Effects of inter-metallic compound on high temperature reliability of flip chip interconnects for fine pitch applications

Solder joint is a method widely used to attach electronic chip on substrate. It is a generally knowledge that solder joint contains inter-metallic compound (IMC) at interconnects of solder bump and copper pads. The magnitude of IMC layer thickness impacts reliability of chip level packages. Extensive experimental investigations are conducted, however complementary numerical studies are needed to fully characterise the effects of IMC on high temperature reliability of flip chip (FC) assembly. In this work, thermo-mechanical response of FC lead-free solder joints to accelerated temperature cycle (ATC) is investigated using finite element analysis (FEA) code. The ANAND's model is employed to study the inelastic, nonlinear, rate dependent and visco-plastic behaviour of two models of FC48D6.3C457DC mounted on printed circuit boards (PCBs). While one model consists of conventional joints without IMC, the other is realistic with IMC embedded. In the result analysis based on damage indicators such as induced strain, stress, plastic work and hysteresis, it is found that negative impact of IMC on static structural integrity of solder joint operating at high temperature ambient is nontrivial

High temperature electronics: R&D challenges and trends in materials, packaging and interconnection technology

The development of new high temperature electronics (HTE)/systems is the key to achieving high reliability safety critical operations in aerospace, automotive and well-logging applications. Reliability issues associated with the operation of HTE devices have been shown to account for some of the recent aircraft crashes as well as failures of the electronic control Unit in modern vehicles. The reliability of electronic systems is partly dependent on its operating ambient conditions; and reliability generally decreases in harsh operating conditions. The life expectancy of components and systems is known to reduce exponentially as the operating temperature increases; adversely impacting long-term system reliability. As under-bonnet, aerospace and well-logging applications require the direct exposure of sensors to very harsh conditions – these applications demand new HTE systems which can operate reliably in harsh conditions whilst preserving their properties/functions over long operating periods. The packaging and interconnection of the new HTE systems requires better understanding of the complex interactions between HTE system parameters and specific environmental conditions. The paper presents an overview of HTE research, reviews the trends in materials, component packaging and interconnect technology. The paper also outlines the key challenges in HTE research and the outstanding R&D issues

Effect of solder joint integrity on the thermal performance of a TEC for a 980nm pump laser module

Purpose – The purpose of this paper is to evaluate the effect of solder wettability on the thermal performance of a thermo-electric cooler (TEC) of a 980?nm pump laser module. Design/methodology/approach – In this paper, TEC thermal performance has been evaluated using a heat pump test. The results were compared with scanning acoustic microscopy (C-SAM) results in order to have a better understanding of the thermal behaviour of the TEC. In the C-SAM experiments, images were taken at the interfaces between the housing and TEC, as well as at the interfaces between the chip-on-carrier (CoC) and TEC. Findings – The heat pump test results indicate a strong correlation with the C-SAM test results. The C-SAM observations show good solder joint at the interface between the TEC and housing in the case of the device that yielded a good heat pump test result (11.5°C) and poor solder joints (gross de-lamination) at the interface between the TEC and housing in the case of the device that yielded a poor heat pump test result (24.4°C). The C-SAM observations did not show much difference at the interface between the CoC and TEC. The results from this study were used to qualify the post-vacuum soldered laser pump devices at JDS Uniphase, Plymouth, UK. Originality/value – The findings presented in this paper indicate that the level of solder wettability at the interfaces between the piece parts impacts the thermal performance of the TEC

Emerging nanotechnology-based thermal interface materials for automotive electronic control unit application

The under-hood automotive ambient is harsh and its impact on electronics used in electronic control unit (ECU) assembly is a concern. The introduction of Euro 6 standard (Latest European Union Legislation) leading to increase in power density of power electronics in ECU has even amplified the device thermal challenge. Heat generated within the unit coupled with ambient temperature makes the system reliability susceptible to thermal degradation which may result in catastrophic failure if not efficiently dissipated. Previous investigations show that the technology of thermal interface materials (TIMs) is a key to achieving good heat conductions within a package and from a package to heat sinking device. With studies suggesting that conventional TIMs contribute about 60% interfacial thermal resistance, innovative technology is required to improve the thermal performance of TIMs. A review of emerging nanotechnology in TIMs shows that carbon nanotubes (CNTs) and carbon nanofibres (CNFs) when used as the structure of TIM or TIM filler could improve the overall thermal and mechanical properties of TIMs. Hence, CNTs/CNFs have the potentials to advance thermal management issues in ECU. This search identifies chemical vapour deposition (CVD) as a low cost process for the commercial production of CNTs. In addition, this review further highlights the capability of CVD to grow nanotubes directly on a desired substrate. Other low temperature techniques of growing CNT on sensitive substrates are also presented in this paper

Thermal management materials for electronic control unit: trends, processing technology and R&D challenges

The development of advanced thermal management materials for Electronic Control Unit (ECU) is the key to achieving high reliability and thus safety critical operations in areas of ECU applications such as automotives and power systems. Thermal management issues associated with the operation of ECU at elevated temperature have accounted for some of the recent reliability concerns which have culminated in current systems failures in some automobiles. As the functions of ECU in systems have increased in recent times, the number of components per unit area on its board has also risen. High board density boosts internal heat generated per unit time in ECU ambient. The generated heat induces stress and strain at the chip interconnects due to variation in the Coefficient of Thermal Expansion (CTE) and thermal conductivity of different bonded materials in the assembly. Thermal degradation impacts device’s efficiency and could become critical. The life expectancy of electronic components reduces exponentially as the operating temperature rises, thus making thermal management pivotal in electronic system reliability. Since materials’ properties vary with operating condition, material performance has become a major consideration in the design of heat dissipation mechanism in ECU. The development of advanced thermal management materials and hence improving the performance of ECU require an in-depth understanding of the complex relationship between materials’ properties and their behaviours at elevated temperatures. The paper presents an overview of thermal management materials for ECU in terms of material properties and processing technology. In addition, the paper outlines the crucial challenges in materials selection, including cost and manufacturing and other outstanding R & D issues

Thermal management materials for electronic control unit: trends, processing technology and R and D challenges

The development of advanced thermal management materials for Electronic Control Unit(ECU) is the key to achieving high reliability and thus safety critical operations in areas of ECU applications such as automotives and power systems. Thermal management issues associated with the operation of ECU at elevated temperature have accounted for some of the recent reliability concerns which have culminated in current systems failures in some automobiles. As the functions of ECU in systems have increased in recent times, the number of components per unit area on its board has also risen. High board density boosts internal heat generated per unit time in ECU ambient. The generated heat induces stress and strain at the chip interconnects due to variation in the Coefficient of Thermal Expansion (CTE) and thermal conductivity of different bonded materials in the assembly. Thermal degradation could become critical and impacts device’s efficiency. The life expectancy of electronic components reduces exponentially as the operating temperature rises thus making thermal management pivotal in electronic system reliability. Since materials’ properties vary with operating condition, material performance has become a major consideration in the design of heat dissipation mechanism in ECU. The development of advanced thermal management materials and hence improving the performance of ECU requires an in-depth understanding of the complex relationship between materials’ properties and their behaviours at elevated temperatures. The paper presents an overview of thermal management materials, review trends in material and processing technology. In addition, the paper outlines the crucial challenges in materials, cost and composite formulations and the outstanding R & D issues

Thermal effects of die-attach voids location and style on performance of chip level package

Thermal characterisation of chip-scale packaged power devices is crucial to the development of advanced electronic packages for communication and automotive applications. Solder thermal interface materials (STIMs) are often employed in the packaging of power semiconductors to enhance heat dissipation from the chip to the heat spreader. However, voids formation in STIMs impedes heat flow and could result in increase in the chip peak temperature. Three-dimensional finite element analysis is employed to investigate the thermal effects of lead-free solder void percentages, locations and styles on packaged semiconductor device. The thermal resistance of each voiding case is calculated to evaluate the thermal response of the electronic package. The results show that the thermal resistance and peak temperature of electronic package can significantly increase depending on the percentage, location and style of voids. The results would assist packaging and design engineers in the characterisation of the thermal impacts of different solder void patterns

Thermal interface materials for automotive electronic control unit: Trends, technology and R&D challenges

The under-hood automotive ambient is harsh and its impact on electronics used in electronic control unit(ECU)assembly is a concern. The introduction of Euro 6 standard (Latest European Union Legislation)leading to increase in power density of power electronics in ECU has even amplified the device thermal challenge. Heat generated within the unit coupled with ambient temperature makes the system reliability susceptible to thermal degradation which ultimately may result in failure. Previous investigations show that the technology of thermal interface materials (TIMs) is a key to achieving good heat conductions within a package and from a package to heat sinking device. With studies suggesting that current TIMs contribute about 60% interfacial thermal resistance, a review of engineering materials has become imperative to identify TIM that could enhance heat transfer. This paper critically reviews the state-of-theart in TIMs which may be applicable to automotive ECU. Our review shows that carbon-nanotube (CNT) when used as the structure of TIM or TIM filler could considerably advance thermal management issues by improving heat dissipation from the ECU. This search identifies chemical vapor deposition (CVD) as a low cost process for the commercial production of CNTs. In addition, this review further highlights the capability of CVD to grow nanotubes directly on a desired substrate. Other low temperature techniques of growing CNT on sensitive substrates are also presented in this paper

Numerical investigation of thermo-mechanical behaviour of ball grid array solder joint at high temperature excursion

The solder joints of surface mount components (SMCs) experience thermal degradation culminating in creep and plastic shear strain deformation when subjected to cyclic temperature load over time. Degradation at the joints is due to thermal stress induced by the incompatible, differential and nonlinear expansion mismatch of the different bonded materials in the assembly. The stress magnitude influences the strain behaviour. Plastic strain response of solder joint is critical at the materials interface at the lower part of the joint due to the occurrence of wider variation in the coefficient of thermal expansion of the bonded materials and this may lead to static structural failure. The life expectancy of electronic components reduces exponentially as the operating temperature increases thus making reliability a key concern for electronic systems operating at high temperatures and in harsh environments. This paper reports on the numerical investigation of thermo-mechanical response of a critical BGA joint especially the character of plastic deformation of SnPb solder used in forming the joint as well as the joint’s high temperature reliability. The analysis uses a 3-D models to predict the effect of the transient thermal load on the static structural integrity of a single BGA joint. In this study, the base diameter of solder ball (interface between the PCB, copper pad and the solder) experienced higher damage than the top diameter interconnects. The paper provides a simplified methodology to study the reliability of BGA solder joint at high temperatures excursion