![]() ![]() The LED junction temperature must be kept below 150☌, because high temperatures will kill the LEDs by either mechanical fracture or diffusion within the junction. High-brightness LEDs are about 30% efficient, which means that 70% of the power (W) used to drive the LEDs is converted to heat. 8 Front and back of the fully assembled LunaLight Rev 2.1 PCB. Content with the finished product, I was ready to test the fully assembled board (Figure 8).įig. ![]() I cleaned off the tacky flux residue with 91% isopropyl rubbing alcohol and an old toothbrush, and I checked all the electrical connections with a continuity tester to ensure that all the intended connections were made and that there were no shorted devices. With the SMD components soldered into place, I manually soldered the remaining PTH components with a soldering iron and SnPb37 solder. 7 Populated PCB being sent into the reflow oven. The tacky flux helped to hold the components in place as I walked over to the reflow oven to insert the populated board (Figure 7).įig. After making these corrections, I applied Kester TSF Tacky Flux onto all the pads and carefully placed the tiny components using tweezers. 6 The unpopulated board through the reflow oven to reflow the solder paste.Īfter reflow of the solder paste, I manually removed solder bridges between pads or excess solder from larger pads. To avoid the cost of buying a solder paste stencil, I applied a layer of Kester SnAg3.0Cu0.5 solder paste onto the SMD pads using a toothpick and sent the board through the reflow oven (Figure 6).įig. The unpopulated boards were shipped to Cal Poly for the students to assemble.įor the SMD on my board, I decided upon reflow soldering technique using the Heller 1500EXLMS SMT reflow oven in the lab set up with the “Marc_Thesis” reflow profile. (a company in Chicago that consolidated the student designs and sent the bulk order to a manufacturer in Taiwan. Once the board design was completed in DipTrace, the Gerber files and N/C Drill file were assembled and sent to Imagineering, Inc. The LEDs are placed on the board to align precisely with the hole in the center of the reflector. These screws will secure the PCB to the reflector, and the board will be oriented with the battery on the bottom so that the LunaLight is bottom-heavy instead of top-heavy. The board has four mounting screw holes for 4-40 screws. ![]() 5 SolidWorks CAD model of the LunaLight board with the large components. I inserted screenshots of my DipTrace board design as decals to double-check that my components were placed precisely where I planned them to be.įig. I created a CAD model of my board plus the large components in SolidWorks to ensure that the system could fit within the LunaLight housing (Figure 5). I measured out the absolute maximum board dimensions to be 2.96”x4.3”, but during the design process I was able to trim the board outline down to 2.75”x3.65”. ![]() 4 PCB-mount battery holder for single-cell 18650 Li-ion batteries.ĭimension limitations of the PCB were important because the board had to fit inside the relatively compact LunaLight housing. The holder snaps into place, and the electrical connections to the PCB are made by soldering the positive and negative PTH leads to the board.įig. 3 The right-angle PTH components that must align along one edge of the PCB.Ī battery holder was selected that holds a Li-ion 18650 battery and mounts directly to the PCB (Figure 4). The orientation of the slide switches was critical to ensure that the “OFF” position was the lowest switch position.įig. These components will then lay flush with the exterior of the housing once the PCB is mounted inside the LunaLight. Right angle PCB mount devices were selected for the USB port, barrel jack, and slide switches so that they can be aligned along one edge of the board (Figure 3). Due to the way the board will mount in the LunaLight housing, the larger components had to be pin thru-hole (PTH) devices that could be soldered onto the back of the board. Size and manufacturability considerations drove the decision to use surface-mount devices (SMD) for the majority of the board components. ![]()
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