Iterative Leakage Screening for Electrolytic Capacitor Reliability
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Solution Overview
Problem
Traditional screening methods for electrolytic capacitors, such as Weibull calculations, fail to detect latent defects and remove unstable parts, leading to potential long-term reliability issues in high-stress applications like medical, military, and aerospace, as they only focus on catastrophic failures and do not account for early failures or self-healing during burn-in.
Innovation Solution
An iterative screening method that measures leakage current at multiple iterations, removes capacitors above predetermined values (set by statistical analysis), and subjects them to burn-in treatments at voltages close to rated voltage to detect unstable parts without causing damage, ensuring high reliability and low failure rates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If highly accelerated voltage conditions (1.5 times rated voltage) are applied during burn-in, then screening time can be reduced, but unstable parts may be damaged and cannot be detected
Solution Approach 1:
The patent performs preliminary burn-in at moderate voltage (0.8-1.2 times rated voltage) to stabilize capacitors before screening. This preliminary action at lower stress prevents damage to unstable parts while still removing early failures, enabling accurate detection through subsequent leakage current measurements.
Solution Approach 2:
The patent applies partial action by using moderate voltage stress (0.8-1.2 times rated voltage) rather than excessive stress (1.5 times rated voltage). This partial stress level is sufficient to reveal latent defects through iterative leakage measurements without causing damage that would mask the defects.
2Ease of manufacture
If Weibull statistical calculation is used to create distribution for grading purposes, then a standardized screening process is established, but unstable parts remain in the population and cannot be removed
Solution Approach 1:
The patent applies feedback by using iterative leakage current measurements where capacitors are measured, those exceeding the threshold are removed, and the process repeats. Each iteration provides feedback on the remaining population's stability, progressively removing unstable parts while maintaining a standardized process through statistical threshold calculation.
Solution Approach 2:
The patent performs preliminary burn-in treatment before the iterative screening process to stabilize capacitors. This preliminary action ensures that the subsequent standardized iterative process can effectively identify and remove unstable parts without being confounded by early failures during screening.
3Productivity
If capacitors are screened using traditional methods, then production throughput is maintained, but defective parts with latent defects are released into the good population
Solution Approach 1:
The patent replaces mechanical/physical stress-based screening (highly accelerated voltage and temperature) with an electrical measurement-based system (iterative leakage current measurements). This substitution enables more accurate detection of unstable parts while maintaining production throughput through automated measurement and removal processes.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The method effectively screens out unstable capacitors, achieving extremely high reliability and low failure rates, allowing capacitors to be used at their rated voltage without derating, thereby enhancing the reliability of capacitors in critical applications.
Implementation Method 1
a capacitor that includes a capacitor element having an anode, a cathode, and a dielectric layer formed over the anode
Implementation Method 2
a dielectric layer formed over the anode
Data Source
AI summary
A method of iteratively screening a sample of electrolytic capacitors having a predetermined rated voltage is provided. The method can include measuring a first leakage current of a first set of capacitors, calculating a first mean leakage current therefrom, and removing capacitors from the first set having a first leakage current equal to or above a first predetermined value, thereby forming a second set of capacitors. The second set can be subjected to a burn in heat treatment where a test voltage can be applied, then a second leakage current of the second set of capacitors can be measured and a second mean leakage current can be calculated. Capacitors having a second leakage current equal to or above a second predetermined value can be removed from the second set, forming a third set of capacitors. Because of such iterative screening, the capacitors in the third set have low failure rates.