In this study, on-board computer (OBC) electronic cards designed for cube satellites (CubeSats) containing a 168-MHz STM32F407 processor were shielded against space radiation and were tested. For shielding, a 6-mm-thick “neat” aluminum plate was used to cover the entire surface of the OBC card. The 6-mm-thick aluminum plate with a hole that matched the size of the STM32F407 processor was filled with either a neat epoxy, a 30 wt% amorphous boron added epoxy, a 30 wt% tantalum added epoxy, or a 20 wt% B4C-30 wt% tantalum added epoxy composite used as shielding materials. Structural and morphological properties of the shielding materials were examined by X-ray diffraction and scanning electron microscopy. The OBC cards covered with different shielding materials were irradiated with 30-MeV protons, while the performance of the cards was observed live. Specifically, the outputs of digital input/output (I/O), universal asynchronous receiver/transmitter, direct memory access, and digital-to-analog converter units were monitored during radiation testing, and the first deteriorations were observed in the digital I/O part. As a result of this study, taking into account just the total ionizing dose, shielded electronic boards showed 2 to 10 times higher radiation resistance than unshielded.