Effect of Dielectric Material on the Reliability of 3640 MLCC Capacitors under High-G Shock Loads

Abstract

Electronic components are often potted to protect sensitive equipment from environmental conditions (such as moisture), as well as to insulate electrical leads in the event at other components fail. Potting of electronics has become one of the most viable and cost-effective solutions to enhance electronic package survivability. At extreme mechanical shock loads, the electronic components undergo tremendous strain which in turn is responsible for solder joint failure in BGA components. At these high-g loads, the surface mount BGA solder joints may not survive due to the large strains and harsh nature of testing. The epoxy potting absorbs the high-g shock forces and transmits reduced amount onto the package solder joints. A multilayer ceramic (MLC) capacitor is a monolithic block of ceramic containing two sets of offsets, interleaved planar electrodes that extend to two opposite surfaces of the ceramic dielectric. Larger physical sizes than normally encountered chips are used to make high voltage MLC chip products. Applications such as snubbers in high frequency power converters, resonators in SMPS, and high voltage coupling/de blocking. High dielectric constant in ceramic capacitors exhibit some low-level piezoelectric reactions under mechanical stress. As a general statement, the piezoelectric output is higher, the higher the dielectric constant of the ceramic. The capacitors used in this study were X7R and COG type dielectrics with a dielectric constant range from 2000–4000 and 15–100 respectively. Reliability study of larger footprint 3640 MLCC capacitors under high-g shock loads is new. In this paper, a circular PCB with an annular hole assembled with fine pitch BGA packages and MLCC capacitors was studied under high-g mechanical shock loads up to 25,000g. The effect of shock pulse variation on the survivability of the board assemblies was reported. Peak displacement contours and the board strains near the corner interconnects/pads for each pulse width variation was presented by utilizing full field 3D digital image correlation. The reliability aspects of MLCC capacitors dielectric material based on their dielectric constant was discussed. The mechanical and electrical performance of the dielectric material in 3640 MLCC capacitors under high-G shock was assessed.