CN106938407A - The dynamic magnetorheological finishing device and its polishing method of a kind of controllable moving field - Google Patents

Abstract

The invention discloses a kind of dynamic magnetorheological finishing device of controllable moving field and its polishing method, including burnishing device rotating mechanism and controllable moving field generation mechanism, burnishing device rotating mechanism includes driving motor, drive, Rotary tray, cup polishing disk etc., and controllable moving field generation mechanism includes frequency changing power device, electric wire group, wire rotating joint, magnet exciting coil etc..The present invention can adjust size of current and alternative frequency to change the magnetic field intensity and change procedure that magnet exciting coil is produced by frequency changing power device, improve abrasive material DYNAMIC DISTRIBUTION and its processing characteristics in " the micro- bistrique " produced in polishing disk by magnetic rheology effect, micro- bistrique formation flexible polishing pad that cluster is produced is carried out high efficiency processing to workpiece in the presence of rotating mechanism.

Description

A dynamic magnetorheological polishing device and polishing method with controllable dynamic magnetic field

technical field

The invention relates to the technical field of ultra-precision processing, in particular to a dynamic magnetorheological polishing device with a controllable dynamic magnetic field and a polishing method thereof, which are used for flattening processing of optoelectronic/microelectronic semiconductor substrates and optical surfaces.

Background technique

With the advancement of science and technology and the growth of demand, the requirements for the optical performance of optical components are getting higher and higher, and the surface precision is required to reach ultra-smoothness (roughness Ra is less than 1nm), and the surface shape precision also has higher requirements (shape Accuracy reaches below 0.5 microns). In the popular LED application fields in the last decade, single crystal silicon (Si), single crystal germanium (Ge), gallium arsenide (GaAs), single crystal silicon carbide (SiC) and sapphire (Al2O3) are used as semiconductors. The substrate material also requires an ultra-flat and ultra-smooth surface (roughness Ra below 0.3nm) to meet the requirements of epitaxial film growth, and requires no defects and no damage. Planarization processing has become an essential process for optical components and semiconductor substrates. The traditional processes are mainly high-efficiency grinding, ultra-precision polishing, chemical mechanical polishing and magnetorheological polishing. The processing quality and precision directly determine the optical devices and semiconductor devices. performance.

Magnetorheological finishing (MRF) is a new optical surface processing method proposed by KORDONSKI and his collaborators in the 1990s by combining electromagnetics, fluid dynamics, analytical chemistry, and processing technology. , has the advantages that traditional polishing does not have, such as good polishing effect, no subsurface damage, and suitable for complex surface processing. It has developed into a revolutionary optical surface processing method, especially suitable for ultra-precision processing of axisymmetric aspheric surfaces, and is widely used. It is the final processing procedure on the surface of large optical components, but in the actual processing process, there will be problems such as low processing efficiency.

In order to improve the polishing efficiency of magnetorheology, patent CN200610132495.9 proposed a planarization grinding and polishing method and polishing device based on magnetorheological effect based on magnetorheological polishing principle and cluster action mechanism, and carried out a large number of experimental studies However, it is found that it is difficult to realize the continuous renewal of the "micro-grinding head" by using the circulation method of the polishing liquid, and the protrusion makes it difficult to solve the problem of the uniformity of the workpiece surface processing. Aiming at the uniformity of plane processing, patent CN201510801886.4 proposes a dynamic magnetic field self-sharpening magnetorheological flexible polishing pad generator and its polishing method, which fully realizes the magnetorheological flexible polishing pad’s ability to control the workpiece during processing. Constant pressure processing, and the abrasive can be updated and self-sharpening in real time during the processing process, but due to the limitation of the device structure in the patent, the distance between the "micro-grinding heads" produced by the magneto-rheological effect is relatively large, and the workpiece idle travel during the processing It is longer, which affects the processing efficiency, and when the magnetic field strength needs to be changed, the polishing disc must be disassembled to replace the permanent magnet, and the steps are cumbersome.

On the basis of the above research, the present invention proposes a dynamic magneto-rheological flattening polishing device with a controllable dynamic magnetic field and its polishing method, optimizes the structure, replaces the permanent magnet with an excitation coil, and adjusts the range of the magnetic field by changing the magnitude of the current and strength, under the premise of self-sharpening of the "micro-grinding heads", the distance between the "micro-grinding heads" is shortened, the effective processing time is prolonged, the processing performance of the magnetorheological flexible polishing pad is improved, and the magnetorheological polishing is improved. Efficiency, to achieve uniform processing of the workpiece.

Contents of the invention

The object of the present invention is to overcome the deficiencies of the prior art and provide a dynamic magnetorheological polishing device with high processing efficiency, simple device structure, convenient operation and controllable dynamic magnetic field.

Another object of the present invention is to overcome the deficiencies of the prior art and provide a polishing method based on the above polishing device.

The object of the present invention is achieved through the following technical solutions:

A dynamic magnetorheological polishing device with a controllable dynamic magnetic field. The polishing device is applied to the processing of semiconductor substrates, and mainly includes a base, a drive unit, a rotating tray, a cup-shaped polishing disc, and a support sleeve for supporting the rotating tray. A cylinder and a controllable dynamic magnetic field unit for controlling the strength of the magnetic field. The supporting sleeve is fixed vertically in the middle of the base, and the driving unit is arranged on the base. The rotating tray is composed of a disc and a neck. The neck of the rotating tray is inserted into the supporting sleeve and is connected with the drive unit, and the driving unit drives the rotating tray to rotate. The cup-shaped polishing disc is fixedly installed on the disc portion of the rotating tray, and the cup-shaped polishing disc is filled with magnetorheological fluid, and the workpiece is polished after the rotating tray rotates.

Specifically, the controllable dynamic magnetic field unit includes a variable frequency power supply device, a wire rotary joint and several sets of excitation coils. The excitation coil is installed in the disc portion of the rotating tray, the variable frequency power supply device is fixed on the base, the electric wire rotary joint is installed at the bottom of the neck of the rotating tray, and is respectively connected with the excitation coil and the variable frequency power supply device through wires. The electric wire rotary joint can keep the electrical connection between the variable frequency power supply unit and the excitation coil when the rotating tray rotates at high speed. After the power is turned on, each excitation coil generates a magnetic field with a specific strength, so that the magnetorheological fluid forms several "micro-grinding heads", and these "micro-grinding heads" will rotate with the rotation of the rotating tray, so as to achieve ultra-fine grinding on the workpiece. Precision Machining.

Specifically, the drive unit is used to drive the rotating tray to rotate, and mainly includes a transmission motor, a driving wheel and a driven wheel. The transmission motor is fixed on the base, the driving wheel is installed on the output shaft of the transmission motor, and the driven wheel is installed on the neck of the rotating tray, and is fixedly connected with the rotating tray. The driven wheel is connected to the driving wheel through a transmission belt, and the rotating tray is driven by a transmission motor to rotate. When the transmission motor starts, its output shaft transmits power to the rotating tray through the driving wheel, driving belt and driven wheel.

Further, the polishing device also includes a bearing end cover arranged on the neck of the rotary tray, a pair of turntable bearings, an inner sleeve and an outer sleeve. The bearing end cover is installed between the disk portion of the rotating tray and the supporting sleeve, and is used to position the main shaft of the rotating tray inside the supporting sleeve, ensure the accuracy of its rotation, and prevent the upper end of the rotating tray from swaying during the rotation process. Phenomenon, affect the processing effect. The turntable bearing is installed in the supporting sleeve, the inner sleeve and the outer sleeve are arranged between the turntable bearings, the neck of the rotating tray is inserted into the inner sleeve, and the inner sleeve is inserted into the outer sleeve Inside. The inner sleeve and the outer sleeve fix the slewing bearing and are mainly used for positioning the inner ring and the outer ring of the slewing bearing.

As a preferred solution of the present invention, the variable-frequency power supply device adopts a low-frequency high-voltage alternating power supply. Preferably, the variable frequency power supply device adopts an alternating power supply with a voltage of 0.5KV-5KV and a frequency of 0.1-5Hz. The variable frequency power supply device can adopt waveforms such as resonant waves, sawtooth waves, and triangular waves, and at the same time ensure that it is a low-frequency high-voltage AC power supply. The advantage of this design is that it is beneficial to form a traveling wave magnetic field. By changing the magnitude of the voltage and frequency, the magnetic field and "micro" can be realized. "Grinding head" update frequency adjustment, so as to obtain better polishing effect.

Further, the excitation coil includes a coil winding base and several turns of copper wire, winding cylinders are arranged at equal intervals on the coil winding base, and the copper wires are wound on the winding cylinders. As a preferred solution of the present invention, the winding directions of the two adjacent winding cylinders on the coil winding base are opposite, so that the end faces of the winding cylinders form a plurality of N-pole and S-pole alternate ring loop magnetic fields , the electromagnetic force is generated under the action of the alternating power supply to realize the circular drive of the "micro-grinding head".

Another object of the present invention is achieved through the following technical solutions:

A polishing method of a dynamic magnetorheological polishing device with a controllable dynamic magnetic field, the method specifically includes the following steps:

Step S1: Utilize paraffin to stick the workpiece on the tool head, the lower surface of the workpiece is parallel to the upper surface of the cup-shaped polishing disc, and the gap between the lower surface of the workpiece and the cup-shaped polishing disc is adjusted to be 0.5mm-5mm;

Step S2: according to the characteristics of the processed workpiece and the processing requirements, add at least two of the following three abrasives to the deionized water, the three abrasives are respectively micron-scale abrasives with a concentration of 2% to 15%, and a concentration of 2% to 15%. 15% of submicron abrasives, 2% to 15% of nanoscale abrasives, and 2% to 20% of submicron carbonyl iron powder and 3% to 15% of micron grade abrasives in deionized water Carbonyl iron powder, dispersant with a concentration of 3% to 15%, and antirust agent with a concentration of 1% to 6%. After the abrasive is added, it is fully stirred and vibrated by ultrasonic waves for 5 to 30 minutes to form a magnetorheological fluid;

Step S3: Pour the magnetorheological fluid into the cup-shaped polishing disc, adjust the output current of the variable frequency power supply device according to the characteristics of the processed workpiece and processing requirements, thereby generating a magnetic field, and forming several dynamic magneto-rheological fluids on the upper surface of the cup-shaped polishing disc. micro-grinding heads, which constitute a flexible polishing pad for grinding the workpiece;

Step S4: Start the transmission motor, drive the rotating tray to rotate at high speed through the transmission belt, and drive the tool head to rotate at high speed and swing at low speed, so as to uniformly polish the surface material of the workpiece.

The working process and principle of the present invention are: the present invention utilizes an alternating electric field to generate a dynamic magnetic field through an excitation coil, and generates a circular driving force on the magnetorheological fluid based on the principle of a traveling wave magnetic field, so that the magnetorheological fluid is placed on the surface of the cup-shaped polishing disc. Form a circular rotating "micro-grinding head". The transmission motor rotates with the rotating tray to make the "micro-grinding head" in the cup-shaped polishing disc rotate at high speed, and the workpiece itself is also rotating and swinging. This design can make the surface of the workpiece smoother and the processing efficiency is higher. In addition, through the optimal combination of frequency and voltage of the excitation alternating current power supply, the dynamic change of the magnetic field can be realized and precisely controlled.

Compared with the prior art, the present invention also has the following advantages:

(1) The dynamic magnetorheological polishing device with controllable dynamic magnetic field provided by the present invention uses excitation coils instead of permanent magnets to realize rapid adjustment of the range and intensity of the magnetic field according to processing requirements.

(2) The dynamic magnetorheological polishing device with controllable dynamic magnetic field provided by the present invention adopts an exciting coil that can precisely adjust the magnetic field strength, which eliminates the cumbersome steps of disassembling the cup-shaped polishing disc, and makes the overall structure of the polishing device more optimized. more reasonable.

(3) The dynamic magnetorheological polishing device with controllable dynamic magnetic field provided by the present invention adopts multiple sets of excitation coils to generate a plurality of flexible micro-grinding heads, and shortens the distance between the micro-grinding heads, thereby delaying the effective processing time , greatly improving the processing efficiency and obtaining the ideal processing effect.

Description of drawings

Fig. 1 is a structural sectional view of a dynamic magnetorheological polishing device provided by the present invention.

Fig. 2 is a schematic diagram of a micro-grinding head formed by the dynamic magnetorheological polishing device provided by the present invention.

Fig. 3 is a polishing schematic diagram of the dynamic magnetorheological polishing device with controllable dynamic magnetic field of the present invention.

Fig. 4 is a perspective view of a single coil winding substrate provided by the present invention.

Fig. 5 is a working principle diagram of a single coil winding substrate provided by the present invention.

Fig. 6 is a working principle diagram of the excitation coil provided by the present invention based on the traveling wave magnetic field.

Explanation of the labels in the above-mentioned accompanying drawings:

1-transmission motor, 2-first fixing screw, 3-driving wheel, 4-flat key, 5-transmission belt, 6-driven wheel, 7-wire rotary joint, 8-second fixing screw, 9-wire group, 10 -base, 11-third fixing screw, 12-variable frequency power supply unit, 13-fourth fixing screw, 14-excitation coil, 15-rotating tray, 16-fifth fixing screw, 17-cup-shaped polishing disc, 18-bearing End cover, 19-supporting sleeve, 20-turntable bearing, 21-inner sleeve, 22-outer sleeve, 23-sixth fixing screw, 24-magnetic field, 25-coil winding substrate, 26-magnetorheological polishing Working liquid, 27-flexible polishing pad, 28-workpiece, 29-tool head.

detailed description

In order to make the object, technical solution and advantages of the present invention more clear and definite, the present invention will be further described below with reference to the accompanying drawings and examples.

Example 1:

As shown in Fig. 1, Fig. 2 and Fig. 3, the present invention discloses a dynamic magnetorheological polishing device with a controllable dynamic magnetic field. The polishing device mainly includes a transmission motor 1, a first fixing screw 2, a driving wheel 3, Flat key 4, transmission belt 5, driven wheel 6, wire rotary joint 7, second fixing screw 8, wire 9, base 10, third fixing screw 11, frequency conversion power supply device 12, fourth fixing screw 13, excitation coil 14, rotation Tray 15, fifth set screw 16, cup-shaped polishing disc 17, end cap 18, support sleeve 19, turntable bearing 20, inner sleeve 21, outer sleeve 22, sixth set screw 23, magnetic field 24. Wherein the transmission motor 1 and the variable frequency power supply device 12 are respectively fixed on the base 10 with the first fixing screw 2 and the third fixing screw 13, the driving wheel 3 is connected on the output shaft of the motor with the flat key 4, and the driven wheel 6 and the rotating tray 15 Connected together by the second fixing screw 8, the cup-shaped polishing disc 17 is connected on the rotating tray 15 by the fifth fixing screw 16, the excitation coil 14 is fixed on the upper end surface of the turntable by the fourth fixing screw 13, and the coil is passed through the wire group 9 at the same time. It is connected with the electric wire rotary joint 7 on the variable frequency power supply device 12, and a pair of turntable bearings 20 are installed on the lower end shaft of the rotating tray 15, and the inner ring and outer ring of the bearings are pressed and fixed by the inner sleeve 21 and the outer sleeve 22 respectively. , the upper end of the bearing is positioned by an end cover 18, the lower end is positioned by the driven wheel 6, and there is a support sleeve 19 outside the bearing to position and fix the outer sleeve 22, and at the same time play a supporting role. The support sleeve 19 uses the sixth fixing screw 23 fixed on the base 10. The transmission belt 5 connects the driving wheel 3 and the driven wheel 6, and the whole polishing device rotates under the drive of the motor. After the exciting coil 14 is energized, a dynamic magnetic field 24 is formed.

In this embodiment, a schematic diagram of the planar position of the "micro-grinding head" in the flexible polishing pad 27 in the polishing disc is shown in FIG. 2 .

The invention also discloses a polishing method of a dynamic magnetorheological polishing device with a controllable dynamic magnetic field. The specific steps of the method are as follows:

Step S1: Utilize paraffin to stick workpiece 28 on the tool head 29, the lower surface of workpiece 28 is parallel to the upper surface of cup-shaped polishing disc 17, and the gap between the lower surface of workpiece 28 and the cup-shaped polishing disc 17 is adjusted to be 1mm;

Step S2: According to the characteristics and processing requirements of single crystal silicon carbide with a diameter of 100mm, adding a concentration of 4% to the deionized water is a diamond abrasive with a particle diameter of 4 microns, and a concentration of 3% with a particle diameter of 200 nanometers. Add carbonyl iron powder with a particle size of 500 nanometers at a concentration of 3% and carbonyl iron powder with a particle size of 4 microns at a concentration of 3% in deionized water, and add a dispersant with a concentration of 3% and an antirust agent with a concentration of 3%. , after fully stirring, vibrate ultrasonically for 30 minutes to form magnetorheological fluid 26;

Step S3: Pour the magnetorheological polishing working fluid 26 into the cup-shaped polishing disc 17, adjust the output current of the variable frequency power supply device 12, generate a magnetic field 24 with a certain range and sufficient strength, and form a magnetic field 24 on the upper surface of the cup-shaped polishing disc 17. A flexible polishing pad 27 composed of several dynamic "micro-grinding heads";

Step S4: start the transmission motor 1, adjust the rotating speed to 120rpm, drive the rotating tray 15 to rotate at a high speed, drive the tool head 29 to rotate at -200rpm, swing at a speed of 10 times/min, swing at 10mm, and process for 90 minutes to realize single crystal silicon carbide High-efficiency ultra-smooth and uniform polishing of surface materials.

Please refer to FIG. 3 . FIG. 3 is a polishing diagram of a dynamic magnetorheological polishing device with a controllable dynamic magnetic field according to the present invention.

In the embodiment of the present invention, the excitation coil 14 is composed of several turns of copper wire with good electrical conductivity wound on a plurality of coil winding substrates 25 , and is fixed on the rotating tray by the fourth fixing screw 13 . The winding directions of the conductive copper wires on the two adjacent cylinders of the coil winding base 25 are opposite. Based on the principle of traveling wave magnetic field, an annular loop magnetic field with N poles and S poles spaced apart is formed on the six cylinder end faces of the base body. Under the AC power supply, the magnetic induction intensity component By perpendicular to the magnetorheological fluid 26 generates an induced current Jz, and then generates an electromagnetic force Fx to realize the circular driving effect of the "micro grinding head".

Please refer to FIG. 4 and FIG. 5. FIG. 4 is a three-dimensional schematic diagram and a working principle diagram of a single coil winding substrate in the present invention, and FIG. 6 is a working principle diagram of the exciting coil of the present invention based on a traveling magnetic field.

In the above embodiment, the variable frequency power supply device 12 is a low-frequency high-voltage alternating power supply, specifically an alternating power supply of 0.5-5 kV and a frequency of 0.1-5 Hz, of course, the selection of the power supply is not limited thereto.

In the above-mentioned embodiment, the processing object is not limited to single crystal silicon carbide, and other semiconductor materials, such as single crystal silicon, sapphire, etc., can also be processed, but it is necessary to add the following three types in deionized water according to the characteristics of the processing object and processing requirements At least two kinds of abrasives in the abrasives, the three kinds of abrasives are micron-scale abrasives with a concentration of 2% to 15%, submicron abrasives with a concentration of 2% to 15%, and nanoscale abrasives with a concentration of 2% to 15%, and deionized water with a concentration of 2% to 20% of submicron carbonyl iron powder and a concentration of 3% to 15% of micron carbonyl iron powder, and a concentration of 3% to 15% of a dispersant and a concentration of 1 % to 6% of anti-rust agent, fully stirred and vibrated by ultrasonic waves for 5 to 30 minutes to form the corresponding magnetorheological fluid 26 for processing the material.

The present invention utilizes an alternating electric field to generate a dynamic magnetic field through an excitation coil 14, and generates a ring-shaped driving force based on the principle of a traveling wave magnetic field, forming a ring-shaped rotating micro-grinding head on the surface of the cup-shaped polishing disc 17. Optimize the combination to realize the dynamic controllability of the magnetic field. Using the excitation coil 14 instead of the permanent magnet can not only realize the rapid adjustment of the magnetic field range and strength, but also eliminate the cumbersome steps of disassembling the cup-shaped polishing disc 17, and the overall structure is more optimized, shortening the length of the flexible micro-grinding process. The distance between the heads prolongs the effective processing time and improves the processing efficiency.

The above-mentioned embodiment is a preferred embodiment of the present invention, but the embodiment of the present invention is not limited by the above-mentioned embodiment, and any other changes, modifications, substitutions, combinations, Simplifications should be equivalent replacement methods, and all are included in the protection scope of the present invention.

Claims (8)

1. A dynamic magnetorheological polishing device with a controllable dynamic magnetic field, characterized in that it includes a base, a drive unit, a rotating tray, a cup-shaped polishing disc, a support sleeve and a controllable dynamic magnetic field unit for controlling the strength of the magnetic field The supporting sleeve is vertically fixed in the middle of the base, the driving unit is arranged on the base, the rotating tray is composed of a disc and a neck, the neck of the rotating tray is inserted into the supporting sleeve, and is connected to the driving unit by transmission ; The cup-shaped polishing disc is fixedly installed on the disc portion of the rotating tray; The controllable dynamic magnetic field unit includes a variable frequency power supply device, a wire rotary joint and several sets of excitation coils; Rotate the bottom end of the neck of the tray, and electrically connect with the excitation coil and the variable frequency power supply device respectively through electric wires. 2. The dynamic magnetorheological polishing device of controllable dynamic magnetic field according to claim 1, characterized in that, the drive unit comprises a transmission motor, a driving wheel and a driven wheel; the transmission motor is fixed on the base, and the The driving wheel is installed on the output shaft of the transmission motor, the driven wheel is installed on the neck of the rotating tray, and is fixedly connected with the rotating tray; the driven wheel is connected with the driving wheel through a transmission belt, and the rotating tray is driven to rotate by the driving motor. 3. The dynamic magnetorheological polishing device of controllable dynamic magnetic field according to claim 2, characterized in that, it also includes a bearing end cover arranged on the neck of the rotating tray, a pair of turntable bearings, and a fixed turntable bearing. The inner sleeve and the outer sleeve; the bearing end cover is installed between the disc part of the rotating tray and the support sleeve, the turntable bearing is installed in the support sleeve, and the inner sleeve and the outer sleeve are arranged on the turntable Between the bearings, the inner sleeve is inserted into the outer sleeve. 4. The dynamic magneto-rheological polishing device with controllable dynamic magnetic field according to claim 1, characterized in that, the variable-frequency power supply device adopts a low-frequency high-voltage alternating power supply. 5 . The dynamic magneto-rheological polishing device with controllable dynamic magnetic field according to claim 4 , wherein the variable frequency power supply device adopts an alternating power supply with a voltage of 0.5KV-5KV and a frequency of 0.1-5Hz. 6. The dynamic magnetorheological polishing device of controllable dynamic magnetic field according to claim 1, characterized in that, the excitation coil comprises a coil winding substrate and copper wires of several turns, and the coil winding substrate etc. The spacing is provided with winding cylinders, and the copper wires are wound on the winding cylinders. 7 . The dynamic magnetorheological polishing device with controllable dynamic magnetic field according to claim 6 , wherein the winding directions of two adjacent winding cylinders on the coil winding base are opposite. 8. A polishing method of the dynamic magnetorheological polishing device of the controllable dynamic magnetic field according to any one of claims 1 to 7, characterized in that, comprising the steps of: Step S1: Utilize paraffin to stick the workpiece on the tool head, the lower surface of the workpiece is parallel to the upper surface of the cup-shaped polishing disc, and the gap between the lower surface of the workpiece and the cup-shaped polishing disc is adjusted to be 0.5mm-5mm; Step S2: according to the characteristics of the processed workpiece and the processing requirements, add at least two of the following three abrasives to the deionized water, the three abrasives are respectively micron-scale abrasives with a concentration of 2% to 15%, and a concentration of 2% to 15%. 15% of submicron abrasives, 2% to 15% of nanoscale abrasives, and 2% to 20% of submicron carbonyl iron powder and 3% to 15% of micron grade abrasives in deionized water Carbonyl iron powder, dispersant with a concentration of 3% to 15%, and antirust agent with a concentration of 1% to 6%. After the abrasive is added, it is fully stirred and vibrated by ultrasonic waves for 5 to 30 minutes to form a magnetorheological fluid; Step S3: Pour the magnetorheological fluid into the cup-shaped polishing disc, adjust the output current of the variable frequency power supply device according to the characteristics of the processed workpiece and processing requirements, thereby generating a magnetic field, and forming several dynamic magneto-rheological fluids on the upper surface of the cup-shaped polishing disc. micro-grinding heads, which constitute a flexible polishing pad for grinding the workpiece; Step S4: Start the transmission motor, drive the rotating tray to rotate at high speed through the transmission belt, and drive the tool head to rotate at high speed and swing at low speed, so as to uniformly polish the surface material of the workpiece.