Assembly of Multiple Ultrathin Chips on Flexible Foils With High Placement Accuracy by a Simple Transfer Process

Abstract

This article presents a simple approach for high-accuracy assembly of multiple ultrathin chips on flexible foil substrates. The chips are placed initially in the cavities on a chip carrier substrate and transferred onto a thermally releasable adhesive tape. After application of the epoxy-based adhesive onto the chip surface, the chips are transferred onto the foil substrate. Finally, the epoxy adhesive is cured and the adhesive tape is removed. It was found that a wafer dicing tape with a releasing temperature of 90 °C as thermally releasable adhesive tape and a two-component epoxy adhesive with a curing temperature of 65 °C is suitable for the process. High placement accuracy of the chips of less than $30~\mu \text{m}$ in the ${x}$ - and ${y}$ -orientation as well as rotational misalignment lower than 0.2° were obtained. The process is demonstrated on a polyimide foil with a resulting chip flatness of $\pm 5~\mu \text{m}$ .