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• 1. [Article] Power core (PC) Embedding a Plurality of IC Devices and Sandwiched Between Two Dissimilar Insulated Metal Substrates (IMS’): Predicted Thermal Stresses

  Power core (PC) sandwiched between two insulated metal substrates (IMS) and embedding active and passive integrated circuit (IC) devices is currently viewed as an attractive advanced packaging option having ...

  Citation × Citation Citation Abstract Copy Title: Power core (PC) Embedding a Plurality of IC Devices and Sandwiched Between Two Dissimilar Insulated Metal Substrates (IMS’): Predicted Thermal Stresses Author: Suhir, Ephraim, Nicolics, Johann Year: 2016 Power core (PC) sandwiched between two insulated metal substrates (IMS) and embedding active and passive integrated circuit (IC) devices is currently viewed as an attractive advanced packaging option having a strong potential in the automotive industry and beyond. A natural reliability concern, however, is the level of the thermally induced stresses in a tri-material assembly of the type in question. Accordingly, an analytical (mathematical) stress model is developed for the evaluation of these stresses. The stresses include normal stresses acting in the cross-sections of the assembly components, and the interfacial shearing and peeling stresses acting at the interfaces of these components and at the interfaces of the embedded IC devices. The model can be helpful in the stress-analysis and physical design of the assemblies, in which the PC is sandwiched between two IMS’. It can be used also in other areas of engineering, where tri-material assemblies comprised of dissimilar materials and subjected to the change in temperature are employed. The general concepts are illustrated by a detailed numerical example. The analysis is an extension of the study carried out earlier for a bow-free assembly. It is noteworthy that although the calculations are carried out for the case when the assembly is cooled down from an elevated temperature to a low temperature, since a linear approach is used and the stresses are proportional to the change in temperature, whatever its sign or the magnitude is, the developed model is equally applicable to any change in temperature. Title: Power core (PC) Embedding a Plurality of IC Devices and Sandwiched Between Two Dissimilar Insulated Metal Substrates (IMS’): Predicted Thermal Stresses Author: Suhir, Ephraim, Nicolics, Johann Year: 2016 Power core (PC) sandwiched between two insulated metal substrates (IMS) and embedding active and passive integrated circuit (IC) devices is currently viewed as an attractive advanced packaging option having a strong potential in the automotive industry and beyond. A natural reliability concern, however, is the level of the thermally induced stresses in a tri-material assembly of the type in question. Accordingly, an analytical (mathematical) stress model is developed for the evaluation of these stresses. The stresses include normal stresses acting in the cross-sections of the assembly components, and the interfacial shearing and peeling stresses acting at the interfaces of these components and at the interfaces of the embedded IC devices. The model can be helpful in the stress-analysis and physical design of the assemblies, in which the PC is sandwiched between two IMS’. It can be used also in other areas of engineering, where tri-material assemblies comprised of dissimilar materials and subjected to the change in temperature are employed. The general concepts are illustrated by a detailed numerical example. The analysis is an extension of the study carried out earlier for a bow-free assembly. It is noteworthy that although the calculations are carried out for the case when the assembly is cooled down from an elevated temperature to a low temperature, since a linear approach is used and the stresses are proportional to the change in temperature, whatever its sign or the magnitude is, the developed model is equally applicable to any change in temperature. Close

• 2. [Article] Bow-Free Tri-Component Mechanically Pre-Stressed Failure-Oriented-Accelerated-Test (FOAT) Specimen

  In some today's and future electronic and optoelectronic packaging systems (assemblies), including those intended for aerospace applications, the package (system's component containing active and passive ...

  Citation × Citation Citation Abstract Copy Title: Bow-Free Tri-Component Mechanically Pre-Stressed Failure-Oriented-Accelerated-Test (FOAT) Specimen Author: Suhir, Ephraim, Bensoussan, Alain, Nicolics, Johann Year: 2015 In some today's and future electronic and optoelectronic packaging systems (assemblies), including those intended for aerospace applications, the package (system's component containing active and passive devices and interconnects) is placed (sandwiched) between two substrates. In an approximate stress analysis these substrates could be considered, from the mechanical (physical) standpoint, identical. Such assemblies are certainly bow-free, provided that all the stresses are within the elastic range and remain elastic during testing and operation. Ability to remain bow-free is an important merit for many applications. This is particularly true in optical engineering, where there is always a need to maintain high coupling efficiency. The level of thermal stresses in bow-free assemblies of the type in question could be, however, rather high. High thermal stresses are caused by the thermal contraction mismatch of the dissimilar materials of the assembly components and occur at low temperature conditions. These stresses include normal stresses acting in the component cross-sections and interfacial shearing and peeling stresses. The normal stresses in the component cross-sections determine the reliability of the component materials and the devices embedded into the inner component (package). The interfacial stresses affect the adhesive and cohesive strength of the assembly, i.e. its integrity. It should be pointed out that although the assembly as a whole is bow-free, the peeling stresses in it, whether thermal or mechanical, are not necessarily low: the two outer components (substrates) might exhibit appreciable warpage with respect to the bow-free inner component (package). While there is an incentive for using bow-free assemblies, there is also an incentive for narrowing the temperature range of the accelerated reliability testing: elevated temperature excursions might produce an undesirable shift in the modes and mechanisms of failure, i.e. lead to failures that will hardly occur in actual operation conditions. Failure oriented accelerated test (FOAT) specimens are particularly vulnerable, since the temperature range in these tests should be broad enough to lead to a failure, and, if a shift in the modes and mechanisms of failures takes place during significant temperature excursions, the physics of such failures might be quite different of those in actual operation conditions. Mechanical pre-stressing can be an effective means for narrowing the range of temperature excursions during accelerated testing and, owing to that, - for obtaining consistent and trustworthy information. If pre-stressing is considered, the ability to predict the thermo-mechanical stresses in the test specimen is certainly a must. Accordingly, the objective of this analysis is to obtain simple, easy-to-use, physically meaningful and practically useful closed form solutions for the evaluation of stresses in a bow-free test specimen of the type in question. The emphasis is on the role of compliant attachments, if any, between the inner and the two outer components. The developed model can be used at the design and accelerated test stages of the development of bow-free electronic and optoelectronic products. The compliant attachments, if any, could be particularly comprised of beamlike solder joint interconnections that, if properly designed, have a potential to relieve the thermal stresses to an extent that the low-cycle-fatigue state-of-stress is avoided. Title: Bow-Free Tri-Component Mechanically Pre-Stressed Failure-Oriented-Accelerated-Test (FOAT) Specimen Author: Suhir, Ephraim, Bensoussan, Alain, Nicolics, Johann Year: 2015 In some today's and future electronic and optoelectronic packaging systems (assemblies), including those intended for aerospace applications, the package (system's component containing active and passive devices and interconnects) is placed (sandwiched) between two substrates. In an approximate stress analysis these substrates could be considered, from the mechanical (physical) standpoint, identical. Such assemblies are certainly bow-free, provided that all the stresses are within the elastic range and remain elastic during testing and operation. Ability to remain bow-free is an important merit for many applications. This is particularly true in optical engineering, where there is always a need to maintain high coupling efficiency. The level of thermal stresses in bow-free assemblies of the type in question could be, however, rather high. High thermal stresses are caused by the thermal contraction mismatch of the dissimilar materials of the assembly components and occur at low temperature conditions. These stresses include normal stresses acting in the component cross-sections and interfacial shearing and peeling stresses. The normal stresses in the component cross-sections determine the reliability of the component materials and the devices embedded into the inner component (package). The interfacial stresses affect the adhesive and cohesive strength of the assembly, i.e. its integrity. It should be pointed out that although the assembly as a whole is bow-free, the peeling stresses in it, whether thermal or mechanical, are not necessarily low: the two outer components (substrates) might exhibit appreciable warpage with respect to the bow-free inner component (package). While there is an incentive for using bow-free assemblies, there is also an incentive for narrowing the temperature range of the accelerated reliability testing: elevated temperature excursions might produce an undesirable shift in the modes and mechanisms of failure, i.e. lead to failures that will hardly occur in actual operation conditions. Failure oriented accelerated test (FOAT) specimens are particularly vulnerable, since the temperature range in these tests should be broad enough to lead to a failure, and, if a shift in the modes and mechanisms of failures takes place during significant temperature excursions, the physics of such failures might be quite different of those in actual operation conditions. Mechanical pre-stressing can be an effective means for narrowing the range of temperature excursions during accelerated testing and, owing to that, - for obtaining consistent and trustworthy information. If pre-stressing is considered, the ability to predict the thermo-mechanical stresses in the test specimen is certainly a must. Accordingly, the objective of this analysis is to obtain simple, easy-to-use, physically meaningful and practically useful closed form solutions for the evaluation of stresses in a bow-free test specimen of the type in question. The emphasis is on the role of compliant attachments, if any, between the inner and the two outer components. The developed model can be used at the design and accelerated test stages of the development of bow-free electronic and optoelectronic products. The compliant attachments, if any, could be particularly comprised of beamlike solder joint interconnections that, if properly designed, have a potential to relieve the thermal stresses to an extent that the low-cycle-fatigue state-of-stress is avoided. Close

• 3. [Article] Predicted Stresses in Ball-Grid-Array (BGA) and Column-Grid-Array (CGA) Interconnections in a Mirror-Like Package Design

  There is an obvious incentive for using bow-free (temperature change insensitive) assemblies in various areas of engineering, including electron device and electronic packaging fields. The induced stresses ...

  Citation × Citation Citation Abstract Copy Title: Predicted Stresses in Ball-Grid-Array (BGA) and Column-Grid-Array (CGA) Interconnections in a Mirror-Like Package Design Author: Suhir, Ephraim, Ghaffarian, Reza, Nicolics, Johann Year: 2016 There is an obvious incentive for using bow-free (temperature change insensitive) assemblies in various areas of engineering, including electron device and electronic packaging fields. The induced stresses in a bow-free assembly could be, however, rather high, considerably higher than in an assembly, whose bow is not restricted. The simplest and trivial case of a bow-free assembly is a tri-component body, in which the inner component is sandwiched between two identical outer components (“mirror” structure), is addressed in our analysis, and a simple and physically meaningful analytical stress model is suggested. It is concluded that if acceptable stresses (below yield stress of the solder material) are achievable, a mirror (bow-free, temperature-change-insensitive) design should be preferred, because it results in an operationally stable performance of the system. Title: Predicted Stresses in Ball-Grid-Array (BGA) and Column-Grid-Array (CGA) Interconnections in a Mirror-Like Package Design Author: Suhir, Ephraim, Ghaffarian, Reza, Nicolics, Johann Year: 2016 There is an obvious incentive for using bow-free (temperature change insensitive) assemblies in various areas of engineering, including electron device and electronic packaging fields. The induced stresses in a bow-free assembly could be, however, rather high, considerably higher than in an assembly, whose bow is not restricted. The simplest and trivial case of a bow-free assembly is a tri-component body, in which the inner component is sandwiched between two identical outer components (“mirror” structure), is addressed in our analysis, and a simple and physically meaningful analytical stress model is suggested. It is concluded that if acceptable stresses (below yield stress of the solder material) are achievable, a mirror (bow-free, temperature-change-insensitive) design should be preferred, because it results in an operationally stable performance of the system. Close

• 4. [Article] Could Application of Column-Grid-Array (CGA) Technology Result in Inelastic-Strain-Free State-of-Stress in Solder Material?

  Physically meaningful and easy-to-use analytical stress model is developed for a short cylinder (beam) clamped at the ends and subjected to bending caused by the ends offset. The offset is due, in its ...

  Citation × Citation Citation Abstract Copy Title: Could Application of Column-Grid-Array (CGA) Technology Result in Inelastic-Strain-Free State-of-Stress in Solder Material? Author: Suhir, Ephraim, Ghaffarian, Reza, Nicolics, Johann Year: 2015 Physically meaningful and easy-to-use analytical stress model is developed for a short cylinder (beam) clamped at the ends and subjected to bending caused by the ends offset. The offset is due, in its turn, to an external lateral force that has to be determined from the known offset. It is envisioned that such a beam can adequately represent the state of stress in a column-grid-array (CGA) solder joint interconnection experiencing thermal loading due to the thermal expansion/contraction mismatch of the IC package and the printed circuit board (PCB). The CGA designs are characterized by considerably higher stand-off heights than ball-grid-array (BGA) systems. The offset Δ = lΔαΔt for a CGA solder joint located at the distance l from the mid-cross-section of the package/PCB assembly (the neutral point (DNP)), can be determined, in an approximate analysis, as a product of this distance and the “external” thermal mismatch strain ΔαΔt between the IC package and the printed circuit board (PCB). Here Δα is the difference in the effective coefficients of thermal expansion (CTE) of the PCB and package materials, and Δt is the change in temperature. The objective of the analysis is to demonstrate that the application of a CGA design, in which the solder joints are configured as short clamped–clamped beams, enables one not only to significantly relieve the thermally induced stresses, compared to the BGA system, but possibly to do that to an extent that the stresses in the solder material would remain within the elastic range. If this is achieved, the low-cycle-fatigue condition for the solder material will be replaced by the elastic-fatigue condition, thereby leading to a significantly longer fatigue lifetime of the joint. The elastic fatigue lifetime can be assessed, as is known, based on the Palmgren–Miner rule of linear accumulation of damages. Our analysis is limited therefore to elastic deformations. Title: Could Application of Column-Grid-Array (CGA) Technology Result in Inelastic-Strain-Free State-of-Stress in Solder Material? Author: Suhir, Ephraim, Ghaffarian, Reza, Nicolics, Johann Year: 2015 Physically meaningful and easy-to-use analytical stress model is developed for a short cylinder (beam) clamped at the ends and subjected to bending caused by the ends offset. The offset is due, in its turn, to an external lateral force that has to be determined from the known offset. It is envisioned that such a beam can adequately represent the state of stress in a column-grid-array (CGA) solder joint interconnection experiencing thermal loading due to the thermal expansion/contraction mismatch of the IC package and the printed circuit board (PCB). The CGA designs are characterized by considerably higher stand-off heights than ball-grid-array (BGA) systems. The offset Δ = lΔαΔt for a CGA solder joint located at the distance l from the mid-cross-section of the package/PCB assembly (the neutral point (DNP)), can be determined, in an approximate analysis, as a product of this distance and the “external” thermal mismatch strain ΔαΔt between the IC package and the printed circuit board (PCB). Here Δα is the difference in the effective coefficients of thermal expansion (CTE) of the PCB and package materials, and Δt is the change in temperature. The objective of the analysis is to demonstrate that the application of a CGA design, in which the solder joints are configured as short clamped–clamped beams, enables one not only to significantly relieve the thermally induced stresses, compared to the BGA system, but possibly to do that to an extent that the stresses in the solder material would remain within the elastic range. If this is achieved, the low-cycle-fatigue condition for the solder material will be replaced by the elastic-fatigue condition, thereby leading to a significantly longer fatigue lifetime of the joint. The elastic fatigue lifetime can be assessed, as is known, based on the Palmgren–Miner rule of linear accumulation of damages. Our analysis is limited therefore to elastic deformations. Close