Head Gimbal Assembly Research Articles

Multi-objective Optimization of UV Spot Curing Technique of Slider - Suspension Attachment Process Using Response Surface Methodology Approach

The ultraviolet (UV) curing of slider-suspension attachment is going to change from a manual to an automated process. As a result, the bonding parameters of adhesive between slider and suspension needs to be optimized. This paper aims to study two output responses of the UV curable epoxy adhesive i.e., shear strength force and pitch static attitude (PSA) of the joint between slider and suspension in a head gimbal assembly (HGA). Four process parameters were investigated using response surface methodology (RSM) based on face-centered central composite design (FCCD). The RSM was applied to establish a mathematical model to correlate the significance of process parameters and the responses. Then the based multi-objective was applied to determine a quadratic model and obtained the output maximization at 224 g of shear strength force and PSA value close to the target at 1.8 degrees. The input process parameters were optimized at 0.7 s of UV bottom cure time, 120 °C of UV dual side temperature, 5.0 s of UV dual side cure time, and 230 μm of adhesive dot size. The validation experiment showed a prediction response error of less than 7% of the actual value.

Fault Detection and Classification for Slider Attachment Process using Convolution Neural Network

Hard Disk Drive (HDD) utilizes automation machines for the assembly processes used in the industry to achieve higher production rates and lower costs. The Head Gimbal Assembly (HGA) production process has two main parts: glue dispensing and slider attaching by an Auto Core Adhesion mounting Machine (ACAM). The slider attaching process produces a mounted head to the suspension utilizing vacuum pressure to hold and position a slider. The errors from a vacuum leak from any step trigger system alarms resulting in machine downtime and slider loss defective (SLD). This paper proposes a classification algorithm derived from 250x250 micron images of mounted heads are 4 different categories: Good, Fault I, Fault II and Fault III using Convolution Neural Networks (CNN). CNN is a performance model for predictive maintenance before failure. The method has achieved a 95 % accuracy for detection and classification

The Effect of Laser Energy and Nitrogen Flow in Solder Joints Properties of Head Gimbal Assembly

The objective of this research is to study the effect of laser energy and Nitrogen flow on the solder joints of the Head Gimbal Assembly (HGA). The soldering of the HGA components isn’t the same as general semiconductors. Since the soldering figure perpendicular to each other so that, it was used the laser solder jet bonding system. The solder jet bonding system uses a solder ball consisting of Sn-2.0Ag-0.7Cu (SAC207) is used for connection of the HGA pad made from a Cu trace coated with Au. The growth of intermetallic compounds (IMCs) and shear strength will be analyzed to investigate the effects of laser energy and Nitrogen flow on solder joint reliability. In this research, laser energy levels since 2, 2.5, 3, 3.5, 4, and 4.5 mJ and keep the Nitrogen flow value at 90 mbar. As for the Nitrogen flow effect analysis, the Nitrogen flow level was used at 80, 100, 120, and 140 mbar and keep the laser energy value 3.5 mJ. The results of the study show that the increased levels of laser energy can inhibit the growth of intermetallic compounds as well as the AuSn4 phase that can present benefit to solder joints with results showing within the shear strength to increase significantly. The increase in Nitrogen flow levels has the same effect as the increase in laser energy levels, which can decreases the growth of intermetallic compounds and AuSn4 phase also including increased shear strength. The difference between laser energy and Nitrogen flow increasing shows the level of laser energy can clearly distinct the effect on each level. But the increase in Nitrogen flow level is statistically insignificant from each level.

Head gimbal assembly automated visual inspection by using digital image processing

This paper presented an approach of Digital Image Processing (DIP) and measurement properties of image region for inspecting the part in Head Gimbal Assembly (HGA) process. Current, the inspection process is performed by the skilled employee, which depends on employee experiences. The inspection method proposed by using digital image processing to do an image enhancement in order to detect the abnormalities and defects on part. The measurement properties of image region is proposed to identify the abnormality occurred on HGA part after image enhancement, in production process. This research aimed to develop the algorithm to inspected HGA part by considered the number of pads, convex area value, and eccentricity value. Then used measurement properties of image region to enhance the algorithm for classifying part in production process. This approach has been developed and proved with the real part in HGA production process. It’s proved that the algorithm and method proposed can be classified the part in HGA production process.

The Study of the Parameters that Affect the Performance of Suspension in HDD

The suspension in a hard disk drive is a component of hard disk drives (HDD(s)) that commonly consist of three main components; Baseplate, Loadbeam and Gimbal, which are welded together. The suspension is attached to a slider fly on the surface of a rapidly spinning disk. The suspension assembly and slider that is formed is called a Head Gimbal Assembly (HGA). If that assembly is not attached to the slider, that is called a Trace Gimbal Assembly (TSA). Defects in the suspension may occur from machining and assembly. The aim of this research is to study the effect of suspension defects on the performance of the suspension resonance using a finite element method, whereby the suspension was created by SolidWorks and imported into Ansys in order to conduct resonance analysis. The results from finite element analysis compared with laser doppler velocimetry (LDV) found that the trend is the same. The suspension bias was revealed, in that Delta RG, welding diameter, program asymmetry, program asymmetry, tip height and tip twist influence the performance of the suspension may possibly come from the suspension production process. Obviously, this process needs to be controlled with regard to certain aspects, such as laser power, fixtures and so on. However, the swaging process in the head stack assembly might also have an impact tin tip height and tip twist.

Transient Thermal-Electric Simulation and Experiment of Heat Transfer in Welding Tip for Reflow Soldering Process

Welding tip is an appliance for making footprint to connect the arm and head gimbal assembly (HGA) together in reflow soldering process. The welding tip is made from 3 materials: copper alloy, stainless steel, and haynes 230. It works based on Joule heating effect. The haynes 230 head tip is the area used to create a footprint. In the past, failure in the reflow soldering process of a hard disk drive factory was found resulting in defective products; therefore, a solution to resolve this problem must be researched. This article reports a solution to the aforementioned problem by using transient thermal-electric simulation to investigate the heat transfer in the welding tip and a simple experiment to verify the simulation. By using ANSYS, the simulation results revealed the temperature of welding tip. The maximum temperature was 406°C on the head tip at t=0.7s and then it rapidly decreased. The reflow soldering process failure occurred when footprint was done after 0.7s causing the temperature to be too low for melting the solder so the arm and HGA were unable to connect to each other. We proposed simple solutions and ways to improve the efficacy of the reflow soldering process; e.g., footprints should be done at 0.7s, and the welding tip’s material should be changed from haynes 230 to 556. After the factory implemented our results, the problem could truly be resolved. Not only do products have a higher quality but also miscellaneous expenses from defective products are saved.

Neurofuzzy c-Means Network-Based SCARA Robot for Head Gimbal Assembly (HGA) Circuit Inspection.

Decision and control of SCARA robot in HGA (head gimbal assembly) inspection line is a very challenge issue in hard disk drive (HDD) manufacturing. The HGA circuit called slider FOS is a part of HDD which is used for reading and writing data inside the disk with a very small dimension, i.e., 45 × 64 µm. Accuracy plays an important role in this inspection, and classification of defects is very crucial to assign the action of the SCARA robot. The robot can move the inspected parts into the corresponding boxes, which are divided into 5 groups and those are “Good,” “Bridging,” “Missing,” “Burn,” and “No connection.” A general image processing technique, blob analysis, in conjunction with neurofuzzy c-means (NFC) clustering with branch and bound (BNB) technique to find the best structure in all possible candidates was proposed to increase the performance of the entire robotics system. The results from two clustering techniques which are K-means, Kohonen network, and neurofuzzy c-means were investigated to show the effectiveness of the proposed algorithm. Training results from the 30x microscope inspection with 300 samples show that the best accuracy for clustering is 99.67% achieved from the NFC clustering with the following features: area, moment of inertia, and perimeter, and the testing results show 92.21% accuracy for the conventional Kohonen network. The results exhibit the improvement on the clustering when the neural network was applied. This application is one of the progresses in neurorobotics in industrial applications. This system has been implemented successfully in the HDD production line at Seagate Technology (Thailand) Co. Ltd.

Effect of Track-Seeking Motion on Off-Track Vibrations of the Head-Gimbal Assembly in HDDs

The lateral flow in hard disk drives is greatly disturbed because of the arm swinging rapidly during track seeking, which can greatly affect off-track residual vibrations during track following of the head-gimbal assembly (HGA), as well as the slider. Until now, no simulation studies have been performed to investigate off-track residual vibrations of the HGA that consider lateral flow effects. In this paper, the effect of track-seeking on off-track residual vibrations of the HGA is investigated for air and helium environments using the so-called “fluid dynamic mesh” and the “fluid-structure interaction” methods for the first time. Three different angular acceleration profiles (a square wave, a triangular wave, and a sinusoidal wave) are investigated as a function of seek time (10 and 5 ms). Results show that the smoothening of sharp transitions in the seek profile improves the performance of off-track residual vibrations and shortens the track-following time of the head positioning servo system. In addition, the effect of lateral flow (windage) on off-track residual vibrations must be considered for a square-wave angular acceleration profile. Simulation results show that helium improves the track-following accuracy compared to air because of the lower windage forces acting on the HGA. We observe that the sinusoidal-wave angular acceleration performs best for the three angular acceleration profiles investigated. Furthermore, seek time is found to have only a small effect on off-track residual vibrations during track following.

Automatic Optical Inspection of Solder Ball Burn Defects on Head Gimbal Assembly

The detection of low-quality solder joints in hard disk drive manufacturing is a time-consuming, error-prone and costly process that is often performed manually. This paper thus proposes two automated optical solder jet ball joint defect inspection methods for head gimbal assembly (HGA) production. The first method uses a support vector machine (SVM) for fault detection, and the second method uses vertical edge detection to identify solder ball and pad burning defects. The methods were tested with 5530 HGA images, and their performance was compared to a Bayesian-based method. Experimental results show that the vertical edge detection method gave the best results, with an under reject rate of 0.75% and an over reject rate of 1.88%. The accuracy of the vertical edge detection method was 98.2%, which is higher than the accuracy of 89.9% for the Bayesian-based method, and 84.6% for the SVM-based method.

Multi-objective optimization on laser solder jet bonding process in head gimbal assembly using the response surface methodology

This paper aims to investigate the effect of laser solder jet bonding parameters to the solder joints in Head Gimbal Assembly. Laser solder jet bonding utilizes the fiber laser to melt solder ball in capillary. The molten solder is transferred to two bonding pads by nitrogen gas. The response surface methodology have been used to investigate the effects of laser energy, wait time, nitrogen gas pressure, and focal position on the shear strength of solder joints and the change of pitch static attitude (PSA). The response surface methodology is employed to establish the reliable mathematical relationships between the laser soldering parameters and desired responses. Then, multi-objective optimization is conducted to determine the optimal process parameters that can enhance the joint shear strength and minimize the change of PSA. The validation test confirms that the predicted value has good agreement with the actual value.

An Area-Based Prior Value Method for Detection of Micro Contamination in Hard Disk Drives

This paper presents a new area-based prior value technique for the improvement of automatic visual inspection in hard disk drive manufacturing. Micro-contaminations are detected on the air-bearing surface of the head gimbal assembly. The new area-based prior value technique uses the locations of contaminations that appear in the inspection area. The experimental results validate the efficiency of the new detection method on low-resolution images, as the proposed method yielded 93.1% accuracy.

A study of laser jet soldering process with 55 μm tin balls for head gimbal assembly manufacturing

This paper presented a study of the laser jet soldering process based on 55 μm tin balls. In the tin ball-based laser jet soldering, the N2 pressure should be increased and the laser energy value should be decreased as the diameter of the tin ball decreased. Moreover, the distribution of laser energy significantly affected soldering quality. Through using DoE methodology, the optimized parameters for laser jet soldering based on 55 μm tin balls were obtained. To eliminate the increasing of dispersity of the pitch static angle (PSA) caused by soldering micro-deformation, an optimized soldering sequence and two additional supports on tongue piece were taken. Volume production showed that the proposed laser jet soldering process based on 55 μm tin balls can manufacture HGA products with a qualification ratio of approximately 99.3%.DOI: http://dx.doi.org/10.5755/j01.mech.22.4.16164

Crosstalk Reduction on 6-line Suspension Assembly Interconnect Trace in Head Gimbal Assembly by using Guard Technique

The guard technique is proposed by adding the stainless steel at backing layer to reduce the crosstalk on 6 lines suspension assembly interconnect trace (SAIT). The Near-End and Far- End crosstalk coefficients (NEXT and FEXT) are used to analyze the crosstalk on the SAIT in the frequency of 0-20GHz. The finite integration technique (FIT) is used in the simulation based on CST microwave studio. The space between heat and read pairs is modified and guard addition at the space is also varied. From the results, it is found that the varying of space cannot reduce the crosstalk. However, the additional guard can reduce the crosstalk by monitoring the NEXT and FEXT. The lowest crosstalk is at 100% of the space with 100% of guard that can attenuate the noise around 4.7 and 3.2dB for NEXT and FEXT, respectively. The 80% of space with 80% of additional guard has the crosstalk less than or equal to the conventional SAIT. In addition, it can also decrease the dimension of SAIT about 11.87% of the conventional SAIT. Hence, this technique can reduce the crosstalk and can decrease the dimension of the SAIT which is useful for the robustness for future SAIT design.

Wireless Communication and Its Effect to Tunneling Giant Magneto-Resistive (TGMR) Reader in Head Gimbal Assembly Process

TGMR reader is current technology of magnetic recording read sensor which dramatically improves readout amplitude, speed and recording areal density. In advanced manufacturing environment, automated tools are increasingly used and wireless communication device is aimed to be employed to enhance the operation efficiency. However, electromagnetic fields from wireless communication devices could harm or damage the most energy sensitive devices/equipment, such as TGMR reader sensor, in head gimbal assembly process. This study surveys, therefore, electromagnetic interference from wireless communication devices using CTM048, EM Field Meter with CTS001 directional antenna and electromagnetic field module, then use Agilent 34410A to measure TGMR resistance and thermal change of TGMR head while placing in the field of wireless communication device. Build-in Differential-Ended Temperature Coefficient of Resistivity sensor is utilized for proximal TGMR temperature. Impact to electrical performance of TGMR pre and post actions simulating HGA assembly process will be confirmed using Quasi-static Tester.

Optimum airflow to reduce particle contamination inside welding automation machine of hard disk drive production line

Welding automation machine (WAM), used for welding minute components to the head gimbal assembly (HGA) of a hard disk drive (HDD), needs to operate in a strictly clean environment. In today’s HDD factories, to prevent airborne particle contamination to the WAM, Fan Filter Units (FFUs) are installed on top of it to supply clean air and blow away outside airborne micro particles, keeping the microenvironment clean. Furthermore, the mass of the clean air should also carry away harmful particles generated inside the microenvironment. In this research, numerical simulation of airflow inside a WAM was performed in order to verify these cleaning functions of the airflow. A transition shear stress transport turbulence model was employed to simulate airflow from the FFUs through and out of the microenvironment. The simulation results showed that the airflow from the FFUs truly performs the two cleaning functions as intended. Moreover, they also revealed that the optimum air speed, the speed resulting in the lowest particle counts, is in the range of 0.35–0.55 m/s. Our findings can be useful for developers who may use FFUs to reduce particle counts in the environment of other types of industrial machinery.

A Bayesian Approach to Automated Optical Inspection for Solder Jet Ball Joint Defects in the Head Gimbal Assembly Process

Automation or selective automation is adopted as a solution to most productivity problems in the hard disk drive (HDD) industry as the industry continues to grow at a 40% compounded annual growth rate. An automated production line for manufacturing the head gimbal assembly (HGA) has been developed as part of the automation solution. In the automated HGA production line, a solder jet ball (SJB) soldering station connects the suspension circuit to the slider body. We propose a Bayesian approach to automated optical inspection (AOI) of the SJB joint in the HGA process, implementing Tree Augmented Naïve Bayes Network (TAN-BN) plus check classifier in-situ using GeNIe/SMILE within the inspection software. The system is further enhanced with a result checker, achieving an overall accuracy of 91.52% with 660 production parts in a blind test.

Design, Fabrication and Evaluation of a Novel Electro Thermal Micro-Gripper for Handling of Head Gimbal Assembly

A development of a novel electro thermal micro-gripper for handling of Head Gimbal Assembly (HGA) is an ultimate goal of this study. The scope of this study covers a design, fabrication and performance evaluation of the electro thermal micro-gripper. ANSYS software was used to examine the magnitude of tip displacement, exerting force and induced stress to investigate the mechanism’s viability for handling of HGA. Electroplating of nickel was employed to construct the micro-gripper’s mechanisms with three different sizes, and their displacement and exerting force were then examined. From the experiments, each mechanism deflected between 100 to 220 μm while the exerting force was over 200 mN at 25oC above room temperature. Therefore, the results suggested that the new electro thermal micro-grippers are viable for the HGA handling application.

Numerical Investigation of Airflow Pattern inside Environmental Chamber

In industrial hard disk drive research and development laboratories, an environmental chamber is normally used to perform a mechanical verification test of Head Gimbal Assembly (HGA). It is very important to verify that the airflow pattern in the chamber is comparable to that in a real hard disk drive. Hence, we applied a transition shear stress transportation turbulence model (transition SST), one of the robust mathematical models in computer fluid dynamics, to simulate the airflow behavior inside both an environmental chamber and a hard disk drive (HDD). We found that, overall, the two patterns of airflow were not comparable at all. The air velocity vectors around the HGA in VENA were smaller than that in HDD. The reason for this is likely to be that there was more space between the top cover of the chamber and the platter than the space between the top cover of the hard disk drive and its platter.

Simulated Trajectories of Particles and the Number of Particles Trapped by the Circulating Filter in a Hard Disk Drive

The particle trajectories and the number of them trapped by circulating filter of a 2.5 inch dual platter hard disk drive (HDD) were numerically investigated using a transition shear stress transport turbulence model (transition SST). Four head gimbal assemblies (HGAs) were placed at the outer diameter positions where tiny particles of alumina were released. The simulation revealed the results of airflow, particle trajectories and efficiency of a circulating filter. This result can be applied as fundamental information to design HDD layout in order to reduce its contamination. Keywords: Airflow, Circulating Filter, Hard Disk Drive, Particle Trajectory, Computational Fluid Dynamics

A Simulation of the Number of Particles Trapped by the Circulating Filter of a Hard Disk Drive and their Trajectories

A transition shear stress transport turbulence model and a discrete phase model of Fluent software were employed to simulate numerically the trajectories of loose particles and the number of them trapped by the circulating filter of a hard disk drive (HDD). The filter was located either at the left or the right of a 2.5 inch dual platter HDD rotating at 7200 rpm. Particles were released from the middle diameter position where four head gimbal assemblies (HGAs) were located. The simulation included airflow and particle trajectories released from any of the four HGAs. The results of this simulation can help determine the efficiency of a circulating filter and its optimal placement.