In an earlier post, I introduced Scott Sangillo of Amphenol Sincere.
http://blog.pcsridgway.com/post/A-Conversation-with-a-flex-e2809cexperte2809d.aspx
I thought it would be beneficial for our web customers, specifically those with design control, to have a better understanding of what is required to design a flexible circuit for application. A flexible circuit is a great design option combining the neatness and smaller package size of a flat cable, with the design flexibility of a wiring harness. PC Systems and our supply base can do it for you at a great price and with great quality by using suppliers like Amphenol Sincere.

Below is a Q&A email that Scott and I had that I would like to share:
KF – When designing a “flex circuit” and requesting a quote, what are the critical specifications that are needed?
SS – These are two very different situations.
When designing a flex, I assume you are referring to laying out a flex from scratch. In this scenario, you need to take all aspects of the application into consideration such as the pinout, electrical requirements of the traces, the termination styles, temperature, UL requirements, RoHS requirements, etc.
When determining cost, the two largest drivers are size and layer count. This will get you in “the ballpark” and then further clarifications will bring you closer to the products final cost.
This is important for you to know as a customer, especially when asking for “ballpark” pricing or budgetary quotes.
KF – With regards to flexible circuits to be used in Automotive glass, there is often concern that they will be able to withstand the Autoclave temperature and pressures. For example, 285°F (140°C) and 185PSI. What type of construction would you recommend for these type of applications?
SS – Any standard flex construction should be able to withstand the above autoclave profile. Although the standard materials are rated for 105 degrees C continuous operation, they can withstand higher temperatures for short durations.
KF – When designing for a current maximum of 15 amps, what would your recommended trace be? How about 30 amps?
SS – This will depend on the copper weight selected. If you are using a 3 oz copper (.0042), the recommended trace width for 15 A would .280 min and for 30 A would be .735 min.
KF – What is the most common and cost effective thickness and width to use?
SS – The most common thicknesses of copper used are 1 oz and 2 oz, however there is not a big increase for 3 oz. Given the amperage requirements and use of your applications, I would recommend 3 oz copper.
KF – In the simplest analysis, maximum current capacity would be a function of cross sectional thickness. Based on some background research, it also evident that form plays an important role as well. Can you elaborate? (Temperature Rise in PCB Traces by Douglas Brooks, UltraCAD Design, Inc. http://www.ultracad.com/article_temperature.htm)
SS- A thin wide conductor will dissipate heat better than a thicker narrower trace carrying the same amperage due to the larger surface area that it has.
KF – Many of our customers are more comfortable describing their traces as a thickness described in mm or inches although the PCB and “flex” industry prefers to use oz/ft^2. Can you provide the conversions?
SS - One ounce of copper weight equals .0014 inch thickness.
Now an opportunity for a pitch since Scott took his time to answer some of these questions.
KF – How does Amphenol Sincere Flex differentiate itself from the many other “flexible circuit suppliers”? 
SS – Amphenol Sincere produces high quality/high technology value added flex circuits at Asia pricing using a high mix, low to moderate volume model. Some specific technology differentiators are heavy copper processing, up to 15 layer rigid-flex, bookbinder technology, impedance controlled circuitry, and full in house assembly to name a few. We have stateside design, technical support, sales, and customer service to support our customer base so that we are the liaison to the factory with no communication or time zone barriers.
If you are experienced with flexible circuits, many of these questions and answers may seem trivial to you. If you have more detailed inquires, I would strongly recommend you contact us at PC Systems Engineering so that we can find a solution for you. In the next post, I hope to talk a little more about how we at PCS are using “flex” today and where we expect to use it in the future!