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DI-145 Data Acquisition Starter Kit Developer's Diary

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3/7/2011 Note #18 First Production Run (5-Up and Stencils)

All the pieces are falling into place for the DI-145's first production run. The parts are in stock and have been transferred from the warehouse to the assembly house. Up until this point all DI-145s that exist, the ones we've used for hardware and software testing for months, have been built by hand, a process that consumes about two hours per board. During the first production run, hands will touch these products only twice. Once to place them on the assembly machine and again to remove them as finished products ready for inspection, calibration and test.

The first production stage applies solder paste to the bare PCB using a stencil, a paper-thin metal mask with holes that precisely align with the areas of the PCB where solder is to be applied. The stencil is placed over the board and a long, thick bead of solder paste is applied to the stencil at one end. A mechanical rubber squeegee moves the paste quickly over the board to apply the paste only where it's needed. This process takes about three seconds. Next the PCB, naked except for the solder paste in select areas, moves on a conveyor to the "pick and place" machine that has been programmed to place all of the electronic parts on the board. Tubes and rolls of literally tens of thousands of components feed the hungry machine as it places parts on the board at blinding speed. It's like watching a sewing machine needle except it moves horizontally as well as vertically. At this point we should mention that DI-145 boards are assembled five at a time (5-up). A single board is too small to reliably pass through the automated assembly process, so the boards were designed in a larger form factor consisting of five to a single slab.

DI-145 Data Acquisition Starter Kit PCB
The 5-up design of five DI-145 PCBs to one slab.

The pick and place machine places all components on all five boards on the slab in less than a minute. The solder paste that was applied earlier performs a dual purpose. It keeps the placed parts from sliding around as the slab heads down the same conveyor toward the oven. Once there it melts in about seven minutes to form a permanent, conductive bond between the components and the PCB. The five boards in a single slab are easily separated. A simple twist and bend breaks them apart along stress lines scored into the slab. The now fully assembled individual DI-145s are ready for inspection, calibration, and final test. What took two hours to build by hand is accomplished in about ninety seconds using hands-free automation.

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