1、Lessons Learned Entry: 0577Lesson Info:a71 Lesson Number: 0577a71 Lesson Date: 1997-11-17a71 Submitting Organization: JPLa71 Submitted by: D. Oberhettinger/D. LordSubject: Verify CAD/CAM Software Compatibility Between Organizations Before Proceeding to Hardware Fabrication (1995) Abstract: The Cassi
2、ni Telemetry and Control module failed during functional bench test. This was due to an electrical trace errors generated during the apparently successful translation of PWB circuit design data from JPL CAD software to vendor CAD software. To prevent undesirable rework on flight hardware, this lesso
3、n suggests several steps to verify the net list, the vendor software compatibility, and the PWB.Description of Driving Event: Printed wiring boards (PWBs) for JPL spacecraft flight control systems are produced in the following sequential steps using specialized computer-aided design (CAD) software p
4、rograms:1. Schematic Capture. A schematic diagram-a functional representation of the circuit design - is produced by the JPL circuit designer using one CAD tool.2. Net List. A functional representation of the PWB interconnections may be generated by a different JPL organization using the same or a d
5、ifferent CAD tool. The schematic is compiled to produce a “net-list,“ which identifies each set of nodes (i.e., set of pins on piece parts) to be electrically connected to form a “net.“3. PWB Design. This net-list is transferred to a PWB design vendor along with physical descriptions of the piece pa
6、rts. The PWB design vendor may use another CAD program to define the physical PWB layout, including placing and routing.4. PWB Artwork. Data files from this CAD program are then sent to an artwork vendor who may use yet another CAD program to create the PWB artwork.5. PWB Fabrication. The artwork an
7、d a fabrication drawing are sent to a PWB fabrication vendor to construct the PWB.Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Errors may be introduced in each step without any indication of CAD/CAM software incompatibility. The Cassini Telemetry
8、and Control (T&C) module failed during functional bench test in June 1995. Inspection of artwork prepared by the PWB artwork vendor revealed three nodes connected to three other nodes in contradiction to the schematic diagram. The errors occurred in the conversion of the net-list, prepared by JPL us
9、ing one CAD program, to the vendor artwork, which utilized a different CAD software program. Node reference numbers possessing common “suffixes“ were interpreted as common nodes without discriminating between the differing “prefixes.“ The incorrect interconnection of certain gate outputs caused cont
10、ention-type failures, disabling the telemetry processing circuitry.The corrective action performed by JPL was to rework the stray node connections with trace cutting and haywires, and to replace many parts which may have been damaged when the T&C module was powered for test.Additional Keyword(s): PW
11、B MiswireReference(s): JPL Problem/Failure Report No. 61810Lesson(s) Learned: Electrical trace errors may be generated during the apparently successful translation of PWB circuit design data from JPL CAD software to vendor CAD software.Such incidents on future “faster, better, cheaper“ projects coul
12、d have a significantly adverse effect on cost, schedule, quality and reliability.Recommendation(s): To prevent undesirable rework on flight hardware:1. Use automated design checks or manual methods to verify the fidelity of the net list to the schematic prior to PWB design.2. Initially verify the co
13、mpatibility of vendor CAD/CAM software generated interconnects with JPL circuit design net list CAD files before committing to PWB fabrication.3. Where cost and schedule allow, use a prototype PWB for complete verification via extensive continuity checking or functional testing of a populated board.
14、Evidence of Recurrence Control Effectiveness: Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-N/ADocuments Related to Lesson: N/AMission Directorate(s): N/AAdditional Key Phrase(s): N/AAdditional Info: Approval Info: a71 Approval Date: 1997-11-21a71 Approval Name: Carol Dumaina71 Approval Organization: 125-204a71 Approval Phone Number: 818-354-8242Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-
