User Manual

Page 11
COPPER TAPE
PIEZO FILM
SOLDER
WIRE
TOP ELECTRODE
BOTTOM ELECTRODE
COPPER TAPE WITH Z-AXIS
CONDUCTIVE ADHESIVE
DT PATTERN WITH COPPER TAPE
Figure 9.
Non-penetrative (and temporary) - Conductive-adhesive coated Copper Foil Tape (e.g., 3M
#1181)—available in widths from 3mm up to 25mm. Best results are obtained by...
! Using a "reasonable" area of
tape (perhaps about 1cm or
more). Small pieces do tend to
lift off easily.
! Soldering wires to the tape
FIRST, then removing the
liner and adhering with gentle
pressure to film. If small areas
are to be used, solder before
cutting the contact pad down
to size, thus leaving the excess
area to act as a heat sink.
Soldering does appear to
degrade the adhesive
properties in the vicinity of the
joint. NOTE: 3M does not
recommend relying on the
conductive adhesive in this
way and suggest an embossed
version of the same tape. The tape is really designed for large area contacts to metal, but results
have shown this method to be an effective, if not guaranteed, technique. An aluminum version
of this product is available (Part No. 1170). Beware of similar tapes that do not have conductive
adhesives (although these can be used for shielding, etc.)
! Conductive Transfer Tape—e.g., 3M #9702 (Preliminary product). An acrylic adhesive layer
loaded with conductive particles giving excellent "Z-axis" conductivity (i.e., through the
thickness of the tape) with very high resistivity in the X and Y axes. Thus single or multiple-way
connections may be made with a single strip. This material is relatively new. Initial results seem
very promising. Obviously this can be used to make direct connection with PC board or strip, or
to sections of foil with soldered leads.
! Negative aspects are a) high cost, and b) like all transfer adhesives, there is a tendency for the
material to adhere to its own liners around the edge so that "stringing" occurs on liner removal.
NOTE: Since time of writing, this product has been superseded by an improved version (#9703)
with an easy-release liner. This may not yet be generally available.
! Conductive Epoxy. This is usually available in two-part form (adhesive and hardener). Precise
metering and mixing of the small quantities usually required is rather difficult and messy. One-
part, pre-mixed material is available as a product which is stored at very low temperature and
should be used and cured at room temperature. Curing of any epoxy mix can usually be
accelerated by use of higher temperature, but since the piezo film has a modest high-temp
capability, curing is often a long term process (many hours, a day). Some mechanical clamping is
usually required on the parts to be bonded. Final reinforcement with "ordinary" epoxy can be
reassuring. Negative aspects: difficulty of use, cure time, higher cost, short "shelf life."
! Low melting-point Alloys—some alloys (e.g., Indium/Tin/Bismuth) which are known as "fusible
alloys" rather than "solders," melt at temperatures which allow them to be used on piezo film
with suitable metallization (e.g., gold, cooper, silver or silver ink). Rather aggressive fluxes are
often required, and the joint may be brittle. Mechanical strength is limited by the adhesion of the
metallization onto the film surface, so once again, reinforcement with epoxy may help. For joints
that must be very small and do not need undue mechanical strength this may prove a valuable
technique. Negative aspects: only certain metallizations are appropriate, sample quantities hard to
come by. Mechanical strength limited [Indium Corp.]
! Zebra® Connectors — Conductive rubber spliced with insulating rubber as used to form
contacts to LCD displays. High density multiple-way contacts may be made. External clamping
of contacts is required.