Controlled Thermal Expansion Printed Wiring Boards based on Liquid Crystal PolymerDielecrics

L iguid crystal polymer (LCP) dielectric materials have been used to fabricate surface mount PWBs with a coefficient of thermal expansion matched to leadless ceramic chip carriers. Proprietary and patented polymer processing technology results in self‐reinforcing material with balanced in‐plane mechanical properties. In addition, LCPs possess excellent electrical properties, including a low dielectric constant (∼3) and very low moisture absorption (< 0.02 %). Laser drilling of blind vias in the LCP dielectric provides a very high density for use in direct chip attach and area array packages. Modelling indicates that the high out‐of‐plane CTE of LCPs does not affect the reliability of the plated‐through‐holes vias. RF characterisation indicates that the material is suitable up to very high frequencies. The material is ideally suited to MCM‐L and PCMCIA applications involving very thin dielectric layers of the LCP.