Some Investigations on Direct Substrate-Attachment Process for Wideband Instantaneous Frequency Measurement Receiver Development

Abstract

Some critical investigations on direct substrate-attachment process over double-sided metallic housing have been discussed in this article under wideband instantaneous frequency measurement receiver development in detail. Conventional reflow method-based substrate-attachment techniques have many issues when the surface area becomes larger. One of the major issues is that it forms unwanted voids beneath the substrate, which affects phase performances at higher frequencies. To overcome these issues, a direct substrate-attachment process has been carried out under inert environment using a customized vapor-phase assembly (VPA) process. The final temperature and its profile have been readjusted by tuning gradient and duration of rise, equilibrium, and fall times to customize the VPA process. Conventional methods are compared with VPA of direct substrate attachment for large ( $\varphi \approx 265$ mm) surface area. Experimentations of direct substrate attachments are carried out for diverse quality of nickel (Ni)- and silver (Ag)-plated housings, respectively. In each step of plating depth, the percentage of impurities in plating and X-ray scan reports have been analyzed to make crucial decisions about attachment improvement, and limits have been set for mass production. Modules have been made and tested over extensive thermal cycling from −40 °C to +71 °C and random vibrations in three axes to establish the analysis.