Mold Compound Research Articles

Bismaleimide/Phenolic/Epoxy Ternary Resin System for Molding Compounds in High-Temperature Electronic Packaging Applications

Development of a new packaging material with superior high-temperature stability is becoming increasingly crucial in high-power and high-density electronics industry. In this study, we employed bis(3-ethyl-5-methyl-4-maleimidephenyl)methane (BMI), para-xylene phenolic resin (PF), and triphenylmethane novolac epoxy resin (EP) as matrix resins to develop high-temperature-stable BPE ternary resin molding compounds for power device packaging. BMI was first melt-blended with PF to obtain the premix with a reduced softening point for meeting the requirement of melt-kneading process. 2-Ethyl-4-methylimidazole with a dosage of 2 wt % of the ternary resins, could effectively promote the curing reaction, making the molding process of BPE molding compounds be compatible with that of the existing epoxy molding compounds (EMC). The introduction of BMI component could enhance the chain rigidity and heat resistance of cured resins. When the BMI content was more than 70 wt % of the ternary resins, the cured BPE molding compounds exhibited the glass transition temperature and initial decomposing temperature larger than 250 and 400 °C, respectively, indicating a much superior thermal performance to that of the cured EMC. Moreover, the flexural performance and the adhesion strength with copper at 260 °C, high-temperature aging resistance, dielectric properties, and thermal conductivity of the cured BPE molding compounds were also improved compared with those of the cured EMC. This study provides a promising strategy for preparing heat-resistant electronic packaging molding compounds.

Advanced process simulation of compression molded carbon fiber sheet molding compound (C-SMC) parts in automotive series applications

The following paper focuses on the development of a 3D virtual process chain (VPC) for parts made from Carbon Fiber Sheet Molding Compounds (C-SMC). The VPC consists of two modules addressing the compression molding and warpage simulation of parts made from two different high fiber volume fraction C-SMC materials. The press simulation module applies a solid mechanics material modelling approach within the Coupled Eulerian-Lagrangian (CEL) simulation framework available in ABAQUS/Explicit. Through a combination of flow characterization experiments and numerical simulations, local mechanical properties and fiber orientation information can be predicted from numerically simulated local flow strains. A warpage simulation module has also been developed in ABAQUS/Standard together with a data processing/transfer interface implemented in ANSA. With these highly integrated numerical tools, process characteristics such as press forces, flow fronts and weld-line development based on material amount, insert geometry and placement position in the mold can all be predicted and analyzed.

Manufacturing Demonstration of Automotive Seat Backrest Using Sheet Molding Compound and Overmolding with Continuous Reinforcement

Manufacturing Demonstration of Automotive Seat Backrest Using Sheet Molding Compound and Overmolding with Continuous Reinforcement

Investigation of the Mechanical Properties of Vinylester-Based Sheet Moulding Compound (SMC) Subject to Particle Recycling

In light of climate change, fiber-reinforced plastics (FRP) are becoming increasingly important due to their lightweight construction potential. This benefit is additionally expanded on with the low cycle times, scrap rates and material costs of Sheet Moulding Compounds (SMC), making it the most often used material on the FRP market. While extensive studies regarding the recycling of SMC with unsaturated polyester-based matrices (UP-SMC) have been conducted in the past, this is not the case for vinylester-based SMC (VE-SMC). In this research, VE-SMC components were subject to a particle-recycling approach. Recyclate in the form of VE-SMC regrind was used to substitute SMC matrices during the compounding process. The dependence of the mechanical properties and failure behavior of VE-SMC containing regrind was investigated by means of microscopic and mechanical test methods for varying mass proportions of SMC regrind. Due to the addition of SMC regrind, a decreased fiber/matrix adhesion was observed. Furthermore, an increase in pore formation was observed with an increasing proportion of SMC regrind. The flexural modulus increased by 20% with a low percentage of regrind (ωrSMC = 10 wt.%) in comparison to virgin SMC. In contrast, the tensile properties decrease (up to 30%) with the addition of SMC regrind independent of the investigated proportions of SMC regrind.

A Mechanistic Model for Plastic Metal Line Ratcheting Induced BEOL Cracks in Molded Packages

Metal line ratcheting and passivation cracking in back-end-of-line (BEOL) structures are significant reliability concerns for molded packages that are in widespread use at the present time. When metal lines plastically deform due to ratcheting, the passivation overcoat accumulates stress at the corner upon temperature cycling and is eventually susceptible to fracture. Since packaging materials’ interaction with the die is the cause of the failure, the problem is inherently multiscale in nature requiring the analysis model to span from package dimension to BEOL length scale. In this article, the mechanistic cause for stress accumulation is elucidated. Furthermore, a global–local modeling strategy is applied to model the passivation crack initiation and growth. A global model with coarse mesh was built of the package. The local region around the interconnect metal line in the die was modeled using boundary conditions extracted from the global model. A novel load decomposition technique is developed to identify the loading mode that best correlates with the experimentally observed fracture. It is shown that shear is the dominant loading mode inducing the observed die cracks. Furthermore, it is demonstrated that the thermal expansion mismatch between the mold compound and the lead frame with the silicon die induces the shear load on the BEOL structure. Due to the fact that mold compound is applied at a temperature that is higher than that seen during thermal cycling, the direction of the induced shear load is constant regardless of whether the package is heated or cooled. As the metal line plastically yields during every temperature cycle, the plastic deformation ratchets or accumulates in the same direction over the course of the thermal cycling test. The yielding of metal line results in stiffness reduction, leading to steady accumulation of stress in the passivation corner, causing it to fracture eventually.

Use of bio-based and renewable materials for sheet molding compounds (SMC) – Mechanical properties and susceptibility to fungal decay

In Europe, Sheet Molding Compound (SMC) has high market relevance in the field of glass fiber reinforced polymer composites (GFRPC). This is based on their wide range of application abilities. Almost 20 wt.-% of GFRPC are processed of SMC material, e.g. for semi-structural components in various applications from construction industry to automotive components. Based on the ability for the production of lightweight structural components in a cost-efficient manufacturing process with high design freedom and high formability, material and process are well established. Standard glass fiber reinforced SMC semi-finished products (GF-SMC) consist of resin paste, based on unsaturated polyester resin, different application specific additives, reinforcing fibers with a length of one to two inches and mineral filler materials. In this paper, the impact of the replacement of conventional mineral filler material by bio-based and renewable filler material sunflower hull meal to mechanical properties and biological decay was analyzed.

Study on the Ion Migration of Silver Ions from Aqueous Solution in Epoxy-Based Molding Compounds by TOF-SIMS Measurements

Epoxy molding compounds are typically used for the encapsulation of modern-day electronic devices. These protect the semiconductor components from environmental influences, such as humidity and oxygen, which could harm the device. However, there is still a risk for corrosion phenomena, when the device is used in harsh conditions (e.g. high humidity and temperature). Electrochemical migration is a mechanism that can occur in the semiconductor device. For instance, silver wires, glues, solders or leadframe-platings used in the package combined with high humidity contact are a huge risk. For this type of corrosion to happen, Ag ions need to migrate through the molding compound. Therefore, measurement of the diffusion coefficient of silver ions in molding compounds can help to better predict the risk of silver migration and corrosion. In this study silver(I)salts were used source for Ag + ions. An Arrhenius correlation was found in the range from 298 K to 393 K. The diffusion coefficient as well as the activation energy of silver ions in four different molding compounds have been evaluated. The investigated activation energies as well as diffusion coefficients are in the range of 0.12 to 0.50 eV.

Unfolding the mechanical properties of buckypaper composites: nano- to macro-scale coupled atomistic-continuum simulations

Carbon-based nanostructures are receiving increasing attention over the past two decades due to their unprecedented multi-functional features. However, the macro-scale structural applications of these nanostructures have not yet come to full fruition due to the involvement of complex multi-scale computations and manufacturing. Recently, the research community has started investigating buckypaper, which can be described as a sheet or membrane developed using a network of bundles of single-wall carbon nanotubes, multi-wall carbon nanotubes, or a mixture of both. This article aims to focus on the computational bridging of different length scales involving six levels in the range of nano- to macro-scale behaviour concerning buckypaper composites. The sequential derivatives of carbon at six levels, as analyzed in this paper, involve graphene, CNT, CNT bundle, buckypaper, and buckypaper composite automotive components. Here, we adopt a coupled atomistic-continuum modelling approach for the multi-level simulations. Graphene, CNTs, and CNT bundles are modelled using atomistic simulations, while the buckypaper and its composites are modelled using equivalent beam representations for the bundles and continuum solid representation for resin. At the macro-scale, an industry-relevant multi-material composite automotive component has been investigated, wherein the buckypaper is proposed to be embedded involving sheet moulding compound and carbon prepreg. The current simulations have led to the determination of mechanical properties at each level of the carbon-based materials and their mutual dependence. The numerical results demonstrate that a buckypaper composite can enhance the natural frequency and stiffness up to 25 and 37% with respect to conventional monolithic metallic designs, while reducing the weight by 57%. Such outcomes lead to the realization that carbon-based nanostructural derivative in the form of buckypaper can significantly improve the mechanical properties of advanced lightweight structural components as reinforcements for the next generation of aerospace and automotive structures.Graphical abstract

Fibre alignment and mechanical performance of carbon fibre Sheet Moulding Compounds under different preform compaction

This work investigates the effect of preform compaction on the mechanical performance and flow-induced fibre alignment of carbon fibre reinforced Sheet Moulding Compounds (SMCs). Two groups of panels have been compression moulded from reclaimed carbon fibre tows in vinyl-ester resin with low (0.5 MPa) and high (10 MPa) preform compaction pressure Additionally, a low-cost fibre orientation analysis method has been further improved in terms of reliability, and a novel flow assessment method has been developed for carbon fibre SMCs. This approach revealed greater fibre alignment with the flow direction in the lower faces of panels as a result of greater contact time with the heated mould and a lower charge viscosity at the time of pressing. As expected, greater fibre alignment in the flow direction was observed outside the initial charge coverage area in both types of panels, where the flow was greatest. Due to additional fibre flow during the high-pressure compaction stage, the mean degree of flow alignment in the high compaction panel was 47% higher than that of the low compaction panel. Improvements in the tensile stiffness (8%) and strength (32%) were also observed as a result of the high-pressure compaction stage and associated flow alignment.

Study on the Strip Warpage Issues Encountered in the Flip-Chip Process.

This study successfully established a strip warpage simulation model of the flip-chip process and investigated the effects of structural design and process (molding, post-mold curing, pretreatment, and ball mounting) on strip warpage. The errors between simulated and experimental values were found to be less than 8%. Taguchi analysis was employed to identify the key factors affecting strip warpage, which were discovered to be die thickness and substrate thickness, followed by mold compound thickness and molding temperature. Although a greater die thickness and mold compound thickness reduce the strip warpage, they also substantially increase the overall strip thickness. To overcome this problem, design criteria are proposed, with the neutral axis of the strip structure located on the bump. The results obtained using the criteria revealed that the strip warpage and overall strip thickness are effectively reduced. In summary, the proposed model can be used to evaluate the effect of structural design and process parameters on strip warpage and can provide strip design guidelines for reducing the amount of strip warpage and meeting the requirements for light, thin, and short chips on the production line. In addition, the proposed guidelines can accelerate the product development cycle and improve product quality with reduced development costs.

Hybridization Process of Carbon Fibre Sheet Moulding Compound with Carbon Fibre Prepregs: a Case Study

The main objective of this work was to show the technical viability of a traditional Sheet Moulding Compound process hybridized with Carbon fibre prepreg reinforcements, in a demonstrative car seat structure. The new reinforced seat is lighter, has better mechanical resistance to impact and the typical carbon fibre visual aspect in the reinforced areas. Currently, the seat structure is composed by the hybrid solution with the matrixes of both materials being epoxy, therefore compatible which promotes a good adhesion under the correct processing conditions. To ensure the viability of this hybridization, an extensive laboratorial test campaign was conducted in a laboratorial hot plate press to study the Sheet Moulding Compound flow dynamics during the moulding process and how it interacts with the prepreg preforms. The cure process of both materials was also analysed to establish the optimal temperature profiles. Finally, mechanical tests were performed according to ASTM D 5868-01 to evaluate the mechanical properties of the bonding between the two materials. The reinforced car seat prototype was validated according to the ECE-R17 and FMVSS202a impact tests on the head rest and a 25% reduction in overall weight was achieved. The life-cycle cost and the visual aspect benefits are expected to compensate the slightly higher manufacturing cost in relation to the original part due to the cost of the prepreg material. Further research will be needed to in terms of process automation to ensure the required process quality.

Influence of fungal decay on mechanical properties of bio-based sheet molding compounds (SMC)

Sheet Molding Compound (SMC) was initially developed in the 1960s and enabled for the first time the production of glass fiber reinforced polymer composite in mass scale production and at an advantageous price. Today, material and process are well established for the production of semi-structural and structural components in various applications such as construction industry, aircraft applications and automotive components. Based on increasing ecological and economical requirements for construction materials a newly and largely bio-based SMC semi-finished material was developed. This paper shows the ability using bio-based components to replace crude oil and mineral based components in SMC. Therefore, test methods for shelf life and fungal decay tests were developed to prove that there is no influence to mechanical properties of the bio-based specimens. The different test series showed that there is a bigger influence of sample preparation for shelf life tests than from fungal decay to the specimens.

Epoxy Molding Compound Filler Clogging Simulation During Integrated Circuit Encapsulation Process

As IC components become denser and smaller in a package, more problems emerge. In the mold filling process, because epoxy molding compound (EMC) contains approximately 80 wt.&#x0025; silica fillers, the fillers may clog at the gate of gap if the gap height between the component and the substrate is too small. This clogging will cause a popcorn effect due to the high resin content in the gap. In order to determine the EMC filling process in the mold cavity and the relation between the gap height and the filler size, we simulate the EMC filling process and the EMC filler concentration distribution in the mold cavity using mold flow analysis software and then use computational fluid dynamics-discrete element method (CFD-DEM) coupling method to simulate the EMC filler motion to determine the relationship between gap height and filler size and the factors that affect filler clogging. Based on the mold flow analysis results, the filler concentration was higher at the gate of gap than in other regions, and the filler concentration at the gate of gap for the 30-<inline-formula> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> gap-height model was higher than that for the 50-<inline-formula> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> gap-height model. Based on the DEM-CFD coupling results, particles with a single diameter larger than one-half of the gap height caused particle clogging the gate of gap, and particles with a mean particle size larger than one-third of the gap height caused particle clogging the gate of gap.

LPM meets latest demands for encapsulation of electronics and medical components

Henkel Adhesive Technologies says that a low-pressure moulding technology it has developed for encapsulating electrical and electronic components in its Technomelt polyamide adhesive moulding compounds is increasingly being used for a range of applications.

Novel Test Cell for Overall and Spatial Mechanical Analysis of Sheet Molding Compound Composite Part in view of Heterogeneity

Novel Test Cell for Overall and Spatial Mechanical Analysis of Sheet Molding Compound Composite Part in view of Heterogeneity

Rheological response of compressible SMCs under various deformation kinematics: Experimental aspects and simple modelling approach

Flow conditions during compression moulding of Sheet Moulding Compounds (SMCs) govern the microstructure and the resulting mechanical properties of composite parts. Low-density and high-fibre content SMCs were subjected to simple compression, œdometric compression and through-thickness shear loadings, using dedicated rheometers. Simple compression and œdometric compression experiments revealed the compaction behaviour of both types of SMCs. During simple compression experiments, the compaction of low-density SMCs was accompanied by in-plane elongational flow phenomena, whereas the high-fibre content SMCs exhibited compaction below a characteristic axial strain and elongation and shear above. Shear tests showed that shear stress did not vary over a wide range of shear strain while being accompanied by axial compression stress. Both SMCs exhibited a shear-thinning behaviour with compression viscosities that depended on the fibre volume fraction. Finally, a transversely isotropic tensorial model for SMCs seen as compressible materials was proposed. Its predictions are consistent with the experiments.

Horizontal Crack Induced Vertical Crack Formation in Epoxy Mold Compound for Electronic Packaging

Epoxy mold compound (EMC) has been widely applied as the packaging material in the electronic industry. It is due to the unique property of EMC such as high temperature stability, low coefficient of thermal expansion (CTE), excellent electrical properties and manufacturability. Despite of superior properties of EMC, several failures have been reported regarding on the electronic packaging application such as crack on the body (EMC). Most of the research reported that the crack defect was originated from the moisture absorption. This research is intended to examine the phenomenon and effect of moisture absorption on the vertical and horizontal crack formation. A comparison between control and conditioned sample was studied where the conditioned sample was subjected to humidity chamber according to the Moisture Sensitivity Level 3 (MSL3) requirement. Horizontal crack occurrence has been observed at the interface EMC. While vertical crack occurrence could be linked with the horizontal crack. Further analysis suggest that horizontal crack occurrence induced vertical crack occurrence. Thus, controlling moisture absorption pathway probably minimize horizontal crack and prohibit vertical crack occurrence.

Space Charge Redistribution in Epoxy Mold Compounds of High-Voltage ICs at Dry and Wet Conditions: Theory and Experiment

Space charge profile plays an important role in defining the charge transport and breakdown field of an insulator. Non-destructive experimental techniques (e.g., PEA measurement) have recently been used to track in-situ the time-evolution of space charge profiles within complex insulators, such as epoxy mold compounds. Unfortunately, the published results are often inconsistent (both positive and negative charge build-up have been reported), and the discrepancy remains unexplained. In this paper, we (i) derive a physics-based compact analytical model of homocharge injection, (ii) explain the time-and voltage-dependent redistribution of homo- and heterocharge, (iii) investigate experimentally and explain theoretically the importance of moisture ingress regarding space charge redistribution, and finally, (iv) summarize strategies to suppress space-charge related instability in modern ICs encapsulated by epoxy mold compounds.

Productivity Enhancement at Molding Compound Manufacturing Plant by Applying Time and Motion Analysis

Commercial boundaries have been erased by markets globalization. Companies around the world compete with each other and thus are enforced to improve their products and processes. These improvements depend on a number of factors such as proper management, working environment, and available technology, etc. Inappropriate design of the working environment is one of the main reasons for lower productivity. Inadequate and incomplete working environments caused by ignoring standard methods in planning level, persistent physical disorders and increase mistakes impact the productivity in the working environment. Maximum productivity, with less physical load and energy consumption, is achieved when the compliance occurs between worker and task. This paper aims to optimize ineffective time and eliminate undesired operations at Molding Compound Manufacturing plants using the time and motion study techniques. The results represent a significant improvement in the production process in productivity and cycle time to optimize the system. There is a substantial increase in the production of the product by simplifying the working method and changing the work sequence. Productivity is improved by eliminating unnecessary movements, simplifying individual tasks and changing operations sequence. Results show that time for each milling operation reduced from 36.3 minutes to 22.5 min, the number of machines reduced from 4 to 3.48 and productivity improved from 5 bags per hour per worker to 7.14 bags per hour per worker.

Viscoelastic Material Characterization: A Realistic Approach to Stress Analysis

This paper presents an advanced method in materials characterization for the mold compound material in semiconductor packages to build models that can technically explain the actual warpage or stress observations under different thermal conditions and time history. In the study, the mold compound material characterization was conducted using Dynamic Mechanical Analyzer (DMA) followed by curve fitting to obtain parameters for the computer modeling input requirement. Thermo-mechanical modeling using viscoelastic material properties was conducted on a bi-material test sample model. Results showed that the new characterized viscoelastic material properties exhibited dependence on time and temperature. Slow cool down from post mold cure (PMC) to room temperature resulted in lower warpage or stress. This observed rate dependent response was explained using viscoelastic material properties in contrast to the usual linear elastic material simplification. Thus, a realistic result from stress or warpage analysis could be achieved using viscoelastic material characterization.