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www.us-
tech.com
February, 2017 Convolution of the THE NEW
BENCHMARK IN WIRE STRIPPING P
BOM: How Much Could a Resistor Cost?
By Stanley L. Bentley, P.E., Senior Technical Advisor, DIVSYS International
ermit me a small history lesson from the perspective of an engi- neer that has been involved with
electronic design and manufacturing for over 50 years. I assembled my first electronic project in the fourth grade, and I fabricated my first PCB in grad- uate school around 1970. Since then, I have been continuously involved with, and owned, companies designing, fab- ricating and assembling PCBs. One of my first projects was a
The
Mira 230 has a new robust and
sturdy design that supports an extraor- dinary processing range from AWG 32 to AWG 8. It sets a new benchmark by its unique sequencing capabilities that can be stored in a library for quick reproduction. The Mira 230 can strip and cut inner conductors with a variety of parameters without a program change. It comes equipped with a simple graphical user interface that ensures a quick learning process.
komaxwire.com See at APEX, Booth 415
quick-turn design and assembly for a company that made caskets. They needed a board with one diode (true story) and needed it quickly because the end customer was truly “out of time.” The circuit was designed on a quadrille pad (no schematic capture) and then laid out 2X on a drafting table (no CAD) with red/blue tape and puppets (remember puppets?). The part was found in the Allied
catalog (remember paper catalogs?) and, with a quick landline phone call, was put on my account (no Visa or Master Card yet) and mailed Parcel Post (no FedEx). The artwork was taken to the photo lab (no Internet) that reduced the artwork and pro- duced negatives (no Gerber). A piece of sensitized laminate
was exposed with a sun lamp, devel- oped, and etched in ammonium per- sulfate (ferric chloride had just been banned). The board was drilled using a manual electromechanical drill and the surface was plated with an im- mersion silver powder. The part was removed from the box (no ERP or re- ceiving inspection), formed, and stuffed into the board (no SMT). I grabbed my Kester 63/37 rosin
core solder (no RoHS) and my Unger iron. Then, using my teeth as a third hand for the solder, soldered top and
Intelligent Dry Storage™
bottom (no tort lawyers). The assem- bly was cleaned with alcohol, tested for polarity, and coated with Krylon. Total project time was approximately two days. The manufacturer was happy with the quick response. The end customer was cool the whole time and never raised a stink!
BOM Complication Let’s evaluate the convolution
of the bill of materials with all of today’s fragmented processes, each with its own jealously protected soft- ware. A design engineer (DE) re- ceives a project request to design a circuit. DE opens the schematic cap- ture program and designs the circuit. As part of the design process, the BOM is started. In this BOM is en- tered a 1k, 1/2W resistor, designated R1, with a tolerance of 0.5 percent and 25 PPM TC. The circuit is run through a simulator and found to de- liver the desired performance. The package is then passed to the me- chanical designer. Initial BOM columns include quantity, descrip- tion, value, tolerance, temperature coefficient, and reference designator. The mechanical designer pro-
duces a 3D model of the PCB with di- mensions in Solidworks that shows a location for a component with dimen- sions of 120 x 60 mils (3.0 x 1.5 mm). The package is then passed to the CAD designer. The CAD designer imports the
schematic and the model into his pro- gram and then chooses a 1206 pack- age for the resistor to match the size provided in the model. The designer goes to the web and downloads a .stp file for this package. The designer then creates a PCB layout by merg- ing the physical location with the log- ical part in accordance with the net list. The package is then passed to the component engineer. Additional data columns not in the BOM: pack- age, x/y location, and rotation. The component engineer (CE)
takes the BOM and goes to the stan- dard parts list to assign a physical part to the logical part, R1. The CE discov- ers they do not have a standard part with these characteristics, so a new part must be created in the part mas- ter of the manufacturing system soft- ware. The BOM is then sent to the PCB engineer. Additional BOM col - umns: manufacturer, manufacturer’s part number, and approved alternates.
No Precedent The PCB engineer is not famil-
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iar with this particular application, and must hold a meeting to deter- mine which standards are required. There is no precedent, so the PCB en- gineer copies and pastes PCB notes for a “wellhead” application. The en- gineer then amends the BOM with the description of the PCB and pass- es the package to document control. No additional columns are required. Document control requests Ger-
ber files from the CAD designer and then assigns part numbers to the ref- erence designators in the BOM. The solid model, the Gerber file and the BOM are now “controlled” in the man-
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