FlexFactor: Advanced Manufacturing and Entreprenuership

Take just a minute and read through this list of new product ideas.  Can you identify the common thread?  Yes, they are all enabled by advanced technology, but would you believe that these are all products that have been pitched in the last year by high school students?

 Drive Alert:

Problem – Drowsy driving.

Solution – A patch placed on the temple can detect if the user is drowsy and wakes the user up.

Technology – Circuits form a flexible patch with sensors detecting theta brain waves indicating if the user is drowsy or daydreaming.

Fast Asleep:

Problem – In 2015, there were nearly 4,000 Sudden Unexpected Infant Deaths (SUIDS) in the U.S. with 1,600 of those being attributed to Sudden Infant Death Syndrome (SIDS).  Because of this, 59% of working parents do not get enough sleep.

Solution – A small wristband fits snugly around baby’s arm while sleeping and measures movements, oxygen and heart rate to let you know the baby is safe and sound asleep.

Technology – Mounted flexible hybrid electronic wristband connected to device via Bluetooth.

RA Solutions:

Problem – RA is a chronic, inflammatory disease that causes mild to severe joint pain and stiffness, which can lead to a wide variety of damaged body systems including skin, eyes and lungs.

Solution – The Relieve Sleeve, a pain reliever that administers heating sensations and applies electric pulses tailored to a user’s needs.  The functions are embedded in a compression sleeve for easy application around joints and muscles.

Technology – Flexible battery, micro coiling embedded in the compression fabric, Bluetooth chip to connect to app, electrical pulses produced form thin wires, wireless charging hub for battery.

Asthmex

Problem – According to CDC, 25.7 million Americans suffer from asthma.  Between the years 1996–2012, 8% of Olympic athletes suffered from asthma.  11.8% of the 7.8 million high school athletes in the U.S. have asthma.

Solution – A chest band with a smart patch to detect asthma symptoms and triggers and administer medication via auto-injector.

Technology – Smart fibers within the band detect symptoms of an attack specific to the individual.

Just to reiterate, these creative new product ideas have all been pitched by high school students!  These students have all participated in the NextFlex, FlexFactor program. Growing the next generation advanced manufacturing workforce is a key component of the NextFlex mission of developing technologies for commercial adoption while supporting a sustainable manufacturing ecosystem.

What is FlexFactor?

This program is designed to enable youth to engage with next generation technology through entrepreneurial immersion. Over the course of this program, students work in teams to conceptualize a Flexible Hybrid Electronics, or FHE-based hardware device that solves a human health issue or performance monitoring program, develop a business model around the opportunity, and pitch “shark tank” style to a panel of industry representatives. In the process, students become immersed in advanced technology and entrepreneurship, are inspired by the advanced manufacturing industry segment, and gain a deeper understanding of the education and career pathways for the future.

This four-week program kicks off in the classroom where students break into teams, are given the mission, the building blocks of flexible hybrid technology, and have the opportunity to define the problem and research hypothesis. Throughout the program, students interact with assigned technical mentors as they develop their product idea. The next week students take a field trip to tour an advanced manufacturing facility which provides a deep dive into the world of hybrid and flexible technology and gives the students the opportunity to interact with manufacturers, technicians and engineers to get a sense of what is like to work in these environments. The third week is a field trip to a local community college where students sit in on two 90-minute entrepreneurship lectures and get to experience the feel of college life. The final week each team pitches their product idea, including target market analysis and cost vs. revenue projections, to industry experts. Through this program, each student is enrolled in the community college and receives college credit upon completion.

How much fun would that be! With enrollment skyrocketing, the program is obviously engaging students and sparking interest. Brynt Parmeter, director of Workforce Development at NextFlex, explained that the first session started in the fall of 2016 with eight students participating. Following its fourth session the spring of 2018, the program will have had over 2,000 participants. That is amazing growth and speaks volumes about the program.

I had the opportunity to speak to Jordan Tachibana, whose was part of the group responsible for the Asthmex product listed above.  Jordan had been taking business classes with a marketing major focus and was introduced to this program through a teacher describing the program as an entrepreunuership program with an emphasis on advanced manufacturing.  “Touring the advanced manufacturing facility is actually what inspired us the most because we got to see all the cool applications and kinds of technology.  That is really what sling-shoted my idea with my group.  After seeing the technology, we saw what was possible and said, let’s go.”  Jordan is continuing to pursue the Asthmex product and has enrolled in the program for a second time.

Through FlexFactor’s collaborative approach to education, entrepreneurship and technology, NextFlex is helping students identify and engage in career pathways in advanced manufacturing, while actively increasing the interest and talent in the U.S.-based STEAM pipeline. The FlexFactor program creates a win for all stakeholders. High schools are able to expose youth to real-world problems, blend STEAM and entrepreneurship in a project learning environment, and students further develop personal and professional skills. Community colleges are able to expand enrollment, create additional educational and career pathway opportunities, and link community college STEAM focus to a Manufacturing USA Institute. Government facilitates the creation of a nationally competitive talent pool prepared to tackle society-wide technology challenges, increase student awareness in STEAM occupations, motivate students to purse STEAM education, and provide students a government-sponsored activity that develops disciplinary based knowledge and promotes critical thinking, reasoning and communication skills. Our industry benefits by the expanded awareness and interest in advanced manufacturing, reduced hiring expenses via a direct channel to qualified resources for both internship and long-term workforce requirements, and increased community exposure through relationships with local high schools and community colleges.

A talent pipeline shortage is looming across all flexible hybrid electronics (FHE) manufacturing occupations. This was validated in a 2016 study for NextFlex[1] by the Workforce Intelligence Network.  This study reported tha 25% of the workforce in FHE is over 55 years old, while only 6% is under the age of 24, indicating a talent shortage that the industry will face as experienced workers retire. There is also enthusiasm in the industry to connect with students that are unsure of career opportunities in advanced manufacturing sectors and are unaware of new technologies now in development that will impact lives in meaningful ways. The FlexFactor program is working to bridge the gap, connect students and organizations, and bring excitement about advanced manufacturing to young people.

What’s not to be excited about: mouth guards that could detect an athlete’s hydration level; non-obstructive patches that could detect blood glucose levels for Type 1 diabetics; an allergen medication patch that would administer the exact amount of epinephrine needed based on inflammation detected in the blood; and a device that can detect the levels of leptin hormone to evaluate sleep quality. Yes, these and many more cool applications are coming from the FlexFactor list of products that have been pitched. If these ideas are generated from a four-week program, I am excited to see what these students will develop in the future, and have renewed faith in the future of our industry and the role that advanced manufacturing and flexible hybrid electronics will play.

Reference

  1. Report available from nextflex.us.

 

www.omnipcb.com

 

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PCB and EMS Process Engineering: The Man Behind the Curtain

“Pay no attention to the man behind the curtain.”  This famous quote from The Wizard of Oz, conjurs up the image of Dorothy, the Tin Man, the Cowardly Lion and the Scarecrow discovering that the great Wizard of Oz isn’t as grand or as magical as he seems.  He is in fact just a guy operating a bunch of controls behind the green curtain.  Today, references to “man behind the curtain” imply someone making decisions and making things happen behind the scenes.  Process engineering at EMS companies and PCB fabricators could be considered “the man behind the curtain”.

I was speaking with Holly Olsen from Electronics System Inc, discussing the fact that customer’s visiting and touring their PCB fabricator or EMS supplier to learn the processes and challenges encountered when building this custom engineered product is something that does not happen nearly as often as it used to.  Without these visits, knowledge of some of the behind the scenes decisions that are made day in and day out to help ensure the best yields are easy to overlook.  Holley and I thought it would be interesting to touch on a few of the key processes and decisions that are made behind the scenes and are often invisible to the customer.

Panelization:

The deliverable is an assembled printed circuit board.  But, throughout processing at both the EMS provider and the PCB fabricator, product is manufactured in larger panels and then broken down to the final product.

Most EMS providers prefer to specify their own panelization.  This allows them to determine fiducial size and location, tooling holes and break off points that best suit their unique process and equipment needs.   The size of the board, components that overhang the edge of the board, and board shape and thickness all play a part in the design of the ideal panel for processing.

Similarly, the deliverable to the EMS company is an array of parts for their further processing.  During the PCB fab process, the size of the manufacturing panel and the placement of parts, or arrays within the manufacturing panel is one factor that is adjusted depending on technology of the design.  A typical fabrication panel will be 18” x 24” or 21” x 24”.  As technology requirements increase, the panel size used will decrease.  Panel size is typically reduced to 12” x 18” when tight features are required or when the process requires tighter registration than standard processing is expected to meet.  With the smaller panel size, there is less impact from standard material movement.  When processing on a 12” x 18” panel does not yield the anticipated results due to material movement, process engineering may suggest using the center or “sweet spot” on the panel to minimize that impact even further.

Processing Thin Materials:

Again, this is an area that both fabrication and EMS work their magic behind the curtain.  From the EMS perspective, PCB’s that are less than .031” or flex materials require additional support for processing.  Thin materials will flex and move during SMT.  A common method to stabilize the array is to create a SMT pallet.  Pallets will cycle through and be reused in the process.  The number of pallets needed is determined by the manufacturing lot size and SMT cycle time to ensure proper manufacturing flow is maintained.

SMT pallets must be made to withstand high temperatures and cannot conduct heat allowing them to go through the reflow process.  CDM Durapol ESD is a commonly used composite material that can withstand the high temperatures and includes static dissipative characteristics.  Tension pins are designed into the pallet to align with the tooling holes on the PCB panel securing the board in place through processing.

Similarly, fabricators take special precautions with thin materials.  Often special carrier panels are used to transport the product from location to location and operators are trained to handle materials picking up from opposing corners to eliminate flex in the material.  Any dents or ding in the copper will have a high probability of creating scrap as the circuit patter is created.  Because automated equipment is not specifically designed for thin materials, leader panels are often taped to the manufacturing panel to provide additional support moving through automated equipment.

Stencil Design:

“The screen printing process is one of the most critical steps in the SMT process”, says Kevin Buffington, Manufacturing Engineer for Electronic Systems, Inc., “The combination of a good stencil and solder paste inspection is vital to the outcome of placement and reflow.”  The screen printing process begins with a well-designed SMT stencil.  Proper volume and placement of solder paste is crucial to the reduction or elimination of solder defects such as insufficient solder, shorts, and solder balls.  This is achieved by choosing the right foil thickness and aperture size for the mix of components on the printed circuit board.  Stencil design parameters are developed based on aspect ratio and area ratios of components.  These ratios are a calculation of the size of the stencil opening and the stencil thickness that allows the solder paste to release.  While not preferred, in limited cases where some very large components are included on a design with very small, fine-pitch components, step stencils may also be used to ensure that enough solder paste is deposited for the larger components.  Step stencils, as the name suggests, step up the stencil thickness in a specific area to place a greater amount of solder paste.

Framed stencils can either be fixed frame or universal frame.  Stencils will typically range from 15” x 15” to 23” x 23” and use either a solid or hollow aluminum frame.  As the name suggests the fixed stencil is permanently fixed to the frame.  The universal frame, the stencil is held within the frame which makes it possible to make changes as they are needed.

 While IPC specifies best practices for component spacing in design, today’s designers are expected to do more with less space and more often need to push the envelope of standard processing.  Fabricators and EMS providers are continually refining their processes to meet tighter pitch components and tighter pitch trace and space.   Involving your PCB fabricator and EMS provider early in the design helps to ensure that manufacturability is designed into the product.  Even better, plan a facility tour and gain a little insight into what goes on behind the curtain when manufacturing PCB’s and PCBA’s!

Click HERE to read the article in The PCB Magazine

Click HERE to visit our website

 

Knowledge is Power: Reduce Cost and Shorten Lead Time

“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 of these 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 truly, one wouldn’t design a flexible circuit without needing to utilize that technology for some reason.  That 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 3 tips for reducing cost and shortening lead-time when working with flex.

Understand your 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 are capable of producing 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 .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 .10” drill to be standard and increased costs are incurred at .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 and 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 adhesiveless 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 .5 mil to 6 mil.  Sounds great, right?  Absolutely!  But while all of 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.

In general terms, laminates with ½ or 1 ounce copper and 1 or 2 mil polyimide will be less expensive than other combinations.  BUT, 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.  Please 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 over-looked.

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 all of these have in common?  I believe the best way to reduce cost and lead-time is 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!

Updated Flex Design Guideline: Best Practices and Cost Trade-Off’s

We are very excited to announce that we have updated our flex circuit design guidelines.

This updated version focuses specifically on best practices and cost trade-off considerations to be aware of.
If you would like a copy, simply email me at: tarad@omnipcb.com  and I will be happy to forward it to you.

 

Enjoy!

Mina: Trouble Free Soldering to Aluminum

I always love to hear about interesting new IoT applications. The other day, a friend was explaining a new product he had recently developed, a home-built RFID-based tracking algorithm used to help improve and change how conferences and events are done around the world. Essentially, this tracking system—enabled by RFID tags and card readers—allows event organizers to analyze attendees’ preferences and interests and create personalized recommendations on topics, somewhat like a Netflix recommendation engine. 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 Al-PET circuits.

Aluminum on polyester (Al-PET) circuits are becoming more popular and have found wide use in RFID tag and single-layer circuits to reduce cost. However, both aluminum and PET have their own constraints and require special processing to make finished circuits. Aluminum is not easy to solder to at lower temperatures and PET cannot withstand high temperatures. Conventional low-temperature solder cannot be used to attach components to these circuits without additional processing or using conductive epoxies. These add costs, which limit the use of Al-PET circuits. Initially developed to help a customer with a manufacturing cost issue, Averatek has recently developed Mina, which can be applied to the antenna as it is being manufactured on high-speed roll-to-roll lines. The antenna can then be sent to customers who assemble the die and then on to the tag makers. This relatively new surface treatment paves the way for large scale, low cost manufacturing of Al-PET circuits.

Conventional Methods to Assemble RFIDs

Assembly of RFID tags involves mounting of chips onto the pads of the circuit. Although the use of solder is preferred, soldering to aluminum is difficult because of the presence of a thin layer of aluminum oxide. This layer forms when the bare metal is exposed to air. Since the manufacturing of Al-PET substrates is done in atmospheric conditions, all aluminum surfaces are covered with aluminum oxide. While the formation of oxide is self-limiting, its presence prevents the bonding of solder to the base aluminum.

Special processing can be done on pads to remove and prevent the formation of aluminum oxide. These include ENIG, nickel-palladium or nickel-silver plating. These need a series of process steps and extensive wet chemistry, which add costs that make it prohibitive for mass production.

Anisotropic conductive paste (ACP) is a common solution to this problem and is widely used for attaching components to aluminum based RFIDs. It is applied on the face of the chip, which is then attached to the antenna using heat and pressure. However, ACP has its own challenges. It is made of adhesive epoxy filled with conductive metal particles, usually silver. These are typically syringe applied, require longer cure times, have pot-life issues and are electrically inferior to conventional solders. In addition, they must be stored at low temperatures in special freezers to control the polymerization of the epoxy.

Assembly of RFIDs with Mina

Evaluations began last November for Mina. This surface treatment can be printed directly on the aluminum pads where components need to be assembled. Any of the conventional printing techniques can be used including screen, stencil, etc. The aluminum surface does not need any surface cleaning or preparation. Once printed, it is then thermally cured and leaves the pad surface active and ready to accept solder. Cured Mina is non-conductive and makes room for easy printing registration. To attach a component, it simply would need solder on it via plated bumps or printing, placed on a Mina activated pad, and then passed through a re-flow oven. Mina removes the aluminum oxide layer and allows the formation of a true metal-to-metal bond between the solder and the aluminum on the pads.  Both the electrical properties and the bond strength are better than ACP. In addition, Mina can be stored at room temperature and reused multiple times.

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Figure 1: Production and assembly process using Mina.

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Figure 2: Graphic of Mina application.

Benefits of Mina

  • Screen-printed on pads leaving an active, but non-conductive surface
  • Cost-effective as it allows the use of conventional solder and only on pads
  • Mina can be applied to the pads and cured in a conventional, low-temperature oven
  • Solder can be plated or printed on the chip using conventional methods and then reflowed onto the active pads
  • Enables solder to bond directly to aluminum metal, ensuring good electrical properties
  • Has no pot-life issues; Mina can be printed, stored and re-used at room temperature

Given the significant growth projected for the RFID tag market in the next several years, it will be interesting to see how this relatively new advanced surface treatment is adopted into mass production and to see what other markets benefit from enabling the ease of soldering to aluminum.

For more information, please contact us:  www.omnipcb.com  Tara Dunn, 507-332-9932

Flex Material Handling: An inside peek

As more and 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 quite a bit of time working through the design to make sure that the flex is as robust as possible. We also spend quite a bit of time on material selection, again to ensure that the flexible circuit withstands the flexing that will be required and performs properly in the end environment.

One thing we do not often talk about is what happens behind the scenes during the fabrication and assembly of the flexible circuit. What types of special handling considerations are in place throughout the manufacturing process to accommodate these thin materials? When you are auditing a potential new supplier, what things should you be asking about and looking for in their procedures?

Undoubtedly, the largest source of defects in flexible circuit manufacturing can be traced back to material handling. Drawing from my own knowledge and soliciting the expertise of several industry veterans  involved in flex circuit manufacturing—David Moody with Lenthor Engineering, Anaya Vardya with American Standard Circuits, Jim Barry with Eltek and Mike Vinson with Averatek—I have put together an insider’s view of the nuances involved in manufacturing flexible circuits.

Fabrication

Everyone agreed that it is the handling of the thin flexible materials that is the key to the successful manufacturing of flex and rigid-flex designs. A wrinkle, ding or dent in the copper material can easily, and will most likely, cause a defect. In fact, wrinkles are typically the leading cause of defects for trace and spaces errors in process imaging. So, what do fabricators do to mitigate this damage?

Skilled technicians are at the very top of the list. Thin, flexible materials require a unique set of processing parameters and significant time and effort is put into training operators on material handling. The movement of product between process steps is as critical as the precautions that need to be taken during each process.

When moving flexible materials between process steps, transport frames, slip sheets, and trays are required to provide the extra support needed to keep these panels absolutely flat—remember a ding or fold in the material will create a defect. When picking the material up for processing, consideration needs to be given to grasping the opposing corners to keep the panel flat.

Special consideration and handling is also needed when processing. Most equipment is not specifically set up to handle thin core, flexible materials. For example, moving product through the etching process or other conveyorized equipment requires “leader boards” or some type of frame to be taped to both ends of the sheet of flex material to provide stability and prevent the sheet from being caught up in the equipment rollers. If not done carefully, the process of applying the frame or leader and the subsequent process of removing the support structure is also an operation prone to damaging the thin materials.

Prior to wet processing, the panels are in full copper sheets. Once the excess copper has been removed to form the space and trace pattern, the panels are even more susceptible to handling damage. Care is given when creating the panel artwork to leave as much excess copper as possible on the panel. This could be the outer edges of the panel, the outer edges of each array, and between individual parts. It is not uncommon that the need for extra copper to add stability takes priority over the desire to maximize panel utilization.

Dimensionally, flex is far less stable than glass-reinforced rigid boards. The added copper in the panels also helps mitigate the material movement. This material movement creates unique challenges for registration both with coverlay application and in layer-to-layer registration for both multilayer flex and rigid-flex. Each manufacturer has a preferred method for registration and how they set up their tooling pin systems to best fit their processes.

Lamination is another area with unique requirements and special equipment for flex processing, including both lamination plates and specific lamination driver materials. Specialized materials are needed to fill air gaps and provide support through lamination. In the case of very thin core (.0005” polyimide) a base support layer may be needed.

More and more fine line flex circuits, particularly medical and sensor applications, are using extremely thin polyimide substrates with densities requiring additive processing rather than subtractive etch processing. These products are primarily double-sided with one side much more densely plated than the other, using both gold and copper to form traces on 0.0005” polyimide or thinner. Because of this, any plating stress will cause the parts to curl. For routing operations, UV-sensitive tape can be added to the panel to improve stability and support and improve handling.  This technology is similar to what is used in wafer processing. The parts will remain flat until the UV tape is removed. When removing the UV tape, the simple effort of being aware of the direction the material stress will cause curling, and then removing the tape by pulling against that direction, will help minimize the effect.

Assembly

Whether the flexible circuit has just a couple of components and is hand assembled, or the circuits are going to be run through a surface mount process, the number one thing that needs to be taken into consideration is the need to bake the material before subjecting the flexcircuits to high temperatures. Hand assembly is especially prone to defects with flexible materials. This process requires special consideration as to temperature and time and is yet another area that operator training is critical.

Flex circuits (and thin core boards in general) require some support mechanism to run through either wave solder or a reflow process. There are several options to accomplish this. A design with many FR stiffeners may move forward by using an FR4 carrier panel designed to provide stability to the array until assembly is complete and then have the excess FR4 removed, leaving the intended stiffeners. While that is one approach, it is more common to build the flex circuit as a single, individual piece and have a carrier fixture made to transport the circuit through the assembly line. This allows the fabricator to maximize the panel real estate and provide a lower cost unit price for the flex circuit. Carrier tooling is relatively inexpensive and is generally more than off-set by the lower cost flex circuit.

Flexible circuits are certainly a growing segment of the market and require not only special design and material consideration, but special handling throughout the manufacturing process. With material handling cited as the largest cause of yield loss during manufacturing, this is an area with (and for) continuous improvement. We all agree that employee training and on-going education is the key to success. Many facilities specialize in just flex and rigid-flex processing and others have teams dedicated to this product subset, but the common theme is knowledge and specialization. Flexible circuits often have a slightly longer manufacturing lead-time than their rigid counterparts and this is often related to the special handling and processing required for flex. Whether that is extra time in tooling and process planning, extra time during wet process, extra care needed to properly register the layers prone to material movement, or extra care needed during assembly, all special handling is done to maximize yield and provide a robust product to the end user.

Click here to read this blog in The PCB Magazine.

For additional information, contact Tara Dunn.  www.omnipcb.com

Final Surface Finish: How do you choose?

There are so many final surface finish options to choose from today, how do you decide which is best?  HASL – lead and lead –free, Immersion Tin, Immersion Silver, ENIG, OSP, and ENIPIG are the primary finishes used in PCB fabrication.  Fabricators and assemblers generally work with the majority of these surface finishes to be able to support their customer’s requirements.  So, the question is, with all of these available, how does an OEM select their preferred surface finish?

In the past, the primary function of the surface finish was to protect the copper from oxidation prior to the soldering of components.   Today’s expectations include:  superior solderability, contact performance, wire bondability, corrosion and thermal resistance, and extended end use life.  Designs have changed.  Lines and spaces are reduced, solder types and flux chemistries are different due to no lead requirements, the number of assembly cycles has increased and the product may need to carry high frequency signals.

Things to think about when selecting a final surface finish:

  • Does the application require lead or lead-free assembly?
  • Will the end environment have extreme temperatures or humidity concerns?
  • What shelf life is needed? Will it be months or years?
  • Volume and throughput
  • Does the design have fine pitch components?
  • How many assembly cycles will be required?
  • Is this a RF or high frequency application?
  • Will probeability be required for testing?
  • Is thermal resistance required?

Once the project requirements have been identified, the surface finish options can be reviewed to find the best fit.

Click here for detailed information for each surface finish.

Tara Dunn, Omni PCB