19 February 2003 Diffractive/refractive hybrid f-theta lens for laser drilling of multilayer printed circuit boards
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Proceedings Volume 4830, Third International Symposium on Laser Precision Microfabrication; (2003); doi: 10.1117/12.486556
Event: LAMP 2002: International Congress on Laser Advanced Materials Processing, 2002, Osaka, Japan
A new type of f-theta lens has recently been developed for microvia laser drilling of multilayer printed circuit boards. It employs a diffractive/refractive hybrid lens which has a blazed surface-relief microstructure on an aspheric surface. By introducing that hybrid lens for CO2 laser system, and by stopping the use of germanium that is optically much sensitive to temperature, the f-theta lens that consists of all zinc selenide lenses is obtained with its optical performance stable on temperature. Achromatic properties against the wavelength fluctuations of actual lasers are also achieved. A prototype is fabricated through the development of single point diamond turning of hybrid surfaces. The performance of the lens is first examined by measuring wavefront error with a tunable infrared interferometer. The results show diffraction-limited performance at all conditions, including different temperatures (up to 50°C) and wavelengths. The temperature dependence of the focal length of the lens is also measured and found to be 5 times as insensitive to temperature as that of a conventional one. Laser drilling experiments are performed for a polymide film on copper foil. The result shows good uniformity of hole size and circularity all over the 50×50 mm2 scan field.
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Keiji Fuse, Takeshi Okada, Keiji Ebata, "Diffractive/refractive hybrid f-theta lens for laser drilling of multilayer printed circuit boards", Proc. SPIE 4830, Third International Symposium on Laser Precision Microfabrication, (19 February 2003); doi: 10.1117/12.486556; https://doi.org/10.1117/12.486556

Laser drilling

Temperature metrology


Carbon dioxide lasers


Lens design

Aspheric lenses

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