Abstract
Drop testing performance of Printed Hybrid Electronic (PHE) assemblies is reported in this paper. These studies assessed PHE assembly mechanical and electronic survivability and durability in a high-shock acceleration environment using accelerated drop towers equipped with dual-mass shock amplifiers (DMSAs). Testing was completed at accelerations from 10,000 G up to 100,000 G with pulse durations of ∼0.05–0.1 ms and impact velocities of 6.5–20.5 m/s.
The test samples were hemispherical domes fabricated using: (a) additive manufacturing with several different ABS compounds, and (b) injection molding with various EXL9330 and EXL1414 polycarbonates. Different combinations of embedded electronic components ranging from passive components to integrated circuit (IC) packages were subsequently embedded into or surface-mounted onto the exterior face of the dome and interconnected with printed silver traces. Dome modifications were completed using 5-axis CNC machining, silver traces were printed using nScrypt and other extrusion 3D printers, and other IC packages were mounted and connected manually.
Specimens were installed on the drop tower by direct threading into custom aluminum fixtures and instrumented with strain gauges and in-situ resistance measurement cabling. Impacts were characterized with multiple accelerometers mounted to the test fixture and high-speed video controlled by digital acquisition systems at sampling rates up to 1 MHz.
This study considered degradation mechanisms for the substrate material, the electronic component assembly, and the printed silver interconnects. Catastrophic failures of compliant additively manufactured ABS domes at relatively low acceleration levels (10,000–30,000 G) motivated the use of molded polycarbonates, which withstood hundreds of drops at over 100,000 G. Printed electrical trace performance was assessed through 4-point resistance measurements and both pretest and post-test optical microscopy. Trace degradation from as-printed condition to open-circuit failure took as few as 1–2 drops at 100,000 G to hundreds at 10,000–40,000 G. Observed failure modes for traces included 1) failure at locations previously determined during pre-testing microscopy to be ‘at-risk’ sites due to printing issues, 2) delamination of the trace from the substrate material, and 3) cracking across the trace due to dynamic flexural response of the substrate. Prior to failure, resistance measurements for traces progressively increased with number of drops, at rates proportional to acceleration magnitude.
