Linear encoders on the alignment stages with linear or DC motors provide 20 nm resolution and a repeatability deviation of less than 100 nm. The stages with stable crossed-roller bearing combine long travel ranges with high speed. This is an excellent basis for unparalleled performance and uptime over a long life time. Fast alignment algorithms pick the initial signal and optimize it by spiral searches, scan routines actuating several axes simultaneously and the feedback via various channels. The starting position is defined by mechanical references and machine vision routines, including edge detection, pattern recognition and autofocus.
Auxiliary axes for moving the weld heads and other equipment are robust stages with stepper or BLDC motors with optical encoders. Their carriages rest on pre-loaded recirculating ball bearings and ensure excellent stability and reliability while the compact size gives high flexibility for the optimum machine design.
The design of NanoWeld is optimized for minimum weld shift. Special assemblies using air bearing technology and force sensing bring the parts to be joined into a uniform surface contact.
The coaxial system geometry is based on a half sphere floating on an air cushion which self-aligns the welding surfaces. This procedure is fast and does not introduce any unbalanced force. For standard devices, no additional correction welds or bending are introduced. This increases process stability, reduces part failures and shortens process times.
In the linear set-up, auxiliary grippers for weld clips ensure a precise insertion of these structures inside the package with a known force and without tilting. As it is more complicated to control all tolerances in this device geometry, bending procedures correct for the mechanical shift either by applying additional weld spots or by a gentle mechanical procedure using special features in the gripper.
During the system design and process development, all factors influencing the weld shift are considered. The weld laser maintains the splitting ratio with less than 1% deviation among the weld heads and their high precision optics ensure identical spot sizes for the individual partial beams. Spot size and weld parameters are adjusted in order to introduce only the energy which is required for the necessary mechanical strength. In addition, a symmetric weld spot pattern reduces possible shift. Offset values are verified during process development. They are introduced before the respective weld procedures avoiding the known displacement.
Superimposed cross-hairs are adjusted to the center of the CCD cameras which are mounted on the weld optics. The high imaging quality allows for automated machine vision in order to set the weld spots in the ideal positions. Stored pictures of the weld spots support process control.