A Low Tg Bonding Material for Use with Wafer-Level System-in-Package (WLSiP) and Fan-Out Wafer-Level Packaging (FOWLP) Processes

The advanced packaging industry is projected to accelerate with the market as demand for newer technologies continues to increase. To meet the increasing needs of high-performance chips for a variety of applications, more techniques are being developed with temporary wafer bonding solutions. These solutions need to address the difficulties of harsher downstream processing conditions as well as ease the cleanability after these processes. Temporary bonding provides a method for many wafer-level packaging wafer and substrate applications such as heterogeneous integration with the use of fan-out wafer-level-packaging (FOWLP). Heterogeneous integration is the stacking of multiple chips in order to improve devices to adapt to the need for high connectivity and artificial intelligence. The smaller interconnect allows for increased capacity, smaller footprint, and opens the door to newer packaging designs. Temporary bonding material provides a layer for stability and platform for heterogeneous assembly to occur. Temporary wafer bonding is a critical technology that continues to enable the use of ultrathin substrates for use in wafer-level packaging. The use of a temporary carrier enables the control of thinned substrates that can no longer self-support during downstream, backside processing. Current backside processing involves the use of aggressive thermal processes that can be in excess of 300°C. As packaging technologies move to larger diameter substrates, wafer warpage, stress from CTE-mismatched materials and adhesion issues after thermal processing have become obstacles. Thinned wafers can sustain damage when the bonding material has high stress and lower survivability at the higher temperatures. Therefore, a simple yet effective temporary bonding process that uses a bonding material that can survive all the backside processes with lower stress and lower warpage is highly desired. In this paper, we will introduce a newly developed temporary bonding material. This material has a thermal stability above 300°C and has very good adhesion to various substrates. It can be debonded after backside processing by using a thermal slide process or it can be laser released when used in conjunction with a laser release layer. After debonding, residual bonding material left on the device wafer can be easily cleaned with common industrial solvents. Substrates bonded using this material demonstrate lower overall wafer warpage with good film uniformity for downstream processing.