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LTCC package integrated actuation for the dynamic alignment of optical components

Stefan Wilhelm, Marc Desmulliez
The project focusses on the design and manufacturing of an LTCC-process compatible meso-scale actuator for the six degrees of freedom dynamic adjustment of micro-optical components.
A variety of micro-devices contains interacting electronic, electro-mechanical and optoelectronic components, which need to be aligned statically or dynamically. Conventional static alignment is often performed before the sealing process using high precision pick-and-placing in combination with adjustable bonding processes (such as U.V. curable glue), or reflow effects. There are however instances where an alignment has to be performed after the sealing of the package. In such cases, structures with temporary actuation functionalities designed within the devices can be exposed to external fields, providing precise positioning with the help of external or temporary internal feedback. Dynamic alignment requires the manufacturing of permanent actuators within the device and must fit the requirements for power consumption, response time, force, deflection range and long term reliability. Conventionally, the function of the package is to provide electrical interconnection, heat transfer and protection against mechanical, electromagnetic and chemical influences. The additional ability of the package to provide actuation and feedback elements for aligning statically or dynamically opens up interesting opportunities for new applications such as the microscope on a chip, and greater ease of packaging by relaxing positioning tolerances at the assembly stage.

The main focus of this project is the design and prototyping of an LTCC-process compatible meso-scale actuator for the six degrees of freedom dynamic alignment of optical components. This encompasses the actuation concept and simulation as well as the manufacturing and characterisation of the prototype, which enables aligning a lenslet array over an LED/CCD array.

Among the analysed actuation methods, electrostatic actuation for the vertical forces and magnetic actuation for the lateral forces were selected because of the highest LTCC standard process compatibility. Using this actuation, only two layers of the whole stack require additional process steps. The restoring forces are generated using beam flexures, which provide as well the electrical connection to the actuated area (“rotor”, “seismic mass”). The six degrees of freedom actuation is achieved using three 120º angular shifted actuation units with three degrees of freedom.

(a) 3D view of the actuator (LTCC bulk material invisible) ; (b) 2D (top) "x-ray" view

Derived from layer based LTCC process, the design is implemented as externally configurable volume assembly using the 3D CAD package Inventor, which includes mechanical features and conductors. This allows volume collision checks as well as data export for simulation (2D and 3D) and CAM. A prototyping model was derived for the in-house manufacturing process to provide solder pads and bulk framing for stability. The CAM templates encompass all process steps: DXF files for laser manufacturing, screen printing, stencil printing and masks for powder blasting. Simulations and testing provide feedback for the iterative development of the prototype device.

CAM export examples: (a) 3D screen assembly model. (b) 2D export for screen manufacturer.