title: Novel Thermally Conductive and Flame-Retardant Substrates for Printed Circuit Boards : Structure-Property-Relationships
Creators: name: Pawelski-Höll, Christin
Publisher: name: University of Bayreuth
Year: 2022
Subjects: subject: Prepregs
subject: Leiterplatte
subject: Printed Circuit Boards
subject: Wärmeleitfähigkeit
subject: Flammschutz
subject: Faserverbundwerkstoffe
subject: E-Mobilität
subject: 500
subject: 600
subject: 620

description: New trends in technology come at the cost of increasing demands on material properties. Prepreg-based materials as used in Printed Circuit Boards (PCBs) are no exception. The short and long-term temperature range which they need to operate in has increased dramatically, critical material failures are often the consequence. Additionally, RoHS compliances and governmental regulations limit the use of i.e., lead-based soldering processes have their share as well. Lead-free soldering requires temperatures about 40 °C higher than State-of-the-Art technologies, making thermal management one of the critical properties of modern PCB base materials. State-of-the-Art polymer-based PCB materials such as glass-fiber (GF) reinforced thermosets lack this requirement due to their low intrinsic thermal conductivity. Pairing high thermally conductive metals that also possess a low CTE with polymers in PCBs creates a challenge as both material classes show a different dimensional behavior under thermal cycling, and PCB delamination or hot-spot formation is the result. The current research is challenged by the broad spectrum of requirements that need to be fulfilled. Increasing thermal conductivity and other thermal properties usually come at the cost of other must-have properties of PCBs, like water absorption, dielectric and mechanical properties. So how does one make the impossible possible? Searching for the “holy grail” in the fields of PCB substrates is finding a material (combination) whose processing is cost-efficient material-wise with a short production cycle at an industrial scale. In addition, the base material must comply with current regulations and has to meet the requirements coming from more demanding and new applications in challenging environments. Therefore, this doctoral thesis, aims to design a process and material that are environmental-friendly and cost-efficient and applicable in industrial scale. The high-Tg base material is tailored towards a simultaneous increase in thermal conductivity and flame retardancy without deteriorating other essential properties (i.e., water absorption, dielectric properties). The workflow involves the screening of different fillers of different nature, different filler sizes, and concentrations in feasibility studies. In addition, filler combinations and their ratios are investigated. The fillers’ dispersion and orientation are vital factors that can be triggered by an optimized processing method. Experimental studies are conducted in different stages: filled resin plates, prepregs, and their corresponding GF-reinforced laminates. The structure-property-relationship is established by comparing the overall results with special attention to the effect of GF. The main aim is to understand the impact of (synergistic) filler combinations, and the increasing FVC on filtration of fillers, filler network formation and the final laminate properties. The transferability between filled resin plates to their fiber-reinforced systems is studied to focus on thermal and mechanical properties. It is of great scientific interest to understand the inter-dependency of different fiber volume contents (FVC) with the thermal properties to describe models and give forecasts.