Temperature Cycling Reliability Research Articles

Solder joint reliability performance study and shear characterization of low-Ag SAC lead-free solders for handheld application

As handheld electronic products move toward smaller and thinner form factor, the demand of high reliability under stringent field usage also increasing. Drop test, based on the JEDEC JESD22-B111A, accompanied with temperature cycling (TC) test, based on JEDEC JESD22-A104F, are two of the most critical board-level reliability tests for handheld makers. In terms of solder joint reliability (SJR), total 7 candidates of LF35-liked lead-free solder alloys are investigated for its drop performance, and TC reliability evaluation. Among 7 solders, leg 4 and 5 exhibit both decent drop and TC behavior, which are likely owing to the silver (Ag) precipitation hardening and bismuth (Bi) solid solution hardening effect respectively. In addition, the shearing mechanical characterization of 7 solder alloys are being studied. Shear strength of leg 4 and 5 shows higher strength value than others. In terms of failure analysis under drop test, three main fracture modes are observed, including via cracking at PCB side, solder/intermetallic compound (IMC) cracking at package side, and Cu trace broken at package side. Furthermore, in terms of failure modes of TC test, solder/IMC cracking at package side are the main fracture modes. In summary, this study provides an overall reliability performance mapping for 7 solders, and list out a table comprising of shear strength, void% analysis, TC reliability, and drop reliability performance for each LF35 solders which lays out potential future solder alloy to meet higher handheld phone drop reliability margin.

Recent advances in energy storage and applications of form‐stable phase change materials with recyclable skeleton

AbstractWith the expansion of the global population, the energy shortage is becoming increasingly acute. Phase change materials (PCMs) are considered green and efficient mediums for thermal energy storage, but the leakage problem caused by volume instability during phase change limits their application. Encapsulating PCMs with supporting materials can effectively avoid leakage, but most supporting materials are expensive and consume huge of natural resources. Carbon materials, which are rich and renewable resources, can be used as economical and environmentally friendly supporting skeletons to prepare form‐stable PCMs. Although many researchers have begun to use recyclable materials especially various derivatives of carbon as supporting skeletons to prepare form‐stable PCMs, the preparation methods, thermophysical properties and applications of form‐stable PCMs with recyclable skeletons have rarely been systematically summarized yet. Form‐stable PCMs with a recyclable skeleton can be used as green and efficient thermal storage materials due to their high heat storage capacity and good thermophysical stability after 2000 thermal cycles. This review investigates the effects of recyclable skeletons on the thermophysical properties including phase change temperature, latent heat, thermal conductivity, supercooling, and thermal cycling reliability. Four major kinds of recyclable skeletons are focused on: biomass, biochar, industrial by‐products as well as waste incineration ash. Additionally, the application scales of form‐stable PCMs with recyclable skeletons are explicated in depth. Moreover, the main challenges confronted by form‐stable PCMs with recyclable skeletons are discussed, and future research trends are proposed. This article provides a systematic review of the form‐stable PCMs with recyclable skeletons, giving significant guidance for further reducing carbon emissions and promoting the development of sustainable energy.

Energy storage properties and stability in Nd3+/Ta5+ modified 0.6Na0.5Bi0.5TiO3-0.4Sr0.7Bi0.2TiO3 lead-free relaxor ferroelectric ceramics under a low electric field

Due to the prevalence of wearable electronic devices, Lead-free dielectric ceramics with excellent recoverable energy storage density and efficiency at low electric fields are well worth investigating. Moreover, maintaining excellent energy storage performance (ESP) in different environments is a huge challenge for researchers. In this study, 0.6Na0·5Bi0·5TiO3-0.4Sr0·7Bi0·2TiO3 lead-free relaxor ferroelectric ceramics were modified by (Sr0.7Nd0.2) (Ta0·4Ti0.5)O3 (BNST-xSNTT x = 0, 0.02, 0.04, 0.06). On one hand, BNT has a very high polarization strength, making it a very suitable basic element for designing high energy storage dielectric materials. On the other hand, Sr0·7Bi0·2TiO3 and (Sr0.7Nd0.2) (Ta0·4Ti0.5)O3 were introduced to improve the performance of ceramics, such as inducing polar nanoregions (PNRs), refining grain size, and increasing impedance. The results demonstrate that the energy storage characteristics of BNST-xSNTT were enhanced by introducing SNTT to the BNST. The ceramics exhibited a significant grain size reduction from 0.946 μm (x = 0) to 0.346 μm (x = 0.06). In addition, a great polarization difference (ΔP = 44.29 μC/cm2) was simultaneously achieved in the x = 0.02 sample. As a result, BNST-2SNTT (x = 0.02) ceramic obtained an excellent recoverable energy density of 3.24 J/cm3 and a satisfactory efficiency of 81.4 % at a low electric field of 190 kV/cm. Furthermore, the BNST-2SNTT ceramic exhibits excellent temperature stability (20°C–140 °C), frequency stability (1 Hz–500 Hz), and cycling reliability (10°-106 cycles). The corresponding fluctuation of ESP is less than 5 %. These properties indicate that the BNST-2SNTT ceramic is an excellent dielectric material for energy storage.

CU Wirebond Technology in 16FFC High Performance Automotive Radar Processor with IR Drop Reduction Methodology

High performance automotive radar front-end processors normally use advanced semiconductor packaging such as Flip Chip, fan-in and fan-out wafer level Ball Grid Array (BGA) packages in order to provide superior performance in their applications. However, for a cost effective package in the competitive business market, wirebonded package can also provide similar uncompromised performance. Advanced Cu wirebond technology was evaluated on the 16FFc radar processor. However, the challenge of high voltage drop, also known as IR drop, in 16FFc technology has to be overcome. As wafer technology moves to smaller advanced nodes, the back-end-of-line (BEOL) metal thickness gets thinner, thus increasing the resistance per unit length. Another trend in semiconductor design has been a reduction in operating voltage, meaning that small changes in supply voltage may represent an increasing percentage of the digital swing and potentially lead to incorrect logic values. As current flows through a resistor, the high voltage drop could slow down the circuitry, impact the circuit timing and lead to functional failure. In order to reduce the IR drop in the radar processor when using Cu wirebond, a large quantity of intra-die wires was applied on the 16FFc silicon. IR drop simulation was performed on 3 layout conditions, 0%, 50% and 100% of the intra-die wires. Empirical data was also collected with actual Cu wirebonded samples. The fully populated intra-die wires reduced IR drop by 30%. To enable the reliable performance of the intra-die wires, Stand-off Stitch Bond (SSB) wirebond technology was introduced within the package. The development and reliability evaluation was conducted for Cu wirebonding on 16FFc automotive radar processor of 30mm2 die size in a 14mm x14mm 2-layer substrate BGA package. Wirebond recipe was developed based on detailed Design of Experiment to establish bonding parameters for both standard wires and the intra-die wires. Packages were tested per AEC Grade 1 and AEC Q006 qualifications requirements. All results from package reliability assessments passed with no abnormality. Board level temperature cycling reliability for the BGA package with the four depopulated corner solder balls was evaluated with results surpassing NXP requirement for AEC Grade 1. This paper will present the results and analysis from (1) IR drop simulation and empirical data collection, (2) wirebond development and reliability of standard and intra-die wires on 16FFc Silicon, and (3) board level reliability of a BGA package with four depopulated corner solder balls.

Temperature Cycle Reliability Analysis of an FBAR Filter-Bonded Ceramic Package.

On the background that the operating frequency of electronic devices tends to the radio frequency (RF) segment, a film bulk acoustic resonator (FBAR) filter is widely used in communication and military fields because of its advantages of high upper frequency, ample power capacity, small size, and low cost. However, the complex and harsh working environment puts higher requirements for packaging FBAR filters. Based on the Anand constitutive equation, the stress-strain response of the bonded ceramic package was studied by the finite element method for the FBAR filter-bonded ceramic package, and the thermal fatigue life of the device was predicted. We developed solder models with various spillage morphologies based on the random generation technique to examine the impact of spillage on device temperature reliability. The following are the primary conclusions: (1) Solder undergoes periodic deformation, stress, and strain changes throughout the cycle. (2) The corner of the contact surface between the chip and the solder layer has the largest stress at the end of the cycle, measuring 19.377 MPa. (3) The Engelmaier model predicts that the gadget will have a thermal fatigue life of 1928.67 h. (4) Expanding the layered solder area caused by any solder overflow mode may shorten the device's thermal fatigue life. The thermal fatigue life of a completely spilled solder is higher than that of a partially spilled solder.

Study on the Solder Joint Reliability of New Diamond Chip Resistors for Power Devices

New diamond chip resistors have been used in high-power devices widely due to excellent heat dissipation and high-frequency performance. However, systematic research about their solder joint reliability is rare. In this paper, a related study was conducted by combining methods between numerical analysis and laboratory reliability tests. In detail, the shape simulation and thermal cycling finite element simulation for solder joints with different volumes were carried out. The optimized solder volume was 0.05 mm3, and the maximum thermal cycling stress under the optimized shape was 38.9 MPa. In addition, the thermal cycling tests with current and high temperature storage tests were carried out for the optimized solder joint, which showed good agreement with the simulation results, clarified the growth and evolution law of intermetallic compound at the interconnection interface, and proved the optimized solder joint had great anti-electromigration, temperature cycling and high temperature storage reliability. In this work, an optimized solder joint structure of a diamond chip resistor with high reliability was finally obtained, as well as providing considerable reliability data for the new type of diamond chip resistors, which would boost the development of power devices.

SrTiO3‐modified Bi0.5Na0.47Li0.03Ti0.99Sn0.01O3 relaxor ferroelectric ceramics with high energy storage performance

Abstract(1 − x)Bi0.5Na0.47Li0.03Ti0.99Sn0.01O3–xSrTiO3 (BNLST–xST) lead‐free ceramics were synthesized by traditional solid phase sintering. When x = 0.4, the ceramic achieves a high energy storage density Wrec of 3.78 J/cm3 as well as a superior efficiency η of 90.3% under 360 kV/cm. The charge–discharge curves related to temperature and cycle show that the 0.6BNLST–0.4ST sample has good temperature stability (20–180°C) and cycling reliability (variation of WD < 5%). Moreover, a fast discharge rate (t0.9 = 0.219 μs) and a large discharge energy density (WD = 1.89 J/cm3) are achieved at 220 kV/cm. The results show that BNLST–xST energy storage ceramics are promising materials for devices with pulsed power capacitor.

Temperature Cycling Test on Ultrasonic Aluminum Bonds and Conductive Adhesive of Copper Indium Gallium (di)Selenide (CIGS) Thin-Film Photovoltaic Solar Panel

This work assesses the bondability and temperature cycling reliability of ultrasonic Al bonds on Molybdenum (Mo) and Molybdenum (di)Selenide (MoSe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ) layers of a Copper Indium Gallium (di)Selenide (CIGS) thin-film photovoltaic (TFPV) solar panel. The bondability and reliability of ultrasonic Al bonds were assessed using a qualitative load–displacement profile and quantitative peel force data obtained from a peel test, as well as contact resistance <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">R_c</i> measured using the transmission line method. It was discovered that using the peel test to examine the bondability and reliability of ultrasonic Al bonds and conductive adhesives was quite beneficial. Varied forms of ultrasonic Al bonds and conductive adhesives, either on Mo or MoSe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> layers, have different shapes of load–displacement profiles before and after the application of temperature cycling. Therefore, comparing the load–displacement profile, peel force, and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">R_c</i> could offer a complete bonding mechanism, failure modes, and failure mechanism for ultrasonic Al bond on MoSe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> and Mo layers of CIGS TFPV solar panels before and after temperature cycling.

Energy storage performance and phase transition under high electric field in Na/Ta co-doped AgNbO3 ceramics

Lead-free antiferroelectric ceramics with high energy storage performance show great potential in pulsed power capacitors. However, poor breakdown strength and antiferroelectric stability are the two main drawbacks that limit the energy storage performance of antiferroelectric ceramics. Herein, high-quality (Ag1-xNax)(Nb1-xTax)O3 ceramics were prepared by the tape casting process. The breakdown strength was greatly improved as a result of the high density and fine grains, while the antiferroelectric stability was enhanced owning to the M2 phase. Benefiting from the synergistic improvement in breakdown strength and antiferroelectric stability, (Ag0.80Na0.20)(Nb0.80Ta0.20)O3 ceramic reveals a benign energy storage performance of Wrec = 5.8 J/cm3 and η = 61.7% with good temperature stability, frequency stability and cycling reliability. It is also found that the high applied electric field can promote the M2-M3 phase transition, which may provide ideas to improve the thermal stability of the energy storage performance in AgNbO3-based ceramics.

Excellent Energy Storage Properties Achieved in Sodium Niobate-Based Relaxor Ceramics through Doping Tantalum.

Lead-free relaxor ferroelectric ceramics are potential for energy storage applications due to their comprehensive energy storage properties. However, the energy efficiency of many relaxor ceramics is not high enough, leading to high Joule heat during the charge-discharge cycles, thus lowering their energy storage performance. In this work, tantalum (Ta) dopants were introduced into sodium niobate-based relaxor ceramics to improve the resistivity and energy efficiency. The leakage current was reduced by Ta doping, especially at the high electric field. The enhanced resistivity is attributed to the increased bandgap induced by Ta doping. The impedance spectroscopy shows that both the grain and grain boundary resistivities are improved in the high temperature region. As a result, the optimal recoverable energy density and energy efficiency are 6.5 J/cm3 and 94% at 450 kV/cm, respectively. In addition, the energy storage properties exhibit satisfactory temperature stability and cycling reliability. All these merits demonstrate that the Ta modified sodium niobate-based relaxor ceramic a potential candidate for high-power energy storage applications.

Encapsulation of inorganic phase change thermal storage materials and its effect on thermophysical properties: A review

Latent heat energy storage has received lots of concern on account of its high energy storage density and almost constant operating temperature. Phase change materials (PCM) possess unavoidable defects, like flammability, low thermal conductivity, subcooling, phase separation, etc. Encapsulation techniques have been adopted to address these challenges. Many efforts have been devoted to this by researchers, but the bulk of the work is based on organic PCMs, and particularly, reviews on encapsulating organic PCMs are frequent. In contrast, there are only a handful of comprehensive reviews on encapsulating inorganic PCMs, which hardly deliver complete information. Therefore, this review aims to provide a comprehensive look at the recent research advances for encapsulated inorganic PCMs. Two broadly adopted encapsulation methods are observed: core-shell encapsulated PCM and shape-stabilized PCM. Three main preparation processes for core-shell encapsulation (in situ polymerization, solvent evaporation and sol-gel methods) are described. The two former techniques are mostly adopted for the microencapsulated hydrated salt PCMs and forming organic shells. The latter is suitable for inorganic shells. The porous skeleton materials widely adopted for shape-stabilized PCMs are presented. The advantages and disadvantages of porous carbon, porous clay minerals, porous silica, and other materials were evaluated. In addition, thermophysical properties, such as supercooling, phase separation, phase change temperature, tent heat, thermal conductivity and thermal cycling reliability are discussed. It was found that encapsulation technology can have positive effects on thermophysical properties. It is hoped that this work will assist readers in gaining a comprehensive insight into the development of inorganic PCMs.

Study on temperature cycling reliability of Sn-5Sb-0.5Cu-0.1Ni-0.5Ag/Cu micro solder joints

PurposeThe purpose of this paper is to study the temperature cycling reliability of Sn-5Sb-0.5Cu-0.1Ni-0.5Ag/Cu micro solder joints compared with Sn-5Sb/Cu and SAC305/Cu micro solder joints, which has important engineering and theoretical significance for the research of micro solder joint reliability. This paper also aims to provide guidance for the selection of solder for third-generation semiconductor power device packaging.Design/methodology/approachThe shear strength, plasticity, bulk solder hardness and creep performance of three kinds of micro solder joints before and after temperature cycling were studied by nanoindentation and micro shear experiments. Scanning electron microscopy and energy dispersive spectrometry were used to analyze the fracture mode, fracture position and compound composition of the solder joints.FindingsThe bulk solder hardnesses and shear strengths of Sn-5Sb-0.5Cu-0.1Ni-0.5Ag/Cu solder joints were higher than those of Sn-5Sb/Cu and SAC305/Cu solder joints before and after temperature cycling. The indentation depth, creep displacement and creep rate of bulk solders of Sn-5Sb-0.5Cu-0.1Ni-0.5Ag/Cu solder joints were the smallest compared with those of Sn-5Sb/Cu and SAC305/Cu solder joints after the same number of cycles. In addition, the fracture mode and fracture position of the micro solder joints changed before and after temperature cycling.Originality/valueA new type of solder was developed with excellent temperature cycling performance.

Reliability Study of Miniaturized Surface Acoustic Wave RF-Filters With Copper Pillar Bump Interconnections

Microacoustic radio frequency filters are essential electronic components for all devices using wireless communication. For miniaturization and cost reduction it is necessary to further reduce the area for the electrical contacts on the chip. CPB (copper pillar bump) interconnections on radio frequency filters can release valuable chip design area of up to 26 % compared to standard SB (solder bump) interconnections on a Qualcomm TFAP (Thin Film Acoustic Package). We developed a process to deposit CPB interconnections on microacoustic radio frequency filters. A 1.20 mm $\times1.60$ mm SAW (surface acoustic wave) LTE (Long Term Evolution) band 26 duplexer with a height of 0.20 mm including the CPB interconnections was investigated. Unbiased highly accelerated stress test, damp heat steady state, dry heat, and temperature cycling reliability tests have shown that the new interconnection technology fulfills the reliability requirements of the smart device industry. Two failure modes caused by extended temperature cycling were identified via scanning acoustic microscopy and scanning electron microscopy analyses on cross sections.

A New Electrodeposition Approach for Multicomponent Solder Alloys

Enactment and enforcement of international regulations restricting the use of lead-bearing solders has triggered plenty of research on Pb-free alloys for Integrated Circuits (ICs) packaging [1]. Nonetheless, Sn-Pb (63/37) eutectic still possesses unique features (e.g. low melting point, optimum mechanical properties, ideal surface tension allowing for holes and gaps wetting, capability of reducing, inhibiting or eliminating tin whiskers formation, etc.) hardly matched by lead-free solders.Alloys belonging to the SAC (Sn-Ag-Cu) category constitute the most widespread alternative to tin-lead solder because of their relatively low melting point [2], “composition-tunable” wettability [3], and high tensile strength (compared to the Sn-Pb eutectic). Particularly, SAC-305 (Sn = 96.5, Ag = 3, and Cu = 0.5 wt%) and SAC-405 (Sn = 95.5, Ag = 4, and Cu = 0.5 wt%) are by far the most employed solders compatible with the PTH (Plating Through Hole) layers connection method, the SMT (Surface Mounted Technology) components placement approach, and the surface finishes routinely used in PCBs manufacturing (e.g. organic solder preservative, lead-free hot air solder levelling, immersion silver, immersion tin, electroless nickel immersion gold, etc.). Furthermore, near eutectic SAC alloys (i.e. comprising 3-4 wt% of silver and 0.5-1 wt% of copper) also benefit from improved temperature cycling reliability mainly due to the high Ag content.The present work puts forward a new multi-layer electrodeposition technique amenable to wafer level chip scale package. By taking advantage of multiple Dynamic Liquid Drop/Meniscus (DLD/DLM), it is possible to plate binary, ternary and even quaternary solders at high-throughput, high precision and low cost [4]. The DLD/DLM exposes a constantly refreshed confined electrolyte volume in contact with the substrate surface [5]. The core of the method consists in interposing a rinse DLD/DLM into a sequential array of multiple independent electroplating DLD/DLMs (one for each component to deposited). Such a configuration results in a synergistic system composed of different plating outputs (plating head). Thereby, scanning the plating head over the wafer surface allows to coat the substrate with a thin layer of each component. Thus, each plating head pass leads to the deposition of a multilayered structure reflecting the targeted composition of the alloy. In other words, the current density is regulated in each DLD/DLM in order to obtain the desired wt% of every single component in the final solder deposit. Obviously, the total film thickness depends on the number of layers and can be varied in a wide range to allow an homogenous structures even without reflow.As a proof-of-concept, SAC-305 and SAC-405 bumps and caps on top of copper pillars [6] were deposited: 30 μm thick structures were electroplated through more than 350 layers of each element. Bumps as high as 10 µm (attained for net electroplating times as low as 14 seconds) were sectioned by FIB (Focused Ion Beam) to verify the agreement between the expected composition and the actual one. EDX analysis performed before and after reflow proved that the high number of layers produces a compositionally homogenous solder regardless of the metal deposition sequence and reflow temperature. A detailed investigation of SAC and quaternary SAC+Me (e.g. Ni, Zn) alloys composition will be presented (e.g. thermal, mechanical and wetting properties); EDX analysis before and after reflow proving that the high number of layers homogenous solder is obtained independently of metal deposition sequence and even without reflow. Furthermore, the nozzle sizes of the multiple DLD/DLM equipment will be correlated to the aspect ratio of the dry film opening.[1] A. Lancaster and M. Keswani, Integration, 75, 77 (2017).[2] A. B. Frazier, R. O. Warrington and C. Friedrich, IEEE Transactions on Industrial Electronics, 42(5), 423 (1995).[3] X. Xu, A. S. Gurav, P. M. Lessner and C. A. Randall, IEEE Transactions on Industrial Electronics, 58(7), 2636 (2011).[4] K. Kholostov, L. Serenelli, M. Izzi, M. Tucci, D. Bernardi, M.Balucani, IEEE Journal of Photovoltaics 5(2), 404 (2016).[5] M. Balucani, K. Kholostov, P. Nenzi, R. Crescenzi, D. Ciarniello, D. Bernardi, L. Serenelli, M. Izzi, M. Tucci,Energy Procedia, 43, 54 (2013).[6] K. Kholostov, A. Klyshko, D. Ciarniello, P. Nenzi, R. Pagliucci, R. Crescenzi, D. Bernardi and M. Balucani, 43, 2014 IEEE 64th Electronic Components and Technology Conference.

Study on Low Warpage and High Reliability for Large Package Using TSV-Free Interposer Technology Through SMART Codesign Modeling

Through-silicon via (TSV)-free interposer (TFI) technology eliminates TSV fabrication and reduces manufacturing and material cost. In this paper, structure–material–assembly–reliability–thermal (SMART) codesign modeling methodology is established for a package using TFI technology by considering wafer process, package assembly and package/board-level temperature cycling reliability, and thermal performance to optimize structure design, assembly process, and material selection. Experimental results are used to validate wafer warpage modeling results first. Through wafer-level modeling, suitable carrier and molding compound materials are recommended to control wafer warpage less than 2 mm for 12-in molded wafer. Effects of coefficient of thermal expansion of package substrate and stiffener on package warpage induced by assembly reflow process are simulated and analyzed. The recommended materials and geometry design based on thermal cycling reliability simulation are aligned with that from wafer and package warpage simulation results. The final test vehicle design and material selection are determined based on SMART codesign modeling results for achieving successful TFI wafer process and package assembly and long-term board-level reliability.

An efficient reliability testing method combined with thermal performance monitoring

Die attach delamination in power electronic devices is a common failure mode besides bond wire damage. This paper describes the chip and packaging level effects of a newly developed power cycling test on novel mid-power automotive MOSFETs. The introduced method was pilot tested with our new approach, using a recently developed test environment. The idea was to combine the existent guidelines of the most relevant semiconductor characterization and cycling standards while saving time and resources during testing. Thermal transient measurements during the actively mimicked temperature cycling reliability test were evaluated along with K-factor calibration to identify different failure modes. This approach allows distinguishing between electrical and thermal related structural failure modes. The major target was to test the reliability of a new thermal interface material which was used in the MOSFETs under test. We found that the new material was able to withstand the 150°C temperature amplitude beyond 100,000cycles without critical failures. The changes of the thermal performance of the complete assembly were tracked from the pre-stress state until a sample reached critical condition.

Material Characterization and Low Cycle Fatigue Model of Low Ag Content Lead-Free Solder

In this paper, a method of design-for-reliability for the advanced electronic package under temperature cycling (TC) condition is demonstrated, including material characterization, reliability test, finite element analysis (FEA), and fatigue life model development. Tensile tests are conducted for Sn–1.0Ag–0.5Cu–0.02Ni (SAC105Ni0.02) solder alloy at four stain rates of $10^{{-5}}$ , $10^{{-4}}$ , $10^{{-3}}$ , and $10^{{-2}}$ and four test temperatures of − 35°C, 25 °C, 75 °C, and 125 °C to develop temperature- and strain rate-dependent material models. Tensile creep tests are carried out at various temperatures and stress levels to study creep behavior. TC reliability test is conducted for ball grid array package with SAC105Ni0.02 solder joints. Thermal fatigue lives are obtained from TC test with different failure rates. FEA simulation is carried out for each package using the developed mechanical properties and creep model of the solder. Fatigue life models with different failure rates are proposed for the SAC105Ni0.02 solder by combining simulation results and experimental data. Fatigue resistance of the SAC105Ni0.02 solder is comparable with that of high Ag content SAC solders.

Design Optimization and Characterization of Silicon Microcooler System Through Finite-Element Modeling and Experimental Analyses

As chip power densities are now increasing beyond air cooling limits, a variety of liquid cooling methods are being investigated. The silicon microchannel cooling is an attractive approach due to its high heat transfer coefficient. In this paper, a thermal test chip with heating spots was mounted onto a synthetic diamond heat spreader, and then mounted onto the SMC cooler through the thermocompression bonding process. Finally, this structure was mounted onto the printed circuit board and connected with the manifold. The reliability of the cooler system was investigated through finite-element analysis (FEA) and characterization. Five types of FEA models were conducted considering process flow and application conditions, including shear test model, model of bonding the thermal chip to the heat spreader, model of the whole cooler system assembly, thermomechanical coupling analysis model considering hotspot heating, and temperature cycling reliability test model. Die attach materials were evaluated based on the shear test and modeling results. The cooler system was optimized based on the FEA results to reduce stress and warpage. The thermomechanical coupling simulation was conducted for the cooler system by considering nonuniform temperature distribution due to hotspots and cooling effect. The experimental results showed that the designed cooler system has good performance and reliability thermally and mechanically.

Non-destructive degradation study of copper wire bond for its temperature cycling reliability evaluation

Wire bonding is essential for the electrical connection of integrated circuit (IC) devices, therefore its quality and reliability is of utmost importance. During the wire bonding process, several parameters need to be well controlled in order to achieve a well bonded wire. Furthermore, the migration to copper (Cu) wire from gold (Au) due to its high cost has resulted in an even more stringent and narrow process window. Current industrial practices to evaluate wire bond quality after the assembly and packaging process are either done destructively which may result in loss of critical information, or non-destructively which are limited by resolution, cost and time. In this work, the quality of copper wire bond is being evaluated by electrical means that is non-destructive, fast and accurate. This makes it suitable for use in the production line for wire bond quality evaluation. Experimental results showed that there is a good correlation with conventional wire assessment methods. Furthermore the electrical method is sensitive enough to pick out degraded wires that conventional methods are unable to identify.

Solder Ball Robustness Comparison between SAC 387 and Polymer Solder Balls under AC and TC Reliability Test

Environment and the health concerns due to the hazardous effects of lead resulted in significant activities to find a replacement for lead-contained solders for electronics industrial. Majority of the semiconductor industrial are now replacing lead solders with Tin-Silver-Copper (SAC 387) solder balls. However, dropped balls in SAC 387 for Ball Grid Array (BGA) products due to poor solder joint strength caused by high thermal stress are a major concern in the semiconductor industries. Polymer core inside the solder ball (polymer core/Cu/Sn) is thus integrated to improve the solder ball joint strength. The function of polymer core inside the solder ball is to absorb and released the stress better as compared to the SAC 387 solder ball. Since the diffusion rate of Cu is faster than the diffusion rate of Sn, hence, this could caused the Kirkendall voids tends to form in between the Cu and Sn IMC layer. This would affect the solder ball joint strength and causing drop balls issue. By implement with an extra of Ni layer to the polymer core solder ball (core/Cu/Ni/Sn), could reduce the diffusion from Cu to Sn, thus to overcome the Kirkendall voids and to further improve the solder ball joint strength. This research work studies the performance of the solder ball shear strength of the two types of solder balls applied to MAPBGA device. In this research, both SAC 387 and polymer solder balls were went through under AC (Autoclave) and TC (Temperature Cycle) reliability test up to 144 hours and 1000 cycles, respectively. Solder ball shear strength test was conducted via Dage 4000 series bond tester. From the research work results of the two types of solder balls, the ball shear strength were decreased with an increased of aging and cycles. Overall, it can be concluded that the polymer core solder ball with an additional of Ni layer showed better performance than the polymer core without Ni layer and SAC 387 solder balls, after subjected to the AC and TC reliability test.