Base Polyimide-flex and rigid flex combinations Good dieletric, mechanical, and rework properties BT (bismaleimide triazine epoxy) Added dimensional stability Excellent thermal and dielectric performance FR-4 Low Tg epoxy laminate Very common board material Not optimal for multiple solder-reflow operations Metal Copper-clad foil on base material Adhesives Modified acrylics Low to medium end-use assemblies Excellent flow and good to moderate flexibility Moderate adhesion to mixed materials Epoxy and prepreg Moderate to high-end performance Poor to good flexibility Moderate to excellent adhesion Modified epoxy Low to high end-use assemblies Good to excellent flexibility Good to excellent adhesion in mixed materials Polyimide Medium to high-end assembly performance Moderate to excellent flexibility Excellent adhesion in mixed materials Multiple surface finish options Nickel Gold Electroless Ni/Immersion Au Solder, aluminum wire bonding applications Thick Electroplate Ni/Au Gold wire bonding applications Thin Electroplate Ni/Au Solder applications Solder OSP Copper (OSP)/Au Solder and gold wire bonding application