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www.us-
tech.com MICROLINE 5000 Flex Drilling and Cutting
in the Cleanroom Continued from previous page
Negative-Stiffness vs. Pneumatic Isolation
Air tables have been used since
the 1960s for vibration isolation, and clearly have the widest installed base within cleanrooms. However, with the increased sensitivity in instru- mentation, particularly at the sub- atomic level, more precise vibration isolation technology is needed to deal with low-hertz vibrations, which neg- atively influence results despite the use of air tables. Introduced 20 years ago by Minus K Technology, nega- tive-stiffness vibration isolation was specifically designed to isolate these low-frequency perturbations. The following key comparisons
between air tables and negative-stiff- ness isolators should be examined when evaluating vibration isolation for cleanroom applications:
The MicroLine 5000 is the flex PCB industry answer to high through-put, high-yield drilling applications. With the ability to drill holes down to 20µm, a variety of both organic and inorganic substrates can be processed, such as:
Flexible PCBs IC Substrates
High Density Interconnect PCBs
1-800-345-5753 |
www.lpkfusa.com/flexdrilling See at APEX, Booth 3509 and at ATX West, Booth 1650
Vertical and Horizontal Isola- tion. Air tables do achieve isolation, but primarily in the vertical vector, with limited horizontal isolation. The horizontal vector is often overlooked because horizontal building vibrations are less obvious, but nevertheless, transmitted to the cleanroom instru- mentation. Negative-stiffness iso lators achieve a high level of isolation in both vertical and horizontal directions.
Transmissibility of Low-Hertz Vibrations. Vibration transmissibil- ity is a measure of the vibrations that are transmitted through the iso- lator relative to the input vibrations. Every isolator will amplify at its res- onant frequency, and then start iso-
8:50 AM
February, 2017 Precision Vibration Isolation
lating. Air systems will actually am- plify, instead of reduce, vibrations in a typical range of 1.5 to 3 Hz, due to the natural frequencies at which air tables resonate. The low-cycle per- turbations will
come straight
through to the instrumentation. Air tables do not isolate to the extent that is really needed at very low res- onance frequencies. Negative-stiffness isolators res-
onate at 0.5 Hz — and in some cases at lower frequencies both vertically and horizontally. At this frequency there is almost no energy present. It would be very unusual to find a sig- nificant vibration at 0.5 Hz. Vibra- tions with frequencies above 0.7 Hz are rapidly attenuated with increas- es in frequency. Note that for an iso- lation system with a 0.5 Hz natural frequency, isolation begins at 0.7 Hz and improves with increase in the vi- bration frequency. The natural fre- quency is more commonly used to de- scribe the system performance. When adjusted to a natural frequen- cy of 0.5 Hz, negative-stiffness isola- tors achieve approximately 93 per- cent isolation efficiency at 2 Hz vi- bration, 99 percent at 5 Hz, and 99.7 percent at 10 Hz. Some low-height negative-stiffness isolators provide natural frequencies of 1.5 Hz hori- zontal and 0.5 Hz vertical. Negative- stiffness isolators have the flexibility of custom tailoring higher resonant frequencies when lower ones are not required.
Mechanical Simplicity. Pneumatic isolation tables operate on a supply of compressed air or gaseous nitrogen.
Continued on next page
See at APEX, Booth 3551
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