Reliability of fine pitch halogen-free organic substrates for green electronics

Abstract

European Union's Regulation on halogens and lead-based solders has lead to the development of new class of high T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">g</sub> halogen-free polymer-glass laminates for package substrates. At the same time, Moore's law and 3D ICs have accelerated the demand for high I/O density. These fine pitch requirements in new substrates can affect reliability in terms of loss of surface insulation resistance (SIR) and formation of conductive anodic filament (CAF) leading to electrical failures. Therefore newly developed materials are required to have excellent resistance to electrochemical migration and high thermal stability for lead-free assembly. This study focuses on experimental reliability study of novel halogen-free substrates under accelerated conditions. This study consists of 1) SIR test with 50μm line width/spacing, 2) CAF test of through-vias of 100μm diameter with pitch of 250μm and 500μm, 3) through-via reliability and, 4) Pb-free flip-chip package reliability with halogen-free substrates. The halogen-free substrate used in this work was observed to have high resistance to surface migration at 50μm line-width/ spacing. However, CAF failures were observed even at 250μm pitch indicating that failures due to CAF at fine pitch are a serious reliability concern. The substrates did not show any failures in through-vias and flip-chip interconnections under thermal cycling indicating good reliability for halogen-free and Pb-free applications.