Capacitance monitoring while flex testing

As most other modes of failure have been dramatically reduced over the years, cracking due to stresses from boards bending have gained prominence. The common printed circuit board (PCB) built of G10 or FR-4 glass epoxy materials will easily bend under moderate forces. Almost all processes involved in populating these boards can involve bending the board - many times unknowingly. The bending of the board causes forces to be transmitted through the solder attach fillets to the surface mount chip. These forces are concentrated at the bottom of the chip, where the termination bands end. The mass of solder is important as this material is malleable, and slight amounts will move more freely. Forces applied very slowly will also allow the solder to stretch and absorb some ofthe force. The ceramic material is hard, non-elastic, and brittle. The shear force pulling at the ceramic along the termination edge will lead to a crack if the forces are sufficient. At what force the chip cracks is thought to be dependent upon the ceramic material, the amount of solder, the termination material and amounts, and possible defects or anomalies within the ceramic structure. In this context, the authors describe flex, bend, or warp testing which was instituted to detect a susceptibility to these forces. >