Epoxy Molding Compound Material Research Articles

Modeling the cure shrinkage–induced warpage of epoxy molding compound

Product packaging processes often encounter issues, such as warping and deformation caused by the mismatch between the coefficients of thermal expansion of materials. Considerable amounts of epoxy molding compound (EMC) are used in packages. EMC exhibits viscoelastic properties and cure shrinkage, which can substantially affect the stress and warpage of packages. Mathematical models of cure shrinkage at isothermal and variable temperatures have not been comparatively discussed. Accordingly, this study aims to clarify the differences between the cure shrinkage during EMC curing estimated by the isothermal and modified two-domain Tait models. A fitting flow and calculation procedure for cure shrinkage was established to analyze the influence of these models on structural warpage. This study involved the experimental measurements of EMC material properties by using the cure reaction kinetics, isothermal and variable-temperature cure shrinkage, and generalized Maxwell models and degree of cure at gel point. Structural warpage was estimated by developing a process-oriented finite element method simulation and validating simulation results against experimental results. Analysis revealed good agreement between the warpage estimated by the two cure shrinkage models and experimental warpage. Compared with those of the other model, the results of the two-domain modified Tait model better matched the experimental results, with a deviation of approximately 1 %, because this model considered cure shrinkage that precisely corresponds to the actual process. Furthermore, the stress relaxation of viscoelastic behavior was validated through a parameterized post-curing process. Results indicated that although warpage occurrence reduced by extending the post-curing process time, it eventually converged to a certain value.

Warpage modeling and characterization of intelligent power modules (IPMs)

Abstract Intelligent power modules (IPMs) are widely used in the electric vehicle (and hybrid electric vehicle industry nowadays due to their high power density and ability to integrate multiple components within a single package. However, the reliability of IPMs is severely degraded by the substrate warpage effect produced during the packaging process. This study therefore develops a computational model to analyze the warpage of the IPM assembly at various stages of the packaging process. The validity of the simulation model is confirmed by comparing the numerical results for the warpage of the direct plated copper substrate with the experimental observations. Taguchi experiments are then performed to examine the effects of eight control factors on the IPM package warpage following the post-mold cure (PMC) process, namely (1) the dam bar layout, (2) the epoxy molding compound (EMC) thickness, (3) the lead frame thickness, (4) the ceramic thickness, (5) the bottom layer Cu foil thickness, (6) the top layer Cu foil thickness, (7) the ceramic material type and (8) the EMC material type. Finally, the Taguchi analysis results are used to determine the optimal packaging design that minimizes the warpage of the post-PMC package.

Effect of Silicon Die Condition on the Breaking Load Performance of a Dam and Fill Semiconductor Package

A semiconductor package has a silicon die on which an integrated circuit (IC) is fabricated. The die is singulated from a single wafer using processes like mechanical sawing or laser grooving. These processes have impact on the final condition of the silicon die after wafer singulation. This paper discusses a study on the effect of the die condition on the breaking load of a package with a dam and fills structure. The encapsulation material of this type of package has lower modulus when compared with the epoxy mold compound material used in most molded packages. The package breaking load was determined using 3-point bend test for two sets of packages. The first set of packages was assembled with silicon die produced using mechanical sawing. The second set was assembled with die produced using laser grooving. Results of the 3-point bend test showed that the breaking load of the package with die from mechanical sawing is higher compared with the package assembled with die from laser grooving. The study revealed that that the silicon die condition has significant effect on the robustness of the final package where the die is used.

FE Simulation Model for Warpage Evaluation of Glass Interposer Substrate Packages

Glass interposer substrates have attracted growing interest as an alternative to traditional organic and silicon-based interposers for 3-D integrated circuit (IC) and 2.5-D through silicon via (TSV) packages in recent years. However, while glass substrates have the advantages of excellent electrical isolation, superior RF performance, good coefficient of thermal expansion (CTE) adjustability, and the potential for large-scale fabrication, they are inherently brittle. Consequently, an appropriate choice of glass and epoxy molding compound (EMC) material is essential for minimizing the warpage of the molded wafer. To facilitate the package design process, this study, therefore, develops an ANSYS simulation model to predict the warpage of the molded glass wafer given the use of different glass and EMC materials. The validity of the simulation model is confirmed by comparing the numerical results for the warpage of an 8-in molded glass wafer with the experimental measurements obtained using an Advanced Metrology Analysis (aMA) system. Single-factor-analysis experiments are then conducted to examine the effects of five different control factors, namely, the glass substrate thickness, the glass CTE, the glass modulus, the EMC CTE, and the EMC modulus, on the warpage performance of the molded glass wafer. The simulation results provide useful guidelines for the design of robust glass substrate packages.

Comparative Study of the Photoelectric and Thermal Performance Between Traditional and Chip-Scale Packaged White LED

The traditional cup-shaped LED packaged with epoxy molding compound materials (EMC-LED) and chip-scale packaged LED (CSP-LED) were prepared and analyzed in this article. It is found that high temperature can result in the spectrum red shift and the photoelectric performance degradation for these LEDs due to the degradation of chip and packaging materials. Compared with EMC-LED, the CSP-LED device has a lower thermal resistance of 3.31 °C/W due to the shorter thermal dissipation path and has better stability under the different temperature and drive current conditions. All the simulation results agree well with experimental and theoretical results, indicating that the photoelectric and thermal properties of the CSP-LED can be improved by introducing ceramic substrate and optimizing the material of the interconnected surface and the size of the conduction area. These results have guiding significance for the future CSP-LED design and application.

Effect of Epoxy Molding Compound Material and Roughness Leadframe to Integrated Circuit Package for Automotive Devices

This research studied about an effect of epoxy molding compound material and roughness leadframe of integrated circuit package for automotive device. In manufacturing process, the epoxy molding compound material and leadframe roughness are main factors that effect to coefficient of thermal expansion (CTE) and reliability for automotive device package with no delamination in high temperature application. In experiment, two types of epoxy molding compound materials were studied and compared between standard and roughened leadframe for quad flat non lead (QFN) package. For reliability test, the epoxy molding compound materials type A and type B with different leadframe were analyzed with moisture sensitivity level 1 to observe delamination inside packages. The results showed that CTE of epoxy molding compound material type A is less CTE mismatch than that of epoxy molding compound material type B with both standard and roughness leadframe. Moreover, the results also found no delamination for epoxy molding compound material type A with roughened leadframe. In addition, both epoxy molding compound materials showed significant delamination inside packages with standard leadframe.

Effect of temperature and humidity on moisture diffusion in an epoxy moulding compound material

In this paper we propose a new multistep characterisation method to be able to map out the dependency of moisture diffusion parameters of a polymeric material over a range of temperature and humidity conditions in a limited amount of time. We do that by (1) using a moisture sorption analyser which can continuously monitor weight changes with microgram accuracy, (2) using thin samples which speeds up the diffusion process and (3) already switch to the next humidity level at 90 or 95% completion of a diffusion step. A multistep diffusion model was developed to account for the overlapping diffusion steps. This model showed to be extremely accurate for fitting experiments consisting of five absorption and one desorption steps. We show that for temperatures up to 85 °C and humidity level between 0 and 85% RH the diffusion of our material was essentially Fickian with a diffusion coefficient ranging from 3.8 × 10−7 mm2/s at 20 °C to 3.6 × 10−6 mm2/s at 85 °C. The moisture saturation concentrations showed a slightly non-linear variation with the applied humidity level.

Advances in Temporary Bonding and Debonding Technologies for use with Wafer-Level System-in-Package (WLSiP) and Fan-Out Wafer-Level Packaging (FOWLP) Processes

AbstractToday's complex fan-out wafer-level packaging (FOWLP) processes include the use of redistribution layers (RDL) and reconstituted wafers with epoxy mold compound (EMC) for use in heterogeneous integration [1]. Wafer-level system-in-package (WLSiP) uses fan-out wafer-level packaging (FOWLP) to build the system-in-package (SiP) by attaching know-good die (KGD) in a chip-first process to a tape laminated temporary carrier. If the dies are attached in a die-up configuration (active area facing up) and then over-molded with EMC, contact pads on the embedded die are exposed during the backside grind process. During the RDL build, the temporary carrier supplies mechanical support for the thinned substrate. In a die-down configuration with the active area facing down (eWLB), the temporary carrier is removed after the molding process thus exposing the contact pads for RDL build and solder ball mount.The ideal chip attachment scheme should minimize lateral movement of the die during over-mold (die shift) and also minimize vertical deformation of the bonding material. Thermal release tape provides a convenient way to attach die to a carrier prior to over-molding with EMC. However, not all bonding materials are suitable for presentation in tape form, so the material used in the tape may not be the optimal choice. An alternative method is to directly apply temporary bonding material to the carrier substrate. This enables the use of bonding materials with higher melt viscosity and improved thermal stability, resulting in less vertical deformation during die placement, and reduced die shift during over-molding. The bonding material will ideally have high adhesion to the EMC wafer to prevent delamination in the bond line during downstream processing. Stack stress and warpage is a major concern which causes handling and alignment problems during processing. The bonding material and carrier will need to be specifically suited to minimize the effects of stress in the compound wafer.Such material must balance rigidity with warp to prevent lateral die shift and deformation induced by coefficient of thermal expansion (CTE) mismatch between the carrier and EMC material [2]. Bonding materials must also have enough adhesion to the EMC material to overcome such stress without bond failure for an associated debond path (such as laser or mechanical release). In this experiment, we will examine a thermoplastic bonding material in combination with different release materials, addressing die shift, and deformation after EMC processing. Successful pairs will then undergo carrier release using either mechanical release or laser ablation release technology.

Technique to predict reliability failure in side-gate transfer molded packages

Scanning acoustic microscopy (SAM) is the primary method to non-destructively detect internal defects in finished semiconductor packages. SAM is heavily used to detect interfacial delamination in the die-package system. Though this method can achieve an acceptable resolution to analyze the quality of the package unit, it is not absolute in all cases. SAM is also time consuming and non-predictable, as it offers a latent response of the finished good to the reliability tests. This paper presents an analytical prediction method defined to gauge whether the epoxy mold compound (EMC) encapsulating a no polyimide (PI) die surface would yield detectable delamination at the die to mold compound interface in the package finished good. The new method can be used to gauge whether top of die to EMC delamination will occur with a change in new wire bond (WB) die layout, new EMC material and new mold process. This new method also provides a way to demonstrate that the observed delamination is not detrimental to package reliability. This method will demonstrate how the no-PI package reliability can be met to not cause electrical failures based on the resin rich (RR) volume.

굴절률이 다른 실리콘 봉지재의 봉지 방법에 따른 UV-A LED의 광 특성에 관한 연구

Optical characteristics including the radiant flux and viewing angle of UV LEDs were investigated according to both silicone encapsulants with different refractive indexes and lens shapes. Lead frame was fabricated using the enhanced heat dissipation characteristics with a heat slug structure and the reflector based on EMC(Epoxy Mold Compound) material. Four types of lens shapes were designed and their optical characteristics depending on the refractive index of silicone encapsulants were evaluated. The maximum radiant flux can be achieved when the height of lens are 1.32mm and 1.08mm for silicone encapsulants with low and high refractive indexes, respectively. Depending on the encapsulating method, the viewing angle changes from 148.9° to 130.2° for low refractive index and from 145.3° to 136.8° for high refractive index. As a result, it is found that the optical characteristics of UV LEDs can be controled through both encapsulating method and the refractive index of encapsulants.

Vacuum effect on the void formation of the molded underfill process in flip chip packaging

The flip chip packaging technology uses solder bumps for the electrical connection between the chip and substrate. A two-step procedure is usually used for the flip chip packaging. In the process, underfill material is filled into the gap between the chip and substrate by the capillary force. After that, epoxy molding compound (EMC) is used to overmold the entire assembly in a mold cavity through the process of the transfer molding. On the other hand, the molded underfill (MUF) process performs the packaging at a single step. In the MUF process, the EMC material fills the mold cavity with preplaced flip chip assembly, and finishes the underfill and overmold at the same time. In this study, experiments were performed to study the mechanism of the void formation in MUF. The effect of vacuum on the void formation was investigated. It was found that high quality of vacuum was necessary in order to eliminate the air pocket enclosed during the filling process. For different materials, the required vacuum quality may be different and it is well below the perfect vacuum.

Comparative characterization of chip to epoxy interfaces by molecular modeling and contact angle determination

An investigation of interfacial interaction has been performed between three epoxy molding compound materials and a native silicon dioxide layer (SiO2) usually found at chip surfaces. The epoxy materials were an industry oriented epoxy molding compound Epoxy Phenol Novolac (EPN), its filled variety EPNF (with silica particles) and a model aromatic epoxy11,3-Bis(2,3-epoxypropoxy)-benzene and a 1,2diamino(ethane)2 hardener in a 2:1 mixing ratio.1 (212). All systems are described in full in [1] and [2]. The free surfaces of the solid materials were experimentally analyzed by contact angle measurements of three different liquids (water, methylene-iodide (MI) and glycerol). Results are compared to interfacial energies obtained by analysis of the interfaces in bimaterial molecular models, yielding reasonable agreement. A qualitative prediction regarding the influence of water on the interfacial strength between chip and molding compound is attempted.

The Effect of Epoxy Molding Compound on Thermal/Residual Deformations and Stresses in IC Packages During Manufacturing Process

Thermal/residual deformations and stresses in plastic integrated circuit (IC) packages caused by epoxy molding compound (EMC) during the manufacturing process are investigated experimentally (only for deformations), theoretically, and numerically. A real-time Twyman-Green interferometry is used for measuring the out-of-plane thermal and residual deformations of die/EMC bi-material specimens. Dynamic mechanical analysis (DMA) and thermomechanical analysis (TMA) are for characterizing thermomechanical properties of the EMC materials. A finite element model (FEM) and theory associated with experimental observations are employed for understanding the thermal/residual deformations and stresses of IC packages due to EMC encapsulation. It is shown that EMC materials must be fully cured so that the material properties are stable enough for applications. Experimental results show that the EMC material experiences stress relaxation due to its viscoelastic behavior during the post mold curing (PMC) process. As a result, the strains (stresses) resulted from the chemical shrinkage of the EMC curing could be relaxed during the PMC process, so that the chemical shrinkage has no effect on the residual strains (stresses) for the plastic packages being post cured. Compared with numerical and theoretical analyses, the experimental results have demonstrated that die/EMC bi-material structure at high temperature (above Tg) warps less than expected, as a result of viscoelastic stress relaxation of EMC at high temperature (during solder reflow process). Meanwhile, this stress relaxation can also cause shifting this zero-stress temperature to the higher one, so that the residual deformations (stresses) of die/EMC bi-material specimens were found to increase by about 40% after the solder reflow process. The residual and thermal stresses have been resolved by FEM and theoretical analyses. The results suggest that the pure bending stresses (without shear and peel stresses) of the bi-material specimens are only limited in the region from x= 0 (the center) to x= 0.75 L due to the free edge effects, but this region is shrunk down to x= 0.4L at 200degC. And the maximum warpage and bending stress per unit temperature change is occurred around 165degC (Tg of the EMC). This study has demonstrated that the Twyman-Green experiment with associated bi-material plate theory and FEM can provide a useful tool for studying the EMC-induce residual/thermal deformations and stresses during the IC packaging fabrication

Warpage Analysis of FBGA (Fine Ball Grid Array) Package by the Altered EMC (Epoxy Molding Compound) Filler Contents

In a semiconductor packaging process, the warpage greatly has influenced the reliability of the package as well as the workability. The strip warpage in FBGA package result from the structure of constitutes and the thermal mismatch by the mechanical or thermal properties such as CTE (Coefficient of Thermal Expansion) and Modulus of EMC, substrate, chip and adhesive materials. Therefore, the optimization of material properties and the package structure design has been needed by the numerical analysis. EMC used as one of the package constituents has a decisive effect on the trend of warpage, and the filler content is dominant in the EMC property. In this research, firstly the effect of the filler contents is evaluated in the warpage of FBGA package and the numerical analysis is performed with the high temperature – material properties to deal with the warpage under the actual measurement value.

Investigation of moisture diffusion in electronic packages by molecular dynamics simulation

Moisture-related failure is one of the main concerns in the integrated circuit (IC) package design. To minimize such failure in multi-layered electronic assemblies and packages, it is important to develop a better understanding of the reliability at a molecular level. In this paper, molecular dynamics (MD) simulations were conducted to investigate the respective moisture diffusion into the epoxy molding compound (EMC) and at the EMC/Cu interface. Moisture diffusion coefficients into the bulk EMC material and at the EMC/Cu interface can be derived from the mean-squared displacements calculated from MD simulations. The MD results showed that the seepage along the EMC/Cu interface is more prevalent when compared to moisture diffusion into the bulk EMC and, thus, rendering it a dominant mechanism causing moisture induced interfacial delamination in plastic packages.

Warpage of Plastic IC Packages as a Function of Processing Conditions

Variation of processing conditions on warpage prediction of a plastic quad flat package (PQFP) is examined. Thermal mismatch between package constituent materials is the major cause of IC package warpage. To minimize the warpage problem, a thorough understanding of epoxy molding compound (EMC) properties with molding parameters is necessary as EMC is epoxy-based with time and temperature dependent viscoelastic properties. This paper first addressed the thermal characterization of encapsulating material. Degree-of-cure (DOC or β), coefficient of thermal expansion (CTE or α), glass transition temperature Tg, and shear modulus G′ and G of the molded specimens were measured by various thermal analysis techniques. The glass transition temperature was shown to be a good and direct measure of the degree-of-cure. The CTEs (α1 and α2),G′ and G″ were found to be decreasing functions of degree-of-cure. Viscoelastic EMC material models with DOC (i.e., Tg) dependent were formulated. Package warpage predictions against different processing conditions were performed via finite element analyses. Out-of-plane displacement measurements were performed on plastic quad flat package (PQFP) to validate the numerical results. Warpage prediction by the viscoelastic material model was found to agree with the measured data better than the thermoelastic one. For a given cured content, less warpage was found in packages molded at low temperature and longer molding time OR high temperature and shorter molding time.