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The heterogeneous 3D integration of temperature sensitive components requires a further development of joining processes at low temperatures. A viable approach is based on In as the low-melting component for eutectic/solid-liquid-interdiffusion (SLID) bonding. In our present study, we investigated the effect of different fluxes and processing conditions on the interconnect quality. The shear strength of the Cu-In fine-pitch interconnects was determined by shearing single-stack samples. Nearly defect-free joining zones and shear strengths up to 120 MPa indicate a high potential of the Cu-In SLID bonding technology.

Heterogeneous integration of different devices by using 3D architectures allows the realization of application specific System in Packages (SiP) with a high functionality in a cost effective way. Enabling building blocks technologies are substrate-, interconnect-, assembly- and device integration technologies to integrate sensors, ASICs, transceiver, memories and passive elements. SiPs based on interposer architectures are very attractive due to system performance improvements and due to optimized form factor achievements on wafer level.

Solid-liquid interdiffusion (SLID) interconnectsbased on Cu and Sn-solder are excellent candidates forstacking of Si chips in 3D integration. If the high-temperaturestable intermetallic compound (IMC) Cu3Sn is desired, themanufacturing of the interconnect can be very time consuming(long annealing time for growth of Cu3Sn). In this paper wepropose a method for the accelerated formation of Cu-Cu3Sn-Cu interconnects by selective dissolution of Sn from Cu6Sn5. This leads to a porous network of Cu3Sn. The influence oftemperature, flux and atmosphere onto the pore formation willbe addressed in detail.

The advancing heterogeneous integration of various electronic components into a single package requires in particular further development of bonding technologies towards lower temperatures. In our present study, we show the successful joining of dies consisting of Cu-microbumps with In solder caps. Stable interconnections were achieved at a bonding temperature of 180 °C in 2 min by solid-liquid-interdiffusion (SLID).

The applications of inertial sensors have a wide variety in terms of accuracy and costs. A new technology approach is joining higher sensor accuracy and lower production costs by using a new Interposer / sensor interconnect technology applied on 300 mm wafer diameter without changing the sensor element itself. The higher accuracy is mainly covered by a multiple point program: (1) stress less assembly due interface silicon Interposer to silicon MEMS; (2) better Signal to Noise Ratio (SNR) by polymer redistribution layer on the interposer (due to better wiring geometry and less parasitic capacities / inductivities); (3) reduction of mechanical stress by using flexible bar springs for mechanical decoupling of sensor and Interposer substrate; (4) additional stress reduction by using a polymer layer for mechanical decoupling of metal redistribution layer (RDL) and Interposer substrate. The cost efficiency even in small scale serial production based on: (1) 300 mm multi project wafer technology including warehouse ready system packaging; (2) a new MEMS contact technology, which gives technical benefit, smaller dimensions and simplifies the assembly of MEMS and ASIC (which are placed on a 2.5D-Interposer in order to enable a System In Package (SiP) as well as for higher sensor accuracy); (3) the flexible ASIC feature enables the integration of different MEMS with analogue signal output; (4) minor costs for integration of different sensors into the existing package. The heterogeneous 3D integration is a key enabler and justifies the additional process steps (mainly TSV-processing, thin wafer handling) by implementing the advantages of the polymer RDL. This integration approach results leads to improved mechanical and electrical properties. This paper will give an overview about the current achievements in the SIMEIT-project, which are predestined to improve the accuracy of different MEMS-applications with analogue signal transfer to the ASIC as well as MEMS-applications with need of stress less integration.

3D system integration is a fast growing field that encompasses different types of technologies. [1] The technology chosen for a specific application will be selected according to the required electrical performance of the systems, the footprint, cost and time to market. Other important factors are the boundary conditions given for the specific components e.g. die size, integration compatibility, component availability (wafer vs. bare die) and testability. The paper discusses a specific 3D image sensor system for automotive applications. The system is based on wafer level technology using silicon interposer with Through Silicon Vias (TSV´s), a flip chip assembled sensor element and a microcontroller. The specific system concept, the technical solution and results are discussed.