3D integration consists of 3D IC packaging, 3D IC integration, and 3D Si integration. They are different and in general the TSV (through-silicon via) separates 3D IC packaging from 3D IC/Si integrations since the latter two use TSV but 3D IC packaging does not. TSV (with a new concept that every chip or interposer could have two surfaces with circuits) is the heart of 3D IC/Si integrations and is the focus of this investigation. The origin of 3D integration is presented. Also, the evolution, challenges, and outlook of 3D IC/Si integrations are discussed as well as their road maps are presented. Finally, a few generic, low-cost, and thermal-enhanced 3D IC integration system-in-packages (SiPs) with various passive TSV interposers are proposed.

Evolution, challenge, and outlook of TSV, 3D IC integration and 3d silicon integration

A double-sided and ultrathin 3-D glass interposer with through package vias (TPVs) at same pitch as through silicon vias (TSVs) in silicon interposers is developed to provide a compelling alternative to 3-D IC stacking of logic and memory devices with TSVs. The 3-D IC stacking approach to achieve high bandwidth has several drawbacks, including the need for TSVs through the logic die, thermal management within the 3-D stack, and the high manufacturing cost associated with wafer-based TSV processing. This paper presents design, fabrication, and electrical characterization of small TPVs (15–40 $\mu{\rm m}$ in diameter) in 30- $\mu{\rm m}$ thin glass to achieve an ultrathin 3-D interposer. This paper also reports the first demonstration of ultrasmall TPVs in glass (15 $\mu{\rm m}$ ) with same dimensions as TSVs in silicon. The signal insertion loss and crosstalk behavior of TPVs in ultrathin glass were investigated and found to be superior to TSVs using 3-D electromagnetic simulations. In demonstrating the 3-D interposers, two process-related challenges were addressed in this paper, namely: 1) defect-free formation of ultrasmall TPV holes with diameters of 15 $\mu{\rm m}$ at 27- $\mu{\rm m}$ pitch and 2) TPV metallization with copper. The fabricated TPVs in ultrathin glass showed a good model to hardware correlation of signal transmission with insertion loss ${ at 20 GHz. The results in this paper suggest that the 3-D interposer concept can be a simpler alternative to 3-D IC stacking with TSVs to achieve high bandwidth between the logic and memory devices.

Design, Fabrication, and Characterization of Ultrathin 3-D Glass Interposers With Through-Package-Vias at Same Pitch as TSVs in Silicon

Forming holes in a material includes focusing a pulsed laser beam into a laser beam focal line oriented along the beam propagation direction and directed into the material, the laser beam focal line generating an induced absorption within the material, the induced absorption producing a defect line along the laser beam focal line within the material, and translating the material and the laser beam relative to each other, thereby forming a plurality of defect lines in the material, and etching the material in an acid solution to produce holes greater than 1 micron in diameter by enlarging the defect lines in the material. A glass article includes a stack of glass substrates with formed holes of 1-100 micron diameter extending through the stack.

Method for rapid laser drilling of holes in glass and products made therefrom

Overview and Outlook of Three-Dimensional Integrated Circuit Packaging, Three-Dimensional Si Integration, and Three-Dimensional Integrated Circuit Integration

In this study, advanced packaging is defined. The kinds of advanced packaging are ranked based on their interconnect density and electrical performance, and are grouped into 2-D, 2.1-D, 2.3-D, 2.5-D, and 3-D IC integration, which will be presented and discussed. Chiplet design and heterogeneous integration packaging provide alternatives to the system on chips (especially for advanced nodes) will be discussed. Different substrates, such as size, pin-count, and metal linewidth and spacing for advanced packaging, are examined. The lateral communication between chiplets, such as the silicon bridges embedded in organic build-up package substrate and fan-out epoxy molding compound, as well as flexible bridges, will be presented. Fan-in packaging, such as the six-side molded wafer-level chip-scale package (WLCSP) and its comparison with the ordinary WLCSP, are presented. Fan-out packaging, such as the chip-first with die face-up, chip-first with die face-down, and chip-last and their difference, will be provided. Low-loss dielectric materials for high-speed and high-frequency applications in advanced packaging will be presented. Flip-chip assembly by mass reflow, thermocompression bonding, and bumpless hybrid bonding will be briefly mentioned first.

Recent Advances and Trends in Advanced Packaging

This paper demonstrates thin glass interposers with fine pitch through package vias (TPV) as a low cost and high I/O substrate for 3D integration. Interposers for packaging of ULK and 3D-ICs need to support large numbers of die to die interconnections with I/O pitch below 50 μm. Current organic substrates are limited by CTE mismatch, wiring density, and poor dimensional stability. Wafer based silicon interposers can achieve high I/Os at fine pitch, but are limited by high cost. Glass is an ideal interposer material due to its insulating property, large panel availability and CTE match to silicon. The main focus of this work is on a) electrical and mechanical design, b) TPV and fine line formation and c) integration process and electrical characterization of thin glass interposers. This work for the first time demonstrates high throughput formation of 30 μm pitch TPVs in ultrathin glass using a parallel laser process. An integration process was demonstrated for glass interposer with polymer build-up layers on both sides. The glass interposer had stable electrical properties up to 20GHz and low insertion loss of less than 0.15dB was measured for TPVs at 9GHz.

Design, fabrication and characterization of low-cost glass interposers with fine-pitch through-package-vias

This paper presents the design, fabrication and electrical characterization of a low loss and low cost non-traditional silicon interposer, demonstrating the high bandwidth chip-to-chip interconnection capability of the 3D silicon interposer, with equivalent or better performance than 3D ICs with TSVs, at a much lower cost. This scalable approach uses thin polycrystalline silicon in wafer or panel form, forms lower cost through-package-vias (TPVs) at fine pitch by special high throughput laser processes. The electrical performance is improved by thick polymer liners within the TPVs. Double side package processes for TPV metallization and RDL layers using dry film polymers and plating leads to significant cost reduction compared to single side TSV and BEOL wafer processes. Combined loss of 3mm long CPW lines and two TPVs in the low loss silicon interposer was demonstrated at less than 1dB at 10GHz. The fine pitch TPV capability and low loss of this non-traditional silicon interposer leads to 3D interposers with double side chips interconnected at equivalent bandwidth to wide bus I/O 3D ICs at a much lower cost and with better testability, thermal management and scalability.

Low-cost and low-loss 3D silicon interposer for high bandwidth logic-to-memory interconnections without TSV in the logic IC

Interposer technology is becoming important to interconnect ultra-high performance ICs with ultra-high density I/Os. Silicon interposers fabricated by back-end of line (BEOL) wafer processes address these wiring density requirements, but are limited by their high cost and by their high electrical losses. Organic interposers have limitations too. Their limitations are due to their poor dimensional stability, which require larger capture pads, which limit the I/O density Glass has been proposed by Georgia Tech [1-4] as a superior interposer material to address the limitations of both silicon and organic interposers in recent years. This paper describes the first demonstration of low cost and double sided glass interposer with 3-5 μm line lithography to form multilayer redistribution layers (RDL) to achieve 20 micron bump pitch, ready for chip-level copper interconnections. Unlike prior work using wafer based RDL processes or thin film wiring applied to organic cores, this research applies low cost laminate-like processes, scalable to large panels for lowest cost. To achieve this, semi-additive plating (SAP) process, combined with high resolution dry film photoresists, was optimized to fabricate fine-pitch copper traces with 3-5 μm lines on thin polymer films, laminated on thin glass. Such an ultra-high I/O density of interconnections form the backbone of 2.5D interposers, interconnecting multiple chips. Such ultra-small pitch copper traces can reduce the number of wiring layers required, thus reducing the cost. Compared to sub-micron Cu traces on Si interposers, these 3-5 μm lines are lower in resistance.

Demonstration of 3–5 μm RDL line lithography on panel-based glass interposers

Consumer demand for mobile services is expected to grow with the continued proliferation of connected devices including smartphones, wearables, and Internet of things. As a result, high-performance computing systems that support the core network and cloud infrastructures for these connected devices require unprecedented die-to-die bandwidth at low latency. To achieve next-generation performance requirements and to apply to commercial products, fundamental parameters for 2.5-D interposers are considered including: 1) high interconnect density at short interconnect length; 2) low power consumption; and 3) low packaging cost. The 2.5-D glass interposer described in this paper is superior to silicon interposer in cost and electrical performance, and to organic interposer in interconnect density. This paper describes a 2.5-D glass interposer as a ball grid array (BGA) package to achieve high bandwidth at low cost to improve bandwidth per unit watt signal power per unit dollar cost (BWF) compared to both silicon and organic interposers. Due to its high modulus and excellent surface finish, glass affords ultrafine line lithography to form high-density interconnects comparable to silicon, and the process described in this paper goes beyond silicon back-end-of-line processes by implementing a double-side semi-additive process (SAP) at increased copper layer thickness. This thicker metallization results in reduced conductor losses and improved bandwidth per channel compared to silicon. In addition, the low loss tangent of glass reduces dielectric losses in nets requiring through vias including clock distribution and high-speed off-package signals. Availability of glass in thin panel as well as in roll-to-roll formats beyond 500 mm in size reduces packaging cost compared to 300-mm wafer silicon interposer. The focus of this paper is on the integration of three enabling technologies: 1) advanced SAP for high-density redistribution layers (RDLs); 2) excimer laser ablation of RDL vias; and 3) fine-pitch thermocompression bonding with copper pillar die assembly—for a 2.5-D glass interposer at interconnect densities comparable to that of silicon to achieve terabit per second interdie bandwidth at highest BWF.

Yuya Suzuki

Papers

Design, Fabrication, and Characterization of Ultrathin 3-D Glass Interposers With Through-Package-Vias at Same Pitch as TSVs in Silicon

Design, fabrication and characterization of low-cost glass interposers with fine-pitch through-package-vias

Low-cost and low-loss 3D silicon interposer for high bandwidth logic-to-memory interconnections without TSV in the logic IC

Demonstration of 3–5 μm RDL line lithography on panel-based glass interposers

Design and Demonstration of a 2.5-D Glass Interposer BGA Package for High Bandwidth and Low Cost