Electroplated Ni/Au over Cu is a popular metallization for PCB finish as well as for component le... more Electroplated Ni/Au over Cu is a popular metallization for PCB finish as well as for component leads, especially wirebondable high frequency packages, where the gold thickness requirement for wire bonding is high. The general understanding is that less than 3 wt% of Au is acceptable in SnPb solder joints. However, little is known about the effect of Au content on the reliability of SnAgCu solder joints. The purpose of this study is to determine the acceptable level of Au in SAC305 solder joints. Three different package platforms with different Au thicknesses were assembled on boards with two different Au thicknesses using a standard surface mount assembly line in a realistic production environment. The assembled boards were divided into three groups: as-built, isothermally aged at 125°C for 30 days, and isothermally aged at 125°C for 56 days. All boards were then subjected to accelerated mechanical reliability tests including random vibration and drop testing. The results show that ...
ABSTRACT A team of engineering students at the University of California Davis collaborated on a d... more ABSTRACT A team of engineering students at the University of California Davis collaborated on a design project investigation to develop a cost effective process for Pb-free solder assembly of a printed circuit based RF multi-chip module (MCM) employed in test and measurement instruments. The students considered the required materials properties, as dictated by the component assembly design, and how the properties are affected by materials selection and the joining process. The team conducted solder joint strength and wetting experiments at UC Davis in order to evaluate the process design. The team also conducted process development, including furnace profiling and reliability testing, at Agilent facilities in Santa Rosa, California. Through applied research and testing the student team developed a reliable Pb-free process for solder assembly of the MCM project vehicle.
Accreditation criteria and employer expectations increasingly require that engineering students o... more Accreditation criteria and employer expectations increasingly require that engineering students obtain “real world” design experience before graduation. To enhance this experience for Materials Science and Engineering majors at the University of California, Davis, the Department of Chemical Engineering and Materials Science offers a senior design course called Materials in Engineering Design (EMS 188). The central feature of the course is a collaborative design project that is taught jointly by a department professor and an engineer from industry. During the 2006-2007 school year, students worked together as a team to define, justify and develop a cost effective production process for a trivalent (Cr3+) chromate conversion coating (CCC) process to replace the hexavalent (Cr6+) CCC process traditionally employed for aluminum alloy EMI shields, waveguides and other aluminum components used in high frequency test and measurement instrumentation applications (a “real” project of technic...
This paper, originally presented at IPC APEX EXPO 2012, reports on a comprehensive study regardin... more This paper, originally presented at IPC APEX EXPO 2012, reports on a comprehensive study regarding the morphology evolution and voiding of SnAgCu solder joints on the central pad of two different packages - QFN and an Agilent package called TOPS - on PCBs with a Ni/Au surface finish. Samples were isothermally aged and representative solder joints were cross-sectioned and analyzed using SEM and EDX spectroscopy to investigate the evolution of the solder joint morphology as a function of Au content and isothermal aging.
Test and Measurement (T&M) products represent a very high performance subset of the monitoring an... more Test and Measurement (T&M) products represent a very high performance subset of the monitoring and control product category. These products are characterized by highly sensitive electrical systems that must perform at levels well beyond the conventional products they test. This is an investigation to define and develop a cost effective production process for application of a trivalent (Cr3+) chromate conversion coating to replace the hexavalent (Cr6+) chromate conversion coating that has traditionally been employed for aluminum alloy shields, waveguides and other aluminum components used in high frequency T&M instruments. Testing and characterization included surface contact resistance, corrosion resistance, paint adhesion and XRay Photoelectron Spectroscopy. It was found that several trivalent chromate conversion coating products demonstrate electrical performance and corrosion resistance that is essentially equivalent to the traditional Cr6+ chromate conversion coating, while miti...
Alloyed Ohmic contacts in GaAs-AlGaAs-InGaAs pHEMTs fabricated by sequential e-beam evaporation o... more Alloyed Ohmic contacts in GaAs-AlGaAs-InGaAs pHEMTs fabricated by sequential e-beam evaporation of Au-Ni-AuGe metallization layers can sporadically suffer from lateral diffusion anomalies, referred to here as "ohmic runout." This investigation studied the influence of Au to Ge compositional ratio and Ni content on the alloyed ohmic runout behavior. It was found that the degree of ohmic runout is critically sensitive to the volume fraction of Ni in the metallization stack and that decreasing the Ni content mitigated ohmic runout without compromising the alloyed ohmic contact resistance.
A team of engineering students in the Department of Chemical Engineering and Materials Science at... more A team of engineering students in the Department of Chemical Engineering and Materials Science at the University of California Davis collaborated on a design project investigation to develop a cost effective process for Pb-free solder assembly of hybrid microcircuit package assemblies employed in test and measurement instruments (a "real" materials design project). The students considered the required materials properties, as dictated by the component assembly design, and how the properties are affected by materials selection and the joining process. The team conducted solder joint strength, Au embrittlement and solder wetting experiments at UC Davis in order to evaluate the process design. The team also conducted process development, including furnace profiling and reliability testing, at Agilent facilities in Santa Rosa, California. Through applied research and testing the student team developed a reliable Pb-free process for solder assembly of the hybrid microcircuit pa...
Au over Ni on Cu is a widely used printed circuit board (PCB) surface finish, under bump metalliz... more Au over Ni on Cu is a widely used printed circuit board (PCB) surface finish, under bump metallization (UBM), and component lead metallization. It is generally accepted that less than 3 wt.% Au in Sn-Pb solder joints inhibits formation of detrimental intermetallic ...
This paper describes a process which uses a multilayered reactive foil to solder gold coated stai... more This paper describes a process which uses a multilayered reactive foil to solder gold coated stainless steel connectors to Rogers PCB at room temperature. The technology is based on a reactive foil comprised of thousands of nanoscale layers that alternate between Al and Ni. After being initiated with a small electrical or thermal stimulus, the reactive foil acts as a local heat source, melting solder on either side of the foil and bonding the two components without exposing them to high temperatures. The use of reactive joining allows for the bonding of the connector at any point during the population of the board at room temperature and without flux. The reactive foil also allows for the replacement of Pb-Sn solder, used previously, with Au-Sn solder. This enables the joint to undergo subsequent reflow steps without any degradation in bond strength. We optimized the reactive bond with regards to reactive foil properties and joining pressure. Numerical simulations were used to estimate the thermal exposure of the components during bonding and melting duration of the solder. Results of mechanical and environmental testing of these components are also presented.
ABSTRACT Hermetic sealing of microelectronic packages was performed using a room temperature, flu... more ABSTRACT Hermetic sealing of microelectronic packages was performed using a room temperature, flux-free soldering process that is based on the use of a reactive multilayer foil as a local heat source. The multilayer foil consists of thousands of alternating nanoscale layers comprised of elements with large negative heats of mixing, such as Al and Ni. The foil is sandwiched between free standing sheets of solder and the assembly positioned between the package housing and lid. A self-propagating reaction within the foil is then initiated using a small thermal or electrical pulse. Heat generated by the reaction melts the solder preforms on either side of the foil and consequently bonds the components. This process is completed within a few milliseconds and results in a solder based hermetic seal between the base and the lid. Reactive multilayer joining is shown to be a viable alternative to laser welding and reflow soldering for hermetic sealing of hybrid microelectronic packages.
Page 125. Proceedings of the 3 International Brazing and Soldering Conference, April 24–26, 2006,... more Page 125. Proceedings of the 3 International Brazing and Soldering Conference, April 24–26, 2006, Crowne Plaza Riverwalk Hotel, San Antonio, Texas, USA rd Hermetic Glass-to-Aluminum Seals for RF Packaging Applications ...
ABSTRACT This paper describes a process which uses a multilayered reactive foil to hermetically s... more ABSTRACT This paper describes a process which uses a multilayered reactive foil to hermetically seal microelectronic packages. The foil is comprised of thousands of nanoscale layers of elements with large negative heats of mixing, such as Al and Ni. When the reaction is activated in the foil using a small electrical or thermal stimulus, the heat generated melts the adjoining solder layers and permanently joins the package lid to the base. The seal is achieved without exposing the components to high reflow temperature. RNT has used this process to create a hermetic seal between an Au-plated stainless steel lid and Au-plated stainless steel base. We show that helium leak rates of less than 1 x 10-10 atm-cc/sec can be achieved by using this method. This process provides an attractive alternative to more expensive methods such as laser welding and eliminates the need for costly fabrication equipment.
ABSTRACT Micro fabrication is generally confined to silicon-based processes for microelectronic a... more ABSTRACT Micro fabrication is generally confined to silicon-based processes for microelectronic applications. The advent of micro electromechanical systems (MEMS) using silicon and silicon based processes has opened up a new basis for micro fabrication technology, but the applications have been limited due to the brittle nature of silicon. Novel technologies have been sought for non-silicon micro components and systems. The electrochemical micro machining (μECM) is standing out among other solutions. An international group comprised of industry and academic institutes in Mexico and USA was formed to provide synergistic effort in developing this new technology. The funding came from the involved companies, National Science Foundation, National Consortium of Science and Technology (CONACyT, Mexico), and Texas A&M University. Both graduate and undergraduate students are involved in this research and educational project. Some research objectives have been achieved by dividing an objective into manageable laboratory projects that can be completed by undergraduate students in a few weeks. The anodic dissolution μECM process effectively forms and shapes micro components from any conductive material. Unlike classical ECM technology, the novel μECM utilizes very high frequency pulses and proprietary electrode shapes/motions to remove materials at the micro or nano scales, and can mass-produce micro components with exceptional quality and surface integrity. A theoretical model is developed which agrees with experimental data for 316L stainless steel and copper beryllium alloy. The environmentally friendly technology shows promise as a high-resolution production manufacturing process with excellent throughput and repeatability.
Electroplated Ni/Au over Cu is a popular metallization for PCB finish as well as for component le... more Electroplated Ni/Au over Cu is a popular metallization for PCB finish as well as for component leads, especially wirebondable high frequency packages, where the gold thickness requirement for wire bonding is high. The general understanding is that less than 3 wt% of Au is acceptable in SnPb solder joints. However, little is known about the effect of Au content on the reliability of SnAgCu solder joints. The purpose of this study is to determine the acceptable level of Au in SAC305 solder joints. Three different package platforms with different Au thicknesses were assembled on boards with two different Au thicknesses using a standard surface mount assembly line in a realistic production environment. The assembled boards were divided into three groups: as-built, isothermally aged at 125°C for 30 days, and isothermally aged at 125°C for 56 days. All boards were then subjected to accelerated mechanical reliability tests including random vibration and drop testing. The results show that ...
ABSTRACT A team of engineering students at the University of California Davis collaborated on a d... more ABSTRACT A team of engineering students at the University of California Davis collaborated on a design project investigation to develop a cost effective process for Pb-free solder assembly of a printed circuit based RF multi-chip module (MCM) employed in test and measurement instruments. The students considered the required materials properties, as dictated by the component assembly design, and how the properties are affected by materials selection and the joining process. The team conducted solder joint strength and wetting experiments at UC Davis in order to evaluate the process design. The team also conducted process development, including furnace profiling and reliability testing, at Agilent facilities in Santa Rosa, California. Through applied research and testing the student team developed a reliable Pb-free process for solder assembly of the MCM project vehicle.
Accreditation criteria and employer expectations increasingly require that engineering students o... more Accreditation criteria and employer expectations increasingly require that engineering students obtain “real world” design experience before graduation. To enhance this experience for Materials Science and Engineering majors at the University of California, Davis, the Department of Chemical Engineering and Materials Science offers a senior design course called Materials in Engineering Design (EMS 188). The central feature of the course is a collaborative design project that is taught jointly by a department professor and an engineer from industry. During the 2006-2007 school year, students worked together as a team to define, justify and develop a cost effective production process for a trivalent (Cr3+) chromate conversion coating (CCC) process to replace the hexavalent (Cr6+) CCC process traditionally employed for aluminum alloy EMI shields, waveguides and other aluminum components used in high frequency test and measurement instrumentation applications (a “real” project of technic...
This paper, originally presented at IPC APEX EXPO 2012, reports on a comprehensive study regardin... more This paper, originally presented at IPC APEX EXPO 2012, reports on a comprehensive study regarding the morphology evolution and voiding of SnAgCu solder joints on the central pad of two different packages - QFN and an Agilent package called TOPS - on PCBs with a Ni/Au surface finish. Samples were isothermally aged and representative solder joints were cross-sectioned and analyzed using SEM and EDX spectroscopy to investigate the evolution of the solder joint morphology as a function of Au content and isothermal aging.
Test and Measurement (T&M) products represent a very high performance subset of the monitoring an... more Test and Measurement (T&M) products represent a very high performance subset of the monitoring and control product category. These products are characterized by highly sensitive electrical systems that must perform at levels well beyond the conventional products they test. This is an investigation to define and develop a cost effective production process for application of a trivalent (Cr3+) chromate conversion coating to replace the hexavalent (Cr6+) chromate conversion coating that has traditionally been employed for aluminum alloy shields, waveguides and other aluminum components used in high frequency T&M instruments. Testing and characterization included surface contact resistance, corrosion resistance, paint adhesion and XRay Photoelectron Spectroscopy. It was found that several trivalent chromate conversion coating products demonstrate electrical performance and corrosion resistance that is essentially equivalent to the traditional Cr6+ chromate conversion coating, while miti...
Alloyed Ohmic contacts in GaAs-AlGaAs-InGaAs pHEMTs fabricated by sequential e-beam evaporation o... more Alloyed Ohmic contacts in GaAs-AlGaAs-InGaAs pHEMTs fabricated by sequential e-beam evaporation of Au-Ni-AuGe metallization layers can sporadically suffer from lateral diffusion anomalies, referred to here as "ohmic runout." This investigation studied the influence of Au to Ge compositional ratio and Ni content on the alloyed ohmic runout behavior. It was found that the degree of ohmic runout is critically sensitive to the volume fraction of Ni in the metallization stack and that decreasing the Ni content mitigated ohmic runout without compromising the alloyed ohmic contact resistance.
A team of engineering students in the Department of Chemical Engineering and Materials Science at... more A team of engineering students in the Department of Chemical Engineering and Materials Science at the University of California Davis collaborated on a design project investigation to develop a cost effective process for Pb-free solder assembly of hybrid microcircuit package assemblies employed in test and measurement instruments (a "real" materials design project). The students considered the required materials properties, as dictated by the component assembly design, and how the properties are affected by materials selection and the joining process. The team conducted solder joint strength, Au embrittlement and solder wetting experiments at UC Davis in order to evaluate the process design. The team also conducted process development, including furnace profiling and reliability testing, at Agilent facilities in Santa Rosa, California. Through applied research and testing the student team developed a reliable Pb-free process for solder assembly of the hybrid microcircuit pa...
Au over Ni on Cu is a widely used printed circuit board (PCB) surface finish, under bump metalliz... more Au over Ni on Cu is a widely used printed circuit board (PCB) surface finish, under bump metallization (UBM), and component lead metallization. It is generally accepted that less than 3 wt.% Au in Sn-Pb solder joints inhibits formation of detrimental intermetallic ...
This paper describes a process which uses a multilayered reactive foil to solder gold coated stai... more This paper describes a process which uses a multilayered reactive foil to solder gold coated stainless steel connectors to Rogers PCB at room temperature. The technology is based on a reactive foil comprised of thousands of nanoscale layers that alternate between Al and Ni. After being initiated with a small electrical or thermal stimulus, the reactive foil acts as a local heat source, melting solder on either side of the foil and bonding the two components without exposing them to high temperatures. The use of reactive joining allows for the bonding of the connector at any point during the population of the board at room temperature and without flux. The reactive foil also allows for the replacement of Pb-Sn solder, used previously, with Au-Sn solder. This enables the joint to undergo subsequent reflow steps without any degradation in bond strength. We optimized the reactive bond with regards to reactive foil properties and joining pressure. Numerical simulations were used to estimate the thermal exposure of the components during bonding and melting duration of the solder. Results of mechanical and environmental testing of these components are also presented.
ABSTRACT Hermetic sealing of microelectronic packages was performed using a room temperature, flu... more ABSTRACT Hermetic sealing of microelectronic packages was performed using a room temperature, flux-free soldering process that is based on the use of a reactive multilayer foil as a local heat source. The multilayer foil consists of thousands of alternating nanoscale layers comprised of elements with large negative heats of mixing, such as Al and Ni. The foil is sandwiched between free standing sheets of solder and the assembly positioned between the package housing and lid. A self-propagating reaction within the foil is then initiated using a small thermal or electrical pulse. Heat generated by the reaction melts the solder preforms on either side of the foil and consequently bonds the components. This process is completed within a few milliseconds and results in a solder based hermetic seal between the base and the lid. Reactive multilayer joining is shown to be a viable alternative to laser welding and reflow soldering for hermetic sealing of hybrid microelectronic packages.
Page 125. Proceedings of the 3 International Brazing and Soldering Conference, April 24–26, 2006,... more Page 125. Proceedings of the 3 International Brazing and Soldering Conference, April 24–26, 2006, Crowne Plaza Riverwalk Hotel, San Antonio, Texas, USA rd Hermetic Glass-to-Aluminum Seals for RF Packaging Applications ...
ABSTRACT This paper describes a process which uses a multilayered reactive foil to hermetically s... more ABSTRACT This paper describes a process which uses a multilayered reactive foil to hermetically seal microelectronic packages. The foil is comprised of thousands of nanoscale layers of elements with large negative heats of mixing, such as Al and Ni. When the reaction is activated in the foil using a small electrical or thermal stimulus, the heat generated melts the adjoining solder layers and permanently joins the package lid to the base. The seal is achieved without exposing the components to high reflow temperature. RNT has used this process to create a hermetic seal between an Au-plated stainless steel lid and Au-plated stainless steel base. We show that helium leak rates of less than 1 x 10-10 atm-cc/sec can be achieved by using this method. This process provides an attractive alternative to more expensive methods such as laser welding and eliminates the need for costly fabrication equipment.
ABSTRACT Micro fabrication is generally confined to silicon-based processes for microelectronic a... more ABSTRACT Micro fabrication is generally confined to silicon-based processes for microelectronic applications. The advent of micro electromechanical systems (MEMS) using silicon and silicon based processes has opened up a new basis for micro fabrication technology, but the applications have been limited due to the brittle nature of silicon. Novel technologies have been sought for non-silicon micro components and systems. The electrochemical micro machining (μECM) is standing out among other solutions. An international group comprised of industry and academic institutes in Mexico and USA was formed to provide synergistic effort in developing this new technology. The funding came from the involved companies, National Science Foundation, National Consortium of Science and Technology (CONACyT, Mexico), and Texas A&M University. Both graduate and undergraduate students are involved in this research and educational project. Some research objectives have been achieved by dividing an objective into manageable laboratory projects that can be completed by undergraduate students in a few weeks. The anodic dissolution μECM process effectively forms and shapes micro components from any conductive material. Unlike classical ECM technology, the novel μECM utilizes very high frequency pulses and proprietary electrode shapes/motions to remove materials at the micro or nano scales, and can mass-produce micro components with exceptional quality and surface integrity. A theoretical model is developed which agrees with experimental data for 316L stainless steel and copper beryllium alloy. The environmentally friendly technology shows promise as a high-resolution production manufacturing process with excellent throughput and repeatability.
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