Reflow Soldering Process Research Articles

Simulation, Optimization and Experimental Verification of the Over–Pressure Reflow Soldering Process

The advanced technologies for electronics production and convection based soldering technologies are growing steadily. The enhanced reflow soldering oven with an integrated hyper pneumatic module ensures a void-free solder connection, but it requires design and installation of the process parameters in the oven in order to ensure optimized heat transfer and derive the best energy efficiency performance. This paper presents a simulation model of the thermal soldering process in the over-pressure convection oven by finite element model. This model considers the effect of the complex boundary conditions during the soldering process. A set of experimental tasks were designed to investigate the variations in the temperature profiles at selected points on the surface of the demonstrator. Moreover, the heat transfer coefficient for each thermal profile has been calculated. The simulation model can be used to predict the temperature distribution for the solder materials together with the demonstrator board. The void content in the solder material was investigated by the X-Ray analysis and correlated with the thermal process in the simulation. Hence, the optimized relation between the process set-up parameters in the oven, simulated thermal behavior, and the voids fraction in solder material are studied in detail.

Failure and stress analysis of through-aluminum-nitride-via substrates during thermal reliability tests for high power LED applications

The objective of this study is to evaluate the reliability of through-aluminum-nitride-via (TAV) substrate by comparing those experimental results with the finite element simulation associated with measurements of aluminum nitride (AlN) strength and the thermal deformation of Cu/AlN bi-material plate. Two reliability tests for high-power LED (Light emitting diode) applications are used in this study: one is a thermal shock test from −40°C to 125°C, the other is a pressure cook test. Also, the strength of AlN material is measured by using three-point bending test and point load test. The reliability results show that TAV substrates with thicker Cu films have delamination and cracks after the thermal shock test, but there are no failure being found after the pressure cook test. The determined strengths of AlN material are 350MPa and 650MPa from three-point bending test and point load test, respectively. The measurement of thermal deformation shows that the bi-material plate has residual-stress change after the solder reflow process, also indicating that a linear finite element model with the stress-free temperature at 80°C can reasonably represent the stress state of the thermal shock test from −40°C to 125°C without considering Cu nonlinear effect. The further results of the finite element simulation associated with strength data of AlN material have successfully described those of the reliability test.

Experimental and Numerical Analysis of Melting and Solidification of SnAgCu Joints

One of the most vulnerable components of electronic circuits is the solder joints. The most common technique of soldering used in electronics is the reflow soldering. During the soldering process, different issues may occur leading to the inception of some defects (tombstone effect, flux spattering, etc.). To avoid these defects, it is mandatory to follow the parameter values of the reflow process, especially temperature values. In this paper, the temperature distribution for three types of samples (two interconnected soldering pads–without solder, with solder on one pad, and with solder on both pads) during the reflow soldering process, calculated with Comsol Multiphysics software (heat transfer 3-D module) is presented. The calculated values are then compared to the ones obtained by experiments in order to verify the accuracy of the numerical model. To carry out the computations, the latent heat of melting/solidification and the variation with the temperature of the solder parameters were considered. The results show that there is a good correlation between the measured and calculated values, the differences (for all types of samples) being lower than ±3 °C.

All-Solid-State Thin-Film Secondary Battery with Lithium-Free Anode for High-Temperature Tolerance

Introduction Recently, smart device which enables IoT (internet of things) has induced a strong demand for high density packaging and miniaturization to fulfill high performance and functionalities simultaneously, and all-solid-state thin-film secondary batteries (TFBs) are most promising to be used as small-format and stand-alone power supplies for smart device due to intrinsically safe, high reliability and long cycle life. TFB is fabricated by forming each layers (i.e. cathode, electrolyte, anode and current collector) using physical vapor deposition process1,2), and metallic lithium is currently the most used material as an anode material in TFB. However, TFB using metallic lithium anode have thermal constraint3,4). For example, the solder-reflow process needs a thermal treatment at up to 250 deg.C, and thermal specification for automotive device is up to 150 deg.C, whereas the melting point of metallic lithium is around 180 deg.C. Therefore, other anode material in place of metallic lithium is necessary to improve high-temperature tolerance of TFB. In this work, we investigated TFB with amorphous silicon (a-Si) thin-film as an anode, and its battery performance. Experimental Lithium cobalt oxide (LCO) film was prepared by RF and DC hybrid power magnetron sputtering method on platinum film as current collector. Ar was used as sputtering gas, and process pressure was kept at 1.6 Pa. Furthermore, LCO was deposited with applying each bias power to the substrate for investigating the planarization. After deposition, LCO was annealed at 600 deg.C under atmospheric pressure by lamp heating system. Solid electrolyte (LiPON) film was prepared by RF magnetron reactive sputtering method with only N2 gas5). a-Si film as an anode was prepared by sputtering method using boron-doped silicon target. Finally, fabricated cell was encapsulated, and then “lithium-free anode” TFB was completed. Results and discussion TFB cell was fabricated with 3-μm-thick LCO, 2-μm-thick LiPON and 200-nm-thick a-Si. Figure 1 shows result of cycle performance under each SOC (state of charge), which is controlled by modulating charging cut-off voltage (3.8, 4.1, 4.2 V). Actual capacity of a-Si can be estimated from result of discharge capacity, and it was found that good cycle performance was obtained when actual capacity of a-Si anode is controlled to 2300 mAh/g. It might be considered that irreversible capacity is generated by breaking a-Si anode in a few cycles due to large volume change in results of 2750 and 3000 mAh/g. Reference; J. B. Bates, N. J. Dudney, G. R. Gruzalski, R. A. Zuhr, A. Choudhury, C. F. Luck and J. D. Robertson, J. Power Sources, 43, 103 (1993). T. Jimbo, P. Kim and K. Suu, Energy Procedia, 14, 1574 (2012). B. J. Neudecker, N. J. Dudney and J. B. Bates, J. Electrochem. Soc., 147(2), 517 (2000). V. P. Phan, B. Pecquenard and F. Le Cras, Adv. Funct. Mater., 22, 2580 (2012). A. Suzuki, S. Sasaki, I. Kimura, T. Jimbo, #449, Proceeding of 227th ECS meeting. Figure 1

Lithium Titanium Sulfide Thin Film Cathodes for All-Solid-State Lithium-Ion Batteries: Taking Advantage of a Dual Cation and Anion-Based Redox Process

The significant growth of both the number and the kinds of portable electronic systems, generally battery-powered has triggered the race for the development of high-performance microprocessors and systems on chips using low power consumption integrated circuits. As a consequence, the energy supply of such optimized components can also be ensured today by miniaturized power sources such as Li microbatteries. The latter have the advantage of being manufactured by vacuum deposition process also widely used in the microelectronics industry [1]. Nevertheless to be considered as an electronic components, the microbattery need to sustain temperature higher than 230°C for the reflow soldering to attach the component to the PCB . As Li metal anode melts at 181°C, Li microbatteries are not tolerant to such high temperature. For this reason we have manufactured Li-ion all-solid-state thin films batteries based on Si at the negative electrode and a new lithiated titanium oxysulfide as a cathode [2]. Lithium titanium sulphide thin films were synthesized by sputtering of LiTiS2 targets. Three different methods including chemical lithiation, solid state synthesis or spark plasma sintering steps were used to prepare the targets in-house and were found to influence the final composition of the films [3]. Due to the high reactivity of titanium, incorporation of some oxygen into the LiTiS2 film is inevitable. The limited oxygenation of the films that occurs, favours the occurrence of the S2-/(S2)2- redox process at the expense of the Ti3+/Ti4+ one during the battery operation. Finally, a perfect reversibility of both electrochemical processes is highlighted, whatever the initial oxygen content. All-solid-state lithium microbatteries using these amorphous lithiated titanium disulphide thin films and operated between 1.5-3.0 V/Li+/Li deliver a greater capacity (210-270 mAh g-1) than LiCoO2, with a perfect capacity retention (-0.0015 % cycle-1). Excellent electrochemical performances in terms of capacity value and cycling stability were also obtained in all-solid state Li-ion cells with Si as a negative electrode. After three successive solder-reflow processes (thermal treatment at 260°C), the capacity, the cycle life as well as the voltage profile remained unchanged. Finally, Li1.2TiO0.5S2.1 is confirmed as a new interesting lithiated positive material for thin film lithium and lithium-ion microbatteries. Moreover, as its synthesis does not require any thermal treatment (contrary to the well-known LiCoO2), is well-adapted to thermally sensitive substrates such as flexible polymers foils.

Al and Si Alloying Effect on Solder Joint Reliability in Sn-0.5Cu for Automotive Electronics

To suppress the bonding strength degradation of solder joints in automotive electronics, we proposed a mid-temperature quaternary Pb-free Sn-0.5Cu solder alloy with minor Pd, Al, Si and Ge alloying elements. We manufactured powders and solder pastes of Sn-0.5Cu-(0.01,0.03)Al-0.005Si-(0.006–0.007)Ge alloys (Tm = 230°C), and vehicle electronic control units used for a flame-retardant-4 printed circuit board with an organic solderability preservative finish were assembled by a reflow soldering process. To investigate the degradation properties of solder joints used in engine compartments, thermal cycling tests were conducted from −40°C to 125°C (10 min dwell) for 1500 cycles. We also measured the shear strength of the solder joints in various components and observed the microstructural evolution of the solder joints. Based on these results, intermetallic compound (IMC) growth at the solder joints was suppressed by minor Pd, Al and Si additions to the Sn-0.5Cu alloy. After 1500 thermal cycles, IMC layers thicknesses for 100 parts per million (ppm) and 300 ppm Al alloy additions were 6.7 μm and 10 μm, compared to the as-reflowed bonding thicknesses of 6 μm and 7 μm, respectively. Furthermore, shear strength degradation rates for 100 ppm and 300 ppm Al(Si) alloy additions were at least 19.5%–26.2%. The cause of the improvement in thermal cycling reliability was analyzed using the (Al,Cu)-Sn, Si-Sn and Al-Sn phases dispersed around the Cu6Sn5 intermetallic at the solder matrix and bonding interfaces. From these results, we propose the possibility of a mid-temperature Sn-0.5Cu(Pd)-Al(Si)-Ge Pb-free solder for automotive engine compartment electronics.

The Effect of Carbon Nanotube Loading on Wettability of Solder Paste SAC 237 and Different Substrates

Wettability of Pb-free soldered surface is one of the main solderability classifications. The aim of this study is to investigate the effect of various percentages of carbon nanotube (CNT) loading (0 – 4%) on the wettability of solder paste SAC 237 and different substrates namely copper (Cu) and tin (Sn). The influence of surface roughness on the wetting behaviour was also studied. Both substrates were undergone a mechanical abrasion process by using four different grit sizes (P240 , P400, P600 and P800) before performing the reflow soldering process using a reflow oven at a temperature of 180°C for 13 minutes. The surface roughness of the substrates was characterized by using a profilometer. Meanwhile, wettability tests were performed by using the optical microscope. Both substrates have shown similar behaviour; the rougher surface gives better wettability compared to the smoother one. The wettability of SAC 237 is not significantly affected by the addition of various percentages of CNT. However, CNT loading in the solder paste has shown the different wetting behaviour for both substrates.

Thermo-mechanical challenges of reflowed lead-free solder joints in surface mount components: a review

PurposeThe purpose of the present study was to review the thermo-mechanical challenges of reflowed lead-free solder joints in surface mount components (SMCs). The topics of the review include challenges in modelling of the reflow soldering process, optimization and the future challenges in the reflow soldering process. Besides, the numerical approach of lead-free solder reliability is also discussed.Design/methodology/approachLead-free reflow soldering is one of the most significant processes in the development of surface mount technology, especially toward the miniaturization of the advanced SMCs package. The challenges lead to more complex thermal responses when the PCB assembly passes through the reflow oven. The virtual modelling tools facilitate the modelling and simulation of the lead-free reflow process, which provide more data and clear visualization on the particular process.FindingsWith the growing trend of computer power and software capability, the multidisciplinary simulation, such as the temperature and thermal stress of lead-free SMCs, under the influenced of a specific process atmosphere can be provided. A simulation modelling technique for the thermal response and flow field prediction of a reflow process is cost-effective and has greatly helped the engineer to eliminate guesswork. Besides, simulated-based optimization methods of the reflow process have gained popularity because of them being economical and have reduced time-consumption, and these provide more information compared to the experimental hardware. The advantages and disadvantages of the simulation modelling in the reflow soldering process are also briefly discussed.Practical implicationsThis literature review provides the engineers and researchers with a profound understanding of the thermo-mechanical challenges of reflowed lead-free solder joints in SMCs and the challenges of simulation modelling in the reflow process.Originality/valueThe unique challenges in solder joint reliability, and direction of future research in reflow process were identified to clarify the solutions to solve lead-free reliability issues in the electronics manufacturing industry.

Temperature prediction for system in package assembly during the reflow soldering process

A system in package (SiP) is a number of integrated circuits integrated into a single module. SiP can perform various functions and are often used in small systems such as mobile phones and wearable devices. The fabrication of SiP can be challenging due to their small size and high complexity. For example, during the reflow soldering process, non-uniform temperature distribution can occur, affecting the reliability of the SiP. In this study, numerical simulation is used to investigate the thermal behavior of a SiP during the reflow process and the model is validated via experimental measurements. A forced convection reflow oven was modeled using computational fluid dynamics software where the heating of the SiP assembly was performed using a conjugate heat transfer model. A complex flow field in the reflow oven was observed from the simulation results, showing a free jet region, a stagnation flow region, a wall jet region, a recirculation region, and vortices. The simulation results agreed well with experimental data. The method developed here can accurately predict the temperature distribution in a reflow oven and allow the design of temperature profiles for the reflow process that result in minimal temperature variations across the SiP assembly.

Effects of post-reflow cooling rate and thermal aging on growth behavior of interfacial intermetallic compound between SAC305 solder and Cu substrate

The interfacial reactions between Cu and Sn3Ag0.5Cu (SAC305) solder reflowed under various cooling rates were investigated. It is found that the cooling rate is an important parameter in solder reflow process because it influences not only microstructure of solder alloy but also the morphology and growth of intermetallic compounds (IMCs) formed between solder and Cu substrate. The experimental results indicate that only scallop-like Cu6Sn5 IMC layer is observed between solder and Cu substrate in case of water cooling and air cooling, while bilayer composed of scallop-like Cu6Sn5 and thin layer-like Cu3Sn is detected under furnace cooling due to sufficient reaction time to form Cu3Sn between Cu6Sn5 IMC and Cu substrate which resulted from slow cooling rate. Samples with different reflow cooling rates were further thermal-aged at 423 K. And it is found that the thickness of IMC increases linearly with square root of aging time. The growth constants of interfacial IMC layer during aging were obtained and compared for different cooling rates, indicating that the IMC layer thickness increased faster in samples under low cooling rate than in the high cooling rate under the same aging condition. The long prismatic grains were formed on the existing interfacial Cu6Sn5 grains to extrude deeply into solder matrix with lower cooling rate and long-term aging, and the Cu6Sn5 grains coarsened linearly with cubic root of aging time.

A High Performance Power Module with >10kV capability to Characterize and Test In Situ SiC Devices at >200°C Ambient

Abstract This paper presents design, fabrication and characterization details of a 10kV power module package for >200°C ambient temperature applications. Electrical simulations were performed to confirm the module design, and that the electric field distribution throughout the module did not exceed dielectric capabilities of components and materials. A suitable copper etching process was demonstrated for DBC layout, and a high melting point Sn/Pb/Ag solder reflow process was developed for device and component attachment. To monitor the operational temperature of the module, a thermistor was integrated onto the substrate. A new silicone gel, having a working temperature up to 210°C, was evaluated and selected for encapsulation and, of great importance, for passivation of high voltage (10kV) SiC dies. An additive manufacturing ‘Design Process’ was developed and applied to printing the housings, molds, and test fixtures. Also, cleaning processes were evaluated for every step in the fabrication process. To verify performance of the modules, mechanical dies were mounted on the substrates, and a high temperature testing setup built to characterize the modules at high temperature. Measurements indicated that the module can operate up to 12kV within 25°C to 225°C, with less than 0.1 μA leakage current. The packaging was used for full-power characterization of developmental 10kV SiC diodes, and proved that the power module packaging satisfied all requirements for high voltage and high temperature applications. This work successfully validated the processes for creating high voltage (>10 kV) and high temperature (>200°C) power modules.

Solder-reflow resistant solid-state micro-supercapacitors based on ionogels

All-solid-state micro-supercapacitors with silicon nanowire electrodes and ionogel thin film electrolyte showed improved frequency response and a sustained solder reflow process.

Microstructure and mechanical properties of Pb-free Sn–3.0Ag–0.5Cu solder pastes added with NiO nanoparticles after reflow soldering process

Incorporating various types of ceramic type nanoparticles into Pb-free solder pastes produces unique nanocomposite solder pastes. In this study, Sn–Ag–Cu (SAC) 305 solder alloys were mixed with 0.5, 1.5, and 2.5wt.% NiO ceramic nano-elements to produce a new set of nanocomposite solder pastes. The displacement phenomenon of NiO nanoparticles during reflow soldering process may contribute efficient idea in the field of microelectronic industries. The reinforcement of reactive nanoparticles in SAC 305 solder paste caused 50% changes in the intermetallic layer thickness and hardness of plain solder. Top-view microstructural analysis wherein dimple surfaces were magnified showed that the combination of SAC 305–2.5wt.% NiO nanopaste exceeded the limits of alloy addition.

RF and Microwave Power Amplifiers assembly – Interaction between materials, design and process on reliability

The demand for data anywhere and at anytime (mobile internet) is putting increasing pressure on network operators in their deployment of wireless communication infrastructure. This has pushed upwards across the supply chain, from suppliers to customers. At the core of the infrastucture are RF power amplifiers (PA) with very costly design, hence important to get it right first time. Thermo-mechanical compliance are key attributes to consistent product performance and reliability amidst stringent mission profiles. Most transistor component manufacturers focus on their core competence – component design. Network operators on the other hand focus on the PA design. In most cases, the assembly of the PA module is an after-thought and a key enabler. These transistors are usually high power devices (> 100 watts), hence demanding excellent thermal management. The packages used have a metal flange in addition to RF/DC leads which are soldered in the PA module. These act as a heat spreader and electrical interconnect which affects the product performance. Since these interconnects are in different planes, assembly requires heatsinks with cavities (flange soldering). The main challenge being tackled in this study is the response of the materials being soldered in a different plane – leads to board and flange to heatsink interface. This is why proper soldering of the transitors (flange & leads) is an essential part in PA assembly due to the impact on module performance & reliability. To achieve the desired thermal and reliability requirements, a variety of factors are critical including the cavity design, solder and reflow soldering process. In this paper, these factors are evaluated via both thermo-mechanical simulations and experimental work. Since there are lots of materials with different properties involved in the assembly, it is vital to evaluate its behavior prior to the actual process evaluation as it has impact on cost and timing effectiveness of the study. These simulations are used as initial indication for trends which are later validated by experimental evaluations. The thermal impedance (Rth) in combination to acoustic microscopy / x-rays is used to assess the soldered flange during assembly & reliability.

Mechanical design and analysis of direct-plated-copper aluminum nitride substrates for enhancing thermal reliability

Direct-plated-copper (DPC) aluminum nitride (AlN) substrate with a high thermal conductivity can provide a good alternative to conventional aluminum oxide (Al2O3) substrate for better heat dissipation in the high-power module applications. However, the DPC AlN substrate suffers AlN crack initiating at the edge corner of Cu film during thermal cycling, due to the higher thermal expansion coefficient mismatch with copper material. This study is to resolve the AlN crack problem of DPC AlN substrate during thermal cycling and further to provide important parameters for mechanical design for ensuring good thermal reliability. Prior to the analysis, the out-of-plane deformation measurement of a Cu-AlN bi-material plate subject to the solder reflow heating and cooling is conducted for evaluating the material property of the plated Cu film and residual stresses induced from the manufacturing and solder reflow process. The results show the hysteresis and Bauschinger-like behaviors for the Cu-AlN plate during the solder-reflow heating and cooling. It is also found from the validated finite element simulation that the Cu-film wedge angle, length, and thickness significantly affect the maximum 1st principal stress of AlN during thermal cyclic loading, and the predicted failure mode and location based on the maximum 1st principal stress is consistent with experimental observation. The other factors, such as single-side and double-side Cu-film (sandwich-structure-alike) substrates, length difference of Cu films, and the nonlinear property of Cu film will be presented and discussed in detail as well.

Realistic warpage evaluation of printed board assembly during reflow process

Purpose – This paper aims to develop an estimation tool for warpage behavior of slim printed circuit board (PCB) array while soldering with electronic components by using finite element method. One of the essential requirements for handheld devices, such as smart phone, digital camera, and Note-PC, is the slim design to satisfy the customers’ desires. Accordingly, the printed circuit board (PCB) should be also thinner for a slim appearance, which would result in decreasing the PCB’s bending stiffness. This means that PCB deforms severely during the reflow (soldering) process where the peak temperature goes up to 250°C. Therefore, it is important to estimate PCB deformation at a high temperature for thermo-mechanical quality/reliability after reflow process. Design/methodology/approach – A numerical simulation technique was devised and customized to accurately estimate the behavior of a thin printed board assembly (PBA) during reflow by considering all components, including PCB, microelectronic packages and solder interconnects. Findings – By applying appropriate constraints and boundary conditions, it was found that PBA’s warpage can be accurately predicted during the reflow process. The results were also validated by warpage measurement, which showed a fairly good agreement with one and another. Research limitations/implications – For research limitations, there are many assumptions regarding numerical modeling. That is, the viscoplastic material property of solder ball is ignored, the reflow profile is simplified and the accurate heat capacity is not considered. Furthermore, the residual stress within the PCB, generated at PCB manufacturing process, is not included in this paper. Practical implications – This paper shows how to calculate PBA warpage during the reflow process as accurately as possible. This methodology helps a PCB designer and surface-mount technology (SMT) process manager to predict a PBA warpage issue and modify PCB design before PCB real fabrication. Practically, this modeling and simulation process can be easily performed by using a graphical user interface (GUI) module, so that the engineer can handle an issue by inputting some numbers and clicking some buttons. Social implications – In a common sense manner, a numerical simulation method can decrease time and cost in manufacturing real samples. This PCB warpage method can also decrease product development duration and produce a new product earlier. Furthermore, PCB is a common component in all the electronic devices. So, this PCB warpage method can have various applications. Originality/value – Because of an economic advantage, the development of a numerical simulation tool for estimating the thin PBA warpage behaviour during reflow process was attempted. The developed tool contains the features of detailed modeling for electronic components and contact boundary conditions of the supporting rails in the reflow oven.

Sn–3.0Ag–0.5Cu Nanocomposite Solder Reinforced With Bi2Te3Nanoparticles

Nanocomposite solders are regarded as one of the most promising interconnect materials for the high-density electronic packaging due to their high mechanical strength and fine microstructure. However, the developments of nanocomposite solders have been limited by the inadequate compatibility between nanoparticles and solder matrix with respect to density, hardness, coefficient of thermal expansion, and surface activity. The compatibility issue will lead to a huge loss of nanoparticles from the solder matrix after the reflow soldering process. The thermal fatigue resistance of solder joint will also become degraded. Therefore, aiming to solve this problem, a novel nanocomposite solder consisting of Bi2Te3 semiconductor nanoparticles and Sn–3.0Ag–0.5Cu (SAC305) solder is presented. The effect of nanoparticles on the viscosity of solder paste and the void content of solder bump was first studied. Then, a series of analysis on the composition and microstructure of the solder bump were completed using transmission electron microscopy, X-ray diffraction, inductively coupled plasma-mass spectrometry, scanning electron microscopy, and energy dispersive X-ray spectroscopy. The survival rate of nanoparticles in the solder bump after reflow soldering process reaches as high as 80%. The refined microstructure was observed from the cross section of the nanocomposite solders. The shear test showed that the average mechanical strength of SAC305 solder after the addition of Bi2Te3 nanoparticles was higher. Meanwhile, no thermal fatigue resistance degradation was detected in the nanocomposite solder after 1000 thermal cycles in the range of −40 °C to 115 °C.

Time-domain viscoelastic constitutive model based on concurrent fitting of frequency-domain characteristics

A numerical procedure for constructing the multiaxial viscoelastic model for polymeric packaging material over a wide range of temperature is presented. By using the proposed best-fitting procedure, experimentally measured frequency-domain Young's and shear storage moduli are used to calculate the time-domain bulk and shear relaxation moduli which describe the three-dimensional constitutive behavior of a viscoelastic solid. The numerical procedure incorporates restrictions that ensure that the derived time-domain material function is physics compatible. The proposed procedure was applied to construct the viscoelastic constitutive models of epoxy molding compounds (EMCs), and compared to results obtained by using approximate-formula based direct conversion procedure. It was shown that, without using the proposed procedure, the directly calculated time-dependent Poisson's ratio oscillates significantly in the rubbery regime and is physically inadmissible. To validate the constitutive model constructed by using the proposed procedure, a numerical finite element model that incorporates the viscoelastic constitutive model of the EMC was applied to simulate warpage of an overmolded package under the solder reflow process and compared to experimental shadow Moiré measurements.

Comparison between SAC405 Lead-Free Solders and EN(P)EPIG and EN(B)EPIG Surface Finishes

In electronics industries, most of them had to shifted their solder materials from leaded solders into lead-free solders due to the environmental concerns and follow the legislation of Restriction of use Hazardous Substances (RoHS). Thus, Sn-Ag-Cu solder is one of the choices that can replace the leaded solder and also offer better properties. This study investigates the comparison between Sn-4.0Ag-0.5Cu (SAC405) and EN(P)EPIG and EN(B)EPIG surface finishes. Reliability of solder joint has been assessed by performing solid state isothermal aging at 150oC for 250 up to 2000 hours. After reflow soldering process, (Cu,Ni)6Sn5intermetallic compound (IMC) is dominated at near centre of solder meanwhile (Ni,Cu)3Sn4IMC is dominated at near outside of solder ball.Moreover, aging time resulted in an increase in thickness and changed the morphology into more spherical, dense and large grain size. Analysis by optical microscope revealed that the IMC thickness of EN(B)EPIG produced thicker IMC compared to EN(P)EPIG surface finish during reflow as well as isothermal aging.

Quantitative Evaluation of Voids in Lead Free Solder Joints

Voiding in solder joints poses a serious reliability concern for electronic products. The aim of this research was to quantify the void formation in lead-free solder joints through X-ray inspections. Experiments were designed to investigate how void formation is affected by solder bump size and shape, differences in reflow time and temperature, and differences in solder paste formulation. Four different lead-free solder paste samples were used to produce solder bumps on a number of test boards, using surface mount reflow soldering process. Using an advanced X-ray inspection system void percentages were measured for three different size and shape solder bumps. Results indicate that the voiding in solder joint is strongly influenced by solder bump size and shape, with voids found to have increased when bump size decreased. A longer soaking period during reflow stage has negatively affectedsolder voids. Voiding was also accelerated with smaller solder particles in solder paste.