6 Key Considerations When Starting a New PCB Design

How often have you said to yourself, "I wish I would have known that earlier!" It's a fact that hundreds of decisions need to be made when starting a PCB design. The real struggle is which decisions need to be made first. A missed (or wrong) choice is similar to casting concrete. Once it's poured and cured, there isn't much that can be changed without a jackhammer. Many PCB designs have often been delayed or scrapped because of an overlooked decision.

This webinar will cover 6 key considerations that need to be made before starting any new PCB design:

• 1. Fabrication
  

• 2. Electrical
  

• 3. Mechanical
  

• 4. Regulatory
  

• 5. Procurement
  

• 6. DFM / DFT (Design for Manufacturing; Design for Test)
  

A cautionary note was brought to our attention regarding the bypass capacitors. "Usually generosity with bypass caps is a great thing, but beware LDOs as most go unstable if you go beyond the specified capacitance in the datasheet. There are a few out there that are stable at any capacitance." One example comes from Analog Devices: https://www.analog.com/media/en/news-marketing-collateral/solutions-bulletins-brochures/257253984LDO.Family.bulletin.pdf

One cannot follow a universal 15% rule of thumb because speed depends on the Dk.

Even if the Dk is the same for all dielectrics involved, a single rule of thumb cannot be created because one must account for the ratio of air and solder mask material, creating an "Effective Dk."

You can see below the effect of the dielectric's Dk getting closer to air:

       For a Dk = 4.6, the stripline would be 182 ps/in
       Microstrip would be 144 ps/in, a speed increase of 20.88%
       Embedded microstrip would be 168 ps/in, a speed increase of 7.68%

       For a Dk = 3.3, the stripline would be 154ps/in
       Microstrip would be 127 ps/in, a speed increase of 30.22%
       Embedded microstrip would be 142ps/in, a speed increase of 21.98%

Also, the microstrip geometry will need to be adjusted for impedance, which depends on Dk.

The Saturn Electronics website provides equation-based calculators. One can get good approximations, which is far better than a universal rule of thumb.

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They want WHAT document?

Despite modern design tools' ability to quickly generate documentation for assembly and fabrication, in many cases, the mentality of document delivery is to still 'throw it over the wall.' Sometimes we give far more information than needed. Other times, the fabricator or assembler comes to us asking for some odd document we may have never heard of, let alone created.

This webinar will discuss what documents are needed for fabrication, assembly, and testing, where it needs to be generated within the PCB process, and what aspects of the schematics, libraries, and PCB layout lend themselves to their creation.

If you are doing any of this documentation by hand, please join us to see what you can do to make the quick generation of accurate documentation much more straightforward.

This presentation is a small slice of the PCB Fundamentals training class that we have developed to assist designers in understanding all aspects of PCBs for successful manufacturing.

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DFM (Post-Layout Considerations) Part 1

Like most electronic engineers, you may find yourself trying to further refine your skills and knowledge of PCB layout, in addition to wrestling with its manufacturing and assembly aspects. In the past 20 years, there have been 4 monumental changes to the electronics industry, much of which we bear the brunt of, yet seem to be ignored by the industry:

• The electronics engineer's function is now 'cradle to grave.' In the past, the electronics engineer could hand it off to another department; now, the EE is responsible for the whole project.
  

• The electronics engineer was not taught layout concepts, let alone high-speed design concepts.
  

• The electronics engineer was not taught about manufacturing or assembly.
  

• Electronics used to start with the electronics itself. Marketing and mechanicals are now demanding form, fit, and function.
  

Fortunately, DFM (Design For Manufacturing) is not that complex. It simply takes a bit of understanding to know what goes on when your designs move through manufacturing and assembly. With this understanding, you can design so that your product will not be hampered by the "gotchas" and, in doing so, provide you with a better schedule and budget predictability and enable you to compress both.

Q&A's from Webinar

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DFM (Pre-Layout Considerations) Part 2

Last month we aired the DFM (Design for Manufacturing) introduction related to PCB layout considerations. We received a significant number of requests for the webinar slides and recording and the additional coverage of the topic.

This month, we will present DFM (Pre-layout Considerations) as part 2 of this series. As with the construction of any building, there must be a blueprint to implement; however, in the electronics industry, in our rush to get to PCB layout and beyond, we dive into the schematic with little or no game plan. Though many DFM concepts are implemented in the PCB layout, the foundation for DFM lies in the pre-layout considerations.

The webinar will include discussions on:

• The need for specifications and how to write a requirement
  

• Schematic 'etiquette' as it relates to the readability and formatting of the schematics
  

• The necessary elements of a footprint to generate good assembly and fabrication documents
  

Q&A's from Webinar

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DFM (Library Considerations) Part 3

Our prior webinar briefly touched on DFM (Design for Manufacturing) considerations related to libraries. Given its importance in DFM, we believe that this topic needs to be covered in greater detail. Therefore, our next webinar will be focused on the component library.

Though the topic generally applies to any EDA tool, examples will be based on the Altium Designer symbol and footprint editors.

Footprints:

• Mechanical layers - what should be included on each layer and the purpose of the layer
  

• Special cases - inductors, jumpers, and other commonly used footprints that tend to cause difficulties with the netlist
  

• Naming conventions - ensuring that names allow for understanding
  

• 3D - its importance in the libraries and how it impacts the component clearance rules
  

Symbols:

• Parameters - understanding the importance of the name given and the value's format to ensure a BOM that will be complete and correct upon completion of the schematic. We will also cover the key parameters that are critical for part identification
  

• Multi-module components - treatment of the pins and some tips to allow modification to the symbol once in the schematic
  

• General tips to ensure that the symbols help your schematic tell a story
  

This webinar "takes the mystery out of creating a library component."

Q&A's from Webinar

Example Robust Libraries

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DFM (Stackup Considerations) Part 4

Printed Circuit Board (PCB) stack-ups are a lot like a car. We use them, but most of us generally bring a car to someone to repair it. The less we know about what's happening under the hood, the more reliant we are upon others to provide recommendations or perform repairs and services. In a way, we are at their mercy.

We do a similar thing with PCBs - we generally hand it off to someone to deal with it. However, like a car, the more we know about the PCB fabrication process, the better informed we are about making decisions and calling the shots rather than throwing it over the wall and simply hoping for the best.

As we continue with our Design For Manufacturing (DFM) series, we will dig deeper into the topic of the PCB layer stack-up. We'll start by reviewing the manufacturing process. This provides us the foundation for the many decisions we have to make.

Topics include:

• How fabrication materials impact impedance
  

• The types of fabrication materials and why one must be cautious about their selection
  

• Via types and why there must be careful planning when using them
  

As a side note, we will be using the iCD's Design Integrity when demonstrating the concepts presented.

Q&A's from Webinar

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Beyond the Design and Layout of Your PCB

For many of us in the design and layout of a PCB, our design's manufacturing and assembly are outsourced. We provide documentation to our contract manufacturer and expect them to work their magic.

Documentation that was successfully submitted to a prototyping manufacturer may be unacceptable to a high-volume manufacturing facility. Libraries may have to be modified to handle pick and place machines. Components are moved to accommodate fabrication equipment tolerances. In some cases, the routing may have to be heavily reworked. Without a proper understanding of the design through the manufacturing flow, more time and money are spent correcting something that could have been done right the first time.

Knowledge of what is required after the Gerbers or ODB++ files are generated is essential. At this webinar:

Paul Taubman Nine Dot Connects
Paul will discuss Gerber files, ODB++, and IPC-2581 and their history, construction, and effective use

Ray Fugitt DownStream Technologies
Ray will discuss DFMstream to allow you to capture manufacturing issues before release to manufacturing.

David Hoover TTM Technologies
David will discuss issues that are commonly detected in the manufacturing process.

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Test Points - Before Layout and Way Beyond Manufacturing

Design for Test (DFT) does not occur naturally in design, especially with the advent of BGAs and components so small that one must use tweezers to grasp them, let alone probe them. Yet, the test points are one of the most straightforward items to add to a design for the test in fabrication, assembly, and labs.

In this webinar, we will cover:

• The benefits of test points
  

• Recommended copper structures
  

• The various approaches to using test points within Altium Designer
  

We provided the Altium PCB project used in the video. Feel free to download it.

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Mechanical Layers - Revisited

In 2017, we conducted a webinar on mechanical layers in Altium Designer. We introduced a mechanical layer set during that webinar, which many of you have used.

Watch the Video

Many innovations have been added to Altium Designer, making it easier to propagate established mechanical sets to new libraries and layouts. We will demonstrate these features in this webinar. Also, we will introduce a revised version of the mechanical layers. For those who are using our existing layer set, have no fear. The new features in Altium make it easy to stick with what you have already established.

The script used in this webinar was not created by Nine Dot Connects. As with any script in Altium Designer, any new version of AD can negatively impact the script's effectiveness. If you are interested in the script, we encourage you to log on to Altium's forum. Threads regarding this script can be found. Here is one thread that contains the script for Altium Designer 21. You need an Altium Live account to view the following posts:

Component Layer-Pair Type in AD18 - Altium Discussion Forums

Additional Information

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How to Tame your Mechanical Layers

Let's face it - mechanical layers are an important 'nuisance' in the design process. Getting everyone to use the layers consistently (or at all) is certainly half the battle; however, organizing the mechanical layers for documentation can be another hassle altogether. All too often, we are constantly turning on and off layers to see what we need to see during the layout process.

It may surprise you that there are ways in most EDA tools to organize all layers so that viewing the different aspects of the design is practically instantaneous. We will demonstrate this concept in Altium Designer. We will also provide valuable collateral at the end of the video to use in your design tools.

We provide the actual Altium Designer project files that we use in the webinar, along with the 6-page Mechanical Layer Configuration Guide.

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Q&A's from Webinar

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