Tag Archives: Dartmouth

Lead Free 2015

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It is hard to believe that in July we will celebrate the 9th anniversary of the advent of RoHS. So the timing seemed right when I was recently asked to speak at the Boston SMTA Chapter on The Status of Lead-Free 2015: A Perspective.

An overview of the entire 75-minute presentation would be a bit long, so I am going to discuss three of the “questions” that I covered.

  1. Q: We are now almost nine years into RoHS’s ban on lead in solder. How has lead-free assembly worked out?

A: Something over $7 trillion of electronics have been produced since RoHS came into force, with no major reliability problems. One senior person, whose company has sold hundreds of millions of lead-free devices since 2001, reports no change in field reliability. The challenge that implementing lead-free assembly placed on the industry should not be minimized, however. Tens of billions of dollars were spent in the conversion. In addition, failure modes have occurred that were not common in tin-lead assembly, such as the head-in-pillow and graping defects. But assemblers have worked hard with their suppliers to make lead-free assembly close to a non-issue. Some people ask how I can say that lead-free assembly is close to a non-issue. My office is across the hall from some folks that purchase millions of dollars of electronics a year for Dartmouth. Several years ago, I asked them how they feel that electronics perform since the switch to lead-free. They answered by saying “What is lead-free?” If people that buy millions of dollars of electronics have not even heard of lead-free it can’t be a big issue.

  1. Q: In light of sourcing difficulties, is there an industry consensus regarding lead-free conversion for military, medical, aerospace etc. assemblers that will continue to be exempt?

A: The main issue is getting components with tin-lead leads, especially BGA balls. Many assemblers are reballing BGAs, which has become a mature technology, although with an added cost. As years go by and there becomes more confidence in medium to long term lead-free reliability, some exemptees may switch to lead-free. However, I think mission critical applications with 40-year reliability requirements must be extremely cautious to make the switch. There may be subtle reliability issues that may show up in 40 years, that are not found in accelerated testing. One concern is aging. Even at room temperature, solders are at over 50% of their melting temperature on the absolute scale (300K/573K = 0.52). So aging can occur at room temperature. Some research suggests that lead-free alloys may be more affected by aging than tin-lead alloys.

  1. Q: It has been said that you claim that lead-free assembly has some advantages. Can this be true?

A: Guilty as charged. Lead-free solder does not flow and spread as well as tin-lead solder. This property can result in poor hole fill in wave soldering and some other assembly challenges. However, this poor wetting and spreading means that pads can be spaced closer on a PWB without the concern of shorting as seen in the image below. Your mobile phone would likely be bigger if assembled with tin-lead solder.

Lead-free solder does not flow as well as tin-lead solder. Hence, closer pad spacings are possible.

 

Cheers,

Dr. Ron

Photo courtesy of Vahid Goudarzi.

 

RoHS, Six Years After

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Folks,

I was at IPC Apex Expo the other week.  San Diego is a great venue for the show, but I always forget how cold it can be (55°-65°F) this time of year.

While at the show, I was interviewed on lead-free reliability and its cost for consumer electronics. These are topics I think about often, so let’s discuss them a bit. First, let’s consider reliability.  RoHS was enacted on July 1, 2006, more than 6 ½ years ago. Each year more than $1 trillion worth of electronics are made, therefore, in this period of time, something over $3 trillion worth of consumer electronics have been manufactured. There have been no “the sky is falling”-type of reliability issues in this time. How can I say this? Well, my office at the Thayer School of Engineering at Dartmouth is across the hall from the IT (information Technology) Dept. They purchase all the millions of dollars worth of PCs, printers, displays etc. that Thayer uses. Several years ago (say early 2011) I stopped by when most of the department was in and cheerfully asked if the reliability of the equipment they purchase has gone down since lead-free assembly was enacted. They asked me in unison, “What’s lead-free assembly.” After I explained what lead-free assembly was, they confirmed that they have noticed no changes in reliability. Since RoHS, my family has purchase about 100+ electronic devices, a few have had reliability problems, about as many as in the past. Most were attributed to hard drive fails. Of the scores of friends and colleagues I have, no one has ever commented that they have noticed an increase in electronics fails. So, my conclusion is that consumer product reliability is not “practically” worse if my family and  these many  other folks haven’t noticed it.

I have made an informal study of reliability data of lead-free vis-a-vis tin-lead solders published in papers. A statement from Rockwell Collins’ JCAA/JGF-PP No Lead solder Project: -55C-125C Thermal Cycle Testing Final Report  sums up my overview conclusion nicely: “Test vehicles assembled with lead-free materials (notably tin-silver-copper) exhibited lower reliability under some test conditions.”  Naysayers might be quick to suggest that this statement says that lead-free is no good. However, the statement could be reworded to say: “In considerably more than half of the test conditions, test vehicles assembled with lead-free materials had higher reliability.” Counting the comparisons in the Rockwell-Collins paper shows lead-free better in 51 cases, tin-lead better in 31 cases, and one draw. However, it is disturbing that a small percentage of lead-free assembled test vehicles had much much worse reliability than tin-lead test vehicles. This later information makes me believe that lead-free is not yet ready for mission-critical, high-reliability, long-life products. These small numbers of much poorer reliability assemblies must be understood and corrected before lead-free is ready for mission-critical prime time. The much shorter lifecycle of today’s consumer electronics may also mask this concern.

What about cost? I don’t at all want to minimize the expense that many went through to go lead-free and RoHS compliant. In about 2007, one of our colleagues estimated that it cost the electronics industry $20 billion to become RoHS compliant. I think this number is low, but, from a consumer’s perspective, there has been no cost hardship. The price of a PC continued to go down during and after RoHS implementation, as shown in the figure below. While performing my non-scientific survey of co-workers, family, and friends on reliability, I also asked about cost. All agreed, electronics are cheaper than ever.

 

Challenges still exist, even in consumer electronics with the Head-in-Pillow, Graping, non wet opens, and other defects.  However, we can all purchase lead-free, RoHS compliant products at a reasonable cost and reliability.

 

Cheers,

Dr. Ron

The source for the image is :http://thomaslah.wordpress.com/2010/02/03/apple-and-intel-defying-gravity/

 

Best Wishes,

Dr. Ron

Electronics Assembly in Action

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Folks,

Struggling to find a good, royalty-free, video of electronics assembly, my Dartmouth ENGM 185 class on manufacturing processes decided to make our own. I think it is pretty good considering our limited ($0) budget.

It was filmed at PCM in Springfield, VT. The young woman in the video is my ENGS 3 student from last summer, Ruthie Welch. The entire ENGM 185 class participated in the production.

As an aside, PCM’s assembly process uses lead-free solder paste.

Cheers,

Dr. Ron