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64 DESIGN007 MAGAZINE I JULY 2023 Heat Dissipation As we add more resistors, capacitors, semi- conductors, and LEDs to flex, there becomes a need for the flex to assist in heat dissipation. In addition, where the flex circuit is creat- ing heat—like a flex heater—there is a need to spread the heat. For heat dissipation, aluminum and ceramic stiffeners have worked well. Common medi- cal applications for us have been small cam- eras and an LED side by side. e LED gives off a fair amount of heat and can disrupt the image sensor (camera). Using an aluminum stiffener supports the SMT placement, pro- tects the components aer assembly, and most importantly, dissipates the heat enough to not disrupt the other components in the area. Alumina has been used for heat spreading. Applications requiring a flex heater and consis- tent temperatures across areas could use alu- minum, alumina, or ceramic. Check with your manufacturer as these are highly custom. Zero Insertion Force Connectors Zero Insertion Force connectors (ZIF), com- monly used in flex circuit applications, have specific thickness requirements for attach- ment. Manufacturers' height requirements vary. FR-4 is too thick. In order to meet the flex height requirement of the connector interface, flex shops will use additional layers of poly- imide. Polyimide adds height and stiffens the circuit at the interface. Stiffeners on flex circuits provide mechanical support and strength, circuit flatness, thick- ness, heat spreading and dissipation, and the protection of solder joints. Your flex manufac- turer will be familiar with the materials and the process. Adding stiffeners to your flex circuit is part of the design process and should be con- sidered carefully. Stiffeners enable and broaden the scope of flex applications. DESIGN007 Mike Morando is director of sales and marketing for PFC Flexible Circuits, a subsidiary of OSI Electronics. Figure 8: Polyimide stiffener for shielded ZIF application.