The transition from thru-hole manufacturing to surface mount technology has made one thing crystal clear: surface mount components and PC boards are easily damaged by the soldering and assembly process. Multilayer ceramic capacitors are sensitive components to damage due to their complex mechanical structure. But experienced users are now finding out the hard way that PC boards, plastic molded ICs or transistors, and even solder places stringent limitations on assembly processing. The entire assembly is now subjected to the soldering process exposing all components and the PC board to high temperatures for long periods of time. Unfortunately some materials, in particular the plastics used to manufacture SMT components and PC boards, are not well suited for high temperature processing. Sources of assembly induced damage fall into two major categories: thermal and mechanical.

Damage to PC boards, plastic molded components, and solder is primarily thermal in nature while chip capacitor and resistor damage is mostly due to external mechanical stress. Thermal shock cracks in ceramic capacitors have been described in detail as to causes and solutions (1, 2). Users are now discovering post solder cracks in plastic IC packages (3), and PC board blistering, measles, or delamination. The main culprits are moisture absorption by the plastics and stress due to large differences in the coefficient of thermal expansion (CTE) of materials used by the manufacturer of plastic molded components and PC boards.

Read more: http://www.avx.com/docs/techinfo/assembly.pdf