S-Connect Fan-out Interposer For Next Gen Heterogeneous Integration

Abstract

Semiconductor products used in high-performance computing (HPC) and artificial intelligence (AI) applications require higher memory bandwidth, greater input/output (I/O) count, better power delivery network (PDN) performance and improved heat dissipation characteristics. To meet these requirements, a 2.5D package architecture with a Through Silicon Via (TSV)-bearing silicon (Si) interposer is mainly used in volume production. However, a redistribution layer (RDL) interposer is emerging as a cost effective and higher performance alternative. To implement an improved high-performance, multifunctional interposer, S-Connect technology has been developed that uses a multi-chip, fan-out interposer with various functionalities, such as a die-to-die (D2D) connection, where integrated passive devices (IPDs) and active devices can be integrated. If active devices are included in the interposer, S-Connect technology enables a 3D system where multiple active chips are vertically integrated. In this paper, the S-Connect design differences from the existing 2.5D package using Si interposer with TSVs and its fabrication process flow are explained. S-Connect technology provides manufacturing flexibility to apply various types of interconnects. Two different connect features will be discussed. Firstly, a Si connect will be explored having a back end of line (BEOL) and TSV approach that can provide the same die-to-die routing with smaller than $1-\mu \mathrm{m}$ line/space (L/S) and vertical connections as a Si interposer. The second option uses a multilayer RDL, which can be fabricated on Si, glass and even on the epoxy mold compound (EMC). The RDL can also provide vertical interconnects such as TSVs in Si. For demonstration, a test vehicle (TV) with one logic chip and two memory chips mounted on a multi-chip, fan-out interposer with an area approximately 1.5 times larger than the reticle was used. The interposer consists of two connect chips with $2-\mu \mathrm{m}$ L/S RDL and 6 mechanical IPDs located under the logic die. Two types of the connect chips were used - RDL on Si wafer and RDL on EMC having TMVs. The top die to interposer joints were made using $\mu$-bumps with $25-\mu \mathrm{m}$ size on a $45-\mu \mathrm{m}$ pitch in the logic and $25-\mu \mathrm{m}$ size on a $55-\mu \mathrm{m}$ pitch in the memory die. Both the top and bottom sides of the fan-out interposer have a single layer of RDL. To interconnect the bottom side of the interposer and the package substrate, copper (Cu) pillar C4 bumps at $150-\mu \mathrm{m}$ pitch were formed. Once the top die and interposer assembly is complete, the subsequent processes are standard flip chip ball grid array (FCBGA) process flows. Moisture sensitivity and long-term reliability test results will be presented as well as warpage behavior, which is critical for the large body packages. Lastly, the advantages of the S-Connect package will be compared to other 2.5D and flip chip solutions in terms of manufacturability, ability to integrate multiple functionalities and cost.