Driven by the European Union's move to ban lead in electronic assemblies by 2006 as well as a similar move in Japan, many passive-component manufacturers are well ahead of the deadline to phase out lead in electronic components. But lead-free components also present reliability and cost challenges that must be overcome before full compliance becomes a reality.
Lead is most often used in the platings of terminals or in the solder pads of most passive electronic components, although a few device types also use lead in their internal construction. For example, older cartridge fuses use lead internally, where the melting wire is attached to the terminals.
Lead can also be used in the internal construction of resistive parts such as those with gull-wing and older dual in-line and single in-line packages. Gull-wing devices most often use an 85:15 or 90:10 tin/lead ratio in the terminal finish. Lead is also used as a plating finish for the terminals and leads in connectors and as an additive to some plastics to improve flexibility.
Many leading passive component manufacturers such as AVX, Murata and Tyco have been working on lead-free plating and soldering processes for the past two to three years. They are converting some or all of their product lines to pure-tin-terminal platings and are transitioning to lead-free solders, of which a tin/silver/copper mix is the most common.
But don't expect all components to be lead-free anytime soon. Though European and Japanese customers are driving that movement, reliability and cost concerns are hindering the transition. In addition, many countries that are big consumers of electronic components-China, for example-have not jumped on the lead-free bandwagon.
One reliability problem, called "tin whiskers," occurs with the production of pure electroplated matte tin, which is the most common lead-free finish.
"Tin whiskers are tiny little slivers [of tin] that grow spontaneously due to stresses in the electroplated tin," said Larry Bos, director of engineering for TT Electronics plc's IRC Advanced Film Division (Corpus Christi, Texas). "If you plate a matte finish, that tin tends to be low-stress. The risk of whiskers is low, but it doesn't totally eliminate the problem."
Tin whiskers can be nanometers in diameter or millimeters in length, and can grow long enough to touch another lead and create an electrical short, said Dr. Robert Hilty, director of materials research at Tyco Electronics (Harrisburg, Pa.).
Bos said that the problem with tin whiskers "has some people involved with military and space programs very concerned."
Indeed, many component manufacturers report that military and aerospace customers will not accept tin-plated terminals because they have reliability concerns.
Despite those concerns, TT Electronics' IRC division has built lead-free prototypes for all of its major families. According to the company, the preliminary tests it has conducted don't indicate any problems in the implementation of those changes.
Though there is no industry-accepted cause for tin whiskering, most component manufacturers know what makes it worse. As a result, Tyco tries to employ a number of techniques that lessen the tendency toward whiskering, like using a smaller grain size in the plating or using a nickel barrier between the tin and copper electrodes.
Another challenge for component manufacturers is the higher temperature requirements for lead-free solders. The most common lead-free solder is tin/silver/copper, which has a melting point that is much higher than conventional eutectic tin/lead solder, Bos at TT Electronics said. The temperature for the lead-free solder is about 220 degrees C compared with 183 degrees C for solder with lead. Because the board and all of its components are exposed to much higher temperatures, the resistive components may experience some changes in their electrical characteristics, such as for resistance, Bos said.
The higher-temperature processes will also affect some components more than others. Although it won't affect chip resistors, Bos said, it will be a concern for more-delicate silicon products in plastic packages that offer a very tight tolerance.
Circuit-protection device maker Wickmann USA (Atlanta) is also converting to lead-free solders, including those made of tin/silver and tin/silver copper. And it is running into similar problems with the high-temperature processes.
Manufacturers have to worry about two problems during the lead-free solder process, said Mark Beldon, sales and marketing manager for Wickmann: the higher process temperatures and the long-term effect those temperatures have on the reliability of the solder joints. Consequently, the key areas to be addressed when eliminating lead are testing and reliability, he said.
"Most solders that include lead content can be used in wave-solder processes that require solder temperatures up to 260 degrees C for 5 to 10 seconds," Beldon said. "With lead-free solders the temperature will rise to 280 degrees C and any plastics used in the fuses or holders must be suitable for use at these higher temperatures," he said.
In the area of fuses, lead is typically found in the terminal platings and in the construction of certain fuse types, particularly cartridge (glass and ceramic cylindrical types) and leaded-axial and radial fuses. Typically, surface-mount fuses only have lead content in the plating of the terminals.
For leaded fuses where standard tin/lead solder is used to attach the melting wire to the terminals, Wickmann has moved to a laser weld to eliminate the soldering. One of the first products designed with the new construction is Wickmann's radial-leaded Series 384, which can be used with leaded and lead-free solders. The company has also expanded the current ratings of the TR5 1-amp and 2.5-A microfuses to include 1.25-A, 1.6-A, 2-A and 3.15-A fuses. Wickmann plans to convert all of its existing TR5 products to the new construction by year's end and will use the same part numbers for the lead-free devices.
Another area of concern that goes hand in hand with the move to lead-free solders is cost: The materials used in the process that must resist higher temperatures cost more. That cost climbs even higher for component suppliers that need to build and stock both lead and lead-free versions of the same component to satisfy the demands of all of their customers.
"There will come a point where we will be supplying both lead and lead-free versions and that puts a burden on our factories to carry two separate inventories," making it "very costly for component manufacturers," said Steve Wade, sales and marketing director for TT Electronics' IRC Advanced Film Division.
AVX Corp. (Myrtle Beach, S.C.) is another company that is well on its way in the drive toward lead-free components. By the end of last month, the company had converted 100 percent of its commercial line of tantalum capacitors from tin/lead to 100 percent tin content.
Meanwhile, AVX will continue to produce 90:10 tin/lead terminations for its military customers, including the CWR, TPJ or TAZ series. AVX has offered 100 percent tin terminations for ceramic capacitors for roughly six to eight years.
To help design engineers with the transition, AVX is offering a technical data sheet on lead-free termination comparisons. Tom Piver, assistant product manager for tantalum capacitors at AVX, said the pure-tin terminations are compatible with both standard tin/lead solders as well as the lead-free solders and can be assembled with the existing mounting equipment and production solders with no changes in solderability or quality of the solder joints.
Similarly, another leading capacitor manufacturer, Murata Electronics North America Inc., expects to eliminate all lead from the terminal platings and solder of its multilayer ceramic capacitors by the end of this year.
The lead-free push is particularly challenging for circuit-protection device manufacturers dealing with older and lower-cost cartridge-fuse technologies. Many are struggling with the question of whether to convert the cartridge fuses, which use 60-year-old technology and typically sell for two to three cents in high volumes, over to lead-free versions. "If you try to take the lead out, combined with a high scrap rate, it can easily double or triple the price of the fuses," Wickmann's Beldon said.
Wickmann expects to complete the transition to lead-free components for many product families by no later than 2005. The biggest hurdle will be converting the 5 x 20-mm cartridge fuses, which are typically manufactured for less than 3 cents in Asia, he said. "Changing the design to lead-free could be price-prohibitive for end users who expect to buy a very cheap fuse."
For connector products, the biggest cost impact in the transition to higher-temperature solders will be the cost of the plastics used to hold the metal contacts in position, Tyco's Hilty said.
Tyco Electronics has developed a portfolio of housing plastics that are lead-free and carry sufficient temperature ratings to endure the higher-temperature processing for lead-free plated connectors.
North America Inc.
TT Electronics plc
IRC Advanced Film Division