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1997 TMS Annual Meeting: Monday Abstracts


Sponsored by: EMPMD Electronic Packaging and Interconnection Materials Committee
Program Organizers: Michael R. Notis, Department of Materials Science and Engineering, Lehigh University, Bethlehem, PA 18015; Dr. Sung K. Kang, IBM, TJ Watson Research Center, Yorktown Heights, NY 10598

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Room: 314B

Session Chairperson: TBA

8:30 am INVITED

INTRODUCTION OF THE NCMS LEAD-FREE SOLDER DEVELOPMENT PROJECT: Jerald Rosser, Hughes Aircraft Company, P.O.Box 11337, Building 801/E-24, Tucson, AZ 85734-1337

Since 1990, proposed legislation and consumption taxes on the use of lead have concerned the electronics industry in this country. Although the consumption of lead for electronic interconnections (via solder) is relatively low in comparison to batteries, the possibility of restricting lead usage for solder alloys would have a dramatic effect on the electronics industry. This concern lead the National Center for Manufacturing Sciences (NCMS), a not-for-profit cooperative research consortium of more than 215 U.S. North American manufacturers, to establish a multi-year Lead Free Solder Project, involving participants from industry, (GM DELCO, AT&T/Lucent Technologies, United Technologies/Hamilton Standard, GM-Hughes, Rockwell International, Ford, Texas Instruments), academia (Rensselaer Polytechnic Institute), and national laboratories (Sandia, NIST, and Electronic Manufacturing Productivity Facility). The objective of the program was to identify lead free solder alternative replacement(s) for lead bearing solders in the electronics industries. The alloy(s) must meet the interconnect performance requirements at operating environments ranging from -40 to +125°C. Over the past three years, numerous lead free alloy solders have been thoroughly evaluated. The project participants will be presenting the results of this four year NCMS evaluation of the material properties, economic impact, toxicological properties, manufacturability, modeling and reliability predictions.

9:00 am INVITED

SOLDER ALLOY DEVELOPMENT: Yun Zhu, Delco Electronics Corporation, 2705 S. Goyer Road, M/S D-16, Kokomo, IN 46904-9005

In this presentation, the process of alloy development and down selection is summarized. An initial list of more than 70 alloys was constructed, including binary, ternary, quaternary, and quinary alloys. he first selection process was applied based on the toxicology, economic, and availability criteria. Then a downselection criteria matrix, including melting temperatures, wetting behavior, and thermo-mechanical fatigue, was generated for a quantitative comparison of alloys with respect to three baseline alloys: eutectic Sn-Pb, Sn-Bi, and Sn-Ag solders. Physical testing was performed to provide the data for downselection. Extensive phase diagrams from literature and thermodynamic calculation were used to predict the melting temperature range, and compare with experimental results. A comprehensive literature search was conducted to identify publications of the past 25 years.

9:30 am INVITED

ECONOMICS, AVAILABILITY, AND TOXICOLOGY: Charles DeSantis, Hamilton Standard Division of United Technologies Corporation, M/S 3-2-F2, One Hamilton Road, Windsor Locks, CT 06096-1010; Joe Fegley, Texas Instruments, 2501 W. University, Box 801/ M/S 8013,McKinney, TX 75070; Tsung-Yu Pan, Ford Motor Company, P. O. Box 2053, SRL Building, M/D 3135, Dearborn, MI 48121-2053

Based on data from the U.S. Department of Interior, an economics/availability study was completed which estimates the impacts on supply and cost to the electronics industry if it were to replace tin-lead solder with a lead-free solder alloy. Considerations in this study included the availability of the replacement materials, world mine production and consumption, world reserves and reserve bases, present world mine production capacity, principal reserve locations, average annual price and price history. Seven alloying elements were investigated. They were antimony, bismuth, cadmium, copper, indium, silver, tin, and zinc. Limits placed on the estimated alloy cost, ore reserve consumption rate, and required mine or refining capacity permitted rank ordering of potential alloys. An extensive literature search on the toxicity of common solder alloying elements was also conducted. Available data on the disposition, toxicity, and exposure limits of these solder alloying elements were analyzed in order to rank their use risk. The process used to evaluate the economics, availability, and toxicity of lead free solders, as well as the findings of the study will be discussed.

10:00 am BREAK

10:20 am INVITED

MANUFACTURING WITH LEAD-FREE SOLDERS: John Greaves, Electronics Manufacturing Productivity Facility, 714 N. Senate Ave., Indianapolis, IN 46202-3112

Successful introduction of lead-free solders into the manufacturing process requires subtle changes in process parameters. Changes in density, melting temperature, wetting and spreading behavior, all affect the parameters necessary for optimum manufacturing and reliability. This currently results in a need to change print speeds, squeegee pressures, and stencil thicknesses. Component placement is relatively unchanged. The largest changes in manufacturing with lead-free solders are those in the reflow process. Manufacturing lead-free solders with RMA fluxes requires modifying reflow profiles to insure that the flux is active when the solder reaches the melting temperature. Manufacturing with fluxes designed for lead-free solders simply requires setting the conveyor speeds and zone temperatures to achieve the suggested profile. No substantial difference has been noticed in the cleaning of lead-free alloys and the lead-free alloys evaluated are compatible with no-clean processes as well. Wave soldering of lead-free solders using RMA fluxes can present some difficulties if the process is not well controlled. While many lead-free solders can be used in wave-soldering with no changes to the profile or pot temperature, using fluxes and profiles designed for lead-free solders can increase yields and simplify the wave-soldering process.

10:50 am INVITED

Pb-FREE SOLDER RELIABILITY COMPARISON: Gordon Whitten, Delco Electronics Corporation, 700 East Firmin St., M/S T100-34, Kokomo, IN 46904-9005

The reliability of several Lead-free solder alloys are compared. Thermal cycle testing was performed using two different profiles: 0 to +100°C, to simulate telecommunications and office environments; and -55 to +125°C, to simulate automotive and military environments. The National Center for Manufacturing Sciences (NCMS) Surface Mount Reliability Test Vehicle(SMRTV) was used to test more than 2000 joints/board with more than 10,000 joints per alloy for each temperature cycle. Five Pb-free alloys are compared to 3 baseline alloys, SnPb Eutectic, SnAg Eutectic, and SnBi Eutectic. Three parameter Wiebull analysis is used to determine failure free time, Wiebull life, and Wiebull shape parameter.

11:20 am INVITED

RELIABILITY MODELING FOR LEAD-FREE MICROELECTRONICS: Scott A. Schroeder, Rockwell International Science Center, 1049 Camino Dos Rios, Thousand Oaks, CA 91360

The NCMS Lead-Free Project Modeling Task Group was formed to determine the capability of existing models developed by the consortium members to predict low cycle fatigue life for specified test vehicles using down-selected lead-free solder alloys. A quantitative summary and objective analysis of predictions and modeling capability for down-selected alloys are generated. Life prediction results are correlated with reliability test vehicle data using a -55 to +125°C thermal cycle. The final project goal is a design guide for predicting joint fatigue life for lead-free leadless capacitors and resisters, 44 LCCC, 32 TSOP, and 132 PQFP components. Solder down-selection guidance is provided through recommendations of mechanical tests, test priority, and evaluation of hysteresis loop, thermo-mechanical fatigue, creep, and tensile property data. Alloy phase diagram modeling information provides manufacturing down-selection criteria. Additional support is provided through stress analysis of manufacturing test vehicles.

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