While flex circuitry has been around for a long time, we still see a lot of bad information or misunderstandings regarding flex. Below are some that seem to be fairly common.
Flexible Circuitry is a Relatively New Technology: Actually the concept of a flexible circuit was developed about the same time frame as rigid printed circuits (aka hardboards). In 1902, Albert Hanson filed a patent for conductive metal patterns on a flexible substrate. Metal foil was stamped out into patterns and glued onto a substrate. This is the first known time when any form of a printed circuit board was conceptualized. High volume manufacturing of printed circuit boards was developed sooner than flexible circuits, but flexible circuits have been built in large volumes since the late 1960’s. Today flexible circuits are estimated to comprise approximately 10% of the printed circuit market…which means the flex circuit market is several billion dollars. And growing.
Flexible Circuits are Expensive: Need to qualify this one. As a standalone product, a rigid printed circuit board is generally sold at a lower cost per square inch than a flexible circuit, but nobody buys a printed circuit board or a flex as a standalone product. These products are used in electronic packages for electronic interconnects. Flexible circuits offer a designer a lot of versatility when developing 3 dimensional packages. Flexible circuits can eliminate the need for components such as connectors, wire harnesses and additional circuit boards. This saves material and labor. Pretested parts help reduce scrap. One needs to look at the entire cost picture of an electronic package before determining the most cost effective solutions. There are many situations where flex is the lowest cost choice when total cost of ownership is considered.
Flexible Circuits and hardboards have the same design rules: There are a number of reasons that flex should be designed differently than hardboards. Dimensional stability of the base materials is one reason. Additionally, flex circuits are flexed, folded and bent to fit in small housings and 3D packages. This drives alternative design rules to minimize mechanical locational stresses. For more details on this, please see this article: Five common design errors in flexible circuitry.
Flexcircuits are cheaper if purchased overseas: The market for extremely high volume flex circuits used in cameras, cellphones, and personal computers is primarily supplied by Asian manufacturers. The cost discussion for lower volumes should include costs for logistics, internal resource allocation, time spent dealing with quality or design issues, language barriers, time to market, etc. There are a number of US based flexible circuit manufacturers providing customers with high volume circuitry, including All Flex. Please refer to a couple of related blog posts: How much electronic manufacturing will return to the US? And The US advantage over China in Flexible Circuits.
Flex doesn’t have a flame retardant option: There are flame retardant substrates and coverlay that can be used in flexible circuitry to meet UL and CSA flame rating requirements. A flame retardant flexible circuit will pass similar fire retardant tests that printed circuit boards pass. A requirement for a flame retardant product should not be a factor when choosing between flex and hardboard.
Flex is not as durable as hardboards: Being more rigid does not necessarily translate into durability. A flex circuit that is designed properly for the application will last as long as a PC board. But durability is a function of use, and a flex that goes into an application that is repeatedly bending it, experiences a lot more stress than a board that is just laying flat. Flexible circuits have been used in automotive, medical, aerospace and industrial applications for decades with outstanding results. Bottom line is both flex and hardboards have their ideal applications. Misusing either one can result in a shortened life.
SMT is better on hardboard: A number of studies have been done demonstrating surface mount on flex is at least as reliable as surface mount on hardboard and sometimes even more reliable. Flex may have gotten a bad rap because of the design layout. If a bend point of the flex comes right up to a solder joint, then that solder joint could possibly fracture. But if industry standards are followed for design, then there should not be an issue with SMT on flex.
All Flex has a number of resources available to everyone that can also help clear up misunderstandings about flex. We encourage you to subscribe to our blog if you haven’t all ready done so as each week we discuss important topics relating to the flex circuit industry. If you have design questions, you can schedule a free design consultation by filling out this form- request a design consultation.