Reflow Profile Research Articles

Study of adhesive flip chip bonding process and failure mechanisms of ACA joints

The flip chip bonding process using anisotropic conductive adhesives (ACA) and the consequent joint reliability were studied. The substrates used were rigid FR-4 boards, which are interesting due to their low cost and wide range of applications. The problems associated with the technique are discussed in this paper from the reliability point of view. Also, some aspects concerning production are introduced.The reliability of the joints was studied by accelerated environmental tests. A temperature cycling test was performed between temperatures −40 and +125 °C. Constant humidity testing was conducted at 85 °C and RH85%. In addition, reflow aging tests were performed using a conventional Sn/Pb reflow profile. For reducing the bonding cycle time, a two-stage curing process was used, which also utilizes the reflow process.The results show that the three bonding parameters, temperature, time, and pressure, all affect joint reliability. Most detrimental, however, seems to be reflow treatment performed after bonding. Most failures occurred only very briefly during the temperature cycling at the moment the temperature changed, while the joints were still conducting at both temperature extremes. However, a different failure mechanism caused a different kind of behavior during temperature cycling. The relationship between the failure modes and the failure mechanisms was studied using a scanning electron microscopy.

Development of new no-flow underfill materials for both eutectic Sn-Pb solder and a high temperature melting lead-free solder

In recent years, no-flow underfill technology has drawn more attention due to its potential cost-savings advantages over conventional underfill technology, and as a result several no-flow underfill materials have been developed and reported. However, most of these materials are not suitable for lead-free solder, such as Sn/Ag (m.p. 225/spl deg/C), Sn/Ag/Cu (m.p. 217/spl deg/C), applications that usually have higher melting temperatures than the eutectic Sn-Pb solder (m.p. 183/spl deg/C). Due to the increasing environmental concern, the demand for friendly lead-free solders has become an apparent trend. This paper demonstrates a study on two new formulas of no-flow underfill developed for lead-free solders with a melting point around 220/spl deg/C. As compared to the G25, a no-flow underfill material developed in our research group, which uses a solid metal chelate curing catalyst to match the reflow profile of eutectic Sn-Pb solder, these novel formulas employ a liquid curing catalyst thus provides ease in preparation of the no-flow underfill materials. In this study, curing kinetics, glass transition temperature (Tg), thermal expansion coefficient (TCE), storage modulus (E') and loss modulus (E'') of these materials were studied with a differential scanning calorimetry (DSC), a thermo-mechanical analysis (TMA), and a dynamic-mechanical analysis (DMA), respectively. The pot-life in terms of viscosity of these materials was characterized with a stress rheometer. The adhesive strength of the materials on the surface of silicon chips were studied with a die-shear instrument. The influences of fluxing agents on the materials curing kinetics were studied with a DSC. The materials compatibility to the solder penetration and wetting on copper clad during solder reflow was investigated with both eutectic Sn-Pb and 95.9Sn/3.4Ag/0.7Cu solders on copper laminated FR-4 organic boards.

Double-layer no-flow underfill materials and process

The no-flow underfill has been invented and practiced in the industry for a few years. However, due to the interfering of silica fillers with solder joint formation, most no-flow underfills are not filled with silica fillers and hence have a high coefficient of thermal expansion (CTE), which is undesirable for high reliability. In a novel invention, a double-layer no-flow underfill is implemented to the flip-chip process and allows fillers to be incorporated into the no-flow underfill. The effects of bottom layer underfill thickness, bottom layer underfill viscosity, and reflow profile on the solder wetting properties are investigated in a design of experiment (DOE) using quartz chips. It is found that the thickness and viscosity of the bottom layer underfill are essential to the wetting of the solder bumps. Chip scale package (CSP) components are assembled using the double-layer no-flow underfill process. Silica fillers of different sizes and weight percentages are incorporated into the upper layer underfill. With a high viscosity bottom layer underfill, up to 40 wt% fillers can be added into the upper layer underfill and do not interfere with solder joint formation.

The Effect of Cooling Rate on the Growth of Cu-Sn Intermetallics in Annealed PBGA Solder Joints

In this study, the diffusion behavior and microstructural evolution of Cu-Sn intermetallics at eutectic Sn-Pb solder/copper substrate interface of PBGA solder joints was studied. The PBGA solder joints were formed by different profiles, which was devised to have the same “heating factor”—the integral of the measured temperature above the liquidus (183°C) with respect to dwell time in the reflow profile, but to have different conveyor speeds. Using the theory of heat transmission, it is shown that the solder joint cooling rate during solidification increases with increasing conveyor speed. As a result, the “crystallization degree” of the solder joint microstructure decreased with the increasing of cooling rate. The thickness of IMC layer increased with extension of aging time. The growth of IMC is a diffusion-controlled process, i.e., tin diffuses into copper, and the diffusion coefficient in the “disordered region” Db is much bigger than that in the “crystallization region” Dl, so the IMC growth rate of solder joint with faster cooling rate was larger. On the other hand, although Db>Dl at all temperatures, the difference increases as temperature decrease, consequently, the difference of IMC thickness growth among different cooling rate solder joints varied according to the aging temperature.

The effect of reflow process on the contact resistance and reliability of anisotropic conductive film interconnection for flip chip on flex applications

The work presented in this paper focuses on the effect of reflow process on the contact resistance and reliability of anisotropic conductive film (ACF) interconnection. The contact resistance of ACF interconnection increases after reflow process due to the decrease in contact area of the conducting particles between the mating I/O pads. However, the relationship between the contact resistance and bonding parameters of the ACF interconnection with reflow treatment follows the similar trend to that of the as-bonded (i.e. without reflow) ACF interconnection. The contact resistance increases as the peak temperature of reflow profile increases. Nearly 40% of the joints were found to be open after reflow with 260 °C peak temperature. During the reflow process, the entrapped (between the chip and substrate) adhesive matrix tries to expand much more than the tiny conductive particles because of the higher coefficient of thermal expansion, the induced thermal stress will try to lift the bump from the pad and decrease the contact area of the conductive path and eventually, leading to a complete loss of electrical contact. In addition, the environmental effect on contact resistance such as high temperature/humidity aging test was also investigated. Compared with the ACF interconnections with Ni/Au bump, higher thermal stress in the Z-direction is accumulated in the ACF interconnections with Au bump during the reflow process owing to the higher bump height, thus greater loss of contact area between the particles and I/O pads leads to an increase of contact resistance and poorer reliability after reflow.

Effect of Under Bump Metallurgy and Reflows on Shear Strength and Microstructure of Joint between Cu Substrate and Sn-36Pb-2Ag Solder Alloy

The interfacial reaction between Sn–36Pb–2Ag (numbers are all in mass% unless specified otherwise) solder balls and Ni, Ag and Ni/Ag electroplated on a Cu substrate was investigated and the joint bonding strength was measured using a ball shear tester. The intermetallic Ag3Sn was observed at the interface of the Cu/Ag/solder joint and Ni3Sn4 was found at the Cu/Ni/solder joint. In the case of Cu/Ni/Ag substrate, the layer sequence was observed to be Cu/Ni/Ni3Sn4/Ag3Sn/solder. The Ag layer was completely consumed by formation of Ag3Sn but the Ni layer remained. Environmental tests showed that the Cu/Ni/Ag substrate retained better solder joint reliability than either Ni or Ag single plated Cu substrate. Two types of reflow profiles were tested and the specimen reflowed by a higher temperature profile showed a higher solder joint strength. Solder joint strength and microstructural change were observed with several reflow cycles in considering the real board mounting conditions. There was significant evolution of solder and joint microstructures with reflow cycles and it explained well the change of solder joint strength.

Processing of fluxing underfills for flip chip-on-laminate assembly

Fluxing underfill eliminates process steps in the assembly of flip chip-on-laminate (FCOL) when compared to conventional capillary flow underfill processing. In the fluxing underfill process, the underfill is dispensed onto the board prior to die placement. During placement, the underfill flows in a "squeeze flow" process until the solder balls contact the pads on the board. The material properties, the dispense pattern and resulting shape, solder mask design pattern, placement force, placement speed, and hold time all impact the placement process and the potential for void formation. A design of experiments was used to optimize the placement process to minimize placement-induced voids. The major factor identified was board design, followed by placement acceleration. During the reflow cycle, the fluxing underfill provides the fluxing action required for good wetting and then cures by the end of the reflow cycle. With small, homogeneous circuit boards it is relatively easy to develop a reflow profile to achieve good solder wetting. However, with complex SMT assemblies involving components with significant thermal mass this is more challenging.

Correlation Between the Mechanical Strength and Curing Condition of No-Flow Flip Chip Assemblies

Flip chip is the emerging interconnect technology for the next generation of high performance electronics. To eliminate the process bottlenecks associated with flip chip assembly, a new assembly technique based around “No-flow” underfill formulations has been proposed. In this paper, we have studied the correlation between the mechanical strength and the curing condition of no-flow flip chip assemblies using six different reflow profiles. It is found that both Ni3Sn4 and Cu6Sn5 intermetallics (IMCs) are formed at the solder/substrate pad and UBM (Under Bump Metallization)/solder interfaces respectively. The thickness of both IMCs increase with the increasing heating factor. The characteristics of the mechanical strength of these IMCs have been demonstrated. A correlation between the mechanical strength and the interfacial metallurgical reaction has been discussed. Also, the fastest possible reflow profile for both the cure of the underfill and maximizing the shear strength is identified. Based on the observed relationship of the mechanical strength and underfill curing of no-flow flip chip assemblies with Qn, the reflow profile should be controlled with caution in order to optimize both the mechanical strength and time for underfill cure. Only a clearer understanding of these correlation can allow manufacturers to develop a optimal, high reliable, low cost, high throughput no-flow flip chip assembly process.

Evaluation of two novel lead‐free surface finishes

Two new electrolytically plated lead‐free surface finishes are evaluated for their wettability, bond strength, and voiding performance, and are compared with electrolytic nickel gold and an OSP. The results indicate that Ni–Sn achieve the highest wettability, one of the highest lap shear strengths, and the lowest levels of voiding. It also performs better under a long reflow profile. Under most instances, the soldering performance is comparable with, or better than, the reference OSP and Ni–Au surface finishes. Ni–PdCo–Au was found to give a poor wettability, fairly low lap shear strength, and have high levels of voiding. However, it is fairly stable, and its soldering performance is not sensitive to the reflow profile length or atmosphere, aging treatment, or flux chemistry. OSP was found to be the poorest in terms of wettability, but one of the best for lap shear strength. It also performs best under long profile, is not sensitive to reflow atmosphere, is slightly sensitive to alloy type, but is very sensitive to aging and flux chemistry.

Solder balling of lead-free solder pastes

Solder balling in Sn/Ag/Cu solder pastes was studied in this work. Three different solder pastes, several different reflow profiles and conditions, and two stencil thicknesses were used in the investigation. During the first phase, called the verification phase, the solder pastes were checked to ensure they met the minimum requirements. In the process-screening phase, the reflow profile was varied. Results show that besides flux chemistry, reflow atmosphere plays the major role in solder balling. The average number of solder balls with the best paste was one fifth of that with the worst paste. Furthermore, with all the pastes, the number of solder balls dropped close to zero when nitrogen atmosphere was used. Another finding during the reflow process screening was the influence of the stencil thickness on the solder-balling result. With a thinner stencil, two of the pastes exhibited significant solder balling. This is assumed to be caused by the different ability of fluxes to withstand oxidation during the preheating in the reflow process. In the last phase, the effect of the solder-paste particle size on solder balling was studied more closely. The flux chemistry was kept unchanged, and the solder particle size was varied between type 3 and type 4. The results show that, with type 4 paste, significantly more solder balls are formed compared to type 3 paste. It was also confirmed that, regarding the reflow profile, the ramp-up rate from 150°C to 217°C and the reflow atmosphere were the most significant factors that determine the solder-ball formation for both types of paste.

Effect of reflow profile on wetting and intermetallic formation between Sn/Ag/Cu solder components and printed circuit boards

The wetting performance and intermetallic formation of a Sn/Ag/Cu alloy on printed circuit board (PCB) surfaces and on component terminations were studied in this work. Two different PCB surface finishes, immersion gold over electroless nickel (Ni/Au) and an organic solderability preservative (OSP), were studied. Chip components with Sn/Pb coating and a gull‐wing type component with 100% Sn coating were used in these experiments. Different reflow profiles were tested, and the dependence of the wetting performance, intermetallic layer thickness and the microstructure of the solder joints on the reflow profile were investigated.It was found that reflow process conditions did not significantly influence the spreading or intermetallic formation on either of the surfaces. Neither the wetting onto the component nor the general microstructure of the solder joints varied significantly with the reflow profile. When a Sn/Pb ‐coated component was used, the content and size of Pb‐rich phases in the solder joint increased with a longer time above liquidus or a higher reflow peak temperature.

Intermetallic morphology around Ni particles in Sn‐3.5Ag solder

The influence of the thermal reflow profile on the formation and resultant morphology of the intermetallic layer that developed at the Ni particle reinforcements within an eutectic Sn‐Ag composite solder matrix was investigated. The composite solder was fabricated by mechanically dispersing 15 vol% Ni particles into eutectic Sn‐3.5Ag solder paste. Two distinct intermetallic compound (IMC) morphological microstructures were observed around the Ni reinforcements. IMC morphological microstructure apparently varied depending on the amount of heat input and differences in heating rates used in the reflow profile. A “sunflower” IMC morphology was typically noted when the total amount of heat input was small. However, with sufficient heat input, a faceted “blocky” IMC morphology was consistently achieved. Multiple‐reflow thermal profiling experiments were conducted to measure and compare the amount of heat input necessary to change the sunflower IMC morphology around Ni particle reinforcements to the blocky morphology.

Impact of JEDEC test conditions on new-generation package reliability

JEDEC Standard has been widely used in the electronic industry to qualify package performance under temperature and humidity conditions. Demands for high packaging density of low pin-count packages have driven the development of a new generation of packages to replace the quad flat packages (QFP). Package size has been reduced drastically. Package reflow temperature has been considerably higher due to the application of lead-free solder. Consequently, the JEDEC standard testing on these packages needs to be re-evaluated. In this paper, moisture diffusion analysis, heat transfer analysis, as well as an interface fracture mechanics-based thermomechanical analysis have been conducted. The impact of different reflow profiles was investigated. Due to the smaller package size and higher reflow temperature, the new packages are more sensitive to the reflow parameters such as peak temperature and cooling rate. For the reliability testing of the new-generation packages, modification of the JEDEC standards may be necessary to ensure that these packages are not subjected to more stringent criteria than their previous counterparts.

Lead-free plastic area array BGAs and polymer stud grid arrays TM package reliability

Many packaging and original equipment manufacturers (OEMs) have initiated a program of introducing lead-free electronics. Although lead usage in the packaging industry is relatively small, major efforts are ensuring to eliminate lead usage. In this context, we manufactured and qualified two “green” package solutions: lead-free low-profile fine pitch ball grid array (LFBGA) and polymer stud grid arrays (PSGA TM) area array packages. The primary source of lead in BGA is in the solder balls. Lead-free solder alloys are readily available, although there is no universal drop-in replacement identified so far for plastic BGAs. One of the most promising alloys for this purpose appears to be the eutectic Sn95.5Ag4Cu0.5, although it involves higher processing temperature. Based on a design of experiment (DOE), the best reflow profile has been determined and used. A lead-free 8×8 mm 2 LFBGA has been manufactured without other process or equipment changes, and has been qualified for JEDEC moisture level 3, with 245°C reflow simulations, and standard 1st level package reliability tests. An alternative to lead-free plastic BGA is the PSGA TM. The PSGA TM package consists of a polymer injection-molded 3D body with a location for chip mounting and polymer studs. The metallized studs, which are by nature lead-free, replace the solder balls within the BGA package. Moisture conditioning and reliability analysis was performed on 8×8 mm 2 PSGA TM. The package passed JEDEC moisture conditioning level 3 as well as standard reliability tests.

Application assessment of high throughput flip chip assembly for a high lead-eutectic solder cap interconnect system using no-flow underfill materials

Flip chip on board (FCOB) is one of the most quickly growing segments in advanced electronic packaging. In many cases, assembly processes are not capable of providing the high throughputs needed for integrated surface mount technology (SMT) processing (Tummala et al, 1997). A new high throughput process using no-flow underfill materials has been developed that has the potential to significantly increase flip chip assembly throughput. Previous research has demonstrated the feasibility and reliability of the high throughput process required for FCOB assemblies. The goal of this research was to integrate the high throughput flip chip process on commercial flip chip packages that consisted of high lead solder balls on a polyimide passivated silicon die bonded with eutectic solder bumped pads on the laminate substrate interface (Qi, 1999). This involved extensive parametric experimentation that focused on the following elements: no-flow process evaluation and implementation on the commercial packages, reflow profile parameter effects on eutectic solder wetting of high lead solder bumps, interactions between the no-flow underfill materials and the package solder interconnect and tented via features, void capture and void formation during processing, and material set compatibility and the effects on long term reliability performance.

Effect of intermetallic compounds on vibration fatigue of μBGA solder joint

This paper studies the vibration fatigue failure of /spl mu/BGA solder-joints reflowed with different temperature profiles, and aging at 120 /spl deg/C for 1, 4, 9, 16, 25, 36 days. The effect of the Ni/sub 3/Sn/sub 4/ and Cu-Sn intermetallic compound (IMC) on the fatigue lifetime is also reported. During the vibration fatigue test, in order to identify the failure of /spl mu/BGA solder joint, electrical interruption was monitored continuously through the daisy-chain network. Our results show that the fatigue lifetime of the solder joint firstly increases and then decreases with increasing heating factor (Q/sub /spl eta//), which is defined as the integral of the measured temperature over the dwell time above liquidus (183/spl deg/C) in the reflow profile. The greatest lifetime occurs when Q/sub /spl eta// is near 500s/spl deg/C. Moreover, the lifetime of the solder joint decreases almost linearly with the increasing fourth root of the aging time. The SEM/EDX inspection shows that Ni/sub 3/Sn/sub 4/ IMC and Cu/sub 6/Sn/sub 5//Cu/sub 3/Sn IMCs are formed at the interface of the solder/nickel-plated PCB pad, and the no-aging solder/component-metallization, respectively. And during long term aging, Ni/sub 3/Sn/sub 2/ and NiSn were found at the Ni/Solder interface with X-ray diffraction, except Ni/sub 3/Sn/sub 4/. For nonaged solder joint, the fatigue crack generally initiates at the interface between the Ni/sub 3/Sn/sub 4/ IMC and the bulk solder. Then it propagates mostly near the Ni/solder, and occasionally in the LMC layer or along the Ni/solder interface. After aging, the fatigue track mostly initiates and propagates in the Cu/sub 6/Sn/sub 5/ -phase/bulk-solder interface or the Cu/sub 3/Sn/Cu/sub 6/Sn/sub 5/ interface on component-metallization. Evidently, the intermetallic compounds contribute mainly to the fatigue failure of /spl mu/BGA solder joints. The thicker the IMC layer, the shorter the fatigue lifetime of solder joint. The initial formation of the IMCs at the interface during soldering ensures a good metallurgical bond between the solder and the substrate. However, a thick IMC layer influences the toughness and strength of the solder joint, which results in mechanical failure.

Yield analysis and process modeling of low cost, high throughput flip chip assembly based on no-flow underfill materials

As a concept to achieve low-cost, high-throughput flip chip on board (FCOB) assembly, a new process has been developed implementing next generation flip chip processing based no-flow fluxing underfill materials. The low-cost, high throughput flip chip process implements large area underfill printing, integrated chip placement and underfill flow and simultaneous solder interconnect reflow and underfill cure. The goals of this study are to demonstrate feasibility of no flow underfill materials and the high throughput flip chip process over a range of flip chip configurations, identify the critical process variables affecting yield, analyze the yield of the high throughput flip chip process, and determine the impact of no-flow underfill materials on key process elements. Reported in this work is the assembly of a series of test vehicles to assess process yield and process defects. The test vehicles are assembled by depositing a controlled mass of underfill material on the chip site, aligning chip to the substrate pads, and placing the chip inducing a compression type underfill flow. The assemblies are reflowed in a commercial reflow furnace in an air atmosphere to simultaneously form the solder interconnects and cure the underfill. A series of designed experiments identify the critical process variables including underfill mass, reflow profile, placement velocity, placement force, and underfill material system. Of particular interest is the fact that the no-flow underfill materials studied exhibit an affinity for unique reflow profiles to minimize process defects.

Reliability studies μBGA solder joints-effect of Ni-Sn intermetallic compound

This paper studies the bending and vibration effects on the fatigue lifetime of ball grid array (BGA) solder joints. The correlation between the fatigue lifetime of the assembly and the heating factor (Q/sub n/), defined as the integral of the measured temperature over the dwell time above liquidus (183/spl deg/C) in the reflow profile is discussed. Our result shows that the fatigue lifetime of /spl mu/BGA solder-joints firstly increases and then decreases with increasing heating factor. The optimal heating factor Q/sub n/ is found to be 300-680/spl deg/C. In this range, the assembly possesses the greatest fatigue lifetime under various mechanical periodic stress, vibration and bending tests. The cyclic bending cracks always initiate at the point of the acute angle where the solder joint joins the PCB pad, and then propagate in the site between the Ni-Sn intermetallic compound (IMC) layer and the bulk solder. Under the vibration cycling, it is found that the fatigue crack initiates at valleys in the rough surface of the interface of the Ni-Sn IMC with the bulk solder. Then it propagates mostly near the Ni-Sn IMC layer and occasionally in the IMC layer or along the IMC/nickel interface. Evidently, the Ni-Sn IMC contributes mainly to the fatigue failure of the /spl mu/BGA solder joints. The SEM and EDX inspection show that only Ni/sub 3/Sn/sub 4/ IMC forms between the tin-based solder and the nickel substrate. Moreover, no brittle AuSn/sub 4/ is formed since all the Au coated on the pad surface is dissolved into the solder joint during reflowing. The formation of the Ni/sub 3/Sn/sub 4/ IMC during soldering ensures a good metallurgical bond between the solder and the substrate. However, a thick Ni-Sn IMC influences the joint strength, which results in mechanical failure. Based on the observed relationship of the fatigue lifetime with Ni-Sn IMC thickness and Q/sub n/, the reflow profile should be controlled with caution in order to optimize the soldering performance.

Aging studies of PBGA solder joints reflowed at different conveyor speeds

In this paper, the shear cycle fatigue properties of plastic ball grid array (PBGA) assemblies' solder joints reflowed with three different profiles, and aged at 125/spl deg/C for four, nine, 16, 25, and 36 days are studied. The profiles were devised to have the same heating factor, which was defined as the integral of the measured temperature above the liquidus (183/spl deg/C) with respect to dwell time in the reflow profile, but to have different conveyor speeds. The effects of conveyor speed on the solder joint (nonaged and aged) fatigue lifetimes were investigated. It was found hat with increasing the conveyor speed the solder joint shear fatigue lifetime could be improved substantially. Also, the shear fatigue lifetimes of aged solder joints decreased with increasing aging time and variation in fatigue lifetimes increased for faster conveyor speed. SEM and optical micrographs show that faster cooling rate caused a rougher interface of solder/IMC and less crystallization microstructure in solder joints. Rougher interface solder joints have a longer nonaged fatigue life. The thickness of IMC increases with increasing aging time and the growth rate for solder with faster cooling rate was larger. SEM cross section views reveal that cracks initiated at the acute position near the solder pad, then propagated along the interface of the bulk solder/IMC layer. Thicker IMC layers deteriorated fatigue life, so the fatigue lifetime variation of aged solder joints with fast cooling rate was larger.

Numerical prediction of mechanical properties of Pb-Sn solder alloys containing antimony, bismuth and or silver ternary trace elements

Solder joint interconnects are mechanical means of structural support for bridging the various electronic components and providing electrical contacts and a thermal path for heat dissipation. The functionality of the electronic device often relies on the structural integrity of the solder. The dimensional stability of solder joints is numerically predicted based on their mechanical properties. Algorithms to model the kinetics of dissolution and subsequent growth of intermetallic from the complete knowledge of a single history of time-temperature-reflow profile, by considering equivalent isothermal time intervals, have been developed. The information for dissolution is derived during the heating cycle of reflow and for the growth process from cooling curve of reflow profile. A simple and quick analysis tool to derive tensile stress-strain maps as a function of the reflow temperature of solder and strain rate has been developed by numerical program. The tensile properties are used in modeling thermal strain, thermal fatigue and to predict the overall fatigue life of solder joints. The numerical analysis of the tensile properties as affected by their composition and rate of testing, has been compiled in this paper. A numerical model using constitutive equation has been developed to evaluate the interfacial fatigue crack growth rate. The model can assess the effect of cooling rate, which depends on the level of strain energy release rate. Increasing cooling rate from normalizing to water-quenching, enhanced the fatigue resistance to interfacial crack growth by up to 50% at low strain energy release rate. The increased cooling rates enhanced the fatigue crack growth resistance by surface roughening at the interface of solder joint. This paper highlights salient features of process modeling. Interfacial intermetallic microstructure is affected by cooling rate and thereby affects the mechanical properties.