塑封胶吸湿对器件分层影响的研究

进行3种塑封胶的吸湿试验来证实其在相同器件中的不同可靠性表现由吸湿量的差异造成,得到了树脂相同的塑封胶的吸湿量与二氧化硅填充量之间的关系。证实了MSL3条件下塑封胶吸湿遵循Fick定律,并且得到了MSL3条件下3种塑封胶中湿气的扩散系数。综合考虑回流过程中蒸汽压、塑封胶吸湿膨胀和热膨胀,进行了界面分层风险的定量分析。     

塑封器件分层失效实例分析

微电子塑封器件常用的环氧树脂塑封料,因其极易吸收周围环境里的水汽而严重影响塑封器件的可靠性。通过一个实例分析,分别从故障定位、机理讨论以及改进措施3个方面对塑封器件分层失效进行详细的论述,从而有效而快速地提升塑封器件可靠性。     

塑封器件可靠性快速评估的研究

本文采用ＰＣＴ试验方法ＳＤ１３００５型ＮＰＮ高反压大功率晶体管进行了加速寿命试验，发现ＢＶｃｅ０是其退化的最敏感参数。并利用自行研究开发的《微电子器个可靠性指标数据处理计算机软件》对试验数据进行统计分析，得知该的失效分布符合威布尔分布，同时评估了不同应力下产品的可靠性寿命特征，外推出１００％相对湿度时，曙下该产品的寿命特征。     

塑封器件芯片与塑封料界面分层的研究

针对一款LQFP塑封器件,利用ANSYS有限软件建立了三维模型,根据断裂参数——J积分,讨论分析了芯片/塑封料界面的三种分层区域模型,得到了分层的主要扩展模型,即凸形分层区域,同时提出了一种分层扩展趋势的新模型,进而对凸形分层模型探讨了温度和裂纹半径对器件分层的影响。仿真数据表明,在极端低温或高温下,器件的分层区域容易扩展;而在一定的应力条件下,裂纹扩展的趋势会受到裂纹半径大小的影响。     

高可靠性塑封器件质量控制措施

随着塑封器件高可靠性应用日益广泛,塑封产品的研制和生产需求不断增加。分析了塑封器件可能存在的热机械缺陷、腐蚀、爆米花效应,以及生产工艺中可能引入的封装、芯片粘接、钝化层等缺陷,从设计和工艺角度给出控制措施。介绍了国内外高可靠性塑封器件筛选、鉴定检验的典型流程及质量控制措施,用于在生产阶段剔除潜在缺陷的不合格品,保证产品具有高可靠性。     

塑封器件分层检测不合格原因探讨

在塑封半导体器件内部裂纹、空洞和分层缺陷的检测中,同样的样品不同单位、不同试验人员总会出现一些器件检测结果不一致的情况。为研究导致检测结果不一致的原因,通过对超声扫描检测技术原理和适用判据标准的阐述,对不同设备的比对验证以及对塑封器件材料的吸湿影响试验和分析,探讨了塑封器件分层检测不合格和不一致的原因,为同行业者提供借鉴和参考。     

热膨胀系数不匹配导致的塑封器件失效

塑封器件使用过程中由于塑封材料和芯片之间热膨胀系数的不匹配,导致在外界温度变化时的应力释放对芯片造成损伤。文中通过VLSI失效分析,对这种应力造成的芯片损伤进行了研究,并提出利用环境应力试验和可靠性分析的方法暴露热膨胀系数不匹配导致芯片损伤的技术。     

集成湿热及蒸汽压对塑封QFN器件的层裂影响

针对微电子封装器件的界面层裂失效问题,利用有限元法,集成湿热及蒸汽压力的作用对塑封QFN器件的界面层裂失效问题进行了建模分析,探索了塑封QFN器件参数的优化组合。结果表明,通过对各参数的优化,如EMC的αv为12×10–6/K,引线框架的E为110GPa等,界面危险裂纹尖端点的J积分降低到优化前的1/10~1/100。研究中还发现,封装器件的参数优化组合不唯一,很有必要探讨并选择一种能适合于这种多优化组合设计的方法。     

回焊炉内氧气体积分数对焊接可靠性的影响

SMT(表面贴装技术)回焊炉工作时,炉中氧气体积分数的差异很大,从100×10–6至10000×10–6不等,在已验证氧气体积分数[(O2)]超过4000×10–6会造成产品不良的前提下,针对500×10–6,1000×10–6,3000×10–6以及4000×10–6这四种不同的氧气体积分数,分别对回焊炉焊接的铜片上的锡焊点进行润湿角、EDS分析,对组装印制电路板(PCBA)上的锡焊点进行X射线、推力、通孔填充量等测试。结果显示,(O2)在4000×10–6以下,元件的焊接可靠性并无明显差异。选择(O2)=4000×10–6可降低回焊炉的氮气用量,节约成本。     

集成湿热及蒸汽压力对塑封器件可靠性的影响

分析了湿热及蒸汽压力对塑封器件可靠性影响的研究现状;结合已有的研究方法,提出一种有限元直接集成湿热及蒸汽压力的分析方法,并以裸露焊盘塑封器件DR-QFN为例进行应用研究。结果表明,该方法能有效分析裸露焊盘塑封器件在湿热、蒸汽压力因素综合影响下的可靠性问题。在无铅回流焊过程中,蒸汽压力为2.5~4.5MPa,对器件可靠性影响很大。     

Reaction kinetics of solder-balls with pads in BGA packages during reflow soldering

The Au/Ni/Cu three-layer structure is one of the most common solder-ball pad finishes for the ball-grid-array (BGA) packages. The first layer, which is to be in direct contact with the solder, is a 1-μm Au layer. Beneath the Au layer is the Ni layer, whose thickness is about 7 μm. The Cu layer is part of the internal wiring of a BGA package. In this study, eutectic PbSn solder-balls were reflowed on the Au/Ni/Cu pads at 225°C for reflow times from 7.5 s to 1003 s. It was found that the Au layer reacted very quickly with the solder to form AuSn₄ and AuSn₂. The growth rate of AuSn₄ + AuSn₂ was very high, approaching 1 μm/s. When the reflow time reached 10 s, all the Au had been consumed, and AuSn₂ had been converted to AuSn₄. Moreover, AuSn₄ grains began to separate themselves from the Ni layer at the roots of the grains, and started to fall into the solder. When the reflow time reached 30 s, all AuSn₄ grains had left the interface and a thin layer of Ni₃Sn₄ formed at the solder-Ni interface. The growth rate of this Ni₃Sn₄ layer was very low, reaching only 6 μm for 1003 s of reflow. This study showed that during reflow the Au layer reacted with Sn to form AuSn₄ first, and then broke off and fell into the molten solder. In other words, the Au layer did not dissolve into the molten solder directly during reflow.     

Kinetics of intermetallic formation at Sn-37Pb/Cu interface during reflow soldering

The kinetics of the intermetallic layer formation at Sn-37wt.%Pb solder/Cu pad interface during reflow soldering were studied. The growth kinetics were analyzed theoretically by assuming that the mass flux of Cu through channels between scalloplike grains primarily contributes to the growth. Rate-controlling steps considered for the mass flux were the Cu dissolution from the bottom of the channels, diffusion through the channel, and the formation reaction of the intermetallic layer. These results indicated that a transition in the growth rate observed around 120–150 sec of reflow time may be associated with transition of the rate-controlling step from the Cu dissolution to the Cu diffusion through the channel.     

热应力影响下SCSP器件的界面分层

通过有限元方法研究了堆叠芯片尺寸封装(SCSP)器件在回流焊工艺过程中的热应力分布,采用修正J积分方法计算其热应力集中处应变能释放率。结果表明:堆叠封装器件中最大热应力出现在Die3芯片悬置端。J积分最大值出现在位于Die3芯片的上沿与芯片粘结剂结合部,达到1.35×10–2J/mm2,表明该位置的裂纹处于不稳定状态;在Die3芯片下缘的节点18,19和顶层节点27三个连接处的J积分值为负值,说明该三处裂纹相对稳定,而不会开裂处于挤压状态。     

塑封器件的贮存环境与使用可靠性

介绍了用潮热环境试验模拟塑封器件在长期贮存时对水汽的吸附以及用潮热试验和焊接热的综合影响来评价塑封器件耐潮湿性能的方法.     

Low temperature delamination of plastic encapsulated microcircuits

Plastic encapsulated microcircuits (PEMs) are increasingly being used in applications requiring operation at temperatures lower than the manufacturer’s recommended minimum temperature, which is 0°C for commercial grade components and −40°C for industrial and automotive grade components. To characterize the susceptibility of PEMs to delamination at these extreme low temperatures, packages with different geometries, encapsulated in both biphenyl and novolac molding compounds, were subjected to up to 500 thermal cycles with minimum temperatures in the range −40 to −65°C in both the moisture saturated and baked conditions. Scanning acoustic microscopy revealed there was a negligible increase in delamination at the die-to-encapsulant interface after thermal cycling for the 84 lead PQFPs encapsulated in novolac and for both 84 lead PQFPs and 14 lead PDIPs encapsulated in biphenyl molding compound. Only the 14 lead novolac PDIPs exhibited increased delamination. Moisture exposure had a significant effect on the creation of additional delamination.     

Characteristics of the Sn-Pb eutectic solder bump formed via fluxless laser reflow soldering

In an attempt to develop a fluxless reflow solder bumping process, the effects of processing variables, which include energy input rate and time, and the shape of solder disk on the microstructure of the solder/Cu pad interface and the shear strength of the joints were investigated. It was demonstrated that a proper combination of the variables could lead to the formation of a spherical solder bump with shear strength comparable to that formed via the conventional reflow soldering process. In addition, the kinetics of Cu pad dissolution into the solder during laser heating was modeled numerically to elucidate intermetallic formation mechanism at the solder/Cu pad interface. Jointly appointed by CAAM at POSTECH     

航空电子产品焊接工艺验证方法研究

针对航空电子产品,阐述了一种相对完善的工艺验证方法,为航空电子产品制造商进行焊接工艺验证提供了指导。电子产品的类型多种多样,文章主要针对航空电子产品的特点,对其焊接工艺的验证方法进行探索和研究。