Packaging and Interconnection Technology

Basically, an electrical contact between the component (sensor or actuator) and a circuit board is created by means of ultrasonic wire bonding. Ultrasonic wire bonding is a welding technique for making discrete electrical connections of chips on PCB substrates. The components to be joined must have suitable contact surfaces ("pads" / landing pads). The wires used are mainly made of gold or aluminium and have a diameter of approximately 10 μm. The wire is not melted, but rubbed against the pad contact surface by pressure, heat and ultrasonic energy, creating a permanent connection. The IMPT has a manual and a semi-automatic bonder for ultrasonic wire bonding. Here, Au or Al wires are bonded to the Au, Cu or Ni contact pads. Electrical contacting can also be produced by soldering.

Different techniques are used to connect micro components with each other. The methods used at the IMPT are adhesive bonding, soldering and anodic bonding. Bonding and soldering belong to the group of material-locking joining processes.

A bonded joint consists of the two parts to be joined and the adhesive layer between them. The wetting at the joining surfaces plays an important role for the final joining strength. To influence the wetting of the joining partners, the surfaces can be treated (machined or coated) or an adhesive with a suitable viscosity can be selected. The adhesive finally gains its internal strength (cohesion) through physical setting processes or through chemical reaction. This process is also called curing. The activation energy for curing can be caused by humidity, temperature or UV exposure. In addition to cyanoacrylate, epoxy resin or UV-curing adhesives, the IMPT uses various washable (easily removable) adhesives (Crystalbond™, Aquabond™, special waxes). Depending on additional particles in the adhesive, one can create electrically conductive or thermally conductive compounds.

Soldering is a thermal process in which a material connection between two base materials is created with an additional material (solder). Either two parts to be joined can be connected with one solder (connection soldering) or an electrical connection between two electronic parts can be created (contact soldering). The prerequisite for soldering is a clean surface of the parts to be joined. During soldering, the connecting material, the solder, melts, but the melting points of the base materials (joining partners) are not reached. The solder is processed in various forms, as paste, as ingots, as preformed elements, as rods, or in special cases it can also be sputtered. Depending on the application, soldering at the IMPT is used for the mechanical connection as well as for the electrical contacting of microcomponents. For an extremely strong mechanical connection with a very thin adhesive layer, micro components with a sputtered glass layer are brazed in a high-temperature furnace (up to 800°C).

Anodic bonding is a process supported by temperature and electrical fields for bonding metals or semiconductors with ion-containing glass substrates. Anodic bonding produces very stable, hermetic and cost-effective connections. However, the process places very high demands on the flatness, quality (low roughness) and cleanliness of the joining surfaces. In silicon micromechanics it enables the construction of three-dimensional systems with integrated data processing. At the IMPT, anodic bonding is used to connect Si or SiO₂ chips, depending on the application.

For years, the Institute of Microproduction Technology has been engaged in the function-oriented assembly of microcomponents undergoing research. Especially moving systems of actuators require a precise and reliable guidance of active and passive parts to each other. In order to guarantee the actuator function within a very small tolerance range, different handling concepts and self-alignment principles are developed and applied. IMPT's many years of experience in precision mechanical machining of hard and brittle materials (Si, Al₂O₃-TiC, sapphire and SiC) could be used to create high-precision assembly components. The use of ultra-precision dicing has made it possible to produce a wide variety of geometrically complex and highly accurate micro-parts and profiles. In these cases a profile accuracy is below 5 µm. An example for the self-aligned micro-assembly of actuators with a ball guide, using 200 µm ruby balls, has been successfully established several times. In this case an air gap of less than 8 µm between the active and passive part was made possible. A further development of this process is a system with a frictionless electromagnetic guide, which has been built and tested in various designs. Before the start of each assembly, all requirement criteria, specifications and the choice of assembly type are selected and defined.

The institute is well positioned in terms of assembly and connection technology with soldering stations, bonding stations and equipment for easier contacting on very small substrates.