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Advanced LASER micromachining for precision component manufacturing in the electronics test industry

In the realm of the electronics test industry, the examination of electronic components and integrated circuits at the wafer level is a critical step in the manufacturing process. This meticulous testing occurs before the components are diced and packaged. The central tool for this purpose is the probe card, comprising guide plates stacked with miniature probes that establish an electrical contact between the integrated circuit on the wafer surface and the test head. The ongoing trend of shrinking integrated circuit sizes necessitates the miniaturization of test head patterns, leading to increased pattern density and decreased probe sizes. While ceramics, chosen for their hardness, low conductivity, longevity, and thermal characteristics, are the preferred material for guide plates, their challenging machinability with conventional microdrilling technologies poses a significant hurdle.

 

Ultrafast laser micromachining solutions

Ultrafast laser micromachining emerges as a ground breaking solution for the electronics test industry. This contact-freeprocess eliminates tool wear, obviating the need for frequent tool head replacements. Notably, the process exerts no physical force on the material and avoids contamination by foreign particles. The ultrashort laser pulses yield a significantly reduced Heat Affected Zone (HAZ), facilitating clean, burr-free micromachining with minimal thermal effects. Moreover, the multi-photon absorption property of these lasers extends their applicability to various substrates,allowing for the precise machining of traditionally challenging materials such as ceramics.

 

5-Axis machining advancements

Utilizing a precession head, the ultrafast laser system achieves 5-axis machining capabilities, enabling not only X-Y translation but also Z-axis (focus variation), changes in the angle of incidence, and angle ofrotation. This advanced functionality facilitates the drilling of square and rectangular holes with small corner radii and straight walls.

Figure 1 illustrates the successful drilling of rectangular holes with dimensions of 25x 50 x 250 μm, exhibiting dimensional stability and positional accuracy better than 2 μm. The resulting holes boast straight walls and a corner radius of less than 5 μm, essential for probes with a square or rectangular profile.

Enhanced flexibility and precision

The lower HAZ inherent in the ultrafast laser process ensures thermal-effect-free holes. The ability to adjust the angle of incidence and rotation allows for the drilling of holes with straight, positively or negatively tapered walls. The contact-free nature of the process facilitates achieving a high density of holes with a remarkable wall thickness down to 6 μm. The precision head's beam steering flexibility enables the creation of complex shapes, such as step holes, with high accuracy and repeatability for industrial applications.

Figure 2 illustrates a positive print of a step hole in an industrial polymer material, showcasing precise control of the step shape. Furthermore, the process successfully produced a step hole with a high aspect ratio of 1:17 in a ceramic material.

 

Foil cutting and shaping for probes

The ultrafast laser system extends its utility to the production of probes for guide plates. By fixing a foil of the desired material on a substrate, the laser can be programmed to direct-write a pattern, shaping the foil into the intended probe form. This process offers exceptional flexibility, allowing easy adaptation to achieve the required probe shape by modifying the laser program.

Figure 3 displays probes developed with a thickness of 30 μm using this technique, with the tips ablated to provide the necessary slope shape as per customer specifications. The process' flexibility accommodates arange of design considerations, facilitating the creation of complex structures, including springs, mechanical stops, and slopes within the probes limitedby the laser spot size. This adaptability enables customers to transform foils of their choice into functional probes with desired

features and encourages research and development into novel probe types and shapes.

 

Femto turning for wire probes

Addressing the demand to convert raw wire material supplied on reels into probes, the Femto Turning Operation (FTO) leverages femtosecond lasers for micro-turning operations. Overcoming challenges related to feed and clamping of the material, the FTO process enables the transformation of wires into small, precisely shaped parts.

Figures 4 and 5 illustrate an FTO-machined probe with a tapered tip, designed for optimal substrate contact. The process allows for the flattening of the tip to prevent substrate damage, achieving a surface finish below 50 nm. The FTO machine accommodates cylindrical parts or wires ranging from a few tens of microns up to 3 mm in diameter, with part lengths up to 8 cm. This technology, initially developed for the electronic test industry, has found applications in the medical and watchmaking sectors, competing with grinding technology while offering the advantages of a contact-free and dry process.

Operational parameters

The presented results were obtained using a femtosecond laser source with pulses of 190 femtoseconds duration at awavelength of 515 nm and an average power of 10 Watts. A spot diameter of 10microns was employed to ensure minimum radius and maximum machining accuracy.The demonstrated capabilities showcase Posalux's commitment to advancing micromachining technology.

 

Collaborative initiatives for technological advancement

Posalux is actively exploring collaborative initiatives with universities and research centers to propel high-end micromachining technology into the marketplace. By fostering partnerships, Posalux aims to contribute to the continued evolution of precision component manufacturing, addressing the intricate demands of the electronics test industry and beyond.

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