BoardSurfers: Some Wisdom from Designing for a High-Volume Production OEM

At what stage in the design cycle do you start to think about the PCB material costs? What about the costs to assemble the PCB? Once a design becomes successful, should you then redesign it to achieve a scalable product? Placing components and routing them is just half the story. Your engineering efforts are paid off by the financial success of the products you create. This blog covers a few tips that you can use at various stages of the design process. Some essential and critical facts and recommendations that are usually not found in books or taught in the classroom; just call it experience!

Panelizing Your Artwork

PCB panelization is a manufacturing technique in which several smaller boards are manufactured simultaneously and mounted together as a single array. To panelize your PCB, you need to consider the points explained here.

Know the Panel

If you plan to produce at higher volumes, you must know your production panel, even if a contractor will assemble it. Creating the panel artwork yourself hands you the control to work with your contractor to get your assembly price down. Investigate their preferred panel widths. Reducing machine downtime due to production rail-width adjustments and recalibrations is a significant production cost factor. 

True high-volume producers standardize their panel widths where possible so that they can start assembling the next product even before the previous product leaves the placement machine. This is known as asynchronous mode and is used for Siemens, Fujitsu, and other placement equipment. These machines are like F1 racing cars—you must keep them moving to stay ahead of the competition with minimal downtime in the pit during changeovers.

Control the Cost

The sizing of your bare board PCB is also critical to your bare board cost. This is typically the component of the highest cost in your BOM, except for advanced chips. The formula for PCB price versus PCB size is a non-linear equation. Small increments in PCB size can sometimes cost zero dollars but can also often lead to a double-digit percentage increase in the cost. Understanding how the production panel size and the fabricator’s material sizes fit together is critical to understanding your bare board costs. This topic is a whole article on its own. Watch this space for more on that!

The key to controlling your panel costs is understanding the requirements of both the assemblers and the fabricators. One approach is to fix the panel width for the best production cost while adjusting the panel length to improve the PCB purchase price.

Control Narrative of Panel

Now that you have created your panel artwork, you should also add information about the position of each PCB within that panel.
How best to determine if you have a systematic problem? With PCB position marking on each PCB in the panel, you can diagnose that “This issue always arises on the component in the bottom-left corner of the panel; there must be a systematic flaw in the production, not the component...”

Self-Annotate

Provide adequate tooling, fiducials, and other aids in your panel artwork. Once again, talk to your assemblers to understand their equipment, the assembly process flow, and what features they need. Also, add appropriate tolerances to your master drawings to ensure the best results in production.

Managing Change Release and PCB Revision Control

PCB revision control is the process of tracking and maintaining changes to a PCB design. Some tips and recommendations for managing the changes are covered here. 

Mark Them All

The first fundamental building block for a controlled environment is to directly number your PCB. If you plan to be in the business for a long time, expect incremental improvements, customer variants, or complete redesigns. Fundamentally, you need to be able to pick up any PCB in the future and recognize that “This is a PCB 248xxx rev01, not a 246xxx-02…”. There are several different ways how firms apply this in practice. Many firms put the bare board number directly into their Gerber artworks. This is the number and revision of the actual board design itself; the item which will be ordered as a commodity from the fabricator. However, once this board gets populated with electronic parts, it becomes a different “thing” requiring an assembly number or designation. Larger firms use Product Life Management (PLM) systems to organize these numbers.

If there is only one physical product variant, then go ahead and put the final product number into the silkscreen or wherever it fits. However, if your board is capable of becoming several different products depending on component population, then you might need a system that can apply extra digits at the assembly site. Consumer electronics will often apply sticker labels onto an IC or other available surfaces. However, in more industrial applications and automotive boards, you will often find copper power planes on outer layers due to significant electrical currents. These surfaces can be used to display PCB information and logos making use of the soldermask layer above. One such approach is to laser 2D barcodes directly onto the soldermask covering the plane.

Historically, PCB numbering would contain a relatable meaning. For example, a 13-0594-01 REV A could mean that the 13 is a PCB board, the 0594 is the project number, and the 01 project variant. However, many firms are already moving away from this system to purely sequential numbering. This is because there are only a limited number of possible four or five-digit combos possible in each meaningful block. We have seen situations where these numbers run out. Sequential numbering makes more efficient use of the total quantity of digits available. The disadvantage of sequential IDs is that you lose all inferred meaning to human operators. But in modern times, you are never far from a computer, a scanner, or a smart device. The days of memorizing numbering systems may be gone when quick access to the information you need is right at your fingertips.

Tracking PCB Supplier Fabrication Date and PCB Supplier Logo Space

To ensure on-time delivery and accurate branding, it's important to track fabrication requirements as discussed here.

Think Tracing

Product tracing becomes critical when your product takes off and moves to high-volume production. Designate an empty box in your PCB layout to reserve space for the fabricators to apply a production date. This enables you to trace any recalls or fallouts due to PCB quality back to a specific date and batch. This can also be useful information to have on lower volume and prototype boards. This date of fabrication is added by the fabricator directly prior to every batch they run. Simply include a note in your master drawing that points to the reserved region on the board. The text simply tells your fabricator to “apply date here” in this artwork layer. Two digits each for both week and year may be sufficient. 

Hedge Your Purchases (Multi-Sourcing)

Having more than one supplier for the same product always makes sense. This can combat any supply chain risk, prevent requalification time lags due to supply disruption, and give you some pricing leverage across suppliers. Supplier market share can also be adjusted based on their quality and performance. Therefore, designate a single space where each PCB supplier can place their logo, so you immediately know when a customer return happens and which PCB supplier that board came from.

Standardizing Footprint Library and Padstack Naming Conventions

Finally, it is important to have control and oversight over the padstacks used in each design. This means any upgrade to pad or soldermask dimensions should be systematically recorded using footprint revision and version control. In high-volume production, padstacks that are not fully optimized for solderability pose significant problems. The high quantity of parts being processed at speed can quickly result in a large build-up of defective parts requiring rework to overcome soldering defects. For example, assembly line production volumes targeting, say 5 million parts per year, means dropping a new part into the delivery box every 4 to 5 seconds. Manually reworking a stockpile of defective parts by hand is both costly and hugely time-consuming by comparison.

To be successful, soldering, therefore, needs to be “right first time”. The feedback from all pre-series manufacturing should be translated into the design as soon as possible. In this eco-system, it is considered a sin to implement footprint updates to one single PCB design. Padstack improvements should be fed back to the library for use by other designers and your next design. This describes the need for padstack version and revision control. No two designs should ever be issued that contain padstack differences without clear systematic indicators of the change. This can be managed using EDM (engineering data management) software tools. Bigger organizations have their libraries managed by a team that maintains the quality of footprints and the introduction of new parts to the library.

If you do not have immediate permission to update your own library, then it is best practice to export any altered padstack files and store them in a folder alongside the board design file. These modified pads will now safely travel along with your design until the library version is updated. This prevents the risk of losing your hard work when some genius takes control of your design and decides to refresh all the padstacks to match the library. If this happens, the altered pad files remain safely intact alongside the design ready to be reimported once again.

A final note on footprint soldermask: If you order PCBs from a high-end fabricator, then you possibly trust them to handle your pad soldermask pullback. In this scenario, the artworks are generated with soldermask information that is 1:1 with the copper pad layer. However, if you rely on low-cost PCB suppliers, then you may need to take control of these soldermask openings for yourself to avoid some potential assembly and fabrication issues. In this scenario, the soldermask pullback is stored in your library and is visible in your artwork. What you see in the artwork viewer is therefore what you get on the board, with a bit of tolerance.

Wrapping it Up

These are just a few pointers from John Tiernan, Cadence Application Engineer's experience. We would also like to thank Patrick Davis for his insights and advice. If you have any further questions on related topics or wish to see a post on a specific topic, do write to us.

If you find the post helpful and want to delve deeper, enroll in the DE-HDL Library Development using DE-HDL training or Allegro EDM PCB Librarian courses. Read through Design in Harmony: Seamless ECAD and MCAD Collaboration (cadence.com) and Allegro Manufacturing Option Panel Editor – Panel Creation (cadence.com).

You can become Cadence Certified once you complete the course.

Cadence Training Services now offers free Digital Badges for all popular online training courses. These badges indicate proficiency in a certain technology or skill and give you a way to validate your expertise to managers and potential employers. You can add the digital badge to your email signature or any social media channels, such as Facebook or LinkedIn, to highlight your expertise.

To find out more, see the blog post Take a Cadence Masterclass and Get a Badge. 

You might also be interested in the training Learning Map that guides you through recommended course flows as well as tool experience and knowledge-level training modules. To find information on how to get an account on the Cadence Learning and Support portal, click here.

SUBSCRIBE to the Cadence training newsletter to be updated about upcoming training, webinars, and much more. If you have any questions about courses, schedules, online training, blended/virtual live training, public, or onsite live training, reach out to us at Cadence Training.