Parameter Drift

Defect Description

Passive parts with electrical parameters that fall out of, or are marginally within the prescribed limits at room temperature.

Defect Formation Process(s)

Many causes can lead to parameter drifts in passive parts. Examples for two commonly used capacitors are included below:

In electrolytic capacitors, vaporization of electrolyte is a primary degradation mechanism which causes equivalent series resistance (ESR) to increase and capacitance to decrease [1, 2]

In solid tantalum capacitors, high ESR can result from the following reasons:

• Mechanical stresses during pick and place, board mounting, etc. can compromise internal connections [3].

• Thermal mechanical stresses during reflow can result in high ESR because materials used in the construction of a typical tantalum capacitor have very different coefficient of thermal expansion (CTE) [3].

• Exposure to high relative humidity at elevated temperature can result in oxidation of the external leads, causing high ESR [3].

• Electrical resistance of manganese dioxide, as a coating on the tantalum oxide dielectric, increases when exposed to moisture, which leads to the increase in ESR of the capacitor [3, 4].
 

Due to the many different degradation mechanisms with respect to different passive devices, it is possible for different stress tests to reveal these defective parts.

List of Tests to Precipitate this Defect

Failure Acceleration

Likihood to Precipitate Defect (condition)

Failure Mechanism(s)

Cold Step Stress

• Parameter drift in components has been revealed in cold step stress [5]

✇

N/A

Hot Step Stress

• High temperature accelerates temperature dependent degradation mechanisms

✇

Vaporization of electrolyte of electrolytic capacitors
(Example)

Thermal Shock

• Thermal mechanical stress accelerates cracking or interfacial delamination of internal connections.

✇

Thermal Fatigue

Thermal Mechanical Overstress

Random Vibration

• Random vibration accelerates the growth of mechanical defects that lead to parameter drifts

✇

Mechanical Fatigue

Mechanical Overstress

Combined Environment

• Combination of thermal shock and random vibration

✇

 Combination of thermal shock and random vibration

References

[1] Sankaran V. A., Rees F. L., Avant C. S., “Electrolytic Capacitor Life Testing and Prediction”, 32th Industry Application Society (IAS) Annual Meeting, vol. 2. pp. 1058-1065, 1997.

[2] Stevens J. L., Shaffer J. S., Vandenham J. T., “The Service Life of Large Aluminum Electrolytic Capacitors: Effects of Construction and Application”, 36th Industry Application Society (IAS) Annual Meeting, vol. 4, pp. 2493-2499, 2001.

[3] Qazi J., “An Overview of Failure Analysis of Tantalum Capacitors”, Electronic Device Failure Analysis, vol. 16, issue 2, pp. 18-23, 2013.

[4] Fresia E. J., Eckfeldt J. M., “Failure Modes and Mechanisms in Solid Tantalum Capacitors”, 2nd Annual Symposium on Physics of Failure in Electronics, pp. 483-497, 1963.

[5] Silverman M., “Summary of HALT and HASS Results at an Accelerated Reliability Test Center”, Proceedings of Annual Reliability and Maintainability Symposium, pp. 30-36, 1998.


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