In Search of Pluto

This isn’t directly related to printed circuits but oh-so-cool nonetheless.

NASA this week snapped this photo of (ex) planet Pluto (shown with its largest moon, Charon, at the left), proving once again that man is capable of remarkable engineering feats:

Pluto, with moon Charon on left

Pluto, with moon Charon on left

This shot was taken by the New Horizons space probe from a focal point several million miles away from the dwarf planet, which seems like a lot only until one considers the ongoing nine-year long trip has taken the probe nearly 3 billion miles from Earth.

Congratulations to the NASA and Johns Hopkins APL team that conceived and executed this mission, and to those behind-the-scenes designers and manufacturers that built this one-of-a-kind system.

Thoughts for the New Year

Folks,

I thought I would post a few short thoughts as the new year begins. Here it goes:

1. A billion hours ago the Stone Age was the future, a billion minutes ago Caesar ruled Rome, a billion seconds ago Jimmy Carter was the US president, a billion passives ago you took your last break (about 4 hours ago). As exciting as the latest quad core microprocessor is, the largest number of components that we assemble is passives, approaching two trillion per year. That is about six billion a day. If you lined up all the seven billion people in the world, each year you could give every man, woman and child several hundred passives from all of the passives that are produced. If two trillion passives (assume 0402s) were lined up end to end they would circle the earth 50 times!

2.    Schools in Indiana are no longer required to teach cursive writing. Keyboard skills are considered more important. Yikes! I’m all for keyboard skills, but I want my grandkids to be able to write in cursive. If not, how do they write their names? Are we less than a generation away from people writing their names as an “X?”

3. Thoughts on lead-free solder reliability in long-term mission critical environments from a NASA study:

“Test vehicles assembled with lead-free materials (notably tin-silver-copper) exhibited lower reliability under some test conditions.”

Some people would respond to this statement by saying, “I told you that lead-free solder was no good.” However, another way of stating the results would be, “Lead-free solder performed better in more tests than tin-lead solder did.” The ratio, by my count, was about 5 to 3 in favor of lead-free. However, I agree that lead-free is not ready for mission critical (>20-year) service life. The main reason being that, in some cases, when lead-free solder joints failed in these types of studies, the results were much, much worse than for tin-lead solder joints. These failure modes need to be understood and addressed. In addition, tin whiskers and pad cratering are looming problems in these, mission critical, long service life quadrant D applications as discussed in the US Navy’s Manhattan Project.

4. I had not planned on reading Steve Job’s biography , as I thought I knew quite a bit about him from reading recent articles in Forbes, Fortune and Business Week. But I went ahead and downloaded it to my Kindle anyway. This work by Walter Isaacson is a masterpiece. To share one tidbit from it that relates to those of us in electronic assembly:

In almost all cases electrical engineers first design the circuits that perform the functions of some device like a mobile phone or tablet. Mechanical Engineers are then left to fit the circuits into the “box.” (Hence MEs are often called “box stuffers” by EEs). Jobs completely changed this approach. He told the engineering team how he wanted the product to look and function first, then they had to determine how to make it work that way. I’m convinced that only through this approach are the revolutionary design concepts that Jobs and Apple came up with possible.

The book also points out his many flaws (e.g., Jobs would regularly park in handicap spots; the author reports several times that Jobs just didn’t think the rules applied to him, etc.). Another interesting thought (read it and see if you agree with me) that if Steve was not Paul Jobs’ adopted son, Apple would have never happened.

Cheers,
Dr. Ron

Pb-Free Reliability Under Harsh and Commerical Environments

Folks,

In gathering information on the status of lead-free soldering, some helpful friends pointed out two great sources of information: NASA and the US Navy.

NASA sponsored an impressive lead-free reliability investigation: “Lead-Free Solder Testing for High Reliability Project 1.” This project is finished and the reports are online. A follow-on project, NASA DOD Lead-Free Electronics Project 2, is underway.

The Navy sponsored a project with ACI and the summary is here. I am currently studying these documents to help develop the consensus. Some preliminary info follows:

Regarding -20°C to +80°C thermal cycling, NASA concluded:

Under the conditions of this test, Sn3.9Ag0.6Cu (SAC) and Sn3.4Ag1.0Cu3.3Bi (SACB) were always more reliable than eutectic SnPb regardless of component type (CLCC, TSOP, BGA or TQFP).

It has been shown that conditions that highly stress the solder joints by maximizing the CTE difference between the PWB and the component will favor SnPb over SAC6. Conversely, conditions that minimize the stress put on the solder joints (e.g., compliant components such as BGA’s and/or a thermal cycle with a small delta T) will favor SAC over SnPb. The current test falls into the latter category and we can say with some confidence that the lead-free alloys tested will outperform eutectic SnPb under field conditions that are even less stressful than the -20 to +80°C thermal cycle test conditions.

For -55°C to +125°C thermal cycling, the conclusions were more cautious, likely because the data were mixed:

The feasibility of using Pbfree solder alloys in place of SnPb solder alloys for new product designs was demonstrated under thermal cycle test conditions. Additional investigation and characterization of Pbfree solder alloys will be required as a segment of a Pbfree solder alloy implementation plan. The application/introduction of Pb-free soldering processes for legacy product designs is not recommended without extensive materials characterization and product design review.

These results seem to be consistent with what others report: namely, lead-free assembly produces good thermal cycle results for commercial-type thermal cycling, but the results are mixed for harsh environment thermal cycling.

More to follow.

Cheers,
Dr. Ron

So Long, Old Friend

Just watching the final shuttle launch and pondering a few questions.

A significant number of innovations came out of the Mercury, Gemini and Apollo programs and filtered down to public life. Some were in materials, some were in electronics, some in software algorithms  and some in other technology areas. It was pretty much all new back then. When the shuttle was first being developed back in the 1970s, innovation in materials and other areas came about as well, though it did use a fair amount of recycled technology in the beginning.

But since that time, have there been any major breakthroughs directly from the shuttle to filter down? Though it never lived up to the “one launch a week” billing, it did, in a sense, become the space “truck.” Sort of an old pick-up truck. Not much new. The occasional upgrade. The occasional breakdown. But mostly just there hauling stuff around.

When the next manned launch vehicle comes out, will it deliver a wealth of innovation as did the first decade of manned space flight? Or will it be designed with primarily off-the shelf or near off-the-shelf technology?

In the 1960’s, private industry benefited greatly from the research that went on in the space program. I suspect that the next time around, whether it’s a NASA design or a commercial design, it will be the other way around and the space vehicle will benefit from research paid for by commercial activities.

Duane Benson
Thanks for all the fish

http://blog.screamingcircuits.com/

No End for Space

I, for one, am thrilled to see the US is not ignoring the challenges of moving beyond our humble domain on Earth.

As NASA announced yesterday, the Obama administration has given the go ahead to push forward on deep space missions. Tapped for the mission is a design called the Multi-Purpose Crew Vehicle developed by NASA and Lockheed Martin.

So much of the communications capability we take for granted today — from cellphones to satellite communications to GPS and so forth — was enabled by federal funding of bleeding-edge technology used in the space program. (And that doesn’t even begin to cover the major advances in rockets, materials science and other areas.)

Even in the midst of a severe cash crunch, the US is betting that the benefits outweigh the costs.

While some opined that it was a mistake for the Bush and Obama administrations to give up on moon landings and obsolete the Space Shuttle, the picture that is now emerging is more complete. Far from completely giving up on space travel, the US is once again putting the proverbial stake in the ground (or its celestial equivalent) and moving the bar well past where man has thus far traveled.

The electronics industry historically has benefited from NASA’s investments. Let’s hope history once again repeats.

Tin Whiskers and Toyota: Collision Course?

New criticism of the reports by the National Highway Traffic Safety Administration and NASA Engineering and Safety Center that led the US Transportation Secretary to publicly absolve Toyota of unintended acceleration problems in its vehicles is breathing new life in what the mainstream media had decided was a closed story.

When the US agencies released their reports in February, Sec. Ray LaHood stated that the findings by the NHTSA and NASA proved Toyota’s electronics were not guilty of causing unintended acceleration. “The verdict is in,” LaHood said. “There is no electronic-based cause for unintended, high-speed acceleration in Toyotas.”

Not so fast, said Safety Research & Strategies, which this week went to press with a report condemning the earlier findings for everything from flawed analysis to conflict of interests.

In the report, SRS claims the tin whiskers found in the vehicle samples provided to NASA did in fact reveal a failure mechanism that was ignored in the NHTSA report, yet that mechanism in accelerator pedal sensor circuits can cause resistive shorts that could lead to acceleration.

The report has become a hot topic among a group of printed circuit board reliability experts, who are pointing to the “extremely small sample size” of vehicles used by NASA to perform its investigations. “There are millions of Toyotas on the road today but NASA was able to look at only a handful,” wrote Bob Landman of HRL Laboratories, on the IPC TechNet Listserv. “Despite the small sample size, they found whiskers.  The Law of Errors tells you what about this fact?  That whiskers are a significant finding.”

Landman noted that in one case, NASA found whiskers in a pedal assembly after a woman who had an incident of sudden acceleration was provided the defective assembly by the dealer that fixed her car. “She learned of the [Department of Transportation] investigation and gave them the assembly, and it found its way to NASA where [researchers] found whiskers shorting the leads of the potentiometer.

Landman also said NASA demonstrated a braking problem under a test track sudden acceleration simulation.  “A NASA driver was strapped in, a NASA passenger had two switches, one to cause sudden acceleration at 45 mph and the other to safely turn off the the sudden acceleration so the vehicle could be brought to a stop.  What happened?  When sudden acceleration was initiated, the throttle was at 100% so there was no vacuum assist and the driver, using both feet on the brake pedal, could not stop the vehicle! It was found that it would take 600 pounds of brake force on the pedal to cause the brake to slow down the vehicle. Clearly, the software does not allow the brake to override the pedal. This is a defective design.”

“Something is rotten in this [NHTSA] report, it seems to me, and SRS found it,” Landman said.

Tin Din

Folks,

Many people responded to my recent post on tin whiskers. A few pointed out that the recent NASA report on the Toyota Unintended Acceleration Issue discussed numerous tin whiskers that were found, one implicated in a failure. The tin whiskers were emanating from tin plating.

We don’t know, however, if tin whisker mitigation techniques were used. In a mission-critical application, such as this, it would appear unwise to use RoHS-compliant electronics, especially since they are not required for automobiles. In other words, autos are exempt from RoHS. Let me be very clear: from a tin whisker perspective, I am uncomfortable with RoHS-compliant tin plating in mission-critical applications. Much more work needs to be done before such tin plating should be used in mission critical applications. In applications where RoHS-compliant electronics cannot be avoided, all tin whisker mitigation techniques should be employed, including conformal coatings.

In addition, in response to my post, a number of people pointed out the difficulty of proving a tin whisker fail and the reluctance of any manufacturer to admit that their products had them.

But my quest remains unfulfilled; the question remains:

“[W]ho knows of any verified tin whisker fails when tin whisker mitigation techniques where used? Tin whisker mitigation techniques typically use 2% bismuth or antimony in the tin, assure that the tin has a matte finish and use a nickel strike plating between the copper and the tin to minimize copper diffusion into the tin.”

Restated, here is my point.  Since RoHS, quite a few people take a position something like this: With RoHS-compliant assembly, even the world of non-mission critical electronics is at considerable risk of numerous catastrophic failures, due to tin whiskers, that will cost hundreds of billions of dollars.

I still maintain, that with mitigation techniques, such as recommended by iNEMI, tin whisker control, for non-critical electronics, can be manageable. Non mission critical electronics is about 80% of the $1.5 trillion of the electronics industry.

As I pack up to leave my office today at Thayer Engineering School at Dartmouth, I am across the aisle from the chaps that provide our computers and IT support.  They buy millions of dollars of electronics a year.  In chatting with them they state two things:

1. They have noted no difference in electronics reliability since RoHS implementation, nearly five years ago.
2. On the very rare occasion that they get an electronics failure, it is almost always a hard drive.

Bottom line: Except for hard drives, modern electronics are very reliable for their use life.

I expect my quest will uncover some tin whisker fails, even with mitigation, but the fails will most likely be isolated and not a significant threat to the industry at large.

Cheers,

Dr. Ron

P.S. The image is from Dr. Henning Leidecker of NASA, one of the world’s leading tin whisker experts.