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22 SMT Magazine • October 2014 The camera board was procured as a kit from Digi-Key Corporation. The kit included soft- ware that provided a smooth interface between the camera and any Windows computer with a USB port. The specific hardware and software used were: • Manufacturer: Aptina Imaging Corporation • Camera board model: MT9V126 • Software name: DevWare • Software Version: 4.1.9.27784 Nanocopper pastes were formulated using methods developed during tensile experiments and included additional steps to improve vis- cosity, minimize void generation during fusion and facilitate bonding to oxidized tin finishes. These formulations were screened for utility by fusing individual surface mount components to a small deposit of nanocopper on a pure tin surface. Some formulations proved so effective that the components broke within their ceram- ic bodies when subjected to stress (Figure 5E). Formulations have been developed for both manual assembly and automated assembly with stencil and pick-and-place equipment. Syringe application can dispense through needles up to G30 (150 μm inner diameter). Various application procedures have been developed in the lab and piloted on a dedicated R&D production line for both SMT and PTH parts. In a typical fabrication procedure, nano- copper was applied in an automated fashion to the boards using a 4–6 mil stencil. Next, SMT parts were automatically placed using a produc- tion pick-and-place machine. Care was taken to minimize short circuits and to ensure wetting of the nanocopper to the pads. The sensor chip was the most complex component, and a number of paste application methods and paste formula- tions were developed for this step alone. Once all of the SMT components were in place (Fig- ure 6A), PTH parts were added manually using a syringe to apply the nanocopper. A complete- ly assembled board was then ramped through a heating cycle with a maximum temperature of approximately 200°C under constant flow of an inert gas. Drying procedures were devel- oped to minimize cracking of the nanocopper and ensure integrity of the joints. After fusion, assembled components were protected with a standard urethane conformal coating cured at a maximum temperature of 100°C. Each camera board was subjected to a suite of electrical tests at the component level, such as a production flying probe, and culminated in a final board-level evaluation by interfacing the board with the corresponding software. Fully functioning boards were able to display real- time images as shown in Figure 6B. Beyond solder replacement, we have ex- plored a number of other applications using nanocopper. Shown in Figure 7 are two flex- ible electronic devices about 10" long with em- bedded LEDs. The traces were formed by sten- cil printing nanocopper and the cured traces sealed-in using a standard $89 laminator. The entire device functions under repeated flexing. Because the required fusion temperature is only 200°C, it is possible to interface with common nanOcOPPer-baseD sOLDer-Free eLectrOnic assembLY materiaL continues FEATurE Figure 6: A) photograph of a camera board populated with all surface mount components. B) demonstration of fully functional camera board using only nanocopper.