Making Connections

Piezo material produces a voltage in response to stress or strain. An electrode must be attached to the material to collect the voltage. With TCL piezo film materials, the electrode is silver loaded polymer ink. It is highly conductive, flexible and durable. Since there is only piezo activity in the material between two electrodes, traces can be used as leads. These traces can be long or short, but at some point must be connected to the output cable. This page will cover some of the ways this can be done.

The discussion of making connections needs to include the issue of shorting across the edges of the film. When cutting very thin flexible material, it is easy to compress or distort the edge. With electrodes only separated by as little as 28 microns, short circuits or current leakage are probable.  A buffer area on at least one side of the film can be cleared of conductive material to prevent this. Clearing the edges of the hot side allows greater shielding by the ground side.  A cotton swab, moist with xylene will easily remove the ink. Mask the area you want left covered with a straight edge. Do not apply adhesive masking tape to the film as it will take some of the electrode with it when removed. The area where the connection will be made needs to have ink on only the side making the connection.

There are many ways to connect to the film. Pressure connections are very common. One type of pressure connection is where piezo material is sandwiched between conductors and kept under pressure. This was a common technique of attaching to electrodes of under-saddle guitar pickups for many years. Conductive adhesives are used in a variety of applications. These include conductive tapes (single and double sided) and conductive epoxy. Conductive inks can also be used to make light weight surface to surface connections. Very robust connections can be made with through-film techniques. These would include stapled connections, blind rivets, or wires twisted through small holes in the film. Each of these can be electrically reinforced with conductive adhesive applied to the connection.
The non-conducting side of the connection should be reinforced with a strengthening laminate.

Conductive adhesives  must be a low-temp cure type. Unlike piezo crystal, PVDF cannot stand high temperatures.  When soldering to crimp on connectors or short wire leads, use a heat sink and short dwell times.

Copper foil with conductive adhesive is the easiest way to connect to the film. When soldering to copper foil,  solder to the foil first, with the lining attached.. Then the foil should be cut to size and attached to the film. Heat will degrade the adhesive of the film, and the lining will act as a heat sink.  This works best when the foil has an undamaged area to make the connection to the silver ink. Pressure increases the effectiveness of the adhesive.

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The drawings to the left illustrate a very simple through-film technique. 

  1. Place with wire in the center of the attachment area.
  2. Staple the wire in place.
  3. Twist the wire around the staple.
  4. Reinforce the mechanical and electrical connection with conductive adhesive.

Start with the lead attachment area cleared and reinforced on the back side.

Another popular through-film technique uses blind rivets and eyelet connectors. The wires are crimped to the eyelets. If a solder connection is preferred, solder the wires to the eyelets before attaching to the film. You can further reinforce the connections with conductive adhesive.

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