Lead-Free Solutions
Making Lead-Free a Reality Today

With the Europeans WEEE Directive now mandating a phase out of lead in electronic soldering by July 2006 and Japan's efforts to do the same even sooner, lead-free is rapidly taking on momentum around the world.

No different than when no-clean fluxes first emerged into the North American market in the mid-eighties due to the elimination of CFC's, electronic assemblers were confronted with not cleaning residues off soldered circuits. The use of no-clean liquid fluxes and no-clean solder pastes were considered by assemblers to be an impossible. Cleaning of flux residue was necessary to insure reliability.

Today however over 85% of assemblies are soldered using no-clean fluxes. No-clean fluxes have proven to be reliable. There has also been a benefit to the environment by eliminating the cleaning process and its effluents.

No doubt lead-free soldering does offer its set of challenges. The lead-free alloys being proposed as the main choices for general assembly are new and less data is available as to their process limits. The two main alloys are variants of Tin-Silver-Copper and Tin-Copper. These alloys have higher melting temperatures and wet metal surfaces more slowly, the joints also look different in that the surfaces are not as reflective as tin-lead joints. The flux chemistries that worked well with a leaded process are not the best fit for lead-free soldering.

There are concerns to be addressed with component and board finish compatibility with lead-free solders. There are concerns about the temperature profile components and boards can sustain to not jeopardize their functionality.

The process changes needed to achieve adequate wetting and flow characteristics of lead-free solders and the determination of when to use nitrogen assisted soldering have to be determined.

As more and more lead-free soldered boards are produced in Asia and Europe, compatible finishes are now available for boards and components. Process modifications such as solder pot finishes for wave soldering equipment to avoid leaching issues are now available. Defining the reflow ovens capabilities for higher temperature reflow profiles is a relatively simple exercise; most ovens will be capable of achieving the necessary thermal demands.

Flux chemistries in no-clean and water washable configurations are also available to enhance the wetting process of lead-free without nitrogen use.

These new chemistries with innovative activator packages, higher temperature resistant resins enable the spread of tin-silver-copper and tin-copper alloys while reducing voiding and bridging. As good as these formulations are today improvements in their functionality are ongoing and the formulations will be better as time goes on.

Lead-free soldering can be a reality today. Looking back about 6 years we have come closer to this reality. Initially as many as 100 lead-free alloy configurations were being considered, today only a dozen or so are being used, with the general alloy being agreed globally as tin-silver-copper and tin-copper alloys mostly for wave soldering assembly.

The process parameters for making lead-free soldering effective without reducing yields are well defined today. Revisiting the process variables from component and board finishes to soldering flux selection, to optimization of the individual variables for lead-free solder usage in the process will render a robust lead-free operation. Establishing suitable guidelines for the inspection process as to recognize adequate lead-free soldered joints and creating a suitable rework process will insure the same reliability as we have become accustomed with a tin-lead process.

The many companies using lead-free soldering today prepared and executed an effective implementation plan. This does take time and with deadlines fast approaching the time is now to investigate and implement lead-free wave, reflow and rework practices.

Lead-free soldering is not a matter of it being feasible; it is more a matter of our time to follow or to lead.

Kester has developed best in class soldering products to enable the effective transition to lead-free assembly. From solder pastes to liquid fluxes to solder wire and performs and solder spheres Kester offers the process engineer products designed with reliable lead-free processes in mind.

Kester continued efforts in developing robust chemistries for lead-free has been the preoccupation of its Global Research and Development Team. Kester also understands that having solid products and the knowledge and know-how to make lead-free a reality go hand in hand. Kester application engineers are certified and able to assist in the technology challenges associated with lead-free assembly.

Kester is making lead-free assembly a reality today.