Solder joints on thick printed copper substrates

Abstract

This article addresses the soldering of larger components onto ceramic substrates with thick printed copper patterns with a reduced amount of flux or using glutaric acid as a flux substitute. The main goal of the research was to create high quality connections by soldering on ceramic substrates, together with elimination of conventional flux from the process, and also to study the reliability of soldered joints on ceramic substrates under thermal shock ageing. The mock-up chips were used in the test and for this reason the test was primarily focused on bottom joint in the structure or sandwich structures. In the experiment, vacuum soldering using formic acid vapors to reduce oxides was used. Then all samples were observed under X-RAY radiation and selected samples were submitted for thermal shock testing (-40°C / 125°C / 1000 cycles). After the shock testing, another X-RAY scan with void area measurement and shear strength testing were realized. The results showed that our contacting soldering processes on ceramic substrates (with diluted flux or glutaric acid) are applicable and the selected samples also endures the shock ageing, especially bottom joint between ceramic substrate with Cu layer and solder alloy. The results also showed that void area and mechanical shear strength of soldered ceramic samples created with diluted flux or glutaric acid are relatively comparable with standard samples (FR-4).