John, Expanding on what Peter said, the contact pressure between two items joined by a pop rivet(s) can only decrease from the as-manufactured value, especially if there is any movement in the joint from rotation, vibration, expansion/contraction from temperature changes, etc. Thus the contact resistance will increase with use and age, especially if there is any oxidation or corrosion of the metals.
I developed network adapters for IBM Lexington and Lexmark for 11 years. At first we pop-riveted the shielding brackets onto printed circuit boards. Then we discovered that we could reduce some radiated emissions by up to 10dB -- ON BRAND-NEW CARDS -- by instead using: * A machine screw. * A split lock washer or star washer under the screw head. * The items to be joined. * Another split lock washer or star washer. * A nut. The split lock washers or star washers ensured that the contact was held under a high, constant pressure throughout the life of the product. We later simplified the assembly to: * A machine screw with integral Belleville washer. * The items to be joined. * A nut with a captive external-tooth star washer. A further simplification for high-volume products was to pierce and tap holes into the bottom piece of metal, making it into the nut(s). This information is from pages 33-2 through 33-3 of my book, Robust Electronic Design Reference Book, Volume 1 (Kluwer Academic Publisher, 2004). John Barnes KS4GL, PE, NCE, NCT, ESDC Eng, ESDC Tech, PSE, SM IEEE dBi Corporation http://www.dbicorporation.com/ - This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. Website: http://www.ieee-pses.org/ To post a message to the list, send your e-mail to [email protected] Instructions: http://listserv.ieee.org/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas [email protected] Mike Cantwell [email protected] For policy questions, send mail to: Jim Bacher: [email protected] David Heald: [email protected] All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
