Ensuring Quality in Tantalum Capacitor Production: The Critical Role of Anode Mechanical Screening

Vladimir Azbel Ph.D., semiconductor process reliability engineer consultant, Israel publishes next article on his proposal an innovative solution for tantalum capacitor production quality enhancement.

Abstract

The anode is the foundation of the tantalum capacitor, and its quality significantly impacts the reliability and stability of the capacitor’s properties. This article explores the importance of mechanical testing throughout the multi-stage anode production process, emphasizing the need for reliable control methods at each stage to ensure product quality.

In mass production, variations in powder batches and equipment stability, along with human errors, can affect quality. Thus, control methods must ensure compliance with technological requirements to guarantee the final product’s quality.

Modern methods of anode control, including metallography, X-ray structural, electron microscopic analysis, and electrical characteristic measurements, are discussed. The stability of powder properties, determined by primary particle distribution, is crucial and often assessed by laser diffraction. Indirect methods, like the pore size distribution curve measured by mercury pycnometer, are also considered.

This article highlights the effectiveness of mechanical testing in detecting defects early, reducing production costs, and maintaining process stability. The method’s application to monitor mechanical characteristics such as porosity, neck size, and defectiveness is validated through studies, demonstrating its capability to ensure the quality of tantalum capacitor anodes. The introduction of standardized mechanical testing enhances reliability and reduces production costs, supporting the manufacturing of higher quality and more dependable products.

Technical Background

Since the first commercial production of tantalum capacitors by Bell Labs in the early 1950s, they have been widely used where reliability is critical. During those years, a wet test on the anode was used, which assessed not only the quality of the anode but also the acceptability of the powder based on its electrical characteristics.

Models and mechanisms that allowed linking the key parameters of the powder with the mechanical characteristics of the test sintered pellet appeared closer to 1985-1990.

This approach is used in practice in powder metallurgy to ensure product quality and consistency. In powder metallurgy, precise control of powder characteristics is important, and mechanical properties such as yield strength and elastic modulus are key parameters for this purpose. As technology has advanced and the CV/g of powder has increased, the reliability of wet tests based on leakage current estimates has not met the requirements. More accurate and reliable methods for controlling their quality are required to produce capacitors from modern powders (more than 50 kCV/g).

The anode is the foundation of the tantalum capacitor, and its quality significantly impacts the reliability and stability of the capacitor’s properties. The production of the anode is a multi-stage process, the quality of which depends on the reliability of control methods at each stage, which must be ensured under current production conditions.

In mass production of capacitors of a single design, batches of the powder used may change, or a similar powder from an alternative supplier may be used. Quality is also affected by the stability of the equipment during the production process and errors caused by human factors. Control methods at each stage of the process must ensure that the product has undergone all stages following technological requirements, which guarantees the quality of the final
product, in our case, the anode.

Modern methods of anode control at each stage of its production, starting from the powder, and sintered pellet, and ending with testing the anode’s tendency to age in subsequent stages of capacitor production, include metallographic, X-ray structural, and electron microscopic analysis, as well as measuring the electrical characteristics of the anode or capacitor. The stability of the properties of the used powder, besides its chemical composition, is determined by the width of the distribution of primary powder particles (before agglomeration), which is often assessed by the laser diffraction method.
As an indirect method for assessing particle distribution width, the pore size distribution curve, in a pressed or sintered pellet using the mercury pycnometer method can be employed. Under current production conditions, the use of the abovementioned methods may be ineffective.

The method is widely used for controlling powder metallurgy products, in particular, for monitoring the morphology of porous structures. The method is based on the mechanical characteristics of the sintered and formation pellet. Although it does not provide direct information about the structure like other methods, it allows for controlling the acceptability of the product structure as specified by the technological process at each production stage.

The method is based on comparing the mechanical characteristics of the tested product with the reference values. When certifying the powder, a base batch is determined. In our case, its indicator is a capacitor made from this batch and passed the tests. Mechanical characteristics of the sintered samples become reference values for evaluating subsequent batches of powder in the same lot. For each new batch of powder in the same lot, control samples (sintered pellets) are made using the same technological conditions as for the base batch, meeting the incoming inspection requirements. If the results are within acceptable tolerances, the powder batch is considered compliant. During the testing of sintered and formation pellets, the mechanical characteristics of the pellets are measured, the capacitors made from these pellets have passed reliability tests.

The mechanical characteristics monitored by this method include porosity, average neck size, and product defectiveness, which are responsible for the anode’s capacitance, formation voltage, and leakage currents. The studies listed below demonstrate the possibility of using this method to control the technological process of producing a tantalum capacitor anode.

Mechanical Tests: The Key to Quality

Consider using mechanical tests to ensure the quality of tantalum capacitor powder by testing a sample. This approach offers several benefits:

• Early Detection of Powder Issues: Mechanical testing allows for the identification of problems at the early stages of production, preventing the use of unacceptable powder.
• Control and Detection of Production Issues: Mechanical testing is used both for controlling sintered samples and for identifying problems in their production.
• Reduction of Production Costs: Early detection of defects reduces the number of defective products, lowering replacement and disposal costs. Continuous monitoring reduces the risk of using unacceptable powders and sintering processes (e.g., passivation), leading to resource savings. Similar problems are typical in the production of tantalum capacitor anodes, which allow the same mechanical characteristics to be used.

Your Path to Perfection

• Yield Strength and Modulus of Elasticity: Key powder parameters, primary particle distribution, and purity, through the developed mechanisms, allowed them to be associated with the mechanical characteristics of the sintered sample, which are measured using:
• Compression tests: to determine the sintered sample’s yield strength, elastic modulus, and strain hardening coefficient.
• The software of modern testing machines allows online assessment of the acceptability of the obtained parameters with a certifying sintered pellet.

Advantages of Our Approach

• Reduced Risk of Failures: Mechanical tests detect defects at early stages, preventing the production and use of defective capacitors.
• Increased Reliability: Quality control at the powder and sintered sample level ensures more reliable capacitors.
• Reduced Production Costs: Early defect detection reduces the number of defective products, lowering the costs of replacement and disposal.
• Support process stability:
• Monitoring the mechanical properties of sintered pellets ensures the stability of the production process. This is especially important in mass production, where even small deviations can lead to significant changes in the quality of the final product.

Ensure Integration into Your Production Process

• Methodology Development: We will establish standardized procedures for conducting mechanical tests to ensure their reproducibility and reliability.
• Staff Training: Our team will train your employees in the correct execution of tests and interpretation of their results.
• Automation: We will assist in implementing automated testing systems to increase the efficiency and accuracy of measurements.
• Regular Control: Mechanical tests will be integrated into your quality control procedures at all stages of production.

Conclusion

The introduction of standardized mechanical testing for quality control of tantalum capacitor powder using test samples is an innovative approach that aims to enhance reliability and reduce production costs. Our method allows for a more precise evaluation of raw materials and intermediate products, ultimately leading to the manufacturing of higher quality and more dependable products.

This method allows not only to maintain stable product quality but also to quickly identify and eliminate possible problems associated with changes in the characteristics of the powder or technological process. This method is an additional screening to avoid problems with the capacitor, on the final tests
caused by the anode

Adaptation of Mechanical Characteristics

In Yuri Freeman’s book [1], the reasons that influence or directly lead to defects in the dielectric of the anode at each technological stage of its production process are thoroughly examined. This is illustrated with data from X-ray structural and electron microscopic analysis, as well as electrical measurements. In my work, I have demonstrated how the presence of defects at these same stages can be controlled by mechanical characteristics, making it possible to use them in ongoing quality control

Mechanical characteristics were adapted to optimize and control the technological processes used for the production of tantalum capacitors. This includes the control of the sintered pellet, the attachment of the lead to the sintered pellet, and the formation process. It involves the monitoring of the growth of internal stresses, which affects the crystallization of the amorphous dielectric, as well as the results of post-formation thermal treatment (thermal crystallization) and the influence of the environment on thermal crystallization. All these aspects are discussed in the works listed below (see list).

• 1. Innovative Quality Control to Improve the Reliability of Tantalum Capacitors https://passive-components.eu/innovative-quality-control-to-improve-the-reliability-of-tantalum-capacitors/
• 2. Optimizing Tantalum Capacitor Manufacturing Through Yield Strength and Plasticity Analysis in Welding Processes https://passive-components.eu/optimizing-tantalum-capacitor-production-through-two-stage-sintering-controlling-warpage-and-enhancing-reliability/
• 3. Anode Heat Treatment Impact on Tantalum Capacitor’s Capacitance and Leakage Current https://passive-components.eu/anode-heat-treatment-impact-to-tantalum-capacitors-capacitance-and-leakage-current/
• 4. Tantalum Capacitor Anode Acceptability Evaluation and Reliability Prediction https://passive-components.eu/tantalum-capacitor-anode-acceptability-evaluation-and-reliability-prediction/
• 5. Modeling of Anode Overheating Risks During the Manufacture of Tantalum Capacitors https://passive-components.eu/modelling-of-anode-overheating-risks-during-the-manufacture-of-tantalum-capacitors/
• 6. Tantalum Capacitor DCL & Life-Time Prediction by Evaluation of Anode Mechanical Properties https://passive-components.eu/tantalum-capacitor-dcl-life-time-prediction-by-evaluation-of-anode-mechanical-properties/
• 7. New Approach to Tantalum Capacitor Anode Design https://passive-components.eu/new-approach-to-tantalum-capacitor-anode-design/
• 8. Tantalum Capacitors Reliability, Leakage Current Stability Prediction and Cost Reduction by Anode Characterization During Manufacturing Process; Vladimir Azbel; consultant; Israel 3rd PCNS Passive Components Networking Symposium 7 – 10TH SEPTEMBER 2021, MILANO, ITALY https://epci.eu/tantalum-capacitors-reliability-leakage-current-stability-prediction-and-cost-reduction-by-anode-characterization-during-manufacturing-process/

References

[1] Freeman,Y.; Tantalum and Niobium-Based Capacitors: Science, Technology, and Applications | SpringerLink