Daisy Chain Research Articles

A Novel Method for Characterization of Ultralow Viscosity NCF Layers Using TCB for 3D Assembly

Abstract For die-to-wafer (D2W) stacking of high-density interconnects and fine-pitch microbumps, underfill serves to fill the spaces in-between microbumps for protection and reliability. Among the different types of underfill, nonconductive film (NCF) has the advantages of fillet and volume control. However, one of the challenges is the solder joint wetting. An NCF must have good embedded-flux activation to mitigate Cu UBM pad oxidation due to the repeated TCB cycles that accelerate oxidation on neighboring dice. The flux in the NCF also helps in wetting the solder bumps. To realize efficient solder wetting, one must also understand the NCF deformation quality, which is a function of its viscosity. This parameter has direct impact on the deformation of solder bumps. High-viscosity NCF would be difficult to deform, thus preventing solder contact to pad during TCB reflow temperature. High bond force is required and could lead to reduced alignment accuracy. For a low viscous NCF, it requires low bond force. Solder joint wetting is a challenge with excessive squeezeout due to fast and instantaneous deformation. We seek to demonstrate in this article a creative methodology for NCF material characterization, considering the factors of NCF viscosity, deformation, and solder squeezeout. We use TCB tool position-tracking data to define the deformation curve of the NCF as a function of temperature and time at very fast profile of TCB. We use the NCF viscosity curve as reference in relation to the actual deformation, and predict dynamic deformation in three different configurations. Deformation test configurations were performed on chips with and without microbumps bonded with a rigid flat glass surface and with a bottom Cu UBM pad. The experiments were performed with different heating ramp rates at target above Sn reflow of ~250°C interface temperature. As validation, we applied the optimized TCB process (force, temperature, and ramp rate) on a test vehicle with 20 and 40 μm pitch daisy chains and obtained very good connectivity with good joint and IMC formation.

Template-Directed Synthesis of Redox-Active [c3]Daisy Chain Rotaxanes

Cyclic daisy chain rotaxanes represent a particularly intriguing class of mechanically interlocked molecules with the potential to generate precisely controlled molecular movements by internal sliding of their chains. In this issue of <i>Chem</i>, Stoddart and collaborators introduce an efficient template-directed strategy for accessing [<i>c</i>3]daisy chain rotaxanes capable of redox switching between a relaxed macrocycle and a tensed trisarm-shaped conformation.

Cyclodextrin-Based [c2]Daisy Chain Rotaxane Insulating Two Diarylacetylene Cores.

A [c2]daisy chain rotaxane with two diarylacetylene cores was efficiently synthesized in 53 % yield by capping a C2 -symmetric pseudo[2]rotaxane composed of two diarylacetylene-substituted permethylated α-cyclodextrins (PM α-CDs) with aniline stoppers. The maximum absorption wavelength of the [c2]daisy chain rotaxane remained almost unchanged in various solvents, unlike that of the stoppered monomer, indicating that the two independent diarylacetylene cores were insulated from the external environment by the PM α-CDs. Furthermore, the [c2]daisy chain rotaxane exhibited fluorescence emission derived from both diarylacetylene monomers and the excimer, which implies that the [c2]daisy chain structure can undergo contraction and extension. This is the first demonstration of a system in which excimer formation between two π-conjugated molecules within an isolated space can be controlled by the unique motion of a [c2]daisy chain rotaxane.

Low Temperature SoIC Bonding and Stacking Technology for 12-/16-Hi High Bandwidth Memory (HBM)

A low temperature system-on-integrated-chip (SoIC) bonding and stacking technology is proposed and implemented for 3-D memory integration, such as 3-D static random access memory (SRAM) or dynamic random access memory (DRAM) cube. It extends not only 2-D pin count to 12 000/mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> but also overcomes the obstacle of the stacking height. 4-Hi, 8-Hi, and 12-Hi stacks, each with 1 base die and 4, 8, and 12 dies, respectively, are realized and demonstrated in this article. The daisy chains in the 4Hi/8-Hi/12-Hi structures incorporating over 10000 through silicon vias (TSVs) and bonds are tested with liner I - V curves, which indicates the good bonding and stacking quality. The electrical link from base controller to top DRAM for 12-Hi and 16-Hi high bandwidth memory (HBM) structure is built up to study the bandwidth (BW) and power efficiency. Compared to μbump technology, the BW for the 12-Hi and 16-Hi structures using SoIC bonding shows the improvement of 18% and 20%, respectively, under same pin pitch and the power efficiency has the improvement of 8% and 15%. For thermal performance, the 12-Hi and 16-Hi SoIC-bond structure is 7% and 8% better than those using μbump technology, respectively. With this innovative SoIC bonding and stacking technology, the bond pitch is scalable to sub-micrometer and the die thickness is manageable to be thinner, which are prospected for the application of higher BW 3-D memory with tera byte (TB)/s per stack.

Church Building, Community, and Nation in Charlotte Yonge's The Daisy Chain

Church Building, Community, and Nation in Charlotte Yonge's <i>The Daisy Chain</i>

Radical Cyclic [3]Daisy Chains

Summary Mechanically interlocked molecules (MIMs) that undergo controllable internal motions of their component parts in more than one dimension are rare entities in the molecular world. Cyclic [2]daisy chains ([c2]DCs) are a class of MIMs that have been identified as prototypes for molecular muscles. It remains, however, a challenge to synthesize [cn]DCs with n > 2 selectively and efficiently. Herein, we report the design and synthesis of [c3]DCs employing radical and anionic templates. Two mechanically interlocked [c3]DCs with 18 positive charges were obtained in >90% yields. One [c3]DC displayed good air stability in its radical cationic form, while the other underwent reversible “co-conformational” switching between open macrocyclic and closed trisarm-shaped forms under electrochemical control. These findings provide not only two-dimensional MIMs with attractive electronic and switchable properties, but also a starting point for the design of extended molecular arrays, which could become the forerunners of adjustable molecular nets and breathable molecular membranes.

Magnetic field imaging and light induced capacitance alteration for failure analysis of Cu-TSV interconnects

This paper discusses Cu-filled Through Silicon Via (TSV) failure analysis cases where known FA methods were used in an alternative way. Results are shown using magnetic field imaging (MFI) on a cross-sectioned chip to detect a leakage current path, and MFI and Light Induced Capacitance Alteration (LICA) to detect opens in TSV daisy chains.

Cover: Journal of the Chinese Chemical Society 10/2020

AbstractIn this figure, hetero type III‐B polyrotaxane den drimers with three different core group functionalities, namely, azobenzene, daisy chain, and cyclobis (paraquat‐p‐phenylene) macrocycle were synthesized and characterized by NMR spectroscopy and mass spectrometry. Their dual molecular switching properties as macromolecular machines are to be further expolred. More details about this figure will be discussed by Prof. Ken Cham‐Fai Leung and his co‐worker on page 1734‐1741 in this issue. image

Full-Azimuth Beam Steering MIMO Antenna Arranged in a Daisy Chain Array Structure.

This paper presents a multiple-input, multiple-output (MIMO) antenna system with the ability to perform full-azimuth beam steering, and with the aim of realizing greater than 20 Gbps vehicular communications. The MIMO antenna described in this paper comprises 64 elements arranged in a daisy chain array structure, where 32 subarrays are formed by pairing elements in each subarray; the antenna yields 32 independent subchannels for MIMO transmission, and covers all communication targets regardless of their position relative to the array. Analytical results reveal that the proposed antenna system can provide a channel capacity of more than 200 bits/s/Hz at a signal-to-noise power ratio (SNR) of 30 dB over the whole azimuth, which is equivalent to 20 Gbps for a bandwidth of 100 MHz. This remarkably high channel capacity is shown to be due to two significant factors; the improved directivity created by the optimum in-phase excitation and the low correlation between the subarrays due to the orthogonal alignment of the array with respect to the incident waves. Over-the-air (OTA) experiments confirm the increase in channel capacity; the proposed antenna can maintain a constant transmission rate over all azimuth angles.

A novel method for characterization of Ultra Low Viscosity NCF layers using TCB for 3D Assembly

Abstract For die to wafer bonding of high-density interconnects and fine pitch microbumps developing and characterizing suitable underfill materials are required. In general, underfill serve to fill the spaces in-between microbumps for protection and reliability. Among the different types of underfill, Non-Conductive Film (NCF) has the advantages of fillet and volume control, and a built-in flux to aid wetting. However, challenges arise for thin dies and microbumps with fine pitches on film lamination, voiding, transparency, filler percentage, dicing compatibility and most importantly, deformation behavior and possibility to improve solder joint wetting. In a Die-to-Wafer D2W stacking with a Sn solder bump interconnect to Cu UBM, concern is high on the Cu pad oxidation due to the repeated TCB cycles that accelerate oxidation on neighboring dies. Process mitigation is needed to help reducing the oxidation. But even so, an NCF must have good embedded flux activation. Another main factor for an NCF to have efficient TCB process with good solder joint wetting, is the NCF deformation quality in which is a function of its viscosity. This parameter has direct impact on the deformation of solder bumps. High viscosity NCF would be difficult to deform, thus preventing solder contact to pad during TCB reflow temperature. High bond force is required and could lead to reduced alignment accuracy. Filler entrapment is also a subsequent concern for high filler loading, high viscosity NCF. For a low viscous NCF, careful attention in process characterization is needed in TCB with low bond force. Solder joint wetting is a problem with excessive squeeze-out due to fast and instantaneous deformation. With low viscosity, not only the bond force applied should be low, but the deformation behavior should also be understood to enable an effective NCF. We seek to demonstrate in this paper a creative methodology for Non-Conductive Film (NCF) material characterization, considering the factors of NCF viscosity, deformation, and solder squeeze-out. Characterizing NCF viscosity at fast TCB profiles is challenging considering deformation behavior of both the NCF itself and the solder bumps that shaped the solder squeeze-out and wetting. Furthermore, in this paper we use TCB tool position tracking to define the deformation curve of NCF film as a function of temperature and time at very fast profile of TCB. We use material viscosity curve as reference in relation to the actual deformation, and predict dynamic deformation based on Reynold’s equation within TCB profile duration. The experiments were performed with different heating ramp rates at target above Sn reflow of ~250C interface temperature. The deformation analysis is not limited to thin film sandwiched between parallel plates. Deformation test was performed on chips with and without microbumps and with rigid flat glass surface and its combinations. Deformation of underfill is recorded in the readout of TCB tool. As validation, we applied the optimized TCB process (force, temperature, and ramp rate) on a test vehicle with 20 and 40um pitch daisy chains and obtained close to 95% electrical yield with good joint and IMC formation. The cross-section SEM images show good wetting, revealing good activation of built-in flux when the optimized TCB profile was used.

Structure and mechanism of B-family DNA polymerase ζ specialized for translesion DNA synthesis.

DNA polymerase ζ (Polζ) belongs to the same B-family as high-fidelity replicative polymerases, and yet is specialized for the extension reaction in translesion DNA synthesis (TLS). Despite its importance in TLS, the structure of Polζ is unknown. We present cryo-EM structures of S.cerevisiae Polζ holoenzyme in the act of DNA synthesis (3.1Å) and without DNA (4.1Å). Polζ displays a pentameric ring-like architecture, with catalytic Rev3 and accessory Pol31, Pol32 and two Rev7 subunits forming an uninterrupted daisy chain of protein-protein interactions. We also uncover the features that impose high fidelity during the nucleotide incorporation step and those that accommodate mismatches and lesions during the extension reaction. Collectively, we decrypt the molecular underpinnings of Polζ’s role in TLS and provide a framework for new cancer therapeutics.

Hetero type III‐B rotaxane dendrimers

AbstractType III‐B rotaxane dendrimer is a member of the rotaxane dendrimer family, but it is defined as dendritic polyrotaxane, branched through rings. Such rotaxane dendrimers have been synthesized through versatile copper‐catalyzed azide‐alkyne cycloaddition reactions. In order to incorporate more functionalities into type III‐B rotaxane dendrimers, three different potential functionalities—azobenzene toward light switch, daisy chain toward higher degree of contraction, and extension and cyclobis (paraquat‐p‐phenylene) (CBPQT) toward redox chemistry—were combined into the original design of type III‐B rotaxane dendrimers. Two azo‐based G1/G2 and four new G1 and G2 hetero type III‐B rotaxane dendrimers were synthesized and characterized by 1H NMR spectroscopy and electrospray ionization mass spectrometry.

The Cybernetic Victorians

The Cybernetic Victorians

Eigendecomposition of a digital iterative decentralised interleaving for multicellular converters

The decentralised control of multicellular converters is an alternative to the usual control techniques. Multicellular converters use interleaved carriers to reduce filtering elements and potentially improve transient response. Decentralised interleaving techniques are scalable, avoid a complex interleaving controller for a high number of cells, and simplify reconfiguration cases like phase shading. Circular chain of communication (ring, or daisy chain) approaches have been proposed in the literature and implemented in concrete applications. However, the analytical study of the stability and dynamic response of this system involving several identical phase-delay local controllers connected in a dedicated communication chain with their close neighbours has not been conducted yet. This paper presents a behavioural discrete model for a digitally implemented decentralised interleaving device. The eigenvalue study gives the stability criterion and convergence speed to choose the appropriate parameters of the controllers. A modal decomposition technique dissociates the various types of differential interactions to observe their respective time response. Simulation results demonstrate that the system is unconditionally stable when all differential modes are properly damped. An analytical expression for the final disposition of the carriers in steady state depending on the start-up condition is established. Lastly, a more precise operator to overcome the singular discontinuity of the model is presented and discussed. Experimental validation by FPGA implementation have been done for reconfiguration and start-up cases.

Active Metal Template Synthesis and Characterization of a Nanohoop [c2]Daisy Chain Rotaxane

Molecules and materials that demonstrate large amplitude responses to minor changes in their local environment play an important role in the development of new forms of nanotechnology. Molecular daisy chains are a type of a mechanically interlocked molecule that are particularly sensitive to such changes where, in the presence of certain stimuli, the molecular linkage enables muscle-like movement between a reduced-length contracted form and an increased-length expanded form. To date, all reported syntheses of molecular daisy chains are accomplished via passive-template methods, resulting in a majority of structures being switchable only through the addition of an exogenous stimuli such as metal ions or changes in pH. Here, we describe a new approach to these structural motifs that exploits a multi-component active-metal template synthesis to mechanically interlock two pi-rich nanohoop macrocycles into a molecular daisy chain which undergoes large conformational changes via thermal energy.

Low Temperature Copper-Copper Bonding of Non-Planarized Copper Pillar With Passivation

Low-thermal-budget (180 °C for 15 sec) Cu pillar to Cu pillar bonding with Pd passivation under the atmosphere is developed without any planarization pretreatment before the bonding process. The bonded structure is investigated with material analysis, electrical measurement and reliability test. The results show that although the Cu pillar has a high roughness surface due to the electroplating process with a high deposition rate, Cu atoms can still diffuse and connect through the passivation layer and perform the low-thermal-budget Cu pillar direct bonding. Low specific contact resistance and stable resistance of daisy chain shown in the reliability test reveal the excellent bonding quality and integrity. This Cu-Cu bonding method is therefore favorable for chip stacking technology development in 3D packaging domain.

Molecular-Pump-Enabled Synthesis of a Daisy Chain Polymer.

The assembly of a kinetically trapped daisy chain polymer under redox control has been achieved with a self-complementary monomer using an energy ratchet mechanism. The monomer is composed of a molecular pump at one end and a cyclobis(paraquat-p-phenylene) (CBPQT4+) ring at the other end. The pump and ring are linked together by a long collecting chain. When the monomer is reduced to its radical state, it self-assembles into a supramolecular daisy chain polymer on account of radical-pairing interactions. When all of the bipyridinium radical cations are quickly oxidized to dications, the CBPQT4+ rings are forced to thread onto the collecting chains, forming an out-of-equilibrium, kinetically trapped daisy chain polymer. This polymer can be switched reversibly back to the supramolecular polymer by reduction, followed by depolymerization to afford the monomer as a result of slow oxidation. This proof-of-concept investigation opens up opportunities for synthesizing mechanically interlocked polymers using molecular machines.

Autaptic Cultures: Methods and Applications.

Neurons typically form daisy chains of synaptic connections with other neurons, but they can also form synapses with themselves. Although such self-synapses, or autapses, are comparatively rare in vivo, they are surprisingly common in dissociated neuronal cultures. At first glance, autapses in culture seem like a mere curiosity. However, by providing a simple model system in which a single recording electrode gives simultaneous access to the pre- and postsynaptic compartments, autaptic cultures have proven to be invaluable in facilitating important and elegant experiments in the area of synaptic neuroscience. Here, I provide detailed protocols for preparing and recording from autaptic cultures (also called micro-island or microdot cultures). Variations on the basic procedure are presented, as well as practical tips for optimizing the outcomes. I also illustrate the utility of autaptic cultures by reviewing the types of experiments that have used them over the past three decades. These examples serve to highlight the power and elegance of this simple model system, and will hopefully inspire new experiments for the interrogation of synaptic function.

Thermosonic fine-pitch flipchip bonding of silicon chips on screen printed paper and PET substrates

In light of the necessity to introduce new techniques for hybrid integration of semiconductor dies on temperature and pressure-sensitive substrates, the feasibility of employing thermosonic flipchip bonding on screen printed paper and PET substrates was the objective of this study. Gold-bumped silicon test chips with internal daisy chain structures were bonded to the corresponding screen printed silver pads on PET and paper substrates by using both thermocompression and thermosonic techniques. The contact resistance of the interconnecting bumps and the die-shear strength of the resulting assembly were evaluated and the optimized bonding conditions on paper and PET substrates were identified. It was proposed that by the introduction of ultrasonic energy, diffusion bonding between the silver flakes and the gold bump were facilitated, whereas in the thermocompression bonding the mechanical interlocking was the main bonding mechanism. As a result, thermosonic flipchip bonding could be conducted in a much shorter time (milliseconds) and at lower bonding pressure (5 N) and temperature (100 °C). It was also found that for screen printed flexible substrates, thermosonic flipchip bonding at lower ultrasonic energy levels is preferential, while the possible bonding-induced damages to the pads and substrates can be avoided. Conclusively, It was proposed that thermosonic flip chip bonding can be regarded as a promising solution for fine-pitch system on paper (SOP) and system on PET (SOPE) technologies.

Daisy Chain Dendrimers: Integrated Mechanically Interlocked Molecules with Stimuli-Induced Dimension Modulation Feature.

The precise construction of the high-order mechanically interlocked molecules (MIMs) with well-defined topological arrangements of multiple mechanically interlocked units has been a great challenge. Herein, we present the first successful preparation of a new family of daisy chain dendrimers, in which the individual [c2]daisy chain rotaxane units serve as the branches of dendrimer skeleton. In particular, the third-generation daisy chain dendrimer with 21 [c2]daisy chain rotaxane moieties was realized, which might be among the most complicated discrete high-order MIMs comprised of multiple [c2]daisy chain rotaxane units. Interestingly, such unique topological arrangements of multiple stimuli-responsive [c2]daisy chain rotaxanes endowed the resultant daisy chain dendrimers controllable and reversible nanoscale dimension modulation through the collective and amplified extension/contraction of each [c2]daisy chain rotaxane branch upon the addition of acetate anions or DMSO molecules as external stimulus. Furthermore, on the basis of such an intriguing size switching feature of daisy chain dendrimers, dynamic composite polymer films were constructed through the incorporation of daisy chain dendrimers into polymer films, which could undergo fast, reversible, and controllable shape transformations when DMSO molecules were employed as stimulus. The successful merging of [c2]daisy chain rotaxanes and dendrimers described herein provides not only a brand-new type of high-order mechanically interlocked systems with well-defined topological arrangements of [c2]daisy chain rotaxanes, but also a successful and practical approach toward the construction of supramolecular dynamic materials.