Accelerated Qualification of Electronic Assemblies Under Combined Temperature Cycling and Vibration Environments: Is Miner's Hypothesis Valid?

Sn-3.0Ag-0.5Cu (SAC305) alloy is the most widely used solder in electronic assemblies. However, issues associated with cost and drop/shock durability have resulted in a search for alternative lead-free solder alloys. One approach to improve the drop/shock reliability has been to reduce the silver content in Sn-Ag-Cu alloys. Another approach is doping Sn-Ag-Cu solder with additional elements. In 2008, the International Electronics Manufacturing Initiative (iNEMI) started the “Characterization of Pb-Free Alloy Alternatives” project to provide a comprehensive study of 15 tin-based solder interconnect compositions benchmarked against the eutectic tin-lead solder. For this study, temperature cycle durability was the primary focus and solders were selected to study the effect of varying silver content, microalloy additions, and aging. This paper reports the findings from one of the test conditions conducted under the iNEMI project. The cycles to failure for a temperature cycling test condition from −15°C to 125°C, with dwell times of 60 min at both extremes, are presented. The test assembly consisted of 16 of the 192 I/O BGAs and 16 of the 84 I/O BGAs soldered onto an LG451HR laminate. Test results revealed that the reduction of silver resulted in a reduction in cycles to failure. In all cases, the 15 tin-based solders were more durable than the eutectic SnPb solder. Aging at 125°C for 10 d did not affect the cycles to failure in SAC105 solder; however, the cycles to failure decreased with aging in SAC305 solder. In addition, aging resulted in a wider distribution of cycles to failure in 192 I/O BGAs. Failure analysis was carried out on all solder materials to identify the failure site and failure mode.

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Thermal Cycling Reliability of Alternative Low-Silver Tin-based Solders

International Symposium on Microelectronics ◽

10.4071/isom-2013-ta45 ◽

2013 ◽

Vol 2013 (1) ◽

pp. 000120-000127 ◽

Cited By ~ 2

Author(s):

Elviz George ◽

Michael Osterman ◽

Michael Pecht ◽

Richard Coyle ◽

Richard Parker ◽

...

Keyword(s):

Silver Content ◽

Temperature Cycling ◽

Temperature Cycle ◽

Sac305 Solder ◽

Test Assembly ◽

Cu Alloys ◽

Primary Focus ◽

Effects Of Aging ◽

Electronic Assemblies ◽

Cycles To Failure

Sn-3.0Ag-0.5Cu (SAC305) alloy is the most widely used solder in electronic assemblies. However, issues associated with cost and drop/shock durability have resulted in a continued search for alternative solder alloys. One approach to improve the drop/shock reliability has been to reduce the silver content in Sn-Ag-Cu alloys. Another approach is doping Sn-Ag-Cu solder with additional elements. Moreover, conflicting results have been reported in literature on the effects of aging on Sn-Ag-Cu alloys. In 2008, International Electronics Manufacturing Initiative (iNEMI) started the “Characterization of Pb-Free Alloy Alternatives” project to provide a comprehensive study of fifteen tin-based solder interconnect compositions benchmarked against the eutectic tin-lead solder. For this study, temperature cycle durability was the primary focus and solders were selected to study the effect of varying silver content, microalloy additions, and aging. This paper reports the preliminary findings from one of the test conditions conducted under the iNEMI project. The cycles to failure for a temperature cycling test condition from −15°C to 125°C, with dwell times of 60 minutes at both extremes are presented. The test assembly consisted of sixteen 192 I/O BGAs and sixteen 84 I/O BGAs soldered on to LG451HR laminate. Preliminary findings revealed that the reduction of silver resulted in a reduction in cycles to failure. In all cases, the fifteen tin-based solders were more durable than the eutectic SnPb solder. Aging did not affect the cycles to failure in SAC105 solder; however, the cycles to failure decreased with aging in SAC305 solder. In addition, aging resulted in a wider distribution of cycles to failure in 192 I/O BGAs.

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Evaluating the Impact of Dwell Time on Solder Interconnect Durability under Bending Loads

International Symposium on Microelectronics ◽

10.4071/isom-2012-poster_menon ◽

2012 ◽

Vol 2012 (1) ◽

pp. 000510-000513

Author(s):

Sandeep Menon ◽

Michael Osterman ◽

Michael Pecht

Keyword(s):

Fatigue Life ◽

Dwell Time ◽

Hold Time ◽

Temperature Cycling ◽

Temperature Cycle ◽

Mechanical Loads ◽

Solder Interconnects ◽

Solder Interconnect ◽

Electronic Assemblies ◽

The Impact

With increased portability and miniaturization of modern day electronics, the mechanical robustness of these systems has become more of a concern. Existing standards for conducting mechanical durability tests of electronic assemblies include bend, shock/drop, vibration and torsion. Though these standards provide insights into both cyclic fatigue and overstress damage incurred in the solder interconnects (widely regarded as the primary mode of failure in electronic assemblies), they fail to address the impact of time dependent (creep) behavior due to sustained mechanical loads on the solder interconnect durability. It has been seen that the solder durability under thermal cycling loads is inversely proportional to the dwell time or hold time at either temperature extreme of the imposed temperature cycle. Fatigue life models, which include dwell time, have been developed for solder interconnects subject to temperature cycling. However the fatigue life models that have been developed in literature for solder interconnects under mechanical loads fail to address the impact the duration of loading. In this study, solder interconnect test vehicles were subject to cyclic mechanical bending with varying dwell times in order to understand the impact of duration of mechanical loads on the solder interconnect durability. The solder interconnects examined in this study were formed with 2512 resistor packages using varying solder compositions (SnPb and SAC305). In order to evaluate the impact of dwell time, the boards were tested with a 60 second and a 300 second dwell time on both extremes of the loading profile. It was observed that an increase in dwell time of the loading profile resulted in a decrease in the characteristic life of the solder interconnects.

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Microstructural Evolution in SAC305 and SAC-Bi Solders Subjected to Mechanical Cycling

ASME 2018 International Technical Conference and Exhibition on Packaging and Integration of Electronic and Photonic Microsystems ◽

10.1115/ipack2018-8414 ◽

2018 ◽

Cited By ~ 9

Author(s):

Md Mahmudur R. Chowdhury ◽

Mohd Aminul Hoque ◽

Abdullah Fahim ◽

Jeffrey C. Suhling ◽

Sa'd Hamasha ◽

...

Keyword(s):

Solder Joints ◽

Temperature Cycling ◽

Electronic Packages ◽

Mechanical Cycling ◽

Intermetallic Particles ◽

Glass Tubes ◽

Lead Free Solders ◽

Electronic Assemblies ◽

Transgranular Cracks ◽

Varying Environment

Fatigue failure of solder joints is one of the most common methods by which electronic packages fail. Electronic assemblies usually must cope with a temperature varying environment. Due to the mismatches in coefficients of thermal expansion (CTEs) of the various assembly materials, the solder joints are subjected to cyclic thermal-mechanical loading during temperature cycling. The main focus of this work is to investigate the changes in microstructure that occur in SAC305 and SAC+Bi lead free solders subjected to mechanical cycling. In this paper, we report on results for the SAC+Bi solder commonly known as SAC_Q or CYCLOMAX. Uniaxial solder specimens were prepared in glass tubes, and the outside surfaces were polished. A nanoindenter was then used to mark fixed regions on the samples for subsequent microscopy evaluation. The samples were subjected to mechanical cycling, and the microstructures of the selected fixed regions were recorded after various durations of cycling using Scanning Electron Microscopy (SEM). Using the recorded images, it was observed that the cycling induced damage consisted primarily of small intergranular cracks forming along the subgrain boundaries within dendrites. These cracks continued to grow as the cycling continued, resulting in a weakening of the dendrite structure, and eventually to the formation of large transgranular cracks. The distribution and size of the intermetallic particles in the inter-dendritic regions were observed to remain essentially unchanged.

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Intermittent Failures in High Pin Count Packaging

ISTFA 2006: Conference Proceedings from the 32nd International Symposium for Testing and Failure Analysis ◽

10.31399/asm.cp.istfa2006p0109 ◽

2006 ◽

Author(s):

Ramesh Varma ◽

Richard Brooks ◽

Ronald Twist ◽

James Arnold ◽

Cleston Messick

Keyword(s):

Failure Analysis ◽

Shape Analysis ◽

State Of The Art ◽

Process Variation ◽

High Reliability ◽

Temperature Cycling ◽

Assembly Process ◽

System Failures ◽

Industrial Grade ◽

Corrective Actions

Abstract In a prequalification effort to evaluate the assembly process for the industrial grade high pin count devices for use in a high reliability application, one device exhibited characteristics that, without corrective actions and/or extensive screening, may lead to intermittent system failures and unacceptable reliability. Five methodologies confirmed this conclusion: (1) low post-decapsulation wire pull results; (2) bond shape analysis showed process variation; (3) Failure Analysis (FA) using state of the art equipment determined the root causes and verified the low wire pull results; (4) temperature cycling parts while monitoring, showed intermittent failures, and (5) parts tested from other vendors using the same techniques passed all limits.

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