Die Deflection Research Articles

Springback Behavior due to Die Deflection during Bending

Springback Behavior due to Die Deflection during Bending

Effect of Die Deflection during Au Wire Bonding Process on Bonding Quality in Overhang Semiconductor Package

Effect of Die Deflection during Au Wire Bonding Process on Bonding Quality in Overhang Semiconductor Package

Springback Behaviour due to Die Deflection during Bending

The material strength of rolled steel sheet for car bodies is increasing considerably. It has been experientially known that the die deflection affects the springback, but there are few experimental verification cases. In this study, two bending dies with different rigidity but the same shape were manufactured. The springback of panels bended by each die was compared in detail. Using 590MPa class and 980MPa class steel sheets, the deformation of the dies due to bending also measured. The springback and deflection of the die were clearly large using the low rigidity die. From these results, it was suggested that it is necessary to consider the die deflection for accurate springback prediction of bending.

Advances in Wire Bonding Technology for Overhang Applications

Abstract 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.

Comparison of different FEM code approaches in the simulation of the die deflection during aluminium extrusion

In this paper a multihole die producing two overlapped U-shape profiles was used in order to analyze the die deflection during the extrusion process thus allowing the benchmarking of different FEM codes. The two die openings were differently designed in order to realize different die deflection (fully supported and partially supported). Profile lengths, die and profile temperatures, process load and die deflections were used as benchmarking parameters for FEM comparison. A summary of the different FEM codes approaches, of the computational times of the main outputs and their comparison with experimental results are presented. A detailed discussion for all output parameters is realized in order to understand the potentials and limits of each code. Finally a discussion on future perspective for FE code application and designing guides is reported.

Machining of dies to reduce the press-die deformation

In this work, a methodological scheme for a reduction of both the try-out and lead-time of complex stamping/draw dies is presented, since it is commonly known that dies and punches are deformed during stamping process leading to changes in the shape and making very costly their manufacturing. The finite element simulation of the system press/tool behaviour along the stamping process results in criteria for the best design of high-cost dies/punches. Die deflection during the pressing process is, in this work, investigated in order to correct the sculptured surfaces of the die or punch in the manufacturing, specifically the finishing milling pass stage. With the proposed methodology, die manufacturers are able to avoid errors coming from die deformation due to their asymmetrical shape, in a systematic form. At the same time, time of manual adjustment and polishing is reduced in a 30%. Examples are deeply explained as well as experimental evidences. Modifications of the main geometry, components and functional parameters are so recommended.

Prediction of press/die deformation for an accurate manufacturing of drawing dies

In this work a methodological scheme for a reduction of both the try-out and lead-time of complex dies is presented. The finite element simulation of the system press/tool behaviour along the stamping process results in criteria for the best design of high-cost dies/punches. Modifications of the main geometry, components and functional parameters are so recommended. Die deflection during the pressing process is in this work investigated. With the proposed methodology die manufacturers are able to avoid errors coming from die deformation due to their asymmetrical shape. At the same time, time of manual adjustment and polishing is reduced in a 30%. Examples are deeply explained as well as experimental evidences.

Prediction of residual stresses in quenched aluminum blocks and their reduction through cold working processes

Residual stresses developed after quenching of aluminum alloys cause distortion during subsequent machining. As a result, machined parts may be out of tolerance and have to be cold worked or re-machined. Experimental measurement of residual stresses is lengthy, tedious and very expensive even with the latest developments in neutron X-ray diffraction techniques, for instance. Therefore, in this study, numerical techniques are used to predict residual stresses after quenching of Al 7050 forged block, and the predictions were compared with experimental measurements. The results indicated that the predicted values are in very good agreement with the experimental measurements with around 10–15% deviation in the worst case. Two different methods of cold working (compression and stretching) are used to reduce the residual stresses. The comparison of results showed that both compression and stretching processes reduced the residual stresses more than 90%. However, single-strike compression of aluminum blocks is found to be more efficient and cost-effective for reducing the residual stresses to very low levels. The effects of elastic die were also investigated. Die deflection was found to affect the residual stress reduction capability negatively by decreasing the magnitude of stress reduction from 90% to about 70%.

Dimensional effects in the warm calibration of a stainless steel cylinder

To reduce the yield stress in austenitic stainless steels, the forming temperature can be increased to 200 °C. In order to assess the effect of this change on component accuracy, a benchmark process of closed-die calibration of a cylinder was simulated using finite element method (FEM). A fully coupled thermal-stress analysis was carried out for the whole process cycle, including closed-die compression, punch retraction, workpiece ejection and cooling to room temperature. The findings of this simulation confirmed the influence of die deflection, secondary yielding and component springback on accuracy. Thermal effects also played an important role. In particular, a modest increase of the initial temperature can compensate for oversizing and barreling errors caused by die deflection and springback. The speed of the process is another variable which influences component accuracy by changing the time scale of thermal phenomena.

Experimental and analytical evaluation for elastic deformation behaviors of cold forging tool

Since the dimensional accuracy of forged parts are largely influenced by elastic behaviors of the tool material. The characteristics of elastic deformation at a forming tool are evaluated for a cold forged alloyed steel by experiment and FEM analysis. Elastic strain at the tool is measured dynamically using strain gauges attached to the surface of die for a ball stud mass-produced continuously in a cold former. Results of FEM analysis are compared to the experimentally measured values at two modeling approaches. The first approach is made by regarding the die as a rigid body at a forging cycle and analyzed the die stress by loading the die with the pressure from the deformed part. On the other hand, the second approach is adopted as that the die and workpiece are simultaneously considered as deformable bodies during contact. Since calculation of the elastic strain and deformation amount of tool can be made at each formation step by the second approach, the elastic deflection of die acts upon the dimension of forged part at each formation step. The second approach relatively takes more time for the simulation. However, the analysis result at the elastic assumption of tool is better for predicting not only the elastic strain of tool but also the dimensional accuracy of forged part.

Extrusion die for in-process compensation of component-errors due to die-elasticity

A proposed die configuration is designed to effect the in-process compensation of the errors in the form of the extrudate which arise from the elasticity of the extrusion dies. The die is in the form of a truncated, conical-shell which is either on a plane or a spherical bearing surface, to enable it to deflect elastically, thereby changing the dimension of the die orifice. FE simulation of the work-material flow and the die deflection was conducted to verify the feasibility of the proposed configuration. The deflection of the die is a function of the extrusion force and the resulting reduction of the die orifice is in proportion to this force. The simulation enabled optimisation of the geometric parameters of the die with respect to component-form errors.

Recent developments on high precision forging of aluminum and steel

Precision forming is a suitable means to meet the increasing demands for the cost-effective prediction of net-shape or near-net-shape parts in large quantities. This article demonstrates the different procedures applied to the precision forming of parts dependent on the specific critical aspects of the process. Examples are given for the geometrical and thermal layout of the forging process, the influence of material behavior on the forged part and a procedure for the compensation of the die deflection. A suitable layout of the forging sequences is the precondition for further optimization steps of the forging parameters. CAE techniques provide state-of-the-art simulation and reproducible manufacturing tools for precision forging. Computer based engineering development systems integrate design and simulation tools to optimize the forging process. The application of these tools increases the basic understanding for the net-shape production of complex shaped parts. Beneath the optimization of the forging process layout the attainable precision also depends on the accuracy of toolmaking and process control. During the forging process the control of forging load and thermal conditions, including thermal treatment, is necessary to establish reproducible conditions for net-shape manufacturing.

FE simulation of the influence of die-elasticity on component dimensions in forward extrusion

The elastic behaviour of the forming die has a direct influence on the quality of the formed component. Simulation of material flow and of die deflection during forward extrusion was conducted using elastic and plastic considerations to establish the influence of die-elasticity on the form of the component under different processing conditions. The simulations show that the dimensions of the work-material are affected by die-elasticity during both, loading and unloading of the die. The change of the die-geometry does not produce obvious differences in the dimensions of the extrudate; however, it influences the geometric errors of the workpiece which is retained in the die. Larger values of friction in the injection chamber result in the corresponding increase of punch pressure which results in larger radial deflection of the die during extrusion (loading), the consequence being a greater variation in extrudate geometry. High levels of friction reduce the elastic contraction of the die during punch retraction (unloading), and hence, larger form-errors are sustained after unloading. The contraction of the die during unloading phase of the process causes plastic deformation of the work-material remaining in the injection-chamber; this plastic deformation is significant to the overall form-error of the component.

Die deflection effects on the metal flow pattern in plane-strain compressions with laboratory testing equipment

This paper develops design procedure for laboratory testing equipment capable of accurately compressing specimens in plane strain condition.