Effects of the functional groups of nonconductive films (NCFs) on materials properties and reliability of NCF flip-chip-on-organic boards

Nonconductive films (NCFs) are one of the conducting polymer adhesives alternatives for flip-chip interconnection. NCFs containing no conductive particles have functions of adhesion, insulation, and encapsulation. The most important issue in NCFs-bonded flip-chip-on-board (FCOB) assemblies is thermal cycling reliability. Thermo-mechanical properties such as glass transition temperature (Tg), modulus (E), and thermal expansion coefficient (CTE) of cured NCFs significantly affect to the thermal cycling reliability of NCFs bonded FCOB assembly. In this paper, we have mainly focused on the improvement of thermo-mechanical properties of NCFs by controlling the number of functional groups of NCFs resin. The functionality modified NCFs-bonded FCOB assembly showed significantly enhanced reliability under thermal cycling test environment (-40 °C ∼ 150 °C, 1000 cycles). To compare the reliability of conventional and modified NCFs-bonded FCOB assemblies after thermal cycling test electrical analysis and scanning acoustic microscopy (SAM) investigation were performed. Thermal deformations of each NCFs-bonded FCOB assembly under thermal cycling environment were also investigated and quantitatively compared using high sensitivity Twyman-Green interferometry. According to experimental results, the functional groups of NCFs have great effects on thermomechanical properties of cured NCFs, the thermal deformation, and thermal cycling reliability of NCFs-bonded FCOB assemblies.