PCB Sourcing? One Size Does NOT Fit All

When I am asked how to improve yields or reduce cost with a printed circuit board design, my mind immediately races ahead to the most common cost drivers: Has the part been designed with manufacturability in mind? Does the material selection make sense when balancing cost and performance? How many layers and lamination cycles are needed and could that number be reduced in any way? Has part size and panelization been considered? Are there any specific design features that push traditional design rules? All of these things have a direct impact on the manufacturers yield and the subsequent cost of the PCB.

One question that is rarely asked however is this:   how does a PCB sourcing strategy impact yields? I know, yields are typically associated with the manufacturer’s process capabilities and process controls as related to the printed circuit board design. But, let me pose a few questions to help shed light on the impact that PCB sourcing can have on manufacturing yields and subsequent profitability.

Have you ever wondered why it is so difficult to find a fabricator that can meet ALL of your needs? Wouldn’t it be great to find the perfect manufacturer, the one that has amazing service, does exactly what they say they are going to do AND has competitive pricing (total value, not just board price) across all the various technology levels?

The fact is, it is extremely rare for an OEM to have a homogeneous technology level across their entire PCB demand. On any given project, there may be a few 2-4 layer designs, a few 12 layer designs, a difficult motherboard design and maybe even a flex or rigid flex design.

It is also a fact that PCB fabricators have a “sweet spot” that best fits their equipment set, engineering expertise, facility size and company culture. Very often, browsing through a website or brochure will leave the impression that a manufacturer provides a “full range of technology”: 2 layer to 30 layer, .010” drill to microvias, standard materials to specialty materials, quick-turn prototype through volume production. At the end of the day, no fabricator wants to turn away business and they try to do their best to supply what their customers need.

BUT, there is always be a technology level, material set, or delivery window that each shop excels at. Their yields are maximized, the corporate culture embraces the technology and lead-time and ultimately prices are the most competitive. As an example, a supplier that excels at building 4-8 layer standard technology, likely runs with yields in the 97%+ range. But, if they were asked to build an 18 layer with blind and buried vias and via fill, the yields would drop dramatically. If the supplier that excels at building 18 layer blind and buried vias and via fill, with yields in the high 90% range was asked to build a rigid flex, yields would drop dramatically.

When sourcing PCB’s and creating a robust sourcing strategy, the challenge is identifying that “sweet spot” that maximizes a manufacturers yields and selecting the best group of suppliers to meet YOUR unique needs. Logically, if a circuit board is being sourced with the supplier that is the “best fit” for that specific technology level, their yields are going to be maximized, pricing will be its most competitive and ultimately profits will be increased for the OEM and the fabricator. While this sounds like a simple concept, the implementation of this strategy takes time and resources that are not always available.

Printed Circuit Board Sourcing Strategy, are you guilty?

Printed circuit boards are often one of the most expensive components of an assembly and arguably the most important due to their functionality and criticality. All too often, when time and resources are stretched too thin, these custom electronic components are purchased using the same strategy and structure as commodity items.

A PCB sourcing strategy might look like this:

  •  Treated as a commodity versus a custom component
  • Procurement strategy is often made at a tactical, not a strategic level
  • Many are doing business with suppliers without a full understanding of the technical capabilities, capacity or financial situations of their suppliers
  • Static strategies in a dynamic market – this market is changing rapidly
  • The same strategy is used for domestic and off shore sourcing. “One size fits all.”

This strategy can result in increased risk in terms of price stability and performance, increased risk of supply chain disruption and increased overall cost.

Do you need to revamp your PCB strategy? Where do you start?

You start with the basics. First review your PCB technology and volume requirements. Your requirements can then be segmented by attributes such as standard technology, HDI, heavy copper, flexible circuits, etc. Then search to match suppliers to these requirements. Audit the facilities. Don’t hesitate to ask the tough questions to REALLY understand the type of work each supplier excels at.

Next make sure that you have fully developed your procurement spec. Does it clearly spell out your requirements? Are any of your requirements adding unnecessary expense? It is not unusual to find that a corrective action implemented for an issue that happened 10 years ago is driving a requirement that increases cost and just isn’t necessary in today’s manufacturing environment.

Case study using strategic sourcing strategy:

Once a strong, diversified supplier matrix is put in place, analysis on large programs is simplified. To give an example, we were asked to assist with a pricing review and analysis of how to reduce cost on a specific project. This project included a set of PCB’s with a wide spread of technology. One design was a simple two layer design, another included microvias with copper via fill and there were three with technology between those two extremes. The volume required was expected to be between 1,000 and 5,000 pieces annually. We started first with the design for manufacturability questions and recommended adjustments where possible to increase yields at the manufacturer and ultimately reduce the total cost of the package.

After this, we looked at the current supply base and sourcing strategy. The decided upon approach was to select three suppliers, each with different technology specialties, gather pricing for the package and review the total package to determine the best path forward. The results of that exercise are included below.

Case Study Picture 2-9-16

Case study: Strategic Sourcing Review, project volume 1,000 to 5,000 annually

As you can see, the lowest price option for each part number is highlighted in yellow. From there, we reviewed the package from a single-source, dual-source or three-source perspective. The single-source option was ultimately the more expensive approach, with a three -source strategy providing the lowest cost option when looking at the PCB’s only.

With a savings of $16 per set over the two-source approach, the company can be expected to save between $16,000 and $80,000 per year on this project. From here, they can determine if the additional costs associated with managing three suppliers on this project is justified by the savings.

Conclusion:

When analyzing a set of PCB’s to improve yields and maximize profits, the first place to start is with a critical review of each PCB design. Are there any attributes that are pushing your manufacturers standard design rules? If so, is this necessary to the design or is there another approach that could improve the manufacture’s yields, reduce cost, and ultimately increase profit? Once the design is finalized, a critical review of the PCB sourcing strategy should be completed. Does the technology of each design fit the sweet spot of the selected fabricator? Would a multi-source strategy result in cost savings that justify the expense of managing more than one supplier on the project? Just as time and effort are spent reviewing and analyzing the design, time and effort should be spent reviewing and analyzing the subsequent sourcing strategy. Matching the technology to the best fit supplier will optimize manufacturing yields and reduce overall cost.

Contact us with questions or for additional information!  www.omnipcb.com

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