Tests of tin-lead BGA packaging for mil-aero applications

Tests of tin-lead BGA packaging for mil-aero applications:
ntroduction

Each year the military and aerospace sector demands higher-speed systems with better accuracy at lower cost. Increasingly stringent size, weight and power constraints, together with the demanding power supply requirements of large FPGAs, have led to a decisive move towards POL (point of load) power supply architectures.

One solution to address these needs is Linear Technology’s µModule technology, providing a system-in-package solution that is claimed to simplify design and minimize external components. 

Figure 1: µModule Product Construction

The original packaging technology selected for µModule switching regulators was LGA (land grid array) and this has served the broad marketplace well. However, some applications subject to very harsh environments prefer BGA (ball grid array) interconnect, and Linear Technology has developed packaging to meet these requirements. 

Figure 2: LGA and BGA package interconnect

In this article, we will take a more detailed look at the comparative performance of LGA and BGA packaging and discuss the merits of gold or tin-lead (SnPb) alloy and lead-free (Pb-free) component finishes.

Component terminal finishes

The European military and aerospace market presents quite a fragmented demand picture when considering component finishes with some companies having adopted Pb-free finishes entirely whilst others have policies to completely avoid them, more common is a mix dictated by the specific needs of individual projects.

A major factor is the continued exclusion of military and aerospace equipment from the RoHS II (Restriction of Hazardous Substances) directive that permits the indefinite use of SnPb component finishes. Of foremost concern is the impact on reliability from the formation of tin whiskers on pure tin plating, leading to potential equipment failures from short-circuits of adjacent fine-pitch conductors. The addition of lead (Pb) to the tin plating remains the industry-standard approach for mitigation of whisker formation.

Weighed against the use of SnPb finishes are the practicalities of component availability, lack of distribution inventory and extended delivery times. By mandating use of SnPb finish companies are also sometimes foregoing access to a wider range of new, Pb-free only components. Whilst this can be overcome by third-party companies offering strip and re-plating or re-balling processes the additional heat cycles and difficultly in re-testing together with the associated costs make this a less desirable approach.

When Pb-free components are used another form of tin whisker mitigation frequently employed is the use of polymer conformal coatings such as Parylene or Arathane which have been shown to resist the penetration of tin whiskers for many years.

Interconnect considerations

Given the mix of needs discussed in the previous section, Linear Technology µModule products in LGA packages offer a universal solution as gold plated pads have been in long-standing use within military and aerospace systems and they have the advantage of also being RoHS compliant.

However, one concern of using gold plated components is gold embrittlement and this is especially true of large BTCs (bottom termination components) subjected to harsh environmental conditions. During reflow gold is dissolved into the solder joint creating weak interfaces in the crystalline structure, the CTE (coefficient of thermal expansion) differences between the gold-tin IMC (intermetallic compound) platelets and the surrounding volume of solder can result in fracturing of the solder joint and an eventual open-circuit when the assembly is repeatedly temperature cycled. A long-standing industry rule of thumb recommends not exceeding a threshold of ~3 wt% gold within the joint, and Linear Technology LGA µModule products meet this requirement for both SnPb and SAC305 paste. Some companies conduct their own trials on BTCs with representative PCBs and environmental conditions using special daisy-chain interconnect samples for this purpose.

Increasing the volume of solder in a joint and the standoff to the PCB improves interconnect reliability by making the joint more compliant. Tests in the military and aerospace industry have concluded that BGA packages are generally preferred over LGA where harsh environmental conditions are likely to be encountered, particularly in airborne systems. An added benefit is that cleaning becomes easier thereby reducing concerns over contaminants.

For these reasons µModule regulators are now offered in BGA packaging in addition to LGA. The downside of the BGA package is slightly reduced thermal efficiency of around 0.5ºC/Watt and an overall increase in component height of 0.6mm. Linear Technology BGA µModule regulators are offered as standard in SAC305 Pb-free configurations and on specific products according to demand with tin-lead Sn63Pb37 balls.

Reliability testing and characteristics

It is important to keep the concerns in perspective, and Linear Technology has conducted extensive trials on interconnect reliability of µModule products with both LGA and BGA configurations.

By way of background, we should distinguish between component tests used in the initial qualification and subsequent reliability monitoring and interconnect tests that are really a characterization of performance with selected PCB configurations, assembly process and temperature cycle parameters.

Extensive µModule product testing at component level indicates an exceptionally high level of reliability with 0.72 FITS (1 FIT = 1 failure in one billion device hours). This article will then focus on interconnect level testing.

Three types of interconnect testing have been performed:

1) Daisy chain testing: where each pad in the µModule regulator is connected to the next to form a complete circuit, monitored in real time during temperature cycling in accordance with IPC-9701 and JESD22-A104. This approach ensures that each pad is tested and since many pads are connected in parallel in the application this is generally preferred over functional testing.

Table 1: LTM4601A daisy chain test results of LGA & BGA
Click on image to enlarge

Note (1): When the 5 failures in table 1 are analyzed with a Weibull distribution plot, it predicts a 1-percent failure point at 1780 cycles. 

Note (2): Subsequent further testing of LGA products with SAC305 (Pb-free) paste to 6000 cycles shows zero failures out of a total of 240 samples of various other µModule products.

Note (3): All BGA packages used SAC305 solder balls

2) Functional testing: where the µModule regulator is temperature cycled and tested for correct operation on an evaluation board. Much testing was performed on LGA µModule regulators comparing Pb-free SnAgCu paste with SnPb paste. However, testing was limited to a maximum of 2000 cycles, which did not produce any failures of either solder.

3) Random vibration testing: conducted in accordance with MIL-STD-202G, method 214A over 50Hz to 2000Hz frequency range and represents a very severe test. Testing of the LTM4610A in LGA-133 passed test letter C at 9.26g RMS but failed in the Z-axis with test letter F at 20.71g RMS. Trials on the LTM4601A in the BGA were conducted and the results are shown below in table 2. Both SnPb and SAC305 (Pb-free) solder gave good results, passing at 20.71g RMS.

Table 2: Random vibration test of BGA-133 package

Conclusions

It is likely that the military and aerospace sector will continue to require a mix of component finishes for the foreseeable future and that manufacturers committed to supporting this market must maintain support for SnPb component finishes.

BTCs such as Linear Technology µModule products with gold-plated LGA packaging have proven reliability and wide industry acceptance. Now BGA versions are providing an alternative to LGA for particularly harsh environment applications.

BGAs with RoHS compliant SAC305 (Pb-free) balls using both SAC305 and SnPb solder paste have been shown to be very reliable and capable of greater than 6000 temperature cycles without failure. For applications where SnPb is mandated, there is now a factory built option of SnPb BGA.

In the limited space available, only a small selection of the reliability data has been shown, for more details please refer to the Linear Technology website.

About the author
Steve Munns is Mil-Aero marketing manager at Linear Technology Corporation

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DLA Demands Chip Makers Tag Products With Plant DNA; A War On Counterfeiters

This November, the Defense Logistics Agency will require companies selling microcircuits to the military to stamp their products with an unlikely seal of authenticity: plant DNA.

It's an innovative initiative in the fight against counterfeit computer chips, which has been a major concern in the Senate, but it's only one piece of the answer. DLA plans to put out a formal Request For Information sometime this month to ask industry to offer other, complementary authenticity-checking technologies, and Congress is watching closely.

"This and programs like it may be good long-term solutions to the problem, but additional steps are necessary to address the short-term problem," said one congressional source, discussing the DNA marking technology with AOL Government affiliate, AOL Defense.

While markers of authenticity are well and good, the source explained, when Congress addressed counterfeit components in Section 818 of last year's National Defense Authorization Act, "the law went way beyond this; it requires them to change the way that they do business. The implementing regs to Section 818 are really the crux of what needs to be done, and they haven't been issued yet."

Vice Adm. Mark Harnitchek, the director of the Defense Logistics Agency, has touted a four-part plan to combat counterfeiting: testing components already in hand, buying from original manufacturers or their authorized distributors wherever possible, using anomaly-checking software to spot suspect transactions, and, finally, requiring microcircuits to be tagged with DNA.

You need to add photos to this gallery.


The brilliance of DNA tagging is that it's inexpensive, widely applicable, and virtually unhackable, at least according to its inventors. "We stand by the strongest claim in the industry, which is our DNA cannot be copied," said James Hayward, the molecular biologist and bio-physicist who heads Applied DNA Sciences. That's company named in the Defense Logistics Agency mandate as the only authorized purveyor of the marking technology, at least for now.

Hayward's firm starts with natural plant DNA. Then they engineer it -- the process is a trade secret -- to create unique strands of genetic code, which in various formulations can be mixed with ink used to mark products or directly infused into materials used to make them like sillicon, plastic, wire, or textiles.

The technology is already widely used in bank notes in Europe, where it has helped convict more than 30 counterfeiters. Applied DNA is even experimenting with ways to "tag" diesel fuel. Once the DNA is embedded in the product, by whatever means, you detect it with a swab test, or you can shine a CSI-style black light (provided by Applied DNA) onto the tag: If it reflects a particular wavelength, it's authentic. (Other, more time-consuming tests give greater detail).

The downside -- that aforementioned "short-term problem" -- is DNA tagging does nothing about all the components already out there that were not tagged at the moment of manufacture. Those chips are now often in the hands of secondary-market distributors, many of whom got them from still other distributors rather than from the original manufacturer, which may no longer exist.

It is parts bought on this byzantine secondary market, not those directly from manufacturers and their authorized dealers, that are sometimes not what their packaging says they are. Sure, a distributor can tag its inventory, and that will help trace the parts back to that distributor later if there's any question, but doing so says nothing about the original provenance of the parts.

It will take years for tagged components to become commonplace in the secondary market. In the meantime the military must keep buying untagged chips because so many of its systems are so old that the original manufacturer has stopped making components or gone out of business altogether, forcing DLA to scrounge for spart parts wherever it can.

"10 years from now if all parts are implanted with DNA or they're all traceable back to the manufacturer with a unique identifier, that's great and this problem may be significantly reduced in scope," the congressional source explained, "but any part produced prior to today and any part that's produced outside of this requirement may not be marked."

The DLA mandate that takes effect in November applies to "manufacturers, franchised distributors and other distributors [on DLA's] Qualified Suppliers List," according to an agency factsheet. But the Defense Department is no longer the dominant buyer in the microelectronics market, and companies mas-producing chips for iPhones or airbags may see no need to add a step to their manufacturing process -- however easy Hayward says it is -- just to keep selling to the military.

"The Department of Defense can't define the market for what gets done on commercial chips because they're such a small customer," said the congressional source, "so are commercial manufacturers going to do this for the defense market?"

That's a business case Hayward and company must make far beyond the Department of Defense. Given rising concerns about counterfeit components and cybersecurity in the commercial world, not just the military, they have a real shot. Certainly the DLA seal of approval will help them sell their seals of authenticity to civilian markets.

High risk defense suppliers soars, report finds

High risk defense suppliers soars, report finds:

Anne-Françoise PELE

10/31/2012 1:30 PM EDT


PARIS – The number of high risk suppliers to the U.S. government agencies, defense contractors and subcontractors, as well as all military and commercial electronics application markets increased by 63 percent from 2002 to 2011, according to market research firm IHS iSuppli.

In 2011, IHS observed that a total of 9,539 suppliers were reported either for known involvement in high-risk, fraudulent and suspect counterfeit part transactions, or for conduct identified by the government as grounds to debar, suspend or otherwise exclude from contract participation. There were 5,849 in 2002.

In all, IHS reported that 78,217 high risk suppliers to U.S. government had been identified during the period from 2002 to 2011.


Click on image to enlarge

Vicki Knauf, parts logistics expert at IHS, declared: “It’s abundantly clear that supplier risk is real, extensive and growing. It’s a federal acquisition requirement to screen for debarred, suspended or otherwise excluded parties. The Department of Defense, as well as its contractors and subcontractors, must comply with new regulations for the use of trusted suppliers and authorized sources."

"A key component of developing a secure supply chain includes the use of Trusted Suppliers. Pinpointing probabilities of risk, blacklisting and vetting high-risk suppliers are crucial to developing a resilient supply chain that fends off devious behavior," Knauf concluded.

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Combating fake chips by controlling supply chain

Combating fake chips by controlling supply chain:



In December 2011, President Barack Obama signed the fiscal year 2012 US National Defense Authorization Act. The budget bill also encourages the implementation of procedures to mitigate the possibility of obtaining counterfeit components by making members of all tiers of the defense supply chain accountable. The meaning of the term counterfeit in this context includes fake, substandard, damaged, or mismarked components.

In the fall of 2011, for the first time in history, U.S. Federal Courts prosecuted an individual for trafficking in counterfeit integrated circuits, many of which were targeted for the U.S. military. Others were to be used in brake systems in high-speed trains and instruments used by firefighters to detect nuclear radiation. The administrator of the company that sold the components was sentenced to 38 months in prison and assessed fines of $166,141 for selling almost $16 million worth of semiconductors falsely marked as military, commercial or industrial grade.

As progressive as all of this news seems to be in the fight against counterfeit semiconductors making their way into the US supply chain, it is just the beginning. In fact, it is estimated that 2 percent of all the semiconductors sold last year were counterfeit. That doesn’t sound too threatening until we do the math: the estimated value of counterfeit parts that made their way into the U.S. supply chain in 2011 is over $5 billion.

Not only do counterfeit components threaten lives, they impose a vast negative financial impact to semiconductor manufacturers, distributors, electronics equipment manufacturers and end users. It is estimated that the actual cost of a failed semiconductor that makes its way into production – in any industry – can be more than 100 times the cost of the original component. That makes the bargain price – often 70 percent less than the “real thing” – look less and less attractive. No matter how hard the industry tries, it can’t get around that old adage: you get what you pay for.



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Pb-free Electronics Risks Mitigation Project - DLA Technical Briefing 24 April 2012

A recent brieifing of PERM has taken place discussing the following

Discussion Topics
• Pb-free Electronics Supplier Issues
• Pb-free Electronics Risks & Failures
– Tin Whiskers
– Issues with Pb-free Alloys in COTS Electronics
– Unpredictable Service Life & Reliability for the Warfighter
• Risk Reduction Strategy
– Pb-free Electronics Risk Management (PERM)  Consortium
– “Manhattan Project” to Scope the Problem
– Pb-free Electronics Risk Reduction Program
• Take Away’s


http://www.dscc.dla.mil/downloads/psmc/Apr12/7PbFreeElectronicRiskReduction.pdf


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THE Pb-FREE IN ELECTRONICS RISK MITIGATION (PERM) CONSORTIUM

A paper has just be released describing the organization, content, and expectations of the newly formed Pb-free Electronics Risk Mitigation (PERM) consortium and its stakeholders. PERM was created as a more focussed group of the LEAP consortium.

The AIA-sponsored Pb-free Electronics in Aerospace  Project (LEAP) has been the premier industry working group in the the defense/aerospace industry since 2004.  It has worked to identify and address the risks and other challenges associated with the use of Pb-free electronics in high performance & high reliability equipment.  It has successfully provided resources such as handbooks and standards as well as templates, guidelines, and other tools to support risk mitigation.  However, the use of Pb-free materials has grown to such an extent that many components/parts are no longer available in tin-lead (either surface finishes or interconnection media).   Engineers have been forced to use some Pb-free parts in their new designs or,  in  many  cases,  as  part  of retrofits and upgrades, leading to concern over performance and reliability.

An ad hoc sub-committee of the LEAP team spent over a year producing a more focused entity called the Pb-free Electronics Risk Mitigation (PERM) consortium, to provide overarching executive leadership and coordination of Pb-free electronics risk management activities for the aerospace and defense community on both the government and industry side.   It is focussed on those activities that provide value-added results.  More information


http://www.ipcoutlook.org/pdf/pb_free_risk_mitigation_smta.pdf

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Tin whisker mitigation research to be performed by Rockwell Collins for DoD program – Military Embedded Systems

A team lead by Rockwell Collins has been selected by the Department of Defense's (DoD's) Strategic Environmental Research and Development Program to lead team a research project on the Tin Whiskers Inorganic Coatings Evaluation (TWICE) program. The research will focus on mitigating the impact of tin whiskers on high-reliability, high-performance electronic systems caused by new lead-free alloys and finishes in the defense and aerospace and defense manufacturing systems and supply chain.

The project is expected to form a better scientific understanding of the mechanisms of tin whisker formation and how they may be managed with conformal coatings. Materials and the processes necessary to generate coatings that could mitigate tin whisker growth on a variety of surfaces over a wide range of environmental conditions will be developed.


Tin whisker mitigation research to be performed by Rockwell Collins for DoD program – Military Embedded Systems:

Soldering equipment concern sees big uptick in sales

Spokane Journal of Business: As the domestic aerospace-manufacturing sector continues to grow, Spokane Valley-based soldering equipment maker RPS Automation LLC is seeing its sales shoot upward and is attributing much of that increase to aerospace-related fabrication.

RPS Automation, based in a 16,000-square-foot warehouse at 3808 N. Sullivan in the Spokane Business & Industrial Park, makes a line of machines used to solder components onto electronic circuit boards.

Thermal cycling ramifications of lead-free solder on the electronic assembly repair process

Scopus: The conversion from tin-lead to lead-free electronics has created concern amongst engineers about the reliability of electronic assemblies and the ramifications that reliability changes may have on the life cycle cost and availability of critical systems that use lead-free electronics.

In order to analyze the impact of the tin-lead to lead-free electronics conversion in terms of life cycle cost and availability, a simulation of fielded electronic systems to and through a board-level repair facility was created. Systems manufactured with tin-lead parts or lead-free parts that are fielded, fail and have to be repaired are modeled. The model includes the effects of a finite repair process capacity, repair prioritization, multiple possible failure mechanisms, no-fault-founds, and un-repairable units. The model is used to quantify and demonstrate the system-and enterprise-level risks posed by the conversion from tin-lead to lead-free electronics. Example analyses were performed on electronic assemblies that use SAC (tin, silver and copper) and tin-lead solder using a repair process modeled after a NSWC Crane Aviation Repair Process (8000 assemblies with 30 year support lives were modeled). The components considered consisted of ball grid array, column grid array and leadless chip carrier packaged parts that experienced three different thermal cycling profiles.

The case studies revealed that when exposed to usage profiles characteristic of consumer electronics, low maximum and mean thermal cycling temperatures with long dwell times, SAC exhibited significantly reduced repair costs compared to tin-lead. For usage profiles characteristic of aerospace and high-performance applications, high maximum and mean thermal cycling temperatures with short dwell times, SAC exhibited significantly increased repair costs when compared to tin-lead.

IEEE Transactions on Components, Packaging and Manufacturing Technology
Volume 1, Issue 6, June 2011, Article number 5784324, Pages 964-974
Thermal cycling ramifications of lead-free solder on the electronic assembly repair process

Chaloupka, A.C. , Sandborn, P.A. , Konoza, A.  

Department of Mechanical Engineering, Center for Advanced Life Cycle Engineering Electronics Products and Systems, University of Maryland, College Park, MD 20742, United States

Effect of aging on tensile properties and microstructures of eutectic Sn-Pb solder with small amounts of Au and Pd for aerospace application

Scopus: In the joint with eutectic Sn-Pb solder and a lead-free Ni/Pd/Au electrode, degradation of mechanical properties of the solder due to dissolution of Au and Pd into the solder would be anxious.

In this study, the effect of aging was investigated on tensile properties and microstructures of the eutectic Sn-Pb solder with small amounts of Au and Pd added. In as-cast solders with both Au and Pd added, the tensile strength increases with increasing contents of Au and Pd. A similar tendency was observed after aging at 100'C for 1000 h. The effect of aging on elongation was relatively small and elongation degraded when brittle (Pd,Au) Sn 4 phases formed in the solder. In solders with Au ranging from 1 to 5 mass%, regardless of aging conditions investigated, the tensile strength is stable at approximately 50 MPa and 45 MPa before and after aging, respectively. The effect of aging on improvement of elongation was negligible and elongation degraded when rod shaped AuSn 4 formed in the solder.

On the basis of the result of microstructural observation, it was clarified that the strengthening by dispersion of (Pd,Au) Sn 4 phases is superior to softening by microstructure coarsening upon aging when the contents of Au and Pd are 2 mass% and 1 mass% or above, respectively

ASME 2011 Pacific Rim Technical Conference and Exhibition on Packaging and Integration of Electronic and Photonic Systems, InterPACK 2011
Volume 2, 2011, Pages 667-672
ASME 2011 Pacific Rim Technical Conference and Exhibition on Packaging and Integration of Electronic and Photonic Systems, InterPACK 2011;Portland, OR;6 July 2011through8 July 2011;Code89456
Effect of aging on tensile properties and microstructures of eutectic Sn-Pb solder with small amounts of Au and Pd for aerospace application  ( Conference Paper )

Kikuchi, R.a, Shohji, I.a, Saitoh, Y.a, Nemoto, N.b, Nakagawa, T.c, Ebihara, N.d, Iwase, F.e  


a  Gunma University, Kiryu, Gunma, Japan
b  Japan Aerospace Exploration Agency, Tsukuba, Ibaraki, Japan
c  Nippon Avionics Co., Ltd., Yokohama, Kanagawa, Japan
d  NEC TOSHIBA Space Systems, Ltd., Fuchu, Tokyo, Japan
e  HIREC Corp., Kawasaki, Kanagawa, Japan

Military/Aerospace Lead-Free Solder Reliability Still Unproven

Ron Lasky Indium Blog 
Indium colleague Ed Briggs and I gave a 3 hour presentation on “Lead-Free Assembly for High Yields and Reliability.” I think Ed’s analysis of “graping” and the “head-in-pillow” defect is the best around.

There was quite a bit of discussion on the challenges faced by solder paste flux in the new world of lead-free solder paste and miniaturized components (i.e. very small solder paste deposits.) One of the hottest topics was nitrogen and lead-free SMT assembly. There seemed to be uniform agreement that solder paste users should be able to demand that their lead-free solder paste perform well with any PWB pad finish (e.g. OSP Immersion silver, electroless nickel gold, etc.) without the use of nitrogen. Not only does using nitrogen cost money, but it will usually make tombstoning worse. However, in the opinion of most people, nitrogen is a must for wave soldering and, since it minimizes dross development, it likely pays for itself.

After Ed and I finished, Fred Dimock, of BTU, gave one of the best talks I have ever experienced on reflow soldering. He discussed thermal profiling in detail, including the importance of assuring that thermocouples are not oxidized (when oxidized they lose accuracy). He also discussed a reflow oven design that minimizes temperature overshoot during heating, and undershoot when the heater is off. Understanding these topics is critical with the tight temperature control that many lead-free assemblers face.

Fred Verdi of ACI finished the meeting with an excellent presentation on “Pb-free Electronics for Aerospace and Defense.” Fred’s talk discussed the work that went into the “Manhattan Project.” A free download of the entire project report is available.

There appears to be agreement that acceptable lead-free reliability has been established for consumer products with lifetimes of 5 years or so, but not for military/aerospace electronics where lifetimes can be up to 40 years in harsh service conditions. These vast product lifetime and consequences of failure differences are depicted in the Fred's chart (above). Commercial products are in quadrant A and military/aerospace products in quadrant D.

One of the greatest risks faced by quadrant D products is tin whiskers. Fred spent quite a bit of time discussing this interesting phenomenon. One of the challenges of this risk is that there is no way to accelerate it, so you can’t do an equivalent test to accelerated thermal cycling or drop shock. Fred mentioned that there have now been verified tin whisker fails, the Toyota accelerator mechanism being a confirmed one.

In addition to tin whiskers, lead-free reliability for quadrant D products (with a service life of up to 40 years) in thermal cycle and other areas remains a concern.  I mention that tin pest was not on the list of issues for this quadrant.

Fred and the Manhattan Project Team have identified many "gaps" that need to be addressed to determine and mitigate the risk of lead-free assembly for quadrant D products.  They plan to start this approximately $100M program in 2013.

For those that missed this free workshop, ACI host Mike Prestoy is planning another one in 6 months.



Read more: http://blogs.indium.com/blog/an-interview-with-the-professor/militaryaerospace-lead-free-reliability-still-unproven#ixzz1ihiB0lvL

US Air Force - Mitigating Reduction of Hazardous Substances (RoHS) Lead -Free Issues in Aerospace Circuit Board Manufacture

Federal Business Opportunities: "This effort investigates the durability and survivability of current technology component families to establish aerospace and defense electronics Pb-free assembly process margins and practices."

Tin-whisker failure problem from lead-free solder in military electronics is target of Air Force research job

Military & Aerospace Electronics: "U.S. Air Force electronics researchers are asking industry to develop a set of requirements virtually to eliminate the risks of tin whiskers and other problems related to lead-free solder in integrated circuit and circuit board manufacturing for aerospace and defense electronics applications.

The Air Force Research Laboratory (AFRL) at Wright-Patterson Air Force Base, Ohio, released a broad agency announcement (BAA-11-16-PKM) last Thursday for a program called Mitigating Reduction of Hazardous Substances (RoHS) Lead-Free Issues in Aerospace Circuit Board Manufacture, which seeks to develop guidelines to help military electronics manufacturers choose lead-free components, as well as control thermal degradation of lead-free solders at the component and materials level."

Scientists at the Materials Integrity Branch of the AFRL Systems Support Division are asking industry experts to find ways of eliminating tin whiskers in lead-free solders to help reduce defects and field failures in aerospace and defense electronics. Tin whiskers, which can grow over time on lead-free solders, can cause short circuits and other defects in electronic systems.

Air Force researchers are interested in using a method that has been used on military-grade electronic parts since the mid-1960s to mitigate tin whisker problems: fusing the matte tin on lead-free parts and boards in a post processing step prior to board assembly, or by requesting a fused tin finish from parts vendors.

As more parts and materials are re-engineered to be compatible with the higher temperatures and longer dwell times necessary when using many lead-free alloys, the number of parts likely to be compatible with tin fusing should grow, Air Force officials explain. To come up with guidelines to achieve this, companies must identify component families normally only available with pure unfused matte tin finishes that are compatible with tin fusing.

For the program, the Air Force is asking companies to find ways to determine the suitability of electronic components or materials for soldering cycles during circuit card assembly, as well as ways to estimate time to failure due to this kind of soldering.

The program also asks companies to find the best ways of selecting components, materials, and vendors for design and manufacture of defense and aerospace electronics equipment using suitable lead-free solder alloys.

The Mitigating Reduction of Hazardous Substances (RoHS) Lead-Free Issues in Aerospace Circuit Board Manufacture program should be a 15-month, $1.7 million effort, with a contract to one company expected to be awarded as early as 30 June 2011.

Lead free solder development and analysis for aerospace applications

Oxford Materials - Personal Homepages: "Due to safety considerations, the aerospace industry is largely exempt from legislation prohibiting the use of lead in interconnects in electronic assemblies, and lead continues to be used in avionics. This situation is unlikely to continue because of further legislation and difficulties in sourcing lead-containing materials and assemblies from suppliers. In contrast to domestic electronics where lead free solders are now standard and reliable, there are no current widely accepted 'drop-in' replacement materials for lead solders that meet the more stringent and hostile aerospace standards for reliability. There is now a pressing need to develop underpinning scientific understanding of the factors governing lifetime of existing and future lead free solder materials for critical aerospace applications"

PERM Update meeting Jan 2011

PERM (Coral Gables, FL: January 11-13)
Jim McLeish will be providing an update on the status of Mil-HDBK-217 at the PERM meeting. For more information or to arrange a meeting, please contact Jim McLeish.

IPC EMS Military Conference

IPC EMS Military Conference: "f you supply the military or are planning to, the IPC Conference for the North American EMS Industry: What It Takes to Supply the Military is for you.

By providing solutions to the many complex challenges faced by EMS suppliers to the military, this event will uniquely position you for success. The day will begin with, 'Department of Defense Electronics Challenges and Opportunities' a keynote address by Brett B. Lambert, Director of Industrial Policy in the Office of the Assistant Secretary of Defense for Acquisition."

Lead-Free in Mission Critical: Failure Is Not An Option

EMS007: "We had already begun addressing lead-free issues of the complex components that are increasingly multi-functional, miniaturized, and subject to reflow during their build. Efforts included adjusted profiling guidelines, component shielding during reflow, more advanced test and inspection (over, under, around and through), and if necessary, hand soldering.

But, because RoHS was only enacted in 2006, we still don't know whether those efforts alone will prove adequate for long-term mission-critical applications. The military, for instance, has said it wants a minimum of 15 years before first-repair. medical wants at least seven (usually more); and even automotive wants components to last seven to 10 years [1].

Lead-free problems exist, some of which we noted. Many will be solved only with increased R&D and empirical evidence. Many boil down to better OEM and EMS communication, particularly when assembling mission-critical components and boards offshore, where differences in language, experience and culture exist.|

There is, however, no agreed-upon scientific evidence that the environment will be helped more by full lead-free implementation than mission-critical industries will be hurt by it. While technology should always show concern for the environment, until environmental-friendly technology is proven to go the distance needed for mission-critical applications, we have much work to do. Failure is simply not an option.

In 2009, David Cavanaugh, Director, Corporate Component Engineering at Benchmark Electronics, said it will take four to five more years before we are able to have the confidence in lead-free that we do in tin/lead [2].�If he is correct, that would mean a minimum of at least three more years to go"

SMTAI Offers Four Important Symposia

EMS007: "The second phase of the NASA-DoD Lead-Free Consortium project is providing unprecedented data on the long-term performance of lead-free interconnections at this year's world renowned Lead-Free Soldering Technology Symposium. The scope of these experiments addresses alternative surface finishes, as well as the performance of mixed SnPb/Pb-free solder joints and the effects of rework activities.

Other sessions will include the Impact of Lead-Free Materials and Soldering Processes and Lead-Free Solder Joint Reliability."

Ruggedness and reliability of lead free electronics

Scopuss: "One might question: How much of the reliability achieved today can be credited to the production process evolution and how much is due to the ruggedization and screening process? There is a strong need to have high reliability in lead-free.

Lacking the many decades of production evolution and lacking in-depth understanding of lead-free capabilities, reliability can be maximized by elimination of old, less effective ruggedization and screening methods. Reliability can be enhanced by using only the 'best of show' methods, capable of understanding products at solder joint level. The common military practice of predefining environmental stress screening (ESS) profiles is counter productive to reliability.

Predefined ESS will be very damaging to reliability when applied to emerging technologies such as lead-free electronics. Predefined ESS for electronics should never be imposed by the military or accepted by developers as a requirement."

Starr, J.E.

CirVibe Inc., 3450 Fernbrook Lane North, Plymouth, MN 55447, United States

Transition to Lead-Free Products in the US Electronics Industry: A Model of Environmental, Technical, and Economic Preferences

Scopus: "The European Union's Restriction on the Use of Certain Hazardous Substances (Directive 2002/95/EC) targeted at electronic products took effect in 2006. In contrast, the USA has no comparable national policy on these products.

To understand corporate responses to policy differences across jurisdictions, we conducted a structured-questionnaire survey of individuals in 109 companies that are representative of the US electronics industry. The results reveal that 70% of these companies have already adopted lead-free solder for electronics with 49% of the total preferring the SnAgCu formulation, despite uncertainties associated with environmental impacts of this alternative alloy

We use a modified life cycle impact assessment method based on endpoint modeling approach to derive weighting factors that represent the respondents' value system for tradeoffs among environmental impacts. We use a modified fuzzy Technique for Order Preference by Similarity to Ideal Solution approach to evaluate technical criteria dominance in declared preferences. A statistical model of corporate behavior is also presented.

The results provide the first systematic framework that accounts for environmental impact, technological challenge, and business strategy concurrently toward formulating a comprehensive national policy for materials selection in electronic products.