In this paper, the drop durability of printed hybrid electronic (PHE) assemblies of various form factors is studied under extreme drop conditions with accelerations up to 20,000 G. Test specimens considered here include: circular disk, cantilever beam, and hemispherical dome samples.
The disk is made from a UV hardened resin material and mounted using a 3-point fixture. This specimen experienced overstress fracture at 20,000 G drops. Additionally, it was very susceptible to repetitive drop failure. The failure site was at the expected site of maximum flexure, as revealed by finite element modeling and by high-speed video recording.
The cantilever beam is a standard 1.6 mm thick FR4 substrate with printed silver traces. The substrate was durable but suffered from high strains near the clamp which are expected to cause damage to the silver conductive traces printed on them. The beam specimen was instrumented with strain gages and was also subjected to high-speed video recording of the drop event. The beam was found to vibrate in its first two bending modes when dropped at 10,000 G.
The hemispherical substrates for the dome specimens were made from several different polymeric materials and were mounted in a threaded fixture. Drop durability varied with choice of substrate material and fabrication method. Some showed catastrophic failures after 1–5 drops at 20,000 Gs while some survived more than 50 drops at 20,000 G. The failure site for all failed dome specimens was at the threads used for mounting to the fixture.