QuickPack - Technical Notes

Tech notes - 1

Attaching the Quickpack/PowerAct Transducer to a structure with epoxy

Many applications of the QuickPack piezoelectric transducer require the device to be attached to the surface of a structure. For these applications, proper attachment of the QuickPack transducer is critical to its performance, because the QuickPack device must transmit mechanical strain energy to and from the structure.

The QuickPack transducer can be attached to a structure by any one of several means. There are two common forms of attachment: embedding the device into a composite structure, and bonding the device to the structure with epoxy. When the QuickPack transducer is bonded to a structure with epoxy, the choice of epoxy should consider many factors, especially performance and cost. For performance considerations, the epoxy should produce a uniform, thin, stiff bond layer. The thinner and stiffer the bond layer, the better the results. For this reason, a high-performance structural epoxy is often the best choice.

Midé ships, free of charge, sample quantities of a two-part, 24-hour cure, high-performance structural epoxy with QuickPack product orders. Midé recommends that this epoxy be used for bonding the device to a structure, because it provides excellent adhesion to the QuickPack actuator’s protective polyimide coating. (NOTE: The sample epoxy shipped with the QuickPack products should be used before the expiration date marked on the package.) Another example of a suitable high-performance structural epoxy is listed below.

ECCOBOND© 45 CLEAR
Richey Electronics 508-664-9355
87 Concord Street 508-664-9356 fax
No. Reading, MA 01864
http://www.richeyelec.com

In cases where assembly costs are a greater consideration, an epoxy that requires a 24-hour cure cycle may not be the best choice. Elevated temperatures can accelerate the cure cycle of most two-part epoxies,including the epoxy Midé provides. Some applications that require high-volume manufacturing processes may call for a different type of adhesive. If you are considering using a QuickPack product for a high-volume application, consult Midé for product integration assistance.

The numbered steps in this QuickNOTE document provide detailed instructions recommended for bonding QuickPack transducers to structures. Italicized steps are required only if a vacuum bonding technique is used. The vacuum bonding technique applies uniform pressure to the QuickPack transducer during the cure cycle and helps to remove trapped air bubbles in the epoxy. An alternative bonding method is simply to apply weights to the QuickPack product to provide roughly 14.7 PSI during the cure cycle. In both cases, the goal is to achieve a uniform, thin bond layer.

Before you start

Once the QuickPack transducer is properly attached to the structure, it cannot be removed without destroying it. Therefore, it is important to determine exactly where you want to place the device before you mix the epoxy. If the desired location is flat, any of the standard QuickPack models may be used. If the desired location is not flat, please note that standard flat QuickPack products may conform to structures with slight curvatures (radius > 0.5m). Tighter curvatures may require a custom QuickPack device.

Surface Preparation

1. To improve adhesion, lightly sand the bonding location, and clean residue with isopropyl alcohol. The structure and the QuickPack transducer should be free of dirt, grease, and oils. Isopropyl alcohol is the best cleaning agent. (Do not use acetone or other organic solvents.) Lightly sanding the surface of the structure should improve adhesion, but do not sand the QuickPack product, as that would damage the protective polyimide coating.
   
2. Place Teflon® tape on the area where the QuickPack transducer will be attached. For standard QuickPack transducers, Midé recommends 0.010 inch thick Teflon tape.
3. While holding the QuickPack transducer down at its desired location on the Teflon tape, trace, cut and remove the tape to create a pocket for the QuickPack transducer.
4. Place Teflon tape on the QuickPack transducer, covering the top surface of the transducer and encircling (i.e., the top and bottom) the flex tab and electrical connector. For standard QuickPack transducers, Midé recommends 0.005 inch thick Teflon tape.
   Teflon tape on the structure and on the QuickPack device helps to position the transducers precisely and to make clean-up much easier.
5. Place bonding tape on the structure to surround bonding area.
   Bonding tape placed around the bonding area will create a seal when a vacuum is applied. If the structure is relatively small, the bonding tape can be placed on a larger bonding surface prepared with a release film to protect it. In this case, the small structure (with QuickPack transducer) would be placed on the larger bonding area when a vacuum is applied.
6. Cut air weave and bagging material to the size of the bonding area.
   The air weave material is a fabric that distributes the vacuum pressure and prevents the bagging material from blocking the vacuum line. The bagging material is a flexible plastic sheet that provides an air-tight seal over the bonding area. The air weave sheet should be large enough to cover the QuickPack transducer and the vacuum hose, but small enough to fit within the bonding tape perimeter. The plastic bagging sheet should be larger than the bonding tape perimeter.
7. Mix the epoxy in appropriate proportions.
8. Spread the epoxy in a thin, even layer on the structure and on the QuickPack transducer.
   For convenience, the epoxy that Midé provides comes in a pre-proportioned mixing dispenser.
9. Place the QuickPack transducer on the structure.
   After the QuickPack transducer is in place, excess epoxy can be wiped off.
10. Lay down the air weave material over the bonding area.
11. Slide the vacuum hose under the air weave, and seal the hose with bonding tape.
12. Lay down the bagging material over the bonding area.
    The vacuum hose should be connected to a standard vacuum pump with the line closed during set-up.
13. Open the vacuum line slowly (approximately five seconds).
14. Close vacuum line to check for leaks.
15. Fix leaks as necessary and open vacuum line again.
    It is recommended that the integrity of the vacuum seal be checked to confirm that proper pressure is applied to the QuickPack transducer during the cure cycle.
16. Remove pressure after 8 to 12 hours to clean up excess epoxy flow.
17. Re-establish pressure for the remainder of the 24-hour epoxy cure cycle.
    Excess epoxy is most easily removed halfway through the cure cycle, after it has solidified but before it has fully set. This is done by temporarily removing any vacuum bag or weight, scraping or peeling away the excess epoxy, and replacing the vacuum bag or weight to re-establish pressure for the remainder of the cure cycle.
18. After the epoxy has cured, remove pressure, bagging material, air weave and bonding tape, and peel off Teflon tape.
    

For further assistance

If you have additional questions about attaching the QuickPack transducer to the surface of a structure, or about the general use and operation of QuickPack products, please contact Midé. You will speak to a knowledgeable representative that will help you with any specific question you may have. And if you are designing a product with high-volume production potential, please contact Midé early in your design process can provide you with recommendations for reducing your production system costs and maximizing the performance of the QuickPack product for your specific application.

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For more information:

Please email Conor Clery (Products), or call: 781-306-0609 x292