Nicolas Boyer

Assembly of mechanically compliant interfaces between optical fibers and nanophotonic chips

Silicon nanophotonics may bring disruptive advances to datacom, telecom, and high performance computing. However, the deployment of this technology is hampered by the difficulty of cost efficient optical inputs and outputs. To address this challenge, we have recently proposed a low-cost, mechanically compliant polymer interface between standard single mode fibers and nanophotonic waveguides. Our concept promises better mechanical reliability and better optical performance than existing technology. To manage the cost of assembly, we show here that self-alignment features can be effectively used to bridge the gap between the accuracy required by single-mode optics (1-2 um) and the capability of high-throughput microelectronic assembly equipment (~10 um). We describe the complaint interface, the assembly strategy, and the design of our re-alignment features. We demonstrate experimentally that misalignments at assembly as large as +/-10 um are re-aligned by our self-alignment structures to +/-1 to 2 um. Our approach enables existing microelectronics equipment to be used for singlemode optics assembly.

Underfill delamination to chip sidewall in advanced flip chip packages

A number of failure mechanisms related to the underfill material in flip chip plastic ball grid array packages are well documented in the literature (underfill-to-chip passivation delamination, underfill-to-substrate soldermask delamination, chip cracking, interconnect fatigue, etc.). This paper discusses the delamination of the underfill from the chip sidewalls, another failure mechanism which has become more prevalent with component material changes, increases in die dimensions, finer C4 pitches and substrates with larger coefficient of thermal expansion. A detailed study is presented for the initiation of underfill-to-sidewall delamination, based on experimental data as well as finite element modeling. It is shown generally that both stress at the chip-underfill interface near the chip corner, and poor adhesion of the underfill to the chip sidewalls contribute to the initiation of underfill delaminations. Various parameters influencing stress (package design, underfill material thermo-mechanical properties) and adhesion (underfill base chemistry and additives, filler treatment, chip sidewall cleanliness) are discussed.

A Novel Approach to Photonic Packaging Leveraging Existing High-Throughput Microelectronic Facilities

Silicon photonics leverages microelectronic fabrication facilities to achieve photonic circuits of unprecedented complexity and cost efficiency. This efficiency does not yet translate to optical packaging, however, which has not evolved substantially from legacy devices. To reach the potential of silicon photonics, we argue that disruptive advances in the packaging cost, scalability in the optical port count, and scalability in the manufacturing volume are required. To attain these, we establish a novel photonic packaging direction based on leveraging existing microelectronics packaging facilities. We demonstrate two approaches to fiber-to-chip interfacing and one to hybrid photonic integration involving direct flip-chip assembly of photonic dies. Self-alignment is used throughout to compensate for insufficient placement accuracy of high-throughput pick and place tools. We show a self-aligned peak transmission of -1.3 dB from standard cleaved fibers to chip and of -1.1 dB from chip to chip. The demonstrated approaches are meant to be universal by simultaneously allowing wide spectral bandwidth for coarse wavelength division multiplexing and large optical-port count.

Automated, self-aligned assembly of 12 fibers per nanophotonic chip with standard microelectronics assembly tooling

Silicon photonics technology aims to leverage microelectronic chip fabrication facilities to bring disruptive advancements in photonic circuits cost and complexity. However, the large scale deployment of silicon photonics is muted by the difficulty of cost-efficient and scalable, single-mode optical inputs and outputs. To disruptively improve on cost and scalability, we believe that the best approach is to enable existing high-throughput microelectronic packaging tools for single-mode photonic packaging. In this paper, we experimentally demonstrate such approach with automated assembly of standard-fiber arrays to photonic chips. We identify the main challenges and solutions to enabling high-throughput pick-and-place tooling for single-mode photonic assembly. These include challenges with fiber handling, placement accuracy and limitations in movement complexity. We present a manufacturability assessment of the employed fiber-to-chip self-alignment. We show through Monte Carlo tolerance analysis an expected manufacturing re-alignment accuracy of <;1.3 um despite initial misalignments of up to ~40 um. We believe the approach proposed and demonstrated here can substantially improve on single-mode optical input and output cost and scalability.

A metamaterial converter centered at 1490nm for interfacing standard fibers to nanophotonic waveguides

We present data with both manual probing and self-aligned 12-fiber automated assembly. We find a peak transmission efficiency of -1.6 dB and a Fabry-Perot oscillation on one polarization induced by a mask layout misstep.

Photonic packaging in high-throughput microelectronic assembly lines for cost-efficiency and scalability

We demonstrate silicon photonic packaging that can be fully exercised in existing microelectronic packaging facilities. We show low optical loss and point towards notably improved assembly cost and scalability in both volume and optical port-count.

Sub-Micron Bondline-Shape Control in Automated Assembly of Photonic Devices

Low-cost and scalable interfacing of optical fibers to photonic waveguides remains a significant challenge for singlemode photonic devices. We have recently proposed a compliant polymer interface connecting optical fibers to nanophotonic waveguides. It involves assembling arrays of polymer waveguides defined on a flexible polymer ribbon to nanophotonic chips. For best performance, the adhesive bondline between the ribbon and the chip must be controlled at the submicron level over the waveguide interface area with a controlled bondline increase near the chip edge. Such bondline shape and control cannot be achieved with standard techniques. In this paper, we address manufacturing compatible solutions to sub-micron bondline-shape control in automated assembly of flexible devices to rigid chips. We introduce a pneumatic chip support for bondline uniformity and employ a patterned vacuum pick tip to adjust the bondline locally to match it to a desired shape. We demonstrate a bondline control of <;0.5 um over a critical interface area of ~1 mm2. The approach presented here applies to sub-micron bondline-shape control of any flexible-to-rigid device assembly.

Breaking the mold of photonic packaging

The packaging of photonic devices remains a hindering challenge to the deployment of integrated photonic modules. This is never as true as for silicon photonic modules where the cost efficiency and scalability of chip fabrication in microelectronic production facilities is far ahead of current photonic packaging technology. More often than not, photonic modules are still packaged today with legacy manual processes and high-precision active alignment. Automation of these manual processes can provide gains in yield and scalability. Thus, specialized automated equipment has been developed for photonic packaging, is now commercially available, and is providing an incremental improvement in cost and scalability. However, to bring the cost and scalability of photonic packaging on par with silicon chip fabrication, we feel a more disruptive approach is required. Hence, in recent years, we have developed photonic packaging in standard, highthroughput microelectronic packaging facilities. This approach relies on the concepts already responsible for the attractiveness of silicon photonic chip fabrication: (1) moving complexity from die-level packaging processes to waferlevel planar fabrication, and (2) leveraging the scale of existing microelectronic facilities for photonic fabrication. We have demonstrated such direction with peak coupling performance of 1.3 dB from standard cleaved fiber to chip and 1.1 dB from chip to chip.

Novel, High-Throughput, Fiber-to-Chip Assembly Employing Only Off-the-Shelf Components

Cost-efficient assembly of single-mode fibers to silicon chips is a significant challenge for large-scale deployment of Si photonics. We have previously demonstrated a fully automated approach to parallelized assembly of fiber arrays to nanophotonic chips meant to be performed with standard high-throughput microelectronic tooling. Our original approach required a customization of a standard fiber component, which could limit cost-efficiency and scalability. Here, we demonstrate a novel approach to fiber assembly employing off-the-shelf fiber components only. The new concept employs a dual vacuum pick-tip that can be integrated in standard high-throughput microelectronic tooling. We validate this approach with assemblies of standard 12-fiber interfaces to nanophotonic chips. The assembly performance is assessed via x-ray tomography cross-sections, polished mechanical cross-sections, and optical coupling measurements.