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In SMT manufacturing, automation is the key to achieving the highest throughput at the lowest cost. Complex devices of various shapes and sizes often require final electrical adjustments under operating conditions to ensure conformance to electrical specifications. This paper describes the process of laser trimming completed SMT devices and the advantages it has over conventional trimming methods. The material presented is based on laser trimming systems currently used in SMT production applications that will also be described.

High speed chip resistor trimming requires a more advanced technology than just passive network‐trimming. Some guidelines have to be observed to obtain a good approach to the desired goal. One fast and inexpensive way of finding the best parameters for a trim cut, i.e., maximum speed and best accuracy, is CAD‐network simulation. Last but not least several parameters should be checked and controlled continuously to optimise yield.

Fired resistors exhibit variations which are minimised by abrasive and laser trimming. The latter may cause unstable behaviour which is further aggravated by thermal shock. The chemical structure of a thick film resistor is analysed with respect to mechanical stress, and the theoretical conclusion that the coefficient of thermal expansion of the resistor should be equal to or smaller than that of the substrate is verified experimentally. The thermal behaviour of ruthenium dioxide is examined and a range of CTE values are determined for materials of varying chemical composition. The relationship between CTE and post laser trimming stability is demonstrated on four thick film resistors which differ in thermal expansion. It is pointed out that formulations with high metallic content can absorb tensile stress by elastic deformation, thus minimising the formation or propagation of laser induced cracks.

Present and future development of laser processing as a production technique for modifying semiconductor devices, improving yields, and decreasing development times are described. Current applications covered include thick‐ and thin‐film resistor trimming, deposited film and polysilicon resistors on silicon trimming and redundant memory repair. Emerging applications include microcircuit mask making and capacitor trimming. Examples of processes still under development include selective annealing, minority‐carrier lifetime doping, and device diagnostics by laser imaging.

Large ohm film resistors that guard sensitive telecommunication devices against the hazards of lightning require a set of exacting characteristics for tolerance, endurance, and productivity. These characteristics largely depend on how the resistor is trimmed. Conventional laser trimming is unable to provide all the requirements for this important resistor application. A new technique developed by Teradyne Inc. called Algorithmic Trimming employs an algorithm and data base to calculate real‐time trim vectors that are used in a trimming hardware processor to overcome the drawbacks of conventional trimming. With this new technique 50‐ohm film resistors were trimmed to specification with 0·1% tolerance while attaining high resistor stability and a trim time of 300 milliseconds.

This paper aims to study the effects of varying laser trim patterns on several performance parameters of thin film resistors such as the temperature coefficient of resistance (TCR) and target resistance value.

The benefits and limitations of basic trim patterns are taken into consideration, and the plunge cut, double plunge cut and the curved L-cut were selected to be modelled and tested experimentally. A computer simulation of the laser trim patterns has been developed for the modelling process of the resistors. The influence of the trim length and resistor dimensions on the TCR performance and resistance value of the resistors is investigated.

It is found that variation in trim length, within the range of 5 to 15 mm, can give significant increases in the TCR of the thin films. Thus, for the plunge cut, TCR can reach up to 11.51 ppm/oC, for the double plunge cut up to 14.34 ppm/oC and for the curved L-cut up to 5.11 ppm/oC.

Research on the effects of various laser trimming geometries on the TCR and target resistance accuracy is limited, especially for patterns such as the curved L-cut, which is investigated in this paper.

This paper provides a technical background and overview of the rôle played by the computer controlled laser trimming system in the thick film industry.

The current state in the application of lasers for cutting and welding is reviewed. Most cutting operations are performed on specifically developed laser machine tools such as the Trumpf Lasercell and its application in the development of trim shapes and low volume panel production at a sub‐contract toolmaker is described. Robots are mainly used with lasers for welding, particularly of vehicle body components where laser welds are found to be advantageous in reducing material weight and improving body strength. One example is the production of differing thickness panels and a robotic installation for producing car door inners is described. The benefits of the new generation of Nd:YAG power lasers are listed, including the ability to transmit the laser beam via fibre optic cables. This is particularly advantageous when robots are used to manipulate the “torch” and a new robot cell from Trumpf is described. Finally, the role of gases in laser processing is discussed.

Focuses on embedded passives (EPs), an emerging technology for the PCB industry, which shows potential for reductions in board area (or increased functionality in a given fixed area), improved signal performance, and attractive cost benefits. Notes that industry acceptance of EPs technology, and its ultimate acceptance in the OEM designers' toolbox may be dependent on some key process tools.