The Definitive Guide to an Electronic Assembly Design Review / 8
Often a tin whisker analysis may also be performed. At Ansys, we explore the
finish on the component leads and printed wiring board (PWB) surface
finish to assess susceptibility. Whiskering occurs because of the presence of
a compressive stress (or, more accurately, a stress gradient) within the tin
deposit. This compressive stress drives the preferential diffusion of tin atoms.
Electrostatic discharge (ESD) susceptibility must also be examined. We
recommend that the user know the ESD rating for each part and select
parts (when possible) to achieve the best ESD rating. The designer should
identify all ESD sensitive parts on drawings and mark locations of ESD
sensitive parts on the board with the ESD symbol. Finally, the user must be
aware that part location, particularly with respect to I/O signals, drives the
appropriate ESD rating.
4
BOM (Component) Stress Review (cont.)
