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“Lead-Free or not to be”, that is the question.
By Dave Corey

The Hot Air Solder Leveling (HASL) process has been the preferred coating procedure utilized by the Printed Circuit Board (PCB) Industry for the past 25 years.  With new regulations for the elimination of lead from solder, the HASL process has not lost its popularity or feasibility and still remains the preferred coating of PCB manufactures worldwide. With the electroless nickel/gold process having a less desirable solderability of components and silver process having an additional decrease in shelf life, the new lead-free HASL process is now a viable lead-free alternative.    

With that being said, HASL equipment and alloy manufacturers have been on the move developing lead-free products to work with the impending lead-free requirements. Currently, due to the lack of installed lead-free HASL systems in the field, there has been a great deal of speculation regarding the new lead-free HASL process. We just don’t have enough data yet.  As of November 2004, a handful of PCB manufacturers located in Texas have taken the necessary steps to convert their process to the new lead-free alloy and HASL System. In addition, a few of these fabricators have kept their tin-lead HASL systems in operation in order to provide both finishes for now.   

ACS would like to commend these fabricators for having the valor to take the necessary proactive steps. Their actions will not only better themselves, but will also benefit the PCB industry as a whole. Up until now, we haven’t had any factual data to support or dispel past or present speculation of the burning question: “Will lead-free work?” The results these fabricators have experienced with the lead-free process have been very encouraging and promising.

The two most Frequently Asked Questions here at ACS are:

Q: Can it be done and are their any current acceptable lead-free alloys available to the industry today?

A: Absolutely! ACS has investigated a variety of lead-free alloy manufactures, in addition to, the different versions of lead-free alloy available. The two major lead-free alloys are tin-nickel-copper (Sn-Ni-Cu) and tin-silver-copper (Sn-Ag-Cu). Upon completion of our investigation,

ACS’ decision was to work closely with the Nihon Superior SN100CL tin-nickel-copper (Sn-Ni-Cu) lead-free alloy in concurrence with the Lantronic Model TT30 Lead-Free HASL System. To this date, all installations conducted by ACS have been with the Nihon Superior SN100CL lead-free alloy. The lead-free installations have been very successful and concluded with a smooth, trouble-free transition with very little interruption in production.

Q: What about thermal shock, delamination, and Z-axis expansion?

A: With the newly designed solder pot of the Lantronic Model TT30 Lead-Free System, ACS was able to successfully run a solder pot temperature of 495F.  The solder pot is designed to generate a significant amount of solder flow which eliminates the need to double cycle every PCB, unlike other competitive lead-free HASL systems. In addition, Lantronic has specially designed their “LanTroFlow” heating system which provides a steady flow of heated air to the air knives. The “LanTroFlow” heating system gives fabricators the ability to run a consistent air knife temperature of 500F. When working with the eutectic 63% - 37% tin-lead (Sn-Pb) HASL alloy, the standard solder pot temperature of the Model TT30 is 485F. As previously mentioned, with the Nihon Superior SN100CL lead-free alloy, fabricators are able to run a solder pot temperature of 495 F, this 10 increase in solder pot temperature is minimal. The aforementioned fabricators have not experienced any issues with thermal shock, delamination, or Z-axis expansion to date.

To everyone’s surprise the surface finish was comparable. You could not tell the difference between the tin-lead and lead-free alloy. The finish is very similar to that of eutectic 63% - 37% tin-lead (Sn-Pb) alloy. The other surprise and advantage of the Nihon Superior SN100CL lead-free alloy was the flow characteristics, through-hole clearance, the uniformity and flatness of the cooper pads as well as the overall smooth shiny finish. In addition, exceptional solderability in assembly has been achieved. Copper leaching and extraction of copper from the solder pot is still under evaluation as well as XRF measurements. ACS will keep you posted.      

Conclusion

Time is of the essence, and procrastinating until the last minute can lead to playing catch up or even loss of work to your competition. As we move ahead into the next generation of HASL finishes, be confident in knowing that the transition is brief and undisruptive. Your current pre-clean and fluxing applications need no modifications. ACS is available to assist you with this procedure. As previously mentioned, with the lead-free deadline now in place, PCB manufactures must embark on the necessary steps to convert their existing HASL systems from the current eutectic 63% - 37% tin-lead (Sn-Pb) HASL alloy, to the new lead-free (Sn-Ni-Cu) HASL alloy.

ACS can be reach at 479-846-2403 or visit their Web site at www.acs-tech.com - click on Lantronic logo for HASL info.