SMTA International Conference Proceedings

Effect of Cure Conditions on the Interface Properties and Reliability of Potted Electronics in 25,000G Mechanical Shock

Authors: Pradeep Lall, Kalyan Dornala, Ryan Lowe, John Deep
Company: Auburn University, ARA Associates, Air Force Research Laboratories
Date Published: 9/22/2019   Conference: SMTA International

Abstract: Survivability of fine-pitch electronics at high-g loads requires the use of additional structural support and shock damping through the use of potting-materials. The potting compounds may serve additional functions including the ability to sustain thermo-mechanical loads and the high humidity in transport, storage and use environments. Failure of potted assemblies has been shown to be at the interface between the potting material and the printed circuit board. There is a dearth of computational tools to allow for the prediction of the initiation of damage and the progression of damage under high-g shock loads. Defense electronics and military systems have longer lifetimes in the neighborhood of 20-40 years and higher reliability requirements. New packaging architectures, cannot be compared with the state-of-art systems and lack decades of historical data to provide robust proof of their survivability. Tools and techniques are needed to determine the failure envelopes for new component technologies for operation under high acceleration loads in current and next generation military systems. Component’s survivability in a product is influenced by many factors including board construction, board size, board thickness, and component design rules. The same component may have large variance in shock survivability depending on the product implementation. The fracture properties and interfacial crack delamination of the PCB/epoxy interface was determined using three-point bend loading with a pre-crack in the epoxy near the interface. The fracture toughness and crack initiation of the three-epoxy systems was compared with the cure schedule and temperature. A finite element model framework was developed for a circular PCB with fine pitch BGA packages, which are encapsulated with potting material. The interface between the PCB and the potting compound was modeled using cohesive zone elements. The test assembly model was subjected to high-g mechanical shock loads up to 25,000g.

Key Words: 

High-g, mechanical shock, reliability, potting compounds, ball-grid arrays, explicit finite elements, cohesive zone models, fracture toughness, interface fracture

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