Thermal Shock Ageing of Joints Soldered Using Formic Acid Vapors on Thick Printed Copper Substrates

This article addresses the soldering of larger components onto ceramic substrates with printed copper patterns with a reduced amount of flux. The main aim of the research was to find a suitable soldering method and 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 the samples were observed under X-RAY radiation and 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 process on ceramic substrates is applicable and the 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 are relatively comparable with standard samples (FR-4).