Design tradeoffs between organic polymer-on-metal PWBs and ceramic thick-film PWBs for high-density operation using leadless ceramic chip carriers

The physical characteristics of a standard 1750A computer card are described. The card has the following parameters: 50- Omega to 100- Omega impedance, card size of 6.58*5.88 in., cards on 0.5-in. centers, and target module weight of 1 lb. The construction chosen for each design is described. Linewidths and spaces that describe a standard design are selected. The impedance is calculated for each design and compared to the desired values. A thermomechanical analysis of the composite structure is shown to achieve a composite module coefficient of thermal expansion to 8.0 to 8.5 p.p.m./ degrees C. A thermal analysis to achieve maximum device junction temperatures of 105 degrees C is described. The resulting polymer-on-metal and ceramic-on-metal interconnect structures are compared, based on resulting card thickness, achievable card-to-card centers, substrate weight and volume, and total card weight.<
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