Surface Mount Design and Assembly for High Density Complex Modules

A packaging system has been developed using surface mounted components on ceramic substrates for conductive‐cooling applications. This has resulted in a high density, high reliability, and highly producible product. A 20 square‐inch module can mount up to 150 leadless chip carriers and can dissipate up to 30 W with a maximum junction temperature (Tj) of 90°C. Design guidelines, processing, and assembly techniques geared to surface mount devices for this high density ceramic thick‐film multilayer interconnect board will be presented. Constraints regarding the thermal characteristics and physical dimensions of the devices and the limitations of CAD routers, processing equipment, and automatic assembly equipment will also be discussed. Design guidelines regarding the electrical characteristics, such as capacitance and resistance in terms of layout and processing, will be defined. Timing criticality and busing layout guidelines will be discussed. Processing design considerations such as power and ground planes, conductor layers, layout boundaries, and surface mount footprints will be outlined. Other considerations taken during the placement, routing, and artwork phases will be presented, as well as those items to be considered during the processing flow. The assembly process will be discussed emphasising problems that can be encountered with tinning, placement, reflow, and cleaning. Rework of defective surface mount components will be reviewed in addition to considerations for design modifications.