Automatic Wire Bonder Research Articles

Effect of Ceramic Capillary Parameters on Bonded Morphology and Strength.

The effects of the geometry parameters of a ceramic cleaver on the morphology of ball and second bonded points were studied using an automatic wire bonder, push pull tester, scanning electron microscope, ceramic capillary with different geometric parameters and φ25.4 μmAg-5Au bonding alloy wire, etc. The result shows that when the inner hole diameter (IHD) of the ceramic capillary is 1.3 times the diameter of the alloy wire (33 μm), the neck morphology of the ball bonded point (first bonded point) meet the requirements. The neck of the ball bonded point appeared to fracture when the IHD is 26 μm; The neck of the ball bonded point appeared as an irregular shape when the IHD is 41 μm. When the inner cutting angle diameter (ICAD) is 64 μm, the size of the mashed ball diameter (MBD) is qualified. When the ICAD is 51 μm, the MBD is too large and mashed ball overflows the pad. When the ICAD is 76 μm, the ball bonded point is too high. When the inner cutting bevel angle (ICBA) is 100°, the MBD size meets the requirements of the pad. When the ICBA was reduced to 70°, the ball bonded point is eccentric. When the ICBA was increased to 120°, the MBD is too large and is connected to the adjacent pad contact. The size of the fish tail of the second bonded point (second bonded point) changed in the same direction as the tip diameter (TD) changes. When the TD is 178 μm, the fish tail shape is regular and symmetrical. When the working face angle (WFA) is 8° and the outer circular radius (OCR) is equal to the diameter of the alloy wire (25.4 μm), the fish tail shape is regular. When the WFA is higher than 11° or the OCR is higher than 30 μm, the fish tail will appear as virtual welding, and when the WFA is less than 4°, the fish tail of the second bonded point will break due to thinning. When the OCR is less than 20 μm, the fish tail of the second bonded point is too long and causes a short circuit.

Wire bonded 3D coils render air core microtransformers competitive

We present a novel wafer-level fabrication method for 3D solenoidal microtransformers using an automatic wire bonder for chip-scale, very high frequency regime applications. Using standard microelectromechanical systems fabrication processes for the manufacturing of supporting structures, together with ultra-fast wire bonding for the fabrication of solenoids, enables the flexible and repeatable fabrication, at high throughput, of high performance air core microtransformers. The primary and secondary solenoids are wound one on top of the other in the lateral direction, using a 25 µm thick insulated wire. Besides commonly available gold wire, we also introduce insulated copper wire to our coil winding process. The influence of copper on the transformer properties is explored and compared to gold. A simulation model based on the solenoids’ wire bonding trajectories has been defined using the FastHenry software to accurately predict and optimize the transformer's inductive properties. The transformer chips are encapsulated in polydimethylsiloxane in order to protect the coils from environmental influences and mechanical damage. Meanwhile, the effect of the increase in the internal capacitance of the chips as a result of the encapsulation is analyzed. A fabricated transformer with 20 windings in both the primary and the secondary coils, and a footprint of 1 mm2, yields an inductance of 490 nH, a maximum efficiency of 68%, and a coupling factor of 94%. The repeatability of the coil winding process was investigated by comparing the data of 25 identically processed devices. Finally, the microtransformers are benchmarked to underline the potential of the technology in rendering air core transformers competitive.

Multipurpose Wire Bonding – Bumps, Wires, Combination Interconnects, and Operation Efficiency

Today's multipurpose wire bonding machines are required to deliver a combination of wires, bumps, and specialty interconnects for RF, automotive, and optical markets with odd-form factor parts. These market production requirements are generally lower volume with a higher mix of products compared to typical high-volume semiconductor packaging of memory and logic. These markets also require multipurpose wire bonders to accommodate large work area, deep access, and a complex mix of bond surfaces, wire shapes, and bumps. The number of components in a package can vary from one with a few wires up to hundreds of components with thousands of wires. Programming methods, process development, traceability, and rework are different for customers using this class of bonder. A survey of customer application cases shows the range of capabilities available to packaging engineers. The four primary cases presented highlight the range of applications that can be handled for odd-form factor packages and specific areas of focus to maximize productivity for these classes of products.Case 1: Ball Bump Size and Shape Examples: acheiving 119μm down to 44μm bonded ball diameters and range of shapes.Case 2: Ambient Wire Bonding to a 6″ Tall Package: demonstrating allowable bonding volume and tooling flexibility plus the ability to bond Au with substrates at ambient temperature.Case 3: Batch Load Tray (Mechanical and Vacuum Clamping): allowing quick change over for radically different sized packages.Case 4: Complex High Part Count Packages: supporting alternate parts and alternate bonding wires, stand-off stitch, and security bonds require special features for programming and navigation methods to allow easy creation and navigation of complex programs for maximum productivity. Breakdown of timing and efficiency is provided showing programming efficiencies of 2X or better. These cases will help packaging engineers extrapolate to their own cases and show how a multipurpose automatic wire bonder can be an effective way of automating or semi automating these manually or automatically presented packages for higher throughput, higher quality and consistency, and less labor usage for lower cost.

Microtransformer-Based Isolated Signal and Power Transmission

Based on an automatic backend wire bonder as a coil winding machine, microtransformers are produced and their feasibility evaluated for isolated signal and power transmission. Automatic wire bonders allow to precisely shape 25-μm diameter gold wire around prefabricated cores and yokes at high speed. Former reports of wire bonded microcoils treated individual solenoids with low mutual inductance, whereas in this study transformers with strongly coupled microsolenoids are presented. The process is fully compatible with standard microelectronic manufacturing and, therefore, enables the direct integration of transformers into a given electronic circuit, either on-chip or on a printed circuit board, without the need for subsequent mounting steps. Unlike typical integrated planar transformers with known disadvantages concerning their electric properties, wire bonding allows the production, for example, of perfectly 3-D solenoidal transformer designs. The microtransformers are evaluated using a custom digital signal isolator system for isolation voltages of up to 5 kV. The microtransformers can also be used in an isolated dc-dc power converter to transmit energy.

Modeling of a Direct-Drive Table for Automatic Wire Bonder

This paper presents the modeling of a high-accuracy and high-acceleration table used for automatic wire bonder. The table is directly driven by linear voice coil motor (LVCM), and thus the mass and inertia of the motion system are significantly reduced by using a novel flexible decoupling mechanism based on flexure hinges and preloaded spring. The decoupling principle of the mechanism was introduced, and the electromechanical coupled mathematical model of Y-axis table was evaluated according to the dynamics of a mechanical mass-spring-damp system and LVCM. The model of Y-axis table was then identified with the aid of a Laser Interferometer and data acquirement card. Model validation experiments were carried out, and the results show that the model has sufficient accuracy when used to predict the performances of the real-world system under new conditions, and meanwhile it also can provide important information for the control of Y-axis table.

Characterization of a 3D MEMS fabricated micro-solenoid at 9.4 T

We present for the first time a complete characterization of a micro-solenoid for high resolution MR imaging of mass- and volume-limited samples based on three-dimensional B0, B1 per unit current (B1unit) and SNR maps. The micro-solenoids are fabricated using a fully micro-electromechanical systems (MEMS) compatible process in conjunction with an automatic wire-bonder. We present 15μm isotropic resolution 3D B0 maps performed using the phase difference method. The resulting B0 variation in the range of [−0.07ppm to −0.157ppm] around the coil center, compares favorably with the 0.5ppm limit accepted for MR microscopy. 3D B1unit maps of 40μm isotropic voxel size were acquired according to the extended multi flip angle (ExMFA) method. The results demonstrate that the characterized microcoil provides a high and uniform sensitivity distribution around its center (B1unit=3.4mT/A±3.86%) which is in agreement with the corresponding 1D theoretical data computed along the coil axis. The 3D SNR maps reveal a rather uniform signal distribution around the coil center with a mean value of 53.69±19%, in good agreement with the analytical 1D data along coil axis in the axial slice. Finally, we prove the microcoil capabilities for MR microscopy by imaging Eremosphaera viridis cells with 18μm isotropic resolution.

Effect of Ca Content on Mechanical Properties of 4N Gold Wire for Quad Flat Nolead (QFN) Stacked Die Package

This paper discusses the effect of two similar gold wire (wire A and wire B) used mainly as a wire bonding material for Quad Flat Nolead (QFN) package. Both wires with diameter of 25.4 μm were bonded using automatic wire bonder by maintaining the temperature at 200°C. The effect of trace elements on the mechanical properties of 4N gold wire has not been widely investigated for some years despite the important of wire-bonding and the move towards fine pitch applications. Due to the element analysis, atomic percentage of Ca in wire B is higher than wire A. Pull strength increase with the increasing of the trace element. The higher pull strength of wire B could improve the yield strength, elastic modulus and recrytallization temperature.

A fully MEMS-compatible process for 3D high aspect ratio micro coils obtained with an automatic wire bonder

We report the fabrication of 3D micro coils made with an automatic wire bonder. Using standard MEMS processes such as spin coating and UV lithography on silicon and Pyrex® wafers results in high aspect ratio SU-8 posts with diameters down to 100 µm that serve as mechanical stabilization yokes for the coils. The wire bonder is employed to wind 25 µm insulated gold wire around the posts in an arbitrary (e.g. solenoidal) path, yielding arrays of micro coils. Each micro coil is bonded directly on-chip, so that loose wire ends are avoided and, compared to other winding methods, coil re-soldering is unnecessary. The manufacturing time for a single coil is about 200 ms, and although the process is serial, it is batch fabrication compatible due to the high throughput of the machine. Despite the speed of manufacture we obtain high manufacturing precision and reliability. The micro air-core solenoids show an RF quality factor of over 50 when tested at 400 MHz. We present a flexible coil making method where the number of windings is only limited by the post height. The coil diameter is restricted by limits defined by lithography and the mechanical strength of the posts. Based on this technique we present coils ranging from 100 µm diameter and 1 winding up to 1000 µm diameter and 20 windings.

High aspect ratio PMMA posts and characterization method for micro coils manufactured with an automatic wire bonder

We present the development of high aspect ratio PMMA posts manufactured in deep X-ray lithography technology. The posts serve as support structures for micro coil windings. The coils are wound around these cores by an automatic wire bonder, and they are fully compatible with MEMS processes. Posts with outer diameters down to 100 μm and minimal sidewall thicknesses of 20 μm have an aspect ratio of up 38, leading to single-layer coils with more than 20 windings. With a flexible software, the winding number is only limited by the post height. We introduce a specially designed structure to determine the forces caused by the winding process. These measured forces are confirmed by shear test data. Electrical measurements show a quality factor of over 50.

Iterative optimization of tail breaking force of 1 mil wire thermosonic ball bonding processes and the influence of plasma cleaning

An online tail breaking force measurement method is developed with a proximity sensor between wire clamp and horn. The wire under the tensile load measures about 1.5cm extending from the bond location to the wire clamp. To increase the sensitivity, the bondhead speed is reduced to 2mm/s during breaking the tail bond. It takes roughly 10ms to break the tail bond. The force resolution of the method is estimated to be better than 5.2mN. An automatic wire bonder used to continuously bond up to 80-wire loops while recording the on-line proximity signals. All wires are directed perpendicular to the ultrasound direction. The tail breaking force for each bond is evaluated from the signal and shown automatically on the bonder within 2min after bonding.Results are obtained for a typical Au wire and a typical Cu wire bonding process. Both wires are 25mm in diameter and bonded on Ag plated diepads of standard leadframes at 220°C. An average Cu tail breaking force of higher than 50mN is obtained if the leadframe is plasma cleaned before the bonding with 100% Ar for 5min. This result is comparable to that obtained with Au wire. The standard deviation of the Cu tail breaking force is about twice that obtained with Au wire. The tail breaking force depends on the bonding parameters, metallization variation, and cleanliness of the bond pad. The cleanliness of the bonding pad is more important with Cu wire than with Au wire.

Automated visual inspection system for bonded IC wires

Abstract This paper discusses an automated visual inspection system for bonded IC wires. The system uses high-contrast image capture, an algorithm for accurately measuring the bonding balls, and a wire inspection algorithm. The high contrast image capture system consists of a wide-area camera and two types of lighting optics, one for ball sensing and the other for wire sensing. The algorithm for measuring the bonding balls is based on morphological techniques, and the wire inspection algorithm is based on a border following algorithm. The automated inspection system measures ball diameters to with in ± μ m accuracy, which corresponds to half a pixel of the captured picture. The system takes 0·2 s to inspect a wire and ball. Combining the inspection system with an automatic wire bonder enables a fully automatic bonding system to be constructed.

Automated visual inspection system for bonded IC wires

This paper discusses an automated visual inspection system for bonded IC wires. The system uses high-contrast image capture, an algorithm for accurately measuring the bonding balls, and a wire inspection algorithm. The high contrast image capture system consists of a wide-area camera and two types of lighting optics, one for ball sensing and the other for wire sensing. The algorithm for measuring the bonding balls is based on morphological techniques, and the wire inspection algorithm is based on a border following algorithm. The automated inspection system measures ball diameters to with in ± μ m accuracy, which corresponds to half a pixel of the captured picture. The system takes 0·2 s to inspect a wire and ball. Combining the inspection system with an automatic wire bonder enables a fully automatic bonding system to be constructed.