Use of microwave technology for rapid cure of chip-on-board glob top encapsulants

Chip-on-board (COB) is widely used in manufacturing electronic packages for automotive, computers and other electronic components. Glob top encapsulation is used to protect semiconductor chips and bonded wires from adverse environments to increase long-term reliability of COB assemblies. However, current manufacturing practice normally involves a 2-4 hour long curing step to cure glob top encapsulants. Variable frequency microwave (VFM) technology was specifically developed to apply microwave energy to the rapid cure of various advanced materials, while not interfering with metallic components or electronic circuitry. VFM curing of COB glob top encapsulants has been performed with a wide range of encapsulants from various vendors. Key materials properties were measured after VFM curing and were compared to those of thermally cured samples. In general, VFM dramatically shortened the cycle time and provided the same cure quality as conventional thermal cure. This study reports that VFM curing of COB encapsulants is a rapid, selective and reliable process. Main results are: (1) the nominal VFM curing cycle is 15 minutes or less as compared to a 2 hour nominal thermal cure cycle; (2) no specific modification of encapsulant chemistry is necessary for VFM curing; (3) glob top encapsulants cured by VFM yielded equivalent extent of cure, T_g and CTE properties as compared to those of convection oven cured samples; (4) VFM has no adverse impact on functionality of the electronic components. VFM processing has therefore been demonstrated as an attractive alternative to conventional thermal processing