Powerful Prototypes: Why Datasheets Matter

Some parts just look cooler than others. One of my favorites is the edge mount high-speed RF connector. I'm not sure why, but I just like the look of them. Unfortunately, "I like the look" doesn't necessarily translate to "It is easy to build." The edge mount connector requires a proper footprint and a match with the PCB thickness, and this is where the datasheet comes in (Figure 1).

Benson fig 1.JPG 

Figure 1: Edge mount connector.

The center pin needs to be flush with the board surface, so if the board is too thin, the assembler will have to use extra caution to ensure that the air gap is on the back side of your board. Doing so will reduce the mechanical strength of the connection. To prevent that from happening, these parts come in multiple varieties to accommodate different board thicknesses. Whenever possible, match the opening of the connector labeled "board thick" in Figure 2. Without the datasheet, you may have a perfect footprint, but still not be able to mount the connector because of the board thickness.

Benson fig 2.JPG 

Figure 2: Table from a Cinch Connectivity datasheet.

If the PCB is too thick for the particular variant of connector, you probably won't be able to put the connector on. If the board is thinner, whoever is assembling it will have to take extra care to ensure a solid and straight connection. Any air gap on the solder side will need to be filled with solder, which can change the signal propagation characteristics of the connection.

Some of these connectors will only have one or two board thickness options, and some more, so you may not be able to match your board thickness exactly. But, if you can, you will end up with a more reliable and robust installation. Just make sure you also follow the electrical and footprint guidance in the component datasheet.

The order of pin numbering is another reason to never assume but to dig up the datasheet. Our all-things-about-electronics-manufacturing standards body, IPC (Association Connecting Electronics Industries), specifies the proper numbering order for most components. That's a pretty nice thing that they do there, but it's not always enough to prevent layout mishaps without the datasheet—case in point, a line of small PCB mount switches.

IPC calls out pin numbering for dual inline components, with pin one on the upper left (at zero degrees rotation), counting down, then over to the bottom right, and counting back up (Figure 3).

Benson fig 3.JPG 

Figure 3: Pin numbering for dual inline components.

Given that, it would be logical to assume that all dual inline components follow the same pattern—logical, yes, but accurate, no. Multi-color LEDs, connectors, and switches are some of the more common offenders.

In this particular switch, it's not just a case of the numbering not following convention; it's also different from one variant to another. I understand why. The switch isn't changed between through-hole, top mount surface mount, and side mount surface mount, but the leads have to be accessible from different parts of the package.

The following two footprints are from the same switch: one mount on its side, and the other, standing up (Figure 4).

Benson fig 4.JPG 

Figure 4: Two footprints from the same switch.

The pin one numbering doesn't follow convention, nor does the numbering of pins 4–6. And, you may have also noticed that the two are top-to-bottom mirror images of each other. Ugh.

This is why my mantra is: Always check the datasheet. Always.

Duane Benson is marketing manager and CTO at Screaming Circuits.

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2020

Powerful Prototypes: Why Datasheets Matter

04-22-2020

Some parts just look cooler than others. One of Duane Benson's favorites is the edge mount high-speed RF connector. Unfortunately, "I like the look" doesn't necessarily translate to "it is easy to build." The edge mount connector requires a proper footprint and a match with the PCB thickness, and this is where the datasheet comes in.

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Powerful Prototypes: Manufacturing in an Uncertain World

03-25-2020

In the best of times, electronics manufacturing is an exercise in taking chaos (in the form of data and information of multiple non-aligned forms and formats) and creating order (in the form of a working PCB). As I write this, the coronavirus has been declared a global pandemic, and the primary theme of the day is uncertainty. Duane Benson shares four things you can do to better ensure that your projects can be built and improve your habits.

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Powerful Prototypes: An Open-source Adventure

02-26-2020

Duane Benson describes the latest board design project he has been working on in his off-hours—a motion-sensitive lapel pin—including compromises, mistakes, and lessons learned

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Powerful Prototypes: Five Technological Shifts in the New Decade

01-08-2020

Depending on your perspective, we are either starting the last year of the old decade or starting the first year of the new decade. But regardless of what you call the decade, a lot of change is in store. Duane Benson shares five of the more significant technological shifts directly ahead of us and how to respond.

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2019

Powerful Prototypes: Cost Reduction in Design

12-11-2019

Getting custom electronics manufactured is not cheap, fast, or easy. Fortunately, there are ways to keep costs down and yields up without adding cost. Duane Benson shares six ways to keep costs down and yields up that you can do without a lot of effort.

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Powerful Prototypes: New PCB Fab Technology—What You Need to Know

11-20-2019

Exotic materials have been around for a while, but being “exotic,” most of us could safely ignore them. However, as clock speeds increase, and board sizes decrease, some of those exotic materials are getting close to mainstream. Duane Benson shares some of the newest terminology you might see in your daily electronics adventures and will need to be familiar with when venturing beyond a standard, rigid FR-4 PCB.

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Powerful Prototypes: Panelization—What Is It and Why Would You Want It?

10-30-2019

We see orders for a single board, and we see orders for thousands. “A few thousand” falls way outside the realm of “prototype,” but in the startup and open-source worlds, the lines are blurred. Once you order more than about 50 boards, a few things change; for example, you should consider ordering your boards in a panel, also called arrays or a palette, of multiple boards.

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Powerful Prototypes: Never Assume—A DFM Story

09-19-2019

I write a lot of words about DFM and best practices for PCB layout. Working for a manufacturer, I regularly see the results of not taking DFM seriously. DFM is something never to be taken for granted at any point in the design cycle, and I mean at any point in the process.

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Powerful Prototypes: 5 Common Myths About Solder Mask

08-14-2019

Before parts are added, a typical PCB has four ingredients: substrate, metal, solder mask, and silkscreen. Solder mask, in particular, seems to be looked at as a great place to cut when costs are tight, but Duane Benson disagrees. Read on as he dispels five common myths about solder mask.

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Powerful Prototypes: The Ideal Bill of Materials

07-10-2019

A good portion of a quality electronics build is simply the result of clear information. Not long ago, I wrote about the set of files containing the information required by your manufacturing partner to ensure a quality build.

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Powerful Prototypes: Moisture Sensitivity—What’s the Risk, and What Can You Do About It?

04-18-2019

I recently traveled to New Orleans, Louisiana, for a week of beignets, fried food, and urban exploration. It’s a good thing that parts of the exploration came in the form of walking as some level of exercise was needed to compensate for the lack of greens and heavy emphasis on the word “fried” that went along with most of the food.

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Proper PCB Storage: Top Three Hazards

03-28-2019

Overall, our modern world could not exist without PCBs; they are everywhere, but they aren’t items to be taken for granted. Like most technology, PCBs need proper handling and storage. PCBs don’t last forever and are even more vulnerable before the parts are soldered on. The solderable metal surface is very thin and subject to a number of potential problems, especially if not stored properly.

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Seven PCB Cost-reduction Design Tips

02-11-2019

Like everything else in the modern world, design decisions can have a pretty big impact on your manufacturing cost. Here's a list of seven design decisions that can make your manufacturing more affordable.

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Eight PCB Assembly Tips for 2019

01-17-2019

It's now 2019, and all I'll say on the coming year is that we are in for a wild ride. The last few years have been pretty crazy, and 2019 looks to continue that trend but amped up. While predictions might be fun to muse upon, they really won't help you get your job done. So, here's my top eight pieces of PCB assembly advice for the coming year to make up for that.

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2018

What Is Your Supply Chain Telling You About Components?

12-24-2018

Right now, many, many parts are in short supply, or unavailable with extraordinarily long lead times. Allocation is the word of the day and substitutions are your friend. Sure, electronics components shortage happens every now and then in this industry. It's a periodic nuisance, but what should you do for the long term? Read on.

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Electronic Manufacturing Files: What We Need for PCB Assembly

12-07-2018

As PCB assemblers, manufacturing is all about taking data and delivering good working circuit boards. It can be just data, as in full turn-key, data plus some parts, or a partial turn-key or a kitted job. Regardless of whether you're sending parts and boards or having us buy everything, PCB assemblers need good data, and a lot of it.

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The Future of PCB Designs

11-28-2018

Duane Benson designed his first PCB using tape and etch-resist pens from RadioShack. He penciled the schematic on graph paper, drew the layout directly onto the single-sided copper-plated board, and then etched it. At the time, commercial PCB design wasn’t too different. In his column, he talks about the advancements in PCB design and the key considerations when designing boards.

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Top 5 Things to Know When Moving from Hand Assembly to Robotic Assembly

11-14-2018

A lot of factors go into the decision to hand-build or outsource circuit boards. When the decision is to outsource, there are a few important things to consider. Some things that work fine when hand soldering may stand in the way of quality, repeatability, and reliability when machine assembling. Here are some of the most important considerations when changing from hand-build to outsourced.

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Top 5 Ways to Mitigate PCB Component Availability Problems

11-07-2018

The electronics design world is by now aware that we're in a very serious period of components shortages. Allocation and shortages hit every few years, but this one seems to be the worst in recent memory. It could be a problem until 2020 and the supply chain and world of components manufactures will likely be a different animal coming out of it. Here are five things you can do to minimize the effects.

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