A reflow profile is proposed which is engineered to optimize soldering performance based on defec... more A reflow profile is proposed which is engineered to optimize soldering performance based on defect mechanism analysis. In general, a slow ramp‐up rate is desired in order to minimize hot slump, bridging, tombstoning, skewing, wicking, opens, solder beading, solder balling, and components cracking. A minimized soaking zone reduces voiding, poor wetting, solder balling, and opens. Use of a low peak temperature lessens charring, delamination, intermetallics, leaching, dewetting, and voiding. A rapid cooling rate helps to reduce grain size as well as intermetallic growth, charring, leaching and dewetting. However, a slow cooling rate reduces solder or pad detachment. The optimized profile favors that the temperature ramps up slowly until reaching about 180°C. Implementation of the optimized profile requires the support of a heating‐efficient reflow technology with a controllable heating rate. Emergence of the forced air convection reflow provides a controllable heating rate. In addition, it is not sensitive to variation in parts’ features, thus allows the realization of the optimized profile.
Assembled BGA/CSP devices with SnAgCu (SAC) solder joints are vulnerable when dropped due to the ... more Assembled BGA/CSP devices with SnAgCu (SAC) solder joints are vulnerable when dropped due to the fragility of solder joints. Although reducing the Ag content of SAC alloy does help, the crack resistance when dropped is still considerably poorer than the eutectic SnPb system. Therefore a new alloy with improved drop test performance is greatly desired. In this work, SAC105 doped with Ti (SAC105Ti) as a BGA/CSP sphere was studied for its drop test reliability. Four different solder combinations were evaluated: 1) SnPb solder paste with SnPb balls, 2) SnPb solder paste with SAC105Ti balls, 3) SAC305 solder paste with SAC105Ti balls, and 4) SAC305 solder paste with SAC105 balls. The number of completely fractured interconnects was counted for each type of component after a total of 100 drops. The cell with the fewest number of fractured joints was the pure SnPb cell, followed closely by SAC305 solder paste/SAC105Ti ball, then SAC305 solder paste/ SAC105 ball and lastly SnPb solder paste/SAC105Ti ball. This trend is consistent with the trend observed by measuring the electrical resistance. The combination of SAC305 solder paste with SAC105Ti balls was the best solder joint structure tested in terms of the lowest number of partial interconnect fractures and outperformed the other three combinations.
In the current work, a mixed powder BiAgX solder paste system with the melting temperature above ... more In the current work, a mixed powder BiAgX solder paste system with the melting temperature above 260°C and comparable, or better, reliability to the high lead-containing solders has been studied. The mixed powder solder paste system is composed of a high-melting first alloy solder powder as a majority and the additive solder powder as a minority. The additive solder is designed to react preferentially with various surface finish materials before, or together with, the melting of the majority solder to form a controllable IMC layer. The IMC layer of the mixed powder system is controllable by the species and quantity of the additive solder, and it is observed to be insensitive to thermal aging and thermal cycling in current tests, while the high lead-containing solders show a considerable increase in IMC layer thickness. Both micron-sized Ag-rich particles and AgSn phases along the Bi colony boundaries in the joints have been observed. The exposed Ag-rich particles and the surrounding stepwise pattern in the Bi matrix on the fracture surface indicate that these Ag-rich particles constrain the dislocation movement in Bi matrix, and thus enhance the strength and the ductility of the joint.
For SiP or SMT assembly process, solder paste has been the choice of primary soldering material. ... more For SiP or SMT assembly process, solder paste has been the choice of primary soldering material. In the meantime, miniaturization has been the trend of electronic industry. While the size of components, pads, stencil thickness, aperture, pitch, and solder powder has been shrinking continuously so far, it is about time to ask whether the solder paste technology is able to support this trend forever. In this study, solder powder oxygen content was observed to increase linearly with increasing powder surface area up to Type 5. Beyond Type 5, it is getting difficult to maintain oxide thickness. Beyond Type 8, the oxide thickness always higher than Type 5 or coarser. The flux burn-off rate increased linearly with decreasing flux size plotted in log scale. However, for solder paste, the paste residue showed a sharp drop initially with decreasing flux quantity, then levelled off at 3 mg flux (∼30 mg paste), and maintained at around 30% residue through the remaining range down to 0.3 mg flux (∼3 mg paste). The constant residue level at small sample size was attributed to the surface adsorption phenomenon, or “Flux Shell” phenomenon, where a layer of flux was strongly adsorbed on the solder powder surface. For solder paste, the flux workload increased rapidly with decreasing powder size. The flux capacity needed in removing oxide was derived as volume fraction of COOH functional group in flux residue, with 10% maximum being set as a guideline for no-clean applications. Type 8 paste may be the limit of SiP or SMT printable no-clean solder paste due to corrosivity consideration. Oxygen barrier and alloy dopants may expand the miniaturization potential. When reviewing the brittleness of solder joint formed, Type 6 may be the limit of fine pitch applications. Beyond that, the joints may be too brittle to be reliable, unless underfill is applied.
Publisher Summary A flip chip is a chip mounted on the substrate with the chip's active surfa... more Publisher Summary A flip chip is a chip mounted on the substrate with the chip's active surface facing the substrate. The bonding feature on the flip chip includes metal bumping or studding, polymer bumping, a combination of metal and polymer bumping, and metal pads. The conventional flip chip attachment process starts with soldering and is then followed by cleaning and under filling. With increasing demands for lower cost and a higher throughput, many new materials and processes have emerged. This chapter discusses no-flow, a process which provides fluxing, and underfilling, or encapsulation at the same time. Depending on the type of materials used, no-flow can be categorized as a “liquid no-flow” process and “film no-flow” process. The first process starts with dispense liquid no-flow underfill, followed by pick and place flip chip, and ends with the reflow/cure step. The second process starts with the heating of the PCB, then placing of the no-flow underfill film, allowing the underfill film to melt, followed by pick and place flip chip, and ends with the reflow/cure step. In both the processes, at the reflow/cure stage, the underfill removes metal oxides and allows solder to wet to the board pads.
A nano-Cu pressureless sinterable paste was developed for joint formation applications. The mater... more A nano-Cu pressureless sinterable paste was developed for joint formation applications. The material was further engineered in both chemistry and process for enhanced oxidation resistance. This oxidation resistance capability allowed the paste exhibited a shelf life of 6 months when stored at -10°C. The paste was insensitive to either sintering atmosphere or surface finish type, and consistently exhibited a joint shear strength around 13 MPa. Nano-Ag pastes were observed to be sensitive to surface finishes, and performed particularly poorly for OSP-OSP system. The shear strength of nano-Cu was sensitive to sintering temperature and time, with shear strength increased from 220°C/15 min, 220°C/30 min, to 240°C/15 min. The joint shear strength deteriorated with increasing TCT (-40°C/150°C) cycle number. After 3000 cycles, the ranking of shear strength can be shown below: Nano-Cu > Ag-N > Ag-H2 > Ag-H1 > Ag-K > Ag-D. The high Pb joint performed the best. The microstructure of Nano-Cu joint formed at 240°C/15 min sintering condition indicated a continuous sintering progress with increasing TCT cycles, with porosity diminishing and smooth area increasing. This strongly suggests that either a higher temperature or a longer time than 240°C/15 min is desired for improved sintering extent
Driven by RoHS regulation, the world has been migrating toward leadfree soldering since late 1990... more Driven by RoHS regulation, the world has been migrating toward leadfree soldering since late 1990s. In this chapter, the main stream lead-free soldering practice was presented, and the properties of lead-free solder materials and soldering joints, including intermetallic compounds and microstructure evolution, were exemplified and discussed. Furthermore, the major categories of reliability of solder joints, including temperature cycling, fragility, electromigration, and tin whisker, were described and the mechanism was elucidated. Lastly, the trends and status of novel lead-free solder alloys, including low temperature, low cost and high reliability, and high temperature alloys were briefly introduced and reviewed.
Publisher Summary Surface mount technology (SMT) is a revolutionary change in the electronics ind... more Publisher Summary Surface mount technology (SMT) is a revolutionary change in the electronics industries. It enables the electronic industry to progress toward the trends of becoming smaller, lighter, denser, faster, and cheaper. Competing with wave soldering, reflow soldering has become the main stream interconnect technology because of higher yield, throughput, and reliability. Area array packages alleviate pressure on peripheral packages toward finer pitch and provide higher I/O density together with easier manufacturability, smaller package size, and higher speed. The chapter also explains surface mount components (SMC). SMCs are available for almost any type of application, such as capacitors, resistors, transistors, diodes, inductors, ICs, and connectors. However, because of the physical size restriction imposed by the surface mounting process, most SMCs are designed for power dissipation no higher than 1 to 2 W. SMCs can be assembled onto PCBs with the use of solder paste reflow, wave soldering, or conductive adhesive curing processes. The use of conductive adhesive is not common but it can be found in some flexible circuit boards or boards with heat-sensitive components.
Table of contents Chapter 1: Introduction to Environmentally Benign Electronics Manufacturing Cha... more Table of contents Chapter 1: Introduction to Environmentally Benign Electronics Manufacturing Chapter 2: Chip (Wafer)-Level Interconnects with Lead-Free Solder Bumps Chapter 3: WLCSP with Lead-Free Solder Bumps on PCB/Substrate Chapter 4: Chip (Wafer)-Level Interconnects with Solderless Bumps Chapter 5: WLCSP with Solderless Bumps on PCB/Substrate Chapter 6: Environmentally Benign Molding Compounds for IC Packages Chapter 7: Environmentally Benign Die Attach Films for IC Packaging Chapter 8: Environmental Issues for Conventional PCBs Chapter 9: Halogenated and Halogen-Free Materials for Flame Retardation Chapter 10: Fabrication of Environmentally Friendly PCB Chapter 11: Global Status of Lead-Free Soldering Chapter 12: Development of Lead-Free Solder Alloys Chapter 13: Prevailing Lead-Free Alloys Chapter 14: Lead-Free Surface Finishes Chapter 15: Implementation of Lead-Free Soldering Chapter 16: Challenges for Lead-Free Soldering Chapter 17: Introduction to Conductive Adhesives Chapter 18: Conductivity Establishment of Conductive Adhesives Chapter 19: Mechanisms Underlying the Unstable Contact Resistance of ECAs Chapter 20: Stabilization of Contact Resistance of Conductive Adhesives Index About the Author
Development of high-temperature lead-free (HTLF) solders to replace high-lead solders for die-att... more Development of high-temperature lead-free (HTLF) solders to replace high-lead solders for die-attachment in power device applications is driven by (1) the harmful effects of lead to human health and the environment, and (2) the demand of the improved bonding materials serving under high-power density and high-junction temperatures, especially for wide-band-gap power devices. A novel design, based on a mixed solder powder paste technology—Durafuse™—has been developed to deliver a Sn-rich HTLF paste, presenting the merits of both constituent powders. The combination of the rigid, high-melting SnSbCuAgX and the ductile, low-temperature Sn-rich solder in one paste enables reflow at a relatively low temperature (barely above the liquidus temperature of the final joint composition) and maintains the joint strength above 15MPa in the temperature range between 270°C and 295°C. The sufficient high-temperature strength has demonstrated the capability of maintaining the joint integrity during ...
2019 IEEE 69th Electronic Components and Technology Conference (ECTC), 2019
Pressure-less silver sintering pastes with high-reliability judged from temperature cycling test ... more Pressure-less silver sintering pastes with high-reliability judged from temperature cycling test (TCT) under -40°C to 175°C were developed. For 3mm x 3mm sized dies, the silver joints formed between the Ag surface finished Si die and the Ag surface finished Si3N4 active metal brazing (AMB) substrate retained the initial shear strength after 1500 cycles, the strength being ~25 Mpa even after 3879 cycles. For 5mm x 5mm dies, the average shear strength was very stable and remained at ~42 Mpa, even after 3879 cycles. For 10mm x 10mm dies, the dies cannot be sheared off (max shear force 200kg) for all the samples before and after 2389 cycles of TCT. Within a standard bondline thickness (BLT) range of 40 to 60µm, the average total voids percentage of the sintered joints for the above different die sizes can be controlled within < 2%. Under ambient atmosphere, the shear strength of sintered joints formed on a bare Cu surface finished AMB substrate reach 62Mpa, slightly stronger than that of Ag-and Au-surface finished ones. TCT shows that these surface finishes have similar decay behaviors, implying that bare Cu surface finished AMB substrate can be used for bonding applications. BLT is critical in determining the bond property and reliability. For a very thin BLT, such as < 10µm, the bond strength decays at about five times the rate that of a joint with ~ 50µm BLT. For a thick BLT, such as > 100 µm with 10mm x 10mm dies, a large amount of voids are generated if using a similar sintering profile, where almost no voids are observed for a ~50 µm BLT joint.
Reliability engineering consists of three major tasks [1–14], namely, design for reliability (DFR... more Reliability engineering consists of three major tasks [1–14], namely, design for reliability (DFR), reliability testing and data analysis, and failure analysis, as schematically shown in Fig. 6.1. Usually, the procedure starts with a design of the interconnects of a particular semiconductor IC (integrated circuit) package with, e.g., the given chip size, the solder alloys, the molding compound, and the corresponding PCB (printed circuit board) and demonstrates that the design is electrically, thermally, mechanically, and chemically sound. As an example, the DFR activity is often performed with a finite-element simulation using the structural geometry, material properties of all the structural elements and the imposed boundary conditions. The next step in the process is for a certain number of samples of the sound or reliable design to be built and tested under certain conditions for a certain period of time. The test data (failures) then are analyzed and fitted into a life-distribut...
Assembly and reliability of lead-free solder joints are very important topics in electronic manuf... more Assembly and reliability of lead-free solder joints are very important topics in electronic manufacturing. There are many books [1–69] and papers [70–315] written on them. In this book, the assembly of lead-free solder joints such as prevailing lead-free materials, soldering processes, advanced specialty flux design, and characterization of lead-free solder joints will be discussed, respectively in Chaps. 2– 5. The reliability of lead-free solder joints such as reliability testing and data analyses, design for reliability, and failure analyses of lead-free solder joints will be discussed, respectively in Chaps. 6– 8. The special features of this book are the materials covered are not only for electronic manufacturing services (EMS) on the second-level interconnects, but also for packaging assembly on the first-level interconnects and for the semiconductor back-end on the 2.5D and 3D IC integration interconnects as shown in Fig. 1.1. The solder joints in various plated-through hole (...
A reflow profile is proposed which is engineered to optimize soldering performance based on defec... more A reflow profile is proposed which is engineered to optimize soldering performance based on defect mechanism analysis. In general, a slow ramp‐up rate is desired in order to minimize hot slump, bridging, tombstoning, skewing, wicking, opens, solder beading, solder balling, and components cracking. A minimized soaking zone reduces voiding, poor wetting, solder balling, and opens. Use of a low peak temperature lessens charring, delamination, intermetallics, leaching, dewetting, and voiding. A rapid cooling rate helps to reduce grain size as well as intermetallic growth, charring, leaching and dewetting. However, a slow cooling rate reduces solder or pad detachment. The optimized profile favors that the temperature ramps up slowly until reaching about 180°C. Implementation of the optimized profile requires the support of a heating‐efficient reflow technology with a controllable heating rate. Emergence of the forced air convection reflow provides a controllable heating rate. In addition, it is not sensitive to variation in parts’ features, thus allows the realization of the optimized profile.
Assembled BGA/CSP devices with SnAgCu (SAC) solder joints are vulnerable when dropped due to the ... more Assembled BGA/CSP devices with SnAgCu (SAC) solder joints are vulnerable when dropped due to the fragility of solder joints. Although reducing the Ag content of SAC alloy does help, the crack resistance when dropped is still considerably poorer than the eutectic SnPb system. Therefore a new alloy with improved drop test performance is greatly desired. In this work, SAC105 doped with Ti (SAC105Ti) as a BGA/CSP sphere was studied for its drop test reliability. Four different solder combinations were evaluated: 1) SnPb solder paste with SnPb balls, 2) SnPb solder paste with SAC105Ti balls, 3) SAC305 solder paste with SAC105Ti balls, and 4) SAC305 solder paste with SAC105 balls. The number of completely fractured interconnects was counted for each type of component after a total of 100 drops. The cell with the fewest number of fractured joints was the pure SnPb cell, followed closely by SAC305 solder paste/SAC105Ti ball, then SAC305 solder paste/ SAC105 ball and lastly SnPb solder paste/SAC105Ti ball. This trend is consistent with the trend observed by measuring the electrical resistance. The combination of SAC305 solder paste with SAC105Ti balls was the best solder joint structure tested in terms of the lowest number of partial interconnect fractures and outperformed the other three combinations.
In the current work, a mixed powder BiAgX solder paste system with the melting temperature above ... more In the current work, a mixed powder BiAgX solder paste system with the melting temperature above 260°C and comparable, or better, reliability to the high lead-containing solders has been studied. The mixed powder solder paste system is composed of a high-melting first alloy solder powder as a majority and the additive solder powder as a minority. The additive solder is designed to react preferentially with various surface finish materials before, or together with, the melting of the majority solder to form a controllable IMC layer. The IMC layer of the mixed powder system is controllable by the species and quantity of the additive solder, and it is observed to be insensitive to thermal aging and thermal cycling in current tests, while the high lead-containing solders show a considerable increase in IMC layer thickness. Both micron-sized Ag-rich particles and AgSn phases along the Bi colony boundaries in the joints have been observed. The exposed Ag-rich particles and the surrounding stepwise pattern in the Bi matrix on the fracture surface indicate that these Ag-rich particles constrain the dislocation movement in Bi matrix, and thus enhance the strength and the ductility of the joint.
For SiP or SMT assembly process, solder paste has been the choice of primary soldering material. ... more For SiP or SMT assembly process, solder paste has been the choice of primary soldering material. In the meantime, miniaturization has been the trend of electronic industry. While the size of components, pads, stencil thickness, aperture, pitch, and solder powder has been shrinking continuously so far, it is about time to ask whether the solder paste technology is able to support this trend forever. In this study, solder powder oxygen content was observed to increase linearly with increasing powder surface area up to Type 5. Beyond Type 5, it is getting difficult to maintain oxide thickness. Beyond Type 8, the oxide thickness always higher than Type 5 or coarser. The flux burn-off rate increased linearly with decreasing flux size plotted in log scale. However, for solder paste, the paste residue showed a sharp drop initially with decreasing flux quantity, then levelled off at 3 mg flux (∼30 mg paste), and maintained at around 30% residue through the remaining range down to 0.3 mg flux (∼3 mg paste). The constant residue level at small sample size was attributed to the surface adsorption phenomenon, or “Flux Shell” phenomenon, where a layer of flux was strongly adsorbed on the solder powder surface. For solder paste, the flux workload increased rapidly with decreasing powder size. The flux capacity needed in removing oxide was derived as volume fraction of COOH functional group in flux residue, with 10% maximum being set as a guideline for no-clean applications. Type 8 paste may be the limit of SiP or SMT printable no-clean solder paste due to corrosivity consideration. Oxygen barrier and alloy dopants may expand the miniaturization potential. When reviewing the brittleness of solder joint formed, Type 6 may be the limit of fine pitch applications. Beyond that, the joints may be too brittle to be reliable, unless underfill is applied.
Publisher Summary A flip chip is a chip mounted on the substrate with the chip's active surfa... more Publisher Summary A flip chip is a chip mounted on the substrate with the chip's active surface facing the substrate. The bonding feature on the flip chip includes metal bumping or studding, polymer bumping, a combination of metal and polymer bumping, and metal pads. The conventional flip chip attachment process starts with soldering and is then followed by cleaning and under filling. With increasing demands for lower cost and a higher throughput, many new materials and processes have emerged. This chapter discusses no-flow, a process which provides fluxing, and underfilling, or encapsulation at the same time. Depending on the type of materials used, no-flow can be categorized as a “liquid no-flow” process and “film no-flow” process. The first process starts with dispense liquid no-flow underfill, followed by pick and place flip chip, and ends with the reflow/cure step. The second process starts with the heating of the PCB, then placing of the no-flow underfill film, allowing the underfill film to melt, followed by pick and place flip chip, and ends with the reflow/cure step. In both the processes, at the reflow/cure stage, the underfill removes metal oxides and allows solder to wet to the board pads.
A nano-Cu pressureless sinterable paste was developed for joint formation applications. The mater... more A nano-Cu pressureless sinterable paste was developed for joint formation applications. The material was further engineered in both chemistry and process for enhanced oxidation resistance. This oxidation resistance capability allowed the paste exhibited a shelf life of 6 months when stored at -10°C. The paste was insensitive to either sintering atmosphere or surface finish type, and consistently exhibited a joint shear strength around 13 MPa. Nano-Ag pastes were observed to be sensitive to surface finishes, and performed particularly poorly for OSP-OSP system. The shear strength of nano-Cu was sensitive to sintering temperature and time, with shear strength increased from 220°C/15 min, 220°C/30 min, to 240°C/15 min. The joint shear strength deteriorated with increasing TCT (-40°C/150°C) cycle number. After 3000 cycles, the ranking of shear strength can be shown below: Nano-Cu > Ag-N > Ag-H2 > Ag-H1 > Ag-K > Ag-D. The high Pb joint performed the best. The microstructure of Nano-Cu joint formed at 240°C/15 min sintering condition indicated a continuous sintering progress with increasing TCT cycles, with porosity diminishing and smooth area increasing. This strongly suggests that either a higher temperature or a longer time than 240°C/15 min is desired for improved sintering extent
Driven by RoHS regulation, the world has been migrating toward leadfree soldering since late 1990... more Driven by RoHS regulation, the world has been migrating toward leadfree soldering since late 1990s. In this chapter, the main stream lead-free soldering practice was presented, and the properties of lead-free solder materials and soldering joints, including intermetallic compounds and microstructure evolution, were exemplified and discussed. Furthermore, the major categories of reliability of solder joints, including temperature cycling, fragility, electromigration, and tin whisker, were described and the mechanism was elucidated. Lastly, the trends and status of novel lead-free solder alloys, including low temperature, low cost and high reliability, and high temperature alloys were briefly introduced and reviewed.
Publisher Summary Surface mount technology (SMT) is a revolutionary change in the electronics ind... more Publisher Summary Surface mount technology (SMT) is a revolutionary change in the electronics industries. It enables the electronic industry to progress toward the trends of becoming smaller, lighter, denser, faster, and cheaper. Competing with wave soldering, reflow soldering has become the main stream interconnect technology because of higher yield, throughput, and reliability. Area array packages alleviate pressure on peripheral packages toward finer pitch and provide higher I/O density together with easier manufacturability, smaller package size, and higher speed. The chapter also explains surface mount components (SMC). SMCs are available for almost any type of application, such as capacitors, resistors, transistors, diodes, inductors, ICs, and connectors. However, because of the physical size restriction imposed by the surface mounting process, most SMCs are designed for power dissipation no higher than 1 to 2 W. SMCs can be assembled onto PCBs with the use of solder paste reflow, wave soldering, or conductive adhesive curing processes. The use of conductive adhesive is not common but it can be found in some flexible circuit boards or boards with heat-sensitive components.
Table of contents Chapter 1: Introduction to Environmentally Benign Electronics Manufacturing Cha... more Table of contents Chapter 1: Introduction to Environmentally Benign Electronics Manufacturing Chapter 2: Chip (Wafer)-Level Interconnects with Lead-Free Solder Bumps Chapter 3: WLCSP with Lead-Free Solder Bumps on PCB/Substrate Chapter 4: Chip (Wafer)-Level Interconnects with Solderless Bumps Chapter 5: WLCSP with Solderless Bumps on PCB/Substrate Chapter 6: Environmentally Benign Molding Compounds for IC Packages Chapter 7: Environmentally Benign Die Attach Films for IC Packaging Chapter 8: Environmental Issues for Conventional PCBs Chapter 9: Halogenated and Halogen-Free Materials for Flame Retardation Chapter 10: Fabrication of Environmentally Friendly PCB Chapter 11: Global Status of Lead-Free Soldering Chapter 12: Development of Lead-Free Solder Alloys Chapter 13: Prevailing Lead-Free Alloys Chapter 14: Lead-Free Surface Finishes Chapter 15: Implementation of Lead-Free Soldering Chapter 16: Challenges for Lead-Free Soldering Chapter 17: Introduction to Conductive Adhesives Chapter 18: Conductivity Establishment of Conductive Adhesives Chapter 19: Mechanisms Underlying the Unstable Contact Resistance of ECAs Chapter 20: Stabilization of Contact Resistance of Conductive Adhesives Index About the Author
Development of high-temperature lead-free (HTLF) solders to replace high-lead solders for die-att... more Development of high-temperature lead-free (HTLF) solders to replace high-lead solders for die-attachment in power device applications is driven by (1) the harmful effects of lead to human health and the environment, and (2) the demand of the improved bonding materials serving under high-power density and high-junction temperatures, especially for wide-band-gap power devices. A novel design, based on a mixed solder powder paste technology—Durafuse™—has been developed to deliver a Sn-rich HTLF paste, presenting the merits of both constituent powders. The combination of the rigid, high-melting SnSbCuAgX and the ductile, low-temperature Sn-rich solder in one paste enables reflow at a relatively low temperature (barely above the liquidus temperature of the final joint composition) and maintains the joint strength above 15MPa in the temperature range between 270°C and 295°C. The sufficient high-temperature strength has demonstrated the capability of maintaining the joint integrity during ...
2019 IEEE 69th Electronic Components and Technology Conference (ECTC), 2019
Pressure-less silver sintering pastes with high-reliability judged from temperature cycling test ... more Pressure-less silver sintering pastes with high-reliability judged from temperature cycling test (TCT) under -40°C to 175°C were developed. For 3mm x 3mm sized dies, the silver joints formed between the Ag surface finished Si die and the Ag surface finished Si3N4 active metal brazing (AMB) substrate retained the initial shear strength after 1500 cycles, the strength being ~25 Mpa even after 3879 cycles. For 5mm x 5mm dies, the average shear strength was very stable and remained at ~42 Mpa, even after 3879 cycles. For 10mm x 10mm dies, the dies cannot be sheared off (max shear force 200kg) for all the samples before and after 2389 cycles of TCT. Within a standard bondline thickness (BLT) range of 40 to 60µm, the average total voids percentage of the sintered joints for the above different die sizes can be controlled within < 2%. Under ambient atmosphere, the shear strength of sintered joints formed on a bare Cu surface finished AMB substrate reach 62Mpa, slightly stronger than that of Ag-and Au-surface finished ones. TCT shows that these surface finishes have similar decay behaviors, implying that bare Cu surface finished AMB substrate can be used for bonding applications. BLT is critical in determining the bond property and reliability. For a very thin BLT, such as < 10µm, the bond strength decays at about five times the rate that of a joint with ~ 50µm BLT. For a thick BLT, such as > 100 µm with 10mm x 10mm dies, a large amount of voids are generated if using a similar sintering profile, where almost no voids are observed for a ~50 µm BLT joint.
Reliability engineering consists of three major tasks [1–14], namely, design for reliability (DFR... more Reliability engineering consists of three major tasks [1–14], namely, design for reliability (DFR), reliability testing and data analysis, and failure analysis, as schematically shown in Fig. 6.1. Usually, the procedure starts with a design of the interconnects of a particular semiconductor IC (integrated circuit) package with, e.g., the given chip size, the solder alloys, the molding compound, and the corresponding PCB (printed circuit board) and demonstrates that the design is electrically, thermally, mechanically, and chemically sound. As an example, the DFR activity is often performed with a finite-element simulation using the structural geometry, material properties of all the structural elements and the imposed boundary conditions. The next step in the process is for a certain number of samples of the sound or reliable design to be built and tested under certain conditions for a certain period of time. The test data (failures) then are analyzed and fitted into a life-distribut...
Assembly and reliability of lead-free solder joints are very important topics in electronic manuf... more Assembly and reliability of lead-free solder joints are very important topics in electronic manufacturing. There are many books [1–69] and papers [70–315] written on them. In this book, the assembly of lead-free solder joints such as prevailing lead-free materials, soldering processes, advanced specialty flux design, and characterization of lead-free solder joints will be discussed, respectively in Chaps. 2– 5. The reliability of lead-free solder joints such as reliability testing and data analyses, design for reliability, and failure analyses of lead-free solder joints will be discussed, respectively in Chaps. 6– 8. The special features of this book are the materials covered are not only for electronic manufacturing services (EMS) on the second-level interconnects, but also for packaging assembly on the first-level interconnects and for the semiconductor back-end on the 2.5D and 3D IC integration interconnects as shown in Fig. 1.1. The solder joints in various plated-through hole (...
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