大尺寸陶瓷BTC器件焊点过应力开裂失效分析

对大尺寸陶瓷BTC器件焊点过应力开裂现象进行了研究。通过有限元仿真和金相切片分析得到了印制板焊盘、器件布局及装配过应力为引起BTC器件焊点过应力开裂主要原因,依此制定了改进焊盘、优化器件布局及减少装配应力的改进措施。有限元仿真分析表明,采用了改进措施后的BTC焊点在温度载荷和螺钉紧固力加载下所受应力减小,对改进后的BTC焊点进行了环境应力、耐久振动、温度循环等试验以及焊点金相切片分析,结果表明焊点未见开裂,验证了改进措施的有效性。     

CQFP器件焊点开裂失效分析

CQFP器件由于其可靠性高的优势已经广泛应用于军事、航天航空领域,但是在实际使用中,特别是在温度和力学条件下容易出现焊点脱落和引脚断裂等问题。针对在工作中遇到的一次典型焊点开裂失效案例进行分析,对问题产生的根源进行了定位,对焊点开裂的失效机理进行了分析,最后简要介绍了提高CQFP器件焊接可靠性的一些工艺措施。     

TSOP器件焊点开裂原因分析

通过对一起TSOP器件焊点开裂案例的原因进行排查,详细分析了引线镀层、引线出线方式、封装体材料、引线材料对焊点开裂形成的作用。总结了焊点开裂的产生机理。阐明了在设计时正确选择TSOP器件类型和规范TSOP器件引线成形的重要性。最后,简要介绍了提高TSOP器件焊接可靠性的措施。     

CBGA、CCGA器件植球／柱工艺板级可靠性研究

陶瓷球栅阵列（CBGA）和陶瓷柱栅阵列（CCGA）封装由于其高密度、高可靠性和优良的电热性能,被广泛应用于武器装备和航空航天等电子产品。而CBGA／CCGA焊点由于其材料和结构特性,在温度循环等可靠性试验中焊点容易发生开裂,导致器件失效。本文以CBGA256和CCGA256封装产品为例,通过陶瓷基板与PCB板的菊花链设计来验证CBGA／CCGA焊点的可靠性,并对焊点的失效行为进行分析。结果表明,CCGA焊点可靠性要高于CBGA焊点,焊点主要发生蠕变变形,边角处焊点在温度循环过程中应力最大,容易最先开裂。     

焊点的失效模式与分析

焊点疲劳寿命通常是通过电子组件进行温度循环加速试验来确定.针对典型元器件进行温度循环试验,在不同的循环周期检查焊点的开裂情况,并采用金相分析观察焊点的显微组织,分析焊点在温度循环条件下的失效模式,为改进工艺参数提供依据.     

LCCC封装器件热疲劳失效分析及结构优化研究

针对LCCC封装器件在温度循环载荷下焊点开裂的问题,首先分析其失效现象和机理,并建立有限元模型,进行失效应力仿真模拟。为降低焊点由封装材料CTE不匹配引起的热应力,提出了两种印制板应力释放方案,并分析研究单孔方案中不同孔径和阵列孔方案中不同孔数量对热疲劳寿命的影响。之后,为降低对PCB布局密度的影响,提出一种新型的叠层焊柱应力缓冲方案,进行了不同叠层板厚度和焊柱间距的敏感度分析。结果表明,更大的开孔面积、更小的叠层板厚度、更密的焊柱可有效降低焊点应力,提高焊点热疲劳寿命,使得LCCC封装器件焊点热疲劳可靠性得到有效提高。     

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.     

某型显示器LCCC器件焊接工艺的改进

某型显示器在长期使用过程中出现了LCCC封装器件焊点重复性失效的故障,对产品的功能、性能造成影响.对焊点失效的原因进行了分析,开展了复现试验,提出了相应的改进措施并对改进措施的有效性进行了试验验证.     

PBGA器件焊点的可靠性分析研究

根据PBGA器件组装特点,分析了器件焊点的失效机理,并针对实际应用中失效的PBGA器件在温度循环前后,分别使用染色试验、切片分析、X-射线分析等方法进行失效分析.分析结果显示样品PBGA焊点存在不同程度的焊接问题,并且焊接质量的好坏直接影响器件焊点抵抗外界应变应力的能力.最后,开展了PBGA器件焊接工艺研究和可靠性试验,试验结果显示焊接工艺改进后焊点的可靠性良好.     

BGA焊点空洞问题分析

BGA器件已经广泛应用于各个领域,首先对BGA器件进行了简介,在给出其焊点质量检验合格判据后,针对BGA组装过程中常见现象空洞,分析了空洞产生的机理,并进一步说明空洞对焊点可靠性的影响。最后根据空洞产生机理提出了一些措施以减少和改善空洞。     

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。     

Thermal Fatigue Endurance of Lead-Free Composite Solder Joints over a Temperature Range of −55°C to 150°C

The thermal fatigue endurance of two lead-free solder/plastic-core solder ball (PCSB) composite joint structures in low-temperature co-fired ceramic (LTCC) modules was investigated using a thermal cycling test over a temperature range of −55°C to 150°C. The investigated solder alloys were Sn-7In-4.1Ag-0.5Cu (SAC-In) and 95.5Sn-4Ag-0.5Cu (SAC). Three failure mechanisms were observed in the test joints. Transgranular (fatigue) cracking mixed with minor intergranular cracking was the dominant failure mechanism at the outer edge of the joints in both test assemblies, whereas separation of the solder/intermetallic compound (IMC) interface and creep cracking occurred in the other parts of the test joints. The propagation rate of the transgranular crack was lower in the SAC-In joints compared with in the SAC joints. Furthermore, the SAC solder seemed to be more prone to separation of the solder/IMC interface, and more severe intergranular (creep) cracking occurred in it compared with in the SAC-In solder. In the thermal cycling test conditions, the better thermal fatigue endurance of the SAC-In solder composite joints resulted in a 75% higher characteristic lifetime compared with the SAC composite joints.     

板厚影响通孔再流焊点抗热疲劳性能的试验研究

针对不同板厚的通孔再流焊点进行了热冲击的可靠性测试，以非破坏性和破坏性的试验方式，对比分析了板厚对通孔再流焊点的抗热疲劳能力的影响。结果表明，热膨胀系数(CTE)失配是焊点产生裂纹的主要原因，使得板厚严重影响着焊点的抗热疲劳性能：厚板焊点断裂程度重于薄板焊点，其循环后的强度下降也快于后者，但二者的电性能变化差异不大。     

Impact of laminate cracks under solder pads on the fatigue lives of ball grid array solder joints

This paper reports how the solder joint fatigue lives of three types of lead free plastic BGA components were affected by cracks formed in the printed PCB laminate during a thermal cycling test. The investigation showed that cracks were formed in the laminate for all three tested components. For one of the components having a large chip with solder joints located under the chip, very large cracks were formed in the PCB laminate beneath some solder pads.For lead-free solder joints to BGA components consisting of near eutectic solders based on tin, silver and copper, a large fraction of the solder joints may consist of one single tin grain. Due to anisotropy of tin grains, each solder joint to a BGA component will experience a unique stress condition which will make laminate cracking more likely under certain solder joints.The laminate cracks increased the flexibility of the joints and thereby improved the fatigue lives of the solder joints. Therefore, an estimation of the fatigue lives of solder joints to BGA components based on the results from a thermal cycling test may lead to an overestimation of the fatigue lives if products will be exposed to smaller temperature changes in the field than in the test.If cracks are not formed in the PCB laminate, or if the extent of cracking is small, single-grained solder joints can be expected to result in a high spread in failure distribution with some quite early failures.     

Failure study of Sn37Pb PBGA solder joints using temperature cycling,random vibration and combined temperature cycling and random vibration tests

In this paper, the tin-lead (Sn-37wt%Pb) eutectic solder joints of plastic ball grid array (PBGA) assemblies are tested using temperature cycling, random vibrations, and combined temperature cycling and vibration loading conditions. The fatigue lives, failure modes for the solder joints and the typical locations of the failed solder joints for single-variable loading and combined loading conditions are compared and analyzed. The results show much earlier solder joint failure for combined loading than that for either temperature cycling or pure vibration loading at room temperature. The primary failure mode is cracking within the bulk solder under temperature cycling, whereas the crack propagation path is along the intermetallic compound (IMC) layer for vibration loading. The solder joints subjected to combined loading exhibit both types of failure modes observed for temperature cycling and vibration loading; in addition, cracking through the IMC and the bulk solder is observed in the combined test. For temperature cycling and vibration loading, the components in the central region of the printed circuit board (PCB) have more failed solder joints than other components, whereas for combined loading, the number of failed solder joints in the components in different locations of the PCB is approximately the same.     

Comparison of in-situ measurement techniques of solder joint reliability under thermo-mechanical stresses

Thermo Mechanical Cycle Lifetime (TMCL) test is a widely used test methodology for evaluating the reliability of solder joints in the microelectronics industry. The commonly used measurement techniques to monitor solder joint failures during the TMCL test are either event detector or data logger. In this study, TMCL test has been carried out on the same devices in parallel with both measurement techniques. The pros and cons of both techniques are compared. It is observed that the solder joint reliability results on the investigated samples by both techniques are comparable. The event detector can catch short intermittent events, while the data logger is able to capture the details of the solder joint degradation process. In applications for which performance is dependent on the transmission of signals with a frequency of several hundred megahertz or more, the event detector technique shall be used. In such cases the data logger technique may overestimate product lifetime. On the other hand, for some applications where the performance is less susceptible to intermittent solder joint interconnect interruption but more to the increase of the solder joint resistance, the data logger shall be used. In such cases the event detector technique may underestimate product lifetime. In conclusion depending on the end application of the device, the most suitable technique can be selected.     

Reliability and RF performance of BGA solder joints with plastic-core solder balls in LTCC/PWB assemblies

In this paper board-level reliability of low-temperature co-fired ceramic (LTCC) modules with thermo-mechanically enhanced ball-grid-array (BGA) solder joint structure mounted on a printed wiring board (PWB) was experimentally investigated by thermal cycling tests in the 0–100 °C and −40 to 125 °C temperature ranges. The enhanced joint structure comprised solder mask defined (SMD) AgPt pad metallization, eutectic solder and plastic-core solder balls (PCSB). Similar daisy-chained LTCC modules with non-collapsible 90Pb10Sn solder spheres were used for a reference test set. The reliability of the joint structures was analyzed by resistance measurements, X-ray microscopy, scanning acoustic microscopy (SAM) and SEM/EDS investigation. In addition, a full-wave electromagnetic analysis was performed to study effects of the plastic-core material on the RF performance of the LTCC/BGA package transition up to millimeter-wave frequencies. Thermal cycling results of the modules with PCSBs demonstrated excellent fatigue performance over that of the reference. In the harsher cycling test, Weibull’s shape factor β values of 7.9 and 4.8, and characteristic lifetime θ values of 1378 and 783 were attained for the modules with PCSBs and 90Pb10Sn solder spheres, respectively. The primary failure mode in all test assemblies was fatigue cracking in eutectic solder on the ceramic side.     

A Novel Design Structure for WLCSP With High Reliability, Low Cost, and Ease of Fabrication

Wafer level chip scale packaging (WLCSP) has some advantages, such as real die size packaging, high electrical performance, and low manufacturing cost. However, because the mechanical reliability of a large die can not be guaranteed due to the coefficient of thermal expansion (CTE) mismatch between silicon and organic printed circuit board (PCB), WLCSP technology is still not fully accepted. We have developed a new solder joint protection-WLCSP (SJP-WLCSP) structure with a delamination layer interposed between the top layer of the chip and the bottom insulating layer of the metal redistribution traces. The stress on the solder joints can be released by the cracks forming in the delamination layer, which protects the solder joints from cracking. Since the cracking of the delamination layer is irrelevant to the electrical circuits of the packaging, the packaged integrated circuits (IC) device remains functional. One of the possibilities for processing the SJP-WLCSP was implemented and validated successfully in the SiLK-wafer samples. The board level packaging samples, using the daisy chain resistance measurement passed 1000 cycles of the temperature cycling testing.     

Study of Solidification Cracks in Sn-Ag-Cu Lead-Free Solder Joints

In the present work, solidification cracks in Sn-Ag-Cu solder joints were investigated. Experimental results indicate that solidification cracks existed in significant numbers in the miniature Sn-Ag-Cu solder joints. In order to create solidification cracks in the miniature solder joints during solidification and evaluate the susceptibility of Sn-Ag-Cu alloys to solidification cracking, a copper self-restraint specimen was designed, which can simulate the process of solidification crack formation. The solidification crack susceptibility of the Sn-Ag-Cu solder alloy was evaluated using the total crack length of the solder joint. In addition, the effect of trace amounts of elemental additions on solidification cracking of Sn-Ag-Cu solder joints was studied. It was found that adding trace amounts of Ni or Ce could depress the solidification cracks in Sn-3.0Ag-0.5Cu solder joints. However, P additions aggravated the formation of solidification cracks.     

陶瓷封装倒装焊器件Sn-Pb微焊点的电迁移行为

高密度陶瓷封装倒装焊器件的焊点尺寸已降低至100μm以下,焊点电流密度达到10~4 A/cm~2以上,由此引发的电迁移失效成为不可忽视的问题。以陶瓷封装菊花链倒装焊器件为研究对象,开展了Sn10Pb90、Sn63Pb37焊点热电环境可靠性评估试验,通过电连接检测及扫描电子显微镜(SEM)等方法对焊点互连情况进行分析。结果表明,Sn63Pb37焊点阴极侧金属间化合物(IMC)增长明显,表现出明显的极化现象,IMC厚度的平方与通电时间呈线性关系。通电时间达到576 h后Sn63Pb37焊点阴极侧产生微裂纹,而Sn10Pb90焊点在通电576 h后仍未出现异常,表现出优异的电迁移可靠性。研究结果对于直径100μm微焊点的陶瓷封装倒装焊器件的应用具有重要的意义。