of the solder and incorporated into the intermetallic. As the concentration of this constituent decreases, the original intermetallic at the interface becomes a nonequilibrium phase, and the spalling of the original intermetallic occurs.

Authors:
; ; ;  [1];  [2]
  1. Department of Chemical and Materials Engineering, National Central University, Jhongli City, Taiwan (China)
  2. (China)
Publication Date:
OSTI Identifier:
20982836
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Applied Physics; Journal Volume: 101; Journal Issue: 8; Other Information: DOI: 10.1063/1.2717564; (c) 2007 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; COPPER; COPPER ALLOYS; CRYSTAL GROWTH; INTERMETALLIC COMPOUNDS; LEAD ALLOYS; NICKEL; SILVER ALLOYS; SOLDERING; SUBSTRATES; TIN ALLOYS; ZINC ALLOYS

Citation Formats

Yang, S. C., Ho, C. E., Chang, C. W., Kao, C. R., and Department of Materials Science and Engineering, National Taiwan University, Taipei, Taiwan. Massive spalling of intermetallic compounds in solder-substrate reactions due to limited supply of the active element. United States: N. p., 2007. Web. doi:10.1063/1.2717564.
Yang, S. C., Ho, C. E., Chang, C. W., Kao, C. R., & Department of Materials Science and Engineering, National Taiwan University, Taipei, Taiwan. Massive spalling of intermetallic compounds in solder-substrate reactions due to limited supply of the active element. United States. doi:10.1063/1.2717564.
Yang, S. C., Ho, C. E., Chang, C. W., Kao, C. R., and Department of Materials Science and Engineering, National Taiwan University, Taipei, Taiwan. Sun . "Massive spalling of intermetallic compounds in solder-substrate reactions due to limited supply of the active element". United States. doi:10.1063/1.2717564.
@article{osti_20982836,
title = {Massive spalling of intermetallic compounds in solder-substrate reactions due to limited supply of the active element},
author = {Yang, S. C. and Ho, C. E. and Chang, C. W. and Kao, C. R. and Department of Materials Science and Engineering, National Taiwan University, Taipei, Taiwan},
abstractNote = {Massive spalling of intermetallic compounds has been reported in the literature for several solder/substrate systems, including SnAgCu soldered on Ni substrate, SnZn on Cu, high-Pb PbSn on Cu, and high-Pb PbSn on Ni. In this work, a unified thermodynamic argument is proposed to explain this rather unusual phenomenon. According to this argument, two necessary conditions must be met. The number one condition is that at least one of the reactive constituents of the solder must be present in a limited amount, and the second condition is that the soldering reaction has to be very sensitive to its concentration. With the growth of intermetallic, more and more atoms of this constituent are extracted out of the solder and incorporated into the intermetallic. As the concentration of this constituent decreases, the original intermetallic at the interface becomes a nonequilibrium phase, and the spalling of the original intermetallic occurs.},
doi = {10.1063/1.2717564},
journal = {Journal of Applied Physics},
number = 8,
volume = 101,
place = {United States},
year = {Sun Apr 15 00:00:00 EDT 2007},
month = {Sun Apr 15 00:00:00 EDT 2007}
}
  • The intermetallic compounds (IMCs) formed at the interface between Cu substrate and an Sn-9Zn-0.5Ag lead-free solder alloy have been investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM) and electron diffraction (ED). The XRD patterns show that the main IMCs formed at the interface of Sn-9Zn-0.5Ag/Cu are {gamma}-Cu{sub 5}Zn{sub 8} and {eta}'-Cu{sub 6}Sn{sub 5}. The Ag{sub 3}Sn IMC with orthorhombic structure was also observed at the Sn-9Zn-0.5Ag/Cu interface by TEM and ED analyses. The interfacial adhesion strength between the Cu substrate and Sn-9Zn-0.5Ag lead-free solder alloy is higher than that of the Sn-9Zn alloy due to the formation of Ag{submore » 3}Sn IMC at the interface.« less
  • Lead free solders currently in use are prone to develop thick interfacial intermetallic compound layers with rough morphology which are detrimental to the long term solder joint reliability. A novel method has been developed to control the morphology and growth of intermetallic compound layers between lead-free Sn–3.0Ag–0.5Cu solder ball and copper substrate by doping a water soluble flux with metallic nanoparticles. Four types of metallic nanoparticles (nickel, cobalt, molybdenum and titanium) were used to investigate their effects on the wetting behavior and interfacial microstructural evaluations after reflow. Nanoparticles were dispersed manually with a water soluble flux and the resulting nanoparticlemore » doped flux was placed on copper substrate. Lead-free Sn–3.0Ag–0.5Cu solder balls of diameter 0.45 mm were placed on top of the flux and were reflowed at a peak temperature of 240 °C for 45 s. Angle of contact, wetting area and interfacial microstructure were studied by optical microscopy, field emission scanning electron microscopy and energy-dispersive X-ray spectroscopy. It was observed that the angle of contact increased and wetting area decreased with the addition of cobalt, molybdenum and titanium nanoparticles to flux. On the other hand, wettability improved with the addition of nickel nanoparticles. Cross-sectional micrographs revealed that both nickel and cobalt nanoparticle doping transformed the morphology of Cu{sub 6}Sn{sub 5} from a typical scallop type to a planer one and reduced the intermetallic compound thickness under optimum condition. These effects were suggested to be related to in-situ interfacial alloying at the interface during reflow. The minimum amount of nanoparticles required to produce the planer morphology was found to be 0.1 wt.% for both nickel and cobalt. Molybdenum and titanium nanoparticles neither appear to undergo alloying during reflow nor have any influence at the solder/substrate interfacial reaction. Thus, doping of flux with appropriate metallic nanoparticles can be successfully used to control the morphology and growth of intermetallic compound layers at the solder/substrate interface which is expected to lead to better reliability of electronic devices. - Highlights: • A novel nanodoped flux method has been developed to control the growth of IMCs. • Ni doped flux improves the wettability, but Co, Mo and Ti deteriorate it. • Ni and Co doped flux gives planer IMC morphology through in-situ alloying effect. • 0.1 wt.% Ni and Co addition into flux gives the lowest interfacial IMC thickness. • Mo and Ti doped flux does not have any influence at the interfacial reaction.« less
  • Ni/Au metallization layers are used with increasing frequency to protect Cu substrates in ball grid array microelectronic packaging. The external Au layer provides oxidation and corrosion resistance during storage prior to assembly, while the intermediate Ni layer acts as a diffusion barrier that inhibits the formation of a thick Cu-Sn intermetallic layer during aging. During soldering with eutectic Pb-Sn, the Au dissolves into the molten solder and forms fine, needle-shaped AuSn{sub 4} intermetallic precipitates that are retained in a dense distribution in the bulk of the solder joint after it has solidified. However, recent research by Mei et al. hasmore » revealed a new and potentially problematic phenomenon that seems to be peculiar to the Ni/au metallization. They found that after extensive aging (150 C for 2 weeks in their case), the Au-Sn intermetallic redeposited onto the solder-substrate interface. The reconstituted interface was significantly weakened and failed by brittle fracture along the surface between the redeposited Au-Sn and the Ni{sub 3}Sn{sub 4} layer that formed during reflow. While the interfacial redeposition of Au-Sn intermetallics has been observed previously, the mechanism remains unknown. The present work was undertaken to identify the mechanism of this phenomenon and explore methods for controlling it.« less
  • In this paper, the effect of 0.1 wt.% Cr addition into Sn-9Zn lead-free solder alloys on the growth of intermetallic compound (IMC) with Cu substrate during soldering and subsequent isothermal aging was investigated. During soldering, it was found that 0.1 wt.% Cr addition did not contribute to forming the IMC, which was verified as the same phase structure as the IMC for Sn-9Zn/Cu. However, during solid-state isothermal aging, the IMC growth was remarkably depressed by 0.1 wt.% Cr addition in the Sn-9Zn solder, and this effect tended to be more prominent at higher aging temperature. The activation energy for IMCmore » growth was determined as 21.2 kJ mol{sup -1} and 42.9 kJ mol{sup -1} for Sn-9Zn/Cu and Sn-9Zn-Cr/Cu, respectively. The reduced diffusion coefficient was confirmed for the 0.1Cr-containing solder/Cu. Energy-dispersive X-ray mapping and point analysis also showed ZnCr phase existing in solder matrix, which can reduce diffusion rate of Zn atoms.« less
  • This work investigates the effects of molybdenum nanoparticles on the growth of interfacial intermetallic compound between Sn-3.8Ag-0.7Cu solder and copper substrate during multiple reflow. Molybdenum nanoparticles were mixed with Sn-3.8Ag-0.7Cu solder paste by manual mixing. Solder samples were reflowed on a copper substrate in a 250 Degree-Sign C reflow oven up to six times. The molybdenum content of the bulk solder was determined by inductive coupled plasma-optical emission spectrometry. It is found that upon the addition of molybdenum nanoparticles to Sn-3.8Ag-0.7Cu solder, the interfacial intermetallic compound thickness and scallop diameter decreases under all reflow conditions. Molybdenum nanoparticles do not appearmore » to dissolve or react with the solder. They tend to adsorb preferentially at the interface between solder and the intermetallic compound scallops. It is suggested that molybdenum nanoparticles impart their influence on the interfacial intermetallic compound as discrete particles. The intact, discrete nanoparticles, by absorbing preferentially at the interface, hinder the diffusion flux of the substrate and thereby suppress the intermetallic compound growth. - Highlights: Black-Right-Pointing-Pointer Mo nanoparticles do not dissolve or react with the SAC solder during reflow. Black-Right-Pointing-Pointer Addition of Mo nanoparticles results smaller IMC thickness and scallop diameter. Black-Right-Pointing-Pointer Mo nanoparticles influence the interfacial IMC through discrete particle effect.« less