Copper Via-Fill Technology in Development

The use of via-in-pad technology is increasing rapidly in today’s printed circuit board designs. The need for miniaturization, combined with the rapidly decreasing pitch of component footprints, drives printed circuit board designers here. Via-in-pad requires the vias to be filled, planarized and then over-plated with copper. Once a designer has decided to move forward with this technology, the next question to be answered is what type of fill material should be specified. Typically, these vias are filled with either epoxy, conductive epoxy or solid copper plating. All have pros and cons to be considered.

I recently had the opportunity to speak with David Ciufo, Program Manager for Printed Circuit Board Technologies with Intrinsiq Materials, to learn about an exciting new product in development that will dramatically change the existing manufacturing parameters of the filled-copper via option.

Intrinsiq’s Nano Copper has been formulated into a screen printable paste that is compatible with commercial via-fill equipment. This paste can be dried and sintered in commercially available ovens and results in pure copper after sintering. The end product is highly conductive, both thermally and electrically, when sintered.

Benefits

Now, for the exciting part, there are two distinct advantages for PCB manufacturing with this product. First, because it is run with commercially available equipment, as seen in the process flow diagram, the capital investment needed to offer copper-filled via technology is significantly reduced. Many printed circuit board manufacturers are not able to offer the copper-filled via option due to the cost of plating equipment and chemistries. The barrier to entry for these PCB manufactures will be eliminated.

The second exciting benefit to this technology is the process time requirement. Solid copper-plated vias typically require 4 to 6 hours of plating time by the manufacturer, along with the specialized equipment and chemistry. This new product will enable PCB manufacturers to produce copper-filled vias in 60-90 minutes. A shortened cycle time will have benefits in lead-time and processing costs.

Via Fill Process Intrinsiq

Product release for this screen printable paste is currently scheduled for the end of 2016. Throughout this year, pilot programs will be released, further testing completed and reliability data gathered.

Product development, an interesting process

Nano copper inks and pastes are typically sintered photonically with broadband (xenon) flash or near IR laser. Because the copper cladding is too thermally conductive to allow complete sintering and high power lasers are a barrier to entry due to cost and complexity, an oven solution was sought to keep the process compatible with existing technology. Heller Industries manufacturers a formic acid environment convection oven to be used for flux-less reflow. This was determined to be the perfect environment to sinter nano copper without oxidation. Nano copper paste can be completely sintered in 40 minutes or less.

The process development for this product has had several iterations. The initial proof of concept was to deposit paste into mechanically drilled blind vias using a vacuum bag to help fill the holes. Those initial coupons were plated and etched prior to filling to allow for laser sintering. As the development progressed, the testing moved to copper clad PCB’s with mechanical blind vias. The panels were electroless copper plated then electroplated to simulate actual via filling requirements. Unfortunately, the thermal conductivity of the copper foil prevented the ability to sinter the copper paste. Research then pointed to thermal sintering in a formic acid environment.

As the development process continued, it was determined that the extended time necessary for formic acid sintering at 250C destroyed the PCB laminate. Moving forward, other nano additives were included in the formulation to lower the temperature requirement to 225C. This formulation and temperature sintered the vias completely in 60 minutes.

The next phase in the development process was to screen print trace patterns on FR-4 to be sintered alongside the via filled coupons. These samples were used to calculate bulk resistivity as compared to copper. Typical measurements were 6X to 8X that of bulk copper. Typical epoxy-based conductive via fills are in the 20X to 50X range.

Today’s product

Moving forward, additional product development was undertaken resulting in the current formulation, which allows the sintering temperature to be reduced to 190C. The paste is sintered to pure copper in only 40 minutes in the Heller conveyor oven. Samples of this formulation were via filled using the vacuum bag technique, on copper clad panels, with copper plated blind vias. The panels were Heller sintered, planarized, over-plated and solder floated. Samples were then subjected to IPC standard reliability testing parameters. Each sample was floated at 288C, held at temperature for 10 seconds, cooled, and refloated 4 times.   The vias survived 5 solder float procedures.

It is always exciting to learn about the new developments in products and processes for the PCB industry. In this case, incorporating nano copper inks and pastes into standard printed circuit board manufacturing techniques will allow manufacturers to offer a solid copper-via option to their customers without significant capital investment in specialized plating equipment.

Please contact us for more information.      http://www.omnipcb.com         tarad@omnipcb.com

 

Gold PCB Traces used in Medical Applications

Medical Research is Golden

Recently, I was involved in a group discussion about flexible circuits and the role of this product in medical equipment development and medical research. We were having a light-hearted discussion over lunch, when I was asked about the most interesting flex application I had been involved with. The first thing that sprang to mind was an application from several years ago. In this application, flex was being used for purely aesthetic reasons. A hand-held piece of surgical equipment included wires that were visible to the patient. The wires were functioning perfectly, but the negative perception of patients when seeing these wires during a medical procedure prompted the equipment designer to replace the wires with a sleek, high-tech looking flexible circuit. In terms of technology, this was probably one of the simplest flex designs to be manufactured: standard materials, single-sided, two big traces, and tolerances that weren’t particularly critical. Needless to say, the group was amused. Of all of the possible medical applications that I have had the opportunity to be involved with, THAT was the first one I thought of? Honestly, I have always appreciated that unusual application!

But, when giving that question more serious consideration, there truly has been a marked increase in flexible circuit designs in medical products over the past several years. Flex is the perfect solution for solving space, weight and packaging issues. A visit to the doctor’s office or hospital clearly reveals that medical equipment has become much smaller, lighter-weight and more portable, all while increasing functionality. Flex and rigid-flex designs are becoming commonplace in this field.   As we see an increase in the number of flexible circuit applications in this field, we also see an increasing need for finer lines and spaces, microvia technology and mixed material stack ups. This is not unlike the technology advancements we see with rigid printed circuit board technology.

Neural Probe Technology:

If I had to choose one of the most interesting flex applications that I have been involved with recently, it would be applications that involve neural probe technologies.   Designers working on research studies designed a sensor that required trace and space in the one mil range, which is not a simple technology to manufacture. Compounding the complexity of this unusual request was the need for those traces to be gold rather than copper. I did need to clarify that this was a need for gold traces, not copper traces with ENIG or gold plated traces! Wanting to learn more about the technology required to accomplish this combination, I reached out to Mike Vinson with Averatek Corp.

Averatek is a high tech company based in Santa Clara, CA that manufactures with a patented innovative and additive metal “print and plate” process. This additive technology enables the creation of trace and space widths below 10 microns and enables the direct deposition of copper and other metals on a variety of substrates.

One of the first questions I wanted to answer was: What would drive the need for gold traces rather than the traditional copper traces?  What I have learned is that neural probes are being used in many clinical settings for diagnosis of brain diseases such as seizures, epilepsy, migraines, Alzheimer’s and dementia. Microelectronic technologies are opening new and exciting avenues in neural sciences and brain machine interfaces. With this area of science and research, biocompatibility of the neural probes to minimize the immune response is critical. Copper, nickel and chromium can all adversely impact cells in the area of the electrodes. Flexible materials, such as polyimide, are commonly used in implanted devices to match the geometric and flexibility requirements of implants. Metalizing with gold provides further compatibility versus less noble conductors such as copper or nickel.

With a better understanding of the reasons behind the request for gold traces, the burning question was, how does the additive print and plate process enable both the fine lines and the gold metallization?

Fine Lines and Gold Metallization:

The traditional printed circuit board manufacturing process is accomplished by a subtractive etch process. The PCB manufacturer will start with a panel of copper-clad material. In other words, the full panel, often 18” x 24” is covered in copper. The traces and spaces are created with a “develop-etch-strip” process that essentially removes the unwanted copper from the panel leaving the desired trace patterns. Often over-simplified, this process is quite complex. After vias are drilled, electroless copper is deposited and resist is laminated prior to the photolithography process. Following the imaging process, panels are developed to remove resist that was not exposed, copper electroplated, and then tin is plated as a temporary etch resist. The remainder of the resist is stripped, the etch process removes the unwanted copper and the temporary tin plating is then stripped.

Additive technology is a reversal of this process. The manufacturer begins with the bare substrate. In the case of a neural probe, this is likely a polyimide material. The desired circuit pattern is then created by adding the metal layer to the substrate. Averatek has developed a proprietary nano-catalytic ink that enables a simplified five step process.

The bare substrate is prepared. Vias are drilled. The ink is coated and cured. The ink is then patterned with photolithographic imaging. Finally, metal is plated to this pattern. In this neural probe application, the metal is gold but metallization could also be copper or other metals. The key to this technology lies with the catalytic ink. Precursor catalysts that are deposited in thin atomic layers have unique properties like so many other nano materials. Additionally, a catalyst that is deposited via a liquid or “ink” can fill in many areas, nooks and crannies that would not be touched by line-of-sight methods like sputtering. This provides a basis for electroless plating that will fill vias of all types with more thorough coverage than conventional methods.

Their semi-additive process works by applying a very thin electroless metal to the base layer, followed by photo resist and imaging allowing the plating of a thicker electrolytic metal when required. As with a traditional semi-additive process, the resist is then stripped and the unneeded metal is etched away forming the trace pattern.   In the neuro probe example, when working with gold rather than copper, a very thin layer of conductive palladium is applied electrolessly followed by the gold plating. Gold is a difficult metal to etch, the palladium is easily removed without impacting the gold plating. The key difference when using Averatek’s catalytic ink technology is the ability to work with thinner metallization than the traditional semi-additive process.

Without the technology barriers associated with the traditional subtractive etch process, the additive process enables both fine lines and spaces (less than 1 mil) and very thin metallization (less than 5 micron).

Medical applications using this technology are often single- or double-sided configurations that have been designed with fine lines and spaces. The ability to design features less than .001” adds a new flexibility to maximize breakouts and eliminate, or minimize, multilayer blind via constructions. When this is coupled with the ability to plate pure gold without nickel, chrome, or exposed copper layers, a unique offering emerges for applications where the circuits may need to be exposed in end use.

This same technology has applications in other medical applications as well. Conductive layers are often used for shielding. In some cases, minimal thickness is required for bulk and flexibility. Utilizing the technology for a semi-additive base layer, as noted above, enables a very thin, yet very conductive metallization on flexible substrates as well as insulation on wires and cables for coaxial type shielding. This thin metalized layer can be cut to a specific size and installed around critical components in the final assembly. Many shielding applications require copper, but both gold and palladium can be used as required by the application.

Metallization of fabric is also an emerging market need. Using this additive technology, electrodes and other conductive paths can be formed by coating individual fibers in fabric, down to two microns in diameter, with thin metal layers. This has been demonstrated in gold, palladium and copper. The metalized surface can provide electrical, mechanical and chemical benefits.

Selecting the “most interesting” flex application related to medical field is not an easy task. There are just so many interesting applications and design developments to choose from. This field is moving at a rapid pace. At least for today, the neural probe technology, requiring both the traces to be metallized with gold instead of copper AND requiring those traces to be at or below .001”, gets my vote. Not only does it push outside of standard technology in one way, but in two ways, simultaneously. I thank Mike Vinson and Averatek for helping me learn more about the technology and processing required to meet these requirements.

Please contact me for additional information on this process.  www.omnipcb.com  tarad@omnipcb.com

My Thoughts on the IPC Flex and HDI Forum

As an attendee at the IPC Flexible Circuits – HDI Conference on October 28th – 30th, 2015, I found myself in a room of people, all eager for technical information, with the opportunity to reconnect with industry friends and to make new connections. The audience was diverse with young people, new to our industry, sitting alongside industry veterans willingly sharing their knowledge and passion for HDI design and flexible circuit technology.   The conference kicked off with intermediate level, half day tutorials on both flexible circuit design and HDI. The second and third days provided advanced level speaker presentations in short 45 minute segments allowing time to digest the information, speak further with the presenters and network with industry peers.

Two comments made early in the technical conference solidified an event message in my mind. Mike Carano, with RBP Chemical Technology and the Event Chair, commented in his opening remarks that networking is one the greatest opportunities with IPC. Brad Bourne with FTG gave the keynote presentation: Organizational Commitment to High Reliability. He presented the message that PCB reliability goes way beyond the manufacturing of the printed circuit board. Everyone in the industry impacts reliability: circuit board designers, raw material suppliers, fabricators, contract manufacturers and end users of the product.

Following the opening keynote, we were treated to a presentation by Andrew Schimmoeller and Jeffrey Friend with Battelle. Their riveting presentation explained the use of flexible circuits in the design of a neurological stimulation system that re-animated a paralyzed hand, controlled by patient thoughts. I have re-watched the short video on this topic several times since the event. https://www.youtube.com/watch?v=BPI7XWPSbS4 This is an inspiring example of the things our industry can accomplish by working together.

Throughout the conference there were several presentations addressing flex and rigid flex including: design rules for flex performance, high reliability flex and rigid flex, flex vs flexibility and new developments in HDI technology. Beyond fabrication and design related information, we also learned of unique challenges with flex and rigid flex in terms of stack up and impedance, reducing fabrication challenges with new materials, metallization for HDI and flex circuit technology. The amount of relevant technical knowledge disseminated in a short time period was staggering. I was continually reminded of the power of the combined knowledge of our speakers.

While many of the presentations detailed proven technology, reliability data and design criteria we were also informed of exciting emerging technologies including the latest developments in thin film metallization and via filling and a novel new approach for applying metallization to ultra-thin substrates.  It will be interesting to follow these new technologies and see how they develop over the next few years.

The presentations on break-through technologies for high reliability and technical organizational innovations were both intriguing and thought provoking. It is always inspiring to listen to examples of people being able to “step outside of the box” and apply existing technology in new and creative ways.

In addition to the remarkable level of technical knowledge presented, there were numerous opportunities each day for networking. I personally had the privilege of meeting several new people and was able spend time with others that I haven’t seen in a while.

Attendees consistently remarked on the value gained from attending this year’s event. Todd MacFadden, Component Reliability Engineer at Bose Corporation commented, “ I am thrilled by the information and insights I gained from this forum on flex and HDI. The event was well-organized and the content was highly relevant to me. The timing of the event couldn’t have been better for me. I came with only the basic understanding of flex, just as we are starting to ramp up our need for this technology, and I am coming away with many tools and a long list of contacts to help my teams design for success. I am grateful to the IPC for assembling such a broad and diverse expertise into a concise and useful conference, and for providing plenty of opportunities to network. Great Job!”

Keith Holman, Sr. Buyer – Electronics, with Orbital ATK – Defense Systems Group remarked, “The IPC Forum was a great educational experience as well as an exceptional networking opportunity. The level of discussion around the current issues and successes with HDI and Flex/ Rigid Flex coupled with the new technology, made for great discussions. Each of the presenters was very knowledgeable about their topics and also made themselves available for further conversations. I would recommend the IPC forum to any technical or non-technical people involved with IPC.”

Ernie Kreiner, PWB Designer III, C.I.D.+ with L-3 Fusing and Ordnance Systems commented, “Attending the IPC conferences has always been an excellent experience. Networking with peers and seeing what technologies are out there and what is on the horizon, is always informative.”

I couldn’t agree with these three gentlemen more. I personally learned something from each speaker. The electronics industry is changing at a rapid pace and both flex and HDI designs are a fast growing segment of the industry.    As valuable as the technical information is all on its own, the networking component gave the time to chat with OEM’s and flex users to learn their challenges and also talk with flex fabricators and materials suppliers to learn of new programs and technologies. The conference gave me the opportunity to meet new people and expand my industry resources.   In this complex industry, there is so much value in the ability to reach out to others in different areas of the industry to help solve new challenges.

Anne Marie Mulvihill and IPC put together a cohesive and well run technical conference. Thank you to IPC for their work and dedication to educating the industry while at the same time providing networking opportunities to tie us all together.

www.omnipcb.com

The Battelle NeuroLife Project

A couple of weeks ago, at the IPC Flexible Circuit – HDI Forum, we had the opportunity to listen to a riveting presentation from Battelle that we felt compelled to share.
The presentation began with the video of a Tedx Talk of Chad Bouton presenting research and the subsequent success of a project designed to reconnect a paralyzed man’s brain to his body through advanced technology.

The presentation concluded with the introduction of, and words from, Ian, a paralyzed man instrumental in both the research and medical trials.

The video is just over 15 minutes long and you could have heard a pin drop.  Not even a piece of paper was shuffled,  truly amazing, when you picture a room of nearly 100 people and the distractions that we all have with our phones and email when we are out of the office.
We encourage you to watch: NeuroLife Project    
It is well worth the time!
This technology shown in this video was enabled by the use of flexible circuits. In fact, by the use of flexible circuits that pushed the limits of most standard capabilities.

Flex was chosen for several reasons: ease of manipulation on a patient, repeatable applications (stable dimensions, silkscreen marked for location identification/mapping), durability of materials, high dielectric strength, and reliable system functionality.

Not only were we fascinated by the development of this technology, we are excited to be part of an industry that pushes established boundaries of manufacturability to create products that enable these type of life changing developments.
I hope you enjoy the video as much as we did!

 

Click here to watch the video

Tips for Time Critical PCB’s

Can you relate to this common scenario? A quotation is received for the fabrication of three different PCB part numbers and a purchase order is placed for delivery in five days, on a time-critical project.

A few hours later, the dreaded email is received. There are questions regarding the design that are putting the project on hold. It takes a day, or possibly two, to coordinate the resolution of the questions between your customer, the PCB designer and the fabricator.

Next, you are informed that the delivery date for the PCB’s is pushed out for the two day delay in answering questions. Ugh! Now the schedule has to be adjusted, the components you paid a premium for will be sitting there waiting for the boards, and your customer is NOT happy.

This scenario occurs time and time again. Approximately 90% of designs that go through CAD/CAM at a PCB fabricator have questions that must be answered before the fabricator can start the board manufacturing. Some questions are minor and can be answered quickly; others can require a partial or complete redesign of the PCB.

Elizabeth Foradori and I sat down to discuss our thoughts and ideas on how to best work with PCB fabricators to reduce the likelihood of any delays during time-critical development of a new product.   Chapters could be written on this topic, but our hope is that these ideas provide a basis to encourage discussion early in the design process.

Prior to placing a purchase order:

Research and select your printed circuit board fabricator early in the process: If the design is going to be a standard design, on common material and fit neatly into any manufacturer’s “standard capabilities”, that makes things much easier. But, if the new design is going to be pushing the limits of standard technology in any way – microvias, fine line, tight pitch or tight tolerance, selective surface finish, exotic materials, rigid-flex – selecting a supplier early in the process, whose capabilities match the technology needed, will ensure that the design can be manufactured quickly once you are ready to release the files.

Involve the fabricator early in the design process: Ask questions. Talk to your supplier frequently during the design of the PCB. They encourage questions and are happy to make recommendations. Once the fabricator understands what you are trying to accomplish, they can make recommendations that will ensure that the design is manufacturable.   As a final step, or even an intermediate step during the design process, ask your fabricator to run a design rule check based on your files. This may not catch every issue and eliminate all engineering questions at the CAD/CAM stage, but it will catch the major issues that would require lengthy redesign once a project is released.

Verify that material is available and will be in stock when the design is complete:   Fabricators do try to stock the common materials and even small quantities of the less common materials to avoid delays. Unfortunately, they cannot stock all materials. Once the stack-up is finalized, ask the fabricator if this is material that will be in stock. If not, work with your supplier to pre-order the material to have in-house when you are ready to release the design. Some fabricators will secure material based on a simple email authorization; others will require a purchase order. Either way, planning for material to be in stock when the design is complete can save anywhere from five days to six weeks.

Once a purchase order is placed:

Send complete files: Review the files being submitted with the purchase order to ensure they are complete. Is the net list included? Are the fab notes complete, confirming any quality requirements, material specifications, and surface finish requirements? Do the fab notes match the gerber data?   These are all very common reasons that files are placed on engineering hold.

When you receive questions from the CAD/CAM tooling group, ask if this includes all questions associated with the design. Sometimes two different engineers may be working on the same design to meet an expedited delivery and both may have questions in their portion of the process. Other times, when the initial issues are encountered, the job is set aside only to find additional issues when work is resumed. The process can be streamlined by taking all questions to your designer or your end customer at one time.

If questions are fairly involved, it is always best to try to schedule a conference call between your fabricator, your designer or end customer and yourself to resolve the issue as quickly as possible. Email offers a great documentation trail for any changes, but can drag the process out longer than necessary. If communicating via conference call, ensure that someone is responsible for documenting the discussion and sending that to all parties involved.

Once the questions are answered, follow up with your supplier to confirm that the questions involved in the tooling process have not impacted your delivery schedule. Delays of a few hours are usually absorbed into the initial lead-time. Longer delays can impact delivery. PCB fabricators are typically very good about notifying customers of any changes in delivery date due to engineering questions, but it is always a good practice to ask. You don’t want to be surprised on the day you are expecting your printed circuit boards.

In summary, communication with your supplier is the best way to reduce the cycle time needed for fabrication of time-critical, new printed circuit board designs. Ask for recommendations during the design phase to ensure the design is manufacturable, verify that material will be available when the design is released, and if there are engineering questions, and communicate quickly to have those resolved.   Take advantage of the fabricators expertise and ask questions!

Contact us for further information!  www.omnipcb.com

PCB Final Surface Finish Selection: No one size fits all solution

Remember the good ole days when hot air solder level was the go-to surface finish for almost all applications? The decision about surface finish was an easy one. The primary function of the surface finish was to protect the copper from oxidation prior to assembly. Wow, have things changed! Today’s expectations include: superior solderability; contact performance; wire bondability; corrosion and thermal resistance; extended end-use life; and of course, all at a low cost.

Common surface finishes now include HASL, both leaded and lead-free, OSP, immersion tin, immersion silver, ENIG and ENEPIG. Unfortunately, there is no one-size-fits-all surface finish that fulfills all the requirements in the industry; the decision really depends on your specific application and design.

Recently, Elizabeth Foradori and I sat down with Robyn Hanson from MacDermid Electronic Solutions to learn about the key considerations for final surface finish choice and the cautions of each from the OEM or assembly perspective. To listen to the discussion, click here. For a concise list of the pros and cons of each finish, click here. Following are some of the highlights.

Considerations for Surface Finish Choice: Does the application require lead or lead-free assembly? Will the end environment have extreme temperatures or humidity concerns? What shelf life is needed, and will it be months or years? Does the design have fine-pitch components? Is this an RF or high-frequency application? Will probe-ability be required for testing? Is thermal resistance or shock and drop resistance required?

Once these questions are answered, the surface finish options can be reviewed to find the best fit.

HASL—Hot Air Solder Leveling:

  • The oldest surface finish
  • Lead and Lead-free versions are available
  • Leaded HASL currently in limited use due to ROHS and WEEE initiatives
  • Currently exempt: industrial vehicles, military, aerospace and defense, high performance electronics
  • Leaded versions are harder to source
  • Long shelf life
  • Not suited for fine pitch

HASL is blown from the PCB surface to remove excess solder; this can create non-uniform coverage which makes component placement of tight pitch components difficult. The hot temperatures of lead-free HASL can cause warpage and soldermask embrittlement. The plated-through-hole may be plugged or reduced.

OSP—Organic Solderability Preservative:

  • Highest volume surface finish, worldwide
  • Applications range from low end to high-frequency server boards, also used in selective finishing
  • Latest versions are copper selective and more thermally resistant for high-temperature, no-lead applications
  • Applied through chemical absorption on the copper surface; no metal-to-metal displacement
  • Inexpensive surface finish
  • Limited shelf life

OSP does have implications at the assembly level. Older versions of this finish are not thermally resistant and couldn’t resist more than one reflow. The coating hardens with reflow exposure and becomes more difficult to solder. Material transfers onto the probe tip (during electrical test) can result in false readings and will require more frequent probe maintenance or a special probe style. Higher OSP thicknesses are detrimental to solder paste flow and hole fill.

Immersion Tin:

  • Applications are predominately automotive, U.S. military and aerospace
  • Excellent for press-fit applications (i.e., large back panels)
  • All contain anti-whiskering additives, but tin whisker elimination is not guaranteed.
  • Low cost, flat and suited for fine pitch
  • Aggressive on soldermask

Cautions at the assembly level include the fact that pure tin thickness is lost to the copper intermetallic with time and temperature. Loss of pure tin will degrade solder performance. The first reflow exposure will dramatically reduce the pure tin thickness and deposit stress could result in tin whiskers. This is a naturally occurring characteristic of tin in direct contact with copper.

Immersion Silver:

  • Greatest conductivity of all the surface finishes; well suited for high-frequency applications
  • Applications range from low end to high-reliability product
  • Topcoats have been formulated to overcome tarnish and corrosion issues in aggressive environments
  • Flat, suited for fine pitch with excellent solderability
  • Easily scratched, sliding connector limitations

The predominant issue seen at the OEM level is micro-voiding. Small voids occurring at the intermetallic layer of the solder joint could cause solder joint fracture. This defect manifests itself preferentially on solder mask defined pads which are more difficult to develop properly.

ENIG—Electroless Nickel Immersion Gold:

  • Highest revenue surface finish
  • Applications associated with high reliability
  • Used often in the flex market
  • Aluminum wire-bondable
  • No degradation between reflow cycles, can be held mid-assembly for extended times
  • New deposit thickness specifications for gold are under review to address the high cost of gold and hyper corrosion/black pad issues with extended dwell times for the gold

This chemistry requires tight process control. Proper plating conditions and control over the entire process are critical to performance. Proper chemical add-backs and numerous chemical analyses are required during start up and during plating. Layer thickness is also critical. Low nickel thickness will result in poor corrosion and thermal resistance in end use. Low gold thickness will result in less resistance to thermal conditioning during assembly and high gold thickness can promote nickel corrosion or black pad. Too much or not enough metal area in the plating bath will affect plating performance.

ENEPIG—Electroless Nickel Electroless Palladium Immersion Gold:

  • Gold and aluminum wire bonding
  • Applications include medical and U.S. military
  • Excellent solderability
  • Mitigation of black pad
  • Gaining interest and acceptance in the market

The primary caution at the assembly level is palladium thickness. Palladium that is too thick reduces the solderability performance. This will be slower to wet and have potentially palladium-rich areas in the solder joint. Palladium does not readily solubilize into the solder joint like silver or gold.

Surface Finish Breakdown by Market Sector:

  • Automotive: Silver, OSP, immersion tin
  • Data/Telecom: silver, OSP, ENIG
  • High end consumer: ENIG, silver, OSP
  • Low End Consumer: HASL, OSP
  • Aerospace, defense and high-performance electronics: HASL, immersion tin, ENIG, ENEPIG
  • Medical: ENIG, ENEPIG, silver

Regardless of whether your application is automotive, medical or military, there are many factors to consider when selecting a final surface finish. Cost, lead or lead-free requirements, end environment, shelf life, fine-pitch components, RF applications, probe-ability, thermal resistance and shock and drop resistance, to name a few. There is not a one-size-fits-all finish. Understanding the advantages and disadvantages of each surface finish allows the designer to select the finish that best fits each particular application.

Please contact us with any questions or for additional information!  www.omnipcb.com

Transition from Domestic Prototype to Off Shore Production for Flex Circuits

A smooth domestic to off shore transition

Designing a flex to be prototyped domestically? No, problem. Designing a rigid flex for production off shore? Got it. Designing a part that will be prototyped domestically with a seamless transition to off shore production? That can be a little more challenging.  We have probably all been there. The prototypes are needed on a very tight delivery schedule and are built domestically. The testing is complete and the same files are sent to an off shore manufacturer for the production build. The order is placed and suddenly, the engineering questions start coming in. Can the materials be changed? Can the hole size or pad size be altered to improve manufacturability? These common questions now require the time and effort to evaluate and ultimately the time and effort to complete the rev spin before production product can be released. We sat down with Ashley Luxton of Graphic, PLC to learn his recommendations to minimize these disruptions . Our discussion focused on the importance of supplier selection, items that are universal and key areas that have more significant variation. A link to our discussion is included here.

Supplier Selection – Choose your supplier carefully and consider the different options available. There are manufacturers that own both domestic and off shore facilities, there are domestic manufacturers that partner with off shore facilities and there are manufacturers that work only domestically or only off shore.

When working with a manufacturer that has both domestic and off shore capabilities, it is critical to communicate with them early in the design process. The fabricator, understanding both the domestic and off shore preferences and capabilities, will be happy to make recommendations for material selection, panel utilization, and also how to maximize yields for the production volumes.

A domestic supplier that partners with an off shore manufacturer will be able to offer this same type of guidance. Due diligence is recommended. Most domestic manufacturers that partner with an off shore supplier do so to offer their customers a full service option. Significant effort is put into learning their partner’s technical capabilities, material preferences and operations. The lines of communication between the facilities are well established.

There are also domestic suppliers that purchase product from off shore suppliers to support a full range of volume requirements for their customers but have not put the extra effort into learning and understanding the details of their off shore partners technical capabilities. This model provides the customer with volume production from off shore, but may not be the best solution when looking for design guidance to ensure a smooth domestic to off shore transition.

When working with two independent facilities, take the time to fully understand the off-shore suppliers capabilities and material preferences and then apply that criteria to the domestic prototype design.

Universal Criteria: Whether your PCB’s are being manufactured domestically or off shore, certain things are universal. Quality specifications such as IPC Class, FAIR requirements, and testing requirements do not change. Some of these specifications may not be as critical at the prototype stage and could be waived, but the interpretation of the specification will be consistent.

Designing to maximize yields may not be as critical with a prototype order, but with the higher volumes typically associated with off shore production, expected yields should be considered. There are universal criteria for maximized yields. Increasing holes sizes, pad sizes, line width and space will all improve yields at the manufacturer and have a direct impact on cost.

Acceptance of X-outs should also be considered. Allowing X-outs in your delivered array will have a direct impact on cost. If X-outs are not allowed, both domestic and off shore manufacturers will factor in the yield loss associated with scrapping any good pieces in an array that has an x-out. If X-outs are not allowed, this should be clearly communicated to avoid any misunderstanding.

Significant Variation: Preferred materials can vary significantly between domestic and off shore manufacturing. This preference is typically a function of material availability and cost.   Logically, off shore suppliers will prefer to use materials that are produced locally. These materials are more readily available, with lower transportation costs. Most off shore suppliers will also use the materials that are more common in the US, but pricing will be higher and lead-time longer.

Be careful not to over specify materials. Referencing the appropriate IPC slash sheet, rather than the specific material, allows more flexibility for the supplier.   This flexibility will result in lower cost and shorter lead-time. If more control is required for material selection, using an “approved list” of materials that has been tested and approved is another option that allows the manufacturer flexibility to use their more preferred materials, while giving the designer more control of materials being used.

Another aspect that varies significantly is panel utilization. Domestically, the most common panel size is 18” x 24” with 16” x 22” of useable space for the manufacturer and it is most cost effective to design the part or the array to best fit that space.   Off shore manufacturers have much more flexibility with their panel sizes, use many different panel sizes to best utilize material and generally work with larger panels. Off shore it is more critical to design the array to best utilize the material within the array and overall array size has much less of a cost impact.

To recap, when looking for the smoothest transition from domestic prototype to off shore production manufacturing, research suppliers and select a supplier that can demonstrate their knowledge of the off shore facility’s technical capabilities, material preferences and clearly have a streamlined form of communication. Quality and testing specs are universal and should transfer from one facility to the other with no issue but special attention should be given to controlled impedance, materials and panel utilization, as these can vary significantly between domestic and off shore manufacturing facilities. A smooth transition from domestic prototypes to off shore production does not need to be difficult, but it does need to be well planned.

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