The paper is discussing a method of increasing the reliability of on-board electronic equipment at the early stages of its design. Authors offer to evaluate and provide deterministic reserves for thermal, mechanical and electrical loads to electronic components using special simulation software. Determinacy of reserves loads on the electronic components is achieved by a result of complex modeling as additional indicators of reliability. The main methods of reliability indicators calculation conducted in enterprises are probabilistic, which are averaged and do not lend themselves to practical verification during testing. Complex modeling of destabilizing effects on the printing circuit board of designed on-board equipment allows to achieve the required reserves on the electrical, thermal and mechanical loads with respect to the maximum permissible temperatures, vibration and shock acceleration in the electronic components, which leads to the guaranteed provision of high levels of reliability.