Investigation on the Flexural Modulus of Silicon Dies to Improve Die Mechanical Modeling Accuracy

Mechanical modeling of integrated circuit (IC) dies is commonly performed using the mechanical properties of the bulk silicon material. However, modeling results such as die deflection and the actual results were observed to have significant difference. This paper discusses the investigation done on the flexural modulus of actual IC dies used in package assembly manufacturing. Results were then compared with the modulus of the bulk silicon die or mirror die. The measurement of flexural modulus was done using the standard 3-point bend test. It was found out that the flexural modulus of the actual IC die is significantly lower than the flexural modulus of the bulk silicon or dummy die. Even with the actual IC die, the flexural modulus of the active side is also lower than the back side. From this study, it can be concluded that mechanical modeling involving IC dies could be improved by characterizing the properties of the actual die used. The common practice of using the properties of the bulk silicon die in mechanical modeling would not provide accurate results.

Numerical analysis of plastic die deformation during high temperature copper extrusion

In copper extrusion, billet temperatures of 600°C or more are very common and the dies are therefore exposed to high thermo-mechanical stress. This causes deflection and wear of the dies and thus reduced quality of the extruded profile. In the present study, die deflection and residual deformation after several extrusion cycles was investigated by means of extrusion trials and numerical analyses. Material models of four tool materials (hot-work tool steels 1.2367 and CS1, nickel-based alloy 718, cobalt-based alloy Stellite 1) and the copper alloy CW024A were provided by hot compression tests. Extrusion trials were carried out applying four different dies, each made of another tool material. Using the FEM based software DEFORM 2D, the extrusion trials were modeled and decoupled die stress analyses were performed, which simulated three consecutive load cycles. The focus of the data interpretation was in die deflection in proximity of the die land due to the thermo-mechanical load and residual plastic deformation after relief of the mechanical load. Larger values of deflection close to the die land were observed for the hot-work tool steels, while the deflection of nickel- and cobalt-based alloys was negligibly small. Also, remarkable plastic deformation was only determined for the hot-work tool steels, with increasing values for every simulated load cycle. This analysis characterizes the performance limits of hot-work tool steels and the benefits of nickel- and cobalt-based alloys regarding contour accuracy during high temperature copper extrusion.

Advances in Wire Bonding Technology for Overhang Applications

Wire bonding is the most popular interconnect technology and the workhorse of the semiconductor packaging industry. Wire bonding is widely used for 3D packaging in which multiple dies are often stacked vertically in a ‘stacked die’ configuration. In such packages, one or more dies may be unsupported in an ‘overhang’ (e.g. cantilever beam) configuration. Wire bonding on an overhang die causes die deflection. If not optimized, it may lead to improper ball shape, inconsistent looping, pad crack and die crack issues. Therefore, careful process optimization is needed to have the best outcome in wire bonding performance. This optimization is often tedious and time-consuming. Moreover, recent trends towards minimizing package size (e.g. ultra-thin dies) and increasing number of die stacks add to the challenges of optimizing a wire bonding process for overhang devices. This paper examines the challenges of wire bonding on overhang devices. Finite element analysis (FEA) of overhang devices is presented. Die deflection data obtained from the FEA correlates well with the experimental results obtained on the ball bonder. The FEA results show that die deflection increases significantly with decreasing die thickness and increasing overhang distance. Other factors such as substrate thickness, and bonding temperature also effect die deflection, although less significantly than die thickness and overhang distance. Various considerations for optimizing a ball bonding process on overhang devices are discussed. Experimental results of ball bonding optimization on 50 μm and 75 μm thick overhang devices with different overhang configurations are presented.

Simulation of Material Flow Coupled with Die Analysis in Complex Shape Extrusion

The paper presents recent studies in simulation of thin profile extrusion technology with the emphasis on interaction between the material flow and the state of the tooling set. To take into consideration die deflection and gradient of the temperature across the die and mandrel during the entire process cycle a transient coupled thermo-mechanical model has been built on the basis of QForm-Extrusion program. The paper explains the background for this model and some tests to verify its accuracy. Practical implementation of this model at several die making and extrusion companies has shown it to be of higher accuracy compared to the results of rigid die simulation.

Extrusion Benchmark 2011: Evaluation of Different Design Strategies on Process Conditions, Die Deflection and Seam Weld Quality in Hollow Profiles

In the paper experimental investigations aimed at allowing a detailed and accurate comparison of different FEM codes were presented and discussed. Two hollow profiles within the same die were characterized by different thicknesses within the profile, two welding chambers and critical tongues (one fully supported and one partially supported). The material flow balance was performed by means of feeder size and position on a profile and by means of bearings on the other one. Accurate monitoring of process parameters was carried out by using a self-calibrating pyrometer for profile temperature, six thermocouples for die thermal monitoring, a laser velocitymeter for profile speed and two laser sensors for die deflection on critical tongues. AA6082 alloy was used as deforming material, while H-11 hot-work tool steel was selected for the die material. The experiments were repeated at least three times under the same conditions in order to provide a nearly steady state statistical distribution of the acquired data. These are used as a reference for the 2011 edition of the extrusion benchmark.