The Characterisation of Novel PWB Substrate Materials for Leadless Ceramic Chip Carrier Attachment

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Abstract
The problems associated with the direct attachment of leadless ceramic chip carriers (LCCCs) to conventional PWB structures subjected to ambient thermal and power (on/off) cycling are now widely documented. The reliability of LCCCs mounted on various novel substrate materials has been assessed here during ambient thermal cycling from −55° to 125°C and −20° to +70°C and during power heat cycling. Polyimide Kevlar material was rejected on the basis that microcracks, formed in the laminate during thermal cycling, propagated to the surface and resulted in copper track breakages. A flexible laminate interconnection structure for strain relief was found to be too cumbersome for most applications and gave only a small reliability improvement. Polyimide quartz and copper‐invar‐copper cored materials were both found to give a high degree of reliability in thermal cycling. The metal cored laminate is preferred because it is also a more rigid structure with the better thermal conductance needed for many high performance and reliability applications. An elastomer coated FR4 material also performed well during lower temperature thermal and power cycling tests and represents a reduced cost option for less severe environments.

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