SMTA Space Coast: What's Needed to Modernize Defense Solder Standards

Estimated reading time: 7 minutes

Long-time lead-free solder investigator, Denny Fritz, hit the SMTA Space Coast Expo in November to drum up support for an initiative to include lead-free solder in milaero-based printed circuit board assemblies. In this interview, Denny provides background on the genesis of the “consider all solders” project and why it matters to continue leading this effort.

Nolan Johnson: Denny, tell me about your recent presentation at the SMTA Space Coast Expo on milaero soldering technology and standards.

Denny Fritz: I provided an overview of how Defense primes have dealt with lead-free solder, which is that they are notoriously reluctant even to consider it. They have pretty well dug their heels in. 

For instance, over half of my audience at Space Coast works for a local aerospace company, but they have no lead-free solder on any of their assembly lines. I asked them what happens when you have a commercial program or with a requirement for lead-free solder. They said that they subcontract it, because “we do not want any cross-contamination between lead-free and eutectic lead-based solder.” 

Even before the Department of Defense got involved, defense primes gathered under the Aerospace Industries Association (AIA) banner, recognizing that, collectively, lead-free was a bigger problem than any one of them could resolve, yet they needed answers quickly. The solution was to work together.

Johnson: How was the Global Electronics Association involved? Did it take a hands-off approach at the time?

Fritz: Yes, it was developing standards for the acceptance of either leaded solder or the new lead-free assemblies, which were developed rapidly by the relevant IPC committees. Also, the Aerospace Industries Association, being a world trade organization, formed an “in process team” (IPT), a standards subcommittee specializing in defense-related aerospace activities. 

For background, the Defense fallout of the 2008 financial crisis had stalled lead-free progress for about two years due to decreasing membership in the AIA. They dumped several activities, including the lead-free effort. At that point, the Global Electronics Association picked up the public effort. SAE, often regarded as the automotive standards authority, adopted the lead-free standards, along with other programs AIA had in development. 

There was also a proposal to fund the $100 million Lead-free Manhattan Project, which 15 industry subject matter experts (SMEs) had identified would make lead-free solder acceptable in milaero applications. 

Many influential aerospace individuals sought funding for this, but they never established a level of credibility within Defense or Congress to secure that funding, so the lead-free Manhattan project languished for three or four years. 

Johnson: Didn’t that change when John Mitchell took the lead at the Global Electronics Association? 

Fritz: Yes. John looked for some additional government related initiatives and identified this lead-free activity. The Association had a goal to apply standards and establish a technical basis for lead-free in aerospace and defense.

Unfortunately, this was a million-dollar solution to a billion-dollar problem, so it languished. A review in 2014 showed that by then, only $40 to $50 million would be necessary to complete an accommodation for lead-free within Defense. Could they find $40 million? No, not right away. 

Johnson: What happened next?

Fritz: After another three-year pause, in 2019, Chris Mitchell, the Association’s VP of global government relations, gathered 10 subject matter experts, including me. We wrote a white paper that detailed the process for achieving lead-free solder in defense for the same $40 million as in 2015. It resulted in getting Congressional funding. The appropriation resulted in an “OTA contract bid” for a mil-std standard, a handbook, and a roadmap.

In the first year of the OTA award, the U.S. Partnership for Assured Electronics organized around university support. The program was designated “Solder Performance and Reliability Assessment.” In the second year, we wrote our first drafts of the solder performance standard and the accompanying handbook, and planned a solder test program. The third year was for implementation. However, years four and five were not funded (Fiscal 2024 and 2025). I suspect the CHIPS Act was drowning out everything else. Therefore, the $20 million we had (2021–2023) has been allocated to write the standard and the handbook, along with some conclusions.

What will really suffer is the testing program to test solder qualifying standards for use within Defense electronics. We’re having to depend more on charity to get this thing done.

Johnson: Denny, how does it stand today? There's an incomplete standard that would benefit manufacturers and the milaero industry, but lead-free isn’t particularly compelling for them. Why would aerospace want to move to lead-free? 

Fritz: In our earliest white papers to Congress, we outlined, with moderate documentation, that the aerospace defense industry is spending $50–$100 million a year to convert lead-free solder balls, finishes, and attachments back to lead-tin to achieve 100% eutectic solder content in the assembly.  

Defense said that primes didn’t want even a hint of directive. Therefore, our approach is to be solder-agnostic and provide test procedures that qualify any number of the 76 new alloys developed since the RoHS directive came into effect. We’re developing the method to qualify what you can use. Defense primes should lobby to add solder composition to heir bill of materials, which almost never happens. Instead, people just note on fabrication prints to “use whatever solder you used previously.” That perpetuates eutectic solder. 

The metallurgists don't like to mix lead-free and leaded solder because of the assembly reflow temperature needs for lead-free. While eutectic solder melts at approximately 183°C, it's usually assembled at about 210 or possibly 220°C. However, lead-free assembly temperatures are typically around 240, possibly 250°C.

A year ago, an Army location said it had a qualified mixed solder joint assembly from a supplier. They made the supplier prove that it’s following the same ISO process it qualified for mixed solder joints—assembly at 250°C. I've never heard that from the Navy or the Air Force, but there are likely many unintentional mixed-service soldier implementations out there. I wouldn't be surprised if we see some failures in the next 10 years due to the low assembly temperature use in mixed solder joint assembly.

Johnson: Other than reballing, why should Milaero move? There must be a reason so many are reluctant besides tradition. What are the advantages and disadvantages for Milaero? 

Fritz: If you reball, you know you will get proper melting of your solder joints at a relatively low temperature. You won’t stress the laminate, even though almost all laminate is now engineered for use in lead-free assembly. If you still use eutectic solder, you've created a solder joint that's softer and more deformable. It will go back in place once you remove an environmental stress.

The metallurgy is stronger in lead-free solder joints. They don’t deform as easily. If lead-free solder ever deforms by more than 6%, it breaks. Lead-free solder is definitely the better option if you don't stress it excessively, meaning products that undergo temperature cycles between 0°C and 100°C. Conversely, lead-free joints can have problems withstanding the shock of taking a torpedo hit to the ship. They don't have to use any stiffeners to keep the helicopter from vibrating components off the board. 

If you re-ball the BGA, then theoretically, you've taken control of the warranty on that ball grid array. If you went through a thermal solder ball removal and a thermal add back, you've subjected it to a couple of additional temperature excursions. Semiconductor companies are not particularly thrilled that you've altered their product.

Johnson: What's left to do to create a standard and a test system that milaero can get behind? Will they get behind it?

Fritz: The standard is currently in revision 3, and the handbook is nearly complete with revision 3. It has been reviewed by the individuals appointed by the Defense Department, with some input from other selected subject matter experts. We've been working closely with Navy Crane to ensure our university-led consortium doesn't put something out that won’t pass. I wish we had more ongoing input from the other service branches. 

If you're sending people to the PERM organization, you're already paying attention to solder on your assemblies. You might even be using lead-free in some of your programs. However, at the second and third tiers of supply levels, where customers are purchasing assemblies based on price, they may not realize that they should also consider lead-free options. I’m an independent voice out there to help folks think about what solder is appropriate for their use. 

Johnson: What needs to happen next?

Fritz: I am trying to be more public about this activity. I went to the Space Coast event because it has a high percentage of people working in Milaero. One solder supplier stated that they were unaware of this program and expressed interest in participating, at least in the evaluation of the test procedure. Our universities believe the easiest way to do this is for every solder supplier to run these tests and obtain a pedigree. Then, when they come out with a new solder, identify which mil specs that product meets.

Johnson: Denny, thanks for the insight.

Fritz: Thank you, Nolan.