Abnormal tin whisker growth in rare earth element-doped Sn3Ag0.5CuXCe solder joints

Scopus; In this study, 0.1̃1.0 wt.% of pure Ce was added into a Sn3Ag0.5Cu solder alloy, resulting in the formation of precipitated CeSn3 clusters of a size greater than 20 μm in the reflowed solder matrix.

After natural aging at room temperature for more than 3 days, oxidation on the surface of the CeSn3 clusters was much heavier than in the undoped Sn3Ag0.5Cu solder matrix. In addition, many tin whiskers with a diameter of about 0.1 to 0.3 μm had been squeezed out of the oxide layer of the CeSn 3 precipitates. The increase in aging time at room temperature causes the tin whiskers to grow rapidly. The whiskers can grow even to a length of over 300 μm after 21 days of storage. The whisker growth rate in one particular case reached 8.6Å/S after room temperature storage for only one day. The whiskers formed during storage at a higher temperature (150°C) have a coarse diameter of 1 to 3 μm. In some cases, high temperature storage results in the formation of short whiskers in a hillock shape with a diameter of about 5 to 10 μm.

Chuang, T.-H., Yen, S.-F.

Institute of Materials Science and Engineering, National Taiwan University, Taipei 106, Taiwan

Improving low-Ag Pb-free solder performance by adding Bi, Ni elements

Scopus: "In this study, some Ni, Bi elements were added into low-Ag (less than 1%) Sn-Ag-Cu (SAC) solder. The effect of these additive elements on the solderability, intermetallic compounds (IMCs), and electromigration performance of low-Ag SAC (LASAC) solder were investigated.

With the increase of Bi content in LASAC-0.05Ni-xBi (x=0, 2.0, 2.5, 3.0, 3.5, 4.0) solders, the peak melting point decreases while the wetting area of solder alloy increases. With the addition of Ni, the IMC between Cu pad and LASAC solder transforms from Cu6Sn5 to (Cu1-xNix)6Sn5 and the morphology of the IMC turns from bulk-like to needle-like. Either the addition of Bi or Ni will slow down the IMCs growth rate during high temperature storage aging (HTS) at 180'C and has a positive effect on electromigration performance of LASAC soldering"

Sun, F.L., Liu, Y., Wang, J.B., Zhang, H.W.

School of Material Science and Engineering, Harbin University of Science and Technology, No.4, Linyuan Road, Xiangfang District, Harbin, 150030, China

Effect of nano-TiO2 addition on the microstructure and bonding strengths of Sn3.5Ag0.5Cu composite solder BGA packages with immersion Sn surface finis

Scopus: "The effects of nano-TiO2 particles on the interfacial microstructures and bonding strength of Sn3.5Ag0.5Cu composite solder joints in ball grid array packages with immersion Sn surface finishes have been investigated.

Metallography reveals that addition of nano-TiO2 particle retarded wicker-Cu6Sn5 IMC formed in the Sn3.5Ag0.5Cu composite solder joints. The thickness of the interfacial intermetallic compounds of the solder joint was reduced with increased additions of nano-TiO2 particles (0.25-1.0 wt%), but further additions up to 1.25 wt% decreased the beneficial influence. This indicates that the presence of a small amount of nano-TiO2 particles is effective in suppressing the growth of the intermetallic compounds layer. In addition, the shear strength of the soldered joints was improved by larger nano-TiO2 particle additions, with the peak shear strength occurring at 1.0 wt% of nano-TiO2 particles into the Sn3.5Ag0.5Cu solder. The fracture mode also changed with increased amounts of nano-TiO2 particles"

Leong, J.C.a , Tsao, L.C.b , Fang, C.J.c , Chu, C.P.b

a Department of Vehicle Engineering, National Pingtung University of Science and Technology, Neipu, Pingtung, 91201, Taiwan

b Department of Materials Engineering, National Pingtung University of Science and Technology, 1, Hseuhfu Road, Neipu, Pingtung, 91201, Taiwan

c Department of New Materials Research and Development, China Steel Corporation, Kaohsiung, 81233, Taiwan

TT says glueable resistors withstand 200'C

Electronics Weekly: "TT electronics has introduced solderless chip resistors which will operate at temperatures up to 200'C.

An application for the glueable resistors is in hybrid microcircuits or medical MRI scanners where non-magnetic components must be used.

Fixing components with conductive adhesive rather than solder is preferred for assembling some types of hybrid microcircuits, non-magnetic electronics and equipment designed to operate at temperatures capable of melting ordinary solder.

These include down-hole drilling equipment, as well as military, aerospace and automotive assemblies."

Nihon Superior's Technical Director to Present Assessment of Microalloyed Sn-Zn as a Solder

EMSNow: "Given the advantages of reduced damage to components and laminate, as well as energy savings that could accrue as a result of a melting point 20'C lower than the liquidus temperature of SAC305, the tin-9 percent zinc eutectic alloy has been attracting the attention of the electronics industry as a potential lead-free solder. If solders based on the tin-zinc eutectic are to find wider application, the problem of corrosion will have to be addressed.

The presentation will provide a detailed assessment of the effect of a microalloying addition of manganese on the mechanical integrity of tin-zinc alloy joints on copper, nickel, and silver substrates after exposure to elevated temperature (150'C) and humid heat (85'C/85 percent RH) for up to 1000 hours. The nature and extent of corrosion on the surface, and the solder/substrate interface was examined using SEM/EDX and found to vary considerably with the substrate.

Solidification process after growth of primary intermetallic compounds in Sn-Ag-Cu alloys

Scopus: "Sn-Ag-Cu alloys are some of the most widely used materials for solder alloys. It has already reported that sometimes unusual microstructure, both Sn-Ag3Sn and Sn-CU6Sn5 binary eutectic, are observed after growth of primary Ag3Sn in the solder instead of ternary eutectic.

However, solidification process after growth of primary Ag3Sn and the mechanism of these unusual microstructures are still not clear. Hence, in this study fundamental experiment was carried out in order to understand the solidification process after growth of primary Ag 3Sn.

For comparison, the solidification process after growth of CU6Sn5 was also investigated. In this study, Sn-4.2Ag-0.5Cu and Sn-1.0Ag-1.5Cu alloys were prepared. In these alloy, both CU6Sn5-Sn and Ag3Sn-Sn binary eutectic were observed in addition to ternary eutectic. One of these reasons is that Ag and Cu may separate in the liquid as binary eutectic and β-Sn grow"

Effect of soldering parameters on reaction kinetics and phase transformations of SAC 305 solder

Scopus: "As technology becomes increasingly reliant on electronics, understanding the reliability of lead-free solder also becomes increasingly important. This research project focused on phase transformation kinetics with the lead-free solder SAC 305.

Today in the electronics industry, SAC 305 is the most widely used solder, making it a high priority to understand its long-term stability and performance in a variety of service conditions. Recent evidence has shifted the focus from thermal aging to reflow temperature and time above liquidus values during initial solder melting. Previous research projects were designed to record the initial growth of Cu6Sn5 and monitor the development of Cu3Sn1[1-3]. These studies analyzed thermally-aged samples prepared at various reflow temperatures and times above liquidus temperatures. The initial growth of Cu6Sn 5 developed as expected, but the Cu3 Sn1 layer did not precipitate as anticipated. The detrimental second layer (Cu 3Sn1) exhibited limited or no growth during this study"

Tensile deformation behavior of nano-sized Mo particles reinforced SnAgCu solders

Scopus: "In this work, tensile deformation of Sn-3.8Ag-0.7Cu (SAC387) solder and composite of SAC387 reinforced with nano-sized Mo particles have been studied with strain rates from 10-5 to 10-1s-1 and temperatures of 25, 75 and 125'C. It is found that the yield strength (σY.S) and strain hardening exponent (n) are increased with the strain rate, but the n values decrease with increasing temperatures"

Rao, B.S.S.C.a b , Kumar, K.M.a , Kripesh, V.b , Zeng, K.Y.a

a Department of Mechanical Engineering, National University of Singapore, 9 Engineering Drive 1, SGP 117576, Singapore

b Institute of Microelectronics, Agency for Science, Technology and Research (A STAR), 11 Science Park Road, Science Park II, SGP 117685, Singapore

Solderless Assembly for Electronics (SAFE), Part III

EMS007: "In the second part of this series on Solderless Assembly for Electronics (SAFE) technologies, the history of solder in electronics was reviewed in brief fashion. It's worth repeating here that solder will likely remain an important technology for making interconnections in the future; however, it will be joined by an increasing number of methods that do not require solder, just as it has been in the past. The next few parts of the series will offer a retrospective on solderless assembly in which the reader will likely find very familiar methods among the not so familiar."

Solder Prices High as LME Tin over 19,000 per ton | AWA Refiners News

AWA Refiners News: "AWA Refiners offer a FREE collection service throughout the Uk, so please contact us if you have any Sn bearing material you would like to offer."

0.2% Zn addition suppresses whisker formation in Ce alloys

Factiva: "Although it has been verified that tin whiskers can be prevented by the addition of 0.5 wt.% Zn into a Sn-3Ag-0.5Cu-0.5Ce solder, no detailed studies have been conducted on interfacial reactions and mechanical properties of Sn-3Ag-0.5Cu-0.5Ce-xZn solder joints with an immersion Ag surface finish,' scientists writing in the journal Microelectronics Reliability report.

'The intermetallic compounds formed during the reflow and aging of Sn-3Ag-0.5Cu and Sn-3Ag-0.5Cu-0.5Ce-xZn solder ball grid array (BGA) packages were investigated. Because more heterogeneous nucleation sites, provided by CeSn3 intermetallics and Zn atoms, formed in the Sn-3Ag-0.5Cu-0.5Ce-xZn solder matrix, and Cu and Zn have a stronger affinity than Cu and Sn, the Cu-Sn intermetallics growth in Sn-3Ag-0.5Cu-0.5Ce-xZn solder joints with Ag/Cu pads was suppressed,' wrote H.J. Lin and colleagues, National Taiwan University.

The researchers concluded: 'The 0.2% Zn addition for inhibiting rapid whisker growth in RE-doped Sn-Ag-Cu solder joints is more appropriate than 0.5 wt.% additions, as excess Zn addition causes poor oxidation resistance and inferior bonding strength.'"

Interfacial microstructure and bonding strength of Sn-3Ag-0.5Cu and Sn-3Ag-0.5Cu-0.5Ce-xZn solder BGA packages with immersion Ag surface finish. Microelectronics Reliability, 2011;51(2):445-452).

Additional information can be obtained by contacting T.H. Chuang, National Taiwan University, Institute Materials Science & Engineering, Taipei 106, TAIWAN

Southampton harsh environment tests

Factiva: "This paper investigates accelerated life behaviour of lead-free solder joints and printed circuit boards using thermal and electrical stress cycling. The aim is to understand the degradation of these materials in a practical operating environment. Whilst corrosion and debris deposits have been found, no significant evidence has been obtained for tin whiskering. EDX analysis has shown the presence of high concentrations of elements considered to arise from the packaging material. Thermal cycling tests have presented an aggressive environment to the samples and the effect on them has been supported by microscopic and macroscopic observations of debris and corrosion,' wrote M. Moshrefitorbati and colleagues, University of Southampton.

The researchers concluded: 'The electrical behaviour, i.e., the joint resistance, has not however, significantly degraded.'"

Solder paste maker Shenmao raises product prices

digitimes: "Shenmao Technology has raised its quotes for solder paste products by a double-digit rate recently and could continue to hike prices in May due to rising tin prices in the global market, according to industry sources"

Tin prices have reached US$33,000 per ton recently, increasing over 6% on average from the levels recorded in March, the sources noted.

Shenmao revealed that it has received more orders for BGA solder balls recently as the supply chain has been affected by the Japan earthquake. Based on its current capacity, Shenmao will be able to fulfill all orders and have to wait until May to see if its sales have been affected by the quake.

However, order visibility of PV ribbons for solar panels has shortened to one month compared to three months in the first quarter as a number of countries have reduced their subsidies for the installment of solar power devices, the company noted.

Shenmao has also decided to invest US$2 million to set up a solder paste plant in Huizhou, China. To finance the investment project, the company plans to increase its capital by issuing 7.5 million new shares and also issue NT$400 million (US$13.79 million) worth of convertible bonds. The new shares will be priced at NT$40 per unit.

Rheology and processing of Ni based nano-composite pastes for electronic assembly

Scopus: "Lead-free solder paste printing process accounts for majority of the assembly defects in the electronic manufacturing industry. In the stencil printing process, the solder paste must be able to withstand low and high shear rates, which results in continuous structural breakdown and build-up. The study investigates the effect of nickel additional to the thixotropic behaviour of lead-free Sn/Ag/Cu solder pastes using the structural kinetic model."

Durairaja, R., Chiawea, L., Leong, K.C., Chu, W.M., Suan, L.M.

Department of Mechanical and Material Engineering, Universiti Tunku Abdul Rahman (UTAR), Jalan Genting Kelang, Setapak, 53300 Kuala Lumpur, Malaysia

Oscillatory and creep recovery test on nano-composite lead-free solder pastes (nickel and platinum powder)

Scopus: "This study investigates the relationship of rheological properties of nanoparticles added to lead-free solders paste. For lead-free solder paste, a large number of combinations can be made from different elements. Every ingredient plays a role of the paste and the rheological properties. The effect of filler concentration was studied in this present investigation. Creep recovery, stress is applied on samples for a period of time and later release in order for it to recovery itself. In the other words, creep recovery involves a tensile specimen under constant load maintained at a constant temperature. Oscillatory tests were carried out to study the visco-elastic behaviour and paste stability."

Durairaj, R., Leong, K.C., Wea, L.C., Chu, W.M.

Department of Mechanical and Material Engineering, Universiti Tunku Abdul Rahman (UTAR), Jalan Genting Kelang, Setapak 53300 kuala Lumpur, Malaysia

Effect of soldering condition on formation of intermetallic phases developed between Sn-0.3Ag-0.7Cu low-silver lead-free solder and Cu substrate

Scopus: "In this paper, effect of soldering time and temperature on formation of intermetallic compounds developed between Sn-0.3Ag-0.7Cu lead-free solder and copper substrate was investigated. Dip soldering was performed at 250, 270, and 290 'C with soldering time of 5, 10, 15, and 20 s"

Either e{open}-Cu3Sn or η-Cu6Sn5 intermetallic phase was found at the interface between the solder and the substrate depending on the soldering condition, i.e., soldering time and soldering temperature. e{open}-Cu3Sn was found only when the substrate was soldered at 250 °C for 5 and 10 s. At other soldering conditions, only η-Cu6Sn5 was found at the interfacial zone. Crystal structure of e{open}-Cu3Sn intermetallic phase was orthorhombic, and it was hexagonal structure for η-Cu6Sn5. Transformation of the intermetallic phases was also discussed

Mookam, N.a , Kanlayasiri, K.b a Department of Industrial Engineering Technology, Rajamangala University of Technology Rattanakosin, Wang Klai Kangwon Campus, Prachuapkhirikhan 77110, Thailand b Department of Industrial Engineering, King Mongkut's Institute of Technology Ladkrabang, Bangkok 10520, Thailand

Hydrometallurgical treatment of used printed circuit boards after thermal treatment

Scopus: "The hydrometallurgical route of copper and tin extraction from printed circuit boards (PCB) of used personal computers after thermal pretreatment is discussed."

The PCB fractions crushed and sorted into -8 + 0, -8 + 3 and -3 + 0 mm were used for the experiments. The samples were thermally pretreated at temperatures of 300, 500, 700 and 900 °C during 15, 30 and 60 min with the presence of air (burning) before the leaching process. The leaching solution of 1 M HCl and temperature of 80 °C was used for the leaching. The original as well as thermally pretreated samples were leached under these conditions. The weight losses within the range from 5% to 35% were achieved by burning depending on the burning temperature. The increase of burning temperature causes the copper extraction into solution up to 98%, while copper extraction into solution from non-burned samples was up to 6%. The opposite effect was observed in the case of the tin leaching, where the highest extraction was achieved when the original sample was leached. The increase of the burning temperature caused the lowering of the copper extraction

Havlik, T., Orac, D., Petranikova, M., Miskufova, A.

Technical University of Kosice, Faculty of Metallurgy, Centre of Waste Processing, Letna 9, 042 00 Kosice, Slovakia