Flex Talk: Knowledge is Power

“What can I do to help drive cost from my design?” This is a question that I am asked routinely. That question is often followed by, “Can I get these faster?” Both questions are even more predominant when talking about flexible circuits or rigid-flex. Flexible circuits are often thought of as a high-priced solution and one truly wouldn’t design a flexible circuit without needing to utilize that technology for some reason. That reason may be space, weight, packaging, flexing requirements or even aesthetics.

I think that most will agree that a quality product that is available when you need it is the primary concern when launching a new design. But, that said, designing the most cost-effective solution to meet your needs is always going to be critical. Today, I want to share my top three tips for reducing cost and shortening lead-time when working with flex.

Understand Fabricators’ Capabilities

In today’s fast-paced electronics world, designers and engineers rarely have time to visit a board shop for a facility tour to better understand the circuit board manufacturing process.

In a perfect world, everyone would have a chance to understand not only the basic process steps that these custom-built products go through, but also understand the complexities that are involved with specialty products such as sequential lamination, microvias, flex and rigid-flex and even flex and rigid- flex with sequential lamination and microvias.

In today’s market, there are many companies that manufacture flex and rigid-flex. There is also a significant difference in capabilities across the market. Some manufacturers specialize in single-sided and double-sided flex, some in multilayer, some in rigid-flex. Within each of these specialties, there are companies that work with leading edge technology and some that do not. All can produce quality product.

But when looking at ways to ensure you are not adding cost to your design, regularly working with your fabricator and understanding their capabilities and sweet spot in the market and then matching those capabilities with the requirements of the design can have a significant impact.

Here are a couple of examples. First, you are working with two different designs. One is a single-sided flex with 0.010” line/space. The second is a complex, 16-layer rigid-flex with stacked microvias. Your approved supplier list consists of three fabricators who offer flex: Company A manufactures primarily single- and double-sided designs, Company B manufactures both flex and rigid-flex, but typically works with designs that are 10 layers or less and Company C specializes in complex rigid-flex. It can get a little tricky. It is very likely that the company that will have the best lead-time and pricing for a complex rigid-flex will not have the best pricing for the simple flex. If cost isn’t a factor, it can be easier to order both from the same fabricator, but if cost is a factor, then finding the best fit for each technology level is going to be most cost-effective.

The second example has to do with understanding the capabilities matrix for each supplier. It is important to understand for each supplier that you work with, what is considered standard, advanced and emerging technology. Using drilled hole size as an example, certain manufacturers consider a 0.10” drill to be standard and increased costs are incurred at 0.008”.

With others there is no increase in cost until you reach .006” drill. This in no way reflects on the quality of the product at each manufacturer, but more reflects their comfort level and their specific cost drivers at a certain level of technology. Once you understand where those thresholds are, you can thoughtfully weigh the cost vs. benefit of moving beyond the standard technology.

Select common materials that are in stock

There are many different types of material available for flexible circuits, and that number grows exponentially when you consider rigid-flex construction. To simplify, using the standard copper/polyimide laminates as an example, the laminate is available in two types: adhesive-based and adhesive-less material. For both types, there are a vast number of combinations of materials. Copper is typically available in ¼ oz. to 2 oz. copper and polyimide thicknesses typically range from 0.5 mil to 6 mil. Sounds great, right? Absolutely! But while these options are available, it does not mean that they are all commonly stocked at a fabricator or that they are low cost. The best advice I can give when designing for cost and reduced lead-time is to work closely with your fabricator to develop a stack-up.

KnowledgeFig1.jpg 

Figure 1: Example of a rigid-flex stack-up. Image source: I-007eBooks, The Printed Circuit Designer’s Guide to...Flex and Rigid-Flex Fundamentals.

In general terms, laminates with ½- or 1-ounce copper and 1- or 2-mil polyimide will be less expensive than other combinations. However, cost and lead-time will boil down to the materials that your selected fabricator works with most regularly. Please don’t spec an adhesive-based laminate just because it should be less expensive. If your fabricator manufactures with more adhesiveless materials (highly recommended for rigid-flex), they may be purchasing laminate in enough volume that pricing is reduced and that savings will be passed along to you. The same thing is true for lead-time; designing with materials that are in stock will eliminate the delays from material lead-time when the prototype is placed and lead-time is critical.

My recommendation is to work with your fabricator for a stack-up and be clear about your requirements. Let them know if materials are not critical and ask that they use commonly stocked materials. That eliminates all assumptions and will result in the lowest cost, best lead-time scenario.

Communicate clearly in the fab notes

Typically, 75% of flex and rigid-flex designs go on hold while being tooled at the fabricator. A significant portion of those questions that need to be asked stem from unclear fab notes. An unclear stack-up is a very common issue with rigid-flex. Make sure that you are clearly calling out which layers are flex and which are rigid. If you have asked for the stack-up prior to releasing the design, this is simple to include.

Flex and rigid-flex designs can make people unsure and the basics are sometimes overlooked.

Another requirement that can be easily overlooked on the fab notes is the UL requirement. There are many examples where after failing a burn test and investigating the cause, it is found that the UL requirements are clear in the assembly drawings, but not in the fab notes. Your fabricator will not necessarily default to UL materials in the absence of the spec and the contract manufacturer will routinely separate the fab notes from the assembly drawings when asking for a flex quotation. Always clearly state any quality requirements in both the assembly drawings and the fab notes.

What do these have in common? I believe the best way to reduce cost and lead-time is to work with your fabricator throughout the design process and communicate requirements clearly. They say experience is the best teacher and they work with new designs every day. Take advantage of that knowledge!

Tara Dunn is the president of Omni PCB, a manufacturer’s rep firm specializing in the printed circuit board industry. To read past columns or to contact her, click here.

This column originally appeared in the August 2017 issue of The PCB Magazine, click here.

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2017

Flex Talk: Knowledge is Power

08-31-2017

“What can I do to help drive cost from my design?” This is a question that I am asked routinely. That question is often followed by, “Can I get these faster?” Both questions are even more predominant when talking about flexible circuits or rigid-flex.

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Flex Talk: Mina—Trouble-Free Soldering to Aluminum

06-22-2017

Thinking about the RFID market and the significant growth projected in this market, I decided to do a little research on RFID tag manufacturing. During this research, I learned of a relatively new offering, Mina, an advanced surface treatment technology that addresses the common constraints of large scale manufacturing of aluminum on polyester (Al-PET) circuits.

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Flex Talk: Squink—Integrating Fabrication and Assembly in one Package

05-01-2017

When walking through trade show expos, I tend to be drawn into product demonstrations on the show floor. Recently, at the IPC APEX EXPO, I stopped in front of a piece of desktop printing equipment that was demonstrating with a flexible circuit.

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Flex Talk: Flex Material Handling—An Inside Peek

04-03-2017

As increasingly more designs move to flexible materials to take advantage of space, weight or packaging benefits, it has been clear that flexible circuits require a different set of rules than their rigid counterparts. We spend substantial time working through the design to ensure that he flex is as robust as possible.

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Flex Talk: Final Surface Finish—How Do You Choose?

01-26-2017

There are so many final surface finish options to choose from today. How do you decide which is best? HASL—both tin-lead and lead-free—immersion tin, immersion silver, ENIG, OSP, and ENIPIG are the primary finishes used in PCB fabrication.

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2016

Flex Talk: A Glimpse into PCB Sales

12-28-2016

Summarizing the feedback from both customers and manufacturers, the most successful PCB salespeople are organized, take a genuine interest in their customers’ needs and business challenges, have a better than average understanding of the PCB industry, fully understand the manufacturer’s strengths and capabilities and advocate for both to find the best solution.

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Flex Talk: Troubleshooting Flex Circuit Applications for Mil/Aero Projects

10-06-2016

I imagine that everyone has been in this position at one time or another: Despite everyone’s best attempt at creating the perfect design, PCB fabrication and assembly, something goes wrong and the troubleshooting begins.

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Flex Talk: Inaugural West Coast Geek-A-Palooza a Fun-filled Success

05-24-2016

Geek-A-Palooza kicked off the 2016 schedule May 12 in Irvine, California. Historically, Geek-A-Palooza has been held in Minneapolis but is expanding this year to include Orange County and Boston as well.

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Flex Talk: PCB Sourcing? One Size Does Not Fit All

04-18-2016

When analyzing a set of PCBs to improve yields and maximize profits, the first place to start is with a critical review of each PCB design. Are there any attributes that are pushing your manufacturer’s standard design rules? If so, is this necessary to the design or is there another approach that could improve the manufacturer’s yields, reduce cost, and ultimately increase profit?

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2015

Flex Talk: Thoughts on the IPC Flexible Circuits–HDI Forum

11-19-2015

As an attendee at the IPC Flexible Circuits–HDI Conference held October 28–30, I found myself in a room of people, all eager for technical information, with the opportunity to reconnect with industry friends and to make new connections. The audience was diverse with young people, new to our industry, sitting alongside industry veterans willingly sharing their knowledge and passion for HDI design and flexible circuit technology.

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Designing Flex Circuits for Domestic Prototyping

08-20-2015

Designing a flex circuit to be prototyped domestically? No problem. Designing a rigid-flex circuit for production offshore? Got it. Designing a part that will be prototyped domestically with a seamless transition to offshore production? That can be a little more challenging.

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Rigid Flex: Total Cost Comparison

07-09-2015

The transition to a rigid-flex design from the traditional approach of using cable assemblies to join two or more PCBs has obvious benefits—space, weight, packaging, reliability and increased currently carrying capabilities. Yet many times the perception that rigid-flex is a high-cost solution causes designers and engineers to hesitate.

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Primary Cost Drivers for Flex Circuit Designs

06-25-2015

Someone once told me that the potential applications for flexible circuits are really only limited by our imaginations. After pondering that a bit, I had to agree. In fact, one of the things I like best about what I do is that moment during a discussion when I can see the light bulb go off in a designer's head.

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The Flex-to-Fit Approach

06-04-2015

The flex-to-fit concept reminds us that creativity and engineering go hand-in-hand. When there is not ample space for a conventional approach, this process, which is the convergence of the mechanical world and the electronics world, results in the ability to design a flexible circuit along the contour of an existing, irregularly shaped structure.

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