Jennings' Failure Analysis Process

A. General
Jennings Technology is committed to producing the highest quality of vacuum products to meet our customers needs. As such, we understand we cannot compromise any part of our manufacturing processes. Although our quality assurance program guarantees the highest standards of manufacturing excellence, we understand that faults do occur. Jennings takes product failure very seriously and assures that an exhaustive analysis and investigation will be conducted and the problem will be furthermore, corrected. Jennings Technology completes a comprehensive and thorough analysis on all of its failed products. The 10-day analysis makes certain that nothing is overlooked; the four-part procedure, which is outlined in a final report, includes an introduction, an evaluation and observation of the product, an analysis, determines a root cause, and implements a corrective action within 24 hours of the preliminary findings.

B. Procedure
The following is a step-by-step breakdown, explaining Jennings' Failure Analysis process.

Introduction: Offers background information about the product that failed. Gives details such as the product, model number, and customer. An initial observation of the failed product.

Evaluation and Observation: Investigates the product. Looks into where the product failed. Analysis: Consists of an in depth analysis of the product. Deconstructs the product to investigate every aspect and determines the possible causes.

Root Cause Analysis: Proposes and outlines the most probable causes and why they happened.

Corrective Action: Once the root cause is determined, Jennings runs a 24-hour turnaround on the preliminary findings.
Please see the section below for a sample of our failure analysis procedure.

Sample Failure Analysis

Introduction: On January 3, 2000 Jennings Technology received a CVCJ-1000 for failure analysis. The unit was mounted in a match during production, and a short was detected at approximately 200pF-350pF while running capacitor from minimum to maximum capacitance.

Evaluation and Observation:
1. The capacitor was received without any evidence of damage other than the clamp marks from the flanges.
2. Capacitor was received at Jennings in the C max position. No adjustment lead screw was received with product.
3. X-rays were taken. No abnormality of the can sets was revealed.
4. Clamp marks were visible at both the variable and movable end assemblies, a result due to the tightening of the flanges on the fixed and variable ends of the capacitor, see figure 1.
5. Electrical testing at Jennings showed that the capacitor shorted at 350.4 pF.

Destructive Physical Analysis:
1. The unit was machined apart to expose the can sets for optical examination.
2. In general the can surfaces were quite clean and reflective.
3. There was a significant amount of arcing (spot knocking, barnacles) at the center cans.
4. The center can on the variable end showed the most damage with a small hole (size of a pinhead) on its wall, located about 1/3 of the way from Cmax, see figure 2a, b, c.
5. The center cans on the fixed and variable ends have an area on their rims that are eroded away, see figures 2a, b, and 3.
6. Several cans on the fixed and variable ends were not exactly round. They have a bump or a waviness on their rims, see Figure 4.

Root Cause Analysis:
The appearance of the cans indicated that they touched, causing the unit to short out. However, it is difficult to determine the root cause of why this occurred. We can only speculate at some possible root causes:
1. Can set misalignment could be caused by rough handling during shipping. This would lead to a reduced voltage gap and arching during ramp up top voltage. Figure 2 shows heavy arc strikes, hole, and "eroded rim of center can", which indicates the area where the cans came in contact.
2. Possible distortion of the can sets from clamping of the mounting flanges.

Corrective Actions:
Currently, Jennings is performing an EOE (execution of experiment) for shock and vibration analysis. In this experiment, we are trying to understand the effects of shock and vibration on vacuum capacitors, so as to determine acceptable levels, and therefore the corrective actions necessary to buffer units to acceptable levels.
Due date for this test is 2/15/00 with an implementation date set for 3/1/00. Also, we are going to perform further vibration testing of in-house units, to determine its effect on the electrical properties of the capacitor by 3/1/00.
New procedures were written for the CVCJ-1000 and the CSVF-500 vacuum capacitors in the form of a Technote, titled: CSV4-1400 Shock Susceptibility Test Report. These new procedures outline proper installation and tightening guidelines for the flange mountings on the CVCJ-1000 and CSVF-500 vacuum capacitors.

Figure 1. Fixed end of CVCJ-1000 with dent from clamping of flange

Figure 2a. Variable end of CVCJ-1000 showing hole in center can (see black arrow) and eroded rim of center can, see white arrow.

Figure 2b. Close-up Figure 2a showing hole on the side of the center can of the variable end. 10x

Figure 2c. Close-up of Figure 2, showing eroded area on rim of center can on the variable end and high arcing activity on the inside of the center can.

Figure 3. Fixed end of CVCJ-1000 showing eroded center can with bump on its sidewalls, see arrows.

Figure 4. Fixed end can set showing waviness on the can rims.



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