L. Musiejovsky

Optimization of process parameters for laser soldering of surface mounted devices

The authors present characteristics of laser soldering the explain their importance for industrial application. The dependence of solder joint quality on the laser beam parameter settings as well as on the properties of the solder and the materials to be joined is discussed. A simple thermal model is used to describe the influence of material properties on the temperature within the solder joint. Temperature courses recorded during soldering processes while applying different parameter settings are analyzed. >

Giant magnetoimpedance sensor integrated in an oscillator system

This article presents a magnetic field measurement system using giant magnetoimpedance (GMI) sensor as a phase shift element. Investigations were carried out using CoFeB trilayer thin films with 2kA∕m anisotropy field structured as strips and meanders of 300μm length presented in previous studies. The GMI sensor is integrated into an oscillator circuit. The measurement system detects the phase change caused by the magnetic field to be measured. A 6.85% impedance decrease at an applied field of 1.4mT was observed. The phase difference in such cases was Δφ=1.12°. The transmission constant was μa∕Δφ=1mV∕deg.

Investigation of magnetoimpedance effect in amorphous thin-film microstructures

The objective of this research is to correlate the magnetic properties of CoFeB trilayer thin films with the impedance responses and to investigate the potential use of this material for magnetoimpedance (MI) sensor applications. Two layers of 50-nm-thin amorphous CoFeB layers with a central 100-nm copper layer were sputtered onto a thermally oxidized Si wafer. Strips and meanders of 4–20-μm width were structured by plasma etching. The MI effect of the 50∕100∕50-nm trilayer was improved after field annealing, exhibiting a maximum of up to 9% in a 20-μm-wide meander.

Characterization of Amorphous GMI Thin-Film Meander Trilayers

This paper presents the magnetic properties of CoFeB trilayer thin films in relation to the high-frequency impedance responses. Fifty- and 100-nm-thin amorphous layers with a central 100- and 200-nm-thin Cu layer, respectively, were sputtered onto a thermally oxidized Si wafer. 300-mum-long meanders of 3-20-mum width were structured using a standard mask with various meanders, which were connected in series and were then formed by plasma etching. Magnetization curves, parallel to the easy axis, and hard axis of uniaxial anisotropy, were measured by the magnetooptical Kerr effect exhibiting anisotropy fields of around 2 kA/m and low coercivity in the hard-axis direction, depending on the film thickness. The magnetoimpedance (MI) effect was measured manually from 10 MHz to 1 GHz by means of a network analyzer using the reflected wave through the sample. The maximum effect occurred for both samples at 850 MHz

Selection of IR detectors for a fast laser soldering process with simultaneous solder joint qualification

High effort is required for quality assurance after mass soldering of electronic devices. In contrast to that, a laser soldering process with an on-line quality control system is well-suited to the production of interconnections with high reliability. This contribution presents a new principle of closed loop control and a solder joint qualification method based directly on the recognition of wetting. In this way, shorter soldering cycles can be achieved compared to other systems. From thermal analysis of laser soldering processes it is known that wetting is related to a significant rise of the heat flow inside the solder joint leading to a characteristic change of the heat radiation which is detectable with an infrared detector. The selection of an infrared detector, the infrared measuring system and its application in a laser soldering system is described. The influences of thermal qualities of the solder joint and solder paste on the slope of the detector signal are discussed. The operating principle of the quality control algorithm is demonstrated at the soldering of 1812 and MELF0204 package components onto a 35-/spl mu/m copper-plated printed wiring board (PWB). >

Laser Welding Process and Packaging for Magnetic Field Sensors

A manufacturing process for the production of miniaturized magnetic field sensors based on the GMI-effect (giant magnetoimpedance) in a thin wire of an amorphous Fe78Si7B15 alloy connected to Cu wires by laser welding is described. Due to the strong inclination of the amorphous structure to recrystallization already at a temperature far below the melting point a thermally optimized welding process is decisive for the success of the manufacturing process. The thermal load in the GMIwire in terms of the temporal temperature distribution caused by the laser welding process has been studied using transient thermal simulation. The length of the wire ends in the vicinity of the welding points in which recrystallization is believed to destroy the GMI effect is estimated. The results show that the length of the remaining active part of the GMI wire can be controlled by the energy and duration of the laser pulse and to a certain extent by the thermal properties of the substrate material. This study should help to understand the influence of welding parameters on the sensitivity of the sensor. The results of the thermal investigation are discussed with respect to the sensitivity of our GMI-sensor prototypes obtained from magnetic field measurements.

Das Laserlöten als Kontaktierungsverfahren für Mikrosensoren

ZusammenfassungMiniaturisierte Sensorelemente (z. B. Temperatursensoren, Strömungssensoren, Gassensoren, Feuchtesensoren usw.) werden häufig nur durch ihre Anschlußdrähte gehalten. Das Laserlöten ermöglicht die Verbindung von relativ dicken Drähten mit sehr dünnen Metallisierungen auf dem Sensorchip. In diesem Beitrag werden zunächst theoretische Aspekte des dynamischen Benetzungsvorgangs und des Ablegierens diskutiert. Anschließend wird der Einfluß des Substratmeterials auf die Lötparameter (Laserleistung, Strahleinwirkdauer) behandelt und der Lötvorgang durch Temperaturmessungen mit Dünnfilm-Thermoelementen, die in die Lötstelle integriert sind, analysiert.AbstractMiniaturized sensor elements (e.g. temperature sensors, flow sensors, gas sensors, humidity sensors, etc.) are frequently carried only by their lead-in wires. Laser soldering provides a possibility to attach relatively thick wires to thin film metallizations on a sensor chip. This paper first discusses theoretical aspects of the dynamic wetting process and the leaching phenomenon. Subsequently, it describes the influence of the substrate material on the soldering parameters (laser power and pulse duration) and analyzes the soldering process by temperature measurements using thin film thermocouples integrated in the soldering pad.