Circuits Assembly - November 2007 - (Page 50)

Tech Tips Wire Harnesses and Cable Routing Best practices for handling, routing and installation. A The American Competitiveness Institute (aciusa.org) is a scientific research corporation dedicated to the advancement of electronics manufacturing processes and materials for the Department of Defense and industry. This column appears monthly. few simple guidelines to follow during cable harness handling, routing and installation will extend their life, ensure Figure 2. Service loops with strain relief. peak performance, facil- Figure 1. Cable strand separation (birditate installation and caging) caused by improper handling. repairs, and provide a visible sign of quality workmanship. Damage to wires shortens the connection life prevents overbending and provides enough wire and could impact the function of associated cirfor strain relief. cuits. Dressing the wires and cables entering and Strain relief is not only important when exiting the bundle presents a neat appearance breaking out of a harness, but is essential at all and facilitates future work on the cable. Strain terminations: post, terminal, screw or multi-pin relief on all terminated ends of a cable or harconnectors. If a radio is mobile, or an electrical ness will make it easier to install and facilitate an cabinet can be moved, the strain relief on the easier repair, if needed. Proper harness routing conductors and connectors will permit flexing and shielding will ensure all signals reach their without breakage. destination free of interference and crosstalk. Temperature extremes can also stress conDamaged cable (like birdcaging, Figure 1) nections, as the wires contract in the cold can be prevented by twisting the insulation from and expand in the heat. Strain relief, in most the end of the wire in the same direction and cases, can be accomplished by either excess wire rate as the manufacturer’s twist. This will make between a fixed mounting point and the consoldering into a cup or on a terminal much nector, or a mechanical grip in the conductor. easier and will prevent shorts. Wires cannot When terminating a wiring harness, strain relief exceed the minimum bend radius as outlined by is achieved by adding a maintenance loop before the manufacturer in IPC-A-610, Acceptability of the termination point. A commercially available Electronic Assemblies. Cut or nicked conductors gripping grommet relief can be used if the conmay degrade signal performance of higher freductor is going through a bulkhead or electrical quency applications, as well as compromise the cabinet. mechanical strength. To prevent nicking or cutRouting cable assemblies and wiring harnessting conductors, use a thermal insulation stripes can accomplish three goals: neat appearance, per, or correctly sized mechanical strippers, and signal isolation and integrity, and material savappropriate hand tools. ings. When designing the wiring harness routDressing the cable is the process in which ing, low voltage or low data rate busses should all the insulated wires in a wire bundle or harnot be run next to RF or high voltage AC cables ness are arranged so that there are no crossed, unless the cables have been properly shielded. folded, strained or loose conductors. Crossed Even shielded data cables can pick up AC and conductors, when tied into a bundle or harness, RF interference when run in the same bundle for can lead to crushed insulation in coax cables or long runs. split insulation on stranded wire. Many times the Also, a well-considered route for cables and crossed conductors are easily loosened and can conductors can minimize cable lengths and be pulled and broken. increase material savings when multiplied by When breaking a wire or conductor out of a the number of products manufactured. Qualharness or bundle, a minimum bend radius of ity workmanship is key to a long service life the conductor and required strain relief must be for harnesses and cables, as well as the associobserved (Figure 2). The location of the termiated electronics. IPC-A-610 and IPC-A-620 are nation and the breakout point should permit the industry standards for cable, harness and conwire to curve gradually to the termination. This nector assembly workmanship. ■ Circuits Assembly NOVEMBER 2007 circuitsassembly.com 50 http://aciusa.org http://circuitsassembly.com

Table of Contents Feed for the Digital Edition of Circuits Assembly - November 2007

Circuits Assembly - November 2007 Contents Caveat Lector Industry News Market Watch Talking Heads Focus on Business Global Sourcing On the Forefront Screen Printing Better Manufacturing Pb-Free Manufacturing from a Tier III EMS Perspective ‘Living Documents, Subject to Change’ Creating Ideal Solder Joints An Alternative Drying Process for MSDs ‘Customer Satisfaction is More than a Score’ Optoelectronic Substrates: Will They Happen? Tech Tips Wave Soldering Process Doctor Test and Inspection Getting Lean Materials World Equipment Advances Product Spotlight Assembly Insider Technical Abstracts Ad Index

Circuits Assembly - November 2007

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