Size Of Solder Joints Research Articles

Microstructure Evolution and Interfacial Reaction of Cu/SAC305/Cu and Co-P/SAC305/Cu Solder Joints under High Current Density

The size of solder joints in electronic packaging is gradually decreasing, which directly leads to a sharp increase in the current density experienced by the solder joints. Therefore, it is of great significance to study the effect of electromigration on the interface of the lead-free solder. In this paper, the effect of electromigration on the microstructure of Cu UBM and Co-P UBM solder joints was compared. By comparing the morphological changes of CoSn3 and Cu6Sn5 at the interface, combined with the calculation of the thickness of the intermetallic compound, it was found that the consumption rate of Co-P UBM in the solder joint was much lower than that of the Cu substrate. Moreover, when the Co-P UBM is completely consumed, the consumption rate of the Cu substrate is also significantly reduced.

Influence of solder condition on effective thermal conductivity of two-directional random fibres: Pore-scale simulation

It is indicated that the solder joint of the metal fibrous materials is a critical factor impacting the heat conduction. To reveal the mechanism by which solder joint sizes, solder joint skips, solder flux materials, and filling media affect the thermal conductivity of fibres, pore-scale numerical simulation is employed to study the thermal transport in two-directional (2-D) random fibres. Satisfactory agreement with existing data validates the numerical model. The dimensionless effective thermal conductivity (ETC) of the porous fibres increases with the solder joint sizes. As the solder joint size (i.e., solder joint ratio) increases by 3.06%, the in-plane (ke-in) and out-of-plane (ke-out) dimensionless ETC increase by 9.0% and 437.2%, respectively. However, the solder joint skips will weaken the thermal conductivity of the fibres. For the same fibre, the ETC of the fibre increases as the thermal conductivity of solders increases. Further, when the dissimilarity in thermal conductivity between the filling medium and the fibre is reduced, the fibre is less affected by the solder joint skips. Finally, it should be supplemented that the in-plane and out-of-plane ETC (ke-in and ke-out) of the fibre without any solder joint are reduced by an average of 14.3% and 98.8%, respectively.

Shear deformation behavior and failure mechanisms of graphene reinforced Sn-based solder joints bonded by transient current

Graphene as a reinforcement is expected to improve the shear strength of solder joint. However, little is known about the deformation behavior and mechanisms of composite solder joints. In this study, sandwich joints are prepared using graphene nanosheets-reinforced Sn-Ag-Cu composite solder (GNSs/SAC) by transient current bonding technology in order to obtain dispersed graphene. Interrupted shear tests combined with orientation image microscopy are conducted at different strain to observe the morphology and crystal orientation evolution of solder joints in situ. Some twins rotate, and the orientation begins to spread during shear, while the orientation of large Sn grain shows a minimal change. Cracks tend to initiate and propagate along the boundary. The failure mechanisms of the solder joint is determined. Molecular dynamics results show that the strain concentration at the boundary. Continuous shear tests show that the shear strength was improved by approximately 50.7% with the addition of 0.1 wt% graphene. Based on microstructure analysis and calculation, load transfer is identified as the dominant strengthening mechanism for GNSs/SAC alloys, followed by Orowan system. Graphene does not refine the grain size of solder joints, and dislocation multiplication from thermal mismatch does not strengthen them.

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.

Effect of solder joint size and composition on liquid-assisted healing

This work presents an experimental and numerical investigation of liquid-assisted healing with respect to solder joint composition and size. A damage-healing model is formulated based on entropy generation of damage and viscous material transport during healing. The model accounts for a composition-dependency of healing by introducing the liquid film thickness, the liquid viscosity and a microstructural mobility parameter. The size dependencies enter the healing model in form of the local capillary pressure of the solder joint. A viscous flow experiment illustrates the compositional dependency of local material transport and a cyclic tensile experiment shows the regain of mechanical properties, such as, stiffness and strength after healing. The flow experiment shows that material transport is retarded for solders of low liquid fraction and crack healing is limited due to partial filling of the crack. Simulation results of a solder array suggest the capillary pressure as the driving force for healing, which leads to a size-dependency of the healing evolution. The required time for complete healing increases with reduced solder dimensions due to higher capillary pressures. Microstructural mobility due to high liquid fractions also promotes healing.

Impact of Mechanical Property Degradation and Intermetallic Compound Formation on Electromigration-Oriented Failure of a Flip-Chip Solder Joint

Due to the increased complexity and optimization in microprocessor packaging from 2D to 3D packages, the size of solder joints is being reduced significantly. This trend currently leads to an increased amount of current density across flip-chip solder joints as well as microbumps and causes electromigration-oriented void formation and subsequent failure of the solder joints. It has been observed from literature that solder material undergoes microstructure evolution and subsequent degradation of mechanical properties under isothermal aging conditions. The current study is based on the effects of material property degradation due to thermal aging of flip-chip Sn-Ag-Cu (SAC) solder joints on electromigration-oriented failure. Finite element analysis has been used to analyze the diffusion characteristics of a SAC solder joint under isothermal aging conditions of 100°C for a period of 1–20 days, and electromigration simulation has been performed at two different temperatures of 100°C and 125°C for 100 h at an input current range of 0.01–0.05 A. The effect of intermetallic compound (IMC) layer thickness is analyzed to reveal the impact on electromigration-oriented failure in isothermally 60 days long aged solder bumps. Results have revealed that resistance to electromigration-oriented failure is higher in the case of aged components compared to unaged components along with the increment of time to failure with IMC formation in the SAC solder joint.

Effect of strain rate on mechanical behavior of Sn0.3Ag0.7Cu solder at macro- and micro-scales

At present, there have been many researches on the effect of trace elements on the mechanical properties of Sn–Ag–Cu solder, and the methods used are mainly shear test or nanoindentation test. However, the size of structural solder joints in electronic packaging has reached the order of micrometers, and the mechanical behavior characteristics related to the strain rate of solder at the micro-scale are obviously more needed for the application of small-scale structural solder joints. For this reason, this paper selects Sn0.3Ag0.7Cu solder with superior comprehensive properties such as ductility and shear strength and low cost, and uses universal testing machine and Split Hopkinson Pressure Bar to perform quasi-static and dynamic compression tests on it. After fitting the Johnson–Cook constitutive model parameters of Sn0.3Ag0.7Cu, the dynamic indentation process at the micro-scale was simulated by ABAQUS, and the effect of strain rate on the mechanical behavior of the material at the macro-scale and micro-scale was analyzed, respectively. Our macro test results show that the yield strength of Sn0.3Ag0.7Cu solder is about 28.74 MPa. Under quasi-static load, the rate of increase of the stress value in the strain hardening stage will increase with the increase of the strain rate; while under dynamic load, the stress value corresponding to different strain rates does not increase significantly, and the main difference lies in the magnitude of plastic strain. In our numerical simulation of dynamic indentation, the result shows that when Sn0.3Ag0.7Cu solder is subjected to a high strain rate load at the micro-scale, a certain degree of hardening occurs in the middle and late stages of indentation propagation. At the same time, the calculated load–displacement curves indicate that the plastic flow ability of Sn0.3Ag0.7Cu solder in the micro-scale increases with the increase of the indentation expansion rate.

Kinetics of Ultrasonic and Current Coupling-Enhanced Dissolution of Copper in Liquid Tin

With the development trend of high speed, light weight, continual miniaturization, and multifunctionality of microelectronic products, the size of solder joints continues to shrink. Therefore, higher requirements are being placed on soldering techniques. This study used the immersion method to investigate the dissolution kinetics of copper in liquid tin at temperatures in the range of 240–300°C with ultrasonic and current coupling. The amount of dissolution and the thickness of the interfacial intermetallic compound (IMC) layer were measured and the dissolution activation energy was calculated. Results showed that the composite fields of ultrasonic and current coupling accelerated copper dissolution in liquid tin and decreased the dissolution activation energy. The dissolution rate was 5–7 times higher compared to that without ultrasound and current, and was 2–3 times higher compared to that using only current. At a certain temperature, with the increase in immersion time, the thickness of the interface IMC layer demonstrated parabolic growth. The sound pressure caused by the ultrasound and the temperature gradient caused by current in the liquid tin were simulated by finite element modeling. The results show that the sound pressure distribution in liquid tin was uneven, and the temperature gradient inside the liquid tin increased with current.

Modeling of Intergranular Mechanical Fatigue of a Sintered Nanosilver Die Attachment for Power Electronics

As a novel promising die-attach material, sintered nanosilver had been widely studied in electronic packaging, especially in applications with high power density. The increased power density, as well as a significant reduction in the solder joint size, could cause considerable thermomechanical stresses in the die attachment and the dies. It should be critical to predict the stress-strain response and the lifetime of the die attachment precisely in order to optimize the reliability of power devices. Instead of the conventional macroscopic constitutive models, e.g., Anand model, OW-AF model, and so on, a crystal plasticity finite-element (CPFE) method, which can involve the effects of grain size, orientation, shape, distribution, and so on, was proposed to predict both the macro- and micromechanical deformation behaviors of the sintered nanosilver. The parameters of the CPFE model of the sintered nanosilver were determined. The simulation results indicated that stress concentration could be present in or among the grains of the sintered nanosilver, locally. The nonuniform stress distribution should be critical to determine the crack initiation of the sintered die attachment. Consequently, the fatigue lifetime could be predicted more accurately using the CPFE model rather than the conventional OW-AF model, especially for the sintered nanosilver with porous microstructures.

IMCs Microstructure Evolution Dependence of Mechanical Properties for Ni/Sn/Ni Micro Solder-Joints.

The current miniaturization trend of microelectronic devices drives the size of solder joints to continually scale down. The miniaturized joints considerably increase intermetallic compounds (IMCs) volume fraction to trigger mechanical reliability issues. This study investigated precise relationships between varying IMC volumes and mechanical properties of Ni/Sn(20μm)/Ni micro-joints. A designed method that followed the IMC volume as the only variable was used to prepare micro-joint samples with different IMC volumes. The continuously thickened Ni3Sn4 IMCs exhibited a noticeable morphology evolution from rod-like to chunky shape. The subsequent tensile tests showed unexpected tensile strength responses as increasing Ni3Sn4 volume, which was strongly associated with the Ni3Sn4 morphological evolutions. Fractographic analysis displayed that the ductile fracture dominates the 20%–40% IMC micro-joints, whereas the brittle fracture governs the 40%–80% IMC micro-joints. For the ductile fracture-dominated joints, an abnormal reduction in strength occurred as increasing IMCs volume from 20% to 40%. This is primarily due to severe stress concentrations caused by the transformed long rod-typed morphology of the Ni3Sn4. For the brittle fracture-dominated joints, the strength appeared a monotonous increase as the Ni3Sn4 volume increased. This may be attributed to the increased crack resistance resulting from continuous coarsening of the chunky Ni3Sn4 without any voids. Moreover, the finite element analysis was provided to further understand the joint failure mechanisms.

Research on life evaluation method of solder joint based on eddy current pulse thermography.

With the wide usage of electronic packaging technologies such as Ball Grid Array in electronic industry, it is necessary to maintain its quality in order to meet the demand of electronic products for function, integration, and size reduction. However, as the size of solder joints in such technology decreases, the solder joints are more and more prone to defects. To solve the life prediction problem of small-size packages having interconnections in the high-density chip, a method based on the eddy current pulsed thermography (ECPT) is put forward to study the remaining life prediction of solder joints. A 3D induction heating finite element model is established, by which the crack length of defect solder joints can be distinguished using temperature field. At the same time, the remaining life of defect solder joints can be characterized by the length of the crack. Furthermore, the experiments are carried out on solder joints whose diameter is 0.4 mm. Both simulation and experiment results verify that it is reliable and convenient to use 3D induction heating based temperature field from ECPT to evaluate the remaining life of cracks in solder joints.

Critical Review of Size Effects on Microstructure and Mechanical Properties of Solder Joints for Electronic Packaging

With the miniaturization of electronic packaging and devices, the size of solder joints in electronics is also decreasing from bulk solder joints to micro-bumps. Both the microstructure and mechanical properties of the solder joints are also evolving with the decreasing size, which brings great concern for the reliability of different sizes of solder interconnections. In this paper, the effect of solder size on the microstructure (i.e., interfacial intermetallic compound (IMC) growth, precipitation in the solder matrix, dendrite arms, and undercooling) and mechanical properties (i.e., tensile property, shear and compression strength, fracture toughness, and creep deformation) are reviewed from the mechanical point of view. In addition, some areas for further researches about size effects on solder joints are discussed.

Size effects on the interfacial reaction and microstructural evolution of Sn-ball/Sn3.0Ag0.5Cu-paste/Cu joints in board-level hybrid BGA interconnection at critical reflowing temperature

The effects of solder joint size on the interfacial reaction and microstructural evolution of Sn-ball/Sn3.0Ag0.5Cu-paste/Cu joints in board-level hybrid BGA interconnection during reflow at two critical temperatures of 217.2 and 227.0 °C were investigated comprehensively. For the joints reflowed at 217.2 °C, which is slightly higher than the melting point (217.1 °C) of Sn3.0Ag0.5Cu solder, the Sn ball does not melt, but coalesces with the melted Sn3.0Ag0.5Cu paste, regardless of change in solder joint size, and the microstructure of the mixed part of the Sn ball and Sn3.0Ag0.5Cu paste does not change significantly. In contrast, for the joints reflowed at 227.0 °C, which is nearly 5 °C lower than the melting point (231.9 °C) of Sn ball, with decrease in joint size, the Sn ball exhibits premelting behavior gradually, and the microstructure of the mixed part of the Sn ball and Sn3.0Ag0.5Cu paste varies obviously. The thickness of the Cu6Sn5 layer at the Sn3.0Ag0.5Cu-paste/Cu interface increases with decrease in size of joints reflowed at 217.2 and 227.0 °C, and the growth of the interfacial Cu6Sn5 is significantly influenced by Cu concentration distribution near the interface between the solder and intermetallic compound layer in the molten solder. The experimental data and two-dimensional finite element simulation results indicate that the Cu concentration in small joints increases faster than that in large ones, and the relatively long time influence of high Cu concentration in the small joints leads to the formation of large Cu6Sn5 grains at the interface.

Size effect on microstructure and tensile properties of Sn3.0Ag0.5Cu solder joints

In the current study, the size effect on microstructure and tensile property of Sn3.0Ag0.5Cu (SAC305) solder joint is investigated. Experiments were performed to solder joints with thickness from 50 μm to 2 mm. The intermetallic compound (IMC) growth rate of solder joints is found to be dependent on the size of solder joints. After soldering procedure, the IMC of smaller size solder joints is thinner than that of larger size solder joints. It is also found that the average grain size of IMC increases with decreasing of the joint size. To better understand the difference of IMC growth during solid-state and liquid-state thermal aging, experiments were performed at 210 and 300 °C, respectively. IMC thickness of solder joints after 210 and 300 °C of thermal aging was measured. It is found that the size effect on IMC growth rate at solid-state and liquid-state is different. The IMC growth rate of smaller size solder joints is higher than larger size solder joints under solid-state thermal aging. Under liquid-state reaction, the IMC growth rate of smaller size solder joints is slower. ‘H’ type and hexagonal prism of Cu6Sn5 were observed in 2 and 1 mm thickness size solder joint, respectively. Fewer Cu6Sn5 prism was found in 50 μm thickness solder joints. Tensile strengths of solder joints with different sizes were measured. The solder joints showed ductile to brittle fracture transition with the decreasing of joints thickness. The H-field fracture criterion is employed to predict the tensile strength of Sn3.0Ag0.5Cu solder joints with different thickness.

Geometric size effect on IMC growth and elements diffusion in Cu/Sn/Cu solder joints

PurposeThe purpose of this paper is to investigate the effect of geometric size on intermetallic compound (IMC) growth and elements diffusion of Cu/Sn/Cu solder joint and establish the correlation model between the thickness of the IMC layer and size of the solder joint on the dozens of microns scale.Design/methodology/approachThe sandwich-structured Cu/Sn/Cu solder joints with different gaps between two copper-clad plates (δ) are fabricated using a reflow process. The microstructure and composition of solder joints are observed and analyzed by scanning electron microscopy.FindingsAfter reflow, the thickness of the IMC and Cu concentration in solder layers increase with the reduction of δ from 50, 40, 30, 20 to 10 μm. During isothermal aging, the thickness of the IMC fails to increase according to the traditional parabolic rule due to changes in Cu concentration. The reduction of δ is the root cause of changes in Cu concentration and the growth rule of the IMC layer. A correlation model between the thickness of the IMC layer and δ is established. It is found that the thickness of the IMC layer is the function of aging time and δ. With δ reducing, the main control element of IMC growth transfers from Cu to Sn.Originality/valueThis paper shows the changes of IMC thickness and elements concentration with the reduction of the size of solder joints on the dozens of microns scale. A correlation model is established to calculate the thickness of the IMC layer during aging.

Mechanistic Prediction of the Effect of Microstructural Coarsening on Creep Response of SnAgCu Solder Joints

Mechanistic microstructural models have been developed to capture the effect of isothermal aging on time dependent viscoplastic response of Sn3.0Ag0.5Cu (SAC305) solders. SnAgCu (SAC) solders undergo continuous microstructural coarsening during both storage and service because of their high homologous temperature. The microstructures of these low melting point alloys continuously evolve during service. This results in evolution of creep properties of the joint over time, thereby influencing the long term reliability of microelectronic packages. It is well documented that isothermal aging degrades the creep resistance of SAC solder. SAC305 alloy is aged for (24–1000) h at (25–100)°C (~0.6–0.8 × Tmelt). Cross-sectioning and image processing techniques were used to periodically quantify the effect of isothermal aging on phase coarsening and evolution. The parameters monitored during isothermal aging include size, area fraction, and inter-particle spacing of nanoscale Ag3Sn intermetallic compounds (IMCs) and the volume fraction of micronscale Cu6Sn5 IMCs, as well as the area fraction of pure tin dendrites. Effects of microstructural evolution on secondary creep constitutive response of SAC305 solder joints were then modeled using a mechanistic multiscale creep model. The mechanistic phenomena modeled include: (1) dispersion strengthening by coarsened nanoscale Ag3Sn IMCs in the eutectic phase; and (2) load sharing between pro-eutectic Sn dendrites and the surrounding coarsened eutectic Sn-Ag phase and microscale Cu6Sn5 IMCs. The coarse-grained polycrystalline Sn microstructure in SAC305 solder was not captured in the above model because isothermal aging does not cause any significant change in the initial grain size and orientation of SAC305 solder joints. The above mechanistic model can successfully capture the drop in creep resistance due to the influence of isothermal aging on SAC305 single crystals. Contribution of grain boundary sliding to the creep strain of coarse grained joints has not been modeled in this study.

The size effect on intermetallic microstructure evolution of critical solder joints for flip chip assemblies

Purpose – The purpose of this paper is to study the intermetallic compound (IMC) thickness, composition and morphology in 100-μm pitch and 200-μm pitch Sn–Ag–Cu (SAC305) flip-chip assemblies after bump reflow and assembly reflow. In particular, emphasis is placed on the effect of solder joint size on the interfacial IMCs between metal pads and solder matrix. Design/methodology/approach – This work uses 100-μm pitch and 200-μm pitch silicon flip chips with nickel (Ni) pads and stand-off height of approximately 45 and 90 μm, respectively, assembled on substrates with copper (Cu) pads. The IMCs evolution in solder joints was investigated during reflow by using 100- and 200-μm pitch flip-chip assemblies. Findings – After bump reflow, the joints size controls the IMC composition and dominant IMC type as well as IMC thickness and also influences the dominant IMC morphology. After assembly reflow, the cross-reaction of the pad metallurgies promotes the dominant IMC transformation and shape coarsened on the Ni pad interface for smaller joints and promotes a great number of new dominate IMC growth on the Ni pad interface in larger joints. On the Cu pad interface, many small voids formed in the IMC in larger joints, but were not observed in smaller joints, combined with the drawing of the IMC growth process. Originality/value – With continued advances in microelectronics, it is anticipated that next-generation microelectronic assemblies will require a reduction of the flip-chip solder bump pitch to 100 μm or less from the current industrial practice of 130 to150 μm. This work shows that as the packaging size reduced with the solder joint interconnection, the solder size becomes an important factor in the intermetallic composition as well as morphology and thickness after reflow.

Reliability of PCB Solder Joints Assembled with SACm™ Solder Paste

The solder alloy SACm™0510 has been reported to be a superior alloy when used as BGA balls, exhibiting not only an outstanding drop test performance when compared to SAC105, but also as having high thermal fatigue reliability when compared to high Ag SAC solders. In this study, SACm0510 solder was evaluated as a solder paste. The voiding behavior of SGA solder joints was comparable for SACm0510, SAC105, and SC305. When evaluating SGA assemblies on a customized drop test, SACm0510 outperformed SAC105 considerably, which in turn was much better than SAC305. The drop test performance was found to improve upon thermal aging at 150°C, and the difference between the alloys reduced significantly. This was explained by the speculated grain coarsening which resulted in a softened solder joint, and consequently, a shift of fracture mode from brittle failure toward ductile failure. This model was supported by the observation of the fractured surface moving away from the interface upon thermal aging. The improvement in drop test performance upon thermal aging can be further explained by the large solder joint size of the SGA employed in this study, where the bulk property of solder weighed more than a small solder joint. When the assembled chip resistors were evaluated with a −55°C/+125°C TCT test, no failure was observed after 369 cycles for all three alloys. SAC305 appeared to be the best in maintaining the integrity of the interfacial IMC layer. SACm0510 showed a few crack lines, but less than that of SAC105. SACm0510 solder paste was found to be very compatible with BGAs with SAC305 solder joints, and no abnormal microstructure was observed after thermal aging at 150°C for 1000 hours.

Geometrical size effect on the interface diffusion of micro solder joint in electro-thermal coupling aging

This paper investigates the influence of diffusion layer (solder layer) thickness (δ) on interface diffusion in both thermal aging and electro-thermal coupling aging. The different δ (δ = 60, 120 and 240 μm) of Cu/Sn–3.0Ag–0.5Cu (SAC305)/Cu butt solder joints are used. The results indicate that the geometrical size (solder layer thickness) of solder joint has significant effect on element diffusion behavior. The diffusion coefficient, time exponent, element concentrations and diffusion flux are greatly dependent upon δ. The effects of δ on the interface diffusion is different between thermal aging and electro-thermal coupling aging, due to driving force for diffusion is different. During thermal aging, concentration gradient is the main driving force of diffusion, and diffusion coefficient, time exponent and diffusion flux are relatively low for a thin solder layer. However, under electro-thermal coupling condition, the electron wind force provides the dominating driving force for diffusion, and diffusion coefficient and diffusion flux of thin δ are significantly larger than the thick ones. The Cu concentration of the area near interface is relatively high for a thin solder layer in both tests. Under the same experimental temperature, the effects of δ on the electro-thermal coupling aging are more obvious than thermal aging.

A Robust Location Algorithm for PCB's Solder Joints

Printed circuit boards (PCBs) are being widely used in the electronic packages. Solder joints are often used to interconnect chip resistors and other components onto PCBs. The defects of solder joints will increase quality costs and deteriorate performance. If solder joints cant be located accuracy, AOI system will not inspect solder joints at the right place of solder joints and must lead to misjudgement. Especially, the misjudgement will increase dramatically under uncertain noise disturbance to micro-size solder joints due to inaccuracy location. In this work, an eliminating uncertain noise method is proposed and a robust location algorithm for PCBs solder joints is present. Firstly, some location windows are set based on technology parameters of chip and its solder joints, and solder joints feature image is obtained from it solder joint image based on series of image pre-processing. Secondly, the layout frame outside solder joints, which is viewed as a noise disturbance to location, is extracted as a binary image and is projected to X axis and Y axis, then the smaller region, which include solder joints but no the layout frame, is obtained based on calculating the sum features function of layout frame. Thirdly, the blob feature image of solder joints is extracted from its gray images of red, green, blue layers; it may have some noise blob around solder joints feature, then an evaluation function is develop to judge blob, which maybe belongs to noise or solder joints feature, and only solder joints feature are remained. Fourthly, with the help of setting solder joints windows, the integrated projection method is developed to locate solder joints. Finally, the proposed location method is compared with other two algorithms in the experiment. Experiments result illustrates that the smaller the solder joint size, the better location accuracy and efficiency is obtained than other two mothers.