Nuclear weaponsComputer modeling aids solder reliability in nuclear weapons

Published 20 December 2017

Solder isn’t the first thing that comes to mind as essential to a nuclear weapon. But since weapons contain hundreds of thousands of solder joints, each potentially a point of failure, Sandia National Laboratories has developed and refined computer models to predict their performance and reliability.

Solder isn’t the first thing that comes to mind as essential to a nuclear weapon. But since weapons contain hundreds of thousands of solder joints, each potentially a point of failure, Sandia National Laboratories has developed and refined computer models to predict their performance and reliability.

“Computational modeling of solder joint fatigue has become critical to Sandia and its role in the current nuclear weapons life extension programs, even before production assembly at the Kansas City National Security Campus,” said materials scientist Paul Vianco, who works with material modeler Mike Neilsen. “Sandia uses the computational model to solve manufacturing issues as well as assess the impact of design changes on solder joint reliability.

“This is critical as we finalize designs and head into production,” he said.

Anything with circuit boards requires countless solder joints, and miniaturization of electronics has vastly increased the number in printed wiring assemblies. Vianco lists two examples among a multitude of printed wiring assemblies for weapons: one with more than 900 solder joints, 400 on a single component; the other with about 300 joints.

Sandia Lab says that the lab has advanced computational modeling to the point it can help guide component design decisions and assembly processes at the Kansas City National Security Campus, establish qualification and acceptance test definitions and provide long-term reliability of solder interconnections in the stockpile, he said.

“In the early stages of model development, we could sit down with designers and give them a very broad reliability window for solder joints. It was a case of saying, ‘Well, you’re not going to get into a lot of trouble because we know what’s going to happen here and here,’’’ Vianco said, stretching out his hands. “What was happening in here” — the space between his hands — “could not be predicted with any confidence that allowed the engineers to use the models to guide their designs of electronic assemblies.”

The making of a solder model
The current solder model resulted from years of research and collaborations with universities and others. Sandia has modeled solder performance for more than thirty years, increasing models’ fidelity based on improved knowledge of properties of materials and experiments to develop and then validate the models.