Environmentally Friendly Lead-free Takes the Lead
10/01/2003
By Chris C. Reynolds
The trend toward lead-free production of electronic components is accelerating rapidly in the U.S. In Asia and Europe, legislation has already been passed that introduces time lines for a ban on the future use of lead-based components in new equipment.
The electronics industry is a key player in the global economy. Environmental impact from any industry is always a high profile topic and lead-free production of electronic components has become a major issue.
In Japan, we are seeing a strong industry trend toward lead-free production, and this has been heightened by some European legislation as well. The primary objective is to reduce negative environmental effects caused when electronic products containing lead are discarded.
Lead often is used in the production of electronic components. Exposure to lead can result in accumulation in the body with the potential for serious, long-term health effects.
In Japan, two industry organizations — the Japanese Institute of Electronic Packaging (JIEP) and Japanese Electronic Industry Development Association (JEIDA) — have put programs in place to eliminate lead in all electronics. Various industry organizations in the U.S. also are taking an active approach, particularly the National Electronics Manufacturing Initiative (NEMI). Europe has become the driving force, although the January 2006 timeline has been revised to January 2008, for a ban on lead in new electronic equipment.
Solder accounts for less than 0.5 percent of world lead consumption. This includes: solderable traces on the printed circuit board (PCB), solderable finish on the components, and solder paste and liquid solder for reflow or wave soldering. The largest applications for lead are batteries, ammunition and oxides for paints — which combined account for more than 90 percent of the total worldwide consumption of lead.
Components typically have small amounts of lead in their terminations. However, the change to lead-free solder alloys will necessitate a move to a compatible termination finish to create acceptable soldering performance. The major concern for component manufacturers is the elevated temperature profiles required by these lead-free solder alloys. These higher temperatures can have dramatic effects on the internal construction of components as well as the external terminations. In some cases, it may be necessary to redesign the component structure or even develop new packaging methods and new materials.
There are several lead-free alternative materials available that have been evaluated by the PCB manufacturing industry, including bismuth, tin, copper and silver. Of these, pure tin or tin/copper alloy appears to be the most widely accepted and used. One reason for the apparent popularity of these materials is their relatively low cost. However, from a process standpoint, the key problem is the higher temperatures these alternative materials require and the effect this has on components. Tin/copper solder requires a temperature rise of only about 30°C more than the typical 220°C of currently used lead-based solder.
The current question remains: When is a material considered lead-free? Initiatives are in place to produce reduced-lead components in the short-term, with long-term objectives to become completely lead-free. Some of today's highest volume products, such as ceramic capacitors and resistors are already available with terminations of pure tin. Tin has emerged as the material of choice due to both cost and compatibility with current systems.
The transition to reduced-lead parts and finally to lead-free electronic components will not come without some bumps in the road. There are also concerns regarding "whiskering" when using pure tin coatings. Whiskering occurs when long, thin strands of crystal grow on tin surfaces. They can cause short circuits between the tracks on a board. Major concerns arise in aerospace and high-reliability applications.
While whiskering is a concern for equipment manufacturers, it does not decrease performance on the component side because the paste, under reflow conditions, will wet most of the termination surface. The other elements in the solder paste will alloy with the tin from the termination plating, resulting in only a small area of the component termination remaining as pure tin. Therefore, the main area for whiskers as a failure mechanism is on the PCB and not the component itself.
Incidence of whiskers can be reduced in a number of ways, including: providing special inter-layer barriers, carefully selecting base materials and specifying pure tin layer thickness, not including any organic brighteners and thermal treatment.
The move toward lead-free electronics now is in full swing. It will not be a simple transition for the industry, but it does serve as another opportunity for our dynamic business to show our innovative capabilities.
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CHRIS C. REYNOLDS, applications manager, may be contacted at AVX Corp., 801 17th Avenue South, Myrtle Beach, SC 29578; (843) 444-2868; Fax: (843) 626-3123; E-mail: [email protected].