Optimum Chip-Tape Adhesion for Reliable Pickup Process

An efficient UV-irradiation process plays an important role for a successful pickup of very thin ( $ ) Si chips, such as for integrated circuits, power semiconductors, or microelectromechanical systems devices. Before the UV-irradiation process, a dicing tape is laminated on the back of the wafer to hold it tightly (high adhesion strength), which enables rapid and smooth dicing of the wafer into separate Si chips. In the second stage, the adhesive layer is irradiated with UV light through the front side of the backing substrate, which decreases the adhesion strength to the level where the diced chips are picked up easily for further die-bonding processes. However, various malfunctions during the UV-irradiation process can lead to a different and occasionally insufficient UV dose. Consequently, the adhesion is not sufficiently reduced, which could later lead to pickup problems at the die-attach equipment during assembly. In this paper, we present the consequences of an insufficient UV dose on adhesion behavior and pickup efficiency. Using calculated adhesive energy, pickup simulation was done, and accumulated stress in the chips was evaluated at different UV doses. At lower UV doses, the adhesive energy showed rate-dependent behavior, while at higher UV doses, such a behavior was not shown. The accumulated stress within chips showed a linear correlation to adhesive energy, where at lower UV doses, the strength of the silicon chip was exceeded. In the practical process, with an increased pickup rate, higher energy is needed to delaminate the chip. With higher energy needed, accumulated stress in the chip is increased and could lead to the breaking of the chip.