Beginning July 1, 2006 all products sold to the European Union must comply with the Reduction of Hazardous Substances (RoHS) in Electrical and Electronic Equipment and the Waste Electrical and Electronic Equipment (WEEE) initiatives. While many North American manufacturers have taken a "wait and see" stance on the subject, the reality of lead-free manufacturing is upon us and electronics manufacturers are beginning to feel the pressure.
The anxiety associated with the transition to lead-free manufacturing is not unfounded. Considering the plethora of often-contradictory lead-free information that is presented as so-called "fact", the task of analyzing all the data and understanding how the switch will impact both a particular product and process is daunting. Making the actual conversion can be intimidating. But, while the transition will most likely not be terribly easy, it is manageable with the right information.
Let's take solder alloys, for example. Much to the industry's chagrin and to those who are promoting otherwise, there is no "drop in" solder replacement material for the currently used Sn63Pb37 or Sn62Pb36Ag2 alloys. However, the SAC396 alloy Sn3.9Ag0.6Cu (±0.2%) recommended by the National Electronics Manufacturing Initiative (NEMI) so far has proven to have similar reliability characteristics to the leaded alloys, under many test conditions. But even this alloy is not the only alternative available for the replacement of tin-lead.
There are many variations of the NEMI SAC alloy some with slightly higher tin content, others with variations on the copper and silver content. There are some formulations such as Sn3.8Ag 0.7Cu and Sn3.0Ag0.5Cu that have shown good performance in a variety of situations, however; some studies show slight performance differences among these various SAC alloys and more work needs to be conducted to validate these claims.
An important consideration in regard to lead-free solder pastes is how they interact with various component and pad metalizations. There are numerous lead-free component lead frames and terminations, which present a very broad range of combination possibilities and significant issues with compatibility. Most IC manufacturers and IC assemblers are in the very early stages of evaluation and only a very few have finalized any type of lead-free solution. Since lead-free finishes look the same as tin-lead finishes, the transition period between tin-lead and lead-free manufacturing can be particularly problematic with a high degree of probability that there will be a mixture of component finish types within the same factory, and even the same assembly, whether by design or accident.
Another major issue is the lack of component standards for lead-free manufacturing. Much of the burden of the lead-free transition rests on the shoulders of the component manufacturers, as they must assess the interactions between solders, fluxes, encapsulants, overmolds, thermal materials and underfills.
To date, materials suppliers have not provided component manufacturers with good data on how various materials work together that R&D effort was left to the component manufacturer. These manufacturers have also been working on the removal of certain flame-retardants that are covered by the same European legislation. This is further complicated by the fact that the WEEE and RoHS initiatives call for a ban on the poly-brominated species used as flame-retardants in molding compounds.
Lead-free manufacturing presents a whole new paradigm and it is imperative that component manufacturers have access to this data. Understanding how material sets will work together is critical to successful lead-free component manufacture and a service that not many materials suppliers can offer. Ensuring that packaging material sets are optimized and understanding this key parameter before investing in expensive product production, will ultimately lead to efficient manufacturing and higher yields. Work with suppliers who understand and can provide data on how materials will work together not just how an individual material performs in a lead-free manufacturing environment.
The transition will not be easy, but with careful analysis and a complete understanding of the issues, it is manageable. Attend seminars and workshops on the subject. Gather as much information as you can and analyze it from every angle: manufacturing viability, cost, performance, reliability, etc. And, finally, work with suppliers that can add value not confusion to your lead-free process.
Neil Poole, Ph.D., is a senior applications chemist with Henkel Technologies. Since obtaining his doctorate from The University of Edinburgh, Poole has worked in basic background research, product research and development, and customer and product technical support. His work has included the study and analysis of a variety of materials including plastics, solvents and solder. Poole is the author of numerous published technical papers and has obtained several patents. His most recent work includes the study of water washable and lead free solder paste formulations.
Brian J. Toleno, Ph.D., is a senior applications chemist with Henkel Technologies and holds a Ph.D. in analytical chemistry from Penn State University. Prior to working at Henkel Technologies, Toleno managed the failure analysis laboratory at the Electronics Manufacturing Productivity Facility (EMPF). He is an active member of SMTA, serves as the Technical Vice-Chair for the IEMT (SEMIcon West) and is active within the IPC, participating on several committees. Toleno chairs the underfill handbook committee (J-STD-030) and co-chairs the Solder Paste Standards Committee (J-STD-005). As a leading industry expert, Toleno has written a course on failure analysis for SMTA and has authored many technical papers for trade journals and peer reviewed publications. Additionally, he has written two chapters for electronic engineering handbooks on adhesives and materials.