Ing. Jakub Zdráhal

This study investigated the thermomechanical behavior of conventional printed circuit board substrate materials, with a particular focus on thermal expansion in the z axis for various combinations of material configurations and thermal stress during manufacturing. The primary focus of this paper is the thermomechanical properties of the substrate FR4, with particular emphasis on the effects of the number of epoxy cores and prepreg layers in multilayer boards. Two additional substrate materials for single-layer boards were incorporated to highlight the differences in the thermomechanical properties between different substrates. CEM1, a potential lower-cost alternative to FR4, and G30, a substrate designed for hightemperature applications. To simulate thermal stress during the manufacturing process of printed circuit boards, selected boards were immersed in molten solder for a brief period of time. The coefficients of thermal expansion in the z-axis and the glass transition temperature were subsequently determined for the analyzed specimens by the thermomechanical analysis. The measurements demonstrated significant discrepancies between immersed and non-immersed specimens, including the extent of the post-curing and the shrinkage effects. The analyses demonstrated that both effects were amplified with a thicker prepreg layer. Conversely, relative z-axis expansion exhibited a minor decrease with increasing prepreg thickness. These findings offer valuable insights into the influence of material composition and layer configuration on the thermal stability of substrate, which in turn affects the reliability of the entire assembly over its lifetime.

The aim of this work is to advance the development of an alternative eco-friendly method of manufacturing printed circuit boards (PCBs) using recycled and recyclable 3D printable polymers as the insulating substrate and a special silver paste for the conductive pattern. The components are embedded in the insulating substrate, and the connection to the PCB is made by overprinting the component with the silver paste. To improve mechanical properties and durability, in this work, the conductive pattern was overprinted on the 3D printer with another layer of recycled polymer, completely encapsulating the component. The results showed that the overprinting post-process led to a significant improvement in the mechanical properties of the interconnects with no negative impacts on the contact resistance of the components. The measurements of contact resistance indicated similarity to ECA joints. According to the pull-off test performed on the assembled two-terminal components, the pull-off force required to detach the component was similar to that of the soldered joints. Although the encapsulation did not apparently affect the change of the mechanical and electrical properties after accelerated aging tests, it showed an increase in reliability for rPLA samples. In this case, the encapsulation eliminated cracks in the conductive pattern. Despite the extensive development that still lies ahead, this alternative, environmentally friendly method could then be used in low-cost electronics or prototyping applications where sustainability is a priority.

This work aimed to evaluate a new approach to electronics manufacturing using recycled and recyclable 3D-printed polymers as an insulation substrate and printing of conductive silver ink as a conductive pattern. Furthermore, connection to the board is realized via embedding the components into the substrate and the ink's overprints. The first results from the measurements showed that this type of connection is comparable to conductive adhesive joints regarding contact resistance. Also, the behavior of the joints during accelerated aging by thermal shocks is relatively acceptable from a reliability point of view. A significant advantage of this manufacturing method is the absence of the high-temperature heating processes and, thus, energy savings compared to conventional production processes. Also, the final product is easily recyclable after its functional life. On the other hand, the overall quality is lower than that of standard printed circuit boards consisting of FR4 substrate and the copper conductive layer. The range of available and suitable components is also much smaller. The proposed solution could find applications primarily in low-cost electronics or prototyping.