Advanced underfill for high thermal reliability

The key to the success of flip‐chip technology lies in the availability of sucessful underfill materials. However, the reliability of flip‐chip technology using current underfill materials is generally found to be lower than that of conventional wire‐bond connection packaging materials such as epoxy molding compound (EMC) because of the high coefficients of thermal expansion (CTE) and moisture absorption of cured underfill material. In this study desbimide (DBMI), which has a low melting point (about 80°C), was used in the underfill materials as a cohardener. As a result, DBMI‐added underfill can show excellent thermal reliability, which is due to the superior properties of the CTE, the elastic modulus, and water resistance. When the properties of a 2 wt % DBMI‐added underfill were compared with those of a typical underfill (epoxy/anhydride), the CTE value was reduced to less than one‐half at the solder reflow temperature (about 200°C), the elastic modulus was reduced to less than one‐half in the temperature region below the glass‐transition temperature, and the water resistance was improved twofold. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 2617–2624, 2002     

新型可返工环氧底部填充料的合成和性能

合成了两种分别含有叔酯键和叔醚键的环氧化合物EP-1和EP-2,其结构通过红外光谱、氢核磁共振谱及环氧当量测定等方法得到证实.EP-1与已有商品ERL-4221以环氧物质的量比1:1混合组成EP-3.EP-2和EP-3用酸酐类固化剂HMPA固化.TGA测试表明它们具有理想的起始热分解温度(IDT=210～220℃),显著低于现在普遍应用的环氧底部填充料ERL-4221(IDT=310℃).它们的粘结强度和玻璃化转变温度Tg在返工温度(225℃)老化数分钟后迅速降低,可以满足当前微电子倒装芯片封装对可返修工艺的要求.     

Interconnection Technology Based on InSn Solder for Flexible Display Applications

A novel interconnection technology based on a 52InSn solder was developed for flexible display applications. The display industry is currently trying to develop a flexible display, and one of the crucial technologies for the implementation of a flexible display is to reduce the bonding process temperature to less than 150°C. InSn solder interconnection technology is proposed herein to reduce the electrical contact resistance and concurrently achieve a process temperature of less than 150°C. A solder bump maker (SBM) and fluxing underfill were developed for these purposes. SBM is a novel bumping material, and it is a mixture of a resin system and InSn solder powder. A maskless screen printing process was also developed using an SBM to reduce the cost of the bumping process. Fluxing underfill plays the role of a flux and an underfill concurrently to simplify the bonding process compared to a conventional flip‐chip bonding using a capillary underfill material. Using an SBM and fluxing underfill, a 20 μm pitch InSn solder SoP array on a glass substrate was successfully formed using a maskless screen printing process, and two glass substrates were bonded at 130°C.     

Novel deprocessing technique for failure analysis of flip-chip integrated circuit packages

A novel technique for flip-chip package deprocessing that allows for detailed failure analysis of internal flip-chip packaging structures and chip circuitry has been developed. A systematic approach of selective wet etching and plasma etching is utilized. Understanding of package level reliability can be greatly enhanced with the capability to systematically access and examine defects in three-dimensions with powerful analytical tools such as the SEM/EDS. Additionally, the ability to inspect large areas of internal packaging structures, e.g., solder bump array, in three-dimensions makes it faster and more convenient to locate defects, compared to two-dimensional techniques such as progressive cross-sectioning. Case studies involving defects in solder bumps, underfill material, and substrate metallization are presented.     

Characterization of Fluxing and Hybrid Underfills with Micro‐encapsulated Catalyst for Long Pot Life

For the fine‐pitch application of flip‐chip bonding with semiconductor packaging, fluxing and hybrid underfills were developed. A micro‐encapsulated catalyst was adopted to control the chemical reaction at room and processing temperatures. From the experiments with a differential scanning calorimetry and viscometer, the chemical reaction and viscosity changes were quantitatively characterized, and the optimum type and amount of micro‐encapsulated catalyst were determined to obtain the best pot life from a commercial viewpoint. It is expected that fluxing and hybrid underfills will be applied to fine‐pitch flip‐chip bonding processes and be highly reliable.     

无铅倒装焊点的热应力与湿热应力分析

板上倒装芯片（FCOB）作为一种微电子封装结构形式得到了广泛的应用。微电子塑封器件中常用的聚合物因易于吸收周围环境中的湿气而对封装本身的可靠性带来很大影响。文章采用有限元软件分析了潮湿环境下板上倒装芯片下填充料在湿敏感元件实验标准MSL-1条件下（85℃／85％RH、168h）的潮湿扩散分布,进而分别模拟计算出无铅焊点的热应力与湿热应力,并加以分析比较。论文的研究成果不仅对于塑封电子元器件在潮湿环境中的使用具有一定的指导意义,而且对于FCOB器件在实际应用中的焊点可靠性问题具有一定的参考价值。     

倒装片可修复底部填充材料的研究现状及发展

有机基板上的倒装芯片一般采用底部填充技术以提高其封装的可靠性.有缺陷的芯片在倒装后难以进行返工替换,使得倒装芯片技术成本提高,限制了此技术的应用.提出新型可修复底部填充材料的开发成为解决这一问题的有效途径.介绍了倒装芯片的可修复底部填充技术和可应用于可修复底部填充材料的技术要求,并综述了国内外对于可修复底部填充材料的研究现状.     

面向窄节距倒装互连的预成型底部填充技术

近年来随着电子产品的小型化发展,窄节距倒装芯片互连已经成为研究热点。传统的倒装芯片组装后底部填充技术(例如底部毛细填充)在用于窄节距互连时易产生孔洞,导致可靠性降低,因此产业界开发了面向窄节距倒装芯片互连的预成型底部填充技术,主要包括非流动底部填充和圆片级底部填充。介绍了这类新型底部填充技术的具体工艺及材料需求,并提出了目前其在大规模量产以及未来更窄节距应用中存在的问题及挑战,总结了目前产业界在提高量产生产效率、提升电互连的可靠性以及开发纳米级高热导率填料等方面提出的解决方案,分析了该技术未来的发展方向。     

覆晶封装底胶充填流动研究

在IC封装中,覆晶封装拥有低成本、低交介口及体积小的特色.文中主要探讨了覆晶封装底胶充填时,锡球、芯片及基板间的流动状况.所使用的制程参数为进浇型式、射出压力、充填时间及锡球尺寸.进浇型式有单点、一字、L型和U型.研究结果显示,在覆晶封装底胶充填时,实验观察和仿真分析所得的平面方向的自由液面形状非常一致.在厚度方向,实验观察的自由液面形状为凹形.不同射出压力下,自由液面的接触角均相同.由此而知,在底胶充填时,表面张力为主要作用力.在相同射出压力下,0.8 mm锡球的自由液面接触角大于1.0 mm锡球的自由液面接触角.     

FPA探测器微细间隙填充工艺研究

介绍了倒焊器件填充工艺原理,分析了胶水粘度、放置时间、填充温度和填充速度对填充效果的影响.在常温条件下,选用的胶水放置时间不超过1h,填充速度为0.20 mg/min时,FPA(焦平面阵列)探测器有效区域的填充率达到100％,测试合格率大于95％.