Thermocompression assembling device used to connect together a wire with an IC

The conical diamond is retained in material of specific thermal expansion coefficient to ensure that it is not loosened when the temperature rises. The tool comprises a head which includes a small diamond (2) fixed to a support body (3). The diamond has a conical shape with its base retained in the support body, and its tip projecting freely. The diamond is fastened by a system which avoids the diamond becoming unseated as a result of different thermal expansion of the diamond and base material. This may comprise a seating in the block which is also conical in shape, or may comprises a welding material (5) surrounding the base of the cone, within a recess formed in the block. Materials are chosen such that their respective degrees of thermal expansion do not allow the diamond to become loose when the device is heated

Influence of abrasive concentration on the qualiy of wire-sawn silicon wafers

The sawing parameters have an impact on the depth of the defects in the wafers, and hence on their mechanical strength. However, as sawing is a highly complex system, the wafering industry is still relying on a “trial and error” approach to improve the sawing parameters. In this contribution, the effects of the abrasive concentration are studied with the help of the “rolling-indenting model”, the model most commonly used to describe the sawing process. From roughness and cracks depth measurement correlated with flexure tests, we show that using a lower silicon carbide concentration in the slurry decreases the depth of the defects as well as the roughness and results in a higher breakage strength of the wafers

Mechanisms of wafer sawing and impact on wafer properties

Silicon wafer wire-sawing experiments were realized with different sets of sawing parameters, and the thickness, roughness, and cracks depth of the wafers were measured. The results are discussed in relation to assumptions underlying the rolling-indenting model, which describes the process. It was also found that the silicon surface at the bottom of the sawing groove is different from the wafer surface, implying different sawing conditions in the two positions. Furthermore, the measured parameters were found to vary along the wire direction, between the entrance of the wire in the ingot and its exit. Based on these observations, some improvements for the wire-sawing model are discussed. Copyright (C) 2010 John Wiley & Sons, Ltd

Effects of edge defects induced by multi-wire sawing on the wafer strength

The focus of the photovoltaic industry is a continuous reduction of the cost of solar energy. Lowering the wafer thickness during the processing by means of multi-wire slurry saw technology is one of the key issue to reduce these costs. However, reducing the wafer thickness without increasing the wafer strength leads to a larger breakage rate during the subsequent fabrication steps. Hence, recent studies have been carried out to enhance the sawing process by minimizing the sub-surface defects. Nevertheless, little efforts have been made to determine at which stage in the wafering process, the most dangerous defects are created for solar cells processing. Are they made during the shaping of the silicon bricks from cast ingots, or during the slicing operation into wafers, or else? State of the art consists in polishing the bricks prior to wafering by multi-wire slurry saw. The goal of this paper is to bring some insights on the importance of the edge defects on the wafer strength. Results using various methods such as roughness measurement, wafer strength measurement with the 4-lines bending tests and finite elements calculations are presented. The main conclusion of this study is that the defects made during the shaping of the bricks prior to wafering can be of high importance with respect to wafer strength