Higher CTE Research Articles

Thermal and dielectric properties enhancement of photocurable acrylate polymers for digital light processing 3D printed electronics

AbstractDigital light processing 3D printing has been rapidly evolving conventional manufacturing industry with the most meticulous resolution and strongest layer‐to‐layer adhesion among all additive manufacturing techniques. In this study, to improve poor polymer thermal stability and dielectric properties from prevailing methyl methacrylate‐based resin, tri‐functional trimethylolpropane tri‐acrylate (TMPTA) is introduced to form a stable polymer network. Meanwhile, monomers carrying non‐polar, bulky adamantane are added to eradicate poly‐TMPTA's notorious high cracking and warping tendency. Test results showed both high 1‐adamantyl methacrylate and 1, 3‐adamantyl di‐acrylate (ADDA) additions can print crack‐free samples. However, only ADDA addition keeps low CTE (82.86 ppm/oC, 200 ~ 260°C) and cuts down Df (0.02, 10 GHz). TMPTA polymer network modifications of both additions are explored. By contrast, poly‐MMA exhibits much higher CTE (323.44 ppm/oC) and Df (0.035). A 3D‐printed curvilinear circuit board from above resin formulation with electroplated copper circuits successfully passes lead‐free level reflow without deformation.

Microstructure and Cyclic Oxidation of Yttria-Stabilized Zirconia/Nanostructured ZrO2 9.5Y2O3 5.6Yb2O3 5.2Gd2O3 Thermal Barrier Coating at 1373 K

This study is intended to improve the high-temperature oxidation of nano-ZGYbY: ZrO2 9.5Y2O3 5.6Yb2O3 5.2Gd2O3 in order to apply it in the new generation of defect cluster thermal barrier coatings (TBCs) through the employment of an intermediate conventional yttria-stabilized zirconia (micro-YSZ) layer between the bond coat (CoNiCrAlY) and top coat. The specimens were deposited with an atmospheric plasma spray (APS) process on IN738LC superalloy. The cyclic oxidation test was performed in air at 1373 K with 4 h in each cycle. The microstructure of the nano-ZGYbY was studied by field emission scanning electron microscopy, revealing the formation of a bimodal microstructure consisted of nanosized particles retained from the initial APS-processed nanopowder and columnar grains, whereas the microstructure of intermediate micro-YSZ layer consisted of columnar grain splats only. X-ray diffraction of TBCs confirmed the formation of non-transformable (t′) ZrO2 phase ( $$ \frac{c}{a\sqrt 2 } $$ < 1.01) as well as the stability of this phase after oxidation. Also, applying an intermediate conventional YSZ layer with a higher CTE and KIC than that of nano-ZGYbY between the bond and top coats improved mechanical properties in new TBCs and it increased the oxidation life.

Effect of Cr2O3 addition on crystallization, microstructure and properties of Li2O–Al2O3–SiO2 glass-ceramics

A new glass-ceramic with high flexural strength and low thermal expansion based on Li2O–Al2O3–SiO2 (LAS) was prepared in this study. The effects of Cr2O3 addition on the crystallization, microstructure, flexural strength, thermal expansion, and electrical properties of LAS system were investigated. The crystallization kinetics based on DSC analysis was calculated using Kissinger and Ozawa methods, which showed that the activation energy E decreases from 158.5 to 149.3 kJ/mol, indicating that Cr2O3 is beneficial to the crystallization of LAS; the crystallization index n varies between 4.46 and 5.09, indicating that the crystallization manner is the volumetric crystallization. XRD analysis was estimated by the whole pattern fitting method, demonstrating that Cr2O3 addition could change the phase contents and promote the crystallinity. The crystallization of CaMgSi2O6 and Cr2O3 with higher CTE not only properly adjusted CTE for matching Si, but also dramatically improved the flexural strength for LAS glass-ceramic. Moreover, we provided a modified formula to calculate CTE of glass-ceramic in the acceptable range. LAS glass-ceramic with 3 wt% Cr2O3 sintered at 800 °C exhibited good properties: σ = 208 MPa, α = 2.64 × 10−6/°C, ε = 8.3, tanδ = 3.6 × 10−3, ρ = 8.82 × 1012 Ω cm, indicating its suitability for LTCC application.

Sealing performance and chemical compatibility of SrO–La2O3–Al2O3–SiO2 glasses with bare and coated ferritic alloy

Sealing performance and chemical compatibility of SrO–La2O3–Al2O3–SiO2 glass sealants with bare and Mn–Co spinel coated SUS430 ferritic alloys are investigated. The low–SrO glasses (≤40mol%) show good wettability and adherence to the bare SUS430 alloy due to their lower viscosity and negligible reactions with the alloy. The high–SrO glass (e.g. 45mol%) exhibits higher viscosity and more serious reactions with the bare SUS430 alloy. The formation of SrCrO4 with higher CTE causes obvious delamination and dramatic oxidation of the alloy at the glass/alloy interface. In contrast, Mn–Co spinel coating has good compatibility with both SrO–La2O3–Al2O3–SiO2 glasses and Fe–Cr ferritic alloy. Moreover, the Mn–Co spinel coating on the alloy can effectively restrain the diffusion of Fe and Cr and the reactions between the glasses and the alloy. Due to the ameliorated interfacial microstructure, sealing performance can be improved by applying the Mn–Co spinel coating on SUS430 alloy, especially for the bonded couple with high–SrO glass.

Effects of M2+ (M = Ca, Sr, and Ba) Addition on Crystallization and Microstructure of SiO2-MgO-Al2O3-B2O3-K2O-F Glass

In understanding the effect of K+ substitution by M2+ (M = Ca, Sr, and Ba) on crystallization and microstructural properties of boroaluminosilicate glass system, the SiO2-MgO-Al2O3-B2O3-MgF2-K2O-Li2O-AlPO4 glasses were prepared by single-step melt-quenching at 1500°C. Density of base glass (2.64 g·cm−3) is found to be decreased in presence of CaO and SrO. Tg is increased by 5–10°C and Td decreased by 13–20°C on addition of M2+. The variation of Tg, Td and decrease of thermal expansion (CTE) from 7.55 to 6.67–6.97 (×10−6/K, at 50–500°C) in substituting K+ by M2+ are attributed to the higher field-strength of Ca2+, Sr2+, and Ba2+. Opaque mica glass-ceramics were derived from the transparent boroaluminosilicate glasses by controlled heat treatment at 1050°C (duration = 4 h); and the predominant crystalline phase was identified as fluorophlogopite (KMg3AlSi3O10F2) by XRD and FTIR study. Glass-ceramic microstructure reveals that the platelike mica flake crystals predominate in presence of K2O and CaO but restructured to smaller droplet like spherical shaped mica on addition of SrO and BaO. Wide range of CTE values (9.54–13.38 × 10−6/K at 50–800°C) are obtained for such glass-ceramics. Having higher CTE value after crystallization, the CaO containing SiO2-MgO-Al2O3-B2O3-MgF2-K2O-Li2O-AlPO4 glass can be useful as SOFC sealing material.

Case Analysis on PTH Fracture Caused by Twin Copper

An actual case of PTH fracture after soldering process was studied. By means of cross section analysis using metallography microscope and SEM, together with thermal analysis results, root cause of PTH fracture was concluded that a high density of twin copper weakened the mechanical strength so seriously that PTHs could not undergo thermal stress from soldering process, and higher CTE was attributed to an accelerative factor. Moreover, it is recommended to enhance current density properly and make sure the effectiveness of electroplating additives to prevent twin copper by theoretical analysis.

Viscoelastic and thermal properties of polysulfide modified epoxy resin: The effect of modifier molecular weight

AbstractIn this research two grades of polysulfide resin with low and high molecular weight (respectively G4 and G112) as reactive modifier was used to toughen epoxy resin. The effect of modifier molecular weight on impact resistance, thermal expansion coefficient, storage and loss modulus, decomposition temperature and adhesion properties of toughened epoxy was investigated. The impact strength and the thermal expansion coefficient (CTE) of epoxy resin was increased with increasing polysulfide but the G112 modified epoxy samples showed higher CTE values and impact resistance than those of modified with G4. Comparing of the same weight percent inclusion of G4 and G112 effect on decomposition temperature show that G4 modified epoxy resin has lower decomposition temperature than the G112 modified epoxy resin. Also addition of G112 up to 10 weight percent leads to higher bond strength with aluminum sheets. According to the DMTA graphs, glass transition temperature (Tg) of the modified epoxy was decreased with increasing polysulfide weight percent in composition. At the same time G4 modified epoxies have lower Tg and storage modulus than that of modified with G112.

몰드물성 종류 및 칩 크기 변화에 따른 웨이퍼 레벨 Sip에서의 열 피로 해석

This paper describes in detail the life prediction models and simulations of thermal fatigue under different mold compounds and chip sizes for wafer-level embedded SiP. Three-dimensional finite element models are built to simulate the viscoplastic behaviors for various mold compounds and chip sizes. In particular, the bonding parts between a mold and silicon nitride (Si3N4) are carefully modeled, and the strain distributions are studied. Three different chip sizes are used, and the effects of the mold compounds are observed. Through the numerical studies, it is found that type-C, which has a relatively lower Young's modulus and higher CTE, has a better fatigue life than the other mold compounds. In addition, the <TEX>$4{\times}4$</TEX> chip has a shorter life than the <TEX>$6{\times}6$</TEX> and <TEX>$8{\times}8$</TEX> chips.

Mechanical strain evolution in Cu/low K interconnect lines

ABSTRACTThe mechanical stresses in Cu interconnect lines arise from thermal expansion (CTE) differences, and the magnitude of the stress can be calculated based on the measured strain. In the current work, the strain (and stress) state of narrow Cu lines fabricated in oxide and porous organic spin-on dielectrics (low K) has been determined with X-Ray diffraction (XRD) during annealing. The room temperature stress along the length (X) and width (Y) of the lines are not dramatically different while the Z component is somewhat smaller with the spin-on ILD. These small perturbations in the magnitude of the Cu stress do not reflect the dramatic differences in the CTE. More insight into the materials system is obtained by studying the strain-temperature behavior, which illustrates the effect of the ILD clearly. The X strain is similar in magnitude and variation with temperature for both ILDs, supporting strain being imposed by the substrate. However, the Z strain is compressive at RT and linearly increases with temperature for Cu in low K, reflecting the lack of constraint by the ILD and the higher CTE of the ILD.

Investigation of the Lead-On-Chip Package’s Reliability

An assembly test chip (ATC), consisting of varieties of test structures, had been utilized to monitor the package integrity of SOJ lead-on-chip (LOC) packages after various reliability tests. Two different types of epoxy molding compounds, namely biphenyl and EOCN epoxies, were chosen to investigate their effects on package’s reliability. After the reliability tests, silicon chip crack was observed in three test samples due to the existence of a large chip backside chipping (˜120 μm). Qualitative study about this failure mechanism was carried out by a finite element analysis and it was found that, due to the higher flexural modulus and CTE of the biphenyl epoxy, the thermally induced stresses developed in the chip encapsulated by this epoxy during reliability tests were more likely to cause the crack propagation in the silicon chip than those induced by using EOCN type epoxy.