Study of the ultrasonic stress relief method for assembly of flex lead in inertial devices

The micro inertial device is widely used in the aerospace field when high measuring precision is required. The reaction torque from the residual stress of flex lead, which is generated in the assembly process, is a significant source of error. To address this problem, a stress relief method based on ultrasonic aging is designed and studied in this paper. An experimental platform is established using a high frequency, low amplitude ultrasonic system to improve the uniformity of the plastic stress distribution. The deformation of flex lead is measured by a visioning system. Experiments are carried out for two kinds of flex lead with Φ150 and Φ30 μm in profile diameter. Ultrasonic loading time and amplitude are studied, and results indicate that the released stress increased gradually with ultrasonic loading time in the initial stage. Up to a specific value, it remains constant with the subsequent ultrasonic loading. The ultrasonic loading times required for the flex leads in different sizes to achieve constant balance are different, and longer times are needed for the thicker sizes. The stress relief degree is about 20%, and it can be enhanced by increasing ultrasonic amplitude. But damage will be caused by the enhanced impact from ultrasonic vibration in larger amplitude.

Experimental Study on the Relationship between Dislocation Density and Internal Stress in Micro Electroforming Layer

In the micro electroforming process, the existence of electroforming layer defects caused by macro internal stress seriously limits the application and development of the micro electroforming technology. Currently, some studies have shown that ultrasonic can reduce the internal stress. But the formation process of the internal stress and the mechanism of ultrasonic stress relief in micro electroforming layer are still unclear now. In this paper, the relationship between dislocation density and internal stress under ultrasonic was studied. The results show that the ultrasonic can make the dislocation density increase and the compressive stress decrease. When the ultrasonic power is 200W, the dislocation density and the compressive stress culminate 3.8×10-15m-2 and-144.4MPa, respectively. The ultrasonic can excite the movement of dislocation proliferation, pile-up and opening, which leads to a micro plastic deformation in the crystal, and thereby releases the internal stress.

Stress Forming of Fine Metal Wire Based on Ultrasonic Vibration

The assembling process of the flex lead of an accelerometer can bring in internal stress, which causes drift error and affects the precision of the accelerometer. The paper introduces a method using ultrasonic vibration to reduce the internal stress, discusses the theory of ultrasonic stress relief on fine wires, shows ultrasonic stress relief experimental apparatus which uses an optimized ultrasonic tool head to inflict ultrasonic vibration to fine wires. By introducing the displacements of the fine wire ends into ANSYS, changes of the internal stress of the fine wire can be obtained. The experiment studies the performance of ultrasonic vibration to fine wire internal stress and deals with the relationship between infliction time and results. The experiment results confirmed that by selecting the suitable experiment parameters, ultrasonic vibration is an effective way to internal stress relief, the internal stress decline as infliction time increase then stays.

Application of Ultrasonic Stress Relief in the Fabrication of SU-8 Micro Structure

SU-8 photoresist has received a lot of attention in the MEMS field because of its excellent lithography properties. However, its high internal stress affects the overall pattern quality of the micro structures. The purpose of this work is to reduce the internal stress in SU-8 micro structure by ultrasonic stress relief technology. The stress relief mechanism of SU-8 micro structure was presented. The effect of ultrasonic stress relief on SU-8 micro structure was studied by experiments. The experimental results show that the internal stress in SU-8 micro structures can be reduced by ultrasonic stress relief technology.