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Testing of Ohmega-Ply® resistors is an integral part of the PC board manufacturing process.
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NOTES ON OHMEGA BURIED RESISTOR ELECTRICAL TESTINGGENERAL TESTINGElectrical testing is required to verify correct resistor values and identify out of tolerance resistors. Electrical tests should be performed for innerlayers and for the final printed circuit (bare) board. 100% testing of resistors on the finished board are within the specified tolerance. Innerlayer electrical testing assures that all resistors are in spec before lamination. AOI by itself is not sufficient. Innerlayer resistors prior to lamination and surface resistors prior to soldermask must be carefully handled to avoid physical damage to the resistive elements. CAD/CAM systems must be modified to enable electrical testing of innerlayers and finished boards having integral resistors. There are three primary test issues: INPUT DATA REQUIREMENTS Net list testing is required for almost all applications as comparative tests can not identify nominal resistors values nor handle overlapping tolerances or incorrect parallel/series resistor networks. Self learn techniques are only recommended for innerlayers or finished boards having surface resistors (no interconnecting networks of buried resistors). Net lists downloaded to the test machine must include resistor locations and values. One of the two following methods are generally utilized;
Custom software may be required. If standard IPC356D net lists are used, the CAD/CAM system must merge the net list with the resistor file prior to download of the modified net list to the test machine. First time users should contact their TEST SERVICE or TEST EQUIPMENT MANUFACTURER to determine the applicability of their test equipment and the availability of the required software. TEST EQUIPMENT REQUIREMENTS There are three types of test equipment available to test Ohmega-Ply® resistors - shown in order of prevalence;
The measurement accuracy for resistors depends on the instrument accuracy, contact resistance, probes and lead resistance. THE MEASURING CURRENT MUST NOT EXCEED THE CURRENT RATING OF THE RESISTORS TO PREVENT RESISTOR DAMAGE: For resistors < 1 kohms, measuring current < 1 mA,RECOMMENDED EQUIPMENT MANUFACTURERS (partial listing)
RECOMMENDED TEST SERVICES (partial listing) APPENDIX B--ELECTRICAL TEST SERVICE BUREAUS
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