The following is an article written by Dave Becker, VP of Sales and Marketing, All Flex Flexible Circuits. The article originally was published in PCB007 in October of 2013
Selection of a supplier for a flexible circuit is a multi-dimensional decision. Searching the internet produces a long list of suppliers capable of building a wide range of products. If you can believe what you read on the internet, there are very few suppliers unable to support any technology (single sided to 30+ layer rigid flex) and volume (prototype to serial production). But if you believe everything you read on the internet, call me directly as my uncle in Nigeria has some money he needs help transferring to a bank account in the US.
Since all flexcircuits are custom designed and manufactured, a more thorough review of a supplier’s capabilities and specialties is critical for the specifics of an individual design. Everyone is not good at everything. Significant characteristics that help distinguish from among the myriad of flexcircuit suppliers include the following.
Most suppliers claim a wide range of volume capability but what does “high volume” mean in this manufacturing world? Flexcircuit suppliers build product with either a panel process or a continuous reel process. The reel to reel processing is used extensively to support the incredibly high volume requirements demanded of cell phone, camera, and automotive applications. Most of these suppliers are located in Asia but Multek Flexible Circuits remains a US based high volume supplier capable of competing with the cost pressures necessary to succeed in these markets. Extensive reel to reel processing provides parts with little direct labor cost and the ability to produce in quantities exceeding millions of parts. Other flexcircuit suppliers provide high volume parts by acting as “brokers” i.e. working with an overseas fabricator and acting as the middleman in the supply chain. As independent agents, these companies often take responsibility for product logistics, transit, quality, and provide domestic applications engineering support.
Panel processing is generally a lower volume option however it does mimic the processing used by high volume rigid printed circuit board suppliers. Unit volume capacity is highly dependent on circuit size so capacity expressed in quantity of units can be misleading. A more meaningful measure is number of panels processed per day/week/month. Circuit board panel fabrication generally follows a sequential flow through multiple pieces of process equipment. Complex part numbers may require 40+ process steps as panel processes include chemical cleaning, imaging, developing, copper plating, etching, automated optical inspection, platen pressing, plasma cleaning and surface treatment finish to mention a few. Actual capacity within a given factory is mostly driven by the number of panels possible through a bottleneck piece of equipment so many shops manage their factory flow with a “Theory of Constraints” manufacturing philosophy
Building a flexible circuit is usually not the extent of a customer’s requirement. Both design services and assembly capability can also be requirements and are often provided by a flexcircuit supplier. Under the umbrella of the word “design” is a wide range of services. Many flexcircuit suppliers are able to provide a completed design (CAD files and drawing) if provided a schematic or netlist and the mechanical outline. Reverse engineering a circuit from a sample part or photograph is also possible. One big advantage of having a design created by the fabrication shop is design for manufacturability is an obvious upfront consideration. The opportunity to minimize and eliminate costs can be carefully considered when the design is embryonic. Fabrication yield is always a significant cost driver so many suppliers “flexize” the artwork patterns to incorporate manufacturability and reliability features such as optimized line widths, enlarged copper via pads, filleted intersections between traces and pads, and rounded traces through curved circuit features. At a minimum, getting early input from a fabrication shop is highly recommended.
Many circuit shops have further integrated vertically by providing assembly services. Most flexcircuit applications require some added value ranging from wire assembly, thru hole connector soldering, to multiple components attached with automated SMT equipment. Most flexcircuit suppliers offer some level of value added assembly as their customer base continues to express a desire for a shorter supply chain. As products become higher volume and/or require more sophisticated assembly, taking advantage of contract manufacturers with specialized capabilities become increasingly tempting.
High Density Interconnect (HDI)
With the constant pressure for miniaturization of electronic products, conductor traces and plated thru holes have become extremely small with tight manufacturing tolerances. Conductor widths are often reduced to .003” or less, and .001” microvias formed with lasers are more common. Specialized high resolution imaging equipment and microvia formation capability are needed to produce these features. Equally important is process control over the multiple pieces of equipment (developing, etching, resist stripping, and plating) also used to build fine featured circuits at a high yield. Suppliers that build these products will generally require additional engineering support and more sophisticated equipment. In the US, these companies often support development projects for products that are eventually sourced overseas as volumes ramp. Another example of parts produced with this technology is hearing aid circuits where pricing based on square inches of area is meaningless.
Quick Turn Capability
Standard lead times for flexcircuits vary considerably among fabricators with a typical “standard” delivery offer of a few weeks. This can obviously vary substantially depending on product complexity and may also be paced by the availability of components when assembly is included. Others specialize in producing parts with highly compressed cycle times and are able to deliver products with lead times of a few days. A portion of this market demand is supported by companies specifically focusing on quick turn as a manufacturing niche. It is also true most “standard delivery” suppliers reserve some portion of their capacity for expedited deliveries done for low volumes at a price premium. Willingness to support a quick turn request is often determined by the availability of factory capacity at a given point in time.
Certifications and Systems
Quality system certifications and registrations are requirements for some applications. The most common of these are:
- ITAR. International Traffic in Arms Regulations which is a set of United States government regulations controlling defense-related products. ITAR regulations require information to be controlled with U.S. citizens. Both the customer and the supplier can face fines if they provide non-US citizens with access to information protected under an ITAR contract. Registration by the flexcircuit supplier as an ITAR company is required.
- ISO 9001. The ISO 9000 family of standards is intended to insure a certified quality management system is in place and is designed to help organizations ensure they meet the needs of customers and regulatory requirements related to their product. ISO 9000 deals with the fundamentals of quality management systems and details certification requirements. Third party certification bodies provide independent confirmation companies are meeting ISO 9001 requirements.
- AS 9100. AS9100 is another standardized quality management system, in this case, specifically designed for the requirements of the aerospace industry. Aerospace manufacturers and suppliers worldwide require compliance and/or registration to AS9100 as a condition of doing business.
- Mil-P-50884, MIL-PRF-31032, and IPC 6013. These quality assurance requirement documents are frequently specified by the government for military applications. The two military specifications require building coupons of generic product samples that are submitted to an independent lab for test and product qualification. This certifies a supplier as having the capability to bid on programs requiring these specifications. In addition, end product quality requirements are defined with frequencies specified for some in-process tests. In an attempt to combine military and commercial program requirements, government and industry representatives have written and widely adopted IPC 6013. Many applications are now specifying the IPC document as a quality standard with IPC Class 3 products defining quality requirements intended for high reliability applications.
The products and capabilities offered by flexcircuit suppliers vary considerably. Fortunately for the US electronics industry, there is a good selection of domestic suppliers available…no need to schedule work in an Asian time zone or learn Mandarin. The above criteria should help determine some of the questions to be asked when considering sourcing a new part number. The internet can help as an initial filter, and then spend some time talking to an applications engineer at a couple suppliers. It does take a little due diligence, but matching the proper source with a new application will save headaches in the future.