Research on Silicon Carbide Dispersion-Reinforced Hypereutectic Aluminum-Silicon Electronic Packaging Materials

The objective of this study is to improve the mechanical properties and machining performance of high thermal conductivity and low expansion silicon carbide dispersion-strengthened hypereutectic aluminum-silicon electronic packaging materials to meet the needs of aviation,aerospace,and electronic packaging fields.We used the powder metallurgy method and high-temperature hot pressing technology to prepare SiC/Al-Si composite materials with different SiC contents(5vol%,10vol%,15vol%,and 20vol%).The results showed that as the SiC content increased,the tensile strength of the composite material first increased and then decreased.The tensile strength was the highest when the SiC content was 15%;the sintering temperature significantly affected the composite material’s structural density and mechanical properties.Findings indicated 700℃was the optimal sintering and the optimal SiC content of SiC/Al-Si composite materials was between 10%and 15%.Besides,the sintering temperature should be strictly controlled to improve the material’s structural density and mechanical properties.

Literature Review of Electronic Packaging Technology and Residual Stress

The rapid development of the electronic information industry brings to the irreplaceable role of electronic components, therefore the search of a more reliable packaging material has become increasingly important. In the electronic packaging system, the failure phenomenon caused by residual stress is one of the key factors restricting the development of electronic packaging technology. In order to use the in-situ characterization technology to explore the residual stress inducing mechanism and failure mechanism of epoxy-based advanced packaging materials, this paper gives a review of related previous research, and lays a theoretical foundation for the upcoming research. The classification and generation mechanism of residual stress are clarified in this paper, which provides data support for future related research.

Microstructure and properties of electronic packaging box with high silicon aluminum-base alloy by semi-solid thixoforming

The electronic packaging box with high silicon aluminum-base alloy was prepared by semi-solid thixoforming technique.The flow characteristic of the Si phase was analyzed.The microstructures of different parts of the box were observed by optical microscopy and scanning electron microscopy,and the thermophysical and mechanical properties of the box were tested.The results show that there exists the segregation phenomenon between the primary Si phase and the liquid phase during thixoforming,the liquid phase flows from the box,and the primary Si phase accumulates at the bottom of the box.The volume fraction of primary Si phase decreases gradually from the bottom to the walls.Accordingly,the thermal conductivities of bottom center and walls are 107.6 and 131.5 W/（m·K）,the coefficients of thermal expansion（CTE） are 7.9×10-6 and 10.6×10-6 K-1,respectively.The flexural strength increases slightly from 167 to 180 MPa.The microstructures and properties of the box show gradient distribution overall.

Microstructure and properties of Al/Si/SiC composites for electronic packaging

The Al/Si/SiC composites with medium volume fraction for electronic packaging were fabricated by gas pressure infiltration.On the premise of keeping the machinability of the composites,the silicon carbide particles,which have the similar size with silicon particles（average 13 μm）,were added to replace silicon particles of same volume fraction,and microstructure and properties of the composites were investigated.The results show that reinforcing particles are distributed uniformly and no apparent pores are observed in the composites.It is also observed that higher thermal conductivity（TC） and flexural strength will be obtained with the addition of SiC particles.Meanwhile,coefficient of thermal expansion（CTE） changes smaller than TC.Models for predicting thermal properties were also discussed.Equivalent effective conductivity（EEC） was proposed to make H-J model suitable for hybrid particles and multimodal particle size distribution.

Microstructure characterization and thermal properties of hypereutectic Si-Al alloy for electronic packaging applications

The rapid solidified process and hot press method were performed to produce three hypereutectic 55%Si-Al, 70%Si-Al and 90%Si-Al alloys for heat dissipation materials. The results show that the atomization is an effective rapid solidified method to produce the Si-Al alloy and the size of atomized Si-Al alloy powder is less than 50 μm. The rapid solidified Si-Al alloy powder were hot pressed at 550 ℃ with the pressure of 700 MPa to obtain the relative densities of 99.4%, 99.2% and 94.4% for 55%Si-Al, 70%Si-Al and 90%Si-Al alloys, respectively. The typical physical properties, such as the thermal conductivity, coefficient of thermal expansion （CTE） and electrical conductivity of rapid solidified Si-Al alloys are acceptable as a heat dissipation material for many semiconductor devices. The 55%Si-Al alloy changes greatly （CTE） with the increase of temperature but obtains a good thermal conductivity. The CTE of 90%Si-Al alloy matches with the silicon very well but its thermal conductivity value is less than 100 W/（m.K）. Therefore, the 70%Si-Al alloy possesses the best comprehensive properties of CTE and thermal conductivity for using as the heat sink materials.

Microstructure and properties of SiC_p/Al electronic packaging shell produced by liquid-solid separation

The electronic packaging shell of high silicon carbide （54%SiC, volume fraction） aluminum-based composites was produced by liquid-solid separation technique. The characteristics of distribution and morphology of SiC as well as the shell’s fracture surface were examined by optical microscopy and scanning electron microscopy, and the thermo-physical and mechanical properties of the shell were also tested. The results show that Al matrix has a net-like structure while SiC is uniformly distributed in the Al matrix. The SiCp/Al composites have a low density of 2.93 g/cm^3, and its relative density is 98.7%. Thermal conductivity of the composites is 175 W/（·K）, coefficient of thermal expansion （CTE） is 10.3×10^-6 K-1 （25-400 ℃）, compressive strength is 496 MPa, bending strength is 404.5 MPa, and the main fracture mode is brittle fracture of SiC particles accompanied by ductile fracture of Al matrix.Its thermal conductivity is higher than that of Si/Al alloy, and its CTE matches with that of the chip material.

Effects of rolling and annealing on microstructures and properties of Cu/Invar electronic packaging composites prepared by powder metallurgy

The Cu/Invar composites of 40% Cu were prepared by powder metallurgy, and the composites were rolled with 70% reduction and subsequently annealed at 750 ℃. Phases, microstructures and properties of the composites were then studied. After that, the amount of a-Fe（Ni,Co） in the composites is reduced, because a-Fe（Ni,Co） partly transfers into y-Fe（Ni,Co） through the diffusion of the Ni atoms into a-Fe（Ni,Co） from Cu. When the rolling reduction is less than 40%, the deformation of Cu takes place, resulting in the movement of the Invar particles and the seaming of the pores. When the rolling reduction is in the range from 40% to 60%, the deformations of Invar and Cu occur simultaneously to form a streamline structure. After rolling till 70% and subsequent annealing, the Cu/Invar composites have fine comprehensive properties with a relative density of 98.6%, a tensile strength of 360 MPa, an elongation rate of 50%, a thermal conductivity of 25.42 W/（m.K） （as-tested） and a CTE of 10.79× 10-6/K （20-100 ℃）.

Laser-weldable Si_p-SiC_p/Al hybrid composites with bilayer structure for electronic packaging

Laser-weldable Sip-SiCp/Al hybrid composites with high volume fraction （60%-65%） of SiC reinforcement were fabricated by compression moulding and vacuum gas pressure infiltration technology. Microscopic observation displayed that the Sip-SiCp/Al hybrid composites with bilayer structure were compact without gas pores and the intergradation between Sip/Al layer and SiCp/Al layer was homogeneous and continuous. Further investigation revealed that the Sip-SiCp/Al hybrid composites possessed low density （2.96 g/cm^3）, high gas tightness （1.0 mPa·cm^3）/s）, excellent thermal management function as a result of high thermal conductivity （194 W/（m·K） and low coefficient of thermal expansion （7.0×10^-6 K-1）. Additionally, Sip-SiCp/Al hybrid composites had outstanding laser welding adaptability, which is significantly important for electronic packaging applications. The gas tightness of components after laser welding （48 mPa·cm^3）/s） can well match the requirement of advanced electronic packaging. Several kinds of these precision components passed tests and were put into production.

Interfacial microstructure and properties of diamond/Cu-xCr composites for electronic packaging applications

Diamond/Cu-xCr composites were fabricated by pressure infiltration process.The thermal conductivities of diamond/Cu-xCr（x = 0.1,0.5,0.8） composites were above 650 W/mK,higher than that of diamond/Cu composites.The tensile strengths ranged from 186 to 225 MPa,and the bonding strengths ranged from 400 to 525 MPa.Influences of Cr element on the thermo-physical properties and interface structures were analyzed.The intermediate layer was confirmed as Cr3C2 and the amount of Cr3C2 increased with the increase of Cr concentration in Cu-xCr alloys.When the Cr concentration was up to 0.5 wt.%,the content of the Cr3C2 layer was constant.As the thickness of the Cr3C2 layer became larger,the composites showed a lower thermal conductivity but higher mechanical properties.The coefficients of thermal expansion（CTE） of diamond/Cu-xCr（x = 0.1,0.5,0.8） composites were in good agreement with the predictions of the Kerner＇ model.

Al-50 wt%Si Alloy by Spark Plasma Sintering(SPS)for Electronic Packaging Materials

A hypereutectic Al-50 wt%Si alloy for electronic packaging was prepared by spark plasma sintering(SPS)technology using gas-atomized Al-50 wt%Si powder.The effect of sintering parameters on alloy phase composition,microstructure,thermal performance and the tensile strength at different temperatures was investigated.The experimental results show that the alloy can obey the diffraction peaks of silicon and aluminum without other peaks appearing.The primary silicon in the prepared alloy can be evenly distributed in the aluminum matrix.The coefficient of thermal expansion(CTE)and thermal conductivity(TC)of the alloy will improve with the increase of sintering temperature,but they will decrease after sintering for a long time,which is caused by the large difference of coefficient of thermal expansion between silicon and aluminum.The tensile properties of the alloy at room temperature will increase with the increase of sintering temperature,but higher test temperatures will inhibit the tensile properties except the elongation.The morphology and fracture mode of the tensile fracture are also analyzed to determine the good bonding strength of the alloy.

Semisolid forging electronic packaging shell with silicon carbon-reinforced copper composites

To fabricate electronic packaging shell of coppermatrix composite with characteristics of high ther mal conductivity and low thermal expansion coefficient, semisolid forming technology, and powder metallurgy was combined. Conventional mechanical mixing of Cu and SiC could have insufficient wettability, and a new method of semisolid processing was introduced for billets preparation. The SiC/Cu composites were first prepared by PM, and then, semisolid reheating was performed for the successive semisolid forging. Composite billets with SiC 35 % vol ume fraction were compacted and sintered pressurelessly, microstructure analysis showed that the composites pre pared by PM had high density, and the combination between SiC particles and Cualloy was good. Semisolid reheating was the crucial factor in determining the micro structure and thixotropic property of the billet. An opti mised reheating strategy was proposed： temperature 1,025 ℃and holding time 5 min.

Numerical simulation on thixoforging of electronic packaging shell with SiC_p/A356 composites

Based on the research of modem electronic packaging materials, thixo-forming technology was used to fabricate electronic packaging shell. The process of thixo-extrusion with SiCp/A356 composites was simulated by the finite element software DEFORM-3D, then the flow velocity field, equivalent strain field and temperature field were analyzed. The electronic packaging shell was manufactured by extrusion according to the results from numerical simulation. The results show that thixo-forming technology can be used in producing electronic package shell with SiCp/A356 composites, and high volume fraction of SiCp with homogeneous distribution can be achieved, being in agreement with the requirements of electronic packaging materials.

Microstructure and properties of electronic packaging shell with high silicon carbide aluminum-base composites by semi-solid thixoforming

The electronic packaging shell with high silicon carbide aluminum-base composites was prepared by semi-solid thixoforming technique. The flow characteristic of the Si C particulate was analyzed. The microstructures of different parts of the shell were observed by scanning electron microscopy and optical microscopy, and the thermophysical and mechanical properties of the shell were tested. The results show that there exists the segregation phenomenon between the Si C particulate and the liquid phase during thixoforming, the liquid phase flows from the shell, and the Si C particles accumulate at the bottom of the shell. The volume fraction of Si C decreases gradually from the bottom to the walls. Accordingly, the thermal conductivities of bottom center and walls are 178 and 164 W·m-1·K-1, the coefficients of thermal expansion(CTE) are 8.2×10-6 and 12.6×10-6 K-1, respectively. The flexural strength decreases slightly from 437 to 347 MPa. The microstructures and properties of the shell show gradient distribution.

A supersaturated Cu-Ag nanoalloy joint with ultrahigh shear strength and ultrafine nanoprecipitates for power electronic packaging

Ag-Cu bimetallic nanoalloy,integrating the advantages of reducing migration and cost of nano-Ag and alleviating oxidation of nano-Cu,is a prospective bonding material for power electronic packaging.The Ag-coated Cu nanoparticles(Cu@Ag NPs)paste can execute bonding with high quality at 250℃,and the achieved supersaturated Ag-Cu nanoalloy joint with ultrahigh shear strength(152 MPa)dramatically exceeds most nano-paste joints.The interstitial solid solutions with atomic-level metallurgical bonds at the interface dominantly promoted the shear strength.Besides,the numerous ultrafine nanograin,high proportion of low angle grain boundaries(7.44%)without deformation,and the Cu nanoprecipitates in the joint would improve subordinately.Furthermore,the high content(16.8%)of∑3 twin boundaries would contribute to the electrical and thermal conductivity.Thus,the multiple strengthening mechanisms with the solid solution,the second precipitated phase,and ultrafine nanograin can dramatically enhance shear strength and electro-thermal conductivity of joints for high-temperature device packaging.

Advanced hermetic electronic packaging based on lightweight silicon/aluminum composite produced by powder metallurgy technique

Silicon/aluminum(Si/Al)composite is a kind of lightweight electronic packaging material that received a lot of attention in the past 20 years.In this paper,a series of Si/Al composites with lowered coefficient of thermal expansion(CTE)and high thermal conductivity were produced by powder metallurgy(PM).The Si/Al composites are fully dense and have fine Si particles uniquely distributed within pure Al matrix.Three 50%Si/Al composites were designed to have strength in the range of 185-290 MPa to meet different demands,while the other properties keep invariable.Fracture toughness of the composites is measured to be 9-10 MPa·m^(1/2).The composites were machined to 50%Si/Al housings and 27%Si/Al lids.Both the hermeticities of housings before and after laser-beam-welding sealing are determined.The measured leak rate of composites and sealed housings is in magnitude order of 1×10^(-10)and 1×10^(-9)Pa·m^(3)·s^(-1),respectively,suggesting high hermeticity.The good hermeticity is attributed to the full dense materials,good weldability,and extremely low weld porosity.The present Si/Al composites are expected to be extensively used in highly hermetic electronic packages.

STUDY OF THERMAL DEFORMATION OF MICROELECTRONICS PACKAGING PRODUCT BY INTERFEROMETRIC TECHNIQUE

In this paper, the out-of-plane deformation of silicon surface of Direct Chip Attachment (DCA) assembly, under thermal loading, was measured in real-time by Twyman/Green interferometry. The contour maps of the out-of-plane displacement fields of silicon surface under thermal loading and cycling of various temperature were obtained, Experimental results show that the relation between the out-of-plane displacement and temperature is nonlinear and varies with temperature cycling, due to nonlinear mechanical behavior of the materials used in electronic packaging. A comparison of the aut-of-plane displacement Gelds of silicon surface measured by T/G interferometry in real-time and replicating technique of high temperature specimen grating of moire interferometry was made.

Heat transfer in high density electronics packaging

In order to get an insight into the thermal characteristic and to evaluate the thermal reliability of the "System in Packaging"(SIP), a new solution of electronics packaging, a heat transfer model of SIP was developed to predict the heat dissipation capacity and to investigate the effect of different factors on the tempe rature distribution in the electronics. The affecting parameters under consideration include the thermophysical properties of the substrates, the coefficient of convection heat transfer, the thickness of the chip, and the density of power dissipation. ALGOR, a kind of finite element analysis software,was used to do the model simulation. Based on the simulation and analysis of the heat conduction and convection resistance, criteria for the thermal design were established and possible measurement for enhancing power dissipation was provided. The results show that the heat transfer model provides a new and effective way to the thermal design and thermal analysis of SIP and to the mechanical analysis for the further investigation of SIP.

Reliability aspects of electronics packaging technology using anisotropic conductive adhesives

Anisotropic conductive adhesive technology for electronics packaging and interconnect application has significantly been developed during the last few years. It is time to make a summary of what has been done in this field. The present paper reviews the technology development, especially from the reliability point of view. It is pointed out that anisotropic conductive adhesives are now widely used in many applications and the reliability data and models have been developed to a large extent for anisotropic conductive adhesives in various applications.

Effects of diamond particle size on microstructure and properties of diamond/Al-12Si composites prepared by vacuum-assisted pressure infiltration

Diamond/aluminium composites have attracted attention in the field of thermal management of electronic packaging for their excellent properties.In order to solve the interfacial problem between diamond and aluminium,a novel process combining pressure infiltration with vacuum-assisted technology was proposed to prepare diamond/aluminum composites.The effect of diamond particle size on the microstructure and properties of the diamond/Al-12Si composites was investigated.The results show that the diamond/Al-12Si composites exhibit high relative density and a uniform microstructure.Both thermal conductivity and coefficient of thermal expansion increase with increasing particle size,while the bending strength exhibits the opposite trend.When the average diamond particle size increases from 45μm to 425μm,the thermal conductivity of the composites increases from 455 W·m^(-1)·K^(-1)to 713 W·m^(-1)·K^(-1)and the coefficient of thermal expansion increases from 4.97×10^(-6)K^(-1)to 6.72×10^(-6)K^(-1),while the bending strength decreases from 353 MPa to 246 MPa.This research demonstrates that high-quality composites can be prepared by the vacuum-assisted pressure infiltration process and the thermal conductivity of the composites can be effectively improved by increasing the diamond particle size.

Preparation,crystallization,and wetting of ZnO-Al_2O_3-B_2O_3-SiO_2 glass-ceramics for sealing to Kovar

A novel type of ZnO-Al2O3-B2O3-SiO2 glass-ceramics sealing to Kovar in electronic packaging was developed, whose thermal expansion coefficient and electrical resistance are 5.2× 10^-6/℃ and over 1×10^13 Ω·cm, respectively. The major crystalline phases in the glass-ceramic seals were ZnAl2O4, ZnB2O4, and NaSiAl2O4. The dielectric resistance of the glass-ceramic could be remarkably enhanced through the control of alkali metal ions into crystal lattices. It was found that crystallization happened first on the surface of the sample, leaving the amorphous phase in the inner, which made the glass suitable for sealing. The glass-ceramic showed better wetting on the Kovar surface, and sealing atmosphere and temperature had great effect on the wetting angle. Strong interracial bonding was obtained, which was mainly attributed to the interracial reaction between SiO2 and FeO or Fe3O4.