Optimizing the thermalsonic bonding process for thick film hybrid IC by the Taguchi Method

In the manufacturing process of IC, the factors that affect the strength of the wire are categorized as control and noncontrol (or termed noise factors). Nine control factors and three noise factors are considered to have effects on the thermalsonic bonding process for thick film hybric IC. The quality control technique named Taguchi Method is employed to find the optimal manufacturing process. While determining the optimal conditions, we use Taguchi's SN ratio (signal to noise ratio) to proceed the analysis. Two types of wire bonding: conductor to conductor and chip to conductor, are investigated and their optimal conditions are derived through the method. Finally, confirmation results based on the optimal conditions are demonstrated. The conditions are then suggested for mass production.     

铜线封装工艺技术和可靠性研究

铜线键合工艺作为当前框架类集成电路封装降低成本的重要措施,但是,铜线带来的相关工艺调整和可靠性认证,以及客户的认证都是当前需要产品公司考虑的问题。本文对于铜线键合工艺和可靠性从多方面进行了研究,对该研究的发展具有借鉴和推广价值。     

Optimizing the controller IC for micro HDD process based on Taguchi methods

The future trend of controller integrated circuit (IC) for micro hard disk driver (HDD) is to be lighter, thinner, shorter and smaller. The storage capacity and unit cost of micro HDD is lower than of flash memory card. The optimal packaging manufacturing process for driver IC for micro HDD is Chip Scale Package (CSP). However, the production and assemble process for CSP is much more difficult. Especially, the warpage problem on modeling results in non-conforming products. This research is to discover the optimal production levels for control factors based on the orthogonal array in Tachugi method. The product size used in the study is the driver IC package overall height less than 0.65 mm for micro HDD with CSP manufacturing process.     

Optimizing the fine-pitch copper wire bonding process with multiple quality characteristics using a grey-fuzzy Taguchi method

This paper presents an application of the grey-fuzzy Taguchi method to derive the optimum parameters for the fine-pitch copper (Cu) wire bonding process with multiple quality characteristics. Cu wire has become an important replacement material without the high manufacturing cost of gold for wire bonding processes in integrated circuit (IC) packaging. However, it sometimes fails to take advantage of the Cu material properties due to an insufficient understanding of the relationship between process inputs and outputs of the fine-pitch Cu wire bonding. To assure the accomplishment of cost savings without losing yield, the proposed grey-fuzzy Taguchi method is utilized with an L18 (2¹ × 3⁷) experimental design and grey relational analysis (GRA) to evaluate the degree of relationship between process inputs and responses, followed by transforming the multiple quality characteristics into a single performance index using a fuzzy inference system. Finally, the process parameters are optimized by the Taguchi method. The proposed optimization methodology provides superior optimization performance compared to the grey-Taguchi method and the parameter setting used in mass production in terms of the conformation experiments.     

IC键合铜线材料的显微力学性能研究

用于IC(集成电路)的键合铜线材料具有低成本、优良的导电和导热性等优点,但其高硬度容易对铝垫和芯片造成损伤,因此对其硬度的测量是一项关键技术。纳米压痕测量技术可以方便、准确地测量铜线材料的显微硬度值和其他力学性能参数。描述了纳米压痕测量技术的原理以及对铜线材料样品进行纳米压痕测量的参数选择,进行了测量试验。结果表明,原始铜线、FAB(金属熔球)、焊点的平均硬度分别为1.46,1.51和1.65GPa,为键合铜线材料的选择和键合工艺参数的优化提供了依据。     

Optimal design for a ball grid array wire bonding process using aneuro-genetic approach

This study presents an integrated method in which neural networks, genetic algorithms, and exponential desirability functions are used to optimize the ball grid array (BGA) wire bonding process. As widely anticipated, the BGA package will become the fastest-growing semiconductor package and push integrated circuit (IC) packaging to higher level of compactness and density. However, wire bonding in BGA is difficult owing to its high input/output (I/O) count, fine pitch wire bonds, and long wire lengths. This study addresses two fundamental issues in the semiconductor assembly facility on its quest toward a defect-free manufacturing environment. First, the problem of exploring the nonlinear multivariate relationship between parameters and responses and second, obtaining the optimum operation parameters with respect to each response in which the process should operate. The implementation for the proposed method was carried out in an IC assembly factory in Taiwan; results in this study demonstrate the practicability of the proposed approach     

Overview of wire bonding using copper wire or insulated wire

Wire bonding using copper or insulated wire leads to many advantages and new challenges. Research is intensively performed worldwide, leading to many new findings and solutions. This article reviews recent advances in wire bonding using copper wire or insulated wire for advanced microelectronics packaging. Journal articles, conference articles and patents published or issued recently are reviewed. The benefits and problems/challenges related to wire bonding using copper wire or insulated wire such as wire open and short tail defects, poor bondability for stitch/wedge bonds, oxidation of Cu wire, and stiff wire on weak support structures, are briefly analyzed. A number of solutions to the problems and recent findings/developments related to wire bonding using copper wire or insulated wire are discussed. With the references provided, readers may explore more deeply by reading the original articles and patent documents.     

Optimum conditions of molding VFBGA chips with very minimal gold wire damage using the Taguchi methods

This study employed the analysis of mean (ANOM) of the Taguchi methods to determine the optimal conditions for the very fine pitch ball grid array (VFBGA) transfer molding of a microelectronic assembly with the aim of minimizing wire damage. The optimal conditions include: (1) a substrate preheat temperature of 177 °C, (2) two-step mold clamping in which the clamping force in the first-stage is 9 t and the full clamping force in the second-stage is 28 t, (3) a mold temperature of 180 °C, and (4) a total of 20 vacuum holes in the bottom mold. Experiments to confirm the efficacy of the optimal conditions indicated that the average percentage of samples with wire damage was reduced to 0.02%. The percentage contribution of each controllable factor in the current investigation was also determined via ANOVA (analysis of variance) of the Taguchi methods. Among the four controllable factors, the number of vacuum holes in the bottom mold proved to be the one with the greatest influence on wire damage with a percentage contribution of 71.25%. We also describe the mechanism underlying wire damage associated with vacuum holes. Our findings led us to modify the existing VFBGA process, wherein the maximum defect percentage per sub-lot was decreased from 1.31% to 0.12%, and the average defect percentage in 14 sub-lots was decreased from 1.10% to 0.03%.     

毫米波电路引线楔焊质量智能预测技术研究

针对毫米波电路引线楔形焊接工艺优化难题,提出将一种带惩罚函数项的改进BP (Back Propagation,反向传播)神经网络算法用于引线楔形焊接质量智能预测中.通过试验分析了影响楔形焊接质量的关键工艺参数,提取了楔形焊接质量评价指标,基于改进的BP神经网络,建立了引线楔焊质量智能预测模型.研究结果表明,所提出的改进...     

Finite element contact analysis on a horn-holder assembly for wire bonding

The joint structure of a transducer horn-holder assembly for a wire bonder was examined through finite element contact analysis. Three-dimensional modeling and analysis was carried out to survey the internal physics of this structure and to verify the accuracy of a proposed computation relative to measurement. After validation, a two-dimensional model was built to conduct parametric studies and improve the efficiency and speed of the computation. Several factors such as boundary conditions, modeling boundary, and mesh density, were considered to obtain consistency with the three-dimensional analysis. Arc angle and the position of each holder boss were chosen as design parameters. A designed computation approach was applied for efficiency in computation. As a result, a guideline for holder boss design was suggested, and the main factors and their influence on stress concentration in the transducer horn were surveyed.     

Platinum wire wedge bonding: A new IC and microsensor interconnect

Ultrasonic ball or wedge bonding of Au or Al has been the traditional method for mak-ing electrical interconnects between die and chip header for most Integrated Circuit (IC) and microsensor devices. Electrical interconnections made from these materials may, however, be unsuitable for some device applications. Some microsensors (e.g., oxygen exhaust gas sensors) can be subject to temperatures as high as 900° C in both oxidizing and reducing atmospheres, conditions for which the properties of Au or Al are unsuit-able. In this report we describe a new means of making electrical connections between die and chip header. Interconnects are made by using a conventional wire bonder to ultrasonically wedge bond 0.032 mm diameter Pt wires to both Pt and Al thin films. Interconnects made in this manner are remarkably strong, as compared with Au wire bonds, with pull strengths of ∼13 g. Electrical measurements show contact resistances of ≲0.05 Ω. Annealing tests show that bonds made to thin metal films of Pt on Ti on sapphire show no appreciable signs of electrical or mechanical degradation after an-neals at 900° C for 1 h in pure oxygen.     

Development of a thermosonic wire-bonding process for gold wire bonding to copper pads using argon shielding

To improve the bondability and ensure the reliability of Au/Cu ball bonds of the thermosonic (TS) wire-bonding process, an argon-shielding atmosphere was applied to prevent the copper pad from oxidizing. With argon shielding in the TS wire-bonding process, 100% gold wire attached on a copper pad can be achieved at the bonding temperature of 180°C and above. The ball-shear and wire-pull forces far exceed the minimum requirements specified in the related industrial codes. In a suitable range of bonding parameters, increasing bonding parameters resulted in greater bonding strength. However, if bonding parameters exceed the suitable range, the bonding strength is deteriorated. The reliability of the high-temperature storage (HTS) test for Au/Cu ball bonds was verified in this study. The bonding strength of Au/Cu ball bonds increases slightly with prolonged storage duration because of diffusion between the gold ball and copper pad during the HTS test. As a whole, argon shielding is a successful way to ensure the Au/Cu ball bond in the TS wire-bonding process applied for packaging of chips with copper interconnects.     

The development of Cu bonding wire with oxidation-resistant metal coating

Although Cu bonding wire excels over Au bonding wire in some respects such as production costs, it has not been widely used because of its poor bondability at second bonds due to surface oxidation. We conceived an idea of electroplating oxidation-resistant metal on the Cu bonding wire to prevent the surface oxidation. The electroplating of Au, Ag, Pd, and Ni over Cu bonding wire all increased bond strengths as expected, but it caused problematic ball shapes except Pd-plated Cu bonding wire. The wire could produce the same ball shape as that of Au bonding wire. It was also proved to have excellent bondability sufficient to replace Au bonding wire. That is, it excelled in bond strengths, defective bonding ratio, and wideness of "Parameter Windows". It also showed the same stability as Au bonding wire in reliability tests, while bonds of Cu bonding wire were deteriorated in a few of the tests. In short, the Pd-plated Cu bonding wire can realize excellent bonding similar to Au bonding wire, while having much lower production costs.     

Corrosion inhibition by self-assembled monolayers for enhanced wire bonding on Cu surfaces

Corrosion inhibition by thiol-derived self-assembled monolayers (SAMs) on Cu surfaces has been characterised using contact angle measurements, X-ray photoelectron spectroscopy, voltammetry, and thermal desorption spectroscopy. Factors influencing SAM formation were investigated to develop an optimised wafer level process. XPS confirms the formation of thiolate species bonded to a mixed metallic Cu and cuprous oxide surface. Stability studies as a function of temperature and electrochemical potential demonstrate promising passivation properties. The feasibility of exploiting SAMs in microelectronics applications was demonstrated by the enhancement of Cu wire bonding onto Cu bond pads.     

Two capillary solutions for ultra-fine-pitch wire bonding and insulated wire bonding

In this article, the new challenges and requirements in wire bonding are discussed, the problems in ultra-fine-pitch wire bonding and insulated wire bonding are analyzed, and then two capillary solutions to the problems are presented. Actual bonding experiments using the new capillaries were carried out and the results were satisfactory. Compared to the standard design, a new capillary design has a larger inner chamfer, a larger chamfer diameter and a smaller chamfer angle. This new capillary design has proved to improve the ball bondability and smaller ball size control for ultra-fine pitch wire bonding. A unique surface characteristic on the capillary tip surface has also been derived. The new finishing process developed creates a new surface morphology, which has relatively deep lines with no fixed directions. Compared to the standard capillary, this capillary has less slipping between the wire and the capillary tip surface in contact, and provides better coupling effect between them and better ultrasonic energy transfer. This capillary has been used to effectively improve the bondability of the stitch bonds for insulated wire bonding.     

GaAs晶体的扩散键合工艺优化

对影响准相位匹配GaAs晶体的键合质量的因素进行了研究,通过对GaAs面损耗、界面损耗和体损耗的分析,优化了键合工艺和参数。通过在光胶前加入酸洗过程,去除GaAs晶片的表面氧化物,并采用X射线光电子能谱仪(XPS)确认了氧化物去除情况,在无氧环境下进行后续过程;在热处理过程中,通过对GaAs电特性、光学透过率及微结构的分析,调整键合的温度和压力参数,制备了16层的准相位匹配GaAs晶体。当键合温度为550 ℃、键合压力为0.25 kgf/mm2时,获得低于0.18 %的单层界面损耗。     

Adaptive fuzzy process control of integrated circuit wire bonding

One step in the assembly of integrated circuits is wire bonding, requiring expert knowledge to optimize critical process characteristics. This paper describes a fuzzy logic controller which sets parameters for the wire bonding process for gold ball wire bonds, specifically controlling bonded ball diameter and shear strength density. While the focus is on control of ball bonds, the method is general and may be applied to other bonding methods with minor modifications. The design of the fuzzy engine and the development of rules based on both operator experience and textual sources are discussed. An adaptation technique is developed to tune the controller's membership functions based on the measured results of the process. The controller has been tested on actual devices in an industrial setting; results show improved process control in terms of consistency and reduced operator adjustment     

More uniform Pd distribution in free-air balls of Pd-coated Cu bonding wire using movable flame-off electrode

The currently high price of gold wire has led to the development of bonding wire made from palladium-coated-copper as a lower cost alternative. Increasing the uniformity of the Pd distribution in free-air balls, formed by melting the wire end with an electric spark, is of interest as it can influence the uniformity of process and reliability. To study this Pd distribution, free-air balls are made using four distinct electrical flame-off (spark) processes with short and long spark times from wire bonders with fixed and movable electrodes. Elemental analysis of the free-air ball surfaces reveal a higher Pd concentration on the movable electrode free-air balls than on the fixed electrode free-air balls. Elemental analysis of cross-sections show that the Pd distribution in free-air balls made with a fixed electrode has Pd trails flowing from the neck into the Cu ball center. Furthermore, micro- and nano-voids are observed to follow the Pd trails. In contrast, free-air balls made with a movable electrode exhibit less severe voiding and retain a uniform, thin Pd layer along the surface up to the tip of the free-air ball (shorter spark time). This can help to increase process consistency and reliability.     

EHF频段芯片引线键合与装配公差的仿真与分析

文章从工程角度出发,使用仿真软件分别对极高频(Extremely High Frequency,EHF)频段芯片的引线键合和装配公差进行了仿真分析,确定键合线的拱高、距离等参数,明确装配公差的合理范围,以便减小芯片级联时的射频损耗,并满足多个射频模块之间的一致性要求。