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18 FLEX007 MAGAZINE I OCTOBER 2018 than is possible with a nominal 1.5-mm rigid board. 3. Reduce assembly costs Before the broad use of flexible circuits, assemblies were commonly a collection of dif- ferent circuits and connections. This situation resulted in the purchasing, kitting, and assem- bly of many different parts. By using a flex- circuit design, the amount of part numbers required for making circuit-related intercon- nections is reduced to one. 4. Eliminate the potential for human error Because flexible circuits are designed as an integrated circuit assembly with all intercon- nections controlled by the design artwork, the potential for human error in making intercon- nections is eliminated. This is especially true in the cases where discrete wires are used for interconnection. 5. Facilitate dynamic flexing Nearly all flexible circuits are designed to be flexed or folded. In some unusual cases, even thin rigid circuits have been able to serve to a limited degree. However, in the case where dynamic flexing of a circuit is required to meet the objectives of the design, flexible circuits have proven best. Modern disc drives, for example, need the flexible circuit endure any- where millions of flexural cycles over the life of the product. Other products, such as laptop hinge circuits, may only require thousands of cycles, but it is the dynamic actuation capabil- ity enabled by the flex circuit that is key to its operation. 6. Improve thermal management due to being well-suited for high-temperature applications High temperatures are experienced both in assembly with lead-free solder and in the operation of higher power and frequency digi- tal circuits. Polyimide materials are well-suited to the management of high-heat applications. Not only can they handle the heat, but their thinness also allows them to dissipate heat bet- ter than other thicker and less thermally con- ductive dielectrics. 7. Improve product aesthetics While aesthetics may seem like a low-order advantage, people are commonly influenced by visual impressions and frequently make judg- ments based on those impressions. Flexible cir- cuit materials and structures look impressive both to the seasoned engineer and the layper- son. It can make a difference in the decisions made in some applications, especially those where the user gets exposure to the functional elements of the product. The increasingly sophisticated electronics being developed are pushing more designs to rigid-flex. Thinking through the benefits listed above, you become convinced that rigid-flex is the right direction for your next project. The next step is convincing your boss or program manager that this concept is the best solution. You are now battling that same perception; rigid-flex is more expensive. However, you can- not compare only the cost of the rigid board and cables to the rigid-flex. You need to look more holistically at the total cost of the design. Costs Here are the key factors to consider when comparing the cost of rigid-flex to a PCB and cable solution: 1. Design Because you are merging multiple boards, only one design is needed with a rigid-flex. With the rigid PCB and cable solution, mul- tiple PCB and cable assembly designs are often required. The cost of generating each design should be included when doing a comparison of both options. 2. Cable and connectors It is common for someone to compare the cost of the rigid boards with the cost of the rigid-flex and jump to the conclusion that the rigid-flex is too expensive. However, the cost of the cable and connectors should also be considered in this decision. This includes the cost of kitting for assembly, labor, in-process inspection, cable assembly test, final test, PCB tooling and test charges, and the cost of engi- neering time required for each of the items.

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