Halogen-Free Electronics Assembly Technical Papers
Lead-Free Soldering of Chip-Scale Packages
By Dr. Ning-Cheng Lee
A host of lead-free solder replacements are coming to the fore, each presenting the user with certain tradeoffs. Many of the replacement solder systems are based on adding a small quantity of a third or fourth element to binary alloy systems to lower the solder’s melting point, which increases wetting and reliability.
Download: English (148 KB PDF)
Conquer Tombstoning in Lead-Free Soldering
By Benlih Huang, Ph.D. and Ning-Cheng Lee, Ph.D.
Tombstoning of SnAgCu is affected by the solder composition. At vapor phase soldering, both wetting force and wetting time at a temperature well above the melting point have no correlation with the tombstoning behavior. Since tombstoning is caused by unbalanced wetting force, the results suggest that the tombstoning maybe dictated by the wetting at the onset of paste melting stage.
Download: English (268 KB PDF)
Control Lead-Free Tombstoning via Alloy Composition
By Benlih Huang, Ph.D. and Ning-Cheng Lee, Ph.D.
Effect of solder alloy composition and properties on tombstoning of SnAgCu has been investigated. Both wetting force and wetting time at a temperature well above the melting point have no correlation with the tombstoning behavior observed at vapor phase soldering. Since tombstoning is caused by unbalanced wetting force, this unbalanced wetting force may occur at the onset of melting. DSC study indicates that the tombstoning rate decreases with increasing pasty temperature range and increasing mass fraction of solid in solder at onset of melting.
Download: English (332 KB PDF)
Effect of Lead-Free Alloys on Voiding at Microvia
By Arnab Dasgupta, Benlih Huang, Ph.D. and Ning-Cheng Lee, Ph. D.
Voiding in solder joints is a major reliability threat, mainly due to its role as stress concentrator, hence it either initiates crack formation or facilitates the crack propagation, and eventually results in joint failure. The problem intensifies with the introduction of microvia and lead-free soldering. The former aggravates the problem by introducing dead corners for adequate solder paste filling and wetting, while the latter worsens the voiding due to its poor solder wetting characteristics.
Download: English (320 KB PDF)
Solder Paste Evaluation Techniques to Simplify the Transition to Pb-Free
By Timothy Jensen
As the July 1, 2006 Pb-free deadline approaches, many electronics assemblers are beginning to fathom the changes and process demands required. The two biggest material concerns involve solder paste and components.
Download: English (428 KB PDF)
Getting Ready For Lead Free Solders
By Dr. Ning-Cheng Lee
This paper reviews the status of lead-free solder developmental works. Some of the solder systems, Bi-Sn, Bi-Sn-Fe, In-Sn, Sn, Sn-Ag, Sn-Ag-Zn, Sn-Ag-Zn-Cu, Sn-Bi-Ag, Sn-Cu, Sn-Cu-Ag, Sn-In-Ag, Sn-Sb, Sn-Zn and Sn-Zn-In are discussed in more details, while the others are briefly commented on. In general, compared with eutectic Sn-Pb solder, all the lead-free solder alternatives investigated more or less exhibit some shortcomings, such as price, physical, metallurgical, or mechanical properties.
Download: English (60 KB PDF)
Implementing Pb-Free Assembly at Your Factory
By Dr. Ronald Lasky, Ph. D, PE and Timothy Jensen
Download: English (2.4 MB PDF)
A Drop-In Lead-Free Solder Replacement
By Ning-Cheng Lee, James A. Slattery, John R. Sovinsky, Iris Artaki and Paul T. Vianco
Environmental and toxicity concerns related to the use of lead have initiated the search for acceptable, alternate joining materials for electronics assembly. This paper describes a novel lead-free solder designed as a "drop in" replacement for common tin/lead eutectic solder. The physical and mechanical properties of this solder are discussed in detail with comparison to tin/lead eutectic solder. The performance of this solder when used for electronics assembly is discussed and compared to other common solders. Fatigue testing results are reported for thermal cycling electronics assemblies soldered with this lead-free composition.
Download: English (208 KB PDF)
Lead-Free Soldering and Low Alpha Solders for Wafer Level Interconnects
By Dr. Ning-Cheng Lee
Lead-free soldering, originally started as an environmental issue, is evolving rapidly into a business survival tool for the worldwide electronic industry. Promising lead-free solder alternatives for surface mount assembly applications include eutectic Sn/Ag, eutectic Sn/Cu, Sn95/Sb5, eutectic Sn/Bi, Sn/Ag/Cu, Sn/Ag/Cu/X, Sn/Bi/Ag/X, Sn/Zn/X, and Sn/In/Ag/(X). However, for wafer level area array solder bump interconnects, most of those options fall short in terms of fatigue resistance.
Download: English (160 KB PDF)
Nothing Solders Like Solder...Or Does It?
By Amanda Gronau
The move to lead-free electronics has had a slow start and many detractors, for a variety of reasons that range from the rational - added costs, new process parameters, extensive testing and approval, the need for consensus within the industry, to the irrational - fear of the unknown. The transition will not be easy, but given the market demand for environmentally friendly electronics, it seems inevitable.
Download: English (1.5 MB PDF)
An Overview of a Successful Pb-Free Implementation
By Ronald Lasky, PH.D., PE, and Timothy Jensen
The clock is ticking, on July 1, 2006 the WEEE Initiative will take effect. Thereafter, all electronic assemblers that sell products in Europe must be ready to convert their assembly processes to Pb-free. The nearness of this date raises the question of what can be done to get ready. In response to this need, we will review a pioneering effort in establishing a Pb-free process.
Download: English (1.1 MB PDF)
Changing to Pb-free Profoundly Impacts the Manufacturing Production Process
By Richard Brooks, David Day and Vahid Goudarzi
This paper will outline the issues relating to the implementation of a Pb-free solder paste into a standard Sn/Pb manufacturing facility and product. The Pb-free study includes the compatibility and impact on the various manufacturing processes that include, printing, component placement, reflow process, and solder joint quality.
Download: English (532 KB PDF)
A Model Study of Profiling for Voiding Control at Lead-free Reflow Soldering
By Dr. Yan Liu, William Manning, Dr. Benlih Huang and Dr. Ning-Cheng Lee
Voiding is attributed to the flux outgassing within the solder joints when the solder is at molten state. The effect of reflow profile on voiding at microvia for lead-free soldering is strongly dependent on the flux chemistry. In general, wetting is more important than melting outgasing behavior, and can be enhanced by employing a higher melting energy, including both higher peak temperature and longer dwell time.
Download: English (456 KB PDF)
Prospect of Lead Free Alternatives for Reflow Soldering
By Dr. Benlih Huang and Dr. Ning-Cheng Lee
The prospects of 10 major lead-free solder alloys for being widely used for reflow soldering are studied in this work. Compatibility of those alloys with a variety of representative flux chemistries is considered essential, and is determined for performance in handling-ability, including shelf life and tack time, and soldering capability, including solder balling, wetting, and solder joint appearance. Results indicate that the control 63Sn37Pb is still the most compatible alloy, rated 27.1 in compatibility out of a full scale 30 when using warm profile.
Download: English (320 KB PDF)
Six Sigma® Techniques for Solder Paste Selection
By Ronald C. Lasky, Ph.D., PE, Professor Daryl Santos, Ph.D., Aniket A. Bhave and Wang Ming
Numerous studies have shown that greater than 60% of end of line defects in SMT assembly can be traced to solder paste and the printing process. Reflowing adds another 15% or so. In light of this fact, it is surprising that no simplified procedure for solder paste evaluation has been documented. This paper is about such a procedure.
Download: English (236 KB PDF)
Tin-Silver-Bismuth: A Better Lead Free Alternative?
By Steve Dowds
As long as we are using components which are finished with Tin-Lead, which we certainly will over the next three to five years, Bismuth-containing solders cannot be used due to the long-term reliability problem associated with Lead-contamination. Despite fears to the contrary there are no problems with the long-term availability of Bismuth.
Download: English (524 KB PDF)
Voiding of Lead-Free Soldering at Microvia
By Dr. Hyoryoon Jo, Benjamin E. Nieman and Dr. Ning-Cheng Lee
Microvia technology is a critical element in high density interconnect development. It allows realization of low cost, high density, high speed and miniaturization for electronic devices. However, accompanied with all of the advantages described above is the observation of a high occurrence rate of voiding in the solder joints. Presence of voids in the solder joints often affects the mechanical properties of joints and deteriorates the strength, ductility, creep and fatigue life, due to the growth in voids, which could coalesce to form ductile cracks and consequently lead to failure.
Download: English (344 KB PDF)
Lead-Free Soldering – Where The World Is Going
Dr. Ning-Cheng Lee
Lead-free soldering for electronic industry is a segment of global trend toward lead-free environment. Although initiated in U.S. in early 1990’s, it advanced much more rapidly in Japan and Europe. This differentiation in Pb-free progress triggered great concerns of users of Pb-containing solders about maintaining business opportunity, therefore further expedites the advancement of Pb-free soldering programs. The favored Pb-free solder alternatives vary from region to region.
Download: English (56 KB PDF)
