Cracking remains the major reason of failures in multilayer ceramic capacitors (MLCCs) used in space electronics. Due to a tight quality control of space-grade components, the probability that as manufactured capacitors have cracks is relatively low, and cracking is often occurs during assembly, handling and the following testing of the systems.
This presentation gives a review of recent project failures caused by cracks in ceramic capacitors and discusses deficiencies of the existing screening and qualification procedures that can reveal the propensity to cracking and effects of soldering stresses. Recent history cases. Effect of hydrogen. A case when derating does not work.
After a number of temperature excursions, for example due to circuit operation, the crack may propagate (Figure 3), creating an open-circuit device. In severe cases, the body of the capacitor may even fall out, leaving just remnants of ceramic surrounded by termination and solder joints.
Typically, flex cracks originate from the terminal ends at the bottom of the capacitor and have a diagonal direction inside the part usually at an angle of approximately 45o (see Fig. 2.8.b). In case of excessive amount of solder, the K-shaped cracks can also develop due to formation of tensile stresses at the top of capacitors .
In severe cases, when a large surface mounted capacitor has been subjected to a sudden thermal shock, a clearly visible elliptical crack may form on the upper surface of the chip (Figure 1). This is primarily due to the tensile forces exerted by the terminations.
Moisture sorption in the cracks that cross opposite electrodes in ceramic capacitors reduces insulation resistance and facilitates dendrite growth that might cause short circuit failures. For this reason, humidity testing might be more sensitive to the presence of cracks compared to life test that occurs in dry conditions.