Tag Archives: printed circuit board

And the Race Goes On

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AUP package The race for the smallest part is still going strong. That and the fact that basic logic gates are still with us is affirmed quite well with a new set of chips from NXP. The 74AUP2G00 is a dual two-input NAND gate in a no lead XSON8 package at just 1 x 1.35mm. That’s not the scary part. The scary part is the lead pads under the part are 0.15mm wide and just 0.35mm pitch center to center. That’s 0.0059″ and 0.0138″ respectively. The gap between the pads is 0.2mm (0.0078″).

To put that in a little bit of perspective, an 0201 passive component is 0.024″ x 0.012″. An 01005 is 0.016″ x 0.008″.

Above is a land pattern for the part with an 0201 bypass cap next to it. The trace going from the pin to ground (Pin 4) is an 0.008″ trace. The trace going to VCC (pin 8) is 0.006″. The via is a pretty standard 0.024″via. As you can see, an 0.008″ trace and space isn’t going to do for a board with this size of part on it. Even 0.006″ is really a bit too big.

Duane Benson
La de da de de, la de da de da

http://blog.screamingcircuits.com/

The ‘Hole’ Truth about Drilling PCBs

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Okay, here we go, blog number 3; but first allow me to do a quick review of what we’ve covered so far:

1.) Not everyone who says they can make RF/MW PCBs really can.
2.) High performance substrates act NOTHING like FR-4 in the fabrication process, and a qualified supplier must be a “Material Guru.”
3.) Just as RF/MW engineering is a specialty, so is RF/MW PCB fabrication.
4.) Don’t be hasty in starting relationships with RF/MW PCB suppliers. Do your homework and ask important questions.

Now, moving along. Let’s talk about drilling holes. Automated drilling machines are incredible, when you think about it. The X-Y axis accuracy of hole placement, the throughput, and the speed of the spindles are all truly amazing! When drilling FR-4 material, the bits cut through material like a hot knife through butter. When you throw some Rogers PTFE, or Taconic in the mix, however, a dramatic shift occurs. The drill operators start throwing back Red Bulls, and all that mindless trust in the drill’s amazing technology vanishes.

Again, remember the Material Guru analogy: for every substrate brand, composition, thickness and copper weight, there is a specific recipe—in this case a drill recipe. (Thankfully, these recipes are supplied by the substrate manufacturers.) The speed of the spindles must be adjusted to keep them from tearing up the softer materials and leaving behind chewed up hole walls. The drill bits must be changed frequently to ensure optimal sharpness. The feed speed must be altered as well, to ensure a clean entry and exit of the drill bits. If you don’t have cleanly drilled holes with smooth hole walls, you will be in deep water once the boards hit plating (no pun intended).

In addition to these adjustments, talented design engineers continually delight us with their ever-so-complex designs that require multiple drill operations (due to buried and blind vias). Sometimes, back drilling or controlled depth drilling is required. All these factors serve to compound the, already complex, challenges. (Yes, there is laser drilling, but that comes with another set of unique challenges — and requires a separate post!)

Needless to say, drilling is a critical step in the manufacturing of RF/MW boards. If you mess it up in drilling, expensive laminates end up on the scrap pile, along with any hope a supplier may have of making a profit. So, here is what I hope you will take away from this brief post: Drilling RF/MW PCBs is dramatically different than drilling standard FR-4 boards. It requires knowledge, skill and experience. It naturally costs more (due to drill bit usage and added labor) and is far more risky, from a profit standpoint, for the supplier. It can be risky for you too, but only if you have inadvertently partnered with an unqualified supplier.

For all these reasons, when you get an opportunity to visit an existing or prospective PCB supplier, keep these things in mind as you ask questions about their drill operations. If you see wide-eyed drill operators, a heap of drill bits and Red Bull cans … you are probably in the right place!

Judy

Are You Living in a ‘Material’ World?

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When discussing RF/MW PCBs, starting with base materials seems like a logical place to start. However, the topic of advanced circuit materials is … well … complicated, especially for a single blog post. I’m sure this is obvious to you, but it took me the better part of this week to come to this conclusion with the help of Dale Doyle of Rogers Corp. and Denis Boulanger of Ventec. (Thank you both for your help, and graciousness!) In the end, I have resolved to leave the “heavy lifting” to the experts. Rogers, Taconic, Arlon, and Isola all have information-rich websites and employ amazing professionals like Dale and Denis who are invaluable resources (as are certain industry blogs).

Nevertheless, I did discover that I have a thing or two to contribute when it comes to this subject, as it is related to printed circuit boards.

There are a wide variety of high performing substrates on the market ideally suited for RF/MW applications. At Transline, we use all of them — because you specify them on your blueprints. In fact, we stock almost every part number of Rogers material, and many of Taconic and Arlon and a few Isola. We do this to shorten lead times and because approximately 60% of our business is in the RF/MW industries. Due to our fluency with these materials, I feel qualified to give you a snap shot of what happens after your order hits our shop floor.

First off, RF/MW materials act NOTHING like FR-4 materials in our manufacturing process! They don’t even behave like each other or one part number to another, or one material supplier to another. That is because they are all made differently and have unique compositions: Teflon, ceramic, duroid, PBD, hybrid mixes, and so on. Further, some are reinforced, some aren’t. Some are reinforced with crushed fiberglass, some with woven fiberglass. The highest-performing materials, with no reinforcement, can have dimensional stability issues so severe that they make your board fabricator want to start parking cars for a living.

A capable, qualified RF/MW PCB manufacturer must be a virtual guru when it comes to materials. They must be experts at knowing how each substrate brand, each composition, each part number, at each copper weight and thickness responds to … (taking a big breath) … etchant, plating chemicals, heat, lamination, moisture, and a whole host of processes met in fabrication. These laminates can be moody and fragile … nothing like good old predictable, robust FR-4. So, just as a good RF/MW engineer brings some art and magic to the science of their design process, so it is with the board manufacturer.

Why is this important to know? Because many an excellent PCB fabricator has made the innocent, though faulty, assumption that because they can make extremely complex boards with FR-4, that this RF stuff will be a cake walk. They may have even enjoyed success with some RF boards made on a specific material, but unable to succeed on another. (Shortly thereafter is when you get that embarrassed phone call informing you that they can’t make your boards after all.)

What I am proposing here is that RF/MW PCB manufacturing is a specialty, just as RF/MW engineering is a specialty within the general discipline of electrical engineering. Far too many PCB suppliers and engineers appear to lack this awareness. Why do I believe this? Because I work with RF engineers daily who have the scars to prove it! I believe this because after having 16 years of experience working with very complex FR-4 boards, and a one year working with RF/MW boards–I still feel like a rookie when it comes to RF boards. I also hear evidence from materials suppliers and buyers. I hear it from engineers on LinkedIn. It is for these reasons that I was compelled to create this blog.

So, here are a few possible solutions I hope may be helpful:

When you evaluate a new RF/MW board supplier, consider asking what percentage of their business is RF/MW, and how long they have been doing RF/MW PCBs? Which materials are they accustomed to working with? Ask questions about their quality and test records that verify their ability to successfully hold the tough impedance tolerances you may expect. Ask for RF/MW customer references. Ask your substrate rep for recommendations — in some ways, I think they have the best seat in the house, often offering some much-needed objectivity.

My advice is this: Don’t rush, headlong, into a relationship with a new supplier because they can save you 10%, because by doing so they may, unwittingly, cost you far more — like the loss of an important customer. Think more along the line of long courtship and marriage, rather than one-night stand in Vegas (a tall order when we are all so price driven!). Finally, look and listen for signs of true expertise. Look for that rare mix of knowledge, skill and experience mingled together with a twist of art and magic.

Blogs are designed for dialogue, so please offer your feedback and comments. If you have more ideas or input on this topic, please share it. We have much to learn from one another and I look forward to hearing from you!

Best wishes,
Judy

From the Office of the Dean

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You know how a song gets stuck in your mind and goes ‘round and ‘round, and you find yourself humming the melody or even singing the song out loud? Well lately Leon Russell has been stuck somewhere between my parietal lobe and medulla oblongata. (Dang it, now I’m stuck on “obla lon, oblagata, yeah, la, la la, la life goes on”). Anyway, the lyric “I’ve been so many places in my lifetime…” has been stuck up there because I’ve been thinking about the path I took to get here. In short, I was a draftsman, PCB designer, editor, publisher, business owner and now a university dean.

That’s right, when we launched Printed Circuit University last February, it was decided I would be Dean Pete, replacing my former job title, Grand Poobah. All of this leads to an update (long promised) on what is going on with Printed Circuit University. For those of you who visited PCU from the days of bethesignal.com, you’ve probably noticed some incremental changes in the layout and navigation of the site, as well as new member content. In addition, we’ve planned a new redesign of the site that you’ll see in the near future. The current layout helped us get PCU launched, and now the goal of the redesign is to make it even easier to locate specific content, and hopefully, more pleasing to the eye.

We’ve also been working with some industry experts – in keeping with the university theme, we’ll call them professors – on new curricula that will come online through this summer and fall. Some of the curricula we have in the works include DFM, HDI, RF and Microwave, Flex/rigid flex and a few others that are still in various stages of planning.

In the meantime, this might be a good time to go over a few basics of the site. With your free membership – it only requires a short registration – you are able to view more than 500 papers, lectures and videos on various topics. Using the search function (search is your friend) will help you drill down to some pretty specific topics, or you can review content by using either the dropdown menus in the nav bar or in the three areas at the bottom of the home page. As a member, you can also review the tuition-based content as a member, but you will be required to subscribe (either by course or as an “all-you-can-eat” annual subscriber) to take the tuition-based courses.

It is a good idea to check the site often, because we are constantly adding content. For instance, just this week we’ve added four new tuition-free presentations on considerations for high-speed design, thermal management for LED applications, wrap plating for blind and buried vias and counterfeit components. All of these are under the tuition-free dropdown. High-speed is under tuition-free>SI>articles, and the rest are under tuition-free>other.
And, of course, I should probably give a shout out to our current sponsors: Mentor Graphics and EMA. We appreciate their support and urge you to visit their offerings by clicking on the appropriate banners and tiles.

Last but not least, this site was born with the goal that it will be THE go-to place for designers, engineers and everyone else who are involved in or have questions about printed circuits. We will be depending on feedback from you regarding the current content and content you want to see on printedcircuituniversity.com. That includes member content, as well as tuition-based content. nd by the way, if you think you have what it takes to be a PCU professor, drop me a note and let’s talk about it.

Until then, stay in touch,

Dean Pete

Done and Done

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LED scroller 005 trimmed And … (drum roll, please) … it works.

I put in a couple of batteries, programmed the MCU and turned it on. It works.

I’m always surprised when something I design works on the first try. This being such a simple design, I probably shouldn’t be surprised, though. I should at least give myself a little more credit.

The unpopulated lands on the board in the photo are supposed to be unpopulated. I left a few things out because they aren’t needed for what I’m doing with this piece now and leaving them off keeps the cost down.

So, what did I learn from the process?

  • If you have a lot of different parts laying around, it’s pretty easy to grab the wrong one.
  • I ran into some variability in the “zero rotation” position in the CAD library land patterns.
  • The whole process is pretty easy, but start to finish, there are quiet a few steps.
  • It’s a nerve-racking wait after sending off a box of parts.
  • Good communications between designer and assembler are very important.
  • Clear documentation from the designer is very important.
  • This was a WHOLE LOT easier than hand soldering all the SMT parts (I’ve done that before).

That’s a good set of educational results. Next time, I think it will be easier.

Note the large diode polarity indicators on either side of the long row of LEDs and by LED D25. D1, the Schottky on the upper right has the same polarity indicator, but it’s in between the pads, under the part. In case you’re interested, I have a 3V supply. The LEDs drop 1.8V and I’ve got a 150 ohm resistor for each. That gives me a theoretical 8 mA per port for a total maximum of 176 mA with all 22 lit up. That’s within spec in the -40C to 85C temperature range but too much when above 85C. I’m not sticking this in an engine compartment or anything, so no worries there.

Duane Benson
0x45 0x53 0x43 0x20 0x62 0x6F 0x6F 0x74
0x68 0x20 0x38 0x32 0x33 0x20 0x20 0x20

http://blog.screamingcircuits.com/

Time to Co-Opt Co-Design?

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In recent conversations, I’m hearing designers say they are spending enormous amounts of time in meetings. These comments tend to come from folks who work for larger OEMs or ODMs and work on teams spread around the globe.

Certainly there is something appealing to upper management about follow-the-sun design. It maximizes time resources and leverages both the lower labor cost regions of the Pacific Rim and the experienced hands in the West.

But whereas the old model of vertically oriented design and manufacturing had its warts, if designers are getting hung up all day in meetings, as opposed to spending time routing boards, one begins to wonder whether the follow-the-sun model has been taken too far. There’s nothing process-oriented about commiserating with a manufacturing engineer over lunch in the cafeteria, but there is something to be said for being able to talk things over as they occur, rather than being holed up in never-ending CYA sessions.

Is round-the-clock design actually a drag on efficiency and productivity?

Sunstone’s ‘Fab’ Design Tool

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Sunstone is again acting as much like a software company as it is a quickturn PCB fabricator.

The board shop, which over the past few years has developed and honed its free CAD/DfM tool known as PCB123, today rolled out a conversion tool that features native file upload functionality.

In short, customers no longer need to export data in Gerber; instead, they can use one of a series of native data formats, including Altium, Eagle, OrCad, NI, and others (including, of course, PCB123).

It’s the second big development by the PCB maker in the past year, having already rolled out a parts library addition to PCB123 that supports some 500,000 components.

PCB123 won’t replace the big ticket CAD suites, of course, but for the types of prototype boards most designers need, it keeps getting better and better. And with its CAD conversion capability, Sunstone further extends its “ease” factor to those who don’t use the company’s own software.

Altium on the Move

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Altium is moving to Shanghai.

Yes, you read that right. Sydney’s favorite EDA software developer is turning Chinese, relocating its headquarters and R&D operations to the mainland.

That’s the “what.” The “why” is not so clear.

In a press release, Altium spoke of the “Internet of Things,” China’s talent pool and the potential for greater revenue in China.

I’m probably on the Web 15 hours a day (or more, according to my wife), but I’m mot sure what the “Internet of Things” is. I’m guessing it has something to do with Altium’s move toward cloud computing. If so, it doesn’t need Shanghai for that. Server containers, especially ones laden with databases, should be located wherever energy is cheapest and IP secure. Shanghai is an incredibly safe metropolis insofar as physical well-being is concerned. For technology protections, not so much.

As for the Chinese talent pool and revenue potential, that’s all true. But it would be equally true if Altium maintained a token HQ in Sydney. Companies do that all the time.

The distance from Sydney to Shanghai is about 5,000 miles (8,000 km). Having been to both, I can also say they are quite a bit farther apart in terms of lifestyles and cultures. I’m not certain how Nick Martin convinced his top execs to move, but it couldn’t have been easy.

Compared to its rather staid EDA competitors, Altium is more unpredictable and daring (and usually more fun as a result), and usually those moves have paid off. I’m having trouble seeing the advantages here, though.

Questions on Tin Whiskers

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Folks,

In a recent post, I shared my perspective on the pluses, minuses and neutral aspects of lead-free solder assembly. In the minus category, I listed tin whiskers. A few people commented that tin whiskers were the biggest concern in lead-free assembly. I have trouble understanding this perspective. I’m not saying these folks are wrong, just that I don’t understand their viewpoint.

First, let me say that I appreciate the concern for tin whiskers in mission critical electronics such as military, aerospace and medical. I am also sympathetic to the fact that, even though these types of electronics are exempt from RoHS, they may have to use RoHS compliant products because non-RoHS compliant products may not be available.

When I discuss the topic of tin whiskers, people will point me to NASA’s tin whisker failures website . However, when one goes to the site, there are only about twenty tin whisker fails referenced, many due to bright tin plate. Bright tin plate should never be used in mission critical electronics as it is virtually assured of producing tin whiskers. In addition, many of the articles referenced do not talk about tin whisker fails. Few if any fails are discussed relevant to RoHS (i.e. almost all fails discussed are prior to July 2006.)

I do not want to minimize the significance of tin whisker fails, some of them cost 100s of millions of dollars (e.g., satellite failures). In addition, there have been a few papers that have discussed the formation of tin whiskers even if mitigation techniques are used. Tin whiskers clearly can cause problems, but do not appear to be common, especially if mitigation techniques are used.

So here is my question, who knows of any verified tin whisker fails when tin whisker mitigation techniques were used? Tin whisker mitigation techniques typically use 2% bismuth or antimony in the tin, assure that the tin has a matte finish and use a nickel strike plating between the copper and the tin to minimize copper diffusion into the tin.

Surely if tin whiskers are a major concern, there should be many fails in the over $3 trillion worth of RoHS compliant electronics manufactured since July 2006.

Cheers,

Dr. Ron

Thoughts on DesignCon

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Back from DesignCon, and thankful I was able to avoid the horrific weather that delayed many traveling to and from this event.

It was the first time in years I attended DesignCon, held at the Santa Clara Convention Center and under the new management of United Business Media (UBM). (As an aside, UBM was our parent company for a few years — small world!)

Our primary focus at the event was to launch printedcircuituniversity.com (PCU), a new online, e-learning and training site for the industry – and a longtime dream of UPMG President (and now Chancellor) Pete Waddell. In a nutshell, the reaction to the site was outstanding. Mere mention of our having built it on the bethesignal e-learning platform was enough to capture attendees’ attention. Add in sharing a booth with Bogatin Enterprises and the presence of the well-known Signal Integrity Evangelist (aka Eric Bogatin) — and we had plenty of enthusiastic eyeballs. (Fortunately, Eric was not seen lobbing candy from the booth at attendees as he has often been known to do during some of his seminars!!)

Mentor Graphics is our first PCU Design Excellence Curriculum sponsor and held a drawing at DesignCon for an annual scholarship to printedcircuituniversity. The winner to be announced shortly.

Show floor traffic was solid, steady, and quite often heavy during both days of the event as attendees wandered in and out of technical sessions. Comments I heard included being pleased with the traffic, but unhappy with disorganization of some technical sessions, and some negative comments on exhibit set up. I’d also say – a very “sparse” evening reception — unlike the usual PCB West style!! So, we’ll see what direction the event takes next year under this new management.

One show down … on to IPC Expo/Apex in April.

–Frances Stewart