A Novel Approach to Manufacturing Surface Mount Assemblies

Abstract

Implementing surface mount technology (SMT) into military systems has not progressed as rapidly as expected. One of the major reasons is the lack of availability of MIL Spec. surface mountable components. Therefore, if one is to realise the benefits of SMT, manufacturing processes must be developed that allow inserted components to be mounted on the same printed wiring board (PWB) with surface mount components (SMCs). Honeywell's Ordnance Division has developed manufacturing processes which allow SMCs to be mounted on both sides of the PWB and inserted components to be mounted on one side of the same PWB. The surface mount solder reflow and wave soldering are performed in a single‐step solder system. This simplifies and reduces the number of manufacturing process steps for this type of surface mount assembly (SMA). This paper describes three major types of SMAs and their complexity levels. Definitions of the SMA types and complexity levels are necessary for selecting production equipment and developing SMA processes. Assembly process limitations are directly related to the SMA type and complexity level. Layout guidelines and processes from solder deposition to cleaning are discussed. Full scale engineering development (FSED) hardware has been fabricated using the single‐step solder process for SMAs with both SMCs and inserted components on the same PWB. The single‐step solder process offers an excellent solution to fabricating electronic assemblies where SMCs and inserted components are mounted on the same PWB. Plans to expand and enhance the first generation SMA fabrication processes to accommodate higher complexity levels are discussed.