Single Pad Lapping Current Crowding via Peripheral Grounding Vias
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Solution Overview
Problem
In single pad lapping of sliders, the resistance detected at one electronic lapping guide (ELG) may not properly correlate to the resistance at another, leading to inaccurate control of the lapping process and varying stripe heights, which affects signal quality and precision.
Innovation Solution
The implementation of a system where the resistance of the ELG is at least 50 times greater than the effective wafer resistance, with a bonding pad and peripheral grounding vias, allows for precise control of lapping by adjusting the current delivery and resistance measurement to achieve consistent stripe heights across multiple sliders without the need for additional connections or wiring, mimicking the precision of double pad lapping.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If single pad connection ELG is used, then fewer connections and more space conservation are achieved, but precision decreases compared to double pad connection ELG
Solution Approach 1:
The patent introduces an intermediary grounding path through the wafer substrate and peripheral grounding vias to compensate for the missing ground connection in single-pad ELG configuration. This intermediary path provides a reference potential that enables accurate resistance measurement without requiring a second bonding pad, thus resolving the contradiction between reduced connection complexity and maintained measurement precision.
2Manufacturing precision
If stripe height is reduced, then areal density and signal quality increase, but control difficulty increases due to signal amplitude variations
Solution Approach 1:
The patent implements a feedback control system that continuously monitors the resistance of electronic lapping guides during the lapping process. By measuring resistance changes and comparing them to target values, the system adjusts lapping parameters in real-time to maintain consistent stripe height across all sliders, even when operating at reduced heights where variations have greater impact on signal quality.
3Productivity
If multiple sliders are lapped simultaneously using single pad lapping, then productivity increases, but resistance detection accuracy decreases due to current crowding
Solution Approach 1:
The patent segments the current path by introducing peripheral grounding vias at multiple locations around the wafer perimeter. This segmentation divides the current flow into multiple parallel paths, preventing current crowding at any single point and enabling accurate resistance measurements even when multiple sliders are lapped simultaneously, thus maintaining measurement precision while achieving high productivity.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach reduces the error in stripe height variation by compensating for effective wafer resistance, maintaining the accuracy of double pad lapping in single pad lapping, thereby ensuring consistent signal quality and precision without increasing costs.
Implementation Method 1
a bonding pad electrically connected to the ELG; end regions formed at one or more ends of the row; and at least two peripheral grounding vias, the vias formed in the end regions and comprising a conductive material formed therein
Implementation Method 2
The ELG is connected to a lapping controller which provides a current to the ELG and determines the stripe height of the ELG based on resistance between the bonding pad and the grounding pad. The ELGs have a known resistance as a function of height so that as the surface of the row is lapped, the resistance of the lapping sensor changes.
Data Source
AI summary
Embodiments described herein generally relate to connecting electronic lapping guides (ELGs) to a lapping controller to prevent the effects of current crowding while reducing connections to the ELGs in single pad lapping. Devices and systems can include a row of sliders including a magnetoresistive (MR) element, a plurality of high resistance ELGs connected to both the wafer and to at least one bonding pad and at least two peripheral grounding vias connected to the wafer. Methods and systems include a wafer comprising a plurality of sliders wherein each slider is connected to a lapping controller and the delivery of current to the ELGs is sequential to groups of sliders such that only one group of ELGs is being measured at any time.