Lubov Zavalij - Academia.edu (original) (raw)

Papers by Lubov Zavalij

53rd Electronic Components and Technology Conference, 2003. Proceedings., 2003

The adoption of Pb-free solders will affect manufacturing processes and joint reliability for ele... more The adoption of Pb-free solders will affect manufacturing processes and joint reliability for electronics packages. Since SAC solder has a higher melting temperature than eutectic Pb-Sn solder, higher processing temperatures will be required. The higher processing temperatures allow for increased solubility of some elements, such as Ni, within the solder melt. The specific selection of pad metallurgies can influence both the type of intermetallics that form at the pad interfaces, and the age related evolution of those intermetallics. In joints where both Nt and Cu pad metallurgies are present, the fast diffusing Cu species can allow the intermetallic compound, (Cu,Ni)6Sns to form at the opposite, Ni, interface. The absence of a Cu pad can starve the system of Cu and effectively stop the growth of this (Cu,Ni)& intermetallic compound. The Ag component of the SAC solder can, under proper conditions, result in the growth of AgJSn plates in the solder melt before the Sn phase nucleates. This is controlled by the specific concentration of Ag in the solder, by the coolmg rate of the solder, and by the tendency of the solder joints to undercool by a typical 30°C before the Sn phase nucleates. The critical cooling rate for the onset of this phenomenon is between 3'Cisec. and 0.3"C/sec., within the range of normal reflow practices of the electronics industry. 101 Relatively small amounts of additional elements such as Cu or Ag are added to Sn to reduce the melting point of the solder alloy, and improve its mechanical and wetting properties. These constituents dramatically affect the mechanical properties of the solder, and possibly the reliability as well. Therefore it is important to understand the evolution of the distribution of these constituents during reflow and long term aging, including changes in the morphology of the intermetallic compounds (IMC's) formed along with Sn by these elements. In SnAg -Cu alloys, Cu&n5 and Ag3Sn form in the equilibrium state, with distinct morphologies, platelets for AglSn and hollow, hexagonal rods for Cu6Sn5. [l-71 We consider the evolution of IMC's during reflow, particularly Ag3Sn, including cooling to the solid state, and during long term aging.

Electronic Components and Technology Conference, 2003

ChemInform, 2002

Crystal Structure of Au 1−x NixSn 4 Intermetallic Alloys.-The title compounds are prepared by arc... more Crystal Structure of Au 1−x NixSn 4 Intermetallic Alloys.-The title compounds are prepared by arc-melting stoichiometric mixtures of the elements followed by annealing at 217 • C for 220-710 h. As revealed by single crystal and powder XRD the samples with x = 0.25 and 0.50 crystallize in the space group Ccca. It is found that Ni atoms introduced into the AuSn 4 structure substitute directly for Au atoms and occupy the Au atom sites statistically.

Proceedings Electronic Components and Technology, 2005. ECTC '05., 2005

The implementation of no-Pb soldering is progressing rapidly, often without immediately obvious p... more The implementation of no-Pb soldering is progressing rapidly, often without immediately obvious problems. However, our current understanding of pertinent materials issues is far from sufficient to prevent surprises, and potentially serious miscalculations. The fundamentally different nature of no-Pb from SnPb solder joints has serious consequences for the design and interpretation of accelerated tests. The present work addresses the behavior of ball grid array (BGA), wafer level chip scale package (WL-CSP) and flip chip assemblies with SnAgCu solder joints in long term thermal cycling. Components were assembled onto either Cu or Ni pads on high-T g printed circuit boards and cycled between 0 o C and 100 o C. Samples were removed at various stages for cross sectioning and microstructural characterization at various stages. Careful examination of the formation of intermetallic compounds at the pad surfaces, the size and orientation of the Sn grains, the morphology and number of precipitates, and the growth of cracks, revealed the sensitivity of the damage evolution to the solder microstructure. The consequences of the observed pattern of damage evolution are discussed.

SAE International Journal of Fuels and Lubricants, 2010

Abstract Selective Catalytic Reduction (SCR) of NO x using reductants such as urea continues to b... more Abstract Selective Catalytic Reduction (SCR) of NO x using reductants such as urea continues to be of high interest to meet impending regulations. Vanadia supported on anatase titania is a well-established catalyst for stationary and heavy-duty-diesel truck ...

We have examined the solidification and deformation behavior of SnCuAg alloys of near eutectic co... more We have examined the solidification and deformation behavior of SnCuAg alloys of near eutectic composition. In these alloys, both Ag3Sn and Cu6Sn5 intermetallic compounds can nucleate and grow with minimal undercooling, while the Sn matrix displays marked undercooling. Thus the protracted growth of one or both the compounds in the melt may be allowed. Furthermore, after the ultimate nucleation of Sn, its growth is rapid, and relatively large (mm) size dendritic crystals are observed. Microstructures deformed at elevated temperatures were examined using electron and optical microscopy. The birefringent properties of Sn allowed delineation of Sn grains by means of optical microscopy in as cast, and in deformed samples. Cracks were observed to propagate along Sn grain boundaries. Dynamic recrystallization effects, including the growth of cracks along recrystallized Sn grain boundaries, were examined for a number of different sample geometries.

Scripta Materialia, 2004

ABSTRACT Linear coefficients of thermal expansion for Au 1−xNixSn4 and AuSn4 alloys have been mea... more ABSTRACT Linear coefficients of thermal expansion for Au 1−xNixSn4 and AuSn4 alloys have been measured by thermo-mechanical analysis at temperatures between 340 and 460 K. These values are compared to those of other constituents of Ni/Au/PbSn solder joints. These joints have previously been shown to crack during thermal cycling in this temperature range.

JOM, 2002

Studies of the formation of intermetallic compounds at some lead-free solder/metallization interf... more Studies of the formation of intermetallic compounds at some lead-free solder/metallization interfaces are briefl y reviewed in this article. SnAgCu/Ni and SnAgCu/Cu interfaces are examined in particular. It has been found that (Cu,Ni) 6 Sn 5 forms at SnAgCu/Ni interfaces until copper is depleted from the solder matrix. This article also contrasts the formation of (Au,Ni)Sn 4 and related compounds in PbSn/Ni and lead-free solder/nickel solder joints is compared and contrasted.

Journal of Materials Research, 2005

The degree of undercooling of Sn in near eutectic, SnAgCu solder balls upon cooling at a rate of ... more The degree of undercooling of Sn in near eutectic, SnAgCu solder balls upon cooling at a rate of 1 °C/s from the melt was examined and found to increase linearly with inverse nominal sample diameter (for balls of radius between 100 and 1000 μm). The mean undercooling for SnAgCu solder balls in a flip chip assembly was 62 °C. The microstructures of these different samples were examined by means of scanning electron microscopy. The Sn dendrite arm width was observed to monotonically increase with ball diameter, indicating a possible dependence of the mechanical response of such solder balls upon size.

Journal of Electronic Materials, 2004

The microstructure of the SnAg -Cu solder is examined by optical microscopy and scanning electron... more The microstructure of the SnAg -Cu solder is examined by optical microscopy and scanning electron microscopy (SEM) for various compositions near the ternary eutectic for different cooling rates from the solder melt. Focus is on the size and orientation of Sn grains as indicated by cross-polarized, light optical microscopy, and pole figures from x-ray diffraction. We find that both composition and cooling rate have strong influences on Sn grain size, with Sn grain size increasing an order of magnitude as Cu concentration increases from 0% to 1.1%. Cyclic growth twinning, with twinning angles near 60°, is observed in SnAg -Cu alloys near the composition Sn-3.9Ag-0.6Cu.

Journal of Electronic Materials, 2001

Journal of Alloys and Compounds, 2002

Ni coated with a thin layer of Au is commonly used as a metallization in electronics packaging. S... more Ni coated with a thin layer of Au is commonly used as a metallization in electronics packaging. Such Ni /Au metallizations are alloyed with Sn at temperatures above the Pb-Sn solder liquidus. Thermal treatment of these joints in the solid state, for instance at 1508C, has been shown to result in the formation of Au Ni Sn compounds at the solder interface. These compounds are found to be deleterious to 12x x 4 joint integrity. In this work, synthesis, microstructural analysis and crystal structure determination of Au Ni Sn alloys were performed. 12x x 4 The alloys were examined by powder and single crystal X-ray diffraction, metallography, electron microprobe analysis, and thermal analysis. It was found that Ni atoms substitute for Au atoms in the AuSn structure giving compounds with general composition 4 Au Ni Sn (with x # 0.5). The structure of the title compounds is considered isotypical with the AuSn phase (the PdSn structure 12x x 4 4 4 type), with a symmetry increment from Aba2 to Ccca. Crystal structure refinement from powder data using the Rietveld method was˚p erformed for two alloys with x50.25 and 0.50 yielding Au Ni Sn (sp. group Ccca, a 5 6.448 A, b 5 11.606 A, c 5 6.441 A) and 0.73 0.27 4˚Å u Ni Sn (sp. group Ccca, a 5 6.424 A, b 5 11.522 A, c 5 6.384 A). A single crystal experiment was performed for compound 0.51 0.49 4˚˚Å u Ni Sn (sp. group Ccca, a 5 6.523 A, b 5 11.676 A, c 5 6.485 A).

MRS Online Proceeding Library

ABSTRACTDiffusion and phase formation were monitored in solder joints consisting of flip chips wi... more ABSTRACTDiffusion and phase formation were monitored in solder joints consisting of flip chips with Ni(V) under-bump metallizations bumped with Ag3.8Cu1.85Sn94.35 (atomic percentage) solder reflowed on printed circuit boards with Cu/Ni/Au metallizations. A ternary alloy, (CuNi)6Sn5, was observed to form during reflow at solder/Ni interfaces in these Ag3.8Cu1.85Sn94.35/Au/Ni solder joints. After extended thermal aging at 150 oC, a second ternary compound, (CuNi)3Sn4 forms at the Ni/(CuNi)6Sn5 interface. The growth of these alloys depletes the solder of essentially all Cu, changing its mechanical properties and melting temperature.