There are some great products utilized making flexible circuits, however there is no product available today that could be called a cure all, having every positive quality and also no drawbacks. This assessment is based upon that there are a variety of different requirements that are made use of to recognize and define the desirable as well as important properties of materials used to create a flexible circuits laminate. This checklist of preferable buildings outlines a wide spectrum of needs and/or demands that may be put on a completed flexible circuit in an application. While no known material could address every one of the sometimes conflicting needs that the manufacturer as well as customer may desire from a material, it is still of some worth to have a mental picture of a suitable gear as a means of keeping in mind what trade-offs may be required when selecting an ideal substrate for a product or application. In time many product combos of movies, foils and/or adhesives, along with procedures and also specialized devices, continuously be developed, offering new possibilities to fulfill the expanding need for smaller sized, light- weight, greater rate wiring for tools calling for less power consumption with more capabilities and also functions. A cell phone is one such device, along with parts of the facilities to sustain it.
A normal flexible circuit today is comprised of a thin base dielectric polyimide (PI) movie at a density of 50 to 125 microns in density (2 to 5 mils) with 1 to 3 oz. copper gage, with or without glue. Thinner gages are readily available, however flexible circuits with the dimensions explained are frequently manufactured with great return and great tolerances, and board/circuit makers have learned to manage these products to additionally have affordable returns in high-volume environments, especially in computerized and also semi-automated procedures.

DIMENSIONAL STABILITY
The flexible laminate needs to be dimensionally secure. Shrinking or growth of a flex circuit base material throughout handling is a concern for both manufacturer and user given that it can impact both the fabrication of the circuit and also its assembly. It is especially aggravating when dimensional modification is not predicable.

While products differ in their dimensional stability, there are a variety of different ways to deal with the results of dimensionally variable materials, which will certainly be discovered in more detail in Practical Design Guidelines for Flex as well as Flex Circuit Manufacturing Processes. It is a certain benefit in manufacturing to avoid resorting to such practices. New film chemistries and also procedures have actually aided in this area by permitting the pattern of thinner products offerings. Examples of these new PI movies as well as properties are defined later on in the chapter. The specifications that influence the dimensional stability of base dielectric products, in order of importance, are:

1) Base movie kind as well as qualities connected to that chemistry
2) Process criteria made use of in manufacturing
If used), 3) Adhesive type(.

THERMAL RESISTANCE.
Since the majority of digital assemblers use raised temperature level procedures such as reflow soldering for part assembly, the flex circuit material chosen for use in manufacture ought to have the ability to reliably endure regular assembly procedure temperatures without distortion. With the well-meaning, yet baseless and also clinically foolhardy, mandated transfer to lead-free soldering in Europe, there will certainly be added stress to enhance thermal resistance efficiency. Lead-free solders have actually further limited the option of products, compeling the user to address the difficulty with either much more ex- serious products or more pricey low melting factor solder when soldering is called for. This, along with laws pertaining to halogenated fire retardants, has triggered numerous friend- rials to be reformulated or stopped.