MONOSTROPIC - Used for fine pitches. It can most readily be recognized by how small the traces are. As a rule of the thumb, if you can hardly see it - it is MONOSTROPIC. This material can be made to a pitch as fine as .22mm. The material contains gold and nickel particles and has a very low contact resistance. It has a yellow color from the titanium dioxide used in the manufacturing process of coating the connector with Thermoset adhesive. i.e. MEMO EXPRESS

ANISOTROPIC - Is the lowest cost material to yield very reliable bonded joints. This material is filled with gold plated nickel particles and is found on most pagers. It is also replacing planar material in pager applications. Many of the pagers manufactured with PLANAR technology have ANISOTROPIC replacement parts. This material can also be produced in pitches as fine as .29 mm, but at these fine pitches look for the MONOSOTROPIC type. Look for green and white as well as black and white to recognize this type. i.e. BRAVO EXPRESS

PLANAR - The original pager material. It is limited to .3mm or larger pitches and is more expensive than other types and contains no metal particles. It is yellow with black traces which are usually visually easy to see. i.e. BRAVO ALPHA

Bonding (establishing a mechanical and electrical connection) of these materials requires temperature, pressure and time. The (fig 6) shows materials and their respective parameters.

Note that there is an operating time, temperature and pressure envelope for each type of material. When replacing an HSC connection, it is important to note the properties for each type of material.

If, for instance, when bonding a monosopotric material, and anosopitric pressure of #70 lb. is applied - the bonded joint will look fine; but, it will not have a proper mechanical connection to the pad. It might even work for a short time - the fail is the device is dropped or sees an environmental temperature change. Is an anisotopic material is bonded at a monosopotric temperature, the insolating material between the conductive traces could melt and short.

If a planar material is bonded at the high end of the monosotropic pressure envelope - the bonding head could cut the material.

If the HSC cable is pealed from the circuit card, the residual conductive material on the pad areas of the PCB will reveal the way a properly bonded joint appears after bonding.

MYLAR TECHNOLOGY

Flexible cable, using MYLAR technology, is essentially a flexible printed circuit board. The conductive traces are copper which, in most cases are plated with solder. The techniques of working with this cable is the same as PCB's; but, the material will not tolerate the usual 600 F - 750 F used on PCB's. The best working temperature is between 375 F to 400 F. A high thermal mass, digitally controlled soldering iron or bonding unit will ensure damage free rework of devices using MYLAR.

Preperation for Flexible Circuit Replacement:

Removal of the old flex cable is usually performed with a digital temperature controlled soldering iron set at less than 700 F. as the solder joints reflow, apply a pealing pressure to disconnect the solder joints. After cooling, the receiving pad areas on the PCB card should be tinned with a 63/37 paste or wire.

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