Electronic packaging

Pad Array Carrier (PAC) packaging is used for surface mounting of modules on printed circuit cards. The package described in this study has an added feature that allows for the testing of the package through the holes laid along the periphery of the package board. MAGIC was used in the design and layout of an 8 x 8 array size PAC. Two key contributors to electrical noise in the package, viz., cross talk and signal reflections were analyzed. Transmission line models were developed for analyzing these parameters. HSPICE and HP 85150B Microwave Design Systems (MDS) were used to simulate the transmission line models to evaluate the effects of cross talk and signal reflections on the package board. The performance of the package for the speed and maintenance of signal integrity was evaluated. Guidelines specifying the physical geometry limitations for line length, line width, line spacing, and layout configurations required to meet specific noise budget (cross talk and signal reflection considerations) were established.

Experimental modal analysis was conducted on a FR-4 epoxy fiber glass electronic printed circuit board (PCB) and a same size PCB with surface mount component to determine the modal parameters of the first four flexural vibration modes. Structural dynamic modification (SDM) and finite element analysis (FEA) techniques were utilized to predict the dynamic behavior of the boards when surface mount assemblies were attached. Details of modal testing procedures and analytical modeling involved in SDM and FEA were described. Processes of investigating suitable predicting model were presented. Results from the study indicate that the component can be modeled as a point mass under certain circumstance. But it is important to include the rotary inertia effects of the component in response prediction for the modes involving torsional vibration.

Simulations of bending and twisting of surface mounted assemblies have been performed using the hybrid analytical/experimental analysis approaches, and the results are presented. Analytical analyses were combined with experimental load-deformation characteristics of the surface mounted assemblies to predict the maximum allowable loadings and deflections that surface mounted assemblies can withstand before incurring failures. Simulation results obtained were in close agreement with the real loading situations.