各向异性导电胶倒装封装电子标签的可靠性

各向异性导电胶(ACA)广泛用于RFID电子标签芯片封装,具有芯片对位方便、热压温度低和工艺时间短的优点.但ACA互连本质上是机械接触,其互连可靠性强烈依赖于粘接界面性质、胶水粘接力及环境稳定性.本文试验表明,168 h高温高湿和D20 mm心轴弯曲对芯片粘接点的电接触性能有所影响;铜模组良品率显著高于铝天线Inlay.     

倒装芯片互连结构中电流聚集研究

由于电流聚集,在倒装芯片封装技术中,电迁移已经成为一个关键的可靠性问题。分析了电迁移力和电迁移中值失效时间,采用二维模型研究了电流密度和焦耳热在倒装芯片互连结构中的分布以及影响电流密度和焦耳热分布的因素。结果表明铝线(Al)和凸点下金属层(UBM)的厚度对电流密度和焦耳热分布有很大的影响。     

倒装封装用各向异性导电胶专利技术综述

如今IC器件的封装集成度越来越高,芯片的封装朝着小间距、高密度的方向发展.利用各向异性导电胶来实现高密度、高稳定性的倒装封装成为近几年的研究热点.本从国内外专利申请量、申请人等多方面进行统计分析.最后总结了在倒装封装用各向异性导电胶领域的国际、国内专利申请分布情况,并对该领域的发展路线进行了梳理.     

倒装芯片各向异性导电胶互连的剪切结合强度

采用冲击试验方法研究了各向异性导电胶膜(ACF)互连的玻璃和柔性基板上倒装芯片(COG和COF)的剪切结合强度.结果表明:COF比COG的剪切强度高.ACF的固化程度达85%时有最大的结合强度.键合温度、导电颗粒状态、缺陷等因素对ACF互连的结合强度有较大影响,而键合压力的影响不大.     

倒装芯片各向异性导电胶互连的剪切结合强度

采用冲击试验方法研究了各向异性导电胶膜(ACF)互连的玻璃和柔性基板上倒装芯片(COG和COF)的剪切结合强度.结果表明:COF比COG的剪切强度高.ACF的固化程度达85 %时有最大的结合强度.键合温度、导电颗粒状态、缺陷等因素对ACF互连的结合强度有较大影响,而键合压力的影响不大.     

倒装芯片及封装技术

介绍了倒装芯片的发展过程，其中主要对制造技术、封装方法及倒装焊焊点的可靠性进行了评述。     

各向异性导电胶互连技术的研究进展

随着微电子封装技术的发展,各向异性导电胶作为一种绿色的连接材料,广泛应用于电子产品中。文中主要介绍各向异性导电胶互连器件的粘接原理和影响其可靠性的各种因素,如粘接工艺参数、外界环境的干扰、各向异性导电胶的物理特性等。     

Transmission property of flip chip package with adhesive interconnection for RF applications

The radio frequency (RF) and high frequency performance of the flip chip interconnects with anisotropic conductive film (ACF) and non-conductive film (NCF) was investigated and compared by measuring the scattering parameters (S-parameters) of the flip chip modules. Low cost electroless-Ni immersion-Au (ENIG) plating was employed to form the bumps for the adhesive bonding. To compare the accurate intrinsic RF performance of the ACF and NCF interconnect without lossy effect of chip and substrate, a de-embedding modeling algorithm was employed. The effects of two chip materials (Si and GaAs), the height of ENIG bumps, and the metal pattern gap between the signal line and ground plane in the coplanar waveguide (CPW) on the RF performance of the flip chip module were also investigated. The transmission properties of the GaAs were markedly improved on those of the Si chip, which was not suitable for the measurement of the S-parameters of the flip chip interconnect. Extracted impedance parameters showed that the RF performance of the flip chip interconnect with NCF was slightly better than that of the interconnect with ACF, mainly due to the capacitive component between the bump and substrate and self inductance of the conductive particle surface in the ACF interconnect.     

Failure mechanism of anisotropic conductive adhesive interconnections in flip chip ICs on flexible substrates

In this work we study how the endurance performance of electrically conductive adhesive interconnections of flip chip integrated circuits with a pitch of 200 and 150/spl mu/m on flexible substrates is affected by varying environmental conditions. This is accomplished by comparison of offline and online control measurements that are carried out to monitor the electrical resistance in temperature-humidity and temperature cycling stress tests. From the gradual degradation of the resistance with time and the failure analysis, it is conjectured that periodic absorption and desorption of moisture forms one of the more important failure mechanisms in this type of assembly.     

Correlation of material properties to reliability performance of anisotropic conductive adhesive flip chip packages

The anisotropic conductive adhesive (ACA) is a promising solder alternative candidate that shows potential for further pitch reduction. Although much work has been published on ACA joint behavior, study on correlation of material properties with reliability performance is still lacking. The main objective in this study was to identify the impact of material properties on reliability, so as to engineer highly reliable microelectronics assemblies. Four representative ACA materials (both film and paste types) with diverse properties were selected. Material properties were characterized as close as possible to "stress test" conditions so as to allow more accurate correlation predictions. Reliability performance was obtained by assembling test chips of 200-/spl mu/m pitch onto BT-substrates, then subjecting them to reliability tests. Correlation analysis was conducted and key material properties that contributed to good reliability performance were identified. Findings indicated that the best properties for high reliability assemblies were: high adhesion strength after subjecting to "stress aging", low coefficient of moisture expansion (CME) and low elastic modulus (E).     

Microwave preheating of anisotropic conductive adhesive films for high-speed flip chip on flex bonding

Anisotropic conductive adhesive film (ACF) can be preheated by microwave (MW) radiation in order to reduce the bonding time for flip-chip technology. Due to sluggish and nonuniform curing kinetics at the beginning of the curing reaction, thermal curing of epoxy is more time consuming. Therefore, MW radiation may be more effective, due to its uniform heating rate during the cycle. In this paper, MW preheating (for 1–4 sec) of ACF prior to final bonding has been applied to determine the electrical and mechanical performance of the bond. Powers of 80 and 240 W MW were used to study the effect of the MW preheating. A final bonding time of 6–7 sec can be used for flip chip on flex bonding instead of 10–15 sec (standard time for flip chip bonding) for MW preheating time and power used in this study. The contact resistance (as low as 0.01) is low in these samples, whereas the standard resistance is 0.017 ohm (bonded at 180°C for 10 sec without prior MW preheating). The shear forces at breakage were satisfactory (0.167–0.183 KN) for the samples bonded for 6–7 sec with MW preheating. This is very close and even higher than the standard sample (0.173 KN). For MW preheating power of 80 W and sweeping time of 2 sec, final bonding at 6 sec can also be used because of its low contact resistance (0.019 ohm). Scanning electron microscope (SEM) investigation of microjoints and fracture surface shows uneven distribution of conductive particles and thick bond lines in samples bonded for 5 sec (with MW preheating). Samples treated with MW radiation (80 W and 2–3 sec time) serve as evidence that well-distributed particles along with thin bond lines cause low contact resistance and high joint strength.     

Humidity and reflow resistance of flip chip on foil assemblies with conductive adhesive joints

The drive toward new first level interconnection technologies is running in parallel with the need to study their reliability as such, as well as in further processes such as second level reflow soldering. Both material properties and process settings have a significant effect on the reliability of adhesive interconnections of flip chips on flexible foil substrates. Integrated circuits (ICs) with pitches of 200 and 300 /spl mu/m bonded on two different foil types were subjected to various moisture preconditioning treatments, and subsequently reflow soldered. Measurements of the daisy chain resistance are used to monitor the yield before and after reflow testing, and to qualify the endurance behavior in the 85/spl deg/C/85% RH stress test. We address here the possible failure mechanisms.     

Moisture-induced failures of adhesive flip chip interconnects

Adhesive flip chip interconnect has been recognized as a promising substitute for solder interconnection due to its fine-pitch, lead-free, and low-temperature processing capabilities. As adhesives are made of polymers, moisture absorption by the polymeric resin remains as one of the principal contributors to adhesive joint failure mechanisms. In this research, the reliability performance of the adhesive flip chip in the pressure cooker test and moisture sensitivity test conditions was investigated. The failure modes were found to be interfacial delamination and bump/pad opening which may eventually lead to total loss of electrical contact. Different sizes of bump/pad opening in the interconnections were discussed in the context of the significance of mismatch in coefficient of moisture expansion (CME) between adhesive and other components in the package, which induces a hygroscopic swelling stress. The effect of moisture diffusion in the package and the CME mismatch were also evaluated from the standpoint of finite element modeling. In this study, it is concluded that hygroscopic swelling assisted by loss of adhesion strength upon moisture absorption is responsible for the moisture-induced failures in these adhesive flip chip interconnects.     

Dynamic strength of anisotropic conductive joints in flip chip on glass and flip chip on flex packages

The work presented in this paper focuses on the behavior of anisotropically conductive film (ACF) joint under the dynamic loading of flip chip on glass (COG) and flip chip on flexible (COF) substrate packages. Impact tests were performed to investigate the key factors that affect the adhesion strength. Scanning electron microscopy (SEM) was used to evaluate the fractography characteristics of the fracture. Impact strength increased with the bonding temperature, but after a certain temperature, it decreased. Good absorption and higher degree of curing at higher bonding temperature accounts for the increase of the adhesion strength, while too high temperature causes overcuring of ACF and degradation at ACF/substrate interface––thus decreases the adhesion strength. Higher extent of air bubbles was found at the ACF/substrate interface of the sample bonded at the higher temperature. These air bubbles reduce the actual contact area and hence reduce the impact strength. Although bonding pressure was not found to influence the impact strength significantly, it is still important for a reliable electrical interconnect. The behaviors of the conductive particles during impact loading were also studied. From the fracture mode study, it was found that impact load caused fracture to propagate in the ACF/substrate interface (for COG packages), and in the ACF matrix (for COF packages). Because of weak interaction of the ACF with the glass, COG showed poor impact adhesion.     

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.     

Corrosion protection of anisotropically conductive adhesive joined flip chips

Corrosion is a common cause of failure in electronic devices. Conformal coatings may be used to prevent corrosion of electronics packages. Water and contaminants are thus not in direct contact with the package surface, which may improve resistance to corrosion. However, it is important to study the effects of corrosion on both coating materials and on the electronics itself. The protection method and the level of protection can then be selected.This study presents a salt spray test of anisotropically conductive adhesive joined flip chip components on FR-4 substrate, where half of the test samples were parylene C coated. A dramatic difference was seen between these two test lots. Parylene C proved to be an excellent barrier against salt spray. The test lots without conformal coating suffered severe corrosion, and were thus considerably less reliable. Scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) revealed the reasons for the failures in the non-coated test samples. The main reason was found to be severe corrosion of the nickel layer. There were no failures among the parylene C coated test samples during the 3000 h test. Moisture absorption of the FR-4 substrate material is also studied in this paper. Both plain FR-4 and parylene C coated FR-4 materials were studied. These tests were performed both at room temperature and in boiling water.