Capillary Trace Research Articles

Robust nanofibrillated cellulose composite SERS substrate for capillary preconcentration and trace level detection of organic molecules

Preconcentration of organic analytes from an aqueous solution onto a substrate surface can significantly improve trace level analyte detection by Raman spectroscopy. Nanofibrillated cellulose (NFC)-based three dimensional (3D) substrates have great potential for this application since they can readily absorb water when exposed to an aqueous analyte solution while adsorbing organic molecules from the solution. However, the transport of organic analytes inside the substrate along with water, loss of mechanical robustness, and disintegration of the 3D structure in water limit the use of porous NFC substrates in aqueous environments. To overcome these deficiencies, a chemically crosslinked network of methacrylated carboxymethyl cellulose was incorporated into the NFC matrices, which improves the stability and robustness of the substrates in water. Application of a polydimethyl siloxane-based hydrophobic coating on four of the five analyte exposed surfaces further improves preconcentration efficiency by forcing the analyte solutions to pass through one hydrophilic surface only. Samples with a range of porosities were investigated to optimize sampling time, solution uptake volume, and substrate robustness in water. Using this substrate, parts-per-million detection sensitivity for organic probe molecules in aqueous solution was possible. Incorporation of silver nanoparticles within the substrates further enhanced substrate sensitivity to parts-per-trillion level detection of probe molecules, due to the Raman signal enhancement by surface enhanced Raman scattering (SERS) effect. A model is presented here which describes the linearity, saturation, and depletion of the SERS signal.

Development of an Ultralong Ultralow n-Loop for Wire Bonding

In this paper, we describe an innovative method to form an ultralong ultralow loop for wire bonding. A resister was used to form kinks and simplify the capillary trace, which yielded a loop-like “n”-shape with two kinks immediately above the first and second bonds that can support the entire long-span loop. A 3-D finite element model was developed to simulate the n-loop formation, and the loop profiles of an n-loop, M-loop, and standard loop were compared. In this paper, we show that this novel n-loop can almost halve the looping time compared to that for the M-loop; and the n-loop can avoid wire sag for a 5000- $\mu $ m-long span. Furthermore, the loop height and wire verticality near the second bond can be modified by regulating the horizontal and vertical positions of the resister.

P059 : META ANALYSIS OF SEQUENCE-BASED HLA TYPING APPROACHES

Sanger nucleotide traces are used in many laboratories and clinics to get accurate and high resolution HLA types, and Next-Generation Sequencing (NGS) reads are just starting to be used for this purpose. Having both capillary and NGS reads from HLA genes makes it possible to study these different approaches to HLA Typing. We present two different NGS HLA typing analysis methods and compare their results to capillary trace based typing. Eight human samples, with amplicons covering HLA-A,B,C and HLA-DRB1 were analyzed. These amplicons were amplified and sequenced by Sanger capillary sequencing, Illumina MiSeq and IonTorrent instruments. The resulting NGS reads were typing by two different HLA typing algorithms. The first algorithm is a probability-based approach which distributes reads among allele candidates and selects the most likely ones using a comparison of coverage statistics. The second algorithm is a consensus-based approach that aims to deliver phased, positioned consensus sequences and then associate these with the alleles that are supported by the most reads from the provided sample data. Capillary reads can be ambiguous, and covering long genomic parts with Sanger traces can be difficult and impractical. However, Sanger traces are the longest available ones with high quality. Statistics based typing can produce reliable results, but can lose local information (i.e. important SNPs). In addition, phase ambiguities, reads from homologous regions and PCR cross-overs may render statistical typing less reliable. Consensus based typing is less sensitive to homologous or PCR cross-over reads, and can deliver long consensus sequence stretches. This makes possible to discover new alleles or extend existing incomplete ones. NGS brings the hope of covering whole genes, but to assign reads among homologous genes and similar alleles has its own challenges. Comparing the three typing methods reveals differences in dealing with phase ambiguity, novel allele handling and quality control. NGS makes it possible to fully resolve phase and obtain long consensus sequences.

Investigation of Complex Looping Process for Thermosonic Wire Bonding

Wire looping is a critical part of a modern wire bonder. A major concern in wire bonding is the loop profile and loop height consistency, particularly for complex loops with more than four kinks for 3-D packages. To understand the effects of various parameters on complex loop profiles, a 3-D finite element (FE) model is developed with LSDYNA. Experiments observation of the looping process is carried out using high speed camera to verify the FE model. This FE model is used for investigating the effect of material properties, wire tension force, and clamp action on loop profile. Experimental and simulation results show that a complex capillary trace is used for a complex loop, and six kinks are formed. The loop profile is mainly determined by the number of kinks, kink position and deformation. The upward stage of capillary trace is mainly used for forming kinks and shape the loop profile, the downward stage only slightly changes the loop profile. Larger tension force, open clamp, softer materials, and larger reverse motion parameter can reduce the loop height. A constant wire tension force and precise clamp action can improve the loop consistency.

Modeling and Experimental Study of the Kink Formation Process in Wire Bonding

Looping is a key technology for the modern wire bonder. A kink is a critical structure in a wire loop. In order to understand the kink formation mechanism, a 2-D dynamic finite element model is developed using ANSYS/LS-DYNA, in which the air tension force, friction between capillary and wire, and real capillary trace are considered. The simulated kink formation process was verified by an experiment. With this model, the strain distribution on a gold wire was calculated, and the effects of wire material properties and capillary trace parameters on the kink number, position, and loop profiles were studied. Simulation results show that a minute average plastic strain of 0.14 is needed to form a distinct kink in a wire. Similarly, an elastic core with an average plastic strain of less than 0.08 at the center of a kink provides stiffness and sag/sway resistance for loops. A kink is a wire segment with plastic deformation outside and an elastic core inside, and the number of kinks and their positions are mainly affected by the capillary trace. In contrast, wire material properties only slightly influence the kink properties. This paper may provide helpful insights into loop design for modern microelectronics packages.

Experimental and Modeling Studies of Looping Process for Wire Bonding

Looping is one of the key technologies for modern thermosonic wire bonders, and it has been affected by many interacting factors. In this study, the wire looping process was observed with a high-speed camera, and the evolution of wire profiles during looping and the capillary trace were obtained through experiments. A dynamic finite element (FE) model was developed to learn the details of the looping process, where real capillary geometry dimensions, capillary trace, diameter of bonded ball and the gold wire material were used, and the friction force and air tension force were considered. The simulated profiles were compared with those of the experiment. Using the verified FE model, the effects of material properties, capillary parameters, and capillary traces on the looping process were studied, and the relationships between the final profiles and parameters were discussed.

The Use of Computer Simulation in the Electronic Packaging Process

This paper deals with the use of the computer simulation for semiconductor chip attach investigation, where the wire bonding is the mostly used process. The main focus lays on the correct definition of the capillary trace, which is essential for creation of a good bond contact as for chip, as well for package or substrate pad. Several simulations for different shapes of loops were created and compared with real bonds, which were done based on the settings from the analysis.

Modeling of Deep Cavity Looping Process on 3-D Stacked Die Package

Three-dimensional (3-D) stacked die packaging can reduce cost and improve performance. It utilizes the oldest process, wire bonding, to connect chips with a large bond height difference (BHD) via deep cavity looping. This paper develops 3-D and 2-D finite element models of the process and validate them against experiments. The effects of the height difference between two bond points, reverse motion parameter, kink height parameter, and elliptic capillary traces on the process are studied. The simulations demonstrate that deep cavity looping produces greater deformation on kink II, a lower loop height, and more violent pulling on the wire than traditional looping. Optimized capillary trace parameters for traditional looping are not suitable for deep cavity looping; however, the trends in the effects of the parameters are the same. Elliptic capillary traces can change wire profiles significantly.

Effect of Capillary Trace on Dynamic Loop Profile Evolution in Thermosonic Wire Bonding

Thermosonic wire bonding remains the most commonly used interconnection technology in microelectronic packaging, and looping is an important aspect in modern wire bonders. To identify the loop formation mechanism, the effect of capillary trace on the standard wire looping process was studied. Dynamic looping processes with different capillary trace parameters and reverse motions of 4, 8, and 16 mil were recorded by a high-speed camera. The capillary trace and wire profile evolution were obtained from the looping videos using a digital image processing program, and the relationship between capillary trace and loop profiles was analyzed. A finite-element model was established to study the strain distribution on wire during looping. Experimental and simulation results show that the wire profile of the standard loop is mainly affected by capillary position and is not sensitive to capillary velocity. The upward capillary trace mainly affects the loop configuration, including the number, position, and deformation of kinks and the loop length. The downward capillary trace affects the stress states, loop height, kink deformation, and loop profiles. A kink is the wire with the largest local curvature, and it is a plastically deformed wire segment with little elastic core. The kink has two functions: 1) shaping the loop and 2) isolating the pulling force on the first bond and neck caused by capillary movement. This paper can be of great help in loop profile optimization in the industry and in academic research of loop dynamics.

Experiment study of dynamic looping process for thermosonic wire bonding

Looping is a complex dynamic process affected by many interacted factors, and is becoming more and more important in the state-of-the-art thermosonic wire bonding. To provide an insight view of loop mechanism, the looping process of standard loop was experimentally studied with a high resolution and high speed video camera. The capillary trace and loop profile evolution process were obtained from looping video with a digital image process program. A phenomenological description was used to understand the looping forming mechanism. The effect of capillary trace on loop profile was investigated, and the kinks forming mechanism were discussed. The spring back and kink up were detaily described. Experiment results show that loop profile was affected by kinks number, position on gold wire and deformation. Kinks were formed by reverse motion of capillary. From the geometry point of view, kink is the wire segment with the local maximum curvature. From the mechanical point of view, kink is the partly plastic deformed wire segment with elastic deformed core inside. This study may be useful for loop design in industry and for loop dynamic research in academic.