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28 The PCB Magazine • March 2017 extensively and work equally well. When a ca- ble is used, with or without a connector, it is typically soldered to the heater and then routed to the power source for attachment. A ZIF con- nector however is an inherent part of the flex- ible heater and requires less cost and inventory. There are no wires or connectors to stock or as- semble. It only requires a mating connector on the power/monitor device circuits. This area of the heater is usually a "non-heated" area. The signals must be adjusted so that the power trav- els through them without heating as they do in the designated heated area. Attachment Methods If the flexible heater is to transfer its heat to a mass or surface, it must be firmly attached to that surface. Some methods that are typical are adhesion, clamping or blanketing. A stan- dard adhesion scenario would include a pres- sure sensitive adhesive (PSA) attached to either the flexible heater or the surface to be heated. The clamping method is, as its name implies, a heater clamped between two surfaces. And the blanketing method is also intuitive. The flexible heater will be wrapped or blanketed around the mass that requires heating. In all cases, it's im- portant that the heat is transferred evenly across the entire surface. Any void in the transfer will create hot spots and deter the heater from per- forming as intended. Heat Spreaders One way to help ensure that there are no hot spots is to include a heat spreader on the back side of the flexible heater. This would be a good practice if the blanket method is used to transfer the heat. Since the blanket method doesn't pro - vide a solid method of transfer, spreading the heat on the heater itself is necessary. A spreader of a good thermally conductive material such as aluminum can be adhered or laminated to the flexible heater and ensure that the heat is spread evenly. It isn't necessary in all applications, but is very useful in some and is easily done. Conclusion Flexible heaters are used throughout the electronics industry because of their lightweight and inherent flexible capabilities. Their use as critical components in aircraft and medical de- vices require a thoughtful approach to their de- sign. As well, their use in products such as heat- ed automobile seats or clothing allows them to provide comfort to their user. They keep elec- tronics warm to provide endless amounts of un- interrupted use in the roughest of conditions. Flexible heaters are useful for many applica- tions and will continue to be valuable far into the future. PCB John Talbot is president of Tramonto Circuits. CRUCIAL CONSIDERATIONS FOR BUILDING FLEXIBLE HEATERS Figure 5: ZIF tail on a flexible heater. Figure 6: Wire cable attachment on a flexible heater.