Novel Toughening Agents for Thermosetting Systems for PWB Base Materials

摘要

The proposed revision of IPC 4101 -Specification for Base Materials for Rigid and Multilayer Printed Boards contains new slash sheets describing FR-4 base materials compatible with lead-free assembly. These specification sheets also outline requirements not found currently for FR-4 including Td, T260 and T288. In order to achieve minimum performance criteria, toughening agents have been incorporated into the FR-4 resin systems both for 135 and 170°C materials. Current modifiers for toughening thermosetting systems exhibit significant drawbacks including depression of the glass transition temperature, instability of the formulation and difficulty of use. Core Shell Rubber (CSR) particles have been used successfully for more than 40 years in thermoplastic applications but have had limited success in thermosetting systems due to difficulty in dispersing the solid powder into the resin system. We have developed a proprietary process for dispersing CSR domains into various thermosetting resins. The CSR particles are perfectly dispersed and remain so during storage under a variety of conditions and after the formulating process is complete. The resulting FR-4 composite exhibits improved inter-laminar adhesion, fracture toughness and lap shear strength without depressing the glass transition temperature or other thermal properties related to the cross link density. The CSR particles are supplied as a 25% concentrate in an epoxy resin chosen by the formulator such as a liquid Bis-A or multifunctional brominated epoxy thus minimizing initial development work. This paper will discuss the merits and use of these novel toughening agents for thermosetting systems for lead-free compatible base materials.