Solder Joint Interconnections Research Articles

Analysis of BGA Lead-Free solder joints failure behavior based on thermal shock testing

The interconnected solder joints within automotive electronic components are the most vulnerable parts of the structure, and their reliability is crucial for the development of new energy vehicles. This study focuses on automotive ADAS (Advanced Driver Assistance System) devices, analyzing the failure behavior of internal BGA (Ball Grid Array) lead-free solder joints under thermal shock conditions.Through thermal shock testing from −40℃ to 95℃, it was observed that microcracks first appeared in the upper intermetallic compound (IMC) layer of corner solder joints after 1600 cycles. As the number of thermal shock cycles increased, the net-like β-Sn phase in the solder joints gradually transformed into block and dot-like structures. Due to the relatively weak strength between the IMC layer and the Ag-Sn compound region, cracks typically propagated along the boundaries of these areas. Recrystallization occurred in the interface between the solder joint and the upper pad, with the proportion of high-angle grain boundaries increasing from 10.74% to 72.43%. The crack propagation mode changed from initial intergranular to transgranular fracture. Throughout the thermal shock test, the upper IMC layer remained thicker than the lower one, with the lower IMC layer thickness showing a minimum point at 750 cycles.The average thrust force between the solder joints and the substrate decreased more rapidly with thermal shock cycles, indicating that non-solder mask defined pads are more effective in improving structural strength.

The design of low-temperature solder alloys and the comparison of mechanical performance of solder joints on ENIG and ENEPIG interface

In recent years, in order to adapt to the trend of low-temperature assembly and integration, low-temperature hybrid solders with multiple elements added to the tin solder matrix have been investigated. In this regard, the morphology and size of intermetallic compounds (IMCs) are altered by adding some alloying elements, and the strength of solder joints is improved to some extent. Different pad surface treatments affect the growth of IMC, which leads to various failure modes in interconnect solder joints. Therefore, it is necessary to study the interfacial reaction, microstructure and mechanical properties of hybrid solder and different metal pads to explore the growth mechanism of IMC and the failure modes of solder joints. In this paper, mixed Sn–3Ag-0.5Cu/Sn–58Bi low-temperature solder joints on Au/Ni/Cu (ENIG) and Au/Pd/Ni/Cu (ENEPIG) substrates are investigated. The results show that the addition of palladium element can change the IMC morphology, refine the grain size of the hybrid solder joints, and affect the fracture failure mode of the solder joints under shear force. The average shear strength is significantly higher than that of solder joints with ENIG surfaces under different process parameters. Thermodynamic calculations of enthalpy change and the effect of Jackson's parameter α value on IMC morphology are also investigated in this paper. The addition of palladium elements increases the α value and is more favorable to the formation of columnar grains. This provides guidance for the grain growth of IMC in hybrid solder joints with added alloying elements.

The doped Pd on the crystal calculation and intermetallic property of low-temperature soldered ENEPIG substrates

The preparation of new solder joint materials for chip packaging by designing a variety of brazing material mixes has become one of the future research directions for solder joints. They added low melting point elements to traditional solder materials to prepare low-temperature hybrid solder to meet the low-temperature packaging trend. To improve the performance of low-temperature solder, adding some alloying elements can refine the grain, change the IMC morphology and size, and improve the joint strength to a certain extent. The design of the hybrid solder joint system needs to be based on different metal pads. There are various failure modes of interconnected solder joints on different metal pads. Therefore, the interfacial response, microstructure, and mechanical properties between different hybrid solder and different metal pads need to be studied to optimize the design of the hybrid solder joint system. This paper investigated hybrid low-temperature Sn–3Ag-0.5Cu/Sn–58Bi solder joints on Au/Ni/Cu (ENIG) and Au/Pd/Ni/Cu (ENEPIG) substrates. The addition of Pd elements can change the IMC morphology of hybrid solder joints and affect the fracture failure mode of the joints under shear, with a higher average shear strength at different process parameters than ENIG welded joints. Finally, the presence form of Pd elements in the solder joints was observed under TEM and the fracture mechanism was analyzed. The results showed that Pd atoms on ENEPIG pads can replace some Cu atoms to form (Cu, Pd)6Sn5 intermetallic compounds, distorting the lattice stripe to produce distortions. And compared to ENIG pads, the IMC morphology is pin-rod-like and finer, with more complex grain boundary paths between the grains of the hybrid solder.

Development of repairing technique for interconnection of silicon photovoltaic modules using an induction heating system

One of the origins for the degradations of the performance in Si photovoltaic (PV) modules is the corrosions of the front-side metallization, joints of solder and electrodes, solder and interconnection ribbons, thus increasing the series resistance after long-term exposure. This work proposes a reliable method to repair the failures of solder interconnections by utilizing the local induction heating system. The method will perform without removing the PV modules from the outdoor installation locations leading to time-saving and low maintenance costs. It reveals that the heating time on the failures of the solder joint and solder interconnection in the Si PV module plays a vital role in decreasing the series resistance and recovering the PV performance. The optimized heating conditions were a time of 2.0 s, a 10% output power of 3.5 kW, and a frequency of 900 kHz. The proposed method is effective and yields the recovery of the conversion efficiency of the Si solar cell module, as also confirmed by electroluminescence imaging.

균열에 대한 전기적 모델과 S-파라미터 패턴을 이용한 솔더조인트 신뢰성 분석

Purpose: Electrical interconnects affect the reliability and performance of entire electronic systems - especially as operating frequencies and clock speeds in processors are increasing annually. We suggest the S-parameter pattern analysis method is used to evaluate the reliability of the commonly-used solder-joint interconnect.BRMethod: An impedance model of the solder-joint interconnect was developed to study the effect of crack evolution. Simulation Program with Integrated Circuit Emphasis (SPICE) simulations, using a suggested impedance model, were then performed and the crack evolution was tracked using the S-parameter pattern analysis.BRResults: In the crack initiation phase, a resonance peak occurred on the S-parameter pattern and it the peak moved toward lower frequencies as the crack propagated until failure.BRConclusion: This study demonstrated that monitoring the resonant frequency in the S-parameter pattern can predict the initiation and evolution of cracks in the solder-joint interconnects.

Effects of Au/Ni coating thickness on enhancing the properties of InPb/MoCu solder joints in microwave modules

Deep understanding of and effective improvement in interconnect performance are of great significance for developing miniaturized and high-performance microwave modules. Herein, the effects of Au/Ni coating thickness on the performance of InPb interconnect solder joints were investigated by the high-temperature storage experiment. At normal Au/Ni joints, the AuIn2 intermetallic compound (IMC) particles bordered on each other, attributing to form a “closed zone” where the diffusion rate of In atoms was faster than that of Au atoms and there was a net flux. Here, the vacancies in the “closed zone” were merged in reaction to form Kirkendall voids. However, the “closed zone” inside the thin Au/Ni joints could be greatly reduced, and thus the generation of voids was significantly suppressed. The diffusion coefficient of AuIn2 IMCs was reduced by 22.34% at the thin Au/Ni joints compared with the normal Au/Ni joints. After aging for 168 h, the shear strength of the thin Au/Ni joints was increased by 25.10% compared with the other one. Therefore, the thin Au/Ni coating could enhance the long-term performance of solder joints in microwave modules and meet the development requirements of microwave module miniaturization.

Corrosion testing of solar cells: Wear-out degradation behavior

Corrosion is one of the main end-of-life degradation and failure modes in photovoltaic (PV) modules. However, it is a gradual process and can take many years to become a major risk factor because of the slow accumulation of water and acetic acid (from encapsulant ethylene vinyl acetate (EVA) degradation). In this work, an accelerated aging test for acetic acid corrosion was developed to probe wear-out and end-of-life behavior and facilitate screening of new cell, passivation, metallization, and interconnection technologies. In the tests, the top glass and EVA layers were removed from PV modules to expose the solar cells and interconnects. These “opened” modules were then placed in acid baths under varying conditions, including acid concentration, temperature, and electrical bias. Three cell technologies were tested, including Al-back surface field (BSF), passivated emitter and rear contact (PERC), and silicon heterojunction (SHJ). For all conditions, the presence of acid accelerated module power loss compared to control tests with water baths. Increased temperature accelerated the rate of degradation by several times. Application of electrical bias led to an initial drop in short circuit current, but these modules eventually outperformed the non-biased modules. In all tests, lead oxides were the primary degradation products detected, and found to accumulate mostly along the printed metallization, especially in proximity to the busbar. SHJ cells with a silver paste-based interconnection outperformed Al-BSF and PERC cells with a solder-based interconnection. The accelerated corrosion test methods can be optimized to match corrosion behavior observed in field modules with greater precision and shorter times than standard damp heat tests, and is especially useful to assess the long-term durability of the continuously increasing variety of corrosion sensitive PV materials and components. • Continued use of EVA poses risk for new cell technologies because of acid generation. • Accelerated corrosion test for solar cells is developed, improving upon damp heat. • Rate of power loss dependent on concentration, temperature, bias, and technology. • Cell interconnect solder joint most susceptible to corrosion by acid.

Avoiding inelastic strains in solder joint interconnections of space electronics

AbstractA simple and physically meaningful analytical (“mathematical”) predictive model is developed for the evaluation of the sizes of the zones of inelastic deformations, if any, at the ends of a soldered electronics assembly in a packaged IC device. The emphasis is on the IC devices intended for space applications and on the incentive for using column‐grid‐array (CGA) rather than a ball‐grid‐array (BGA) technology for lower thermal interfacial stresses. Such devices, when employed outside spacecraft, experience extraordinarily low temperatures, and their solder joint interconnections, when used interchangeably inside and outside the craft, are subjected to significant and variable inelastic strains, possibly leading to low cycle fatigue conditions. Because of that, the useful lifetime of the device might be shorter than required for particular applications. There is an obvious incentive to avoid, if possible, the inelastic deformations in the solder material or, at least, to predict the sizes of the inelastic zones at the peripheral portions of the assembly. The developed model shows how this could be done. Both shearing and peeling interfacial stresses are addressed. The numerical examples are carried out for an IC‐package mounted on a ceramic (Al203) substrate using 3%–4%Ag0.51%Cu lead‐free solder alloy. In addition, an extreme response of an assembly of the type in question to the random temperature cycling is briefly addressed. It is concluded that several possible and independent ways to avoid or, at least, to minimize the inelastic deformations in the solder material could be employed: the use of high yield stress solder and/or a solder with a low melting temperature and/or a low expansion substrate and/or compliant interfaces, such as, for example, low‐modulus‐and‐compliant CGA design instead of high‐modulus‐and‐stiff BGA, and/or inhomogeneous attachment designs, such as, for example, those, when high‐modulus and/or high‐soldering‐temperature solder is used in the assembly's major mid‐portion, where heat‐transfer considerations play the major role, and low‐modulus and/or low‐melting‐temperature solder – at its peripheral portions, where mechanical strength is critical. It is concluded also that because, based on the calculated data, the peeling stresses are typically considerably lower than the shearing ones and are proportional to the shearing stresses, only the latter could be considered and possibly minimized. As to the random loading, whose effect was assessed by considering the extreme elastic shearing stress in an assembly with an extraordinarily high yield stress (so that inelastic deformations in it are impossible), it has been concluded that a probabilistic‐design‐for‐reliability of the solder joint interconnections in IC packages intended for space application should be considered in addition to the deterministic approach taken in this paper, but this analysis is beyond the scope of the present study and will be done as future work. Finally, it is concluded that the analytical ("mathematical") modeling should always be considered, in addition to computer simulations, in every important physical design related undertaking, such as the one addressed in this analysis: these two major modeling tools are based on different assumptions and employ different calculation techniques, and if the calculated data obtained using these tools are in agreement, then there is a good reason to believe that these data are accurate and trustworthy.

Effects of Interconnect Shape and Thermal-Electro-Migration on Solder Creep of Copper-Pillar Flip Chip Joints

With the development of electronic products toward high density and high reliability, the size of interconnect solder joints and interconnect pitch continues to decrease. Under normal service conditions, solder joints are subjected to thermal–electric–mechanical loads simultaneously, resulting in reliability problems for many package structures. This article investigated the effects of interconnect shape and thermal-electro-migration on solder creep of copper-pillar flip chip joints and analyzed the corresponding failure modes and mechanisms. In this article, solder joints with different shapes were obtained by adjusting the thermal compression bonding process parameters, and creep experiments were performed on the solder joints under different temperature and stress conditions. In addition, we have performed thermoelectric coupling experiments and finite element simulations for different shapes of solder joints. Moreover, creep experiments were conducted on three types of solder joints after 10 and 40 h of thermoelectric coupling pretreatment. The results show that the three solder joints exhibit typical creep characteristics under different experimental conditions and the creep strain rate increases with the increase of shear stress and temperature. Under the same conditions, the creep strain rate of the hourglass-shaped solder joint is always higher than that of the other two solder joints. The electromigration reliability of the hourglass-shaped solder joint is the worst, and the electromigration reliability of the cylinder-shaped solder joint is the best. With the increase of thermoelectric coupling pretreatment time, the creep strain rate of solder joints increased significantly, and the fracture mode of solder joints gradually changed from ductile fracture to brittle fracture. Among the three types of solder joints, the creep resistance of the hourglass-shaped solder joints is greatly affected by the thermoelectric coupling pretreatment.

Predicted Low-Cycle-Fatigue Lifetime of Solder Joint Interconnections: Application of Hall's Approach and Boltzmann-Arrhenius-Zhurkov (Baz) Model

A predictive model is suggested for the evaluation of the low-cycle-fatigue lifetime of a solder joint interconnection in an avionic IC package subjected to temperature cycling and experiencing low cycle fatigue conditions. The model is based on two significant findings in the field of electronic materials reliability. The first one is Hall's plastic strain energy approach suggested about forty years ago.

An Investigation into Thermomigration Failure of Flip Chip Solder Joint Interconnects Used in High-Reliability Applications

An Investigation into Thermomigration Failure of Flip Chip Solder Joint Interconnects Used in High-Reliability Applications

Expected life-time of an optical silica fiber intended for open space applications: Probabilistic predictive model

The recently suggested probabilistic design-for-reliability (PDfR) concept in microelectronics and photonics reliability engineering enables quantifying the static fatigue (delayed fracture) lifetime and the corresponding (in effect, never-zero) probability of failure of optical silica fibers intended for open space (outside the spacecraft) applications. In the author's opinion, an adequate operational reliability of space photonics cannot be assured, if it is not quantified, and, because of numerous inevitable intervening uncertainties, such a quantification should be done on the probabilistic basis. Multi-parametric Boltzmann–Arrhenius–Zhurkov (BAZ) constitutive equation is used to design and interpret the results of a highly-cost-effective and highly focused failure-oriented accelerated testing (FOAT). Such testing is both the experimental basis of the PDfR and a physically meaningful proof-test for optical fibers. The combined action of a moderately low temperature, tensile loading, ionizing radiation and random vibrations is considered. Although random vibrations might not be an actual stressor in the application in question, it is nonetheless included in the analysis as a critical stimulus: fracture mechanics studies indicate that fatigue and brittle cracks propagate particularly rapidly, when the material under test is subjected to a low-temperature/vibration bias. The general concept is illustrated by a detailed numerical example. It should be pointed out, however, that the calculated data, although confirm the viability of the suggested methodology, use hypothetical input information and should be viewed just as a suitable illustration, not more. The developed approach is rather broad, and could be applied to any type of optical fibers, including laser fibers, and, perhaps, with some modifications, also to other types of optical, opto-electronic and even non-optical materials and vulnerable structural elements (such as, e.g., solder joint interconnections) intended for highly demanding space applications. The approach could be applied also, as has been indicated by one of the reviewers, in other astrophysics related conditions and locations, where optical fiber instrumentation is intended to be employed in low temperature conditions, such as, e.g., those that take place at the bottom of the Shackleton impact crater at the lunar south pole. The important restriction of our model has to do with the fact that the BAZ equation, which is based on classical thermodynamics, assumes that no failure could possibly occur at absolute zero. Because of that, the suggested model should be used at temperatures, sufficiently remote from the absolute zero. Future work should focus, first of all, on the experimental verification of the suggested approach and model.

An Investigation into Thermomigration Failure of Flip Chip Solder Joint Interconnects used in High Reliability Applications

Abstract The experimental study described herein investigates thermomigration of both eutectic Sn/Pb and lead free Sn/Ag/Cu solder joints, with the additional focus on the development of an Arrhenius failure model of time-to- failure as a function of temperature. Flip chip test vehicles were assembled with daisy chain die, with and without underfill, attached to ceramic and organic package substrates, using standard reflow processes. Three different under bump metallurgy technologies were investigated: sputtered thin film Al/NiV/Cu, thick electroplated nickel, and thick electroplated copper (i.e., copper pillars). The test vehicles were subjected to unbiased high temperature storage (HTS) testing with temperatures ranging from 125°C to 200°C. Failure was determined from continuity testing at regular intervals until an open circuit or high resistivity was detected. The results demonstrate the robustness of Al/NiV/Cu UBM at temperatures less than 130°C, and of the thick electroplated UBM at temperatures of 150°C. Based on the HTS test results, and corresponding analyses, a thermomigration failure model was generated for eutectic Sn/Pb and lead free Sn/Ag/Cu solder alloys using an Arrhenius-like fit to the failure data.

Inhomogeneous Bonding in Low-TemperatureSoldering: Brief Review

Thermal stresses [1-4] in solder joint interconnections (see, e.g., [5]) used in electronic and photonic packaging are proportional to the thermal contraction mismatch strains T [3-9]. Here  is the effective coefficient of thermal expansion (CTE) mismatch between the soldered materials (the chip or the package to their substrates), and T is the change in temperature from the elevated manufacturing (bonding/fabrication/solder ing) temperature, at which, because of the interaction of shrinkage and stressrelaxation processes, the induced stresses are next-to-zero, to the low, room, testing or operation, temperature, at which the induced stresses are the highest. Clearly, these stresses are lower for lower soldering temperatures, and therefore there is an obvious incentive for using low temperature solders. What is less obvious is that significant stress relief in solder joints can be achieved also by employing, for the same materials and the same thermal mismatch strain T, inhomogeneous bonds [10-19], when, e.g., a solder material with a high soldering temperature and/or with a high Young’s/shear modulus is employed in the mid-portion of the assembly, where the stresses in this material are low (at the mid-cross-section of the assembly these stresses, distributed in an anti-symmetric fashion, are always zero), and a low-melting-point solder and/or a solder with a lower modulus is employed at the assembly’s peripheral portions, where the interfacial shearing and peeling thermal stresses are the highest. Ultimately, when only the elevated stresses, and not heat transfer considerations, are viewed to be critical, even assemblies bonded at the ends only are viable [16,17].

Research on Wiener Degradation Model and Failure Mechanism of Interconnect Solder Joints Under Random Vibration Load

Electronic packaging solder joints are the key parts of mechanical fixation and electrical interconnection between electronic chips and printed circuit boards, which are prone to failure and lead to electronic device failures under the action of vibration environment stress. In regard to the failure characterization and degradation modeling of electronic packaging solder joints under vibration load, this paper adopts environmental stress tests, builds a vibration failure test platform, designs a vibration load excitation spectrum, and obtains solder joint degradation data under vibration stress; it uses the square root amplitude, form factors, and kurtosis factors to characterize the solder joint degradation process, which effectively identify the solder joint degradation node, and improve the data monotonicity of the solder joint degradation process; the Wiener process is used to build a solder joint multi-stage degradation model. Based on the EM algorithm, the hyperparameters of the degradation model have been optimized, and the universal test of the Wiener degradation model with multiple samples is carried out in accordance with the LB index. The analysis shows that the effectiveness of different samples is as high as 87.5%, which verifies the universality of the Wiener degradation model; Based on the crack morphology subject to the solder joint test and the features of the solder joint in the multi-stages, the paper analyzes the crack propagation behavior of the solder joint, and clarifies the failure mechanism of the solder joint.

Crack initiation and growth in PV module interconnection

As the cost of PV (photovoltaic) solar panels drops, it is widely expected that solar energy will become the cheapest source of electricity in many parts of the world over the next two decades. To ensure that PV solar modules have a long service life and can meet the PV manufacturer’s warranty, the PV modules need to have high reliability. Solar PV module manufacturers typically provide two warranties: a performance warranty which guarantees 90% of original power output after 10 years and 80% of original output of at 25 years; and an equipment warranty which guarantees their PV module will have a minimum of 10–12 years operation before failure. A critical part of the solar PV module assembly is the ribbon interconnection between the solar cells (i.e. the solder joint interconnections), and failure of the ribbon interconnection can adversely affect the performance and reliability of whole PV module. Ribbon interconnection failures have been linked to the thermal cracks which are initiated in the solder joint material during the high temperature ribbon interconnection manufacturing process; and then the crack propagation and growth associated with the thermal cycling of the ribbon interconnections under higher than ambient temperature PV module operating conditions. This paper reports on the study of high temperature crack initiation and propagation in different PV Module interconnection configurations by using XFEM in ABAQUS software. It concerns a necessary, urgent and fundamental revision of the manufacturing process that lies at the heart of PV module ribbon interconnection manufacture.

Fatigue Behavior of SAC-Bi and SAC305 Solder Joints With Aging

Reliability of microelectronic assemblies is typically limited by the fatigue failure of one of the interconnected solder joints. The fatigue behavior of the lead-free solder joints doped with bismuth under different stress loading and aging conditions is not yet understood. This article investigates the effect of adding bismuth on the mechanical reliability of SAC alloys considering different loading and aging conditions. The fatigue behavior and shear strength of individual SAC305 (Sn–3.0Ag–0.5Cu) and SAC-Q (Sn–3.4Ag–0.5Cu–3.3Bi) solder joints are examined and compared. A unique experiment is designed to test the individual solder joints using a micromechanical testing system. The results show that the fatigue life and shear strength of SAC-Q with Bi are much higher than SAC305 regardless of the aging and stress conditions. It was also found that increasing stress amplitude leads to a decrease in the fatigue life for both alloys. The aging time has a negative effect on the fatigue life and shear strength of both alloys. The impact of aging on SAC-Q solder joints is significantly less than that for SAC305. Microstructure analysis shows a substantial amount of precipitates coarsening with aging for SAC305 compared with SAC-Q. Hysteresis loop analysis shows that increasing the cycling stress amplitude and aging time leads to an increase in the work per cycle and plastic strain. Common fatigue models, such as Morrow energy model and Coffin–Manson model, fail to predict the life considering the effect of aging; aging affects the constants of both models.

Solder Joint Interconnections in Automotive Electronics: Design-for-Reliability and Accelerated Testing

Abstract Three practically important reliability-related questions for solder joint interconnections (SJIs) in automotive electronics, and particularly in its actuator and sensor electron devices, are addressed in this analysis:Could inelastic strains in the solder material be avoided by a rational physical design of the IC package, and, if not, could the sizes of the peripheral inelastic strain areas be predicted and minimized? It is clear that the low cycle fatigue lifetime is inversely proportional to the sizes of the inelastic zones and that the material's fatigue lifetime could be improved dramatically, if the induced strains remain within the elastic range. The Palmgren-Miner rule of linear accumulation of damages can be used, instead of Coffin-Manson relationships, in such a situation.Realizing that, because of the inevitable uncertainties, the difference between highly reliable and an insufficiently robust electronic products is “merely” in the levels of their never-zero probabilities of failure, could these probabilities be assessed, and could this be done at the design stage? A possibility of doing that is particularly critical for SJIs, the most vulnerable structural elements in the today's IC package designs. Reliability of an electronic material or a product cannot be assured, if it is not quantified, and, because of the inevitable and critical uncertainties, this should be done on the probabilistic basis.Should SJI accelerated testing based on costly, time- and labor-consuming and, because of temperature dependency of material properties, possibly even misleading temperature cycling, be replaced by a more physically meaningful, less expensive and more trustworthy accelerated test vehicle, and could low-temperature/random-vibrations bias be employed in this capacity? The rationale behind such a question has to do with the facts that the highest thermal stresses take place at the lowest temperature conditions, and that fatigue cracks, whether elastic or inelastic, propagate most rapidly, when the material experiences random vibrations. This technique has been already reduced to practice in an industrial lab two years ago. The objective of the analysis is to shed light, by using analytical (“mathematical”) modeling, rather than widely spread computer simulation, on the mechanical behavior and the underlying physics of failure in the SJI. Future work should focus primarily on experimentations to confirm theoretical findings and recommendations.

Elevated Standoff Heights of Solder Joint Interconnections Can Result in Appreciable Stress and Warpage Relief

Abstract The “head-in-pillow” (HnP) defects in lead-free solder joint interconnections of Integrated Circuit (IC) packages with conventional (small) standoff heights of the solder joints, and particularly in packages with fine pitches, are attributed by many electronic material scientists to the three major causes: attributes of the manufacturing process, solder material properties, and design-related issues. The latter are thought to be caused primarily by elevated stresses in the solder material, as well as by the excessive warpage of the Printed Circuit Board (PCB)-package assembly and particularly by the differences in the thermally induced curvatures of the PCB and the package. In this analysis, the stress and warpage issue is addressed using an analytical predictive stress model. The model is a modification and an extension of the model developed back in 1980s by the first author. It is assumed that it is the difference in the postfabrication deflections of the PCB-package assembly that is the root cause of the solder material failures and particularly and perhaps the HnP defects. The calculated data based on the developed stress model suggest that the replacement of the conventional ball grid array (BGA) designs with designs with elevated standoff heights of the solder joints could result in significant stress and warpage relief and, hopefully, in a lower propensity of the IC package to HnP defects as well. The general concepts are illustrated by a numerical example, in which the responses to the change in temperature of a conventional design, referred to as BGA, and a design with solder joints with elevated standoff heights, referred to as column grid array (CGA), are compared. The computed data indicated that the effective stress in the solder material was relieved by about 40% and the difference between the maximum deflections of the PCB and the package was reduced by about 60%, when the BGA design was replaced by a CGA system. Although no definite proof that the use of solder joints with elevated standoff heights will lessen the package propensity to the HnP defects is provided, the authors nonetheless think that there is a reason to believe that the application of solder joints with elevated standoff heights could result in a substantial improvement in the general IC package performance, including, perhaps, its propensity to HnP defects.

The Effect of the Thermal Mechanical Properties of Nonconductive Films on the Thermal Cycle Reliability of 40-<inline-formula> <tex-math notation="LaTeX">$\mu$ </tex-math> </inline-formula>m Fine Pitch Cu-Pillar/Ni/SnAg Microbump Flip-Chip Assembly

Nonconductive films (NCFs) have been introduced for 3-D through-silicon via chip stacking interconnection using reliable fine pitch Cu-pillar/Ni/SnAg microbumps. In this paper, four NCF materials with various elastic modulus and coefficient of thermal expansion (CTE) values were used to investigate the effect of the thermomechanical properties of the NCFs on the thermal cycle reliability of fine pitch Cu-pillar/Ni/SnAg/Cu-pad interconnections. The NCFs’ materials properties were adjusted by changing the ratio of epoxy resins and the curing accelerators. Compared with the borate curing accelerator, the use of the imidazole curing accelerator resulted in better thermomechanical properties on NCFs. And, NCFs containing higher ratio of solid epoxy resins showed higher elastic modulus and higher Tg values when using imidazole curing accelerator. After thermocompression bonding using four different types of NCFs, a thermal cycle reliability test (−40 °C–125 °C) was performed to investigate the effects of the NCFs’ thermomechanical properties on the reliability of Cu-pillar/Ni/SnAg/Cu-pad joints. Due to the CTE mismatch of chips and printed circuit board (PCB) substrates, the SnAg solder joint interconnections were damaged during the thermal cycling. Compared with the four types of NCFs, NCFs with higher elastic modulus at 30 °C showed better thermal cycle reliability. And among the NCFs with similar CTE values, those with higher Tg and higher elastic modulus at 30 °C value showed better thermal cycle reliability. In summary, the NCFs with lower CTE and higher elastic modulus at 30 °C were suitable for highly thermal cycle reliable Cu-pillar/Ni/SnAg/Cu-pad bump joints.