Plastic packaging in circuit board assemblies for space applications

Recently, high density packaging technologies which incorporate plastic, such as plastic ball grid array (PBGA) packaging, and the availability of less expensive commercial or near commercial off-the-shelf (COTS) plastic encapsulated microcircuits (PEMS) have provided an impetus to re-examine the use of plastic packaged parts in space applications. The use of PEMS can reduce assembly cost and weight and significantly reduce thermal-expansion mismatches between typical circuit board materials and components. However, certain issues need to be addressed before a clear understanding emerges of how plastic components should be incorporated in space hardware. The most important of these are: (1) how well plastic encapsulation protects components from deleterious moisture absorption; (2) the optimal handling procedures for plastic encapsulated components during assembly and storage; (3) the best ways to protect plastic components from radiation damage. In addition, from a practical standpoint, makers of space electronics hardware need to understand the steps involved in converting existing board and package designs to those that incorporate PBGA packaging. This paper reviews some of the currently available data on moisture absorption and storage and handling issues. To illustrate the steps required in repackaging, an example is presented that describes the repackaging of a high input/output count ASIC into a PBGA.