A review on thermal cycling and drop impact reliability of SAC solder joint in portable electronic products

Purpose – The purpose of this paper is to discuss the reliability of board level Sn‐Ag‐Cu (SAC) solder joints in terms of both thermal cycling and drop impact loading conditions, and further modification of the characteristics of low Ag‐content SAC solder joints using minor alloying elements to withstand both thermal cycle and drop impact loads.Design/methodology/approach – The thermal cycling and drop impact reliability of different Ag‐content SAC bulk solder will be discussed from the viewpoints of mechanical and micro‐structural properties.Findings – The best SAC composition for drop performance is not necessarily the best composition for optimum thermal cycling reliability. The content level of silver in SAC solder alloys can be an advantage or a disadvantage depending on the application, package and reliability requirements. The low Ag‐content SAC alloys with different minor alloying elements such as Mn, Ce, Bi, Ni and Ti display good performance in terms of both thermal cycling and drop impact loadi...

A review on effect of minor alloying elements on thermal cycling and drop impact reliability of low‐Ag Sn‐Ag‐Cu solder joints

Electromigration mechanisms in Sn-0.7Cu/Cu couples by four dimensional (4D) X-ray microtomography and electron backscatter diffraction (EBSD)

The iNEMI Cu Wire Reliability Project Team has performed reliability tests on a copper wire bonded QFN (Quad Flat No-Lead) package to assess its long term reliability. Bare copper (Cu) and Palladium coated Cu (Pd/Cu) bonding wires were used with a low chlorine mold compound as test vehicles using 5 DOE legs comparing wire type and process conditions. Five HAST (Highly Accelerated Stress Test) conditions with fixed bias voltage, varying temperature and humidity, and one condition of HTS (High Temperature Storage) and TC (Temperature Cycling) were used for the reliability test. The TC test resulted in no failures for all segments up to 3000 cycles; however, different results were obtained from HAST. The packages were tested for a longer time to achieve failures. With longer times and cycles, the bare Cu package was found to fail due to oxidation around the bonded ball area and Cu/Pd packages failed due to the Pd distribution pattern in the bonded ball. A humidity level of 55%RH was sufficient to affect the oxidation of the bare Cu wire but to a lesser degree than at 85%RH.

Copper wire bonded package characterization and reliability for QFN package from iNEMI collaborative project

This research focuses on Ag-Cu powder particles processing by mechanical alloying (MA) route. The powder mixture is representative for the eutectic composition, respectively 72%wt. Ag + 28% wt. Cu. The milling process is developed in high energy ball mill Pulverisette 6, using different size for the milling balls, in wet conditions for 80 hours. One of the most important parameter studied in this research is the particle size distribution of the processed powder mixture. Thus, it changes along the milling time, from 10…75 µm at the beginning of MA process up to (60 – 80) nm at 80 h. The milling parameters will be optimized in future research depending on the particle size distribution related with thermophysical and thermodynamic properties focused on electrical and optical properties improvement.

Research of the Milling Time Influence on Ag-Cu Powder Particles Size Processed by Mechanical Alloying Route

Significant innovations in Pb-free solder alloy compositions are being driven by volume manufacturing and field experiences. As a result, the industry has seen an increase in the number of Pb-free solder alloy choices beyond the common near-eutectic Sn-Ag-Cu (SAC) alloys. The increasing number of Pb-free alloys provides opportunities to address shortcomings of near-eutectic SAC, such as the poor mechanical shock performance, alloy cost, copper dissolution, and poor mechanical behavior of joints in bending. At the same time, the increase in alloy choice presents challenges in managing the supply chain and introduces a variety of technical and logistical risks, such as a potential decrease in thermal fatigue resistance and the complexity of managing process parameters given the variability of alloy compositions. This paper summarizes the results of an iNEMI project to address the opportunities and risks of new Pb-free alloy alternatives. The results of our analysis of the state of industry knowledge on Sn-Ag-Cu alloy alternatives are provided, and focus areas for closing key gaps are identified. Progress in updating or creating industry standards to manage the introduction and use of new alloys is also presented. Finally, our plans to investigate thermal fatigue reliability of new alloys are described.

Addressing opportunities and risks of pb-free solder alloy alternatives

Gold (Au) wire bonding is one of today's most common and well understood first level interconnects. However copper (Cu) wire bonding is increasingly being used for a wide variety of components, predominantly driven by the cost benefit of Cu. As the application moves from mostly consumer products to high-reliability electronic systems, the long term reliability of fine-pitch Cu wire bonding must be better understood. A collaborative project has been launched by iNEMI (International Electronics Manufacturing Initiative) member companies to assess the current adoption landscape of Cu wire bonding in the industry, and to understand the critical factors that impact component reliability. An industrial survey has already been conducted by the project. The results of the survey not only provide a clear overview of the general application status of Cu wire bonding, but also illustrate key technical concerns such as reliability performance, materials and process capability (or optimization), and qualification standards requirements.

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Current industry adoption of fine-pitch Cu wire bonding and investigation focus at iNEMI

NEMI has been publishing its Technology Roadmap biannually for the last 14 years. The strength of these roadmaps has been the depth of the knowledge from experts worldwide combined with the breath of view taken across the whole electronic manufacturing supply chain. Every new roadmap helps identify the technology gaps in various aspects of the supply chain. These gaps then stimulate and encourage dialogue to develop consensus-based strategies resulting in industry-based joint project work or promoting research areas to the academic communities. Since 2007, there has been a focus on three main technology areas for iNEMI industry-based projects: Energy and the Environment, Miniaturization and Medical Electronics. This paper will cover the goals of these three areas and the strategies being adopted to address the present and future technology gaps, as identified in the most recent roadmaps. Results from key projects in the three areas will be presented. These will include projects on Pb-free alloy alternatives and HFR-free substrates; higher density testing and nanosolders, and Medical Components Reliability.

http://ieeexplore.ieee.org/iel5/5238690/5272842/05272913.pdf

Grace O'Malley

Papers

Addressing opportunities and risks of pb-free solder alloy alternatives

Current industry adoption of fine-pitch Cu wire bonding and investigation focus at iNEMI

Closing technology knowledge gaps: Projects arising from the iNEMI technology roadmap