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One of the main drawbacks of silver-filled isotropically conductive adhesives (ICAs) is the high cost of silver fillers, while low cost copper-filled ICAs are not reliable due to the oxidation of copper fillers. In this paper, we develop highly conductive, highly reliable, and low cost ICAs filled with silver-coated copper (Ag-coated Cu) flakes, i.e. an anhydride-cured ICA filled with Ag-coated Cu...
The η-η' transformation of interfacial Cu6Sn5 in solder joints was studied. Two cooling rates were selected to obtain different grain sizes of intermetallic compounds (IMCs). In the case of air cooling, the compounds were tiny and no η-η transformation was detected in the as-soldered state. Under furnace cooling, however, thick and coarse interfacial IMCs were obtained and η was still stable. After...
In this study, the reliabilities of low Ag SAC alloys doped with Mn or Ce (SACM or SACC) were evaluated under JEDEC drop, dynamic bending, thermal cycling, and cyclic bending test conditions against eutectic SnPb, SAC105, and SAC305 alloys. The Mn or Ce doped low cost SAC105 alloys achieved a higher drop test and dynamic bending test reliability than SAC105 and SAC305, and exceeded SnPb for some test...
The formation and growth of intermetallic compound layer thickness is one of the important issues in search for reliable electronic and electrical connections. Intermetallic compounds (IMCs) are an essential part of solder joints. At low levels, they have a strengthening effect on the joint; but at higher levels, they tend to make solder joints more brittle. If the solder joint is subjected to long-standing...
In this work, the SAC solder joints with minor Mn or RE (rare earth) additions were bonded on the substrate of OSP Cu surface finishes for evaluating the influence of minor alloying on BIT (ball impact test) behavior. The Mn-doped samples had a better resistance to the degradation in BIT performance suffering long time aging at 150??C. The greater impact force and toughness compared to the other samples...
It is of importance for the reliability of lead-free and lead-bearing solder joints to have better understanding and control of the solder/metallization interactions during soldering. In the reactions between solders and Cu substrate, the formation of micro voids within the Cu3Sn layer had been report by many research groups. Because the Cu3Sn growth had been linked to the formation of micro voids,...
This paper deals with presentation of some new aspects of solder ternary alloy 96.5Sn3Ag0.5Cu (wt.%) - SAC305, in order to determine variations in mechanical properties and microstructure caused by treatment in vapour phase soldering (VPS) as well as by accelerated isothermal aging. These specimens have been melted and solidified on HASL (hot air solder levelling) and Ni/Au (ENIG) PCB (printed circuit...
The morphological features and growth kinetics of interfacial IMCs have shown significant effect on the mechanical properties, and hence, on the reliability of lead free solder joints. The growth behavior of the interfacial IMCs of SnAgCu/Cu solder joint, in reflow and thermal cycling, was investigated with the focus on the influence of reflow dwell time and the cyclic parameters on the growth kinetics...
Ball grid array (BGA) solder interconnecting is one of the key technologies in electronic packaging and assembly. Legislation of lead-free process has made the application of lead-free solder become wider in electronic products. Compared to the lead-tin solder, the relatively higher melting points of most lead-free solders call for a higher reflow temperature. Thus conventional integral-heating process...
Electronic assembly technology is in the transition from traditional tin-lead to lead-free, which leading to challenge in many aspects. It is accepted that nitrogen can improve the wettability and reliability of lead-free solders; however, few systemic researches have been reported. In this work, the spreading ratio of Sn-Ag-Cu solder was measured through spreading tests under different atmosphere...
In this study, the reliabilities of low Ag SAC alloys doped with Mn or Ce (SACM or SACC) were evaluated under JEDEC drop, dynamic bending, thermal cycling, and cyclic bending test conditions against eutectic SnPb, SAC105, and SAC305 alloys. The Mn or Ce doped low cost SAC105 alloys achieved a higher drop test and dynamic bending test reliability than SAC105 and SAC305, and exceeded SnPb for some test...
The properties of lead free solder joints continue to change over a very long period of time in service before the microstructure becomes stable. The quantitative assessment of long term service life by accelerated testing invariably misses this significant effect, and may thus end up seriously misleading. The long term goal of the present work is to establish a protocol for preconditioning of lead...
The excessive growth of intermetallic compound (IMC) and the formation of microvoids in the interface between Sn-Ag-Cu (SAC) solder and Cu substrate have been a serious problem which may degrade the solder joints reliability. Recently, a new Cu-Zn alloy solder wetting layer for the Pb-free solders has been developed to reduce the IMC growth rate. In this paper, the kinetics of IMC growth and the shear...
Sn-8Zn-3Bi solder balls with different weight percentages of Sn-Ag-Cu addition were bonded to Au/Ni metallized Cu pads, and the effect of multiple reflow and aging on impact reliability was investigated. In the Sn-Ag-Cu content Sn-Zn-Bi solder joints, the AgZn3 intermetallic compound layer was clearly observed at the interfaces and its thickness increased with an increase the number of reflow cycles...
Reliability of SnAgCu solder joints under mechanical stress is not proven, in particular for Aeronautic and High Performance (AHP) products. They are subjected to high temperatures, severe mechanical stresses and long-term mission profiles. This work is comprehended within a larger study, which has as objective the characterization of the SnAgCu alloys mechanical behaviour at the solder joint scale...
Sn-Ag-Cu (SAC) solders are susceptible to appreciable microstructural coarsening during storage or service, resulting in evolution of joint properties, and hence reliability, over time. Although the problem of microstructural coarsening in joints has been studied extensively, the effect of joint scale on aging kinetics has never been investigated. Understanding the scale dependence of aging is particularly...
The intermetallic growth in the Sn-Ag-Cu (SAC) solder joints fabricated on Cu or Cu-Zn solder wetting layer and its effect on the drop impact reliability have been studied. The drop test specimens were fabricated by connecting two printed circuit boards by reflowing SASC 405 solder balls on Cu or Cu-Zn wetting layers. And the drop test specimens were aged at 150degC up to 500 hrs. The well known bi-layer...
The reliability of lead free electronic devices depends strongly on the reliability of the soldered joints while the later one was controlled, mainly, by the formation and growth of the interfacial intermetallic compounds (IMCs) between the solder matrix and the substrates. The morphological features, microstructural evolutions and growth kinetics of the IMCs on the interfacial of SnAgCu/Cu soldered...
With the proliferation of mobile electronics in everyday life, the ability of electronic packages to sustain impact loading under drop conditions has become a paramount reliability concern. Since solder joints, which serve as mechanical and electrical interconnects in a package, are particularly prone to failure during a drop, the fracture behavior of solders at high strain rates is a critically important...
Predicting reliability of solder joints requires a thorough understanding of solder constitutive behavior. Recent studies on SnAgCu solder alloys have reported that pre-test conditions of aging-time and aging-temperatures can be factors that significantly affect solder constitutive behavior. The results presented here are a part of ongoing efforts to construct constitutive models that can predict...
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