Lead-free Solder
The future is now

Jim D. Raby, P.E.

Lead-free solder is in our not so distant future. We are making preparations every day in some way, but how soon will it be here? Well established methods, techniques, and procedures are available to all of the industry. Yet even with all this information and understanding it is not easy to change. Our competition from outside the country, in the final analysis, drive the change; our industry just does not make change until forced to do so. The old adage of "lead, follow, or get the hell out of the way," applies here. Here in the U.S., we have a tendency to want to lead unless it involves change, in which case we tend to follow and let someone else set the standard. Then we improve on the process and take the lead again. In the mean time we take lots of hits from our competitors, pay legal costs, and wait to be pushed.

So where are we on the issues that count?

The solder companies have made tremendous headway; research on this subject has been underway on alloys for many years. Some have forgotten lessons learned in the past, but that is okay, we learn better the second and third times. For example, the problem of "tin-pest" seems to have been forgotten. Tin-pest is the disintegration of metallic tin into a grey powdery substance. This transformation occurs at its highest rate at temperatures below –30 degrees C. (Wassink). This condition was experienced early in the history of soldering in military hardware with failures in extreme cold areas of the world. The element antimony (Sb) was added at an extremely low level to the alloys to stop this deterioration. It was used in the military QPL and was maintained until the military did away with its specifications. But it continues to be an option that is available to the industry. With the higher tin content in the lead-free solders this becomes more of a concern. This subject is being pursued by independent research to remove any and all biases.

Looking at strengths and weaknesses of the solder terminations made by lead-free solders, we know that some of the alloys have much better strengths than those containing lead. Yes, we do need to use a slightly higher temperature for making the termination, but all that means is we need to work a little harder in selecting parts and materials, give a little more thought to the subject. We have for years run solder pots (wave solder) at 500 degrees F and AIM's (Castin), will run at that with great success. This alloy also comes in a solder paste, which runs well through my Heller model 1700 (with nitrogen).

I believe that the solder companies must do more for us with the flux issue since we do run these alloys at a little higher temperature and a little longer dwell time and as a result our flux needs more life. If we are to use an OSP over copper then we need a more aggressive flux. We may need to reassess the clean vs. no-clean issue, since our no-cleans are very mild.

So what needs to happen next to get things started, and to make progress toward true lead-free soldering?

The Japanese, with their proactive approach, will get things going. Their products will be in the market place while we watch and wonder how they can do it. They will go there using our technology and materials. The Europeans will also lead us with their requirements for more environmental friendly needs, and the fact that they have set a date for change already. Again, they will use our technology and materials. Our industry will trail; we will spend money in court as in California Proposition #65 which addresses the issue of landfill-friendly materials. Then in a few years we will change to one of the lead-free materials that exist today. We will wonder why the Japanese and the Europeans beat us to the punch. If we have not felt the pressure directly on our pocketbooks, we will be slow to change.

We will need to re-train our inspectors because the solder joints will look different. They will have a little more white in them; they will not be as bright and shiny, and we will not like what we see. The wet-ability and shape of the termination will look the same but the brilliance will be different. Training will be important. Operator training will also be important. Operators need to see that the time to wet is different, and that dwell time may change. Touch-temperature may be the same, but the dwell time will be longer.

All of the following photos show good positive wetting and small grain structure.
All were of SN 1.9 Ag, 0.8 Cu, 0.5

 
The above photo is a D-Case Capacitor made with CASTIN

 
Photo #2 is MELF

 
Photo #3 is a Gullwing Package

Solderability issues will be important just as they are today. Hot air leveling equipment manufacturers have already proved the use of their equipment using AIMs Castin, and say that they can deliver hot air leveled boards now. The component lead manufacturer may be a little slower for thru-hole components, but for the most part, many of the lead frame manufacturers are close to being ready now. The chip capacitor/resistor manufacturers may have some problems but it is believed that they too are close to being ready.

Conclusion: It is almost a drop in. No one wants to say that because we do have a good thing going now with what we have. But all we need to do is make a decision to go for it and we could be there very quickly. My company, Soldering Technology International (STI), will have a lead-free training course on line by January 1, 2000. It will be the same as our existing programs, and will be in compliance with specifications, The only difference will be the alloy and all the details that go along with it. This will be for a full SMT line, work cell training program, including wave soldering and solderability testing, as well as the J-STD-001 and IPC-A-610 programs. There is ample data available to get the job done, the only thing missing from the puzzle is a better flux, and then the industry can respond and, sooner or later, it will respond. Competition has a way of making that happen.

Jim Raby can be reached at his company, Soldering Technology International, 102 Tribble Drive, Madison, Alabama, Phone 256-461-9191 or Fax 256-461-9566. E-mail him at Jrabysti@aol.com. or visit Internet: www.solderingtech.com