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HSC - MYLAR FLEXIBLE CABLE TECHNOLOGY There are two types of
flexible cable used in telecommunications devices. The
most prevalent use is for connecting a LCD (liquid
crystal display) to a PCB (printed circuit board). Mylar technology can be recognized by the presence of solder joints, an amber dark green color and the presence of a TAB chip bonded to the cable. HSC (heat sealed connector) can be recognized by the absence of solder, sot pliable cable and black, green, yellow coloring. All Mylar technology can be repaired, reworked and replaced with a soldering iron, wire solder, solder paste or a bonding unit. HSC technology is divided into three groups each having different criteria for repair and can only be replaced with a process controlled bonding unit. For factory bonded results HSC material requires the application of controlled pressure and specific temperature for an exact time. HSC Technology HSC (heat sealed connectors) are not a soldered material, rather a flexible substrate with conductive traces attached. The joint created by bonding (electrically and mechanically attaching) the connecting end of HSC type flex cable is the HSC (HEAT SEALED CONNECTOR). The conducting traces - wires, so to speak - are filled with conductive material (fig 2)
Conductive epoxy and polymer technology, information and specifications are not readily available to the community of technicians and engineers working in the PCB environment. It is not necessary to understand the nuances of this technology to successfully deal with it in the repair of products using it, an understanding is sufficient to successful repair. To that end, it is more effective to use analogous examples to explain how to deal with equipment using the technology.
A good analogy, is to think of the flex (ribbon) connector as a flat wire harness with each wire replaced by a bead if conductive epoxy. Visualizing this bead of conductive epoxy as being much the same as a bead of caulking compound filled with metal particles will help in seeing the reasons for various time, pressure and temperature profiles which are required for different types of HSC material (fig 3)
Understanding the properties of the various HSC materials will allow an intelligent approach to repair of various products, as well as an appreciation of the restraints of their use and removal and replacement limitations.
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This technology was developed to
provide a quick and easy - yet reliable - interconnect
method for connecting LCD (liquid crystal displays) to
printed circuit boards. Telecommunications devices such
as pagers, cell phones, two way radios, fax machines and
business telephones use this technology extensively. It
is not necessary to understand the precise mechanics of
this technology to replace or repair devices which have
used HSC material; however, a technician will be more
comfortable knowing why a repair or replacement is
successful instead of only knowing how to do the
replacement.
The object of the temperature,
time and pressure profile is to get the conductive
material to become plastic and make a mechanical, as well
as an electrical connection to the circuit pad area.
Different types of material require different profiles. 
Some HSC material has different
metal particles and different amounts and sizes of metal
particles. Some require higher temperatures than others
to change from the solid to the plastic state, The
pressure requirement is easily understood if it is
thought of as having to squeeze the particles together to
get them to contact each other so they will be
electrically conductive (fig 4)
Presently, in telecommunications,
there are three main types of HSC materials in use. Each
type has its own mechanical and electrical
characteristics which are unique and give a range of
price - performance features which can be applied to
various products depending on cost vs. performance
considerations. The electrical and mechanical differences
as well as pitches - the spacing and size of the trace
(fig 5) - are different as well.