NEPP program objectives are to: (1) Access the reliability of newly available electronic parts and packaging technologies for usage on NASA projects through validations, assessments, and characterizations, and the development of test methods/tools; (2)Expedite infusion paths for advanced (emerging) electronic parts and packaging technologies by evaluations of readiness for manufacturability and project usage consideration; (3) Provide NASA projects with technology selection, application, and validation guidelines for electronic parts and packaging hardware and processes; nd (4) Retain and disseminate electronic parts and packaging quality assurance, reliability validations, tools, and availability information to the NASA community.

NASA Electronic Parts and Packaging Program

The fracturing and failures of multilayer ceramic capacitors (MLCCs) after manual soldering onto printed wiring boards are often associated with a soldering-induced thermal shock that results in substantial mechanical stresses in the parts. Recommendations and guidelines for safe soldering conditions are well developed and documented; however, there is a lack of adequate testing for the selection of MLCCs that are robust enough to sustain stresses related to manual soldering. In this paper, various lots of X7R-type material MLCCs with different size have been subjected to three types of thermal-shock testing: terminal solder-dip test, ice-water test, and liquid-nitrogen drop test. The electrical characteristics of the parts were measured through various test conditions to determine critical temperatures that resulted in fracturing and electrical failures. Optical examinations and cross-sectional analysis were used to confirm the presence of cracks. The mechanisms of fracturing, factors affecting crack formation, and the effectiveness of different thermal-shock methods are discussed.

Thermal-Shock Testing and Fracturing of MLCCs Under Manual-Soldering Conditions

In this work, results of multiple temperature cycling (TC) (up to 1,000 cycles) of different types of solid tantalum capacitors are analyzed and reported. Deformation of chip tantalum during temperature variations simulating reflow soldering conditions was measured to evaluate the possibility of the pop-corning effect in the parts. To simulate the effect of short-time exposures to solder reflow temperatures on the reliability of tantalum capacitors, several part types were subjected to multiple cycles (up to 100) between room temperature and 240 C with periodical measurements of electrical characteristics of the parts. Mechanisms of degradation caused by temperature cycling and exposure to high temperatures, and the requirements of MIL-PRF-55365 for assessment of the resistance of the parts to soldering heat are discussed.

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Effect of Temperature Cycling and Exposure to Extreme Temperatures on Reliability of Solid Tantalum Capacitors

I. Introduction. Solid tantalum capacitors are widely used in space applications to filter low-frequency ripple currents in power supply circuits and stabilize DC voltages in the system. Tantalum capacitors manufactured per military specifications (MIL- PRF-55365) are established reliability components and have less than 0.001% of failures per 1000 hours (the failure rate is less than 10 FIT) for grades D or S, thus positioning these parts among electronic components with the highest reliability characteristics. Still, failures of tantalum capacitors do happen and when it occurs it might have catastrophic consequences for the system. This is due to a short-circuit failure mode, which might be damaging to a power supply, and also to the capability of tantalum capacitors with manganese cathodes to self-ignite when a failure occurs in low-impedance applications. During such a failure, a substantial amount of energy is released by exothermic reaction of the tantalum pellet with oxygen generated by the overheated manganese oxide cathode, resulting not only in destruction of the part, but also in damage of the board and surrounding components. A specific feature of tantalum capacitors, compared to ceramic parts, is a relatively large value of capacitance, which in contemporary low-size chip capacitors reaches dozens and hundreds of microfarads. This might result in so-called surge current or turn-on failures in the parts when the board is first powered up. Such a failure, which is considered as the most prevalent type of failures in tantalum capacitors [I], is due to fast changes of the voltage in the circuit, dV/dt, producing high surge current spikes, I,

/pdf/nasa-electronic-parts-and-packaging-nepp-program-58fnzjyny1.pdf

NASA Electronic Parts and Packaging (NEPP) Program

Different size X7R MLCCs have been subjected to three types of thermal shock testing: terminal solder pot dip test, ice water test, and liquid nitrogen drop test. Electrical characteristics of the parts were measured through various test conditions to determine critical temperatures that result in fracturing and electrical failures. Optical examinations and cross-sectional analysis were used to confirm the presence of cracks. Mechanisms of fracturing and the effectiveness of different thermal shock methods are discussed. It is shown that the heat conduction and direction of temperature changes (heating or cooling) are critical factors of thermal shock testing of MLCCs. The probability of fracturing depends also on the level of residual mechanical stresses, mostly in terminal areas of ceramic capacitors.

https://nepp.nasa.gov/files/25591/EMPC2011_Teverovsky_Thermal_Shock.pdf

Effect of thermal shock conditions on reliability of chip ceramic capacitors

The authors report on failure analysis results on miniaturized multilayer ceramic capacitors ('0402', '0603', '0805', and '1206' sizes) which have been subjected to various degrees of thermal shock up to 450/spl deg/C by ice-water or dry-ice quenching. The thermal shock resistance of '0402' multilayer ceramic capacitors is found to be about 400/spl deg/C and considerably better than that of the larger ones. Microstructural and layer-by-layer insulation resistance analyses have clearly identified the physical locations responsible for the electrical leakage of defective capacitors. No evidence of silver migration as a dominant failure mechanism has been observed for any of the defective capacitors under usual operating stresses. Comparisons of I-V characteristics for multilayer ceramic capacitors quenched by ice water and dry ice confirm that water plays a significant role in causing electrical failure at nominal bias. Failure mechanisms are then proposed to explain the failure of miniaturized multilayer ceramic capacitors under normal service conditions. >

Y.C. Chan

Papers

Failure analysis mechanisms of miniaturized multilayer ceramic capacitors under normal service conditions