Influence of Rigid Carrier Substrate and its Release Layer on Warpage of Fan-out chip last WLPs & PLPs

Abstract

In recent years, the need for ultra-high density chip packaging devices and heterogenous integration devices require strategic placement of various components for high-performance computing (HPC), artificial intelligence (AI), etc. The fan-out chip last process with redistribution layer (RDL) first is expected as a solution to assemble these modules in advanced packages, which is essential for avoiding the risk of known good die (KGD) loss. During the assembly of the fan-out chip last WLP, elimination or minimizing warpage is an inherent challenge. It is caused by a thermal mismatch between various organic-inorganic – metallic – non-metallic – composite materials used in different layers of the package. If not controlled, then warpage from stresses induces alignment mismatch impacting package yield loss and reliability related issues. Warpage is minimized by using a rigid carrier substrate to build the RDL layers. The selection of this rigid carrier and its release layer influence the package warpage during the fan-out chip last WLP fabrication process. This paper focuses on the influence of rigid carrier substrate and its release layer on the warpage of fan-out chip last WLPs. Further, a solution towards controlling warpage has been provided using a novel material set referred to as HRDP® (High Resolution Debondable Panel). This is a drop-in approach compatible with the existing assembly flow. One of the important features of the HRDP® carrier is that it is offered in various dimensions and thicknesses. The HRDP® carrier is available for round wafers as well as for square/rectangular panel shapes in glass or silicon substrates to match the coefficient of thermal expansion (CTE) of the metal RDL, dielectric material, and Epoxy molding compound (EMC). This contributes to optimizing CTE related interfacial stresses and minimizes assembly warpage. Another key attribute of the HRDP® is its ease of debonding. Contrary to conventional debonding/release polymer layers, the HRDP® structure is composed of 100% inorganic material. It improves processing capability during RDL manufacturing, showing better chemical resistance and heat resistance than alternate technologies such as laser lift-off (LLO) type carrier