Archive for February, 2016

Conductive Inks vs. Nonconductive Inks – Part II

Written by Rush PCB Inc on . Posted in PCB Manufacturing

In the first half of this column, we began a discussion of the pros and cons regarding the use of conductive inks versus nonconductive inks to fill vias. The images below show cross-sections of a via-in-pad with nonconductive ink on the left and VIP with conductive ink on the right.

Via-in-pad  2

Via-in-pad (VIP) filled with conductive ink.

Via-in-pad

Via-in-pad (VIP) filled with nonconductive ink.

In that column, we discussed a design that required a nonconductive ink in the through-hole via and conductive ink in the blind via. Now we ask, what were the drivers behind this decision?  Why would one use two different types of inks in vias in the same PCB, and why conductive vs. nonconductive ink? The answers are actually a bit more complex.

Copper plating is one factor, as an example. For years it has been generally accepted that copper plating is not a viable substitute for ink (conductive or nonconductive) to fill a through-hole via, buried via, or blind via. It was believed that to plate a via shut and to cover the surface with copper would take “forever,” relatively speaking, if it could be done at all.

One reasoned that not only would the process of plating the via shut with copper be prohibitively time-consuming, but even if it were technically possible to fill the hole with plated copper, the unwanted consequence of plating so much copper in the hole would result in excessive “button” or surface copper height that would lead to other defects and/or reliability risks.

Blind via plated

Blind via plated shut with copper.

Nowadays there are several efficient processes for copper plating to fill vias; two of these are pulse and DC rectification. Some require button plating, a two-stage process; others have evolved to the point where a single-stage panel plate will fill certain via structures while depositing less material on the surface, thereby leaving a manageable surface copper thickness. In this way, one can continue to produce a high-density product without the need for a secondary ink-filling operation.

Further, there are solutions to filling micro, blind and buried vias that require no additional process time or steps; e.g., resin or B-stage fill. The consensus was that it wasn’t possible to do this reliably. While conventional prepreg (B-Stage) historically struggled to fully and consistently fill vias, there are now specialized prepregs and bonding materials specifically engineered to do just this process reliably.

One laminate company produces a series of FR-4, lead-free, polyimide, low-loss and other high-performance laminates and prepregs.  Within their product line they offer a sub-set of prepreg (B-Stage) called the VF-series (whereby VF is an abbreviation for via fill).

Via Fill

Via Fill (VF) prepreg product, where core and prepreg are combined to create a pure, homogeneous material package.

Where we have the instance of a buried via filled with one ply of VF material, the blind via is fully filled with resin, and the dielectric distance between outer foil and inner sub assembly is very uniform. In this case, the VF matches the family of core and prepreg it is combined with, so that it permits the creation of a pure homogeneous material package, eliminating the need for a hybrid material / laminate package. The VF prepreg has been engineered for enhanced rheology and filler content so that during the lamination process the blind and buried vias found in a sequential lamination sub assembly will be fully filled.

VF Prepreg is just one example of available materials designed to fill vias during the lamination process, thus eliminating the need for a secondary operation. What process and material should you use? To make the best decision, you need to understand not just what result you want to achieve, but why.

Not long ago I had an application involving a customer’s requirement of a specific brand of conductive ink to fill a small through-hole via. The assembly was a double-sided PCB on a relatively thin (0.010″ thick) PTFE/Teflon material.

The ink-filling process requires a planarization or sanding operation after the ink is cured in order to remove excess ink from the copper surface. The planarization process always includes some inherent risks and/or limitations such as:

  • Dimensional distortion of the panel of PCB material.
  • Imprecision, resulting in uneven copper thickness and poor control of circuit etching.
  • Reduced peel strength of the surface copper.

In this case, all these negative aspects of planarization were amplified because the material was a soft; thin Teflon with RA copper. This material is highly unstable to begin with and susceptible to distortion.

The PCB manufacturer struggled to meet the customer’s requirements, but excess cost, time to produce, delays, and lower yields resulting when compliant product was finally produced were a real problem, prompting further discussion with the customer.

A breakthrough occurred when we began to ask why we were using certain materials and questioned the necessity and benefit of each step in the process. We realized that the via filling; i.e., the specific material requested by the customer, was being used to prevent solder from flowing through the vias during assembly. But what else was it there for?

After critical examination, we realized:

  • That there was no need for conductivity in the filling material , let alone any reason for it to be limited to the customer’s specifically preferred ink material.
  • There was no need for a copper pad to be plated over the surface of the material or via, since nothing was being soldered on top of the via.
  • There was no need for a specific brand of ink material.
  • Alternative materials and processes could therefore be explored.

After all, we began to examine the real purpose that the via filling was intended to address, and more importantly, what it was not there for. The material had been used, all along based upon a group of assumptions that, when examined, weren’t true and did not justify the use of that specific (and costly) ink material. Its use simply could not stand up to challenging questions, such as added reliability, electrical advantages or mechanical aspects or even thermal characteristics or properties. It contributed to none of these justifying criteria.

rush_figure5

Buried via fully filled with resin; note that the dielectric thickness between the outer foil and the inner subassembly is very uniform.

In summary, when evaluating a new product, manufacturing process, etc.:

  • Challenge any long-held assumptions.
  • Gather information from multiple sources.
  • Qualify that what you have been told by others is really best for your needs and not skewed merely to support the choice of a specific product.

Manufacturers must talk with the designer to understand what designers really want to accomplish and why. Designers must speak with manufacturers in order to understand the intricacies of the process. Finally, as technology evolves and more innovative solutions for emerging applications or enhanced solutions for existing ones are found, cooperation and collaboration are the keys to optimizing decisions and selections.

Guidelines for Application Driven Crucial Pcbs

Written by Rush PCB Inc on . Posted in PCB Manufacturing

pcb application

Manufacturers are rapidly adapting to the increased demands for printed circuit boards, specifically where the data transmission speeds are becoming a matter of life and death. With a growing number of applications and equipment using PCB technology, it is crucial that you communicate your needs with your manufacturer to ensure that the final product meets or exceeds the expectations.

Uses in Drone Operation

 

The rapid growth in drone technology is even outpacing our own understanding of the use of this technology.  Already we are seeing stories in the media about the public use of these devices which are creating the need for regulation that has not yet been established.  Used by marketers, commercial photographers, and even in livestock management functions and surveying, drones are becoming a both a cost effective and innovative tool to accomplish jobs in new ways that were previously not possible.

 

However, one of the most critical uses for drone technology has been adopted by the military.  The use of drones has the capability to evolve combat strategy around the world, reducing the number of casualties every year and helping to augment existing surveillance technology.  Used for reconnaissance in areas too dangerous to risk human lives, drones can also be equipped for targeted air strikes.

 

However, when innocent lives hang in the balance, nowhere is it more important to ensure that printed circuit boards controlling this hardware will perform flawlessly, collect and transfer information in real time and better equip operators with the information that they need to effectively use this tool in their arsenal.

 

Medical Applications

 

In medical environments, the importance of real time communication can mean the difference between life and death.  From use in devices as standard as heart monitors to more advanced life support systems, the significance of timely data transfer without delay can influence the success of medical response and intervention.

 

Printed circuit boards in medical devices include applications in equipment such as CT scanners, magnetic resonance imaging, medical imaging systems, flow rate and dispensing systems and so much more.  It is an area of electronic performance that cannot be compromised and requires that the right PCB’s are installed at the outset. 

 

Learn From Others’ Mistakes

If you have not fully disclosed your needs in a printed circuit board with your manufacturer, you may find that you are not working with the right devices to meet your needs.  This can create delays and cost time, money and even lives.  By sharing your design and functional needs with your PCB supplier, you can rely in input from their industry expertise that you will be purchasing the best possible product to achieve your objective.

 

Among the common omissions that manufacturers are tasked to address after the fact that are being discovered include omission of apertures required, exclusion of the drill file, the tool inventory is missing, as well as deficiencies of inner clearances and/or the annular ring.

 

When placing your order for PCBs, ensure that you have provided enough information to your customer service representative to empower them to get you the right product for the job, within your budget and by your deadline.

Present Trends in Laminate Materials for Printed Circuit Boards

Written by Rush PCB Inc on . Posted in PCB Manufacturing

 

Laminate Materials PCB

 

FR4 Has Been the Standard

FR4 has long been considered the standard for performance in printed circuit boards.  Composed of woven fibreglass with epoxy resin, the fire resistant nature of this component has made it very popular for application in high electrical insulation as well as consistent mechanical performance even in very diverse environments.

 

While also popular for use in switches, relays, arc shield and screw terminal applications, FR4 is now being replaced by newer technology when electrical performance considerations require a more efficient solution.

 

Halogen Free

The migration to FR4 printed circuit boards that are halogen free has been driven by increasing concern over the environmental impacts.  While this is not currently a regulated requirement by governing jurisdictions, it is believed that this could occur in the future, so many are exploring the possibility now.  However, while there is observed to be some competitive advantages for companies to be able to label their products as Halogen-free, the electrical differences in the composition of these PCBs is what creates a concern for users.

 

The Emergence of Polyimide

But even as effective as FR4 has been for electronic and computing applications, it did recognize some deficiencies and that has led to the development of polyimide laminates which are seeing tremendous growth.

 

Featuring a higher heat tolerance and physical flexibility, polyimides are manufactured for use in high temperature fuel cells and can be used by the electronics industry in flexible cables. The largest segment of growth for this printed circuit board technology is found in the military and aerospace industries.

 

When Every Loss Matters

Over distance and time, as frequency increases losses can occur. The development of high frequency laminates has been undertaken to address these concerns. These printed circuit boards offer more stable characteristics and allow for a smaller percentage of loss. 

 

While FR4 circuit boards might experience dielectric or conductor losses of up to 10%, ceramic filled PTFE circuit boards are showing increased efficiency with losses of only 2%. With improved performance, many new applications are requiring this narrower margin of performance.  Ceramic is proving to be great for high heat conditions such as solar energy boards and is more robust for uses in outdoor environments.  However, while resilient to temperature and humidity, it is more expensive and not ideal of installations that require high speed data transfer.

 

Selecting the Right Material for Your Need

When selecting the appropriate printed circuit boards for your project, it is important to identify the required properties needed for successful performance within your application. 

 

It is possible that FR4 may still continue to meet your needs, however when specific criteria such as increased heat resistance and/or the efficiency of electronic transmission, you may want to consider some of the emerging products which have been designed to meet these needs. 

 

Your provider should be able to assist you beyond just finding the best price, but also helping to assess the best product with the proven performance to ensure your success.