稀释剂对环氧树脂电子束辐射固化性能的影响

对分别加入4 种稀释剂的双酚A 环氧树脂和酚醛环氧树脂的电子束辐射固化性能进行了研究。分析了稀释剂种类及含量对环氧树脂体系辐射产物的固化度、固化均匀性、固化区域大小及其动态力学性能的影响规律。结果表明: 电子束固化环氧树脂体系中加入稀释剂后, 辐射产物的固化度、玻璃化转变温度及储能模量有所下降, 但固化均匀性得到提高; 加入稀释剂的环氧树脂电子束固化区域的厚度均小于未加稀释剂树脂, 而底面直径却大于未加稀释剂树脂; 随着树脂中实际稀释剂含量的增加, 电子束固化环氧树脂固化度逐渐降低, 固化层厚度减小, 固化区域的底面直径先增加后减小。      

Effect of adhesive fillet geometry on bond strength between microelectronic components and composite circuit boards

Printed circuit boards (PCBs) assembled with ball grid array (BGA) microelectronics packages were tested in a double cantilever beam (DCB) configuration. The results were compared for a filled and an unfilled underfill epoxy adhesive as well as a cyanoacrylate adhesive. The original fillet, formed in the underfilling process, was modified to create fillets of different sizes. Regardless of the underfill thermal and mechanical properties as well as its curing profile, the crack initiation load and the failure mode were solely a function of the size of the underfill fillet, and the failure always initiated within the PCB. Moreover, the strength of the underfilled solder joints was increased significantly (approximately 100%) by the presence of a relatively large fillet. This effect of the underfill fillet on the crack path and the fracture load was then examined in terms of differences in the stress states using a finite element model.     

Enhanced reliability of high-density wiring (HDW) substrates through new base substrate and dielectric materials

Flame retardant glass/epoxy composite (FR4) has been extensively used as a substrate material for microelectronic packaging due to its cost effectiveness and overall performance. However, to be able to fabricate high-density wiring with microvias, and embed capacitors, inductors, resistors, and RF and optoelectronic waveguides into a single substrate, we need materials other than FR4 as a base substrate to meet the stringent warpage requirements during fabrication. Typically, these base substrate materials should have a high modulus and good planarity in addition to having a coefficient of thermal expansion (CTE) that is close to that of silicon so that flip-chips can be attached directly to the substrate without the need for an underfill. Although low-CTE and high modulus base substrate materials can result in low warpage and can eliminate the need for an underfill, they can potentially cause delamination and cracking in the interlayer dielectric. This is due to the high CTE mismatch between the base substrate and a typical polymer dielectric. This paper aims to explore a combination of a base substrate material and an interlayer dielectric material such that the warpage is minimal, the dielectric will not crack or delaminate, and the flip-chip solder joints, assembled without an underfill, will not crack prematurely during qualification regimes or operating conditions. Non-linear finite element models with a design-of-simulations approach are used in arriving at optimized thermo-mechanical properties for the base substrate and the dielectric materials to enhance the overall reliability of the integrated substrate with flip-chip assembly. It is seen that an aluminum nitride base substrate with resin-coated foil C provides the best combination against dielectric cracking, high warpage, and solder joint fatigue. The results from the models have also been validated with experimental data.     

The fracture energy of some epoxy resin materials

The double cantilever beam technique has been used to measure the fracture energy of a series of cured epoxy resins. A range of materials was produced by varying the proportion of resin to hardener agent (Araldite CT200 and hardener HT901 — phthalic anhydride, CIBA Ltd) and by adding silica flour or aluminium powder as a filler. The fracture energy for crack initiation in the cured epoxy resins ranged from approximately 10³ to 10⁵ erg cm⁻², and in the “filled resins” from 10⁴ to 5×10⁵ erg cm⁻², as the proportion of hardener increased. The fracture energy for crack arrest was somewhat lower at the higher hardener contents and particularly for the Al-filled material.     

Flexural and interlaminar shear strength properties of carbon fibre/epoxy composites cured thermally and with microwave radiation

The ease of heating an epoxy resin with microwaves depends, among other factors, on the dielectric properties of its components at the frequency of the radiation used. The majority of the papers published on the microwave curing of reinforced epoxy resin composites have used widely available DGEBA type resins and amine hardeners such as 4,4′-diaminodiphenylsulphone (DDS). This paper investigates the use of two epoxy systems where the choice of resin and hardener was based on their measured dielectric loss factors. System 1 contained a resin and hardener with higher loss factors than those used in System 2. The two systems are formulated with polyetherimide (PEI) as a toughening agent. Unidirectional carbon fibre prepregs were prepared from both systems. Composites were laid up from these prepregs, which were then cured in three different ways: autoclave curing, partial autoclave curing followed by microwave post-curing, and microwave curing. System 1 composites had greater flexural properties and interlaminar shear strengths than System 2 composites when autoclave cured. Flexural properties and interlaminar shear strengths were greater for System 2 in the microwave post-cured composites. When fully microwave-cured the properties were similar. In the microwave-cured composites the flexural and interlaminar shear properties were influenced by the structure of the phase separated PEI and the void content.     

热塑性塑料对环氧树脂热膨胀系数的影响研究

环氧树脂基体的热膨胀系数(CTE)对碳纤维增强环氧树脂层状材料的性能影响巨大,如何降低环氧树脂基体的CTE是提高碳纤维增强环氧树脂复合材料低温使用性能的关键。本研究采用聚对苯二甲酸丁二醇酯(PBT)、聚碳酸酯(PC)和聚醚酰亚胺(PEI)3种热塑性塑料改性环氧树脂,研究了这3种热塑性塑料对环氧树脂基体CTE的影响。结果表明:这3种热塑性塑料分子链中的羰基在环氧树脂固化过程中可与环氧分子侧链上的羟基形成氢键作用,从而加强了热塑性塑料与环氧树脂的界面作用;采用这3种热塑性塑料改性环氧树脂均可提高环氧树脂基体的玻璃化转变温度;相对于纯环氧树脂,PBT、PEI和PC改性的环氧树脂在玻璃化转变温度下的CTE分别降低了14.99%、17.44%和23.96%,但在玻璃化转变温度上的CTE均高于纯环氧树脂。     

用DSC技术研究环氧树脂体系的固化反应

本文用差示扫描量热法(DSC)研究了九种环氧树脂与六种固化剂的反应性。分析了环氧树脂的结构和固化剂的结构对各环氧树脂体系的固化反应的影响,并结合热失重分析(TG)研究了间苯二胺(m-PDA)和二氨基二苯基砜(DDS)与各种环氧树脂固化物的分解温度。      

Effect of underfill on bending fatigue behavior of chip scale package

This study evaluated the mechanical behavior of chip scale packages (CSPs) with the underfills using the four-point bending test. The bending fatigue durability in the CSP increased with increasing glass transition temperature (T _g ) of the underfill. The mechanical fatigue cracks occurred in the region between the (Ni,Cu)₃Sn₄ layer and the solder region near the upper substrate and the solder region of the CSP with the underfill which had the higher T _g . However, these cracks occurred in the region between the (Ni,Cu)₃Sn₄ layer and the Ni₃P layer near the bottom substrate and the solder region of the CSP with the underfill which had the lower T _g .     

聚氨酯接枝改性环氧树脂的微观结构

由端-NCO基聚氨酯预聚物(PU)与环氧树脂(EP)反应制备了聚氨酯接枝改性环氧树脂(EP-g-PU),考察了PU和活性稀释剂含量及异氰酸酯结构对EP-g-PU固化物玻璃化转变温度(Tg)和微观形貌的影响。结果表明,EP-g-PU固化物的Tg随PU含量增加而升高,随活性稀释剂含量增加而降低;三种异氰酸酯制备的EP-g-PU固化物的Tg顺序为IPDIMDITDI。异佛尔酮二异氰酸酯(IPDI)和二苯基甲烷二异氰酸酯(MDI)型EP-g-PU固化物的断面形貌为以EP为细胞核、PU为细胞壁的两相细胞状结构,甲苯二异氰酸酯(TDI)型EP-g-PU固化物的断面形貌为PU以岛状分布于EP基体中的海岛结构,但岛相也是以EP为细胞核、PU为细胞壁的两相细胞状结构。     

环氧树脂预聚物分子量对其固化物性能的影响

本文着重研究了环氧树脂预聚物分子量对叔胺促进剂催化的酸酐固化剂固化的环氧树脂体系固化物电气、力学和耐热性能的影响。结果表明,环氧树脂预聚物分子量对性能有显着影响,且具有规律性。      

Investigating of polysulfide and epoxy‐polysulfide copolymer curing

Polysulfide can be cured in various methods. In this work, the effect of various oxidative curing agents (manganese dioxide and para quinonedioxime) in presence of curing accelerator (Diphenylguanidine) on mechanical‐dynamical properties and cure time of polysulfide resin (G4) was investigated. Results showed that mentioned oxidative curing agents have no remarkable effect on mechanical properties and cure time. But preferred method is preparation of polysulfide‐epoxy copolymer. This copolymer is a new class of liquid polymer composition containing block copolymers, with alternating blocks of polysulfide and polyepoxide. in different epoxy/polysulfide ratio, the epoxy‐polysulfide copolymer showd different tensile strenght, elongation, hardness, gel time, viscosity and Tg, but epoxy free polysulfide approximately revealed constant mechanical and dynamical properties so that epoxidized polysulfide had excellent mechanical properties and suitable curring times in comparison with those samples which were cured in other methods. FT‐IR spectroscopy, viscometry and GPC were used to verify the formation of epoxy‐polysulfide copolymer. Results obtained from DMTA and SEM showed that phase separation of epoxy resin from the copolymer matrix took place and The glass transition temperature (Tg) of the cured copolymer was between the cured epoxy and polysulfide glass transition temperatures.     

Production of novel epoxy micro-balloons

Epoxy micro-balloons are prepared by dropping and stirring of epoxy mixture in heated silicon oil. The mixture of epoxy, curing agent and blowing agent forms sphere particles, which are then blown via the function of blowing agent and simultaneously cured to form epoxy micro-balloons. Different ratio of epoxy and hardener will produce different types of epoxy micro-balloons. Schematic illustrations to produce the epoxy micro balloons are also proposed.     

含磷双环戊二烯酚醛固化剂的合成及固化环氧树脂的性能

合成了一种含磷酚醛型环氧树脂固化剂DCPD-DOPO,通过红外光谱和核磁共振谱对其化学结构进行了表征,采用凝胶渗透色谱测量了其相对分子质量。以DCPD-DOPO、苯酚型酚醛树脂(PF8020)或其复合物为固化剂,双酚A环氧树脂(DGEBA)为基料,制备了不同磷含量的阻燃环氧树脂。通过热重分析、差示扫描量热分析研究了环氧树脂固化物的热性能和阻燃性能;通过极限氧指数(LOI),垂直燃烧实验和锥形量热法研究了固化后环氧树脂固化物的燃烧特性。结果表明,DCPD-DOPO固化的环氧树脂的LOI可达31.6%,垂直燃烧性能达到UL94 V-0级,玻璃化转变温度(T_g)为133℃。采用DCPD-DOPO与PF8020复合物固化的环氧树脂的T_g提高到138℃以上,LOI值略有降低,但仍能通过UL 94V-0测试。DCPD-DOPO与PF8020添加DCPD-DOPO后,复合固化的环氧树脂的热释放速率峰值及总释热量较PF8020固化的环氧树脂大幅度降低。此外,还用Kissinger法对环氧树脂固化反应动力学进行了研究。     

Electrical properties and interfacial reaction of BGA package with underfill

This study evaluated the electrical properties and interfacial reaction of the ball grid array (BGA) packages with various underfills under thermal shock and isothermal aging conditions. The BGA packages were composed of two surface finishing materials on the bottom substrate, viz. bare Cu and electroless nickel-immersion gold (ENIG). The thickness of the intermetallic compounds (IMCs) formed at the interface between the solder and substrate increased with increasing number of thermal shock cycles and isothermal aging times. Also, the growth rate of the IMCs during the isothermal aging condition was faster than that during the thermal shock condition. The electrical resistance of the BGA package with the underfill was lower than that of the BGA package without the underfill under thermal shock condition. The electrical resistance of the underfill with silica particles was lower than that of the underfill without silica particles.     

Impact of packaging materials on reliability test for low-K wire bond-stacked flip chip CSP

As the consumer electronics market keeps expanding, the system-in-package (SiP) has become more and more popular. The SiP has the benefits of space efficiency and an integrated flexible function by stacking different function dies in a single package. With die stacking, bi-material interfacial delamination becomes a primary concern of reliability testing. This work evaluates the impact of encapsulated molding compound (EMC) and underfill material on the reliability test for the low-K wire bond-stacked flip chip CSP (WB-sFC CSP). The CSP packaging size is 16 × 16 × 1.2 mm with a 4 × 5 × 0.15 mm low-K wire bond die stacked on a low-K 8 × 8 × 0.15 mm flip chip die. The reliability testing condition is JEDEC MSL 2a (reflow peak temperature is 260 °C) followed by the temperature cycling test (TCT, −55 to 125 °C) of 1000 cycles. The severe pre-conditioning environment makes the packaging materials selection a challenge. Delamination between the interface of the underfill and other packaging components leads to premature failure during preconditioning. TCT stress also induces delamination between the interface of the backside of the bottom die and the encapsulated molding compound. Initially, the EMC selection was decided by the first stage experimental result based on the assembly yield. A DOE was performed to study the effect of underfill property on the packaging stress using the finite element analysis (FEA). According to the FEA results, the trend of underfill property selection for solving the underfill delamination and the backside of the bottom die delamination were in conflict. The low coefficient of thermal expansion (CTE) and the high Young’s modulus (E) underfill can reduce the stress located at the backside of the bottom die corner but it will increase the underfill stress. Plasma cleaning was applied to improve the underfill and the packaging components interface bond strength prior to dispensing the underfill. In the second stage, three underfills were evaluated based on the three different reasons, low modulus for preventing underfill delamination, high modulus for reducing the backside of the bottom die stress, and low moisture absorption by reducing steam pressure during preconditioning. The experimental results in this work demonstrate that only a high modulus underfill can pass the reliability test.     

Effect of structure on properties of vinyl ester resins

The paper describes the synthesis of vinyl ester resins based on diglycidyl ether of bisphenol-A (epoxy equivalent = 450–465 g/eq) (VR resin) and tetrabromobisphenol-A (epoxy equivalent = 380–420 g/eq) (VR-1 resin). The viscosity of styrenated VR resin was higher than VR-1 resin. The effect of styrene andα-methyl styrene on curing of VR resins was studied. An increase in styrene from 30 to 50 wt% resulted in an increase in gel time and a decrease in exothermic peak. Addition ofα-methyl styrene delayed and depressed the exotherm. The mechanical properties of VR resin sheets and glass fabric reinforced laminates were better than VR-1 resins; whereas LOI of VR-1 was higher. A resin formulation containing 20–30 wt% of VR: VR-1 showed optimum mechanical properties and LOI.     

Ultra low-k die crack study for lead free solder bump flip-chip packaging

Ultra low-K (ULK) dielectric has lower mechanical strength (E < 8 GPa), lower cohesive strength and lower adhesion (<5 J/m²) than low-K and SiO₂ dielectric material. The packaging reliability test has shown that delamination between copper (Cu) and ULK is a major concern. In addition to the Cu and ULK delamination issue, the ULK die crack after temperature cycling test (TCT) showed die crack failure to be another issue. ULK die crack failure can be detected by C-mode scanning acoustic microscopy (CSAM). The CSAM image of the die crack mostly shows a crescent moon shape. The crack initiates at the upper edge of the underfill fillet penetrating the sidewall of the die, and then propagates toward the inside of the die. Finite element simulation indicates that the die crack failure starts at the backside edge of the die. The ULK die crack is caused by two mechanisms. First is the bending stress at the backside of the die, which is the result of the coefficient of thermal expansion (CTE) mismatch between the silicon die and the organic substrate. Second is the thermo-mechanical stress, which is the result of the local CTE mismatch between the silicon die and the underfill. The finite element simulation parametric study performed in this paper shows that a low underfill fillet height and a small fillet tip angle reduce the thermo-mechanical stress. In addition, attaching a heat sink to the surface of the flip-chip die increases packaging stiffness and resists the bending stress induced by the shrinkage of the substrate. Experimental results demonstrate that lowering the height of the underfill fillet, reducing the angle of the fillet tip and attaching a heat sink to the flip-chip die are effective ways to solve the ULK die crack issue.     

Preparation of Microcellular Epoxy Foams through a Limited‐Foaming Process: A Contradiction with the Time–Temperature–Transformation Cure Diagram

3D cross‐linking networks are generated through chemical reactions between thermosetting epoxy resin and hardener during curing. The curing degree of epoxy material can be increased by increasing curing temperature and/or time. The epoxy material must then be fully cured through a postcuring process to optimize its material characteristics. Here, a limited‐foaming method is introduced for the preparation of microcellular epoxy foams (Lim‐foams) with improved cell morphology, high thermal expansion coefficient, and good compressive properties. Lim‐foams exhibit a lower glass transition temperature (T_g) and curing degree than epoxy foams fabricated through free‐foaming process (Fre‐foams). Surprisingly, however, the T_g of Lim‐foams is unaffected by postcuring temperature and time. This phenomenon, which is related to high gas pressure in the bubbles, contradicts that indicated by the time–temperature–transformation cure diagram. High bubble pressure promotes the movement of molecular chains under heating at low temperature and simultaneously suppresses the etherification cross‐linking reaction during post‐curing.     

电子束固化环氧树脂温度效应影响因素分析

对环氧树脂电子束辐射过程中的温度特性进行了研究。利用实时3D温度场采集系统测定了辐射过程树脂体系的温度,探讨了环氧树脂化学结构、分子量、引发剂、稀释剂及其含量对体系温度的影响。结果表明,电子束作用于体系后,体系温度随辐射剂量的加大而升高,但当剂量达到某一值后,体系温度不再升高而保持恒定;此种热效应主要是由被辐射体系吸收高能电子能量引起的。树脂分子的吸电子能力取决于环氧树脂分子的化学结构,与分子量无关。加入稀释剂之后,体系会出现温度峰,且随着稀释剂含量的增多,温度峰峰顶温度升高。