微电子封装中Sn-Ag-Cu焊点剪切强度研究

提出了一种对微电子封装器件中焊点剪切强度进行测试的方法,可有效降低测试误差.利用该方法,对Sn-Ag-Cu无铅焊料分别在Cu基板和Ni-P基板上形成的焊点,经不同的热时效后的剪切强度进行了测量,并对断裂面的微观结构进行了研究.结果表明,新的剪切测试方法误差小,易于实施,焊点剪切强度、断裂面位置与焊料在不同基板界面上金属间化合物的形貌、成分有关.     

微电子封装中Sn—Aq—Cu焊点剪切强度研究

提出了一种对微电子封装器件中焊点剪切强度进行测试的方法，可有效降低测试误差。利用该方法，对Sn—Ag—Cu无铅焊料分别在Cu基板和Ni-P基板上形成的焊点，经不同的热时效后的剪切强度进行了测量，并对断裂面的微观结构进行了研究。结果表明，新的剪切测试方法误差小，易于实施，焊点剪切强度、断裂面位置与焊料在不同基板界面上金属间化合物的形貌、成分有关。     

不同加载速率对SAC/Cu焊点剪切强度的影响

通过对Sn0.3Ag0.7Cu/Cu和Sn3.0Ag0.5Cu/Cu焊点进行剪切测试结果表明:两种钎料焊点的剪切强度与加载速率有着明显的相关性,即焊点的剪切强度都随着加载速率的增加而增加。当加载速率为0.01 mm/s时,断裂模式为韧脆混合断裂,随着加载速率的增加,两种钎料焊点断口的韧窝数量不断增加,呈现韧性断裂特征,断口以韧窝为主。另外在相同加载速率下,Sn3.0Ag0.5Cu/Cu焊点断口的韧窝数量和分布情况都优于Sn0.3Ag0.7Cu/Cu焊点,即其韧性断裂的趋势更加明显,剪切强度更大。     

基板焊盘的金属层结构对焊接点强度的影响

球栅阵列封装具有高密度、低成本的特点被内存领域广泛采用。在实际的使用过程中由于遭受外界各种形式的机械负载和冲击造成器件失效,典型的失效模式有5类,突出问题是焊点失效,而焊点破裂是失效的主要形式。为了改善焊点的强度,提出了焊球的快速剪切测试以及BGA器件的快速剪切测试方法来检测焊点强度,设计了4种不同金属层结构的基板焊盘,对比了不同基板焊盘的快速剪切强度和失效模式。通过数据分析和失效模式研究,证明含较厚铜层或者镍层的焊盘具有更强的焊接强度。     

微米银焊点的超快激光图形化沉积及其在芯片连接中的应用探索

集成电路(IC)芯片封装中小尺寸、细节距焊点采用的传统锡基钎料在服役过程中存在桥接、电迁移、金属间化合物等问题,在大电流、大功率密度的应用中受到限制。采用脉冲激光沉积(PLD)技术,在覆铜陶瓷(DBC)基板上图形化沉积了多孔微米银焊点,用于替代传统的钎料凸点,并将其应用于Si芯片与DBC基板的连接。结果表明:采用不锈钢作为掩模,可沉积出500μm及300μm特征尺寸的疏松多孔银焊点阵列,银焊点呈圆台形貌;在250℃温度、2 MPa压力下热压烧结10 min, Si芯片与DBC基板连接良好,连接后的银焊点边缘的孔隙率为42%左右,银焊点中心区域的孔隙率为22%; 500μm和300μm特征尺寸的银焊点的连接接头的剪切强度分别为14 MPa和12 MPa;接头断裂主要发生在银焊点与芯片或DBC基板的连接界面处。     

Sn-9Zn/Cu焊点剪切强度及断口形貌分析

研究了BGA直径分别为750μm、1 000μm、1 300μm的Sn-9Zn/Cu焊点剪切强度及其变化规律。采用SEM和EDX对剪切断口进行观察和元素成分分析。试验结果表明,随着焊球直径的增大,焊点剪切强度先减小后增大。剪切断裂位置大部分位于钎料内部,局部位于界面化合物Cu5Zn8处。在相同的剪切高度与剪切速率下,随...     

Sn-9Zn/Cu焊点的结合强度与抗蠕变性能

基于前期进行的锡锌合金无铅钎料新型助焊剂研究,实验考查了其中二氯化锡活化剂含量水平对Sn-9Zn/Cu焊点剪切强度和常温抗剪切蠕变性能的影响.结果表明:就上述焊点强度而言,二氯化锡含量的影响与它对润湿性的影响[5]不尽一致,存在一个最佳的质量分数5%,超过该含量后尽管润湿性还继续提高,上述强度值却均会下降.在二氯化锡质量分数为5%时制得的焊点在剪切实验中呈良好韧性断裂模式.实验还显示:焊剂中较高的松香浓度明显有益于焊点的抗剪切蠕变强度,而对瞬时剪切强度影响不大.     

电迁移对Sn3.0Ag0.5Cu无铅焊点剪切强度的影响

通过热风回流焊制备了Cu/Sn3.0Ag0.5Cu/Cu对接互连焊点,测试了未通电及6.5 A直流电下通电36 h和48 h后焊点的剪切强度.结果表明,电迁移显著地降低了焊点的剪切强度,电迁移36 h使剪切抗力降低约30%,电迁移48 h降低约50%.SEM观察断口和界面形貌表明,界面金属间化合物增厚使断裂由韧性向脆性...     

In基钎料低温钎焊界面组织与性能研究

军用高可靠电子器件的组装工艺复杂性要求开发适用于低温钎焊的钎料。对InSnPb和InSnPbAu钎料在Cu/Ni/Au体系钎焊界面进行研究。利用DSC、SEM对钎料热性能和焊点界面显微组织进行检测,并进行剪切强度测试。结果表明,焊点金属间化合物为AuIn_2。两种钎料剪切强度均满足军用标准,InSnPb略高于InSnPbAu。经过高温老化后由于原子扩散和IMC层的继续生长使焊点剪切强度略有提升,而经过温度循环后剪切强度显著下降。剪切断口形貌表明,断裂位置主要位于钎料处,对于提升塑性变形能力是有利的。厚金界面(2～3 μm)更利于提升焊接强度且不会引起"金脆"。     

Sn-3.0Ag-0.5Cu/Ni/Cu微焊点剪切强度与断口的研究

用直径为200~500μm的Sn-3.0Ag-0.5Cu无铅焊球分别在Ni和Cu焊盘上制作焊点,并对焊后和时效200h后的焊点进行剪切测试,并采用SEM观察剪切断口形貌。结果表明,焊后和时效200 h后焊点接头的剪切强度都随焊球尺寸增大而减小。焊后断口处韧窝形状为抛物线型,断裂方式为韧性断裂;随着焊球尺寸的增大,剪切断口处的韧窝数量增多,韧窝的变小变浅。时效200 h后,韧窝变浅,趋于平坦,韧窝数量也明显减少,材料的韧性下降,脆性增加,断裂方式由韧性向脆性发生转变。     

Solder joint reliability of TFBGA assemblies with fresh and reworked solder balls

In this article, the solder joint reliability of thin and fine-pitch BGA (TFBGA) with fresh and reworked solder balls is investigated. Both package and board level reliability tests are conducted to compare the solder joint performance of test vehicle with fresh and reworked solder balls. For package level reliability test, ball shear test is performed to evaluate the joint strength of fresh and reworked solder balls. The results show that solder balls with rework process exhibit higher shear strength than the ones without any rework process. The results also exhibit that the different intermetallic compound (IMC) formation at solder joints of fresh and reworked solder balls is the key to degradation of shear strength. For board level reliability tests, temperature cycling and bending cyclic tests are both applied to investigate the fatigue life of solder joint with fresh and reworked solder balls. It is observed that package with reworked solder ball has better fatigue life than the one with fresh solder ball after temperature cyclic test. As for bending cyclic test, in addition to test on as-assembled packages, reworked and fresh samples are subjected to heat treatment at 150 °C for 100 h prior to the bending cyclic test. The purpose is to let Au–Ni–Sn IMC resettle at solder joints of fresh solder ball and examine the influence of Au–Ni–Sn IMC on the fatigue life of solder joints (Au embrittlement effect). The final results confirm that reworked solder balls have better reliability performance than fresh one since Au embrittlement dose exist at fresh solder ball.     

A review of board level solder joints for mobile applications

The reliability of electronics under drop-shock conditions has attracted significant interest in recent years due to the widespread use of mobile electronic products. This review focuses on the drop-impact reliability of lead-free solder joints that interconnect the integrated circuit (IC) component to the printed circuit board (PCB). Major topics covered are the physics of failure in drop-impact; the use of board level and component level test methods to evaluate drop performance; micro-damage mechanisms; failure models for life prediction under drop-impact; modelling and simulation techniques; and dynamic stress–strain properties of solder joint materials. Differential bending between the PCB and the IC component is the dominant failure driver for solder joints in portable electronics subjected to drop-impact. Board level drop-shock tests correlate well with board level high speed cyclic bending tests but not with component level ball impact shear tests. Fatigue is the micro-damage mechanism responsible for the failure of solder joints in the drop-shock of PCB assemblies and the fatigue strength of solder joints depends strongly on the strain rate, test temperature, and the sequence of loading. Finally, tin-rich lead-free solders exhibit significantly higher strain rate sensitivity than eutectic SnPb solder.     

The effect of Ag content on the formation of Ag3Sn plates in Sn-Ag-Cu lead-free solder

The formation of Ag₃Sn plates in the Sn-Ag-Cu lead-free solder joints for two different Ag content solder balls was investigated in wafer level chip scale packages (WLCSPs). After an appropriate surface mount technology reflow process on a printed circuit board, samples were subjected to 150°C high-temperature storage (HTS), 1,000 h aging, or 1,000 cycles thermal cycling test (TCT). Sequentially, the cross-sectional analysis was scrutinized using a scanning electron microscope/energy dispersive spectrometer (SEM/EDX) to observe the metallurgical evolution of the amount of the Ag₃Sn plates at the interface and the solder bulk itself. Pull and shear tests were also performed on samples. It was found that the interfacial intermetallic compound (IMC) thickness, the overall IMC area, and the numbers of Ag₃Sn plates increase with increasing HTS and TCT cycles. The amount of large Ag₃Sn plates found in the Sn-4.0Ag-0.5 Cu solder balls is much greater than that found in the Sn-2.6Ag-0.5Cu solder balls; however, no significant difference was found in the joint strength between two different Ag content solder joints.     

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.     

Contact resistance and shear strength of the solder joints formed using Cu bumps capped with Sn or Ag/Sn layer

Solder joints were successfully bonded by joining Ag/Sn/Cu bumps and Ag/Sn/Cu layers at 200°C for 30 sec under 20 MPa, 40 MPa, and 80 MPa using thermo-compression bonder. The solder joints were aged at 150°C up to 1000 h. The strength of the solder joints was measured by the shear test and the contact resistance was measured using four-point probe method. The microstructure of the solder joints and the fracture modes after shear test were analyzed by scanning electron microscopy (SEM) with the energy-dispersive spectrometry (EDS). Results showed that the electrical resistance of the solder joints decreased, and the shear strength of the solder joints increased after aging treatment. The fracture modes were observed to move from the interfacial failure between solder and intermetallic compounds (IMCs) to the interfacial failure between IMCs. It was considered that the transition of fracture modes was closely related with the microstructure evolution of the solder joints, especially the transformation of IMC phases during the aging treatment.     

A new experimental method to evaluate creep fatigue life of flip-chip solder joints with underfill

A new accelerated stress test method was developed to evaluate creep life of flip-chip solder joints with underfill. With this method, a cyclic creep test can be done simply by applying a displacement to the FR-4 printed circuit board (PCB) board in the axial direction. The creep fatigue test was performed under displacement control with real-time electrical continuity monitoring. Test results show that the displacement arising from the force is equivalent to the thermal stress during thermal expansion. It was found that the magnitude of displacement was proportional to the inelastic strain sustained by the solder joints. This indicates that the creep fatigue life obtained will not only reflect the quality of the solder joints, but can also be used to characterize the reliability of the flip-chip assembly. Finite element modeling was also performed to confirm the agreement of deformation of the solder joints under mechanical and thermal loading. Results suggest that deformation and strain of the flip-chip assembly are consistent or comparable between the mechanical and thermal cycling. The failure analysis indicates that fatigue cracks often initiate from the top edge of a corner solder joint in the creep fatigue test, which is similar to what would happen in thermal cycling test. Lastly, the effect of underfill on the creep fatigue test is discussed. It is postulated that the test method is applicable to other flip-chip assemblies, such as conductive adhesive interconnections.     

Design of Solder Joint Structure for Flip Chip Package with an Optimized Shear Test Method

The structure of flip chip solder bumps was optimized in terms of shear height and shear speed using a shear test method with both experimental investigation and nonlinear, three-dimensional, finite element analysis being conducted. A representative, Pb-free solder composition, Sn-3.0Ag-0.5Cu, was used to optimize the shear test of the flip chip solder joints. Increasing the shear height, at a fixed shear speed, decreased the shear force, as did decreasing the shear speed, at a fixed shear height. These experimental and computational results supported the recommendation of low shear height and low shear speed condition for the shear testing of flip chip solder bumps. This optimized shear test method was applied to investigate the effect of various heights of mini bumps on the shear force of the solder joints. The shear force increased with increasing Ni-P mini bump height.     

基于机器视觉的焊点检测算法研究

为了提高电路板焊点检测的准确率,提出了改进的K-近邻法。首先,采用工业相机采集图像并选取470个焊点作为训练样本,利用模板匹配法对图像中的焊点进行定位。然后根据特征分布直方图提取焊点的特征并绘制特征分布情况,选择能区分不同类别焊点的特征作为有效特征。最后,建立改进的K-近邻法焊点检测分类器,选取559个焊点作为测试样本对模型进行测试。实验结果表明改进的K-近邻算法检测的准确率96%以上,可以有效地提高检测效率。