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Mechanical strength and its variability in Bi-modified Sn-Ag-Cu solder alloy

Matahir M, Chin L T, Tan K. S., Olofinjana A. O.

Journal of Achievements in Materials and Manufacturing Engineering

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2011

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Vol. 46, nr 1

50--56

EN

Purpose: Many previous work on Sn rich Pb-free soldering had focused on the evolution, morphology and the role of interfacial intermetallic compounds (IMC) layers of Cu3Sn and Cu6Sn5 on the mechanical integrity of soldered joints. However recent studies had shown that under static shearing stress, more fracture failures had been found to occur through the solder and thus indicate the significance of solder microstructures in the joint integrity. In this work, we investigated the effect of Bi substitution for Sn on the shear strength of solder joints of near eutectic SAC alloy Sn3.5Ag0.9Cu. Design/methodology/approach: Ingot alloy were prepared from pure elements and their melting characteristics were followed with thermal analyses. Copper plates were soldered together in lap joints that were subjected to shear testing in the as-soldered conditions. The microstructures were followed by SEM and EDS. Findings: Results show that failures occurred in quasi-brittle manner, with large variability. The ternary SAC alloy had average shear strength of 30 MPa better than binary eutectic Sn/Cu. Small Bi substitution of Sn up to 2 wt% lead to increased average shear strengths with maximum strengths of about 50 MPa recorded for compositions with Bi content of 0.5 to 1.5 wt%. Bi substitutions beyond 2wt% gave substantially lower strength values. The application of Weibull criteria suggest untypical high variability in strength with Webuill moduli less than 10. Higher variability in shear strengths were found in compositions containing more than 2 wt.% Bi. Research limitations/implications: Micro-structural evidence suggest that the role of Bi in increasing strength may be related to the high solubility of Bi in Sn and this would have provided some solution hardening effect. Higher Bi content however, lead to the formation Bi rich phases in the microstructure and this would have affected the mechanics of deformation thus leading to generally lower strength values and much higher variability in measurements. Originality/value: This paper clarifies the role of Bi substitution in improving the mechanical properties and reliability of soldered joints with unleaded solders.

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SURDAT : baza danych właściwości fizycznych lutowi bezołowiowych

Moser Z., Gąsior W., Dębski A.

Elektronika : konstrukcje, technologie, zastosowania

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2005

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Vol. 46, nr 11

53-54

PL

Wyniki prowadzonych od szeregu lat badań napięcia powierzchniowego metodą pomiaru maksymalnego ciśnienia w pęcherzykach gazowych oraz gęstości metodą dylatometryczną dla czystych metali, układów dwu- trój- cztero- i pięcioskladnikowych zostały wykorzystane do stworzenia bazy danych SURDAT materiałów dla lutowi bezołowiowych. Umożliwia ona porównanie eksperymentalnych danych napięcia powierzchniowego z wartościami obliczonymi z zależności Butlera oraz istniejącymi w literaturze danymi innych autorów, co pokazano na przykładzie ciekłych stopów Sn-Ag-Cu-Sb.

EN

Experimental studies of surface tension and density by the maximum bubble pressure method and dilatometric technigue were undertaken and the accumulated data for liguid pure components, binary, ternary and multicomponent alloys were used to create the SURDAT data base for the Pb-free soldering materials. The data base enabled also to compare the experimental results with those obtained by the Butlers model and with the existing literature data. This comparison has been extended by including the experimental data of Sn-Ag-Cu-Sb alloys.

3

Ekologiczna elektronika : uwarunkowania materiałowe i technologiczne

Kisiel R., Felba J.

Elektronika : konstrukcje, technologie, zastosowania

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2005

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Vol. 46, nr 12

75-77

PL

Od co najmniej 50 lat w montażu sprzętu elektronicznego stosowane są luty SnPb. Dwie dyrektywy Unii Europejskiej, WEEE oraz RoHS, wymuszają stosowanie technologii bezołowiowych od 1 lipca 2006 r. Konieczne jest zatem wykluczenie ołowiu z lutów, metalizacji pokryć kontaktów płytek drukowanych oraz kontaktów podzespołów. Przedstawiono przegląd zmian materiałowych i technologicznych, jakie muszą być wdrożone w tym zakresie.

EN

Soldering processes with SnPb solders was standard interconnection technologies of electronic components on PCBs from few decades. From more than ten years there are strong market, society and legal pressure on ecological electronic assembly. The EU Directives WEEE and RHS oblige the manufactures to elimination Pb from electronic products by 1 July 2006 in Europe. The development of Pb-free interconnects require the exclude of lead from three key elements of typical solder joint: the solder, the PCB finishes and component leads metallization. The intend of this paper is to provide the overview of materials and technological aspects of applying "green technology" in electronic assembly.