It is widely accepted that the intermetallic layer that forms at the interface between a solder a... more It is widely accepted that the intermetallic layer that forms at the interface between a solder and a copper substrate has an effect on the properties of the solder joint, particularly under high strain rates such as occur in drop impact. The nature and extent of the effect is related to the thickness and morphology of this interfacial layer and the phases present in the layer. It has been recognized also that thickness, morphology and mix of phases changes over time as a result of diffusion across the interface in both directions as the solder/substrates system moves toward thermodynamic equilibrium and these process are accelerated at the elevated temperature to which some electronic circuitry is exposed. While the basic composition of the solder obviously has a major effect on the thickness, morphology and growth of the interfacial intermetallic microalloying additions have also been found to have an effect. In this paper the authors report a study of the thickness morphology and...
Lead-free solder alloys, particularly those with higher silver and lower copper contents, have be... more Lead-free solder alloys, particularly those with higher silver and lower copper contents, have been shown to react with the copper on circuit boards, dissolving the copper much more quickly than tin-lead solders. Rapid dissolution of copper into tin-rich alloys can create hidden ...
2014 International Conference on Electronics Packaging (ICEP), 2014
ABSTRACT Tin is the main component of contemporary lead-free solders. Under equilibrium condition... more ABSTRACT Tin is the main component of contemporary lead-free solders. Under equilibrium conditions, tin exists as either a tetragonal β-Sn) or cubic (α-Sn) allotrope at temperatures above and below approximately 13°C, respectively. The transformation from β to α, often referred to as 'tin-pest' is poorly understood, despite the phenomena being documented over 100 years ago. Possibly because the high lead content in traditional solder alloys offers some protection against 'tin-pest', this transformation has not been a priority in solder-related research. With the transition to lead-free solder alloys and the availability of modern analytical techniques there is both an increased need and opportunity to better understand the transformation. This research was conducted to investigate the phase-transformation kinetics of the β to α transformations in high-purity powdered tin using variable temperature synchrotron XRD analysis and electron microscopy. From the results, time-temperature-transformation (TTT) diagrams were developed, with the intention of being used as a baseline for examining the effects of composition in current generation lead-free solders. The effects of pre-exisiting α-Sn and the impurity elements of Pb, Cu, Si and Ge on the β to α transformation kinetics were measured. α-Sn accelerates transformation kinetics, while all other elements tested delayed the transformation.
One of the factors that has contributed to the establishment of the Ni-modified Sn-Cu eutectic as... more One of the factors that has contributed to the establishment of the Ni-modified Sn-Cu eutectic as one of the major alternatives to the widely promoted Sn-Ag-Cu alloys as an RoHS compliant lead-free solder has been its apparent fluidity at temperatures close to its 227°C melting point. This fluidity results in the alloy behaving similarly to lower melting point alloys in which tin dendrites start to freeze out at temperatures higher than the nominal melting point. This in turn has meant that the Ni- modified Sn-Cu eutectic can be used as a wave solder and a HASL alloy at process temperatures not much higher than those that have been used with Sn-37Pb solder. More recently it has been found that this fluidity also permits the use of the alloy in reflow soldering with peak temperatures around 245°C, which is in the middle of the range used with the Sn-Ag-Cu alloys that have a nominal melting point 10°C lower. In a study reported at APEX 2005 it was found that the Ni addition has the ef...
Concern about the failure of lead-free BGA packages when portable devices such as cell phones are... more Concern about the failure of lead-free BGA packages when portable devices such as cell phones are accidentally dropped and a general concern about the resistance of these packages under shock loading has prompted an interest in the impact strength of the soldered BGA connection. This paper reports the results of the measurement of the impact strength of lead-free 0.5±0.01mm diameter BGA spheres on 0.42mm solder mask defined pads on copper/OSP and ENIG substrates using recently developed equipment that can load individual BGA spheres at high strain rates in shear and tension. Impact strength is measured as the energy required to detach the sphere from the substrate to which it has been soldered. Two lead-free solders, Sn-3.0Ag- 0.5Cu and a silver-free Sn-0.7Cu-0.05Ni-0.006Ge were studied with Sn-37Pb included as a benchmark. To study the effect of intermetallic growth on impact strength BGA were tested after up to two reflow cycles and 200 hours ageing at 150°C. BGA were tested in sh...
Abstract To the extent that it provides a potential low energy route for crack propagation the in... more Abstract To the extent that it provides a potential low energy route for crack propagation the intermetallic compound that forms at the interface between a tin-based solder and the substrate can play a critical role in determining the likelihood of joint failure in impact loading such as can ...
2008 33rd IEEE/CPMT International Electronics Manufacturing Technology Conference (IEMT), 2008
... Gregory HenshalL Ph.D. Hewlett-Packard Co. Palo Alto. CA. USA greg. [email protected] Robert He... more ... Gregory HenshalL Ph.D. Hewlett-Packard Co. Palo Alto. CA. USA greg. [email protected] Robert Healey and Ranjit S. Pandher. Ph.D. Cookson Electronics South Plainfield. NJ. USA Keith Sweatman and Keith Howell Nihon Superior Co .. Ltd. Osaka Japan Richard Coyle. ...
The influence of trace level Ni additions on the eutectic solidification mode of Sn–0.7Cu has bee... more The influence of trace level Ni additions on the eutectic solidification mode of Sn–0.7Cu has been studied using continuous torque experiments during solidification. The solid fraction at which resistance to paddle rotation at the thermal centre of the sample occurs is related to the spatial distribution of solid during solidification. The results indicate that a transition in solidification mode occurs
While previous iNEMI projects have focused on lead free joints soldered by the use of convection ... more While previous iNEMI projects have focused on lead free joints soldered by the use of convection reflow ovens, since 2004, only a limited number of comprehensive investigations have taken place 1,2,3 . As a result, the lead free wave soldering project was developed in order to characterize and quantify the impact caused by the transition to lead free solder on the wave process itself as well as the impact on the performance and reliability of lead free solder joints. Within the board assembly chapter of the 2007 iNEMI roadmap the technology forecast 4 continues to provide consistent data on the nature of the wave soldering landscape. The issues today continue to be led by the enduring changes in materials and their maturity combined with a significant effort to minimize cost. Alloys containing silver adversely affect cost thus pressuring assembly houses to find alternative cheaper materials. Another pressure is the complexity of board technology. This results in an overall situation where materials are pushed to the limits of their respective specifications in terms of exposure to elevated temperature for extended times. The lead free wave soldering project focused on three critical areas: Materials selection, process optimization and solder joint performance. In order to achieve these goals the project participants developed a two-phase approach. The companies supporting this project during the execution of phase I are Cisco Systems, Cookson Electronics, Delphi Corporation, Foxconn, IBM, ITW Kester, Jabil, Microsoft, Nihon Superior, Plexus, Solectron and Vitronics Soltec. The first phase of the project focused on characterizing processrelated challenges and optimization of a lead free wave soldering process for various factors including: Fluxes, alloys, and board thicknesses. Characterizing the window of opportunity for various materials specifically designed for lead free assembly and its impact on wave soldering process is based on the quantification and analysis of specific defects. The findings provide insight into the optimization of the wave soldering process for given material combinations. Confirmation of the data analysis was achieved by soldering boards utilizing the optimized parameter settings for the respective material combinations. The focus of this latter effort was to provide a data driven solution for the optimized wave soldering process which is an essential part of a robust and reproducible lead free assembly process. The goal of the iNEMI lead free wave project is to ultimately characterize solder joint performance. Phase I provides the optimized settings that result in IPC class 3 acceptable through-hole fill for specific material combinations. Phase II of the project focuses on standardizing the lead free wave assembly process based on the phase I process development and optimization so that only solder joint performance will be evaluated. The intent of phase II is to provide the electronics assembly industry with timely and statistically backed understanding of lead free wave soldered joints. In order to achieve this goal, the team designed and fabricated a test vehicle that aims to understand future assembly requirements and consequently develop new standards and best practices for lead free wave soldering assembly. The board's name is GTLO (Get the lead out!). As shown in figure 1.
ABSTRACT The influence of 1 wt.% Pb, Cu, Ge and Si on the transformation kinetics of the β-Sn→α-S... more ABSTRACT The influence of 1 wt.% Pb, Cu, Ge and Si on the transformation kinetics of the β-Sn→α-Sn transformation in high-purity powder mixtures was examined using synchrotron powder X-ray diffraction. Pb and Cu were found to be effective in suppressing α–tin growth. Ge and Si inhibited the β→α transformation. The kinetics of the transformation are largely determined by the nucleation of α-Sn.
This study aims to investigate the shear and tensile impact strength of solder ball attachments. ... more This study aims to investigate the shear and tensile impact strength of solder ball attachments. Tests were conducted on Ni-doped and non-Ni-doped Sn–0.7wt.% Cu, Sn–37wt.% Pb and Sn–3.0wt.% Ag–0.7wt.% Cu solder ball grid arrays (BGAs) placed on Cu substrates, which were as-reflowed and aged, over a wide range of displacement rates from 10 to 4000mm/s in shear and from 1
It is widely accepted that the intermetallic layer that forms at the interface between a solder a... more It is widely accepted that the intermetallic layer that forms at the interface between a solder and a copper substrate has an effect on the properties of the solder joint, particularly under high strain rates such as occur in drop impact. The nature and extent of the effect is related to the thickness and morphology of this interfacial layer and the phases present in the layer. It has been recognized also that thickness, morphology and mix of phases changes over time as a result of diffusion across the interface in both directions as the solder/substrates system moves toward thermodynamic equilibrium and these process are accelerated at the elevated temperature to which some electronic circuitry is exposed. While the basic composition of the solder obviously has a major effect on the thickness, morphology and growth of the interfacial intermetallic microalloying additions have also been found to have an effect. In this paper the authors report a study of the thickness morphology and...
Lead-free solder alloys, particularly those with higher silver and lower copper contents, have be... more Lead-free solder alloys, particularly those with higher silver and lower copper contents, have been shown to react with the copper on circuit boards, dissolving the copper much more quickly than tin-lead solders. Rapid dissolution of copper into tin-rich alloys can create hidden ...
2014 International Conference on Electronics Packaging (ICEP), 2014
ABSTRACT Tin is the main component of contemporary lead-free solders. Under equilibrium condition... more ABSTRACT Tin is the main component of contemporary lead-free solders. Under equilibrium conditions, tin exists as either a tetragonal β-Sn) or cubic (α-Sn) allotrope at temperatures above and below approximately 13°C, respectively. The transformation from β to α, often referred to as 'tin-pest' is poorly understood, despite the phenomena being documented over 100 years ago. Possibly because the high lead content in traditional solder alloys offers some protection against 'tin-pest', this transformation has not been a priority in solder-related research. With the transition to lead-free solder alloys and the availability of modern analytical techniques there is both an increased need and opportunity to better understand the transformation. This research was conducted to investigate the phase-transformation kinetics of the β to α transformations in high-purity powdered tin using variable temperature synchrotron XRD analysis and electron microscopy. From the results, time-temperature-transformation (TTT) diagrams were developed, with the intention of being used as a baseline for examining the effects of composition in current generation lead-free solders. The effects of pre-exisiting α-Sn and the impurity elements of Pb, Cu, Si and Ge on the β to α transformation kinetics were measured. α-Sn accelerates transformation kinetics, while all other elements tested delayed the transformation.
One of the factors that has contributed to the establishment of the Ni-modified Sn-Cu eutectic as... more One of the factors that has contributed to the establishment of the Ni-modified Sn-Cu eutectic as one of the major alternatives to the widely promoted Sn-Ag-Cu alloys as an RoHS compliant lead-free solder has been its apparent fluidity at temperatures close to its 227°C melting point. This fluidity results in the alloy behaving similarly to lower melting point alloys in which tin dendrites start to freeze out at temperatures higher than the nominal melting point. This in turn has meant that the Ni- modified Sn-Cu eutectic can be used as a wave solder and a HASL alloy at process temperatures not much higher than those that have been used with Sn-37Pb solder. More recently it has been found that this fluidity also permits the use of the alloy in reflow soldering with peak temperatures around 245°C, which is in the middle of the range used with the Sn-Ag-Cu alloys that have a nominal melting point 10°C lower. In a study reported at APEX 2005 it was found that the Ni addition has the ef...
Concern about the failure of lead-free BGA packages when portable devices such as cell phones are... more Concern about the failure of lead-free BGA packages when portable devices such as cell phones are accidentally dropped and a general concern about the resistance of these packages under shock loading has prompted an interest in the impact strength of the soldered BGA connection. This paper reports the results of the measurement of the impact strength of lead-free 0.5±0.01mm diameter BGA spheres on 0.42mm solder mask defined pads on copper/OSP and ENIG substrates using recently developed equipment that can load individual BGA spheres at high strain rates in shear and tension. Impact strength is measured as the energy required to detach the sphere from the substrate to which it has been soldered. Two lead-free solders, Sn-3.0Ag- 0.5Cu and a silver-free Sn-0.7Cu-0.05Ni-0.006Ge were studied with Sn-37Pb included as a benchmark. To study the effect of intermetallic growth on impact strength BGA were tested after up to two reflow cycles and 200 hours ageing at 150°C. BGA were tested in sh...
Abstract To the extent that it provides a potential low energy route for crack propagation the in... more Abstract To the extent that it provides a potential low energy route for crack propagation the intermetallic compound that forms at the interface between a tin-based solder and the substrate can play a critical role in determining the likelihood of joint failure in impact loading such as can ...
2008 33rd IEEE/CPMT International Electronics Manufacturing Technology Conference (IEMT), 2008
... Gregory HenshalL Ph.D. Hewlett-Packard Co. Palo Alto. CA. USA greg. [email protected] Robert He... more ... Gregory HenshalL Ph.D. Hewlett-Packard Co. Palo Alto. CA. USA greg. [email protected] Robert Healey and Ranjit S. Pandher. Ph.D. Cookson Electronics South Plainfield. NJ. USA Keith Sweatman and Keith Howell Nihon Superior Co .. Ltd. Osaka Japan Richard Coyle. ...
The influence of trace level Ni additions on the eutectic solidification mode of Sn–0.7Cu has bee... more The influence of trace level Ni additions on the eutectic solidification mode of Sn–0.7Cu has been studied using continuous torque experiments during solidification. The solid fraction at which resistance to paddle rotation at the thermal centre of the sample occurs is related to the spatial distribution of solid during solidification. The results indicate that a transition in solidification mode occurs
While previous iNEMI projects have focused on lead free joints soldered by the use of convection ... more While previous iNEMI projects have focused on lead free joints soldered by the use of convection reflow ovens, since 2004, only a limited number of comprehensive investigations have taken place 1,2,3 . As a result, the lead free wave soldering project was developed in order to characterize and quantify the impact caused by the transition to lead free solder on the wave process itself as well as the impact on the performance and reliability of lead free solder joints. Within the board assembly chapter of the 2007 iNEMI roadmap the technology forecast 4 continues to provide consistent data on the nature of the wave soldering landscape. The issues today continue to be led by the enduring changes in materials and their maturity combined with a significant effort to minimize cost. Alloys containing silver adversely affect cost thus pressuring assembly houses to find alternative cheaper materials. Another pressure is the complexity of board technology. This results in an overall situation where materials are pushed to the limits of their respective specifications in terms of exposure to elevated temperature for extended times. The lead free wave soldering project focused on three critical areas: Materials selection, process optimization and solder joint performance. In order to achieve these goals the project participants developed a two-phase approach. The companies supporting this project during the execution of phase I are Cisco Systems, Cookson Electronics, Delphi Corporation, Foxconn, IBM, ITW Kester, Jabil, Microsoft, Nihon Superior, Plexus, Solectron and Vitronics Soltec. The first phase of the project focused on characterizing processrelated challenges and optimization of a lead free wave soldering process for various factors including: Fluxes, alloys, and board thicknesses. Characterizing the window of opportunity for various materials specifically designed for lead free assembly and its impact on wave soldering process is based on the quantification and analysis of specific defects. The findings provide insight into the optimization of the wave soldering process for given material combinations. Confirmation of the data analysis was achieved by soldering boards utilizing the optimized parameter settings for the respective material combinations. The focus of this latter effort was to provide a data driven solution for the optimized wave soldering process which is an essential part of a robust and reproducible lead free assembly process. The goal of the iNEMI lead free wave project is to ultimately characterize solder joint performance. Phase I provides the optimized settings that result in IPC class 3 acceptable through-hole fill for specific material combinations. Phase II of the project focuses on standardizing the lead free wave assembly process based on the phase I process development and optimization so that only solder joint performance will be evaluated. The intent of phase II is to provide the electronics assembly industry with timely and statistically backed understanding of lead free wave soldered joints. In order to achieve this goal, the team designed and fabricated a test vehicle that aims to understand future assembly requirements and consequently develop new standards and best practices for lead free wave soldering assembly. The board's name is GTLO (Get the lead out!). As shown in figure 1.
ABSTRACT The influence of 1 wt.% Pb, Cu, Ge and Si on the transformation kinetics of the β-Sn→α-S... more ABSTRACT The influence of 1 wt.% Pb, Cu, Ge and Si on the transformation kinetics of the β-Sn→α-Sn transformation in high-purity powder mixtures was examined using synchrotron powder X-ray diffraction. Pb and Cu were found to be effective in suppressing α–tin growth. Ge and Si inhibited the β→α transformation. The kinetics of the transformation are largely determined by the nucleation of α-Sn.
This study aims to investigate the shear and tensile impact strength of solder ball attachments. ... more This study aims to investigate the shear and tensile impact strength of solder ball attachments. Tests were conducted on Ni-doped and non-Ni-doped Sn–0.7wt.% Cu, Sn–37wt.% Pb and Sn–3.0wt.% Ag–0.7wt.% Cu solder ball grid arrays (BGAs) placed on Cu substrates, which were as-reflowed and aged, over a wide range of displacement rates from 10 to 4000mm/s in shear and from 1
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