热超声倒装键合换能系统 多模态振动与有限元分析

研究了热超声倒装键合设备的核心执行机构——换能系统的动力学特性.利用激光多谱勒测振仪测试系统末端各方向的振动速度,发现系统以轴向振动为主,但受到其他非轴向振动的干扰.非轴向振动对芯片造成芯片倾斜、键合强度降低等负面影响.采用有限元方法对换能系统建模,仿真计算发现换能系统振动是各方向振动的耦合结果,且工作模态附近存在多种干扰模态.最后分析了系统多模态产生的根源并提出抑制方法.     

多向复合超声换能器有限元分析与试验

超声换能器是微电子封装技术的核心执行元件,为解决传统一维纵振超声换能器键合效率低、键合面不均匀及键合点不牢靠等问题,采用ANSYS仿真软件建立换能器有限元模型进行模态分析及谐响应分析,设计了一种可同时实现轴向纵振、水平弯振及竖直俯仰振动的40 kHz多向复合夹心压电式超声换能器。其中,压电部分由整圆环和可单独激励的1/4圆环陶瓷片组成。利用阻抗分析仪实物测试,得到换能器纵振、弯振及俯仰振动的阻抗 频率特性曲线。结果表明,测试值与仿真值基本一致,且结构性能参数均符合键合要求,验证了该结构的合理性。     

芯片键合换能系统中接触界面的影响分析

接触界面对超声能量传递与振动特性的影响是各类压电换能器的共性问题。在超声芯片封装领域,各子部分之间的接触界面是影响系统超声能量传递的强非线性因素,直接影响芯片与基板的键合质量。该文通过有限元法与激光多谱勒测振仪等技术,获得系统中接触界面对超声能量传递与振动特性的影响规律,发现不合理的接触界面会引发系统多模态与频率混叠效应、超声能量输出不稳定、系统迟滞响应等,导致键合强度下降、芯片与基板倾斜、键合效率下降等封装缺陷。研究结果对理解超声键合与系统设计具有指导意义。     

夹持环对换能系统振动模态影响的有限元分析

换能系统是热超声引线键合装备的核心部分,夹持环对系统起安装支撑的作用,其安装方式直接影响换能系统的能量传递与振动模态。利用有限元法分析了夹持环对换能系统振动模态的影响,结果表明,对夹持环未施加约束、施加z向约束时换能系统的夹持环会出现振动现象,而施加x向约束时,工作频率下的主振型完全不符合要求;改变夹持环的安装位置,对换能系统的节点位置及谐振频率都有一定的影响,实验测得在全约束情况下,换能系统的节点位置为58 mm,与分析结果一致;换能系统在工作频率附近包含有其他的振动模态,在键合过程中易被激发出来,由此消耗超声能量而降低芯片的键合质量,这些振动模态必须得到抑制。     

键合工具对超声换能器系统谐振频率的影响

建立了超声引线键合机换能器系统振动分析有限元模型,利用ANSYS软件分析了换能器系统与键合工具组成的纵-弯复合振动系统的振动特性。计算结果表明,键合工具的弯曲振动与换能器系统纵向振动存在耦合关系,劈刀长度增加50%将使换能器系统谐振频率下降5.6%;实验中测试了换能器系统的阻抗与导纳特性,发现当劈刀长度为16 mm时系统的阻抗匹配较为理想;换能器系统的谐振频率的实测值与有限元分析结果一致,最大误差为3.51%。     

Ultrasonic Bonding Using Anisotropic Conductive Films (ACFs) for Flip Chip Interconnection

In this paper, a novel anisotropic conductive film (ACF) flip chip bonding method using ultrasonic vibration for flip chip interconnection is demonstrated. The curing and bonding behaviors of ACFs by ultrasonic vibration were investigated using a 40-kHz ultrasonic bonder with longitudinal vibration. In situ temperature of the ACF layer during ultrasonic (U/S) bonding was measured to investigate the effects of substrate materials and substrate temperature. Curing of the ACFs by ultrasonic vibration was investigated by dynamic scanning calorimetry (DSC) analysis in comparison with isothermal curing. Die adhesion strength of U/S-bonded specimens was compared with that of thermo-compression (T/C) bonded specimens. The temperature of the ACF layer during U/S bonding was significantly affected by the type of substrate materials rather than by the substrate heating temperature. With room the temperature U/S bonding process, the temperature of the ACF layer increased up to 300degC within 2 s on FR-4 substrates and 250degC within 4 s on glass substrates. ACFs were fully cured within 3 s by ultrasonic vibration, because the ACF temperature exceeded 300degC within 3 s. Die adhesion strengths of U/S-bonded specimens were as high as those of T/C bonded specimens both on FR-4 and glass substrates. In summary, U/S bonding of ACF significantly reduces the ACF bonding times to several seconds, and also makes bonding possible at room temperature compared with T/C bonding which requires tens of seconds for bonding time and a bonding temperature of more than 180degC.     

热超声键合换能系统接触界面非线性振动研究

为了减小热超声键合换能系统的振动稳定性、提高键合强度,从超声波在热超声键合换能系统中的传播出发,建立了超声波在接触界面处传播的微观模型.研究表明,当静应力较小时,输出的超声波不完整,材料内部质点的有效振动较小;当静应力逐渐增大时,材料进入弹性变形阶段,输出的超声波波形与输入的超声波的波形一致,材料内部质点的有效振动最大;当静应力太大时,材料进入塑性变形区域,材料内部质点的有效振动减小.通过在芯片倒装键合实验台上实验,测量在不同压电陶瓷片预紧力下,变幅杆的振动速度和芯片的键合强度,证明了所提出模型的正确性.     

微生物诱变功率超声装置的研制

一定强度的超声波作用于微生物反应过程可缩短反应时间,改善生物反应条件,提高生物产品的质量和产量。该文介绍了超声波作用于微生物反应过程的基本原理,详细讨论了微生物诱变功率超声装置设计的基本方法,采用厚度振动模式的压电陶瓷圆盘换能器,并将换能器置于反应器表面,采用单片机、可控整流器和半桥逆变器等构成超声波发生器,并对超声输出功率进行反馈控制。文中对红曲霉菌进行了简单的超声诱变实验研究,结果表明,选择合适的超声频率和功率以及照射时间,该装置可显著提高微生物的产量。     

MOSFET器件引线键合技术

MOSFET器件由于高阻抗、低功耗等特点,在电脑电源、家用电器和自动控制系统等方面得到广泛应用。但由于其芯片结构的特殊性,在封装制造过程中容易受到静电、应力、环境条件等多种因素的影响。引线键合过程是影响封装成品率的关键工艺环节。引线键合是电子工程互连的重要方式,MOSFET器件通常采用超声键合的工艺进行引线互连。影响引线键合质量的因素较多,其中引线键合工艺、引线材料和设备维护是最重要的三个因素。通过实际生产过程的试验、分析和提炼,研究引线键合技术,总结了引线键合工艺、引线材料和设备维护三个方面的实践经验,为提升和稳定封装成品率提供参考。     

金丝楔形键合强度的影响规律分析

金丝楔形键合是一种通过超声振动和键合力协同作用来实现芯片与电路引出互连的技术。现今,此引线键合技术是微电子封装领域最重要、应用最广泛的技术之一。引线键合互连的质量是影响红外探测器组件可靠性和可信性的重要因素。基于红外探测器组件,对金丝楔形键合强度的多维影响因素进行探究。从键合焊盘质量和金丝楔焊焊点形貌对键合强度的影响入手,开展了超声功率、键合压力及键合时间对金丝楔形键合强度的影响研究。根据金丝楔焊原理及工艺过程,选取红外探测器组件进行强度影响规律试验及分析,指导实际金丝楔焊工艺,并对最佳工艺参数下的金丝键合拉力均匀性进行探究,验证了金丝楔形键合强度工艺一致性。     

Advanced process characterization for 125 kHz wire bonder ultrasonic transducers

A high frequency ultrasonic transducer for wire bonding is conceived, designed, prototyped, tested and industrially produced. The influence of each feature of the ultrasonic transducer design, such as constituent material, amplifier geometry, mounting flange, capillary fixing, on the wire bonding process results is clearly identified and carefully analyzed through thorough process tests. The assembly and aging characteristics of the transducers are measured and the scattering of the vibration properties in the mass production is statistically quantified by laser interferometer measurements and compared with that of conventional horns. The transducer is mounted on the wire bonder with a flange whose special geometry is calculated by means of FEM simulations and patented. This flange allows the mechanical stiffness of the coupling transducer-wire bonder to be dramatically increased and the parasitic mechanical dynamical vibrations at the horn tip to be significantly reduced. Process tests show that the reduction in mechanical vibrations obtained in this way allows a wire bonder scarcely capable normally to attain the 80 /spl mu/m fine pitch process, to perform easily the 60 /spl mu/m fine pitch process. A beneficial impact of the mechanical coupling horn-wire bonder on the process performance is ascertained. The use of titanium as horn material, characterized by a low thermal expansion coefficient, is proven by process tests to be effective in improving the placement accuracy of the wire bonder. The high vibration frequency of the transducer (125 kHz) is proven by process tests to be effective in improving the ball roundness and the fine pitch wire bonding capabilities of the wire bonder and in decreasing the minimum wire bonding temperature and the applied bond force. The new approach to characterize the process performance of new ultrasonic transducer designs is of general importance for wire bonding technology.     

基于ANSYS的压电陶瓷晶片PZT仿真分析

电力支柱瓷绝缘子超声波检测对预防和检测绝缘子裂纹和断裂起到重要作用,换能器是超声波检测的基础元件,而换能器的核心部件是压电陶瓷晶片,其性能直接影响到检测结果。该文研究针对有限元法和传统解析法在压电陶瓷晶片特性分析中的不足,采用ANSYS有限元分析软件对压电陶瓷锆钛酸铝(PZT)晶片进行特性分析,基于ANSYS的电-结构耦合场模型,对超声波换能器的矩形压电晶片进行静态、模态、谐响应和瞬态分析。通过模态分析和谐响应分析可得到晶片的一阶纵向振动和二阶弯曲振动的固有频率、振型及频率位移响应及影响因素等信息,研究结果对提高超声辐射功率及超声换能器的性能有一定的理论指导和工程应用价值。     

Real-Time Quality Evaluation of Wire Bonding Using Input Impedance

Input impedance characterizes the dynamic property of a linear system. A few existing technologies thus exploit input electrical impedance of wire bonders as the signature to monitor ultrasonic wire bonding processes. However, the waveforms of "impedance" in these technologies are evaluated only approximately. To overcome the shortcoming, we propose a method to detect the true waveforms of both the real and imaginary part of the input impedance. In the method, the voltage and current at the input port of a wire bonder are probed and processed to obtain impedance via Hilbert Transform. Because dynamics of a bonding process represented by these waveforms is fully responsible for the resulted bonding quality, a quality evaluation system based on pattern recognition of these waveforms is further proposed. An artificial neural network using back propagation as training scheme learns from a set of training data to correlate a few features of the impedance waveforms with the bonding strength of the corresponding bond identified by shearing tests. Through a set of verification data, the built system is validated to be capable of evaluating bonding quality right after a bonding process. The proposed method is not only in situ and real-time, but also sensorless, which means that the system is easy to be implemented without interfering operation     

基于面内弯曲模态直线超声电机振子研究

提出了一种矩形振子面内弯曲模态直线超声电机,分析了振子面内弯曲模态的激发原理及电机的驱动机理。运用动力学分析法,建立了矩形振子的动力学模型,分析讨论了振子结构参数及弹性体材料对振子模态频率的影响,并进行了相应的扫频实验研究。动力学计算与实验测试结果比较表明,在自由边界条件下,理论分析结果与实测结果基本一致,研究结果为利用面内模态直线超声电机的设计提供了依据。     

Power and Interface Features of Thermosonic Flip-Chip Bonding

Driving voltage and current signals of piezoceramic transducer were measured directly by using digital storage oscilloscope, and interface microcharacteristics of the specimens of flip-chip bonding were inspected by using a transmission electron microscope. Results show such a trend that power curves of badly bonding were much lower than that of hard bonding, and indicated a monitoring system of ultrasonic bonding reliability. The acceleration of ultrasonic vibration was about several ten thousand times as acceleration of gravity, which activates dislocations inside the metal crystalline lattice which act as the fast diffusion channels. Dislocation diffusion is more prominent than the crystal diffusion when the temperature is low. Differing from thermal melting mechanism of the reflow bonding, the ultrasonic bonding is much faster than the reflow solder bonding.      

基于薄板理论的密排结构CMUT发射声场研究

由微机电系统(MEMS)工艺制作的电容式微机械超声换能器(CMUT),其具有宽频带,易与电子电路集成制作等优势,在医学成像领域具有广阔的应用前景。为了研究一种密排结构CMUT超声换能器的发射声场特征,该文提出了一种简单的物理域相互作用分析方法。基于薄板的振动理论,由CMUT单元的声学辐射原理及特性计算得到CMUT阵元辐射声场的解析解。通过振膜振动分布实验验证了采用薄板振动理论一阶振型方程的正确性。通过仿真和实验研究了CMUT发射单元在不同排布方式和条件下的声场分布、声轴声压和指向性,为CMUT的设计和性能分析提供了理论依据。     

Study of Temperature Parameter in Au–Ag Wire Bonding

The effect of the temperature on bondability and bonding process for wire bonding are investigated. Bondability is characterized by shear bonding strength and bonding process is represented by input and output power of ultrasonic transducer. A laser Doppler vibrometer and Labview software were used to record the velocity, voltage and current of transducer at different temperature settings. A K-type thermocouple sensor was used to measure the bonding temperature. Experimental results show that unsuccessful bonding happens at low temperature, and over bonding appears if the temperature is too high. Only when the temperature is at appropriate settings, can a stable and satisfied bondability be attained. The reason for this experimental observation is analyzed. By using a high resolution transmission electron microscope, the atom diffusion depth of Au-Ag bonding interface was measured and the result is about 200 nm. By using joint time-frequency analysis, the instantaneous characteristics of bonding process were observed completely and clearly. It is found that input and output ultrasonic power vs. time-frequency in a bonding process, including resonance frequency, harmonic components and amplitude of ultrasonic energy, vary along with the change of temperature settings.      

固结磨料超声磨削用压电换能器等效阻抗分析

固结磨料超声磨削加工过程中,随着负载的快速变化,压电换能器必须保持快速的频率跟踪与功率匹配响应,才能满足高效精密加工需求。该文从微观角度分析了固结磨料超声磨削的材料去除过程,通过建立压电换能器的力学模型,基于力电类比,得出压电换能器的等效阻抗与负载变化关系,即换能器的负载越大,其等效阻抗越大。当采用恒压源驱动压电换能器时,当换能器的负载越大,输出功率越小;反之,负载越小,输出功率越大,换能器无法工作在最佳状态。因此,为改善加工稳定性,提高材料表面完整性,提出了压电换能器的智能化恒流激励电源驱动方案,并进行了空载和负载状况下的电源系统测试试验,为进一步展开相关加工工艺研究奠定了坚实的基础。     

变频式超声波发生器的高速锁相研究

用于超声键合工艺的超声波发生器是引线键合封装设备的主要装置,其核心与关键是频率自动跟踪与锁相速度。文中构建了一种变频式超声波发生器,并对其中的高速锁相进行分析。通过换能器的电流反馈,采用基于嵌入式的数字式真有效值试探算法,超声波发生器锁相速度比传统速度提高数十倍,达到高速锁相的要求,满足了换能系统工作时的高速谐振需求。     

Low-Stress Thermosonic Copper Ball Bonding

Thermosonic ball bonding processes on test chips with Al metallized bonding pads are optimized with one Au and two Cu wire types, all 25 $mu{hbox {m}}$ diameter, obtaining average shear strengths of more than 120 MPa. The process temperature is $sim {hbox {110}}~^{circ}{hbox {C}}$. Ball bonds made with Cu wire show at least 15% higher shear strength than those made with Au wire. The estimated maximum shear strength $c_{pk}$ value determined for Cu ball bonding $(c_{pk}=3.7pm 1.2)$ is almost 1.5 times as large as that of the Au ball bonding process $(c_{pk}=2.3pm 0.9)$, where $LSL$ is 65.2 MPa. However, the ultrasound level required for Cu is approximately 1.3 times than that required for Au. Consequently, about 30% higher ultrasonic forces induced to the bonding pad are measured using integrated real-time microsensors. The accompanying higher stresses increase the risk of underpad damage. One way to reduce ultrasonic bonding stresses is by choosing the softer of the two Cu wire types, resulting in a measured ultrasonic force reduction of about 5%. A second way is to reduce the ultrasound level. While this causes the average shear strength to fall by 15%, the ultrasonic force falls by 9%. The $c_{pk}$ value does not change significantly, suggesting that a successful Cu ball bonding operation can be run with about 0.9 times the conventionally optimized ultrasound level. The process adjusted in this way reduces the extra stress observed with Cu wire compared to that observed with Au wire by 42%.