-
- News
- Books
Featured Books
- smt007 Magazine
Latest Issues
Current IssueComing to Terms With AI
In this issue, we examine the profound effect artificial intelligence and machine learning are having on manufacturing and business processes. We follow technology, innovation, and money as automation becomes the new key indicator of growth in our industry.
Box Build
One trend is to add box build and final assembly to your product offering. In this issue, we explore the opportunities and risks of adding system assembly to your service portfolio.
IPC APEX EXPO 2024 Pre-show
This month’s issue devotes its pages to a comprehensive preview of the IPC APEX EXPO 2024 event. Whether your role is technical or business, if you're new-to-the-industry or seasoned veteran, you'll find value throughout this program.
- Articles
- Columns
Search Console
- Links
- Events
||| MENU - smt007 Magazine
Are You Ready for Lead-free Assembly?
December 31, 1969 |Estimated reading time: 10 minutes
The lead-free challenge lies in using technology that allows electronics assemblers to maintain optimal thermal processes in the reduced lead-free process window.
By Greg Jones, Ph.D.
In the 1980s, the shift to unleaded fuels forced auto makers to redesign power plants and engine controls, resulting in more efficient vehicles and a cleaner environment. The current shift to lead-free solders in the electronics industry is inevitable and will have similar results. In Japan, consumer goods manufactured with lead-free solders are already in production. In Europe, solder alloys containing lead soon will be banned. In the United States, where lead-free solder legislation originated, assemblers of electronic assemblies will be forced to adopt lead-free solders by global marketplace necessity. Lead-free solder adoption will require electronics assemblers to allocate greater resources to their thermal processes.
Lead-free solders reach liquidus at temperatures 20° to 50°C higher than the lead-based solders currently used. Because many components cannot tolerate peak temperatures above 235°C, one characteristic of lead-free solders will be drastically reduced thermal process windows. Strategies for minimizing the pain associated with this reduced process window, and the opportunities for optimizing the thermal process, comprise the silver lining in the lead-free cloud.
Current Situation
At the Surface Mount Technology Association (SMTA) conference in September 1999, there was some question whether the European and Japanese initiatives to remove lead from electronic assemblies would be followed worldwide. By IPCWorks '99 there was little doubt that lead-free soldering is not just coming, but it is here. Participants at IPCWorks '99, International Summit on Lead-free Electronics Assemblies, included major electronics manufacturers and assemblers, most solder paste manufacturers and representatives of the automotive industry's electronics subsidiaries. Papers presented covered all aspects of the shift to lead-free assemblies, which was approached from three principle angles: legal, marketing and technical.
Legal Considerations
Europe: The final draft of the Waste from Electrical and Electronic Equipment (WEEE) Directive is expected to be completed soon. The document is still changing, but it is certain that electronic assemblies containing lead will be banned from the European Union as of January 2004. Motivation behind this ban is that electronic waste is growing at a rate three times greater than other solid wastes, and this has raised concerns about lead leaching into water supplies.
Japan: The Japanese have a greater waste problem than the Europeans, and are working aggressively toward lead-free electronics assemblies. In 1998, the Japanese Electronics Industries Association decided to voluntarily eliminate lead from electronic assemblies. The association's goal is to have half of Japanese electronics production lead-free by 2002, and to be completely lead-free by 2004.
Figure 1. The environmentally safe symbol used by Panasonic on its lead-free mini disc player is an example of green marketing.
United States: Ironically, the initial impulse for lead-free electronics originated in the United States. Following the ban on leaded plumbing solders in the early 1980s, electronic assembly was the next logical industry target for lead removal. The Reid Act of 1992, an omnibus environmental bill, would have accomplished that, but was defeated when Congressional control shifted from the Democrats to the Republicans. Currently, there is no legislation proposing a leaded solder ban, but there are legal threats on the horizon. The Environmental Protection Agency (EPA) may drop the regulatory limit on lead as a hazardous material from 10,000 to 10 pounds per year, making almost every leaded solder user subject to EPA regulation, reporting and inspection. There is little chance that leaded solders will be banned in the United States in the near future, but there are many compelling reasons that will persuade numerous U.S. electronics assemblers to go lead-free.
International: One concern to all electronics manufacturers is the prospect that the European ban, which is as close to a done deal as anything can be, will touch off trade disputes. The prospect of a major trade war involving one of the world's largest and most critical industries is something to be avoided.
Marketing Considerations
On the adoption of lead-free solders, many prognosticators feel that the legal issue is a moot point, and marketing considerations alone will force a change to lead-free electronics assemblies in the near future. Marketing research presented at IPCWorks '99 by Dr. Iwona Turlik, director of the Motorola Advanced Technology Center, indicates:
- 20 percent of consumers actively consider the environment when making a purchase.
- 45 percent of consumers have bought a product because it is environmentally safe.
- 50 percent of consumers have switched brands upon finding that a product hurts the environment.
- 76 percent of consumers will switch to an environmentally safe product if price and quality are comparable.
Japanese electronics manufacturers have taken the lead in "green" marketing. Panasonic's lead-free mini disc player, packaged with a green leaf environmentally safe symbol (Figure 1) and released in October 1998, has gained significant increases in market share, moving from 4.7 to 15 percent of the mini disc market. In the United States, Ford Motor Co. has launched what is perhaps the largest green marketing campaign to date. Ford has gone on record that their electronic assemblies will be lead-free by 2002 and vehicles, aside from batteries, will be lead-free by 2004.
Technical Considerations
Controversy over lead-free solders has shifted from whether they are adequate replacements for traditional tin/lead solders to which of the many possible replacement alloys will be selected as a new standard. This will be critical. Currently, electronic assemblies can be repaired worldwide with standard leaded solder. There are numerous solderability and wetting issues between lead and lead-free solders - lead-free solders wet poorly to components with leaded leads, for example. Also critical are compatibility issues between various lead-free alloys. The global electronics industry must settle on a single standard alloy to ensure that assemblies can be repaired expeditiously and reliably. Another issue is recyclability of assemblies - a single standard alloy will make it much more feasible to recover and recycle the base metals in these assemblies. Currently, most paste manufacturers and many electronics manufacturers have developed proprietary alloys.
The alloys that look most promising to become the industry standard are tin/silver/copper (Sn/Ag/Cu) and tin/silver/bismuth (Sn/Ag/Bi). Between the two choices lies a trade-off. Sn/Ag/Cu provides solder joints that are more reliable than the current Sn/Pb alloys and has liquidus temperatures around 217°C.
Bismuth alloys, which have liquidus temperatures from 206° to 213°C, provide inferior solder joints to those provided by current leaded solders, mainly because of a phenomenon known as "fillet lifting." Bismuth alloys are preferred by some because they are the closest thing to a "drop-in" replacement for leaded solders, are favored by the Japanese and currently are used in the lead-free electronic assemblies on the market. They are more expensive than Sn/Ag/Cu alloys and there are concerns whether the world's current bismuth resources are adequate to fulfill the entire market's needs.
Americans and Europeans favor an Sn/Ag/Cu alloy as the standard because of its greater reliability and lower cost, but acknowledge that the higher process temperatures required present a challenge for electronics assemblers. Both alloy types have been tested extensively and soon will be used in volume production. An additional factor in choosing a standard alloy is that Sn/Ag/Cu alloys are favored by the automotive industry, as their higher melting points give better reliability in under-hood applications. The more robust joints will also be favored for military and aviation applications.
The Challenge
Regardless which alloy becomes the world standard - if it is possible to settle on a standard - the primary challenge that lead-free solders will present to electronics assemblers is higher process temperatures. The current thermal process window is a wide one, with the lower limit set at 183°C (the liquidus temperature of leaded solders) and the upper limit at 235°C, which is the maximum temperature that some sensitive components can withstand. These process limits provide a temperature Delta (DT) of more than 50°C - wide enough that a monitored process can be expected to produce low defects and high yield with little fear of defects caused by process drift.
For lead-free assemblies, the process window will shrink dramatically (Figure 2). With the bismuth alloys favored by Japanese assemblers (206° to 213°C liquidus), the window will shrink by half (22° to 29°C). Using the Sn/Ag/Cu alloys (217°C liquidus), the window will be cut by 65 percent, to 18°C. Given that few assemblers want to get within 5°C of their control limits, the true process window with Sn/Ag/Cu alloys will be 8°C. This very narrow process window is the challenge that will confront electronics assemblers shifting to lead-free production.
Figure 2. There is a dramatic shrinkage in the reflow process window when lead-bearing solders are replaced by lead-free solders.
The window is unlikely to expand in the near future. It is widely acknowledged that the component sector is lagging behind other sectors - assemblers, soldering materials suppliers and soldering equipment manufacturers - in preparing for the shift to lead-free assemblies. Component manufacturers are faced with a three-part challenge: they must remove lead from their products, develop leads that are compatible with lead-free solders and, eventually, develop components with higher temperature tolerances. The first two tasks must be successfully completed to assemble products that meet European standards. The question is whether component manufacturers will be able to raise temperature tolerances in the short term. In the long term, the question will be whether raising the process temperature limits of components will be economically justifiable or even necessary.
The problem of narrow process windows will be further exacerbated by the move to more complicated assemblies with increased component density. Finding a profile that reliably reflows these assemblies, especially larger ones that can experience large peak DTs across the board, has never been easy. Real-world production issues, such as maintaining high throughput and minimizing oven changeover times between production runs, also figure into the equation. The lead-free challenge lies in finding and utilizing technology that allows electronics assemblers to define and maintain optimal thermal processes in the drastically reduced lead-free process window.
The Solution
For more than a decade, the key to a reliable and repeatable thermal process has been real-time continuous thermal monitoring. An automated thermal management program allows electronics assemblers to obtain and analyze real-time live data on their soldering process. Critical process temperature variations are detected and revealed as they occur, allowing deviations to be corrected immediately. Given the tight process windows required by lead-free soldering processes, real-time monitoring has become an essential process control tool.
Additionally, state-of-the-art software that simplifies conversion to lead-free electronics assembly is now available. An automated profiling program, which has the capability to communicate with the oven controller, allows manufacturers to handle the lead-free challenge and optimize their thermal processes. A self-profiling software option can automate oven setup, allowing even minimally trained operators to perform error-free profiling using any solder paste, lead-based or lead-free.
When used with modern thermal processing equipment, this combination of process control tools lets manufacturers resolve many technical challenges posed by the smaller process window required for lead-free soldering. The issues of meeting legislative mandates, responding to market trends and selecting appropriate lead-free solder pastes remain matters to which each manufacturer must respond individually.
Lead-free Future
Lead-free electronics assembly is coming faster than anticipated. The shift to lead-free solders will present electronics assemblers with significant challenges, but higher process temperatures and reduced process windows do not have to be among them. New thermal profiling technology is available now and, with the proper tools, most assemblers can produce high-quality products with only moderate thermal process changes.
Benefits of lead-free electronic assemblies include the environmental advantages, the marketing gains associated with green products, and the potential for more robust and reliable soldered connections. Benefits associated with advanced thermal management and profiling systems are also apparent: higher quality products combined with greater throughput and reduced manpower requirements equals a better bottom line.
WORKS CONSULTED
- Edwin Bradley, NEMI Pb-free Interconnect Task Group Report, presented at IPCWorks '99.
- Carol Handwerker, NCMS Lead-free Solder Project: A Summary of Results, Conclusions and Recommendations, presented at IPCWorks '99.
- Kay Nimmo, Worldwide Environmental Issues in Electronics and the Transition to Lead-free, presented at IPCWorks '99.
- Iwona Turlick, "Electronics and the Environment," keynote address at IPCWorks '99.
GREG JONES, Ph.D., may be contacted at KIC Thermal Profiling, 15950 Bernardo Center Drive, # E, San Diego, CA 92127; (858) 673-6050; Fax: (858) 673-0085; Web site: www.kicthermal.com.