Aging Induced Mechanical Property Degradation and Microstructure Evolution of SAC+X Lead Free Solder Alloys

2013 ◽  
Author(s):  
Zijie Cai ◽  
Jeffrey C. Suhling ◽  
Pradeep Lall ◽  
Michael J. Bozack
Keyword(s):  
Thermal Cycling ◽  
Aging Time ◽  
Aging Temperature ◽  
Lead Free ◽  
Lead Free Solder ◽  
Solder Alloys ◽  
Stress Strain ◽  
Free Solder ◽  
Effects Of Aging ◽  
Lead Free Solders

The microstructure, mechanical response, and failure behavior of lead free solder joints in electronic assemblies are constantly evolving when exposed to isothermal aging and/or thermal cycling environments. In our prior work on aging effects, we have demonstrated that large degradations occur in the material properties (stiffness and strength) and creep behavior of Sn-Ag-Cu (SAC) lead free solders during aging. These effects are universally detrimental to reliability and are exacerbated as the aging temperature and aging time increases. Conversely, changes due to aging are relatively small in conventional Sn-Pb solders. In our current work, we are exploring several doped SAC+X alloys in an attempt to reduce the aging induced degradation of the material behavior of SAC solders. The doped materials are lead free SAC solders that have been modified by the addition of small percentages of one or more additional elements (X). Using dopants (e.g. Bi, In, Ni, La, Mg, Mn, Ce, Co, Ti, Zn, etc.) has become widespread to enhance shock/drop reliability, wetting, and other properties; and we have extended this approach to examine the ability of dopants to reduce the effects of aging and extend thermal cycling reliability. In this paper, we concentrate on presenting the results for SAC+X (X = Zn, Co, Ni). The enhancement of aging resistance for the doped lead free solders was explored. Comparisons were made to the responses of non-doped SAC lead free solder alloys. The effects of aging on mechanical behavior have been examined by performing stress-strain and creep tests on solder samples that were aged for various durations (0–6 months) at elevated temperature (100 °C). Variations of the mechanical and creep properties (elastic modulus, yield stress, ultimate strength, creep compliance, etc.) were observed and modeled as a function of aging time and aging temperature. Our findings show that the doped SAC+X alloys illustrate reduced degradations with aging for all of the aging temperatures considered. Also, the stress-strain and creep mechanical properties of doped solders are better than those of reference solders after short durations of aging. After long term aging, doped solder alloys were found to have more stable behaviors than those of the standard SAC alloys. A parallel microstructure study has shown that less degradation and coarsening of the phases occurs in doped solder materials relative to non-doped solders after severe aging.

Effects of aging time on the mechanical properties of Sn–9Zn–1.5Ag–xBi lead-free solder alloys

2014 ◽  
Vol 582 ◽  
pp. 229-235 ◽  
Author(s):  
Chih-Yao Liu ◽  
Min-Hsiung Hon ◽  
Moo-Chin Wang ◽  
Ying-Ru Chen ◽  
Kuo-Ming Chang ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Aging Time ◽  
Lead Free ◽  
Lead Free Solder ◽  
Solder Alloys ◽  
Free Solder ◽  
Effects Of Aging

Solder Joint Reliability of Sn-Cu and Sn-Ag-Cu Lead-Free Solder Alloys Solidified on Copper Substrates with Different Surface Roughnesses

2015 ◽  
Vol 830-831 ◽  
pp. 265-269
Author(s):  
Satyanarayan ◽  
K.N. Prabhu
Keyword(s):  
Solder Joint ◽  
Solder Matrix ◽  
Lead Free ◽  
Lead Free Solder ◽  
Solder Alloys ◽  
Cu Substrate ◽  
Cu Substrates ◽  
Free Solder ◽  
Substrate Surfaces ◽  
Lead Free Solders

In the present work, the bond strength of Sn-0.7Cu, Sn-0.3Ag-0.7Cu, Sn-2.5Ag-0.5Cu and Sn-3Ag-0.5Cu lead free solders solidified on Cu substrates was experimentally determined. The bond shear test was used to assess the integrity of Sn–Cu and Sn–Ag–Cu lead-free solder alloy drops solidified on smooth and rough Cu substrate surfaces. The increase in the surface roughness of Cu substrates improved the wettability of solders. The wettability was not affected by the Ag content of solders. Solder bonds on smooth surfaces yielded higher shear strength compared to rough surfaces. Fractured surfaces revealed the occurrence of ductile mode of failure on smooth Cu surfaces and a transition ridge on rough Cu surfaces. Though rough Cu substrate improved the wettability of solder alloys, solder bonds were sheared at a lower force leading to decreased shear energy density compared to the smooth Cu surface. A smooth surface finish and the presence of minor amounts of Ag in the alloy improved the integrity of the solder joint. Smoother surface is preferable as it favors failure in the solder matrix.

Nanoindentation Characterization of Lead-free Solders and Intermetallic Compounds under Thermal Aging

2010 ◽  
Vol 2010 (1) ◽  
pp. 000314-000318
Author(s):  
Tong Jiang ◽  
Fubin Song ◽  
Chaoran Yang ◽  
S. W. Ricky Lee
Keyword(s):  
Mechanical Properties ◽  
Thermal Aging ◽  
Solder Joints ◽  
Lead Free ◽  
Small Range ◽  
Lead Free Solder ◽  
Solder Alloys ◽  
Aging Test ◽  
Free Solder ◽  
Lead Free Solders

The enforcement of environmental legislation is pushing electronic products to take lead-free solder alloys as the substitute of traditional lead-tin solder alloys. Applications of such alloys require a better understanding of their mechanical behaviors. The mechanical properties of the lead-free solders and IMC layers are affected by the thermal aging. The lead-free solder joints on the pads subject to thermal aging test lead to IMC growth and cause corresponding reliability concerns. In this paper, the mechanical properties of the lead-free solders and IMCs were characterized by nanoindentation. Both the Sn-rich phase and Ag3Sn + β-Sn phase in the lead-free solder joint exhibit strain rate depended and aging soften effect. When lead-free solder joints were subject to thermal aging, Young's modulus of the (Cu, Ni)6Sn5 IMC and Cu6Sn5 IMC changed in very small range. While the hardness value decreased with the increasing of the thermal aging time.

Aging Effects on the Mechanical Behavior and Reliability of SAC Alloys

2009 ◽  
Author(s):  
Yifei Zhang ◽  
Zijie Cai ◽  
Jeffrey C. Suhling ◽  
Pradeep Lall
Keyword(s):  
Thermal Cycling ◽  
Mechanical Behavior ◽  
Room Temperature ◽  
Material Behavior ◽  
Lead Free ◽  
Lead Free Solder ◽  
Aging Effects ◽  
Free Solder ◽  
Effects Of Aging ◽  
Temperature Aging

The microstructure, mechanical response, and failure behavior of lead free solder joints in electronic assemblies are constantly evolving when exposed to isothermal aging and/or thermal cycling environments. In our prior work on aging effects, we have demonstrated that the observed material behavior variations of Sn-Ag-Cu (SAC) lead free solders during room temperature aging (25°C) and elevated temperature aging (125°C) were unexpectedly large and universally detrimental to reliability. Such effects for lead free solder materials are especially important for the harsh applications environments present in high performance computing and in automotive, aerospace, and defense applications. However, there has been little work in the literature, and the work that has been done has concentrated on the degradation of solder ball shear strength (e.g. Dage Shear Tester). Current finite element models for solder joint reliability during thermal cycling accelerated life testing are based on traditional solder constitutive and failure models that do not evolve with material aging. Thus, there will be significant errors in the calculations with the new lead free SAC alloys that illustrate dramatic aging phenomena. In the current work, we have extended our previous studies to include a full test matrix of aging temperatures and solder alloys. The effects of aging on mechanical behavior have been examined by performing stress-strain and creep tests on four different SAC alloys (SAC105, SAC205, SAC305, SAC405) that were aged for various durations (0–6 months) at room temperature (25°C), and several elevated temperatures (50, 75, 100, and 125°C). Analogous tests were performed with 63Sn-37Pb eutectic solder samples for comparison purposes. Variations of the mechanical and creep properties (elastic modulus, yield stress, ultimate strength, creep compliance, etc.) were observed and modeled as a function of aging time and aging temperature. In this paper, we report on the creep results. The chosen selection of SAC alloys has allowed us to explore the effects of silver content on aging behavior (we have examined SACN05 with N = 1%, 2%, 3%, and 4% silver; with all alloys containing 0.5% copper). In order to reduce the aging induced degradation of the material behavior of the SAC alloys, we are testing several doped SAC alloys in our ongoing work. These materials include SAC0307-X, SAC105-X, and SAC305-X; where the standard SAC alloys have been modified by the addition of small percentages of one or more additional elements (X). Using dopants (e.g. Bi, In, Ni, La, Mg, Mn, Ce, Co, Ti, etc.) has become widespread to enhance shock/drop reliability, and we have extended this approach to examine the ability of dopants to reduce the effects of aging and extend thermal cycling reliability.

How Silver Powder Metallurgy Affects the Physical Properties of Low Temperature Firing Silver Conductor

2011 ◽  
Vol 2011 (1) ◽  
pp. 000099-000106 ◽  
Author(s):  
Samson Shahbazi ◽  
Mark Challingsworth
Keyword(s):  
Powder Metallurgy ◽  
Thick Film ◽  
Silver Powder ◽  
Lead Free ◽  
Lead Free Solder ◽  
Pure Silver ◽  
Solder Alloys ◽  
Film Conductor ◽  
Free Solder ◽  
Lead Free Solders

With the implementation of RoHS (the Restriction of Hazardous Substance) Directive banning the use of Lead, Cadmium, Mercury and Hexavalent Chromium, hybrid microelectronic manufacturers are globally embracing the lead free movement. These manufacturers must not only understand the implications of their material choice but must be aware of the interaction between lead free solder alloys and their RoHS compliant thick film materials. It is commonly known that lead free solder alloys process at much higher reflow temperatures than lead containing solder which can directly impact the fired film leach resistance and the loss of adhesion. There are also other concerns; lead free solders alloys generally require a different organic flux system to promote wetting and reflow, but this change may cause a fired film conductor to leach more easily than the flux used in the lead containing solders. The use of lead free solders such as SAC305, SAC405 or 95/5 on a low firing (550–570 °C) pure silver conductor has the tendency of leaching the fired film more readily than conductors containing small amounts of palladium or platinum. Many of these situations provide new challenges for the hybrid circuit manufacturer. There is little information available regarding the effects of the lead free solders on low firing silver thick film conductors. This paper discusses the results of a newly developed Pb and Cd free silver thick film conductor paste with a modified silver powder metallurgy to improve the leach resistance, solder acceptance and adhesion using lead free solder. In addition, the pure silver conductor was fired on top of a low temperature dielectric paste. This conductor was evaluated by comparing lead free solder alloys to traditional tin-lead-silver solder alloys. This study included evaluations based on SEM photos, solderability, leach resistance, and initial and long term adhesions. Results are published describing the difference in behavior between the different solder alloys in conjunction with the different silver powder metallurgy.

Bismuth-Antimony as an Alternative for High Temperature Lead Free Solder

2012 ◽  
Vol 476-478 ◽  
pp. 1163-1168 ◽  
Author(s):  
M.Z. Shahrul Fadzli ◽  
M.A. Azmah Hanim ◽  
T. Sai Hong ◽  
A. Aidy ◽  
R. Rohaizuan
Keyword(s):  
High Temperature ◽  
Solder Alloy ◽  
Lead Free ◽  
Lead Free Solder ◽  
Solder Alloys ◽  
Bulk Analysis ◽  
Rich Phase ◽  
Solder Bulk ◽  
Free Solder ◽  
Lead Free Solders

The development works on high temperature lead free solder are mostly discussed nowadays. To replace the current high temperature lead free solders, further research need to be done. A great deal of effort has been put into the development of lead free solder alloys. Bi (Bismuth) and Sb (Antimony) solder system proved as one of the promising candidates for electronic assembly. Melting temperature of three Bi-Sb solder alloys studied in this research enhanced their potential as the alternative solder candidates for high temperature lead free solder. At interface, Cu3Sb IMC layer was formed for 95Bi-5Sb solder alloy. Spallation of Cu3Sb IMC layer took placed with the results of Cu3Sb IMC also found in the solder bulk. Analysis of 97.5Bi-2.5Sb solder alloy classified as no metallurgical reaction at the interface and only the mechanical joining existed at the interface. The dissolution of Cu from subtrate affected the formation of Cu rich phase and the unstable Bi-Cu rich phase phenomena act as the isothermal product found in solder bulk. Mechanical grain boundary grooving observed in 98.5Bi-1.5Sb solder alloys at interface. Different compositions of Bi-Sb solder alloys resulted in different types of microstructures at interface and in solder bulk after reflow.

Cyclic Mechanical Durability of Sn-3.9Ag-0.6Cu and Sn-3.5Ag Lead-Free Solder Alloys

2002 ◽  
Author(s):  
Qian Zhang ◽  
Abhijit Dasgupta ◽  
Peter Haswell
Keyword(s):  
Thermal Cycling ◽  
Strain Range ◽  
Mechanical Tests ◽  
Test System ◽  
Lead Free ◽  
Lead Free Solder ◽  
Solder Alloys ◽  
Mechanical Cycling ◽  
Mechanical Durability ◽  
Free Solder

The isothermal mechanical durability properties of two lead-free solder alloys, Sn3.5Ag and Sn3.9Ag0.6Cu, are presented and compared to that of the baseline eutectic Sn37Pb solder. Cyclic mechanical tests are performed at room temperature at various strain-rates and load levels, using a thermo-mechanical-microstructural (TMM) test system developed by the authors. The data is analyzed using standard power-law durability models based on work and inelastic strain range. The Sn3.9Ag0.6Cu lead-free alloy is found to be most durable, followed by the Sn3.5Ag solder and finally the baseline Sn37Pb eutectic alloy, under the test conditions investigated. However, tests at high load levels show a greater difference in durability than tests at low load levels. This trend is the opposite of that reported in the literature for thermal cycling durability. A hypothesis is put forward to explain the observed differences between mechanical cycling and thermal cycling, based on the energy-partitioning damage model.

Evaluation of the Creep Response of Lead Free Solder Materials Subjected to Thermal Cycling

2020 ◽  
Author(s):  
S. M. Kamrul Hasan ◽  
Abdullah Fahim ◽  
Jeffrey C. Suhling ◽  
Pradeep Lall
Keyword(s):  
High Temperature ◽  
Thermal Cycling ◽  
Isothermal Aging ◽  
Lead Free ◽  
Secondary Creep ◽  
Lead Free Solder ◽  
Temperature Extreme ◽  
Free Solder ◽  
Aging Phenomena ◽  
Lead Free Solders

Abstract In the electronic assembly arena, lead is being targeted due to the concern regarding environmental pollutants. So, the lead-free solder and its reliability are getting highlighted. During qualification testing or actual use lead-free solders in electronic assemblies, they are often subjected to thermal cycling. In the lead-free solder material, microstructural evolution and material property degradation occurs due to the thermal aging phenomena during dwell periods at the high temperature extreme of thermal cycling. In addition, during ramping between low and high temperature extreme, lead-free solders can experience additional aging phenomena. In our prior work, we have compared material properties (stiffness and strength) degradation of lead-free solder materials in isothermal aging and five different thermal cycling exposures. Changes in material properties were higher for all the thermal cycling exposures compared to the aging. In addition, microstructural evolution and material property degradation were exacerbated as the ramp rate decreased in the thermal cycling. In this study, the creep behavior evolutions occurring in SAC305 lead free solder subjected to isothermal aging and slow thermal cycling exposures have been investigated. Uniaxial test specimens were prepared by reflowing solder in rectangular cross-section glass tubes with a controlled temperature profile. Afterwards, the reflowed samples were exposed to either isothermal aging at 125 °C, or to thermal cycling from −40 to +125 °C, under a stress-free condition (no load) for various durations in an environmental chamber. A slow thermal cycling profile, e.g. 150 minutes cycle with 45 minutes ramps and 30 minutes dwells, was chosen for this study as it was found in our previous work that it caused the most detrimental effects on the mechanical behavior evolution. The thermally exposed samples were isothermally aged for 0, 1, 2, and 5 days; or were thermally cycled for 0, 48, 96, and 240 slow thermal cycles, which had the same aging times at the high temperature extreme of T = 125 °C. After aging or cycling, creep testing was performed at room temperature on the thermally exposed samples at three different stress levels (10, 12, 15 MPa). The evolutions of the secondary creep strain rate were obtained as a function of the stress level, as well as the net aging time at the high temperature extreme, and then compared. Results showed that secondary creep strain rate increased dramatically with equivalent aging time, and that the degradation effects were larger for slow thermal cycling than for pure aging. For example, the creep rate increased by 3.0–3.4X for 5 days of pure aging at T = 125 °C; while they increased by 10.9–13.1X for 240 thermal cycles, when there had been 5 days of equivalent aging at the T = 125 °C high temperature extreme.

Sign in / Sign up

Export Citation Format

Share Document