Analysis of selective bonding processes using reactive multi-layers for system integration on LTCC based SiPs

This paper discusses the use of reactive multi-layers for selective assembly of ICs (Integrated Circuits) in an LTCC (Low Temperature Co-fired Ceramics) based SiP (System-in-Package). To understand the requirements for the use of self-propagating reactive multilayers in die bonding, CFD (Computational Fluid Dynamics) simulations have been carried out to simulate the die bonding process of a silicon chip onto a ceramic LTCC substrate. Reactive foils of 40 and 80 µm thicknesses and a simulated reaction propagation speed of 1 m/s were studied and used to melt a solder preform underneath a silicon chip. The results of the CFD simulations were analysed, particularly with respect to temperature and liquid fraction contours, as well as time-temperature histories obtained from temperature probes which were included in the model, such as to approximate the real behaviour of Pt-100 temperature probes, when a real bonding process is being tracked. The CFD method, in this instance realised with ANSYS Fluent software, can track the melting and solidification of the solder as well as model the influence of latent heat, which is crucial to ascertaining the true evolution of the bonding process

Analysis of selective bonding processes using reactive multi-layers for system integration on LTCC based SiPs

This paper discusses the use of reactive multi-layers for selective assembly of ICs (Integrated Circuits) in an LTCC (Low Temperature Co-fired Ceramics) based SiP (System-in-Package). To understand the requirements for the use of selfpropagating reactive multilayers in die bonding, CFD (Computational Fluid Dynamics) simulations have been carried out to simulate the die bonding process of a silicon chip onto a ceramic LTCC substrate. Reactive foils of 40 and 80 lm thicknesses and a simulated reaction propagation speed of 1 m/s were studied and used to melt a solder preform underneath a silicon chip. The results of the CFD simulations were analysed, particularly with respect to temperature and liquid fraction contours, as well as time–temperature histories obtained from temperature probes which were included in the model, such as to approximate the real behaviour of Pt-100 temperature probes, when a real bonding process is being tracked. The CFD method, in this instance realised with ANSYS Fluent software, can track the melting and solidification of the solder as well as model the influence of latent heat, which is crucial to ascertaining the true evolution of the bonding process

Swept boundary layer transition

Boundary layer transition has been investigated for incompressible three-dimensional mean flows on a flat plate with a 60° swept leading edge for a nominally zero, a positive, and a negative pressure gradient for three freestream turbulence intensities using a low speed blower tunnel with a 1.22 x 0.61 m working section at the University of Liverpool. The freestream turbulence intensities were generated using grids upstream of the leading edge, producing turbulence levels of approximately 0.2 %, 1.25 % and 3.25 %. For each of these nine (3 x 3) test cases detailed boundary layer traverses were obtained at ten streamwise measurement stations, at a fixed spanwise location, using single-wire constant temperature hot-wire anemometry techniques and digital signal processing. The location for the onset and end of transition was obtained for each case, in terms of distance from the leading edge and local momentum thickness Reynolds number. These results are compared with the 2-D unswept empirical transition correlations of Abu-Ghannam and Shaw (1980) and the differences in the results between the two flows are highlighted. It was found that transition starts and ends earlier than for similar unswept flows, complementing the transition observations of Gray (1952) for swept wings. Further to this the receptivity of the swept boundary layers to freestream turbulence (in the bypass transition regime) was determined by comparing near wall and local freestream spectra, for the pre-transitional boundary layers. These experimental results were compared with numerical predictions from a fourth order accurate computational fluid dynamics method which considered a multitude of perturbation waveforms. This numerical approach was also able to identify the waveform frequency and orientation combinations which drive receptivity in swept boundary layer transition and indicate the manner in which receptivity scales with momentum thickness Reynolds number. It was found that the most receptive waveforms correspond to the streamwise streaks which are frequently observed in flow visualisations and direct numerical simulation studies of pre-transitional boundary layers. Additionally it was also found that the numerical receptivities to freestream turbulence were highest for the positive pressure gradient and, in contrast, lowest for the negative pressure gradient – a similar finding to that in 2-D boundary layers. Transition was seen to commence prior to the advent of the intended non-zero pressure gradients in the experiments and thus direct comparisons are not strictly available. The results obtained, and synthesis undertaken for this thesis, contribute towards an improved understanding of the transition process, particularly with respect to receptivity, in regard to flat plates with swept leading edges in various pressure gradients and highlight the differences between swept and unswept flows. Furthermore, additional avenues have been identified for future work on more complicated topologies where potential problems have also been highlighted

Ungating community: opening the enclosures of financialised housing

An ideology of globalisation and neoliberal progress has led governments across the world to enable and encourage investors and property developers in constructing real estate projects that appeal to a mobile, global elite. This thesis examines four topologies of financialised housing and the ways in which they construct borders and form exclusions within their cities, arguing that each one is a variation of the gated community. The gates – both real and affective - consist of spatial, social and political infrastructures that work together to produce homogenised spaces of exclusion. Firstly, the luxury investor-focused property that we see in abundance in major cities across the globe. Secondly, private student housing that caters to a community of short-term international students looking for maximum convenience. Thirdly, the ‘co-living’ complex that rebrands the precarity of contemporary labour and the insecurity of a private rental market in crisis, capitalising on these characteristics towards selling a lifestyle of flexibility and the illusion of togetherness. And finally, the ‘expat’ compounds in China that aim to attract international professionals through the construction of convenience and familiarity: a smooth transition from one context to another. Interrogating these four housing topologies – which have to date not been examined in relation to each other - I will argue for their ungating: the constructive interruption and dismantling of their borders, barriers, exclusions and divisions via strategies of collectivisation, intervention and the radical imagination, as demonstrated by four case-study projects I will outline as examples of ungating. This is important work that must be done towards transforming the exclusionary mechanisms of financialised housing and establishing communities and spaces that are inclusive of difference. My research is presented in three parts: this written thesis, my project ASSET ARREST, and two films titled Gated Community. Each part works in dialogue with the others, using artistic, performative, action research and theoretical methods. Overlapping at points, the research is conducted and performed from positions that move between the embedded and the distanced. My aim in positioning these three parts alongside each other is to construct a multi-dimensional and fragmented image and exploration of financialised housing that generates and presents knowledge in different ways: an approach that is vital towards developing a theory and practice of ungating

The simulated effect of adding solder layers on reactive multilayer films used for joining processes

In order to introduce new bonding methods in the area of electronic packaging a theoretical analysis was conducted, which should give substantial information about the potential of reactive multilayer systems (rms) to create sufficient local heat for joining processes between silicon chips and ceramic substrates. For this purpose, thermal CFD (computational fluid dynamics) simulations have been carried out to simulate the temperature profile of the bonding zone during and after the reaction of the rms. This thermal analysis considers two different configurations. The first configuration consists of a silicon chip that is bonded to an LTCC-substrate (Low Temperature Co-fired Ceramics) using a bonding layer that contains an rms and a solder preform. The reaction propagation speed of the reactive multilayer was set to a value of 1 m/s, in order to partially melt a solder preform underneath a silicon chip. The second configuration, which consists only of the LTCC-substrate and the rms, was chosen to study the differences between the thermal outputs of the two arrangements. The analysis of the CFD simulations was particularly focused on interpretations of the temperature and liquid fraction contours. The CFD thermal simulation analysis conducted contains a melting/solidification model which can track the molten/solid state of the solder in addition to modelling the influence of latent heat. To provide information for the design of a test-substrate for experimental investigations, the real behaviour of Pt-100 temperature probes on the LTCC-substrate was simulated, in order to monitor an actual bonding in the experiment. All simulations were carried out using the ANSYS Fluent software

The Simulated Effect of Adding Solder Layers on Reactive Multilayer Films Used for Joining Processes

In order to introduce new bonding methods in the area of electronic packaging a theoretical analysis was conducted, which should give substantial information about the potential of reactive multilayer systems (rms) to create sufficient local heat for joining processes between silicon chips and ceramic substrates. For this purpose, thermal CFD (computational fluid dynamics) simulations have been carried out to simulate the temperature profile of the bonding zone during and after the reaction of the rms. This thermal analysis considers two different configurations. The first configuration consists of a silicon chip that is bonded to an LTCC-substrate (Low Temperature Co-fired Ceramics) using a bonding layer that contains an rms and a solder preform. The reaction propagation speed of the reactive multilayer was set to a value of 1 m/s, in order to partially melt a solder preform underneath a silicon chip. The second configuration, which consists only of the LTCC substrate and the rms, was chosen to study the differences between the thermal outputs of the two arrangements. The analysis of the CFD simulations was particularly focused on interpretations of the temperature and liquid fraction contours. The CFD thermal simulation analysis conducted contains a melting/solidification model which can track the molten/solid state of the solder in addition to modelling the influence of latent heat. To provide information for the design of a test-substrate for experimental investigations, the real behaviour of Pt-100 temperature probes on the LTCC-substrate was simulated, in order to monitor an actual bonding in the experiment. All simulations were carried out using the ANSYS Fluent software