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Enhancing Signal Processing Capability with Tabu Search Algorithm Utilization for Rate-4/5 Modulation Coded Bit-Patterned Magnetic Recording
(2025-12-01)
Mattayakan, Mutita
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Warisarn, Chanon
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Lee, Jaejin
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Kankhunthod, Kittipon
To meet the growing demand for higher storage capacities, bit-patterned magnetic recording (BPMR) has emerged as a leading solution for achieving ultra-high user densities (UDs). However, BPMR systems are significantly impacted by two-dimensional (2D) interferences, specifically inter-symbol interference (ISI) and inter-track interference (ITI), which can degrade the quality of the readback signal. This paper introduces a rate-4/5 constructive ITI (CITI) modulation scheme, combined with a Tabu search (TS)-based error correction algorithm, to address the limitations of conventional CITI modulation codes. In the original encoding scheme, some codewords still contain forbidden patterns within their borders. The TS algorithm enhances the performance of the outermost tracks by refining unreliable bits identified through a distance-based reliability metric, which differs from earlier TS-based detectors that were directly used for multi-track detection. A proposed soft-information adjuster is then used to correct the poor reliability of soft information, resulting in improved soft-information reliability and decoding performance. A modified TS detector is also proposed, where the single-bit criterion for selecting the number of input bits is adopted, to improve neighbor selection and better align with the signal characteristics of the inner tracks. Simulation results show that the proposed system can achieve up to 2.7 dB and 4.0 dB improvements in bit error rate (BER) at a user density (UD) of 2.4 Terabits per square inch, compared to conventional uncoded and coded systems, respectively, while also reducing computational complexity. Furthermore, the results also imply that when the recording systems must operate under fluctuations in the size and position of the bit-island, our proposed system can provide superior performance.
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Anomaly Flying Height Prediction Based on Clustering Techniques in Hard Disk Drive Manufacturing
(2025-01-01)
Kanjanapruthipong, Worawit
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Konghuayrob, Poom
In this research, we present a method for predicting anomaly flying height (FH) profiles in hard disk drive (HDD) manufacturing by analyzing FH data at the FH1 stage. Anomalies at FH1 can lead to calibration issues at FH2, disrupting the production process. We propose an AI-based approach using unsupervised clustering techniques to group FH profiles of the read/write head. We evaluated four clustering algorithms, KMeans, MiniBatchKMeans, Birch, and BisectingKMeans, along with the Elbow method to determine the optimal number of clusters. By identifying anomalous FH profiles early at FH1, the method enables proactive intervention, reducing calibration process time and improving production efficiency. Our model achieved an accuracy of 0.939 without relying on manual feature selection (e.g., pressure and temperature), which is often difficult to capture using traditional linear or rule-based models owing to the nonlinear nature of FH profiles. These results demonstrate the practical potential of clustering techniques in enhancing HDD manufacturing processes.
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A Feasibility Study for the Hot-Air-Assisted Reflow Soldering Process Based on Computational Fluid Dynamics
(2024-10-01)
Kanjad, Natcha
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Chanbandit, Chanapat
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Thongsri, Jatuporn
In hard disk drive (HDD) manufacturing, a reflow soldering process (RSP) employs heat generated at the welding tip (WT) to bond tiny electrical components for assembling an HDD. Generally, the heat was generated by an electric current applied to the WT. This article reports a feasibility study of using hot air based on computational fluid dynamics (CFD), a choice to assist heat generation. First, the WT and hot air tube (HAT) prototypes were designed and created. The HAT is a device that helps to supply hot air directly to generate heat at the WT. Then, the experiment was established to measure the temperature (T) supplied by the hot air. The measure results were employed to validate the CFD results. Next, the prototype HAT was used to investigate the T generated at the WT by CFD. The comparison revealed that the T measured by the experiment was in the 106.2 °C–133.5 °C range and that the CFD was in the 107.3 °C–136.6 °C range. The maximum error of the CFD results is 2.3% compared to the experimental results, confirming the credibility of the CFD results and methodology. The CFD results revealed that the operating conditions, such as WT, HAT designs, hot air inlet velocity, and inlet temperature, influence the T. Last, examples of suitable operating conditions for using hot air were presented, which confirmed that hot air is a proper choice for a low-temperature RPS.
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Multiphysics to Investigate the Thermal and Mechanical Responses in Hard Disk Drive Components Due to the Reflow Soldering Process
(2024-09-01)
Kimaporn, Napatsorn
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Samakkarn, Chawit
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Thongsri, Jatuporn
In hard disk drive (HDD) manufacturing, a reflow soldering process (RSP) implements heat generated by the welding tip to melt a solder ball for bonding the following essential HDD components: a flexible printed circuit (FPC) and a printed circuit cable (PCC). Since the mentioned components are tiny and comprise many thin material layers, an experiment to study thermal and mechanical responses is complex and not worth it. Therefore, a static state multiphysics consisting of thermal analysis (TA) and structural analysis (SA) was employed to investigate both responses. First, the experiment was established to mimic the RSP, measuring the temperature generated by the actual welding tip. Then, the measured temperature was defined as the boundary conditions with the pressing force (F) for the TA and SA based on the actual operating conditions. As expected, the TA results revealed the temperature distribution in the HDD components, which was consistent with the theory and results from previous work and confirmed this work’s credibility. Significantly, the SA reported severe total deformation (δ) in FPC’s top and bottom ends. The maximum δ was 0.72–0.88 mm for the F of 0–1 N. The stronger the F, the greater the δ. This research highlights that multiphysics can investigate both responses in HDD components as slight as 0.1–100 microns thick, which can be used to develop a high-efficacy RSP.
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Prediction of Flying Height Using Deep Neural Network Based on Particle Swarm Optimization in Hard Disk Drive Manufacturing Process
(2024-01-01)
Kanjanapruthipong, Worawit
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Prasitmeeboon, Pitcha
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Konghuayrob, Poom
In contemporary hard disk drive (HDD) manufacturing processes, after the assembly of the HDD from the production line, a series of diverse calibration procedures are necessary to ensure standardization. These include capacity calibration, which determines the storage space in terabytes (TB) presently available, and flying height (FH) calibration, which evaluates the distance between the head and the disk by applying electric current to the heater coil element to achieve the desired FH, thus optimizing the writing and reading performance and tailoring it to each HDD. Additionally, electric current is saved in a digital-to-analog converter (DAC) unit for the utilization of a read/write head, while a preamp collaborates with the drive firmware to convert the electric current in the DAC unit to milliwatts. In the present scenario, multiple calibrations of flying heights (FHs), specifically flying height 1 (FH1) and flying height 2 (FH2), are performed. Each FH calibration requires a testing time of approximately 5 h owing to the separation of measurement points into 240 locations across the disk surface, referred to as test zones, with a total of 20 heads. The primary objective of this study is to reduce the testing time by using a combination of deep neural network (DNN) and particle swarm optimization techniques to predict the DAC profiles of FH2 as it approaches FH1, where FH1 is the input for the DNN model.
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Optimization of Process Conditions for Hard Disk Drive Assembly for Defect Reduction
(2023-11-01)
Sirikasemsuk, Kittiwat
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Leerojanaprapa, Kanogkan
A spoiler installed in a hard disk drive can reduce the airflow velocity that causes vibration at an actuator arm and its head. In the case study, a hard disk drive manufacturer identified the defect of a loosely tightened spoiler in the hard disk drive by the spoiler installation machine. This occurred as a result of incorrect screw spacing (also called ‘the screwdriver encoder’). There was no study that specifically specified or created a suitable relationship model between the screwdriver encoder and associated parameters for the installation of a spoiler. Factors affecting the screw spacing were determined using multiple regression analysis, and a mathematical model of the significant factors of the screwdriver encoder was built. Data were collected from the spoiler installation machine and its software. Four factors were identified with the potential to impact the screwdriver encoder as (1) vacuum level for picking up the screw, (2) time spent in tightening the screw, (3) bit angle, and (4) screw torque. The ANOVA results pointed out that the screw torque within the range of experimental values did not affect the screw spacing, and a quadratic regression model was the most appropriate under various statistical criteria. This research demonstrated that a sophisticated regression model, i.e., a cubic model, is not always a good choice for an agent. In addition, the optimal values for the spoiler installation machine were determined. The faults decreased by 0.0096% from 0.055% each month. For choosing the relationship model of additional workpiece screw tightening variables, this research phase can be utilized as a guideline.
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A Proper Lubricant for a Swage Process in a Hard Disk Drive Factory Determined by Explicit Dynamics Analysis
(2023-01-01)
Bubpatha, Watchara
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Pattanapichai, Sorathorn
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Thongsri, Jatuporn
Since the hard disk drive industries continue to be highly competitive, many factories aim to reduce waste costs by developing their manufacturing process. This article presents the swage process (SP) development to join components: the head gimbal assembly with an actuator arm by explicit dynamics analysis (EDA). First, EDA was employed to determine the total deformation (δ) and equivalent (von Mises) stress (σ) after joining both components in the SP using a traditional lubricant currently used in the factory calculated by the friction coefficients. Then, the EDA results for the traditional lubricant were compared with the experimental results, and an agreement between both results was observed, confirming the EDA's credibility. Next, two additional different lubricants, including a non-lubricant as a control case, were investigated using the EDA. Finally, after comparing the EDA results for all four lubricants, the EDA results showed the proper type of lubricant, which can reduce the δ by 16.40% and σ by 9.40% compared to the traditional lubricant. Accordingly, the research findings were applied as important information for determining the best lubricant for other HDD generations to suit the SP, which can reduce waste costs from the trial and error method.
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A simulation of swage process for hard disk drive factory based on explicit dynamics analysis
(2022-01-01)
Bubpatha, Watchara
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Thongsri, Jatuporn
Nowadays, the hard disk drive (HDD) industry is very competitive and focuses on enhancing the performance and capacity of HDD. To serve these purposes, HDD manufacturers prefer to increase the number of media, thus adding more head gimbal assemblies (HGAs) as well. A swage process (SP) assembles between HGAs and arm actuators into a head stack assembly (HSA). The greater the number of HGAs, the thinner it gets. Such thinness in some products, after passing the SP, there could be higher deformation and stress in arm actuators than expected values. To investigate and understand this problem. This article proposes an explicit dynamic analysis (EDA) in ANSYS software to solve the problem and simulate the SP using an actual condition from a manufacturer. The EDA provides simulation results that are consistent with the experimental results. The analytical results lead to understanding the SP's deformation, strain, and lubricant effect. Therefore, the EDS is a precise and appropriate method for developing the SP in the HDD manufacturing process.
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Apparatus for inspection of low-coercivity magnetic force microscopy tips
(2018-08-13)
Damrongsak, Badin
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Photaram, Worachote
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Saengkaew, Karnt
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Cheowanish, Ittipon
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Damrongsak, Pattareeya
In hard disk drive manufacturing, magnetic force microscopy (MFM) is employed to provide feedback for process control. This requires accurate and precise measurement of the intensity and the width of the write field generated from fabricated recording heads. Thus, the response of MFM tips when exposed to the write field must be consistency, run to run and machine to machine; however, no specific tool that can inspect and separate out-of-spec or defective MFM tips is available so far. In this present work, we designed and developed a new apparatus that is suitable to quantitatively evaluate the performance of low-coercivity MFM tips. The detailed discussion of the design of the proposed system is given as well as the inspection algorithm. Basically, a solenoid coil is used as a magnetic field generator which can generate the field strength up to 500 Oe, enough to saturate the tip magnetization. When the tip was exposed, a phase difference of the oscillating MFM tip, which is directly proportional to the field intensity, is employed as a measure of the tip response. In addition, the capability of the implemented apparatus to inspect low-coercivity MFM tips was demonstrated. Results were then compared with those obtained from a conventional MFM machine with the reference magnetic write head as a test sample. Several tests with different sets of low-coercivity MFM tips were carried out to evaluate the implemented system. Results showed that it can distinguish the response of different MFM tips; however, as the results were not too different, only three samples were selected to present here, including the tips with typical magnetic response, low response and out-of-spec response. The measured phase shifts of those samples were 54.5 ± 0.3, 36.3 ± 0.3 and 15.4 ± 0.2 degrees, respectively.

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