Archives for December 2014

3D PCB Design – Far from Flat

Being the young whipper-snapper that I was, I never considered the manufacturing issues that could occur during the assembly phase of any of my designs. My mentor at Rockwell International, Frank Caster, was an engineer and after my first layout placement for a Peacekeeper Missile Program design, he schooled me on the need to verify that the placement would work with the overall system design. I had no idea what he was talking about!

Frank asked me to follow him to a lab with a security guard at the door and a combination lock on the door. Upon entry to the lab, I got my first look at a portion of stage IV of the Peacekeeper missile, called the Missile Guidance Computer System (MGCS).

My PCB design was just one of the over 20 boards that made up the MGCS. Frank told me, “Vern, the world is not flat and neither is your PCB!” He explained that my board had to fit into one of the slots in the chassis I was looking at and that it could not interfere with any of the other cards within the chassis. The cards would have to be able to be maintained for years, and it would not be good if parts were knocked off the other boards when cards were replaced.

I was then shown a mockup of the MGCS and some lab technicians that were using X-ACTO blades to cut tiny 1:1 scale PCB components out of foam board. They were making a mockup of my design placement, completely to scale, that they could fit into the chassis with other scale cards in order to make interference measurements – a process that I was told took an extremely long time.

A light came on, and a bell rang in my head. I now understood that just because my design worked for me, it did not mean that it would work for everyone else!

In essence, every PCB we design has to go somewhere else. Whether it is an intricate missile guidance chassis, or a simple box, it has to fit perfectly into the full system.

Fortunately today, we have powerful computers that allow us to create 3D models to check mechanical measurements within our designs. But, until recently these systems had to be run by highly trained mechanical engineers. The PCB guys were at the mercy of another process to let them know if their designs would work.

But NOT ANYMORE! Xpedition is now available with integrated 2D and 3D layout, and the power of 3D has been put into the hands of the PCB design engineer.

Take a look at this video, 3D Layout with Photo-realistic Visualization, and see how 3D layout helps you visualize and validate your design as if it were already manufactured.

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5 Proven Strategies for Reducing PCB Prototype Spins

For PCB designers, there are two choices. First, you can design in a vacuum, and then hunt for a manufacturing chain that can build the design. Second, learn about your manufacturing chain and optimize your design to the fabricator’s strengths while maintaining desired functionality.

Here are five strategies that help you plan ahead for success, without adding weeks or unnecessary cost to your design cycle.

1. Research and select suppliers earlier in the design cycle.

The design team knows that at prototype design completion, the next logical step in the design process is to get back a working example of the prototype design for testing. Though this represents one logical step to the design team, this process consists of multiple steps—components must be procured; the PCB has to be fabricated; and the parts need to be correctly attached to the PCB. How this manufacturing flow ultimately occurs is up to the design team to select and manage.

Understanding the manufacturing flow, including component availability and service-provider capability, ahead of time can reduce the chances of rework and redesign, says Duane Benson, marketing manager at Screaming Circuits, a Canby, Ore.-based assembler,  Knowing what you’re up against reduces risk.

In our discussions with PCB design teams, we find a correlation. Professional teams turning lots of simpler designs with wide tolerances in the process window tend toward using a one-stop supplier for the overall convenience. Professional teams whose designs require careful tuning and attention to manufacturing details tend toward managing each relationship throughout the build process, handpicking each supplier for their strengths, abilities, and turn times. For some teams with limited budgets, price can be much more important than turn times. For other teams under tight deadlines, fast becomes a priority. Of course, in all cases, the PCB must be manufactured to the design.

Requirements can change from project to project. But that doesn’t necessarily mean you need a different supplier for each project. Talk with suppliers’ customer service technical teams or sales teams, and determine just how well they can respond with quality/turn times/pricing/delivery across the whole range of your anticipated project styles. Chances are good that the conversation time will be well spent by finding the right supplier for your team’s typical project constraints.

Three key items that will come up in the discussion are PCB fabrication, parts procurement, and assembly:

? Fabricating the PCB that serves as the connection medium for all the components and connectors that make up your circuit design. While this may seem like just another part on the design team’s bill of materials (BOM), this is a critical, custom-manufactured part. It requires adherence to your design parameters and can represent the most variable cost in the BOM.

These are the chips, connectors, and other parts that operate to make your circuit perform as intended. The components come from a parts distributor or retailer. The more one-stop services your manufacturing chain supplies, the more likely they will offer the parts procurement services for you… at a price, of course.

? Many design teams prefer to take a very hands-on approach with parts for their prototypes. This is neither the time nor place for parts substitutions to save cost; that step comes later. Direct involvement by the design team requires careful attention to detail and time, but the team also eliminates a number of potential bugs in the prototype with this approach, saving time and cost in the long run.

? The process of attaching components to the printed-circuit board. Depending on the design team, you may or may not have the expertise or equipment to perform this function yourself. As parts and designs get smaller and denser, the need for an outside service becomes more indispensable.

In the process of getting to know your manufacturing chain, you should assess your contacts for their ability to consult on your design particulars. The more advice a manufacturing supplier can give you, or help make your design optimization more efficient, the more value they provide to the design process, and that’s free consulting help to you!

2. Optimize for cost and performance before layout.

Not long ago, our colleague at Screaming Circuits, Duane Benson, blogged about optimizing designs to remove unnecessary components. In a general sense, the fewer components that are needed to implement your circuit, the more reliable your end product. Screaming Circuits’ Benson says, Reuse of code and of schematic modules can be a great help in keeping schedules under control. However, if you do so, it’s important to make sure every part of what you’re reusing is necessary.

Costs don’t simply refer to the number of components used in a design. They also tie into PCB real estate and design complexity, flying probe test times, and opportunities for design-related manufacturing issues.

3. Develop your layout to the fabricator’s sweet spot.

Nancy Viter, Sunstone Circuits’ manufacturing director, has wise words about fabrication: While almost anything that you can lay out can be built, it is much more cost-effective to design to the heart of the capability range of your manufacturer, when possible.

Regardless of whom you choose, your fabricator has a sweet spot—that place where designs are well inside the middle of the manufacturing process window. From this spot, minor variations in manufacturing still keep your design well inside manufacturing capabilities, and thus increase your yields and reliability.

4. Verify your layout’s manufacturability with a supplier DFM tool.

A reputable PCB fabricator will run your design through a design-for-manufacturability (DFM) tool to check for errors above and beyond any visual inspection of the design details. A top-tier fabricator will make that report available to you when submitting your design for quotation. Using the contents of that report, which verifies if your design will fit inside the manufacturing process, is a valuable step to getting a properly fabricated board, and is the first measure toward developing a board optimized for production.

5. Manage prototyping costs and hidden costs.

Prototyping creates more robust designs from the first revision with proper preparation. While it may seem like a lot of useless preparation work, consider the hidden costs of a five-person design team, spending five person-days to complete the preparations mentioned here. Such a preparatory process might save you at least one prototype spin of—you guessed it—five calendar days. Except five calendar days for a design team of five is a total of 25 person-days.

Conclusion

When the PCB design is simple, or far away from the current technological edge, these strategies have less impact on your design cycles. One school of thought is that, as you move to surface mounts to QFN/QFP packages, or as you move to tight tolerances in circuit timing, then these strategies become more and more important.  Of course, the other school of thought is that, as you start out, even though the designs may be simpler, it’s the designer’s skimpy knowledgebase that needs more support.

We consider ourselves partners with our customers and as an important resource for them, says Sunstone’s Al Secchi, We are only successful when we can help our customers be successful in avoiding design issues that can affect either the manufacturability or functionality of their PCB. We know how important it is for them to receive functioning boards on time, and we pride ourselves with an on-time rate that consistently exceeds 99.5%.

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