用于大功率半导体激光器的新型焊料

在大功率半导体激光器列阵及叠阵的组装中,焊料的选择是极其关键的,因为焊料直接参与对激光器的导电、导热激光器所需的电流全部从焊料通过,而半导体激光器列阵或叠阵工作时电流是很大的,可达50A～100A。同时半导体激光器工作时产生的热量非常大,如焊料的导热性不好,由于电流的热效应,就会在焊料上产生巨大的热量,使焊料熔化。文中研制了一种新型的焊料,这种焊料在两层铟之间蒸镀几层金,焊料由钨/镍/金/铟/铜等多层金属构成。利用这种焊料研制出脉冲功率达100W的半导体激光器列阵。     

电化学制备金锡合金薄膜技术研究

共晶成分的金锡合金具有诸多优异性能,文章介绍了一种制备金锡合金的方法,采用该方法在陶瓷基体上面制备金锡薄膜焊料.对焊料的成分进行了检测,对焊料的焊接性能和焊接可靠性进行了测试.试验结果满足GJB548相关要求.     

半导体激光器焊接的热分析

为了解决大功率半导体激光器的散热问题,利用有限元软件ANSYS,采用稳态热模拟方法,分析了半导体激光器内部的温度分布情况,对比分析了In、SnPb、AuSn几种不同焊料烧结激光器管芯对激光器热阻的影响。由模拟结果可见,焊料的厚度和热导率对激光器热阻影响很大,在保证浸润性和可靠性的前提下,应尽量减薄焊料厚度。另外,采用高导热率的热沉材料和减薄热沉厚度可有效降低激光器热阻。在这几种焊接方法中,采用In焊料Cu热沉焊接的激光器总热阻最小,是减小激光器热阻的最佳选择。通过光谱法测出了激光器热阻,验证了模拟结果,为优化激光器的封装设计提供了参考依据。     

长波长InGaAsP/InP LD焊接热阻的探讨

介绍影响 InGaAsP/InP 双异质结激光器可靠性的一个主要因素——热阻。通过分析表明,焊料的选择是决定器件实际寿命的关键因素。实验中采用不同的锡(Su)焊料,结果表明,对于高可靠的 InGaAaP/InP 双异质结激光器,金锡焊料(AuSn)是理想的选择。     

共晶焊料焊接的孔隙率研究

大功率或高功率密度的高可靠集成电路等通常采用合金焊料焊接芯片,以降低封装热阻和提高芯片焊接的可靠性。合金焊料焊接方式主要有真空烧结、保护气氛下静压烧结、共晶摩擦焊等。不同焊接工艺有其不同的适应性和焊接可靠性。文章以高可靠封装常用金基焊料的共晶焊接为例,探讨在相同封装结构、不同共晶焊接工艺下焊接层孔隙率,以及相同工艺设备、工艺条件下随芯片尺寸增大孔隙率的变化趋势。研究结果表明:金-硅共晶摩擦焊工艺的孔隙率低于金-锡真空烧结工艺和金-锡保护气氛静压烧结;同一焊接工艺,随着芯片尺寸变大,其孔隙率变化不显著,但单个空洞的尺寸有明显增大趋势。     

用于大功率半导体激光器的Ag-In焊料研究

大功率半导体激光器的封装对焊料选择极其重要,因为焊料导热或导电性差,激光器工作产生的大量热量使焊料焊接失效,激光器也会遭到损坏。为此,文中研究了软焊料In及其保护层Ag作为一种焊料组合,通过真空蒸发镀膜仪蒸发蒸镀Ag-In与Ag-In-Ag-In两种薄膜方式。根据微结构知识及扩散动力学与热动力学相结合讨论了Ag-In焊料产生间隙的原因,通过XRD衍射仪了解到薄膜间界面化合物AgIn2的生成可能导致表面微结构的改变,结果表明Ag层对In层易被氧化的性质起到了保护作用,多层的Ag-In焊料层可抑制大量间隙的产生,提高器件工作可靠性及稳定性。     

大功率半导体激光器贴片层空洞热效应影响

随着输出功率、转换效率、可靠性和制造工艺的提高以及成本的降低,大功率半导体激光器越来越广泛地应用于许多新的领域。大部分商业化销售的半导体激光器阵列/巴条是用铟作为焊料封装的。然而,在半导体激光器封装过程中不可避免地会在贴片层形成一些小空洞,这些小空洞在铟的电迁移和电热迁移作用下逐渐变大,这将导致芯片贴片层形成大量的空洞,造成芯片局部温度迅速上升。针对808 nm连续波40 W传导制冷单巴条半导体激光器阵列,系统地分析了半导体激光器贴片层空洞对发光点温度的影响以及贴片层内不同位置不同尺寸的空洞对发光点温升的影响,得到了发光点温升与空洞尺寸间的关系曲线。提出了利用空洞与发光点温度的关系及空间光谱来估算贴片层的空洞分布的方法,并将估算结果与实验测得的贴片层扫描声学显微图像进行了对比。     

真空炉金锡封焊

文章在介绍半导体金锡焊料封装工艺的基础上,重点对金锡焊料、炉温曲线设置等工艺技术问题进行了深入研究。基于大量的金锡焊料真空焊接封装实验及理论分析,研究了器件气密封装技术。讨论了封焊夹具、管帽镀层、合金状态、封接面表面、压块、焊料厚度以及加热程序对焊接质量的影响。密封后的产品在经过环境试验和机械试验考核后,封装气密性能很好地满足要求。并且结合应用背景证明了所采用的合金及封装工艺的可行性。     

电镜原位电子束辐照下Au85 Sn15纳米线的动态熔化过程（英文）

金锡合金焊料由于其良好的性能逐渐成为一种可能替代锡铅焊料的无铅焊料,并且利用电子束辐照的焊接方式,一维金锡纳米线已经成功用于TiO_2纳米线的焊接,这为钛基半导体氧化物纳米材料的焊接提供了实验经验。然而,金锡焊料在电子束焊接时的熔化机制和动态过程的研究还很贫乏。在本文中,我们通过电化学沉积的方法制备了一维Au₈₅ Sn₁₅合金纳米焊料,并详细地研究了在透射电镜中的电子束辐照下,其形貌,晶体结构,化学元素分布的演化过程,并进一步探究了电子束辐照熔化纳米焊料的机理。研究发现,在电子束辐照下,一维Au₈₅ Sn₁₅合金纳米焊料的形貌由线状熔化为液滴状;其晶体结构由AuSn和Au_5 Sn为主,少量Au,β-Sn,SnO_2的混合相转化为单一的Au_5 Sn相;其化学元素在电子束辐照下发生质量损失,该过程既有物理相变又有化学相变。在电子束辐照传递的能量作用下,原子的流动或扩散迁移和重新排列是形成新的结合层的动力学机制。该工作不仅为应用纳米焊料进行电子束焊接提供了实验依据,而且为电子束辐照熔化金锡纳米合金纳米焊料的内在机制的研究提供了宝贵经验。     

金锡共晶烧结工艺及重熔孔隙率变化研究

文章论述了金锡共晶烧结工艺在功率器件焊接中的应用,分析了金锡共晶烧结温度、时间和压力对芯片粘接质量的影响。同时分析了金锡焊料重熔后粘接层孔隙的变化,试验表明金锡共晶烧结时控制好烧结工艺参数,可以保证多次重熔对粘接层孔隙率的影响,粘接质量能满足相关要求。     

Mounting of high power laser diodes on boron nitride heat sinksusing an optimized Au/Sn metallurgy

High power diode lasers have become more and more important to industrial and medical applications. In contrast to low power applications, long cavity lasers or laser bars are used in this field and mounting quality influences considerably laser performance and life time. In this paper we focus on the solder metallurgy and stress-induced laser behavior after mounting. The laser chips have been bonded fluxless epi-side down on translucent cubic boron nitride (T-cBN) using Au/Sn solder. The laser behavior has been tested with different chip metallizations preserving the eutectic solder composition or forming the Au rich ζ-phase during reflow. The resulting additional stress in the lasing region has been independently indicated by polarization measurements of the emitted light. A metallization scheme has been developed which forms the highly melting ζ-phase during soldering within a wide process window. This procedure yields better results then using eutectic Au/Sn which has a higher hardness than the ζ-phase. Laser diodes up to a cavity length of 2000 μm and an aperture of 200 μm have successfully been mounted on T-cBN. State of the art laser data, excellent thermal stability, high yield and reliability have been obtained     

Mechanical response of solder joints in flip-chip type structures

The mechanical response of PbSn solder joints of two different solder alloys (37 wt.% Pb - 63 wt.% Sn and 95 wt.% Pb - 5 wt.% Sn) used as flip-chip type interconnects is measured through mechanical testing (in tension and in shear). The influence of solder pad composition (Au and Ni) upon the behaviour of the solder joints is examined. Fatigue testing performed upon flipchip samples demonstrates the difference in mechanical comportment between Pb37Sn63 and Pb95Sn5 solders. A model for predicting fatigue life is put forward.     

A metallization scheme for junction-down bonding of high-power semiconductor lasers

High-power semiconductor lasers have found increasing applications in industrial, military, commercial, and consumer products. The thermal management of high-power lasers is critical since the junction temperature rise resulting from large heat fluxes strongly affects the device characteristics, such as wavelength, kink power, threshold current and efficiency, and reliability. The epitaxial-side metallization structure has significant impact on the thermal performance of a junction-down bonded high-power semiconductor laser. In this paper, the influence of the epitaxial-side metal (p-metal) on the thermal behavior of a junction-down mounted GaAs-based high-power single-mode laser is studied using finite-element analysis. It is shown that a metallization structure with thick Au layer can significantly reduce the thermal resistance by distributing the heat flow to wider area laterally, and the thermal resistance of a junction-down bonded laser with thick Au metallization is much less sensitive to the voiding in the die attachment solder interface than a laser with thin Au metallization. A metallization structure of Ti-Pt-thick Au-Ti-Cr-Au is designed and implemented, and the metallurgical stability of this metallization scheme is reported. It was found that, without a diffusion barrier, the thick Au layer in the epi-side metallization would be mostly consumed and form intermetallics with the Sn from the AuSn solder during soldering and thermal aging. The Ti-Pt-thick Au-Ti-Cr-Au metallization scheme prevents the diffusion of Sn into the thick Au layer and preserves the integrity of the metallization system. It is a promising candidate for junction-down bonding of high-power semiconductor lasers for improved thermal management and reliability.     

Metallurgical reactions in composite 90Pb10Sn/lead-free solder joints and their effect on reliability of LTCC/PWB assembly

Use of 90Pb10Sn solder as a noncollapsible sphere material with 95.5Sn 4Ag0.5Cu and SnInAgCu lead-free solders is investigated. Practical reflow conditions led to strong Pb dissolution into liquid solder, resulting in >20 at.% Pb content in the original lead-free solders. The failure mechanism of the test joints is solder cracking due to thermal fatigue, but the characteristic lifetime of 90Pb10Sn/SnInAgCu joints is almost double that of 90Pb10Sn/95.5Sn4Ag0.5Cu in a thermal cycling test (TCT) over the temperature range from −40°C to 125°C. It is predicted that this is mainly a consequence of the better fatigue resistance of the SnPbInAgCu alloy compared with the SnPbAgCu alloy. Indium accelerates the growth of the intermetallic compound (IMC) layer at the low temperature co-fired ceramic (LTCC) metallization/solder interface and causes coarsening of IMC particles during the TCT, but these phenomena do not have a major effect on the creep/fatigue endurance of the test joints.     

A Study on the Thermal Fatigue Behavior of Solder Joints Under Power Cycling Conditions

Failure mechanisms exposed by environmental accelerating testing methods such as thermal cycling or thermal shock test, may differ from those at service operating conditions. While the device is heated up or cooled down evenly on its external surface during environmental testing, real operating powered devices experience temperature gradients caused by internal local heating, components' different heat dissipation capability, and ambient temperature variation, etc. In this study, a power cycling technique is introduced to better approximate the field operating conditions so as to activate the field failure modes. Power cycling thermal fatigue test is performed with different ball grid array solder joints, that is, lead contained [Sn/37 Pb (SP)] and lead free [Sn/4.0Ag/0.5 Cu (SAC)], and the result is compared. In order to account for the thermal fatigue life behavior discrepancy for different solder joint composition, real time Moire interferometry is applied to measure the global/local thermo-mechanical behavior during power cycling excursion. Effective damage parameter, the total average shear strain, is extracted from the experiment and applied to account for the difference in fatigue life result of two different solders. In addition, amount of experimentally measured total average shear strain is mutually verified with finite element method analysis. It is clear that total average shear strain of a solder joint can be an effective damage parameter to predict thermo-mechanical fatigue life. A physical mechanism in terms of thermal material property of solder joints' is proposed to offer some thoughts to abnormal shear strain behavior that leads to discrepancies in fatigue life of two solders. An importance of power cycling testing method is emphasized for certain package designs.     

Solder joint reliability of indium-alloy interconnection

Recent high-density very large scale integrated (VLSI) interconnections in multichip modules require high-reliability solder interconnection to enable us to achieve small interconnect size andlarge number of input/output terminals, and to minimize soft errors in VLSIs induced by α-particle emission from solder. Lead-free solders such as indium (In)-alloy solders are a possible alternative to conventional lead-tin (Pb-Sn) solders. To realize reliable interconnections using In-alloy solders, fatigue behavior, finite element method (FEM) simulations, and dissolution and reaction between solder and metallization were studied with flip-chip interconnection models. We measured the fatigue life of solder joints and the mechanical properties of solders, and compared the results with a computer simulation based on the FEM. Indium-alloy solders have better mechanical properties for solder joints, and their flip-chip interconnection models showed a longer fatigue life than that of Pb-Sn solder in thermal shock tests between liquid nitrogen and room temperatures. The fatigue characteristics obtained by experiment agree with that given by FEM analysis. Dissolution tests show that Pt film is resistant to dissolution into In solder, indicating that Pt is an adequate barrier layer material for In solder. This test also shows that Au dissolution into the In-Sn solder raises its melting point; however, Ag addition to In-Sn solder prevents melting point rise. Experimental results show that In-alloy solders are suitable for fabricating reliable interconnections.     

The influence of thermal aging on joint strength and fracture surface of Pb/Sn and Au/Sn solders in laser diode packages

The joint strength and fracture surface of Pb/Sn and Au/Sn solders in laserdiode packages after thermal-aging testing were studied experimentally. Specimens were aged at 150°C for up to 49 days. The joint strength decreased as aging time increased. The microstructure and fracture surface of the Pb/Sn and Au/Sn solder joints showed that the joint strength decrease was caused by both the enlargement of the initial voids and an increase in the number of voids as aging time increased. The formation of Kirkendall voids with intermetallic-compound (IMC) growth of the Pn/Sn solder as aging time increased was also a possible mechanism for the joint-strength reduction. Finite-element method (FEM) simulations were performed on the joint-strength estimation of Pb/Sn and Au/Sn solders in thermal-aging tests. The coupled thermal-elasticity-plasticity model was used to simulate distributions of the thermal and residual stresses, creep deformation, and joint-strength variations in the solder joints under various thermal-aging tests. Simulation results were in good agreement with the experimental measurements that the solder-joint strength decreased as aging time increased. The result suggests that the FEM is an effective method for analyzing and predicting the solder-joint strength in laserdiode packages.     

Characterization of 63Sn37Pb and 80Au2OSn solder sealed opticalfiber feedthroughs subjected to repetitive thermal cycling

A highly accurate prediction of hermeticity lifetime is made for eutectic 63Sn37Pb and 80Au20Sn alloy solder sealed optical fiber-Kovar ^TM nosetube feedthroughs subjected to repetitive thermal cycling. Thermal fatigue fracture of the Sn-Pb solder/Kovar^TM interface develops when cracks, initially generated from creep deformation of the solder, propagate gradually through the junction in the axial direction. A nonlinear axisymmetric finite element analysis of the 63Sn37Pb fiber feedthrough seal is performed using a thermo-elastic creep constitutive equation, and solder joint fatigue based on accumulated strain energy associated with solder creep imposed by temperature cycling is analyzed. Additionally, thermal effective stress and plastic strain is studied for alternative 80Au20Sn solder by the finite element method with results indicating significant increase in useful life as compared to 63Sn37Pb. SEM/EDX metallurgical analysis of the solder/Ni-Au plated Kovar^TM nosetube interface indicates that AuSn₄ intermetallic formed during soldering with 63Sn37Pb also contributes to joint weakening, whereas no brittle intermetallic is observed for 80Au20Sn. Hermetic carbon coated optical fibers metallized with Ni,P-Ni underplate and electrolytic Au overplating exhibit correspondingly similar metallurgy at the solder/fiber interface. Combined hermeticity testing and metallurgical analysis carried out on 63Sn37Pb and 80Au20Sn alloy solder sealed optical fiber feedthroughs after repetitive temperature cycling between -65 and +150°C, and -40 and +125°C validated the analytical approach     

超大面积芯片烧结技术研究

随着半导体大功率器件的发展,芯片的散热一直是制约功率器件发展的因素之一。而器件内部散热主要是通过芯片背面向外传导,芯片焊接工艺是直接影响器件散热好坏的关键因素之一,合金焊料的一个显著优点就是其导热性能好,因此在散热要求高的大功率器件中使用较为广泛(如Au80Sn20、Au99.4Sb0.6等),但由于合金焊料烧结后会产生较大的残余应力,在尺寸大于8 mm×8 mm的芯片上,烧结工艺应用较少。文章针对11.5 mm×11.5 mm超大面积芯片进行金锡合金烧结试验,经过对应力产生的原因进行分析,从材料、封装工艺等方面采取措施来降低缓释应力,并对封装产品进行可靠性考核验证。试验结果表明,没有芯片存在裂纹、碎裂现象,产品通过了可靠性验证。