贴装用高热导率集成电路基板的水热法制备研究

针对当前SMT中集成电路基板散热难的问题,结合热设计方法,系统地研究了热液条件下在高纯度铝基片上生长氧化铝膜的技术,并对制成的基片电性能及其温度特性、表面形貌做了详细的测试与分析。结果表明:有氧化铝膜的铝基片既有高的散热性,又有好的电性能,完全符合SMT基板的要求,有广泛的应用前景。     

Growth of polycrystalline silicon films on titanium and aluminum layers

Adherent, polycrystalline silicon films were vacuum deposited onto titanium passivated steel alloy substrates at substrate temperatures between 535 and 650°C and onto aluminum films at substrate temperatures between 480 and 520°C. Silicon films deposited onto titanium layers are characterized by a sub-micron grain size and a preferential orientation of the <110> direction perpendicular to the growth surface. Resistivities of ∿10⁴ ohm-cm are measured for the undoped films. Silicon films deposited onto aluminum layers have a larger grain size, ∿5μm, a columnar morphology and a preferential orientation of the <111> direction perpendicular to the growth surface. As-deposited resistivities of ∿10² ohm-cm are measured for these films. Boron and phosphorus doped silicon films on titanium layers were annealed. The behavior with annealing of the electrical properties of the films depended on which doping impurity was used. Silicon films on aluminum were annealed to reduce lattice damage within the silicon grains and to dope the films with aluminum from the aluminum layer. Resistivities of several ohm-cm were measured for the annealed films on aluminum.     

微电路封装中的铝钎焊技术

为满足电子系统小型化、轻量化、高性能、高可靠等要求,采用铝合金材料做封装外壳和布线基板已提到议事日程.但铝合金外壳的密封和钎焊存在一系列有待解决的问题,影响了铝合金材料的高导热率和质量轻等性能的充分发挥.文章介绍了一种采用低温铝钎焊料和钎焊技术的铝合金外壳基板钎焊和密封方法.     

Performance Improvement of Flexible Thermoelectric Device: FEM-Based Simulation

Possibilities for improving the performance of the flexible thermoelectric (TE) device were discussed on the basis of heat conduction analysis by the finite element method. The flexible TE device consists of two flexible substrates and thin films of n- and p-type TE materials placed between the substrates. To enhance the device performance, the use of higher-performance TE materials and improvement of the flexible substrate will be effective. In the present study, the effect of the thermal conductivity of the materials used in the device on the output voltage was examined. The calculations indicated that there is a certain combination of thermal conductivities of the components which gives the maximum output voltage. Although a lower thermal conductivity of the TE material leads to higher output voltage, influence of the thermal conductivity on the maximum voltage was not significant under the condition of the present study. As a result, it is effective to improve device performance by choosing an appropriate combination of TE material and substrate material. According to the calculations, approximately 60% increase in output voltage is expected compared with that of the present combination of materials used in the prototype device.     

The effect of thin film structure and properties on gold ball bonding

The gold ball bonding process is widely used for making interconnections between integrated circuit chips and package lead frames, yet the relationships between the wire/substrate materials properties and the bond formation processes are not yet well understood. While the creation of a metallurgical bond at the interface between the wire and substrate is required, the deformation of the wire and substrate also play an important role in bond formation. Bonding to thin film substrates is of particular interest, since thin films often exhibit mechanical behavior distinctly different from bulk materials. In the present study, a systematic investigation has been conducted to understand the effects of the structure and properties of aluminum thin films on the quality of gold ball bonds. A series of aluminum thin films was fabricated with systematic variations in hardness, roughness, thickness, and composition. Gold wires were ball bonded to these substrates, and the bondability and bond shear strengths were assessed. Metallographic sections of several of these specimens were made and examined in the scanning electron microscope. The results show that the film thickness has the most dominant effect on the bondability and bond strength; films that were 0.5 μm thick often exhibited low strength or poor bondability. Very hard films also gave poor results. Ultimately, these results can be used to predict the wire bond reliability expected from various types of thin film metallization.     

Formation of Thick Porous Anodic Alumina Films and Nanowire Arrays on Silicon Wafers and Glass

A method for the fabrication of thick films of porous anodic alumina on rigid substrates is described. The anodic alumina film was generated by the anodization of an aluminum film evaporated on the substrate. The morphology of the barrier layer between the porous film and the substrate was different from that of anodic films grown on aluminum substrates. The removal of the barrier layer and the electrochemical growth of nanowires within the ordered pores were accomplished without the need to remove the anodic film from the substrate. We fabricated porous anodic alumina samples over large areas (up to 70 cm²), and deposited in them nanowire arrays of various materials. Long nanowires were obtained with lengths of at least 9 μm and aspect ratios as high as 300. Due to their mechanical robustness and the built‐in contact between the conducting substrate and the nanowires, the structures were useful for electrical transport measurements on the arrays. The method was also demonstrated on patterned and non‐planar substrates, further expanding the range of applications of these porous alumina and nanowire assemblies.     

Substrate‐Dependent Molecular and Nanostructural Orientation of Nafion Thin Films

The effects of film thickness and substrate composition on the ionomer structure in porous electrodes are critical in understanding pathways toward developing higher performance electrochemical devices, including fuel cells and batteries. Insights are gained into the molecular and nanostructural orientation dependence for thin Nafion films (12–300 nm thick) on gold, platinum, and SiO₂ model substrates. Molecular orientation is determined from the birefringence measured using spectroscopic ellipsometry, while the nanostructural orientation of the ionic domains is measured using grazing‐incidence small‐angle X‐ray scattering. Density functional theory calculations for the molecular polarizability of the Nafion backbone and side chain show complimentary contributions to the measured birefringence values for the material. Nafion films prepared on SiO₂ substrates exhibit a nearly isotropic molecular and nanostructural orientation. Films on gold and platinum display parallel backbone orientations, relative to the substrate, with decreasing film thickness. However, a birefringence transition toward molecular isotropy is observed for 30 nm thick films on Au and Pt; while the ionic nanostructured domains continuously align parallel to the substrate. This apparent isotropic molecular orientation with increasing domain orientation highlights the difference between the backbone and side chain orientation, a key finding for elucidating transport in confined films at the interfaces.     

功率HIC基板及其工艺布局设计研究

基板选用和工艺布局是功率混合集成电路两项重要技术内容。根据基板材料不同，功率基板及其布线工艺主要分为陶瓷基板和金属基板两大类。常规陶瓷基板以96％Al2O3陶瓷为代表，高导热陶瓷基板以BeO、AIN陶瓷为代表。陶瓷功率基板大部分采用厚膜布线工艺，另一种布线方式是DBC布线。绝缘金属基板的种类很多，最常使用的是铝基板，另...     

Architectured Materials to Improve the Reliability of Power Electronics Modules: Substrate and Lead-Free Solder

Power electronics modules (>100 A, >500 V) are essential components for the development of electrical and hybrid vehicles. These modules are formed from silicon chips (transistors and diodes) assembled on copper substrates by soldering. Owing to the fact that the assembly is heterogeneous, and because of thermal gradients, shear stresses are generated in the solders and cause premature damage to such electronics modules. This work focuses on architectured materials for the substrate and on lead-free solders to reduce the mechanical effects of differential expansion, improve the reliability of the assembly, and achieve a suitable operating temperature (<175°C). These materials are composites whose thermomechanical properties have been optimized by numerical simulation and validated experimentally. The substrates have good thermal conductivity (>280 W m^?1 K^?1) and a macroscopic coefficient of thermal expansion intermediate between those of Cu and Si, as well as limited structural evolution in service conditions. An approach combining design, optimization, and manufacturing of new materials has been followed in this study, leading to improved thermal cycling behavior of the component.     

Glass‐Like Through‐Plane Thermal Conductivity Induced by Oxygen Vacancies in Nanoscale Epitaxial La0.5Sr0.5CoO3−δ

Ultrafast time‐domain thermoreflectance (TDTR) is utilized to extract the through‐plane thermal conductivity (Λ _LSCO) of epitaxial La_0.5Sr_0.5CoO_3?δ (LSCO) of varying thickness (<20 nm) on LaAlO₃ and SrTiO₃ substrates. These LSCO films possess ordered oxygen vacancies as the primary means of lattice mismatch accommodation with the substrate, which induces compressive/tensile strain and thus controls the orientation of the oxygen vacancy ordering (OVO). TDTR results demonstrate that the room‐temperature Λ _LSCO of LSCO on both substrates (1.7 W m^?1 K^?1) are nearly a factor of four lower than that of bulk single‐crystal LSCO (6.2 W m^?1 K^?1). Remarkably, this approaches the lower limit of amorphous oxides (e.g., 1.3 W m^?1 K^?1 for glass), with no dependence on the OVO orientation. Through theoretical simulations, origins of the glass‐like thermal conductivity of LSCO are revealed as a combined effect resulting from oxygen vacancies (the dominant factor), Sr substitution, size effects, and the weak electron/phonon coupling within the LSCO film. The absence of OVO dependence in the measured Λ _LSCO is rationalized by two main effects: (1) the nearly isotropic phononic thermal conductivity resulting from the imperfect OVO planes when δ is small; (2) the missing electronic contribution to Λ _LSCO along the through‐plane direction for these ultrathin LSCO films on insulating substrates.     

Frequency effects on the dielectric properties of AlN film deposited by radio frequency reactive magnetron sputtering

Applications insulated metal substrates (IMS) for high-density and high-power mounting are greatly extending with miniaturizing of electronic components. Recently, aluminum nitride film has been used as a potential insulator and/or passivation material in insulated metal substrate because of its high intrinsic thermal conductivity, low thermal expansion coefficient, low dielectric constant and high electric resistivity. In this investigation, AlN films were deposited on Al substrates by radio frequency (RF) reactive magnetron sputtering. The metal-interfacial insulator layer-metal (Al/AlN/Al MIM) structures were obtained with AlN layer on Al substrates. Electrical properties of the MIM structures were investigated by meaning of C-V and C-f characteristics in the frequency range of 100 Hz-500 kHz and voltage range of −4 V to 4 V. Experimental results show that the dielectric constant of this structure decreases gradually with increasing frequency. While the dielectric loss tangent was tested from low frequency to high frequency, it is found that the dielectric loss tangent decreases from 0.03375, reaches a minimum (0.00424) at approximately 65 kHz and then increases sharply. These results are in accordance with modified model of Goswami and Goswami for such structure. The dielectric dispersion is observed due to distribution of interface states as well as ionized space charge carriers such as the oxygen atoms, nitrogen vacancies and defects. The AC conductivity results show that the electrical resistance decreases as the frequency increasing due to hopping type conduction.     

Orientation Control of Linear‐Shaped Molecules in Vacuum‐Deposited Organic Amorphous Films and Its Effect on Carrier Mobilities

The molecular orientation of linear‐shaped molecules in organic amorphous films is demonstrated to be controllable by the substrate temperature. It is also shown that the molecular orientation affects the charge‐transport characteristics of the films. Although linear‐shaped 4,4′‐bis[(N‐carbazole)styryl]biphenyl molecules deposited on substrates at room temperature are horizontally oriented in amorphous films, their orientation when deposited on heated substrates with smooth surfaces becomes more random as the substrate temperature increases, even at temperatures under the glass transition temperature. Another factor dominating the orientation of the molecules deposited on heated substrates is the surface roughness of the substrate. Lower carrier mobilities are observed in films composed of randomly oriented molecules, demonstrating the significant effect of a horizontal molecular orientation on the charge‐transport characteristics of organic amorphous films.     

Rational Design of a Printable,Highly Conductive Silicone‐based Electrically Conductive Adhesive for Stretchable Radio‐Frequency Antennas

Stretchable radio‐frequency electronics are gaining popularity as a result of the increased functionality they gain through their flexible nature, impossible within the confines of rigid and planar substrates. One approach to fabricating stretchable antennas is to embed stretchable or flowable conductive materials, such as conductive polymers, conductive polymer composites, and liquid metal alloys as stretchable conduction lines. However, these conductive materials face many challenges, such as low electrical conductivity under mechanical deformation and delamination from substrates. In the present study, a silicone‐based electrically conductive adhesive (silo‐ECA) is developed that have a conductivity of 1.51 × 10⁴ S cm^?1 and can maintain conductivity above 1.11 × 10³ S cm^?1, even at a large stain of 240%. By using the stretchable silo‐ECAs as a conductor pattern and pure silicone elastomers as a base substrate, stretchable antennas can be fabricated by stencil printing or soft‐lithography. The resulting antenna's resonant frequency is tunable over a wide range by mechanical modulation. This fabrication method is low‐cost, can support large‐scale production, has high reliability over a wide temperature range, and eliminates the concerns of leaking or delamination between conductor and substrate experienced in previously reported micro‐fluidic antennas.     

Characterization of underfill/substrate interfacial toughnessenhancement by silane additives

This work experimentally measures the apparent fracture toughness of the interfaces between epoxy-based underfill materials and various substrates including aluminum, polyimide, BCB, and printed wiring boards (FR-4) with solder mask. A small amount of silane coupling agent is added to the base underfill in order to form various underfill derivatives, and double layer specimens with preexisting interfacial cracks are prepared for four-point bending tests. The measurements are qualitatively correlated to each silane additive. The purpose of adding silane additives was to enhance the adhesion; the enhancement of interfacial toughness was found to strongly depend on the type of substrate. The results of this study have important implications in flip-chip reliability where interfacial cracking is one of the major failure modes     

Soft Graphoepitaxy for Large Area Directed Self‐Assembly of Polystyrene‐block‐Poly(dimethylsiloxane) Block Copolymer on Nanopatterned POSS Substrates Fabricated by Nanoimprint Lithography

Polyhedral oligomeric silsequioxane (POSS) derivatives have been successfully employed as substrates for graphoepitaxial directed self‐assembly (DSA) of block copolymers (BCPs). Tailored POSS materials of tuned surface chemistry are subject to nanoimprint lithography (NIL) resulting in topographically patterned substrates with dimensions commensurate with the BCP block length. A cylinder forming polystyrene‐block‐polydimethylsiloxane (PS‐b‐PDMS) BCP is synthesized by sequential living anionic polymerization of styrene and hexamethylcyclotrisiloxane. The patterned POSS materials provide a surface chemistry and topography for DSA of this BCP and after solvent annealing the BCP shows well‐ordered microphase segregation. The orientation of the PDMS cylinders to the substrate plane could be controlled within the trench walls by the choice of the POSS materials. The BCP patterns are successfully used as on‐chip etch mask to transfer the pattern to underlying silicon substrate. This soft graphoepitaxy method shows highly promising results as a means to generate lithographic quality patterns by nonconventional methods and could be applied to both hard and soft substrates. The methodology might have application in several fields including device and interconnect fabrication, nanoimprint lithography stamp production, nanofluidic devices, lab‐on‐chip, or in other technologies requiring simple nanodimensional patterns.     

PLZT薄膜的结构、介电与光学性能的研究

以硝酸镧、醋酸铅、钛酸丁酯和异丙醇锆为原料，乙二醇甲醚作溶剂。用简单的溶胶一凝胶法和快速退火工艺在Si(111)、石英和Pt／Ti／SiO2／Si(100)基片成功地制备出了高度多晶和(111)取向生长的(Pb，La)(Ti，Zr)O3(PLZT)薄膜。用原子力显微镜分析了薄膜的表面形貌；测试了薄膜的铁电和介电特性。PLZT薄膜的剩余极化强度和矫顽场分别为10．3μC／cm^2和36kV／cm；在100kHz，薄膜的介电常数和损耗因子分别为682和0．021。生长在石英基片上的薄膜具有好的透光性，当波长高于360nm，其透过率高达72％。     

Finite element method investigation into nanoimprinting of aluminum/polyimide bi-layer substrates

Finite element method (FEM) simulations are performed to investigate the nanoimprinting of aluminum/polyimide bi-layer substrates at temperatures ranging from 25 to 200 °C. In constructing the FE analysis model, the mechanical properties of the aluminum and polyimide layers are obtained from thermo-mechanical micro-force tensile tests. The validity of the FE model is confirmed by comparing the results obtained for the formation height ratio in single-layer aluminum substrates with the experimental results. Thereafter, simulations are performed to investigate the effects of the aluminum-to-polyimide thickness ratio and the substrate temperature on the imprint pressure required to obtain a complete filling of the mold cavities. The simulation results show that under low temperature conditions (i.e. <100 °C), the imprint pressure reduces as the aluminum-to-polyimide thickness ratio decreases. In addition, for temperatures lower than 100 °C, the use of a polyimide layer reduces the imprinting force by around 38% compared to that required to imprint a single-layer aluminum substrate of an equivalent total thickness. However, for temperatures higher than 150 °C and a polyimide-to-substrate thickness ratio of more than 40%, the imprint force reversely enlarged due to the strain-hardening of the polyimide film at elevated temperatures. The simulation results obtained for the variation of the imprint pressure with the aluminum thickness ratio, the polyimide thickness ratio, and the substrate temperature are compiled in the form of a contour chart. The chart provides a convenient means of establishing suitable processing conditions for a variety of nanoimprinting applications.     

Influence of the grain boundary phase on the mechanical strength ataluminum nitride substrate surfaces

The influence of grain boundary phases on the mechanical strength at aluminum nitride (AlN) substrate surfaces, after a wet chemical process, was studied using AlN substrates doped with 2 wt% CaO or 4 wt% Y₂O₃. Mechanical strength was measured by pin pull-off, pin bending tests and Vickers hardness measurements. Test specimens were obtained by the processes of lapping, polishing, thin-film metallizing, photoengraving, plating, and brazing. The test results showed that the mechanical strength at the surface of Y₂ O₃-AlN substrates was higher than at CaO-AlN surfaces, where it was under the adhesion strength between the metallization layer and the AlN substrate. The mechanical strength at the surface of the CaO-AlN substrate was lost during patterning and plating. This was accompanied by an important weight loss in HNO₃ and K₂ O·n(B₂O₃) aqueous solution, due to dissolution of the grain boundary phase. The reason for the difference in the mechanical surface strength of AlN substrates after patterning and plating is that the CaO-AlN grain boundary phase dissolves in the chemical solution in the process more easily than the Y₂O₃-AlN gram boundary phase. The Y₂O ₃-AlN substrate showed unchanged pin pull-off and bending strength even after thermal cycling (1000 cycles) and 1000 h of a pressure cooker test. Although the CaO-AlN grain boundary phase seemed to cover all the grains, thermal conductivity was only slightly affected, because the grain boundary film was very thin     

Analysis of a microstrip crossover embedded in a multilayeredanisotropic and lossy media

The equivalent circuit and the scattering parameters of the orthogonal microstrip crossover discontinuity are determined by assuming that the conducting strips are embedded in a multilayered substrate which may contain both anisotropic dielectrics and materials with a nonnegligible conductivity. The equivalent circuit of the crossover is obtained in terms of the complex excess charge densities on the strips. These excess charge densities are computed by means of the Galerkin method in the spectral domain. Comparison is carried out with previously existing results for microstrip crossovers on lossless isotropic substrates and original results are presented for crossovers on anisotropic and lossy substrates     

CdZnTe substrate producibility and its impact on IRFPA yield

The need for cost effective production of HgCdTe infrared detectors and focal plane assemblies has led to increased attention to the availability of high quality large-area CdZnTe substrates. Reasonable yield of large-area substrates (≥4 cm×6 cm format) is necessary for fabrication of focal plane assemblies (FPAs) now in production, and for future infrared (IR) detectors which are growing in size and complexity. Raytheon’s infrared materials producibility (IRMP) program has addressed this issue, after identifying critical drivers of FPA yield coming from substrates, and targeted certain improvements in substrate process steps for highest impact on large-area substrate yield. Three specific areas of improvements in the substrate process were addressed: (1) compounding of a large 6 kg charge of CdTe; (2) vertical Bridgman growth of 92 mm diameter CdZnTe boules in both quartz and pyrolytic boron nitride (PBN) crucibles; and (3) optimized Cd overpressure control during growth and cool-down of the boule. It was shown that the Cd overpressure and the cooling schedule had the strongest effects on defect populations. The resulting improvements include a 33% increase in wafer yield per unit starting weight, an estimated 50% reduction in substrate cost per cm², better morphology of epitaxial HgCdTe layers, and improved yield of satisfactory IR detectors. The criteria for selecting substrates have also improved as a result of this work. In addition, photovoltaic detectors were fabricated on wafers from a variety of sources, and tested. Results compare favorably with those on baseline (earlier process) substrates.