Epoxy Molding Compound Research Articles

Adhesion improvement of Epoxy Molding Compound – Pd Preplated leadframe interface using shaped nickel layers

The weak adhesion between the Epoxy Molding Compound (EMC) and Pd Preplated leadframes (Pd PPF’s) often causes delaminations and reduces the reliability of integrated circuit. This paper reports on a practical method of dramatically improving the adhesion between EMC and Pd PPF’s using electroplating of shaped nickel layers. Button shear tests indicate that the adhesions between the EMC and three different shaped PPF’s are 100%, 160%, 169% higher than that of conventional PPF’s. The mechanical interlocking effect caused by increased surface roughness is the major reason for the improved adhesion as well as for the failure mode transition from adhesive failure to cohesive failure.

Thermal conductivity and fire resistance of epoxy molding compounds filled with Si 3N 4 and Al(OH) 3

The production of composites of epoxy molding compounds (EMCs), which can feature a good balance between thermal conductivity and flame-retardant behavior in terms of flammability and burning behavior, was achieved by incorporating high thermal conductivity Si 3N 4 and flame retardant Al(OH) 3 (ATH) fillers in the epoxy matrix. The experimental results were obtained from thermal conductivity measurements and limiting oxygen index (LOI) and UL-94 tests. These results showed that the Si 3N 4 filler has a great influence on thermal conductivity, which markedly increased for Si 3N 4 volume fractions >40%, whereas the ATH filler greatly improved the flame resistance of EMCs. The simultaneous presence of both Si 3N 4 and ATH fillers in the EMCs positively influenced both properties. The aim of this study was to produce composites suitable for electronic packaging applications: an optimum combination of the two fillers was determined for a total volume fraction of fillers in EMC of 60 vol.% and a volume ratio of Si 3N 4:ATH at 3:2; this composite had a thermal conductivity of 2.15 W/m K, an LOI of 53.5, and a UL-94 vertical burning test ranking of V-0.

Preparation of Hexaphenylamine Cyclotriphosphazene and its Green Flame Retardance on Epoxy Molding Compound for Large-Scale Integrated Circuit Packaging

The hexaphenylamine cyclotriphosphazene (HPACTPZ) was synthesized using titrating technology of hexachlorocyclotriphosphazene solution and the synthesis parameters were investigated, and the structure of HPACTPZ was analyzed by FTIR and NMR in this paper. Using HPACTPZ synthesized in the work as flame retardant, the epoxy molding compound(EMC) for packaging of large-scale integrated circuits with halogen-free flame retardance was prepared. The results have shown that the flame retardance of EMC flame-retardanced by HPACTPZ was up to UL 94 V0 rating(3.2mm) and the oxygen index of the EMC was up to 35.8%, which indicates that HPACTPZ has much better flame retardance for EMC than traditional halogen flame-retardants. Meanwhile, HPACTPZ accelerated the curing reaction rate of EMC, which can be used for manufacturing the quick-curing EMCs or afterward-curing-free EMCs.

Study of EMC for Cu Bonding Wire Application

The influence of EMC (Epoxy Molding Compound) and reliability with fine Cu wire was studied. It is found that the failure mode was corrosion at the intermetallic layer of the wire bonding part by failure analysis after HAST (Highly Accelerated Temperature & Humidity Stress Test). Al elution and Cl ion was observed at the intermetallic layer. EMC with lower Cl ion content and Al inhibitor of corrosion shows better HAST property. The selection of flame retardant for green EMC is important because some retardant has a negative impact on HAST performance.

MUF Technology Development for SiP Module

In this study, we developed the molded underfill (MUF) technology for system in package (SiP) module with fine pitch flip chip in RF application, in which two flip chips, LC filter, and additional passive components are integrated side-by-side. This study covered not only MUF reliability performance but also MUF design study focused on minimizing voids between flip chip bumps in the SiP module. The investigation comprises several aspects: A design study that present a printed circuit board (PCB) and epoxy molding compound (EMC) selection approach, air vent design of cavity vacuum molding, and results of void free from Design of Experiment (DOE) of several SiP module layouts. In the end, Scanning Acoustic Tomography (SAT) result of void, moisture sensitivity test, thermal cycle test and pressure cooker test had also been carried out for reliability evaluation. The test result shows that the optimized SiP module with fine flip pitch has a good reliability performance.

Synthesis of Phosphazene Flame Retardant and its Application in Epoxy Molding Compound for Large-Scale Integrated Circuit Packaging

The tri(o-phenylenediamine) cyclotriphosphazene (TPCTP) was synthesized using titrating technology of hexachlorocyclotriphosphazene solution and the synthesis parameters were investigated, and the structure of TPCTP was analyzed by FTIR in this paper. Using TPCTP synthesized in the work as flame retardant, the epoxy molding compound(EMC) for packaging of large-scale integrated circuits with halogen-free flame retardance was prepared. The results have shown that the flame retardance of EMC flame-retardanced by TPCTP was up to UL 94 V0 rating(1.6mm) and the oxygen index of the EMC was up to 34.5%, which indicates that TPCTP has much better flame retardance for EMC than traditional halogen flame-retardants. Meanwhile, TPCTP accelerated the curing reaction rate of EMC, which can be used for manufacturing the quick-curing EMCs or afterward-curing-free EMCs.

The Effects of Particle Size-Matching Filling of Spherical Silica on the Flowability of Epoxy Molding Compounds for Large-Scale Integrated Circuits Packaging

By means of matching filling of five kinds of spherical silica with the particle size of 2μm, 3μm, 5μm, 10μm, 20μm respectively, the epoxy molding compounds(EMC) for integrated circuits(IC) were manufactured. Using classical particle accumulation theory, the particle distribution according with Dinger-Funk-Alfred equation was calculated by Matlab simulation software, and then the optimal particle size formulations were obtained. Adding the mixed silica according to the above optimal formulations into epoxy resin, the EMCs were manufactured by twin-roll compounding at 95~105°С . The melt viscosities of varied EMCs were measured by Rotating Rheometer. The results showed that the matching filling of different silica with different particle size can improve the flowability of EMC greatly.

Studies of Mesoscale Models Parameterized by Molecular Models for Interface Failure in Epoxy Molding Compounds

Deeper understanding of material failure must include consideration of contributions from the molecular and atomistic scales from which a more complete root cause picture may be constructed. The current study, supported by an international consortium effort (NanoInterface) [1], reports efforts to bridge the gap between molecular models and macroscale models by use of a mesoscale discrete particle method. Both the initial stress-strain curve and the latter part of the stress strain curve has been developed for perfect (flat) interfaces as well as simulated rough interfaces, using a saw-tooth configuration.

Comprehensive Moisture Diffusion Characteristics of Epoxy Molding Compounds Over Solder Reflow Process Temperature

We address moisture diffusion in epoxy molding compounds (EMCs) at temperatures higher than 100 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sup> C. The objectives of this paper are thus: 1) to obtain diffusion properties of EMCs in both absorption and desorption modes at a wide range of temperatures; 2) to establish a non-Fickian correlation for diffusivity; and 3) to assess moisture diffusion behaviors during a solder reflow process, described by two different Fickian diffusivities of absorption and desorption and the non-Fickian diffusivity. An experimental procedure is established to measure the diffusivity and solubility of selected EMC materials. The results are utilized in a numerical simulation to analyze the effect of the non-Fickian diffusion characteristics on the moisture distribution during the reflow process.

Determination of residual strains of the EMC in PBGA during manufacturing and IR solder reflow processes

Even though recently published results indicated that residual strains of the epoxy molding compound (EMC) play a key role on the warpage values and shapes of the plastic ball grid array (PBGA) packages, it is still unknown about how these residual strains build up and change during the manufacturing and infrared (IR) solder reflow processes. The purpose of this study is to quantify the residual strains of the EMC in the PBGA packages during the aforementioned processes using a combination of experimental, theoretical and numerical approaches. In the experiments, a full-field shadow moiré is used for measuring their real-time out-of-plane deformation (warpage), during heating and cooling conditions, of two types of the PBGA specimens (without a silicon chip inside) with the same EMC but different substrates (with glass transition temperature T g = 172 and 202 °C). Furthermore, Timoshenko’s bi-material theory associated with the measured and temperature-dependent elastic moduli and coefficients of thermal expansion for the EMC and substrates is applied for extracting residual strains of the EMC from shadow moiré results. In the analysis, the finite element method cooperating with those determined residual strains is employed to numerically simulate the thermal-induced deformations of the PBGA specimens, in order to verify mechanics. The full-field warpage of the specimens from shadow moiré is documented before and after post-mold curing, solder reflow and during the temperature cycling (from room temperature to 260 °C). The residual strains of the EMC for the specimens with low- T g and high- T g substrates after post-mold curing are found to be 0.059% and 0.134%, respectively, which double those before post-mold curing, and further down to 0.035% and 0.08% after the first thermal cycling. After the first cycling, the residual strains remain almost constant during heating and cooling processes. This phenomenon is also observed at lead-free solder reflow processes. Therefore, the residual strains of the EMC induced by the chemical shrinkage of the EMC curing and possibly mold flow pressure are different between the specimens with low- T g and high- T g substrates, and these residual strains could change during post-mold curing and the first solder reflow processes.

Plasma Surface Modification of Silica and its Application in Epoxy Molding Compounds for Large-Scale Integrated Circuits Packaging

The surface modification of silica for epoxy molding compounds (EMC) was conducted by plasma polymerization using RF plasma (13.56MPa), and the modification factors such as plasma power, gas pressure and treatment time were investigated systematically in this paper. The monomers utilized for the plasma polymer coatings were pyrrole, 1,3-diaminopropane, acrylic acid and urea. The plasma polymerization coating of silica was characterized by FTIR, contact angle. Using the silica treated by plasma as filler, ortho-cresol novolac epoxy as main resin, novolac phenolic-formaldehyde resin as cross-linking agent and 2-methylmizole as curing accelerating agent, the EMCs used for the packaging of large-scale integrated circuits were prepared by high-speed pre-mixture and twin roller mixing technology. The results have shown that the surface of silica can be coated by plasma polymerization of pyrrole, 1,3-diaminopropane, acrylic acid and urea, and the comprehensive properties of EMC were improved.

충전재 변화에 따른 Chip Scale Package(CSP)용 액상 에폭시 수지 성형물 (Epoxy Molding Compound)의 흡습특성

반도체의 경박단소화, 고밀도화에 따라 향후 반도체 패키지의 주 형태는 CSP(Chip Scale Package)가 될 것이다. 이러한 CSP에 사용되는 에폭시 수지 시스템의 흡습특성을 조사하기 위하여 에폭시 수지 및 충전재 변화에 따른 확산계수와 흡습율 변화를 조사하였다. 본 연구에 사용된 에폭시 수지로는 RE-304S, RE-310S, 및 HP-4032D를, 경화제로는 Kayahard MCD를, 경화촉매로는 2-methyl imidazole을 사용하였다. 충전재 크기 변화에 따른 에폭시 수지 성형물의 흡습특성을 조사하기 위하여 충전재로는 마이크로 크기 수준 및 나노 크기 수준의 구형 용융 실리카를 사용하였다. 이러한 에폭시 수지 성형물의 유리전이온도는 시차주사열량계를 이용하여 측정하였으며, 시간에 따른 흡습특성은 <TEX>$85^{\circ}C$</TEX> and 85% 상대습도 조건하에서 항온항습기를 사용하여 측정하였다. 에폭시 수지 성형물의 확산계수는 Ficks의 법칙에 기초한 변형된 Crank 방정식을 사용하여 계산 하였다. 충전재를 사용하지 않은 에폭시 수지 시스템의 경우, 유리전이온도가 증가함에 따라 확산계수와 포화흡습율이 증가 하였으며 이는 유리전이온도 증가에 따른 에폭시 수지 성형물의 자유부피 증가로 설명하였다. 충전재를 사용한 경우, 충전재의 함량 증가에 따라 유리전이온도와 포화흡습율은 거의 변화가 없었으나, 확산계수는 충전재의 입자 크기에 따라 많은 변화를 보여주었다. 마이크로 크기 수준의 충전재를 사용한 경우 확산은 자유부피를 통하여 주로 이루어지나, 나노 크기 수준의 충전재를 사용한 에폭시 수지 성형물에서는 충전재의 표면적 증가에 따른, 수분 흡착의 상호작용을 통한 확산이 지배적으로 이루어진다고 판단된다. Since the requirement of the high density integration and thin package technique of semiconductor have been increasing, the main package type of semiconductor will be a chip scale package (CSP). The changes of diffusion coefficient and moisture content ratio of epoxy resin systems according to the change of liquid type epoxy resin and fillers for CSP applications were investigated. The epoxy resins used in this study are RE-304S, RE310S, and HP-4032D, and Kayahard MCD as hardener and 2-methylimidazole as catalyst were used in these epoxy resin systems. The micro-sized and nano-sized spherical type fused silica as filler were used in order to study the moisture absorption properties of these epoxy molding compound (EMC) according to the change of filler size. The temperature of glass transition (Tg) of these EMC was measured using Dynamic Scanning Calorimeter (DSC), and the moisture absorption properties of these EMC according to the change of time were observed at <TEX>$85^{\circ}C$</TEX> and 85% relative humidity condition using a thermo-hygrostat. The diffusion coefficients in these EMC were calculated in terms of modified Crank equation based on Ficks' law. An increase of diffusion coefficient and maximum moisture absorption ratio with Tg in these systems without filler can be observed, which are attributed to the increase of free volume with Tg. In the EMC with filler, the changes of Tg and maximum moisture absorption ratio with the filler content can be hardly observed, however, the diffusion coefficients of these systems with filler content show the outstanding changes according to the filler size. The diffusion via free volume is dominant in the EMC with micro-sized filler; however, the diffusion with the interaction of absorption according the increase of the filler surface area is dominant in the EMC with nano-sized filler.

Hardness Test on an Epoxy Mold Compounds of a Quad Flat No Lead Package Using the Depth Sensing Nanoindentation

This study focuses on the effect of stress and load towards hardness at epoxy mold compounds (EMCs) of a Quad Flat No- Lead (QFN) package using indentation technique. A series of three points bending cyclic test were performed with four different loads between 60 N to 120 N on QFN package. The nanoindentation with the maximum load of 300 mN was indented at five locations that perpendicular to the stress line on EMCs of QFN package after three points bending cyclic test were performed. The findings showed that the mean value of hardness was varied with load and stress. Higher load and stress were found to be not affected by hardness of EMCs. From the results, it is believed that the applied load and stress not play a role towards the hardness of EMCs. A polynomial relationship was plotted and shown that correlation of coefficient (R2) between stress and hardness of the studied EMCs was found to be at 97%. Finally, the finding suggested that a close correlation between the stress and hardness since it correlation coefficient gave a higher value with the polynomial relationship.

Effects of Molding Parameters and Addition of Fillers on Gate Chip Off Formation during the Degating Process in Transfer Molding

In the electronics packaging industry, Epoxy Mold Compound (EMC) polymer matrix is filled with fused silica (SiO2) to obtain the required roughness and hardness. Gate chip off, which occurs during the degating process in transfer molding is one of the common defects which contributes to the failure in the proper functioning of the package. During the degating process, surface contact between two solid bodies (degating blade and gate) generate a high shear stress on package, thus creating a high potential for the incidence of gate chip of. In this study, the influence of transfer molding parameters and size of fillers (normal and fine) on the gate chip off were investigated. The application of Design of Experiments (DOE) using regression model and Analysis of Variance (ANOVA) showed that molding parameters do not significantly influence the incidence of gate chip off. Numerical simulation was used to investigate effect of two filler sizes and molding parameters on the mold fill time, end pressure of fill and shear stress at the wall. The results showed there were no significant influences on mold fill time but the fine filler showed lower pressure at the end of fill and lower shear stress at the wall. Experimental results of two sizes if filler shown that fine filler mold compound exhibited in reduction of gate chip off formation, compared to normal filler mold compound. Smooth surface of fine mold compound lead to decrease of friction shear stress during degating is expected contribute to this finding.

High-g impact resistance for epoxy molding compound

The behavior of resistance high-g impact of EMC (epoxy molding compound) with two package models, small outline package (POS) and Globtop, was evaluated by experimental method used Hopkinson bar. At 120,000 g (generated in the Hopkinson bar with widths about 70 μ s) no damage in either the POS devices or the Globtop devices was observed. In order to enhance the EMC’s ability of resistance high-g impact, buffering effect of epoxy resin was also studied. The experimental results above all show that EMC has a better performance of impact resistance at about 120,000 g, and epoxy resin can absorb the stress wave to have the protected ability. The study of this paper could serve as a basis for selection packaging materials and enhance its reliability in high-g impact environment.

Stabilized filling simulation of microchip encapsulation process

The filling process is a key stage of plastic encapsulation, which mainly affects the reliability of chips. This paper presents a stabilized filling simulation method of microchip encapsulation process. In this method, the non-isothermal and incompressible N–S equations coupled with the Kamal curing equation is introduced in as governing equations, and the Castro–Macosko model is employed as the constitutive model of the epoxy molding compound (EMC). The Galerkin/least-squares (GLS)-stabilized finite element method is used to solve the governing equations. With GLS scheme, numerical surge during the solution is relieved and equal order interpolation for velocity field and pressure field is achieved at the same time. A new kind of Euler’s method named piecewise linear interface calculation (PLIC)–flow analysis network (FAN) is proposed to track and describe the flow fronts for each time step. The experimental and numerical results are found to be in good agreement, which proves the accuracy and stabilization of this method.

Reliability and failure analysis of fine copper wire bonds encapsulated with commercial epoxy molding compound

The small outline transistor (SOT) devices which were interconnected with 20 μm copper bonding wire and encapsulated with commercial epoxy molding compound (EMC) have been used in a series of reliability tests which including the thermal shock test, the electrical service life test, and the isothermal aging test. Isolated IMC spots were found at the bonding interface during the thermal shock test. No void or crack was observed even after 1500 cycles thermal shock test. No electrical failure was happened. The isolated IMC spots also occurred at the Cu/Al bonds interface after 500 h electrical operation. After 1000 h electrical operation, the sizes of the IMC spots were about 0.5 μm. No layered IMC was observed. The IMCs were formed at the bonding interface when the aging temperature was between 150 °C and 250 °C. Micro cracks and Kirkendall voids were observed with the aging time of 9 days at 200 °C and the aging time of 9 h at 250 °C. The minor element in the EMC, Sb, has reacted with Cu wire and Cu bond surface at 250 °C when the aging time was more than 16 h. Cu 3Sb was the main product of the diffusion reaction. With the aging time of more than 49 h, the Cu wire was crashed into pieces and the Cu bond periphery has been severely corroded.

Effect of PCB Surface Modifications on the EMC-to-PCB Adhesion in Electronic Packages

The characteristics of interfacial adhesion between epoxy molding compound (EMC) and printed circuit board (PCB) were investigated. The surface conditions of solder resist (SR) layers, which were used as an outer skin of PCB, were varied within the range that would be encountered in the manufacturing process and reliability test conditions. First, the number of times of plasma treatment on the SR surfaces and the delay time prior to EMC molding on them were considered to examine the surface cleaning process and the aging effect, respectively, on adhesion. Second, moisture on the surfaces of PCB prior to EMC molding and moisture absorption and desorption at the interface were considered to investigate the environmental effect on adhesion. An unsymmetric double cantilever beam test method was devised by modifying the conventional symmetrical double cantilever beam. As a result, the phase angle of fracture could be controlled to achieve stable crack propagation along the desired interface, which enabled valid adhesion energy to be measured. The adhesion energy increased with plasma treatment by over 50%, from 55 to 86 J/m2. The improved adhesion was attributed to the increased the polar groups on the SR surface due to plasma treatment, which helped enhanced chemical bonding between the EMC resin and the SR resin. However, excessive plasma was counterproductive as it weakened the SR surface and caused cohesive crack propagation to occur within the SR layer. Adhesion remained nearly constant for delay time up to several hours between plasma treatment and EMC molding. However, small degradation of adhesion was observed when the delay time was extended to 12 h. Moisture on and in the SR material before EMC molding had a significant effect on adhesion. Absorbed moisture at the interface decreased the adhesion. However, when the moisture was baked out, adhesion was recovered almost to the original reference.

Three-Dimensional Modelling to Study the Effect of Die-Stacking Shape on Mould Filling During Encapsulation of Microelectronic Chips

Multistacked-chip scale package (S-CSP) is a new technology that provides high density electronic package. A fully 3-D numerical model is developed to simulate mould filling behavior in the epoxy moulding compound (EMC) encapsulation of multi-S-CSP. Four different shapes of chip arrangement namely uniform, rotated, z-staggered-Type A and z-staggered-Type B, have been tested. The EMC is treated as a generalized Newtonian fluid (GNF). The developed methodology combines the Kawamura and Kuwahara technique-based finite difference method (FDM) and the robustness of volume-tracking (VOF) method to solve the two-phase flow field around the complex arrangement of microchips in a cavity. The Castro-Macosko rheology model with Arrhenius temperature dependence is adopted in the viscosity model. Short-shot experiments are conducted to investigate the filling patterns at several time intervals. The results show that the rotated shape die-arrangement gives minimum filling time and better mould filling yield. The close agreement between the experimental and simulation results illustrates the applicability of the proposed numerical model.

Interface delamination analysis of TQFP package during solder reflow

Interface delamination during solder reflow is a critical reliability problem for the plastic IC packages. The main objective of this study is to apply modified virtual crack closure method (MVCCM) for the analysis of interface delamination between the leadframe pad and the encapsulant during a lead-free solder reflow after the level 1 moisture preconditioning. In this study, the moisture diffusion parameters and the coefficient of moisture expansion (CME) of two different epoxy molding compounds (EMC) are characterized for moisture diffusion analysis and the deformation analysis due to hygroscopic swelling. At the same time, the entire thermal and moisture history of Thin Quad Flat Pack (TQFP) package is simulated from the start of level 1 moisture preconditioning (85 °C/85%RH for 168 h) to subsequent exposure to a lead-free solder reflow process. Finally, the transient development of the stress intensity factors due to thermal stress only K t , hygrostress only K h , vapor pressure only K p and combined energy release rate G tot are computed and studied by using MVCCM. Based on the calculated stress intensity factors and energy release rates, it seems that for the EMC, the Young’s modulus, moisture diffusion coefficient, CME and adhesion strength with leadframe at high temperature appear to be the most significant variables for the MSL performance of TQFP package and this matches well with the experimental finding.