Clamshell Style Cell Phones Pack Multiple Features and High Resolution Color Displays into Compact Designs
Challenge: Reliability and Folding / Flex Performance in a Small Space
Solution: DuPont™ Pyralux® AC - Adhesiveless Copper Clad Laminate – Flexibility and High Modulus for Through Hole Reliability
Cell phone providers are continuing to push the envelope by designing and introducing smaller lighter weight phones with an ever-expanding array of available features. Customers are demanding that the latest cell phones have completely integrated communication, computing, personal assistant and entertainment functions. Large color displays with full motion video supporting 1.5 megapixel digital cameras are the norm. Packing these features into the highly desirable clamshell format has created an interconnect challenge: how to reliably route as many as 80 individual signal traces through a small opening while surviving a minimum of 100,000 180 degree flex cycles.
Materials Selected and Why
Flex circuit designers have converged on multi-layer "air gap" constructions to solve the reliability and signal integrity requirements in the limited available space. In this approach, as many as 8 individual single layer flex circuits are laminated together in a non-traditional way. The ends are solidly bonded together with through hole interconnects for reliability while the center sections are allowed to remain "independent" to withstand the high stress generated in the bending area. This combination of multi-layer through holes and single sided flex constructions gives a well engineered interconnect that has been proven to be a reliable cost effective solution.
DuPont™ Pyralux® AC is a single-sided adhesiveless copper clad laminate that is ideally suited for use in cell phone air gap circuits. The high modulus polyimide core has outstanding flex performance and excellent through-hole processability. Pyralux® AC can easily be mechanically drilled or laser ablated to the tightest specifications. In addition, its roll format facilitates high productivity roll-to-roll processing. A wide range of polyimide thicknesses and copper foils is available to accommodate all line and space and electrical performance requirements.
In the near future cell phone interconnects will also need to be compatible with lead free processing and be "halogen free". As an all-polyimide laminate Pyralux® AC meets both of these requirements today.
As a result of this success, it is expected that air gap circuits using DuPont™ Pyralux® AC will continue to be the chosen design for clamshell phone display interconnects thus helping expand the availability and elegance of the clamshell cell phone design.