When the electronics industry shifted to lead-free solder in the wake of the European Union passing the Restriction on Hazardous Substances (RoHS) directive, naysayers predicted a wave of product failures. Well, where are the failures?
Dr. Ronald Lasky, Dartmouth professor of engineering and a frequent blogger on solder, claims the transition to lead-free was a grand success. “A lot of people claim that lead-free solder is not as reliable as lead-based solder,” Lasky told me. “We’re now five years into the implementation of RoHS, and we’ve made $3 trillion work of electronic. We haven’t really noticed any big change in reliability.”
He says long-term reliability is still a mystery, since most of the products with lead-free solder have not been deployed that long. Yet he points to benefits of today’s solders, noting they are easier to mass-produce when pitches are tight. When high-density semiconductors are packaged in small form factors, using lead-free solder can result in boards with fewer problems. “Lead-free solder doesn’t wet well, so you can get better lead spacing,” Lasky says.
He notes a study by Motorola where design engineers built identical boards with lead-based and lead-free solder. The results showed that leads printed close together shorted out when lead solder flowed during melting.
Lasky concedes that high temperatures needed to melt lead-free solder have created some problems. “Moisture sensitivity is a big issue that’s often overlooked,” he says. “Much of the moisture research was done for lead-based temperatures, not the higher temperatures of lead-free processes.”
He explains that if you have a moisture rating of four for lead, it might be five or six at lead-free temperatures. “This new situation can cause problems such as popcorning, as well as board warpage.”
Lasky will discuss many of the facets of designing and processing boards using lead-free technologies during the IPC Midwest conference on September 21 and 22 in Shaumburg, Ill.
I find it hard to believe that anyone directly involved in the circuit board industry would agree with Rob Spiegel’s contention that there was no affect on yield or reliability as a result of the implementation of RoHS requirements and the subsequent switch to lead free solder. There are many studies that found just the opposite. The studies find a significant reduction in reliability as a result in implementation of RoHS. There is objective evidence that reliability in HDI applications is reduced by 50%. The extra 30C, from 230C for tin lead assembly to 260C for lead free assembly, is right at the limit of the epoxy systems capability. The dielectric is degraded and the copper interconnect are stress with increases the z-axis expansion of the circuit board. Studies presented repeatedly at IPC in (Schaumberg and Los Vegas), SMTA, EIPC and other professional organization throughout North America, Europe, and Asia. The results have repeatedly demonstrated a significant negative impact due to RoHS.
The facts are that scrap rates at PWB fabricators and at assembly have increased. Field life is demonstrated to be reduced based on reliability testing and this is reflected in field data. The failures include breaks in copper interconnections and degradation of dielectric materials. The first reliability studies on the effect of RoHS on 23 lead free materials demonstrated 19 experienced delamination. Products that used to be robust in a tin-lead application were failing assembly. Designs that were robust in tin lead applications were found not to be viable in lead free applications.
Weekly tests of representative coupons that are exposed to both tin lead and lead free assembly and rework simulation post results that there is consistently a 50% reduction in reliability. This trend is seen in the medical, military, aerospace, commercial, telecommunications … in every application tested. The results are always a reduction in cycles to failure, failing either copper interconnection or dielectric material as a result of the increased temperature required for lead free assembly. In assembly we see copper dissolution and cratering increase by those extra 30C.
Data that confirms my contention is available through papers given at IPC SMTA and EIPC to name a few. I believe that HDPUG alone offered five papers related to the affect of lead free assembly in Las Vegas this spring. My question is what credible data is there that shows that RoHS does not affect scrap rates, field life and reliability. I have heard of anecdotal evidence where companies switch tolead free and there was no affect as far as they know, but that is not data. Data from side by side tests comparing tin lead to lead free PWB reliability, does not support the contention that RoHS is benign.
Rob, your article had me take a trip down memory lane.Back in 2003 I spent a lot of time on the road introducing companies to the EU RoHS directive and many “experts” were predicting the demise of the electronics industry as a result of the ill conceived restriction of hazardous materials, AKA lead free.If you remember some not to be named industry associations were waging a campaign to stop the restriction of lead solder.Those individuals and associations leading the charge, I’ll call them “the sky is falling gang”, now seem to be reversing their positions and are now offering training, certification, standards, and whitepapers.Whenever I met up with one of these individuals I always asked one very simple and logical question, what data do you have to support your position and I never did get a fact-based answer.
Doug, solder pretty much remains the solution. They took the lead out (except in excepted areas such as military and aerospace because of reliability issues). The lead accounted for only about 2 percent, but it was an important 2 percent since lead mitigates the formation of tin whiskers that can short out a component. The military and aerospace are still shy about going to unleaded solder, since their products need to last 20 or 30 years and there just isn't data on non-lead solder that shows it working over the span of decades.
In the meantime, other materials are filling in for lead, from nickel to silver and gold. Gold, of course, seems to work best, but we all know that adds expense beyond what most manufacturers want to pay for.
I didn't realize that even hobbyists can get lead-free solder at Radio Shack. If you do a Google search on "lead-free solder," there are a bunch of FAQs and many vendors of the solder itself. It'll be interesting, as you note, to see if the long-term reliability holds up. Materials substituted for environmental reasons always have issues; I always think here of the unpleasant squeal of non-asbestos brake pads.
Thanks Rob. Do you think there has been a move away from soldering to other sealing/joining methods as a result of concerns about lead-free solder (e.g., long-term reliability and thermal resistance issues for surrounding materials)?
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