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  • Choosing the Right Surface Finish

    Choosing the Right Surface Finish

    Balancing environment, shelf life – and cost.  READ MORE...

  • Elements of PCB Panelization

    Elements of PCB Panelization

    Panelize to optimize: faster builds, better boards.  READ MORE...

  • Flexible Heater Temperature Limits

    Flexible Heater Temperature Limits

    How high can they go?  READ MORE...

  • Collaborating with Service Bureaus

    Collaborating with Service Bureaus

    Time-to-market advantages encourage getting designs to scale quickly.  READ MORE...

  • Optimizing Mixed Signal Circuit Designs

    Optimizing Mixed Signal Circuit Designs

    Navigating the analog and digital worlds.  READ MORE...

  • Developing Organizational Culture for Troubleshooting

    Developing Organizational Culture for Troubleshooting

    Solving problems and adding value.  READ MORE...

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Designer’s Notebook

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Category: Designer’s Notebook

Small differences can have big consequences.

For as long as there have been printed circuit boards, the nominal thickness seems to have been set at 0.062″ – or in Latin, 1.5748mm, but call it 1.6mm for short. In practical terms, the standard dielectric materials available support this board thickness while providing anything from two to 20 layers. I imagine four layers is still the most common use case.

Larger boards will need more connections and require more stiffness. To manage connectivity and flatness requirements, standard PCB thickness targets ratchet up to 2.4mm and 3.2mm. On the low side we find 1.0mm and go down to 0.8mm. All these targets are related to using so-called gold fingers as a printed edge connector.

It’s about connectivity and solderability. This was handed down from the backplane and daughtercard configurations found in our tower computer systems. The motherboard has expansion sockets and the memory cards come with fingers to plug and play. As a result of this variety, many connector vendors that market to plated through-hole technology users will offer different pin lengths that fit the range of board thickness options.

Read more: Designing for Board Thickness

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Category: Designer’s Notebook

Rigid-flex brings the best – and worst – of both worlds.

Combining all aspects of a flex circuit with a rigid board that makes full use of HDI techniques is one of the breakthroughs of our time. The stacking connectors for board-to-board or the typical flex circuits are bypassed. If you've ever tried to connect a flex circuit to a stacking connector, you know that's a bottleneck in the process – blindly positioning the flex connector over the mating connector can be fiddly to the point of destroying the connectors. Now what?

Rigid-flex projects remind me of digital/analog projects: the best of both worlds and the worst of both. Just for starters, if the team is taking this route, you know they are serious about holding things together with all possible integration. Both technologies are well understood on their own, though the rigid camp is larger and better understood.

Flex circuits on their own. Flexible printed circuits (FPCs) require more than a change of materials from their stiffer cousins. Additional tolerance must be designed into the data. Reason: The different types of material stacks used in the manufacturing process. For the most part, a flex will also have a rigid section where the connector is mounted. The stiffened area could also be extended to host the ESD protection, an LED or microphone; we're flexible.

Read more: Getting Flexible

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Category: Designer’s Notebook

Put the pedal to the metal in your PCB layouts.

Printed circuit board design evolves over time and the rate of the evolution is not slowing. High-speed digital design becomes a key topic as we move forward.

By the time you read this, I’ll be officially old. Early retirement age is 62 and I was born in ’62 so I’m eligible for those senior discounts. One of the things that happens as we age is time seems to go by even faster. We’ve seen so much, less is novel. We’re not plowing new furrows but rather deepening ones we’ve tracked before.

I say that to say this: Circuits keep switching faster all the time. What worked in my early days no longer gets it done. My first computer didn’t have a hard drive. It had two floppy disk drives, and they were the ones with 360KB­ rather than the smaller, stiffer 1.4MB. I had DOS on one floppy and a modem driver on the other. The baud rate was a blazing 1,200B.

Read more: The Need for Speed

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Category: Designer’s Notebook

Which PCB technologies are best suited to survive 100 years?

The Goal: Build an electronic device that will outlast everyone currently living on Earth. Looking back 100 years, few of us were here and the same will be said in the year 2124. Just reflecting on the brevity of life but we will take a century as forever.

One hundred years ago – 1924 – was the year that the Computer-Tabulating-Recording Company rebranded itself as IBM. Electric blenders, vacuum cleaners, traffic signals and television are among the inventions of the period. Two inventors of the era were leading us toward printed circuit boards though their patents were not commercially successful. Time would prove them to be quite insightful.

Looking back to move forward. PCBs finally took hold around the middle of the century while integrated circuits followed another 25 years later. My "forever" board is going to make use of these early transistor-to-transistor logic (TTL) components that predated complementary metal-oxide-semiconductor (CMOS) technology. The physically larger transistor gates and the 5V logic are a concern. Both types were used on the Voyager space probes to build the guidance and other systems. There was also a fully discrete version of the computer as a backup to the backup. I have confidence in those old Texas Instrument parts.

Read more: Century Circuits

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