Any component can fail–but if it is designed correctly and the user application is within specification, this leaves the component manufacturing process as the limiting factor in reliability and overall life expectancy. And the further along into the production process that a part fails, the more costly it is in both repair and cycle time.
While component quality and reliability are the responsibility of the supplier, the entire risk of failure lies with the end user. To reduce this risk, end users may employ any of these inspection methods:
· 100% incoming electrical inspection.
· Burn-in or preconditioning.
· Precap visual and final-inspection monitors by a resident source inspector.
· Destructive Physical Analysis (DPA).
Electrical inspection or test can determine if the components function properly at the time of the test, but does not provide insight into future reliability and life expectancy. Burn-in will find failures due to infant mortality; however, this will not help anticipate when end of life could occur. Precap visual inspection closely monitors the manufacturer’s process but does not supply in-depth material analysis or electrical testing.
DPA of a finished part provides the most complete approach. It offers a thorough physical, mechanical and electrical review of the component and compares it to previous production lots, allowing an assessment of the component’s anticipated life expectancy and robustness for its intended application.
A
Case Study
The analysis of a system-level failure of an RF hybrid amplifier is an example of the value added by an effective DPA program. The part in this example had corrosion of the internal interconnection substrate metallization and leads (Figure 1).
The testing lab suspected the corrosion originated during the manufacturer’s solder and cleaning process, when corrosive fluxes and solvents were trapped inside the component. The corrective action recommended that the manufacturer improve the cleaning process after soldering.
Samples from the next production lot were subjected to follow-up DPA. The analysis revealed that the problem was not due to improper cleaning by the manufacturer, but by a poor seal at the outer case. This allowed flux and cleaning solvents to enter the component during the board assembly process.
The cost of preventing failures from reaching the production floor–or, even worse, the customer–greatly outweighs the cost of the DPA at incoming inspection. An average DPA should cost from $500 to $1,200. Troubleshooting, repair and root-cause-analysis of the failure, not to mention associated schedule delays, could cost orders of magnitude greater than the cost of the DPA.
In this example, the hermetic seals of the rejected units were quickly and cost-effectively tested by the lab. The units were then returned to the part manufacturer for a simple rework of the solder seal. This was far more economical than possible failures and delays in production.
The DPA Program
A DPA program evaluates samples of selected component types before they are released to production. The program will identify variations in the manufacturing process and the integrity of part construction by exposing the device to a battery of analysis and evaluation techniques. History is important here, because comparisons to prior findings may lead to less obvious conclusions.
Process
Many labs offer DPA programs and the tests performed are fairly standardized. Typically, three to five samples are subjected to the test plan shown in Table 1, although the analysis varies according to part type and project or customer requirements.
The lab generates a report commenting on the physical and mechanical condition of the component. It typically includes photographic documentation of significant findings.
The report also contains details on the test methods, appropriate references to specifications, historic comparisons if available, and specifics on anomalies. Lot acceptance or rejection recommendations are based on the current results and prior history.
If the lab rejects the lot, the problem can be reviewed in detail with the component supplier. An experienced lab will offer suggestions for possible screens, rework or scrapping of the material, if warranted. Since the questionable material has still not entered the manufacturing process, real-time prevention of factory problems is realized with this program.
Typically, this lab effort should take only a couple of days to complete. The response time is important because, if not properly implemented, the DPA program is a gating factor to the release of components to production.
Component Selection and Maintenance
The DPA program is directed toward components that have a history of problems/failures, parts that are critical to equipment performance, or for which site inspection would be too costly to perform. A DPA parts list is usually updated and reviewed for each production buy. Components are added or deleted depending on DPA trends, factory failure data or changes in the baseline hardware design. The inspection samples are removed from the incoming lot and analyzed at the laboratory to a test plan tailored to the component type.
The component’s previous DPA or failure history is reviewed and used as an aid during the analysis for possible defect reoccurrence and identification of subtle changes in the manufacturer’s process.
Summary
Production-line component failures caused by supplier defects can be fixed to put out the immediate “fire” or used as a learning experience to prevent future failures. Since the failure occurred sometime during, and perhaps well into, the test process, significant time and money may already have been lost even if clear and correctable findings resulted from the failure analysis.
Failure analysis provides the reasons for failure and may offer corrective action, but this does not ensure that the supplier has taken the appropriate action. It is often useful to institute an analysis or check of the next production run to monitor the supplier response to the DPA. This is most useful if the defect is not obvious during normal incoming inspection test, burn-in or precap visual. DPA verifies that corrective action has been instituted and is consistent with previously analyzed failures.
About the Authors
Bill Tice is Manager of the Reliability Analysis Laboratory at Raytheon. He has 14 years of experience in product assurance, and is a total quality instructor and facilitator and an internal ISO auditor. Mr. Tice holds a bachelor’s degree in electrical engineering from Stevens Institute of Technology and an M.B.A. degree from Babson College.
Ken Rispoli is responsible for DPA programs at Raytheon’s Reliability Analysis Laboratory. Previously, he was affiliated with Prime Computer and Underwriters Laboratory. Mr. Rispoli has a bachelor’s degree in electrical engineering from Merrimack College and an M.S. degree in electrical and computer engineering from the University of Massachusetts.
Raytheon Co., Equipment Division, Reliability Analysis Laboratory, Mail Stop IJ3, 528 Boston Post Rd., Sudbury, MA 01776, (508) 440-2378.
PRODUCTION: Please put in table form with bullets. Thank you.
External Visual Inspection
Radiographic Evaluation
Particle Impact Noise Detection
Dimensional Evaluation
Electrical Test (optional)
Solderability Test
Hermeticity (fine and gross leak test)
Delid or Disassembly
Internal Visual Inspection
Internal Measurements
Bond Pull
Die Shear
Photographs (external and internal)
Copyright 1995 Nelson Publishing Inc.
June 1995
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