Passive Die Alignment in Glass Embedded Fan-Out Packaging

The objective of this paper is to demonstrate the feasibility of glass mounting substrates made by Laser Induced Deept Etching (LIDE) technology, which include newly developed passive die alignment structures. The aim of these structures is to compensate for potential die misalignments and die shift issues which become severe when moving to panel level fan-out packaging. The passive alignment structures are located at two adjacent edges of the rectangular cavity and are created in the same process step as the open cavities. The filigree spring-like alignment structures benefit from being processed in a crack- and stress-free manner. Although the spring elements have a minimal dimension of less than 100 μm, these structures show an outstanding break strength while deformed when active dies are placed in the mounting cavity. Depending on the design, the spring elements can have a stroke of several tenths of micrometer which enable the compensation of rather large die displacements. Here, we present examples for LIDE-processed mounting glass substrates with the described features. The performance of the proposed design and method was evaluated with a die accuracy study. Test dies with alignment marks were placed in the cavities and measured relatively to alignments marks on the mounting glass substrate. The Fan-Out packaging concept based on the research shown here combines several advantages: due to the relatively high Young's modulus of the glass, the reconstituted wafer shows less warpage than in the state-of-art; while the passive alignment structures reduce the die shift to a minimum (depending on dicing accuracies and through package vias for package-on-package or antenna-in-package application), and can be readily integrated.