The Myth About Rigid-Flex Costs

As seen in the October issue of Flex007 Magazine. With Anaya Vardya of American Standard Circuits.

Do you cringe when you think of the option of rigid-flex? It is not an uncommon reaction
when talking with designers and engineering managers about using rigid-flex to solve a
packaging problem. Why? The most frequent answer is, “They are so expensive.” While it
is true that a rigid-flex PCB is typically more expensive on the surface when compared to
rigid-board solutions with cables and connectors, a lot is being missed with that mindset.

Benefits
First, let’s discuss the many technical benefits associated with rigid-flex solutions. Rigidflex PCBs can:
1. Serve as a remedy to natural product packaging problems
Flexible circuits are often chosen because they help solve problems related to adding
electronics inside the product they serve. They are a true three-dimensional solution that
allows electronic components and functional and operation elements (i.e., switches, displays, connectors, etc.) to be placed in optimal locations within the product, assuring ease of use by the consumer. They can be folded and formed around edges to fit the space allowed without breaking the assembly into discrete pieces.
2. Reduce both weight and volume requirements
Flexible circuits are appreciably lighter than their rigid circuit counterparts. Depending on the components used and the exact structure of the assembly and final products, they can save as much as 60% of the weight and space for the end-product compared to a rigid-circuit solution. Additionally, their lower profile can help a designer create a lower profile product than is possible with a nominal 1.5-mm rigid board.
3. Reduce assembly costs
Before the broad use of flexible circuits, assemblies were commonly a collection of different circuits and connections. This situation resulted in the purchasing, kitting, and assembly of many different parts. By using a flexcircuit design, the amount of part numbers required for making circuit-related interconnections is reduced to one.
4. Eliminate the potential for human error
Because flexible circuits are designed as an integrated circuit assembly with all interconnections controlled by the design artwork, the potential for human error in making interconnections is eliminated. This is especially true in the cases where discrete wires are used for interconnection.
5. Facilitate dynamic flexing
Nearly all flexible circuits are designed to be flexed or folded. In some unusual cases, even thin rigid circuits have been able to serve to a limited degree. However, in the case where dynamic flexing of a circuit is required to meet the objectives of the design, flexible circuits have proven best. Modern disc drives, for example, need the flexible circuit endure anywhere millions of flexural cycles over the life of the product. Other products, such as laptop hinge circuits, may only require thousands of cycles, but it is the dynamic actuation capability enabled by the flex circuit that is key to its operation.
6. Improve thermal management due to being well-suited for high-temperature applications
High temperatures are experienced both in assembly with lead-free solder and in the
operation of higher power and frequency digital circuits. Polyimide materials are well-suited to the management of high-heat applications. Not only can they handle the heat, but their thinness also allows them to dissipate heat better than other thicker and less thermally conductive dielectrics.

7. Improve product aesthetics
While aesthetics may seem like a low-order advantage, people are commonly influenced by visual impressions and frequently make judgments based on those impressions. Flexible circuit materials and structures look impressive both to the seasoned engineer and the layperson. It can make a difference in the decisions made in some applications, especially those where the user gets exposure to the functional elements of the product.
The increasingly sophisticated electronics being developed are pushing more designs to
rigid-flex. Thinking through the benefits listed above, you become convinced that rigid-flex is the right direction for your next project. The next step is convincing your boss or program manager that this concept is the best solution. You are now battling that same perception; rigid-flex is more expensive. However, you cannot compare only the cost of the rigid board and cables to the rigid-flex. You need to look more holistically at the total cost of the design.

Costs
Here are the key factors to consider when comparing the cost of rigid-flex to a PCB and
cable solution:

1. Design
Because you are merging multiple boards, only one design is needed with a rigid-flex.
With the rigid PCB and cable solution, multiple PCB and cable assembly designs are often
required. The cost of generating each design should be included when doing a comparison of both options.

2. Cable and connectors
It is common for someone to compare the cost of the rigid boards with the cost of the
rigid-flex and jump to the conclusion that the rigid-flex is too expensive. However, the cost of the cable and connectors should also be considered in this decision. This includes the cost of kitting for assembly, labor, in-process inspection, cable assembly test, final test, PCB tooling and test charges, and the cost of engineering time required for each of the items.

3. Assembly operation
Similar to the concept of the cost of the design, a rigid-flex solution requires only one
assembly. The PCB and cable solution can require two, three, or even more individual
boards to be assembled. The total cost of assembly should be included in this review.
This includes a similar list to the one in point two, along with multiple set-ups of the assembly equipment, and engineering time required for each assembly operation.

4. Testing
Not only does rigid-flex require one test operation compared to possibly several for
individual boards connected by cable, but it also provides the ability to test the full assembly before installation.

5. Order processing
The cost associated with processing orders is often overlooked. Rigidflex is one unit. Multiple boards, cables, and connectors can require several purchase orders to
be placed, monitored, received, inspected, handled, stored, and payment
processed. These costs should also be captured in a comparison of both options.

Reliability
Without question, the rigid-flex option is considered a high-reliability alternative to the PCB and cable solution. For many years, rigid-flex was predominately a mil/aero solution, but over time has become common in nearly all markets. The connector is an
integral part of the board; there are no solder connections between boards.
With rigid-flex, the reliability is dependent on design, not on the assembly process.
It is easy to arrive at the conclusion that moving to a rigid-flex design does simplify things for designing, purchasing, assembling, inspecting, or even accounting. However, the question is, “Does this simplification justify the cost?”
Each application should be reviewed individually.

Fabricators
Moving ahead with your rigid-flex design, how can your fabricator help?

1. Stiffeners versus rigid-flex
Flex with stiffeners to support component areas is a less expensive alternative to rigidflex and worth the discussion. The primary difference in a simple design is the rigid-flex will have a plated through-hole connecting all the layers, while the FR-4 stiffener is used only for component support. The density of component areas is often the driving factor toward rigidflex.

2. Stackup
Your fabricator can help ensure that you are meeting thickness and impedance requirements for the design. They will also provide guidance on materials that are in stock and materials that may need to be special ordered so that material lead-time can be factored into the project plan. Further, your fabricator can also discuss tradeoffs of various materials, so you can be sure you are designing with the most cost-effective construction.

3. Array design and panel utilization
Typically, panel utilization or the “number up” is the biggest cost driver for flexible circuit designs. As with rigid designs, fabricators price by production panel, with the piece price being the panel price divided by the number of parts per panel. It is important to understand your fabricator’s preferred panel size. Common panels sizes are 12” x 18” and 18” x 24”. Fabricators commonly use the outside one-inch border of the manufacturing panel for coupons and tooling holes. Effectively, when designing, optimizing the usable space of 16” x 22” and 10” x 16” with individual pieces or arrays will result in the lowest cost option.
Rigid-flex often takes on unusual shapes that are not necessarily the standard square or
rectangle we see with rigid boards. Standard panelization software may not consider this.

If the design can be reverse-nested to increase the number of parts per panel, this can significantly impact price and is worth time for review when setting up the array configuration.

4. Dynamically flexing
Clearly communicating areas that your flex circuit will be dynamically flexing will greatly benefit your design. Your fabricator will be able to review the design to ensure you are following best practices. Further, when setting the tooling for manufacturing, they will be able to orient the circuits on the production panel properly. Copper grain structure now becomes critical. The orientation with the grain structure could impact the material utilization and piece price.
5. Blind and buried via structures
It is always recommended to interact with your fabricator when developing blind and
buried via structures with flex and rigid-flex. As you develop these structures, you are adding base copper on various layers. This can impact the smallest lines and spaces possible on those layers.

A Case Study
The following is a case study that illustrates why it is important to work with your PCB
fabricator during the design phase. We once encountered a telecommunication application that had a 50% failure during installation due to cracking of the copper in the flex area. When the customer came to us, we reviewed the stackup and redesigned it by:

• Converting stackup to adhesiveless
materials
• Decreasing flex thickness from 11.8 mils
to 8.4 mils (29% decrease)

The extra thickness was adding rigidity to the flex area and causing cracking.

Summary
There are many things to think about when considering a rigid-flex design to solve a packaging problem. Flexible solutions provide numerous benefits, including space, weight, packaging, reliability, and more. Even with these benefits in mind, it can be difficult to justify the added expense when compared to the traditional approach of a rigid PCB and cable solution. It is easy to only make a comparison at a surface level. Digging deeper into the total cost also includes purchasing, receiving, inspection, and administrative cost. A higher number of purchase orders being generated for
the PCB and cable solution when compared to a single rigid-flex design provides a more holistic view of total cost.

Moving forward with a rigid-flex design, it is highly recommended that you work closely
with your fabricator for stackup, array design and material utilization, dynamic flex requirement, and advanced via structures to ensure that you are not unnecessarily introducing added cost. Your fabricator works with rigidflex designs daily—take advantage of that knowledge!

 

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Additive Electronics: PCB Scale to IC Scale

As seen in the September issue of PCB007 Magazine

SAP, mSAP, SLP—what kind of crazy acronyms have we adopted now, and how much
do you really need to know? In terms of consumer electronics, there is a good chance that the smartphone attached to your hand at all times contains a PCB fabricated with this technology—or at the very least, the next-generation smartphone that you purchase will utilize mSAP technology. In terms of current-day PCB design and fabrication, that really depends on where you are now with technology.
The standard subtractive-etch process serves the industry well. Developments in materials, chemistry and equipment enable the traditional PCB fabrication process to achieve feature sizes such as line and space down to 30 microns. Larger shops with more sophisticated capabilities are building this technology today. Mainstream PCB manufacturing is often limited to 50-75 microns (mm) line and space. But the electronics industry is evolving quickly. Propelled by the demand for more sophisticated electronics, the PCB design is being tasked with finer lines, thinner materials and smaller via sizes. A traditional progression is to first move to HDI technology with microvias and multiple lamination cycles for fabrication. Today’s mSAP and SAP technology offers an advanced approach, with line and space capabilities of less than 25 microns, to meet these exceedingly complex design requirements.

A Few Definitions
• Subtractive etch process: commonly used to fabricate printed circuit boards. This
process begins with copper-clad laminate, which is masked and etched (copper is
subtracted) to form traces
• Additive PCB fabrication: this process utilizes additive process steps, rather than
subtractive process steps to form traces
• SAP: semi-additive process, adopted from IC fabrication practices
• mSAP: modified semi-additive process, adopted from IC fabrication practices
• SLP: substrate-like PCB; a PCB using mSAP or SAP technology instead of subtractive etch technology

SAP and mSAP are processes commonly used in IC substrate fabrication. As this technology is adapted to and integrated into PCB manufacturing it has the potential to fill a gap between IC fabrication and PCB fabrication capabilities. Subtractive etch PCB fabrication has a limiting factor of finer line/space capability and IC fabrication is limited by a small overall panel size. As these processes are adapted to PCB manufacturing, there is the opportunity to fabricate on larger panel sizes with sub-25- micron trace and space.

In PCB manufacturing, both SAP and mSAP processing start with the core dielectric and a
thin layer of copper. A common differentiation between the two processes is the thickness of the seed copper layer. Generally, SAP processing begins with a thin electroless copper coating (less than 1.5 µm) and mSAP begins with a thin laminated copper foil (greater than 1.5 µm). There are multiple ways to approach this technology and decisions can be based on volume requirements, costs, capital investment needed and process knowledge.

The Process
Both the SAP and mSAP, follow a similar process. First, a thin layer of copper is coated
on the substrate. This is followed by a negative pattern design. Copper is then electroplated to the desired thickness and the seed copper layer is removed.
For insight into additive PCB processing steps, I spoke with Mike Vinson, president and
CTO of Averatek, a California-based company specializing in a catalytic ink that enables additive processing. He shared information and insight into technology based on Averatek’s IP. Averatek’s Atomic Layer Deposition (ALD) precursor ink can be utilized for both low-volume and high-volume applications and fully additive or semi-additive processes. The catalytic ink controls the horizontal dimensions of the line width and spacing. The vertical dimension of the metal thickness is controlled by an additive process that deposits metal only on the patterns defined by the photoresist.

Averatek’s process consists of six basic steps:
1. Drill vias in the substrate using either mechanical or laser drills. (Note: This step
is optional if the customer’s process includes creating vias after the Averatek process has been completed or does not include vias.
2. The substrate is then prepared for processing. In most cases, this is a simple
cleaning and mounting of the material in the appropriate material handling system.
3. Coat and cure the substrate with the Averatek ALD precursor catalytic ink, resulting in a sub-nano-layer (<1 nm thick) of catalytic material.
4. Deposit electroless copper on the precursor. The copper thickness ranges
from 0.1 µm to 1.0 µm.
5. Image a layer of photoresist using photolithographic techniques to create the
patterns where copper will be deposited. The geometry of lines and spaces that can be produced at this point is anything above 5 µm.
6. Electrolytic copper plating will finish out the circuits, followed by stripping the
remainder of the resist and flash etching. This technology enables very fine lines on
flexible or rigid substrates, among other materials, at a very competitive cost. Since the holes are plated along with the traces, a smooth and seamless transition can be made. Many of the applications requiring fine-line geometries support high-speed and therefore high-frequency signals, the smoothness and quality of the conducting metal is critical. The process described above produces conductors whose cross-sections are rounded and whose surfaces are smooth. Both qualities are ideal for high-frequency circuitry to minimize crosstalk, shorts, and energy losses.

Markets Utilizing Additive Fabrication
The smartphone market is the most visible market to bring mSAP processes to high volume production, with Apple leading the pack with the launch of the iPhone 8 and iPhone X in 2017 and other manufacturers quickly adopting the technology. Current designs are blending a combination of layers done with subtractive etch and layers with the mSAP technology. mSAP technology allows for a thinner, smaller motherboard design. This was critical to the design to allow more room for the battery and extended battery life for consumers. The technology in the iPhone X reveals 30-micron trace
and space. Predictions for the coming years are for trace and space to be in the
10-micron range.
The concept of blending the layers, utilizing the mSAP process for layers with tight pinouts and tough routing, and combining with other layers that are processed with subtractive etch, was proven to be effective in the smartphone market and is spreading to other markets: wearables, medical devices, medical implantables, automotive and aerospace and defense. It is hard to deny the advantages of moving from 10-layer HDI with four-lamination-cycles designs, to a 6-layer single- or double-lamination design. But, this does force us to look at both design and fabrication in a new way. As fabricators develop processes for this type of requirement, design rules need to be established and reliability testing needs to be completed.

Real-World Applications
What type of applications are discussing or adopting this new PCB technology? Applications that need extremely thin copper, applications that are concerned with space and weight, and applications that have complex pin-outs pushing the capabilities of traditional PCB manufacturing are all ones that could utilize SAP or mSAP technology.
One example is medical implantables using 20-micron trace and space technology, with a
double-sided design, on polyimide, with gold conductors. The combination of polyimide and gold is also compelling for biocompatibility reasons. Military/aerospace applications with highdensity interconnect designs requiring tight pin-outs now have the option of finer lines and smaller vias. Following stack-up structures similar to the work done in the smartphone designs, success is being found domestically by integrating layers with SAP technology and layers with subtractive etch technology, reducing layer count and reducing costly lamination cycles.

Wearable technology is another forerunner. SAP and mSAP enables thinner, lighter weight, more flexible circuity—all attributes catering to the wearable technology market.
Averatek’s ALD ink enables printing circuit patterns directly on rounded or unusually shaped structures, including 3D products, the curved end of a catheter and others that
the traditional subtractive etch processes have not been able to serve. This ALD ink has also found success in the emerging e-textiles market. Applying the ALD ink to various fabrics and plating with electroless copper results in conductive material that can then be integrated in e-textiles applications. Both these application areas enable design development in growing markets not traditionally served by PCB fabricators.

Recapping, SAP, mSAP and SLP is a process that is currently serving the highly visible,
high-volume, smartphone market. The PCB industry world-wide is taking notice and looking for other opportunities to implement this technology in designs with requirements for thin copper, sub 25-micron line and space and complex HDI designs. This is a new technology pushing fabricators to look at equipment and processes to determine how to adapt from a subtractive process to an additive process.
This technology also pushes designers to look at printed circuits in a new way and provides a new tool to solve complex design issues. I believe pushing us outside of our comfort zone is a good thing, even though it is difficult, and the resulting additional technical capabilities will propel us forward to solve the increasingly sophisticated electronics requirements. Watch for information from SMTA regarding a new conference in 2019, “Additive Electronics: IC Scale to PCB Scale,” which intends to address the gap between traditional subtractive etch processing and mSAP and SAP technology.

The Learning Curve: Your First Flex Circuit

As seen in the July issue of The Flex007 Magazine: http://iconnect007.uberflip.com/i/1007258-flex-july2018/58

Can you relate to this? You are tackling your first flexible circuit design. It is a simple circuit, with just two layers. Lines and space are generous, the hole size isn’t pushing any limits, and this seems like a perfect design to cut your teeth on.

You do your research, complete the layout, send the design package in for a quotation and then place the order, confident in the process. There are a few engineering questions related to materials, and you make a note for future applications: Be more specific about the coverlay requirements and whether flexible solder mask or film-based coverlay is needed. Things are going smoothly. The circuits are delivered, assembled, installed right on schedule. But something isn’t working. Now the fun begins—troubleshooting. Where do you start? After the painful process is complete, you discover that one of the components was too heavy and bulky for the flexible circuit to support without reinforcement and traces had been broken during installation. A quick redesign adds a rigidized stiffener, the circuits are ordered again, and the project moves forward.
In my experience through the years, when first working with flexible circuits or rigid-flex circuits, this is a learning curve that everyone goes through.

With this learning curve in mind, I reached out to customers and industry friends to ask
them to share some of their first experiences with flex, “gotcha” moments and advice for
those new to flexible circuit design. A few common themes stood out.

Materials
Material selection is critical in some designs, especially dynamically flexing applications,
and anecdotal information tells the story that the options available are more complicated
than one would anticipate when first working with flex. Several decisions must be made:
RA or ED copper, adhesive-based materials, or adhesiveless materials, copper thickness,
dielectric thickness, coverlay or flexible solder mask, what type of stiffener, polyimide or
FR-4? Skill and knowledge is required to balance those decisions with the end use of the
circuit, available materials, and cost.

There were a few stories about “the flex that didn’t flex” when a multilayer stack-up
became so thick there was no way to bend the circuit without cracking the copper. This
seems to be a common occurrence—it has happened to me in the past! As a side note,
most were resolved using unbonded layers in the stack-up. Another common message was that material lead time seems to be longer than expected, with more questions about the stack-up than anticipated. It is true there are a lot of variables in inventory, preferences, and capabilities between fabricators. The piece of advice given most often was, “Work with your fabricator during the design and to understand their capabilities.” Great advice.

Conductor Routing
Conductor routing practices was another category that stood out in the conversations
about lessons learned. Nearly everyone has a story about cracked traces and the learning
curve they went through to be confident in the flex design and performance. A flexible circuit is a hybrid of mechanical and electrical design. This introduces a lot of variables. I’ll share one story that stood out. The application required a double-sided circuit that was expected to be flexed during installation and test, but not over the life of the product. The first design used solid copper for shielding and was manufactured with adhesive-based materials. It cracked in the bend area during installation.

Several new ideas were implemented for the second revision. The traces were rerouted
perpendicular to the bend area, materials were changed to adhesiveless, and crosshatch shielding was added. These are all great options for improving flexibility. The second
revision cracked in the same location.

For the third revision, traces were routed to just one side of the bend area, and all
copper was removed in that area. In addition, polymide stiffeners were added to help
more specifically direct where the bend was occurring. Even though all the best practices
were employed in this design, the third revision cracked also. The problem was resolved
when they realized that the circuit was not just absorbing the stress from the known bend area, but as the unit was working stress was being applied in another axis. A slight redesign of the unit eliminated the cracking. This had to be a painful and frustrating experience for all involved, but it also was a good lesson in ways to improve the flexibility in any design.

I received a lot of real-world advice for conductor routing. A few of the key items
included: avoid abrupt changes in conductor size and direction, route conductors uniformly and perpendicular to the bend area, add radius to all inside corners, make pad patterns bigger to add stress relief, and add anchoring tie points to the solder pads to reduce the opportunity for pad lifting during assembly.

Improving Flexibility
Another common topic of discussion was the learning curve for options to improve flexibility. The previous example provides many tips and tricks pertaining to conductor routing. Wisdom was shared for additional options to consider, especially relevant for dynamically flexing and applications and when tighter than recommended bend radiuses are required. To share a few key pieces of advice, consider removing material in the bend area; this could be cut-outs in the circuit or removing coverlay and adhesive to provide a thinner package. Eliminate the ED copper in a design by requesting button plating for your design and adding copper only to the plated through-holes, not the rest of the panel. Add stiffeners to move stress points to other areas in the package that may be better able to withstand the stress.

This process was certainly interesting. Everyone seems to have a favorite story of lessons
learned when starting to work with flexible circuits. Most are told with a slightly humorous spin after the fact, but I am certain it felt anything but funny at the time. Flexible circuits are a growing portion of the PCB market and more and more applications are expected to require flexible circuits.

For those new to flex, or anyone considering using a flexible circuit in their next design,
there was one piece of advice that was repeated by nearly everyone I spoke to: Work with your fabricator early in the design. I couldn’t agree more with that advice. Not only will this help avoid material availability issues, your fabricators work with flexible circuit designs day after day and are happy to share their experience to help ensure the product works as you intend it. Take advantage of the expertise!

Mina: RFID, LED and What Else?

As seen in the August issue of PCB007 Magazine: http://iconnect007.uberflip.com/i/1011746-pcb007-aug2018/78

“The science of today is the technology of tomorrow.” This Edward Teller quote is an
apt description of the Mina product. This advanced surface treatment, recently developed to enable low-temperature soldering to aluminum in the RFID market, is not only finding success in that market, but quickly finding a home in other markets, including the LED market, where the incentive is both cost and improved LED performance. I recently had the opportunity to speak with Divyakant Kadiwala, from Averatek, to discuss the development of Mina and potential applications for this surface treatment. The science behind the ability to solder to aluminum can be summarized as the battle against aluminum oxide. Removing the oxide is easy but keeping it from reforming is extremely hard in ambient conditions. Development was focused on coming up with a surface treatment that removes this oxide at the correct temperature—the temperature at which solder reflows. This would ensure the formation of a strong bond between the bare aluminum and molten solder as it cools down. This advanced surface treatment is enabling technology across more than one market.

RFID Tag Market
This surface treatment was originally designed for the high-volume RFID tag market.
For cost reasons, aluminum-polyester (Al-PET) materials are a preferred choice, but this material does present some challenges. Aluminum is difficult to solder to at lower temperatures and PET cannot withstand high temperatures. Soldering to aluminum is difficult because of the presence of a thin layer of aluminum oxide that is present when Al-PET is exposed to air. The oxide can be removed with extensive wet chemistry but adds cost and makes this material cost prohibitive in high volume. Anisotropic conductive paste (ACP) is a common solution to this challenge and is widely used for attaching components to aluminum-based RFIDs. It is applied to the face of the chip, which is attached to the antenna using heat and pressure.  However, ACP has its own challenges. It is typically syringe applied, requires longer cure times, has pot-life issues and is electrically inferior to conventional solders. In addition, it must be stored at low temperatures in special freezers to control the polymerization of the epoxy.

LED Market
As Mina is entering the market and people are learning more about it, discussions of applications in other industries are happening and other potential uses are being explored.  One prominent market also poised to benefit from Mina is the rapidly growing LED market. According to a study from Zion Market Research, the LED market is predicted to have a 13% CAGR from 2107 to 2022, with an estimated market of $54 billion in 2022.  In the LED market, Mina can both lower cost and improve performance. The underlying goal for better performance in the LED market is keeping the LED cooler. One segment of the LED market, using thinner aluminum and less expensive materials, has similarity to the RFID tag market. Currently, base materials vary between copper-PET laminate and aluminum-PET laminate. Applications using Al-PET materials also typically bond to aluminum using the conductive epoxy method mentioned earlier. The use of Mina in these applications results in a true metal-to-metal bond that improves both the electrical performance and the thermal conductivity. As a result, the LED stays cooler.
Oftentimes in this segment of the market, copper-PET materials are being used when the
conductive epoxy approach to assembly does not provide the needed performance. Mina
would enable the adoption of the Al-PET materials which can reduce the cost of the base
materials by 80%. Once Mina is applied, the traditional soldering process used on copperPET circuits can be performed. In the high-power LED segment of the market, thicker copper with a polymer dielectric is most commonly used. This dielectric does provide some thermal performance. The introduction of Mina has provided another option for consideration and improved performance of LEDs. LED systems typically consist of a package, board and heat-sink. The package consists of the LEDs with
two leads, and a separate thermal pad in case of high power LED systems. The traditional board can be eliminated by the combination of Mina and Averatek’s ALD additive circuitry process. Alumina, the anodized layer of aluminum, is a thermally conductive, electrically insulated dielectric layer. From a 10,000-foot view, Averatek’s ALD ink additive circuitry process generates the copper traces directly on the alumina or dielectric layer. Mina can be used to solder both leads that need to be electrically grounded and the thermal pads, directly to the aluminum. This can be done by
masking the bonding areas when anodizing the aluminum prior to building the copper traces and then applying Mina to those previously masked areas allowing soldering to the aluminum. This provides better thermal management and significantly improves performance. Mina has been developed to work with standard screen printing, baking and assembly equipment. This allows a simple adoption without incurring significant capital equipment costs. As a new with benefits to two markets, I have to wonder which industry will be next to discover Mina. Hard disk drives? Connectors? Shielding wire and cable? Mina is an excellent example of innovation and technology development benefiting multiple segments in the rapidly changing electronics industry.

 

 

 

Flexible Circuits: Something New For Everyone

As seen in the March issue of PCB007 Magazine:  http://iconnect007.uberflip.com/i/950499-pcb-mar2018/62

Just the other day, I was recording a podcast with Altium discussing flexible circuit cost drivers.  During that discussion, I was asked a question about what I see as a trend in the market.  My first thought was that I am seeing an increase in frequency of questions coming from people that are just new to flex and rigid flex design.  There are enough idiosyncrasies with flex, people are a little unsure and are reaching out with questions.  Around this same time, I had been contemplating what would be a good topic to write about for the New Technology theme of this month’s magazine.  The lightbulb went off, with flex and rigid flex, there is such a range of experience, comfort and skill that most everyone feels they are working with new technology.

Single and Double Sided Flex:

Single layer flex, flex with one layer of copper, is a place many new to flexible circuits start.  This is used when all conductors can be routed on one layer of copper.  This may be replacing wire, solving a packaging problem or even be used for aesthetic reasons in a package that will be visible to the end user.  When circuitry can’t be routed on a single layer, or shielding is needed, the progression is to move to double sided (2 copper layer) flex, or even multilayer flex.

If single and double sided flexible circuits are a new technology for you, material selection can be daunting.  There are many material options to consider, but the predominant material is rolled annealed copper/ polyimide laminate. Within this material type, there are two different options.  Adhesive based, with either acrylic adhesive or flame retardant adhesive or adhesiveless material.  Many single and double sided designs will use the adhesive based materials.  These materials are often less expensive than the adhesiveless version.  Laminates are typically provided with ½ oz. to 2 oz. copper and ½ mil  to 6 mil polyimide.  The most commonly spec’d materials tend to be ½ and 1 oz. copper with 1 mil or 2 mil polyimide and because they are the most common materials, pricing tends be lower and fabricators will often have this material in stock.  Adhesiveless materials are most often recommended for higher layer count flex designs and rigid flex construction.

Rigid Flex:

Rigid flex construction consists of a flexible section and rigid section on the same board.  What differentiates this construction from flex with a stiffener is that plated through holes extend through both the rigid and flexible section.  This construction is most often used when the design requires dense surface mount pads on both sides of the circuit.

If rigid flex is a new technology for you, there are a few key things to keep in mind.  The term “bikini cut” is important.  It is recommended to keep the adhesive within .050” of the edge of the rigid portion of the design.  Adhesiveless flex materials should be used and coverlay should not extend into the plated through areas.  There is a z-axis mis-match between the rigid materials and the adhesive that can impact the reliability of the design.

The simplest version of a rigid flex construction is to keep all plated through holes in the rigid area of the designs.  It is certainly possible to create a rigid flex with plated through holes in the flex regions as well, but this type of design requires additional processing, adding cost to the design.

The flex layers can also be “bonded” or “unbonded”.  If there are several flex layers or flexibility is a concern, one common solution is to eliminate the adhesive between selected flex layers, providing more flexibility to the overall design.  Often times this is confused with bookbinder rigid flex construction.

Bookbinder Rigid Flex

Bookbinder construction has been around for decades, but seems to be regaining popularity in the market.  A bookbinder rigid flex is similar to a hard covered book.  The flex layers are staggered, each flex layer gaining length as it is stacked on the bend so that when the flex area is bent, it does not buckle and create stress on the flex layers.  Bookbinder construction is both labor and engineering intensive and there are only a handful of fabricators that specialize in this construction.

If bookbinder rigid flex is new to you, attention should be given to the variables that need to be considered to allow the proper fit.  It is advisable to add extra length if air circulation is required to keep the flex cool in a high current application rather than tightly nest the layers.  It is also important to plan for the mechanical space this bulge will require in final assembly.  Moving along the technology scale would be dual bend bookbinder rigid flex, which includes multiple bookbinding areas that do not all bend it the same direction causing a hump on both sides of the board.

Additive Process, Sub 1 mil line and space

Using an additive process, rather than a subtractive etch process to form the circuitry, opens up significant advantages in the HDI and fine line market.  The process I am most familiar with uses a special catalytic precursor “ink” that can imaged to create the patterns or areas where conducting metal is to be deposited.  The ink controls the horizontal dimensions of the line width and spacing and the vertical dimension is controlled using an additive plating process that deposits metal only on the patterns defined by the ink.

If this additive process is new technology for you, this is your chance to use your imagination and think outside of the box.  Vias can be drilled prior to the metallization process and are then plated at the same time that the surface conductors are formed, eliminating several process steps. This process can deliver fine lines down to 5 micron in width.    There is a significant advantage to RF designs with this process.  Because the traces are formed with an additive process, the trapezoidal effect from the subtractive etch process is removed.  This process also offers the option of using metals other than copper, which is critical for applications with biocompatibility concerns.

Whether you are new to single and double sided flex, moving into rigid flex construction, thinking of using bookbinder technology, or investigating an additive process, working with new technology can be both exciting and challenging.  My best advice when working with flex and rigid flex is to involve your fabricators as early in the design process as possible.  They work with this technology every day, have an enormous wealth of knowledge and are happy to share and guide designers as they learn and adjust to new technology.

Customers: Invited Guests to the Party

Hanging on the wall in my office is a quote from Jeff Bezos that says, “We see our customers as invited guests to a party, and we are the hosts.  It’s our job every day to make every important aspect of the customer experience a little bit better.”

For this column, following the theme of “who is my customer?”, I am going to use this quote to explain my thoughts on how we define who our customers are and how we interact with our customers.  I am sure the people that know me well and have attended one of our Geek-A-Palooza events are shaking their heads and thinking, “of course she is going to talk about a party!”

Invited Guests:

Isn’t it interesting to think of our customers as invited guests? As someone in PCB sales, the quick answer to “who is my customer” is anyone that is using printed circuit boards.  From there it is traditional to break that down by industry sector, or company size, or technology.  Once that scope is narrowed down, marketing and sales craft their message to best reach those defined segments.  Sales people identify a list of target companies; find prospects at those companies and work hard to differentiate their technology or services to purchasers of printed circuit boards.

But what if “who is my customer?” was broken down using the criteria/framework of invited guest?  Wouldn’t this change the traditional model of sales person trying to win over the prospect to one of two people, or two companies, working together in a mutually beneficial relationship?  While we are ruminating over this, lets expand the definition of customer to people that can influence the customer’s decisions, expand our guest list and invite them to the party also.

When you plan an event, who do you invite?  People that you enjoy being around, people that you trust people that you respect?  Isn’t that who “anyone that uses PCB’s” would want to buy from and as equally important, isn’t that who we would want to sell to?  I cannot think of one customer that I have that I would not “invite to a party”.  I don’t know if it has been a conscious or subconscious effort, but my customers are people that I truly enjoy working with.  There is a mutual respect and trust.

Working with custom products, that often push limits of technology, there are always going to be difficulties and issues that come up, but working with people that you like, trust and respects goes a long way to resolving those issues quickly and easily.

Instead of targeting customers based on industry sector, company size or technology, what if we targeted potential customers based on how they like to do business and how that fits with how we like to do business?

There are customers that like detailed negotiations and sales people that thrive on negotiating price and terms.  There are customers that don’t spend time on those details and want to work with someone they can trust to run with the program and handle the details… and there are sales people that prefer being a trusted resource and not having to negotiate all the finer points. There are customers that view business transactionally, and suppliers that do the same.  There are customers that build long-term relationships, and suppliers that see beyond short-term issues and operate with the long-term goals in mind.

Hosting a party

The host of a party is ultimately responsible for making sure that their guests are enjoying themselves.  Isn’t that what we want for our customers too?  We want to them to have a favorable, positive experience and want to do business with us again.  Have you ever hosted a party hoping your guests would think it was average?  Of course not!

Have you ever used a football party as a reason to go get that big screen TV?  How about served your guests fancy hordevours, butler style instead of a traditional buffet?   Maybe live music at the party as a treat when people aren’t expecting it?  For all of you Geek-A-Palooza attendees, how about the ring toss as an unexpected party game?  Aren’t these added touches similar to the added value services we like to provide to our customers?  Do the added value services we provide add to the overall customer experience?  How can we do better?

In the PCB industry, how do we ensure our customers have an unexpectedly positive experience?  It is very easy to focus on product, but for this discussion, let’s take that out of the equation and assume that high quality product is delivered on time.  What are the other intangible things that are important to our customers that could make their job a little easier and provide a chance to really wow them?

The success of any event lies in the details.  Do we take enough time to dig into the details with our customers?  What are the different touchpoints that our customers have with us?   What is important to them? What is the message that we send?  Do we make it easy for our customers to share the things that are important to them?  Do we put the same level of thought and planning into our customers experience that would into hosting and planning an event?

Isn’t our marketing program similar to inviting them to the party?  All of our communication, from advertising to our website, to customer service, should be consistent and engaging, exactly like an event invitation would be.

Working in an industry that manufactures custom products, it is natural to place the focus on the product and technology.   But, we can’t forget the people and that business is built by people interacting with each other. The next time your customer places an order will they experience, “the beer is in the fridge, help yourself, I’ll be on the couch watching the game” or will they have an unexpectedly positive experience that they talk about for days to come?

Visit our resource websites:

Omni PCB

PCB Advisor

 

The Power of Flexible Circuits

I have a story to share.  Picture a beautiful, fall day filled with sunshine and warm winds.  Just after dinner a family is out in their yard.  The father and older son are finishing chores before dark and a little boy is playing in the yard with the family puppy.  In a split second that puppy ran into one a thick, dense cornfield and this four year old boy followed, chasing after his favorite pet.  It was one of those split second moments that every parent fears.   If you have ever been in a corn field in the Midwest, you know, your visibility is limited to maybe a row or two in front of you and maybe a row or two to the sides.

It quickly became apparent that this family was going to need help and law enforcement was called.  Within an hour there were 160 trained volunteers from the surrounding communities and a command center was set up.  Ten years ago, this would have been what you would typically think of as a man-hunt with chains of people walking through the fields.  The scene looked significantly different on this fall day.  The command center was able to utilize drones enabled with infrared and heat sensing technology, a helicopter with similar technology to cover a larger area, the GPS from the tractor that planted that field was able to accurately display where each and every stalk of corn was and all 160 of those searchers were able to communicate real-time.

So, why do I tell you this story in a flexible circuit column?  I tell this story, because each of those items just listed contain a flexible circuit.  Our industry accomplishes some pretty amazing things.  We regularly hear that flex and rigid flex is a significantly growing portion of the world wide PCB market but, speaking only for myself, I don’t always take time to really think about the end applications that flex enables.  Let’s look at a few of the known benefits of flexible circuits and what type of products we may interact with that have been, or are being, developed to take advantage of this.

Advantages of flexible Circuits:

Solve Product Packaging Problems:  Flex allows for a 3-axis connection.  It is able to bent and folded around corners eliminating the need for discrete pieces.  It is easy to think of products that take advantage of the space saving benefits of flexible circuits:  portable medical devices such as insulin pumps or heart rate monitors, hearing aids, smart phones and tablets, cameras.  As consumers, we are requiring our electronics to be smaller, lighter and at the same time have increased functionality.  Flexible materials allow designers to meet those demands.

Reduce Assembly Cost:  Flex eliminates hand-wiring and provides additional cost savings when purchasing costs for multiple wiring and component pieces are factored in.  Home monitoring bracelets and wearable electronics are a good example.  The product needs to be light weight and durable, wire and flexible circuits are both options.  A simple flex circuit eliminates time for assembly, purchasing costs and inspection costs by solving the problem with just one unit.

Reduces both weight and volume:  This is a big one.  Bulky wire harnesses and solder connections can be replaced with thin, light weight rigid flex.  It is not uncommon to see studies showing that this savings in weight and space can be near 60%.  Aerospace is a perfect example of an industry that benefits from reduction in weight and volume.  With aircraft, rockets, missiles, etc., weight is an expense.  Any opportunity to reduce weight and space translates to a product that is less expensive to operate.  The fun little TV screens that are being built into aircraft so we are always entertained, lighting systems in the airplane, engine controls, braking systems, are all products that have been able to take advantage of flexible materials.

Dynamic Flexing:  This is easy.  Anything with a hinge!  The one I use every day is my laptop.  Let’s not forget printers, disk drives, cameras, and robotic arms.

Thermal Management:  Flexible dielectrics offer a greater surface to volume ratio than round wire and this extra surface facilitate the heat away from the circuit.  Rigid PCB dielectrics often act as a thermal insulator inhibiting the flow of heat.  One area of significant growth in flexible circuit designs is the LED lighting market.  Automotive and aircraft applications, especially with the combined benefit of lighter weight and improved thermal management, are increasing the usage of flex.  Examples include headlamps, interior lighting, and interior electronics, just to name a few.  One of my favorite applications is LED lights in a pair of high top tennis shoes.  This application is not just your typical shoe that lights up when you walk; this high top was designed with an artistic LED lit pattern throughout the shoe.  It might not be the most high-tech application, but it is eye catching and fun.

Improved Aesthetics and Bio-Compatibility:  Appearance can impact decisions when the end user is exposed to functional elements of the product.   For example, a simple hand-held medical device being used in a doctor’s office had a wire that was visible to the patient.  Although the medical device was working perfectly, patients perception of and confidence in the procedure was not high.  This was traced back to patients not being comfortable with the perception of the wire.  That simple wire was replaced with a very simple flexible circuit, so simple, there were only two traces.  But, by making this simple change, the patient’s perception and confidence in the medical device skyrocketed.

Polyimide is also bio-compatible.  Most often, the polymide material is fully encapsulated before being inserted into the body.  New developments are exciting.  Polyimide laminate with gold, rather than copper traces are fully bio-compatible and being tested as sensors to be implanted into the human body.  This development is also aided by additive technology that allows trace size in the 5 to 10 micron range, significantly shrinking the package size as well.  There are exciting things on the horizon.

Intrinsically more reliable and reduce the opportunity for operator error:  Flexible circuits can significantly simplify the system design by reducing the number and levels of interconnection required.  Because the design is controlled by the artwork, the opportunity for human error is eliminated.   Aerospace is great example.  Spacecraft are subjected to many kinds of dynamic forces, especially during take-off.  In traditional PCB’s these vibrations contribute to failure.  Rigid flex are made to twist and flex and are a benefit in these harsh environments.  Solder joints, crimps, etc., are also at risk for failure in these conditions.  Flexible circuits can remove this concern by eliminating connections.

Yes, our industry has developed so many interesting, life enhancing and lifesaving products and for that we should all be proud to be a part of the growth in this market.  To finish the story I started earlier, this little boy emerged from the field, a little tired, very muddy and mostly angry that he still had not found his puppy.  Guess what.  The person stationed at the edge of the field that spotted him was able to notify his parents and the command center immediately with his cell phone.  Which, yes you guessed it, also contains a flexible circuit.

Contact us if you need any advice or assistance with your flexible circuit needs!

Tara Dunn, Omni PCB