Dynamic magnetic information storage or retrieval – Head mounting – Disk record
Reexamination Certificate
2000-09-07
2002-12-10
Evans, Jefferson (Department: 2652)
Dynamic magnetic information storage or retrieval
Head mounting
Disk record
C360S264200
Reexamination Certificate
active
06493190
ABSTRACT:
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not Applicable
REFERENCE TO A MICROFICHE APPENDIX
Not Applicable
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to disk drive suspensions, and more particularly to wireless suspensions in which the flexure comprises a laminate of plastic film, trace conductors, and a metal layer. In a specific aspect, the invention relates to improvements in the design and manufacture of suspension flexures to have capacitance and thus impedance values controlled separately for each trace and each pair of traces to have constant values throughout their lengths, as desired, and the same or different absolute impedance values for optimizing read and write circuit pairs, and to accommodate mechanical limitations of the flexure design, as needed for optimum flexure performance.
The invention achieves control of impedance by increasing or decreasing capacitance (to correspondingly decrease or increase impedance) of each conductive trace of a pair or pair of conductive traces through modification of trace width, and/or spacing from adjacent traces, or by changes in effective length by varying the length of a trace between defined places on the flexure, while not altering the distance between those defined places.
2. Description of the Related Art
Existing trace flexure designs have layouts that feature conductive trace paths generally as straight as possible, with any change in path direction being curved with as large as possible a radius. Generally, with multiple conductive traces routed side by side, the spacing between the traces will be at least locally uniform, that is, in any given portion of the trace flexure, the spacing between adjacent conductive traces and the trace width will not vary much. If, however, the traces after being routed alongside each other go to different destinations on the layout, such as occurs when the traces are divided to reach both sides of a slider along the outriggers.
A currently typical spacing for 0.0016 inch wide and 5 to 20 micron thick conductive traces in a wireless flexure is a 40 micron (1 micron equals 1 micrometer equals 40 micro inches) space laterally between adjacent traces. The traces thickness is determined by the flexure laminate, and is assumed to be fixed by the laminate supplier for purposes of this invention.
This width and spacing combination results in a characteristic impedance referred to as Z
0
, for the device and for each pair of conductive traces considered. Presently used trace flexures have a characteristic impedance of 30 or so ohms.
BRIEF SUMMARY OF THE INVENTION
The putative “characteristic impedance” is not found at all points along the trace or pair of traces. Rather many variations from that impedance are found. This occurs, for example, in a disk drive suspension flexure because Z
0
changes with differences in trace cross section or trace spacing arising from diverging trace pairs, and changes in routing and bends in traces around mechanical features of the flexure, such as tooling holes or weld points. It is, however, desirable that the flexure have a Z
0
that is constant along the length of the traces and trace pairs throughout the flexure, and in the case of read-write circuits, constant at about 110 ohms for the write lines and at about 60 ohms for the read lines.
As the operating frequency of the disk drive increases, the importance of adhering to the constant and correct impedance becomes ever more important. Any change in impedance Z
0
causes a reflection of the signal being sent along that path; the reflection represents wasted signal and an increase in noise. Both wasted signal (lost signal strength) and increased noise effectively decrease the signal to noise ratio (SNR) and thus decrease this important measure of the quality of an electronic device.
Historically, trace flexure layouts have to the good had generally large radius curves, but also uniform trace widths and spacing, all in accordance with the design rules of printed circuit boards (PCBs), which is the preceding technology to flex circuits and wireless flexures. But, PCBs were a different animal from flexures since there device placement was at the whim of the PCB designer, and mechanical constraints, so important in flexures, were not really a factor. The PCB designer could place the devices to be connected anywhere he wanted to, constant width and spacing of conductors was a design that was both correct and easy.
In making this invention it has been recognized that the simple default design taken from PCB technology does not apply to the very different case of trace flexures in which the end points of the traces are immutably fixed by exigencies of disk drive suspension technology, and their intermediate lengths are necessarily detoured around fixed obstacles implicated in suspension design, such as tooling holes and weld points.
Time Domain Reflectometry (TDR) analysis computes Z
0
as a function of time as the energy passes down the trace length. TDR shows that the Z
0
for an apparently uniform trace varies dramatically along the length of the trace in previously known flexure design, and even the nominal value of Z
0
value about which the variation takes place is less than specifications require.
It is, accordingly, an object of this invention to provide a wireless flexure for a disk drive suspension having a constant characteristic impedance Z
0
over the length of the flexure traces regardless of the presence of mechanical obstacles, curves in layout, or other factors that have caused unwanted variations in impedance along and between conductive traces and trace pairs in the flexures. It is another object to provide an improved flexure design in which the conductive traces are customized along their length to meet situations that might limit the constancy of the impedance of the trace. It is a still further object to vary locally the width and spacing of conductive traces to offset locally unwanted variations and lack of constancy in impedance imposed by the flexure design or application. Yet another object is to increase the effective length of one or more traces to increase capacitance relative to one or more adjacent traces and thus limit inversely changes in impedance constancy. It is yet another object to vary the length and configuration of one or more traces relative to another trace or traces between fixed points to change to a desired value the impedance of the one relative to the other, e.g. to increase the impedance of a write line over that of an adjacent read line.
These and other objects of the invention to become apparent hereinafter are realized in a controlled impedance trace flexure for a disk drive suspension, the trace flexure comprising a laminate of a metal layer, an insulative film layer and one or more pairs of conductive traces comprising paired trace members that extend together differentially in a pattern between two fixed points such that there tend to be unwanted local variations in the respective impedances of the paired members over their extent and therefore a lack of constancy in conductive trace impedances, the paired members being locally modified in their relative spacing, length and/or width in capacitance-varying relation sufficiently to offset the impedance variations, whereby the paired members are controlled to a constant impedance.
In this and like embodiments, typically, the paired members at a predetermined locus tend to unwanted variations in their respective impedances, and the paired members are locally differentiated in width at the predetermined locus to locally vary their capacitance against the impedance variations, or the paired members are locally differently spaced at the predetermined locus to locally vary their capacitance against the impedance variations.
Alternatively, the paired members are made locally of different effective lengths within the predetermined locus to locally vary their capacitance against the unwanted impedance variations.
In a further embodiment, the invention provides a con
Bachand Louis J.
Evans Jefferson
Magnecomp Corporation
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