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.

Reactive bonding can overcome the issues associated with conventional soldering processes, such as potential damage to heat-sensitive components and the creation of thermomechanical stress due to differing coefficients of thermal expansion. The risk of such damage can be reduced by using localized heat sources like reactive multilayer systems (RMS), which is already a well-established option in the field of silicon or metal bonding. Adapting this process to other materials, such as low temperature co-fired ceramics (LTCC), is difficult due to their differing properties, but it would open new technological possibilities. One aspect that significantly affects the quality of the bonding joints is the pressure applied during the bonding process. To investigate its influence more closely, various LTCC samples were manufactured, and cross-sections were prepared. The microscopical analysis reveals that there is an optimum range for the bonding pressure. While too little pressure results in the formation of lots of voids and gaps, most likely in poor mechanical and electrical properties, too high pressure seems to cause a detachment of the metallization from the base material.

Multilayer ceramic capacitors (MLCCs) are critical components when thermal processes such as reflow desoldering are used during rework of electronic assemblies. The capacitor’s ferroelectric BaTiO₃ body is very brittle. Therefore, thermomechanical stresses can cause crack formation and create conductive paths that may short the capacitor. In order to assess the thermally induced mechanical stresses onto an MLCC during reflow desoldering, simulations were carried out, which make use of a framework of computational fluid dynamics and thermomechanical models within the ANSYS software package. In the first step, CFD simulations were conducted to calculate the transient temperature field in the surrounding of the MLCC component, which was then used as an input for FEM simulations to compute the arising mechanical stresses inside the MLCC. The results of the simulations show that the major contribution to mechanical stresses within the MLCC component comes from the mismatch in thermal expansion between the printed circuit board and the MLCC. The temperature gradients along the MLCC component are rather small and account only for moderate internal stresses within the brittle BaTiO₃ body.

A rework of electronic assemblies and the reuse of electronic components are the most effective ways to reduce electronic waste. Since neither components nor substrates were developed with the intention of multiple usage, the question of how the integrity of lead-free solder joints is affected by multiple reflow operations is crucial for the implementation of any reuse strategy. Therefore, various types of 1206 multilayer ceramic capacitors (MLCCs) differing in their capacitance value and dielectric type (X5R, X7R, Y5V, NP0) were soldered on test printed circuit boards (PCBs) having a pure Cu-metallization surface in order to investigate the intermetallic reactions during multiple reflows. The metallization system on the MLCC-component side consisted of a thick film of Ni covered by galvanic-deposited Sn. The reflow experiments were conducted using a hypoeutectic SnAgCu solder. The results show the formation of a Cu₆Sn₅ intermetallic phase on both metallizations, which grows homogeneously with the number of reflows. Moreover, an ongoing decomposition of the solder into Ag-enriched and depleted zones was observed. The effect of these microstructural changes on the functionality of the solder joint was investigated by mechanical shear experiments and electrical four-point capacitance measurements.

The deposition of reactive multilayer systems (RMSs) is investigated on low‐temperature cofired ceramic (LTCC) substrates having different surface morphologies. In this study, the morphologies of RMS layers that are deposited on glass‐ceramic LTCC substrates are analyzed. Different surface morphologies are prepared through pretreatments of the LTCC surface. The considered surfaces encompass an untreated natural LTCC surface, a modified sintered LTCC surface by laser ablation, a surface with a deposited metallization layer, and finally, a surface with an additional solder layer put on the deposited metallization layer. The different pretreatments lead to significant differences in the roughness of the LTCC substrates, resulting in different reaction velocities and peak temperatures on the various surface morphologies after the RMS's reaction. As a result, different grades of structural integrity (liftoff, crack formation) between the reacted RMS layer and the LTCC are observed.

This paper discusses the application of reactive bonding for the area of L ow Temperature Cofired Ceramics (LTCC) assemblies. The goal is to reduce the thermal-mechanical stresses during soldering by transferring heat only locally to the solder joints without heating the entire component. Such a reactive multilayer system (R MS) consists of alternating nanolayers (10 - 300 nm) of at least two metal components which produce an exothermal reaction after ignition. Although the deposition of an RMS is established on silicon substrates for the use in micro-electromechanical systems (MEMS), it is very challenging to create them on LTCC substrates. One of the main obstacles is to over come all issues connected with the significant roughness, because it is not an optimum territory to deposit nanolayers. In this paper, different methods like chemical mechanical polishing (CMP) and laser ablation, to modify the surface morphology, are presented. A direct relation between the morphology and the exothermal reaction can be observed. In addition, 3-D Computational Fluid Dynamics (CFD) simulations were conducted to analyze the process in more detail. These simulations make use of a shoebox model with different layers and an adjustable user-defined function for the heat release of the RMS to adapt the reaction front velocity and the combustion temperature to the experimental values.