Peter Zimprich

Anwendung eines Laser-Speckle-Korrelationsverfahrens zur Messung lokaler Dehnungen in Mikromaterialien (Application of a Laser-Speckle Correlation Technique for Measuring Local Strain in Micromaterials)

Abstract Berührungslose Dehnungsmessverfahren für Materialien in Mikrometerdimensionen, wie sie in der Mikroelektronik und Mikrosystemtechnik Verwendung finden, gewinnen in den Materialwissenschaften zunehmend an Bedeutung. Die mechanischen Eigenschaften dieser „Mikromaterialien“ können deutlich von jenen, die an Makroproben gewonnen wurden, abweichen. Zur Erhöhung der Zuverlässigkeit von Mikrosystemen ist daher die Materialprüfung in kleinen Dimensionen notwendig. Dabei spielen optische Methoden, die ohne Messmarken an der Probenoberfläche und ohne Probenpräparierung auskommen, eine besondere Rolle und eröffnen völlig neue Prüfmöglichkeiten, die mit Standardmethoden nicht gegeben sind.

Size Effects in Lead Free Solder-Joints

Due to the environmental and health concerns the usage of lead based solders in electrical and electronic equipment is restricted. Recent regulations require the replacement of these solders by non toxic lead free solders, thus numerous scientific and technical investigations has been performed on the properties of the solder joints produced using these new materials [1].

Hochauflösende Laser-Speckle-Methode zur Charakterisierung komplexer thermomechanischer Eigenschaften von Vielschicht-Systemen (Application of a High-Resolution Laser-Speckle Strain Gauge for the Characterization of Thermomechanical Properties of Multilayer Systems)

Berührungslose Dehnungsmessverfahren für Materialien in Mikrometerdimensionen, wie sie in der Mikroelektronik und Mikrosystemtechnik Verwendung finden, gewinnen in den Materialwissenschaften zunehmend an Bedeutung. Die mechanischen Eigenschaften dieser “Mikromaterialien” können deutlich von jenen, die an Makroproben gewonnen wurden, abweichen. Zur Erhöhung der Zuverlässigkeit von Mikrosystemen ist daher die Materialprüfung in kleinen Dimensionen notwendig. Dabei spielen optische Methoden, die ohne Messmarken an der Probenoberfläche und ohne Probenpräparierung auskommen, eine besondere Rolle und eröffnen völlig neue Prüfmöglichkeiten, die mit Standardmethoden nicht gegeben sind. Nontactile strain measurements of materials with micrometer dimensions, as used in microelectronics and microsystems, are rapidly expanding fields in materials science. Mechanical properties of “micromaterials” can differ significantly from those determined from their bulk counterpart. To enhance the reliability of microsystems, materials testing in small dimensions is necessary. Optics-based methods circumventing surface marking or preparation therefore play an important role and open new testing potentials where standard testing techniques cannot be used.

Exploring the world of micromaterials using laser-speckle techniques

Laser speckle based methods for measuring strain within specimen have been devised by several authors using a wide variety of optical arrangements.1-3 Almost all of the proposed methods aim at measuring strain over an extended baselength given, in case of the laser speckle strain gauge4 by the distance at the specimens surface of two impinging beams of laser light that is usually on the order of 5 mm to 50 mm. Others reported on encouraging results using a set-up employing a single illuminated spot at the specimens surface.1, 5 Still the extend the mechanical strain is averaged over is given by the beam diameter which using HeNe lasers is somewhat limited to approximately 1 mm. In this proposed paper we report on the development and application of a laser speckle shift strain sensor that employs a laser beam focussed down to only several tens of micrometers thus allowing a very localized strain reading.5 Although as is known from the fourier optical analysis the average speckle size is inversely proportional to the spot diameter and directly proportional to the projection distance by miniaturizing the sensor a true microscopic strain gauge can be devised. Thus some problems in material physics can by addressed, like measuring strain - mostly caused by thermal imbalance - within an extended micro chip, or measuring mechanical strain within thin fibres or foils, or determining strain caused by the mismatch of thermal expansion coefficients between a copper substrate and AgSn solder in electronic circuits, where averaging the strain reading over extended strain fields would definitely underestimate true mechanical (over-) loads that could lead to catastrophic failures.