Anna Sypień

Influence of phosphorous content on microstructure development at the Ni-P Plating/SAC interface

Studies of the commonly used Ni-P surface finish of 4.3 and 11.6 wt. % of P content electroless plated on nickel substrates followed by their reaction with SAC305 solder were performed. It was demonstrated that the Ni-4.3P plating was crystalline, while the Ni-11.6P was mostly amorphous. The transformation of the Ni-P into Ni3P phase took place at 672 K and 605 K for low and high P amount, respectively. The activation energy (Ea) of the crystallization processes in the Ni-P plating was lower for the Ni-11.6P plating. Interaction of SAC305 solder with both types of the inspected plating showed the creation of (Cu,Ni)6Sn5 phase in the form of thin layer and large scallops, while for Ni-11.6P/SAC305 interface also (Ni,Cu)3Sn4 phase. The thickness of these phases was larger in the case of low phosphorous containing plating. The Ni-11.6P plating after the reaction with SAC305 totally transformed into Ni12P5, while the enrichment in P up to 10.5 wt. % occurred in the Ni-4.3P which did not lead to the appearance of any NixPy type phases. After the reaction of plating with solder the Ni2SnP phase was not identified. This was related to the absence of spalling phenomenon of the intermetallics into solder.

Properties of Ni-based amorphous ribbons consolidated by high pressure torsion

Two amorphous ribbons, of compositions (Ni56Cu2)Zr18Ti16Al3Si5 and (Ni36Cu23)Zr18Ti14Al5Si4, were subdued to the similar process of cold consolidation by the high pressure torsion (HPT) method. The first ribbon, that revealed higher thermal stability of the amorphous phase, higher GFA and better mechanical properties like tensile strength, Young modulus and hardness, partially crystallized in the HPT process. The second ribbon, revealing lower Tg and Tx temperatures, tensile strength and hardness, could be consolidated preserving amorphous structure. Such result suggests that the thermal stability against crystallization was not responsible for the preservation of the amorphous phase in the cold consolidation by the HPT. It rather seemed that a proper relation of the undercooled liquid temperature range to the local temperature increase during consolidation is suggested and it was a decisive parameter.

Microstructure of the Ni-W Solid Solution Prepared by Levitation and after High Pressure Torsion Severe Plastic Deformation

The Ni-4at%W alloys was prepared with cold crucible levitation, subsequent levitation re-melting and high pressure torsion (HPT) intensive deformation. In samples after levitation precipitates of Ni4W phase as well as grain boundary continuous phase were formed. Levitation re-melting resulted in partial dissolution of the precipitates, increasing W content in the matrix and lead to the microstructure refinement. The deformation by HPT, in the range of 300-400%, lead to the lead to the homogenization of the solid solution and partial decomposition of the alloys into pure Ni and W. In the homogenous majority of the sample the microstructure transformed from dendrite microstructure to faceted grains. The analysis of the grains sizes and shapes showed that the average grain size in the sample re-melted by levitation was twice the grain size of the sample only prepared with CCLM. Also, the grains in this sample were elongated by 50-60% in one direction, while in the sample prepared by CCLM they were equiaxial. As the nominal composition of the alloys in both cases was the same, differences observed in the microstructure after re-melting and HPT processing must result only from the differences in the cooling rate leading to small differences in W content in solid solution and phase composition after solidification. High rate of cooling in the levitation methods resulted in Ni4W metastable phase precipitation as well as in the refinement of the microstructure, stronger after additional re-melting of the alloy by levitation.

Crystallization and mechanical properties of the NiNb(ZrTi)Al amorphous alloys with 10 and 25 at % of Nb and 3 to 7 at % Al content

The results of the investigations of alloys of compositions Ni58Nbx(ZrTi)39-xAly and Ni58Nbx(ZrTi)32-yAly with x = 10, 25 and y = 3, 7 respectively, are presented. The structure of the all melt spun ribbons was amorphous, however the crystallization process proceeded in a very different way in the ribbons with x = 10, y = 7 and ribbons with x = 25 and y = 3. In the first compositions typical primary crystallization of the 50 nm grains of the NiTi(Zr) cubic phase was observed while the ribbons containing 25 at.% of Nb and 3 at.% of Al revealed very stable thermally amorphous phase, nano-crystallizing at the range of primary crystallization but preserving large fraction of the amorphous phase high above the primary crystallization temperature. The tensile curves were determined for ribbons of both compositions and were different, but revealed quite large range of the plastic elongation. The HREM experiments did not reveal any crystallization in the shear bands, after the fracture of the ribbons.

New kind of Cu based paste for Si solar cells front contact formation

Abstract Potential impact of copper replacing silver in the paste used for the front electrode fabrication in crystalline silicon solar cells was investigated. The copper was applied as a new CuXX component with about 2 wt.% to 6 wt.% share of XX modifier. The generated CuXX molecules were analyzed using transmission microscopy. Based on the commercial Du Pont PV19B paste, CuXX and XX materials, the new PV19B/CuXX paste with 51 wt.% share of Cu and the PV19B/XX paste with 51 wt.% share of XX only were developed. Comparative studies of the effect of the commercial PV19B paste made by DuPont Company, and the pastes with the CuXX component and with the modifier XX alone on the electrical parameters of solar cells produced on crystalline silicon were carried out. The solar cells were characterized by the current-voltage technique. As a final result, the Cz-Si solar cell with the 51 wt.% share of Cu in the front electrode having a series resistance of 0.551 Ω·cm2, an efficiency of 14.08 % and, what is more important, the fill factor of 0.716, was obtained. It is the best result ever obtained concerning direct Cu application for solar cells fabricated in thick-film technology.

Microstructure, Chemistry and Mechanical Properties of the Ni/AgBiCuSn/Ni Interconnections

The paper presents results of electron microscopy studies on the microstructure, chemical composition and mechanical properties of the Ni/AgBiCuSn/Ni interconnections obtained due to the conventional soldering. The scanning (SEM) and (TEM) transmission electron microscopy combined with an energy dispersive X-ray spectroscopy allowed to reveal the presence of two intermetallic phases (Ag3Sn and Cu6Sn5) in the whole interconnection area for all the applied solders and soldering times. In the vicinity of Ni substrate both phases were modified with Ni (2-4.5 %at.). Some of Ag3Sn precipitates took the elongated shape and they were located across whole interconnection width. The SEM examination after shear test showed that the joints ruptured in a ductile manner, as manifested by the dimples present on the fracture surfaces. The dimples prove also that the plastic deformation occurred along the loading direction.

Microstructure Evolution and Mechanical Properties of the Ni/Ni Soldered Joints

The paper presents the results of studies on the microstructure, chemical composition and mechanical properties of the Ni/SnAuCu/Ni interconnections obtained due to the conventional soldering at 300 °C for different times and subsequent aging at 150 °C. The EDX microanalysis allowed to detect at the Ni/solder interface the (Ni,Cu,Au)3Sn4 phase which transformed to (Cu,Ni,Au)6Sn5 after longer time of soldering. In the central part of the interconnection AuSn4 brittle phase was present. This phase was responsible for the significant decrease of the shear strength in the joints subjected to aging at 150 °C for 1000h, 1500 hours. The fracture behavior of such joints appeared to be caused partly by the coalescence of the microvoids in the bulk solder, cleavage of η-phase grains and decohesion at the interface.

The Microstructure and Mechanical Properties of the Ni-Al-V Alloys Prepared by Levitation and Crystallization in Copper Mould

Microstructure and mechanical properties of NiAlV alloys of the composition belonging to the pseudo-binary Ni3Al-Ni3V cross-section were investigated. The samples were prepared by the cold crucible levitation melting (CCLM) and by re-melting and crystallizing in the small volume copper mould. The phase composition of the samples, with should result from the eutectoidal decomposition was not found. Instead the Ni3(Al,V) and Ni(Al,V) solid solution or seldom disordered solid solution were retained due to the relatively high cooling rates. In the compression test the NiAlV alloys crystallized in the copper mould revealed high ductility and strength.