CBGA器件焊点温度循环失效分析

陶瓷球栅封装阵列(CBGA)器件的陶瓷器件与印制电路板之间热膨胀系数的差异是导致焊点失效的主要因素,其可靠性一直是CBGA封装器件设计时需重点考虑的问题[1].对CBGA植球器件的板级表贴焊点在-55～105 ℃温度循环载荷条件下的失效机理进行了研究,结果表明,CBGA板级表贴器件的焊点的主要失效部位在陶瓷一侧焊料与焊球界面和焊点与焊盘界面两处,边角焊点优先开裂,是失效分析的关键点;随着循环周期的增加,内侧链路依次发生断路失效.     

CCGA焊柱加固工艺技术研究

针对陶瓷柱栅阵列(CCGA)封装的焊接界面在热冲击试验中出现的断裂失效问题,探讨了如何通过加固CCGA焊接界面来提高器件可靠性的工艺技术.该工艺通过在焊接区域涂覆适量的环氧胶来对焊接界面进行加固保护,对于提高焊柱的抗热冲击能力具有明显的作用,并且能够有效地提高焊柱的可靠性.此外,为了进一步地提高CCGA器件的组装可靠性,对新型结构焊柱进行了相关的试验验证.     

HDI板埋孔半固化片填胶区域爆板问题研究

随着电子产品的升级与发展，高密度互连印制板（HDI板）的应用越来越广，盲埋孔的叠加设计密度也不断地提高，同时对下游表面装贴制程的潜在品质风险也在增加。针对HDI板组装再流焊后的爆板失效问题，研究印制电路板（PCB）的设计、生产和加工中存在的潜在失效模型，分析区域面积填孔密度所需填胶量与再流焊后爆板失效问题之间的关联。     

二极管玻璃封装机械裂纹的产生原因和改良措施研究

在电子设备中广泛应用的玻封二极管属于机械应力敏感器件,异常的封装烧结工艺或过大的安装应力都可能导致玻壳发生开裂失效.通过对一例玻封二极管玻壳开裂失效的问题进行分析,发现杜美丝表面氧化层裂纹缺陷会导致玻壳烧结界面局部产生较大内应力,烧结后冷却速率过快,就会导致这些较大的内应力无法充分释放,产生残余应力,较大的残余应力会造...     

高功率半导体激光器互连界面可靠性研究

随着高功率半导体激光器（HPLD）在极端环境中的应用越来越广泛，互连界面的可靠性已成为制约其性能和寿命的关键瓶颈之一。文中利用有限元方法（FEM）对传导冷却（CS）高功率半导体激光器巴条互连界面在-55~125℃热冲击条件下的失效行为和寿命进行了模拟与分析。基于粘塑性Anand本构模型和Darveaux能量积累理论，对比了热冲击后界面层边缘及中心位置铟互连界面的可靠性，发现互连界面边缘的应力最大，达到0.042 5 GPa；相应的边缘位置的寿命最短，只有3 006个周期，即边缘位置为互连界面的最危险单元。预测了采用铟、金锡合金和纳米银焊膏封装的半导体激光器巴条的寿命，计算出铟、金锡合金和纳米银焊膏三种不同键合材料在边缘位置的寿命分别为3 006、4 808和4 911次循环，表明纳米银焊膏和金锡合金在热冲击条件下具有更长的寿命，更适合于用于极端环境的高功率半导体激光器封装。     

表贴元件与双列直插器件温循过程中焊点可靠性研究

研究了表贴电阻及插装DIP器件的焊点可靠性。参照ECSS相关标准对装联后表贴电阻及插装DIP进行温循试验,借助光学显微镜及SEM电镜分析焊点内裂纹位置及影响因素。结果表明,DIP焊点裂纹产生于焊料与引脚的焊点上圆角处以及焊料与焊盘界面拐角处,PCB厚度对裂纹长度影响不大。表贴电阻裂纹产生于电极与焊料界面拐角处及下界面处,器件尺寸越大裂纹尺寸越长。     

圆片级封装的板级跌落可靠性研究

圆片级封装(WLP)具有尺寸小、散热性能好、封测成本低等优点,广泛应用于便携式电子产品,其在跌落、碰撞等环境下的可靠性越来越受到重视。将WLP器件组装到PCB基板上,按照JEDEC电子产品板级跌落实验标准进行实验,研究了WLP元件引脚节距、焊球尺寸、PCB焊盘工艺等因素对样品可靠性的影响。对失效样品进行了切片制样,通过金相显微镜、能量色散X射线光谱(EDX)和扫描电子显微镜进行了分析,研究了WLP器件失效机理及其与器件焊球尺寸、节距之间的关系,讨论了底部填充料对WLP封装可靠性的改进作用。     

微波组件绝缘子与微带线连接故障分析及改进

某型微波组件射频绝缘子与外部微带线采用焊锡直接焊接方式,在产品试验验证阶段出现了绝缘子与外部微带线的连接故障。先对故障现象进行分析判断,再利用有限元仿真软件比较焊锡焊接（硬连接）和铜带搭焊（软连接方式之一）在温度循环载荷下的应力情况,从而获得最优化的连接方式;最后在产品上使用铜带搭焊方式进行试验验证和技术指标仿真验证,验证结果证明铜带搭焊方式可靠。研究结果可为同类产品中绝缘子和微带线互联提供了一定的参考。     

一种新型FC和WLP的柔性凸点技术

FC(倒装片)和WLP(圆片级封装)均要在圆片上制作各类凸点,它们与基板焊接互连后,由于各材料间的热失配可能造成凸点——基板间互连失效,从而影响了器件的可靠性和使用寿命。解决这一问题的通常做法是对芯片凸点与基板间进行下填充。本文介绍的柔性凸点技术是在焊球下面增加一层具有弹性的柔性材料,当器件工作产生热失配时,由于柔性材料的自由伸缩,将大大减小以至消除各材料间的失配应力,使芯片凸点与基板下即使不加下填充,也能达到器件稳定、长期、可靠地工作的目的。     

环氧/Cu界面混合分层断裂研究

高密度塑封器件不同材料间分层断裂常导致器件失效,且界面通常为正应力作用下的张开型(模式I)断裂和切应力作用下的滑开型(模式II)断裂的混合模式。环氧塑封料和Cu引线框架之间热失配较大,在热、力学载荷作用下,环氧/铜界面易发生界面分层断裂。设计了一种双相材料样品和一种可以对样品施加不同角度拉力的装置,用于测试环氧/铜界面混合断裂参数。通过弹性断裂力学分析,基于实验结果可以得到界面断裂能量释放率和混合断裂相位角。该方法可以应用于电子封装中其他界面断裂参数的表征。     

Comparison of thermo-mechanical behavior of lead-free copper and tin–lead column grid array packages

Thermo-mechanical behavior of the lead (Pb)-free ceramic copper column grid array (CuCGA) package under accelerated thermal cycling is characterized and compared with the conventional tin–lead (Sn–Pb) ceramic column grid array (CCGA). In situ thermal deformations of the highest DNP (distance to neutral point) copper column is measured for an initial isothermal loading of ΔT = −75 °C and subsequent accelerated thermal cycling of −40 °C to +125 °C. The deformed shape of the column and the distribution of inelastic strains are measured from the displacement fields. The dominant deformation mode is bending of the column due to thermal expansion mismatch between the module and the printed circuit board (PCB). The results are compared with those of tin–lead CCGA tested under similar conditions. Unlike tin–lead columns, where the failure occurs at the column near the top of the solder fillet and through the thickness of the column, in the CuCGA, the failure is found to occur first in the solder fillet at the solder/copper column interface and the crack propagates along the periphery of the copper column. The accumulated plastic deformation per cycle is larger in tin–lead columns compared to the copper columns. A deformation mechanism is provided to explain the nature of this failure.     

CQFP器件板级温循可靠性的设计与仿真

温度循环是考核封装产品板级可靠性的重要试验之一。陶瓷四边引脚扁平封装(CQFP)适用于表面贴装,由于陶瓷材料与PCB热膨胀系数的差异,温循过程中引线互联部分产生周期性的应力应变,当陶瓷壳体面积较大时,焊点易出现疲劳失效现象。CQFP引线成形方式分顶部成形和底部成形两类。针对CQFP引线底部成形产品在板级温循中出现的焊接层开裂现象,采用有限元方法对焊接层的疲劳寿命进行了预测分析。采用二次成形方法对引线进行再次成形以缓解和释放热失配产生的应力。仿真和试验结果显示,引线二次成形有利于提高焊接层的温循疲劳寿命。与引线底部成形相比,当引线采用顶部成形时,焊接层的温循疲劳寿命显著提高。     

Coupling effects of mechanical vibrations and thermal cycling on reliability of CCGA solder joints

The microstructures and crack propagation behavior of CCGA (ceramic column grid array) solder joints after sinusoidal vibration loading, random vibration loading, and thermal cycling test have been discussed in this study. The failure mechanism of solder joints was analyzed using an experimental method and finite element analysis. It was found that the failed solder joints mainly distributed at the peripheral area in the solder column arrays and the crack initiation was mainly caused by mechanical vibrations. The deformation of PCB (printed circuit board) introduced by mechanical vibrations brought the outermost solder columns in CCGA devices with significant stress concentration and induced the initiation of cracks. Furthermore, cracks propagated during the process of mechanical vibrations and thermal cycling. The cracks propagated rapidly and the solder joints finally failed. The structure of the PCB holder was improved to relieve the vibration response from the peripheral joints. No visible crack was found in the solder joints after the same mechanical vibrations and thermal cycling test. The reliability of solder joints have been greatly improved with the new PCB holder.     

Bonding stress and reliability of high power GaAs-based lasers

GaAs-based lasers were bonded to oxygen-free high-conductivity (OFHC) copper heat sinks using a eutectic PbSn solder or a silver-filled conductive epoxy, and life tested. Epoxy-bonded devices were observed to have a larger failure rate on life test than solder-bonded devices. Bonding stress, as measured by the degree of polarization (DOP) of photoluminescence, was found to be the largest in epoxy-bonded devices. As well, the type of heat sink and bonding adhesive affected the stress in the laser material, with bonding stress increasing when there was a larger mismatch of coefficients of thermal expansion between the laser material, adhesive, and heat sink. Results suggested that heat sink material and bonding adhesive contribute to stress within the laser material and the resulting performance of the device     

Thermal cycling lifetime of flip chip on board circuits with solder bumps and isotropically conductive adhesive joints

Flip chip on board (FCOB) circuits with solder bumps or isotropically conductive adhesives (ICA) may be subject to joint failure during thermal cycling. Although use of epoxy underfill can increase the lifetime significantly, there is still a risk of failure if the material properties of the underfill material are not adequate to prevent excessive values of stress and strain in the joints. This paper presents experimental measurements of the number of thermal cycles to failure for both solder reflow and ICA joint FCOB circuits. Measurements have been carried out for several different material systems with various types of underfill. The measurements of solder bump lifetime are compared to a lifetime model based on analytical calculations of solder strain. For an underfill type without filler (CTE=58 ppm//spl deg/C), the measurements are in excellent agreement with the model predictions, both giving an average lifetime of around 1500 thermal cycles between -55 and 125/spl deg/C. For two filled types of underfill with CTE nearly matched to that of solder, the measured average lifetimes vary from around 2700 to 5500 cycles. The corresponding model predictions are around 6000 and 7000 cycles, respectively. Measurements of the lifetime of FCOB's with ICA connections have been carried out for two different material systems. The obtained lifetimes vary between approximately 500 and 4000 cycles. No systematic lifetime variation with the thermal expansion of the underfill has been observed, but the lifetime seems to be dependent on the properties of the bump on the chip pad. Delamination, for instance at the ICA/bump interface, is found to be an important cause of failure.     

Mechanical behavior of solder joints under dynamic four-point impact bending

Reliability of solder joints under drop impact loading is important to mobile electronic products. In this paper, dynamic four-point impact bending tests of board level electronic packages are carried out to investigate mechanical behavior of solder joints. In the test, strain gauges, a high speed camera and the digital image correlation method are used to acquire strain and deflection of the printed circuit board (PCB). After validated by the test data, a finite element model of the dynamic four-point impact bending test is used to obtain strain and stress in the solder joints. Then, failure predictions of the solder joints are made by strain index, and the predictions are compared with the experimental observations. Furthermore, a strain rate dependent Johnson-Cook material model and rate independent elastic-plastic model of lead-free solder are used to investigate the effect of strain rate on behavior of solder joints under drop impact loading. We find that the material model has insignificant influence on the deflection of the PCB during the drop impact but severely affect the stress and strain in solder joints. The rate independent elastic-plastic solder material model always underestimates the stress and overestimates the strain of the solder joints. The index of equivalent plastic strain computed by the strain rate dependent Johnson-Cook model can predict more realistic failure behavior of the solder joints.     

Board level solder joint reliability analysis of stacked die mixed flip-chip and wirebond BGA

Stacked die BGA has recently gained popularity in telecommunication applications. However, its board level solder joint reliability during the thermal cycling test is not as well-studied as common single die BGA. In this paper, solder joint fatigue of lead-free stacked die BGA with mixed flip-chip (FC) and wirebond (WB) interconnect is analyzed in detail. 3D fatigue model is established for stacked die BGA with considerations of detailed pad design, realistic shape of solder ball, and non-linear material properties. The fatigue model applied is based on a modified Darveaux’s approach with non-linear viscoplastic analysis of solder joints. Based on the FC–WB stack die configuration, the critical solder ball is observed located between the top and bottom dice corner, and failure interface is along the top solder/pad interface. The modeling predicted fatigue life is first correlated to the thermal cycling test results using modified correlation constants, curve-fitted from in-house lead-free TFBGA46 (thin-profile fine-pitch BGA) thermal cycling test data. Subsequently, design analyzes are performed to study the effects of 20 key design variations in package dimensions, material properties, and thermal cycling test conditions. In general, thinner PCB and mold compound, thicker substrate, larger top or bottom dice sizes, thicker top die, higher solder ball standoff, larger solder mask opening, smaller PCB pad size, smaller thermal cycling temperature range, longer ramp time, and shorter dwell time contribute to longer fatigue life. SnAgCu is a common lead-free solder, and it has much better board level reliability performance than eutectic solder based on modeling results, especially low stress packages.     

Board level investigation of BGA solder joint deformation strength

In this paper we present a method to determine the stress in BGA solder joints on complex, real assembled circuit boards.To be able to investigate the mechanical effects of post-reflow assembly within the solder joints of BGA components, it is necessary to undertake a mechanical investigation at board level by taking into consideration the effect of the adjacent components and the interconnection layer layouts.In our project, we have developed a method of how to investigate the board level deformation strength of BGA joints. The elastic properties of a real assembled circuit board and of a circuit bare board are measured; an FEM model is then created, both of the bare board and of the assembled printed circuit board taking into account the layout of the interconnection layers. The advantage of this PCB FEM model is that the deformation of a PCB of any size and for any load can be calculated quickly using any ordinary computer. In our project, we also have created another detailed FEM model for the BGA solder joints.Using the constructed FEM models, we are able to determine the stress in BGA solder joints on a real electronic product for a typical type of load (i.e. bending of PCB) thereby verifying our method. Since the simulated results correspond well to previous literature written on this topic, we consider that our method is appropriate for calculating stress in the solder joints of multi-lead components on complex, fully assembled circuit boards.     

倒装焊器件封装结构设计

倒装焊是今后高集成度半导体的主要发展方向之一。倒装焊器件封装结构主要由外壳、芯片、引脚(焊球、焊柱、针)、盖板(气密性封装)或散热片(非气密性封装)等组成。文章分别介绍外壳材料、倒装焊区、频率、气密性、功率等方面对倒装焊封装结构的影响。低温共烧陶瓷(LTCC)适合于高频、大面积的倒装焊芯片。大功率倒装焊散热结构主要跟功率、导热界面材料、散热材料及气密性等有关系。倒装焊器件气密性封装主要有平行缝焊或低温合金熔封工艺。     

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。