Forum: Reliability & Maintainability Questions and Answers
Topic: Reliability & Maintainability Questions and AnswersTopic Posted by: Reliability & Maintainability Forum (firstname.lastname@example.org )
Organization: System Reliability Center
Date Posted: Mon Aug 31 12:47:36 US/Eastern 1998
Original Message:Posted by: Roy Shepard (email@example.com )
Organization:Inex Vision Systems, Inc.
Date posted: Thu Jul 27 15:19:35 US/Eastern 2000
Subject: Defective 10K RCO7 resistors from Taiwan
Industrial and Electronic Manufacturers and other end users are alerted to the presence of defective type RCO7, 10K ohm, 1/4 watt, 5%, Carbon Composition resistors entering this country from Taiwan. These resistors are identified by a shiny "wax" seal on both ends of the body of the RCO7s. Further examination under a powerful magnifying glass or microscope will reveal the presence within the wax seal of an as yet unidentifed contaminant, currently believed to be organic, scattered randomnly thorugh out the wax. When these defective RCO7 resistors are installed on a CCA and processed through a standard wave solder process, the "wax" seal melts. By a process believed at present to thermally outgass the wax and/or to thermally generate a chemical reaction with the carbon composition, the result is the same. Nine (9) out of every ten (10) of the 10K resistors INCREASE their resistance by a measured 8 to 16 percent out of tolerance. Manual resoldering has disclosed that the heat from the manual soldering process will cause, on average, two (2) out of every ten (10) resistors to fail out of tolerance. Circuit Card Assemblies (CCAs) containing these defective 10K resistors in timing circuits have been observed to drift out of spec as the CCA heats up. Six (6) additional RCO7 resistance values, described above have been identified in stock to date and are awaiting testing.