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Original Publication Date: 1999-Oct-01
Included in the Prior Art Database: 2003-Jun-17

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Disclosed is a method that improves the 4 tiered resistive lapping system employed in the lapping of thin film heads during slider machining. In this system, all 4 resistive lapping guides, 2 pairs of Rough Lapping Guides (RLG) and Fine Lapping Guides (FLG) on each side of the chip, must be manufactured defect free with nominal resistances in order for accurate lapping to occur. The equation Rs (W h) R describes the relationship between an element’s geometry and its electrical resistance, where Rs is the sheet resistance of the element, h is the stripe height of the element, W is the width of the element and R is the electrical resistance of the element. For an element with uniform Rs and fixed W, the R increase as the h decreases. In the 4 tiered system, the pair of RLGs on each side is monitored, allowing dynamic balance adjustment if the rate of change in resistance on one side becomes too high. The function of the FLG is also critical; its resistance is used to zero out the small, localized variations in Rs, W and h that are inherent to all thin film manufacturing. For each pair of RLG and FLG, the equation above is adopted and solved differentially for both RLG and FLG to obtain a target resistance for a desired stripe height. Typically, the FLG is recessed and not lapped and used only in the calculation. When the FLG is damaged, process variations can not be zeroed out and when the RLG is damaged, lapping can not be monitored. Therefore, if any one of the RLGs or FLGs is damaged, the slider cannot be lapped accurately to the desired stripe height. The method disclosed copes with certain damages to this RLG/FLG system and allows for accurate lapping to occur in an otherwise lost slider. The most common damage to the lapping system is a defect to the FLG. Because of the differential nature of the solution to the resistance equation, the stripe of the FLG is made a lot smaller the stripe of the RLG. A smaller stripe means that the FLG is less tolerant to handling and/or contamination issues that are common detractors in manufacturing. When the damage occurs, the disclosed method searches through the FLG resistance of the neighboring sliders and uses the closest resistance for the differential calculation. Typically, the closest match comes from slider from the same row or column within the wafer. If the FLGs from the entire row and/or column are damaged, then the wafer average is found to be the next closest match. The second most common damage to the lapping system is a defect to the RLG. Since the stripe of the RLG is large, the resistance of the RLG is not sensitive to cracks in the element. If the RLG has a small crack in the bottom portion of the stripe, then when the slider is lapped to the tip of the crack, an open circuit results and the RLG ceases to function. This type of damage is hard to detect before lapping since the small crack contributes to a small increase in the initial RLG resistance. The solution for this type of RLG defect is to use the FLG as a backup guide. If the FLG can be lapped, then it can be used to monitor the stripe when the RLG fails for lap through.