Category Archives: Laying It Out

Off-grid thoughts from a burned-out designer turned editor.

Why DfM?

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Design for manufacture is the practice of designing board products that can be produced in a cost-effective manner using existing manufacturing processes and equipment. — Ray Prasad

I’ve mentioned before that one of my early design gurus gave me a piece of advice that stayed with me throughout my design career. He said that after I finished a drawing or design, I should stand back and ask myself if I could build the product from the information I was providing. Well, to do that I had to know how the product would be built and the processes involved in manufacturing the product. Fortunately I was raised in a fabrication environment and had a fair knowledge of metal fabrication.

But when I started designing PCBs, I didn’t have the luxury of being around a PCB fab shop, where I could spend time with people who built the boards. I had to depend on other designers who had a wealth of knowledge about PCB fabrication.

Several years later, I worked for a couple companies that not only did design work but also had a board shop. Any time I had a question about something, I could walk over to the board shop and get some on-the-job schooling. The folks there would not only tell me what I needed to do to make the job more manufacturable, they’d walk me down the line and show me the whats and whys. I can’t help but think that this made me a better designer. I know that it gave me a better understanding of how the things that I was doing in a design affected every step and downstream process.

Over the years since I became involved in the magazine and conference side of PCBs, I’ve stressed the importance of DfM and the manufacturing process. We made it a significant part of the message and information in everything we produced, including the magazine, conferences and in later years, our websites. But DfM is still one of the major issues in the PCB design world. With the compartmentalization and outsourcing common today, it may be more difficult to get out to the board shop that builds our boards.

However, it is doable. Even when – for whatever reason – it isn’t feasible, designers and engineers need to know everything possible about board fabrication and assembly. So we keep running articles in the magazine and doing sessions at PCB West on DfM. We’re also working on some in-depth DFM courses for Printed Circuit University (PCU). In fact, we just loaded a video on PCU called Why DFM? that is available to all PCU members. (Membership is free.) In the video, Darren Hitchcock of Multek talks about some basic issues about which every designer should know. It is just a part of our effort to get every designer educated on DfM and other subjects relating to PCBs. Visit PCU today to see for yourself.

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Through-Hole to SMT

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Thanks to a comment from Michael yesterday, I think everything is now cool with my Geiger counter. I had left the AT2313 default fuse setting at clock/8. That dropped the RS232 speed from 9600 to 1200 and it made the clicking sound into more of a tone, which just didn’t sound right for a Geiger counter. I still need a good radiation source though. I think I’ve picked up just a few clicks of background radiation, but that could just be wishful thinking.

Wishful thinking or not, that’s not the point. The point is that this was an example of migrating from through-hole parts to SMT. I managed to get virtually everything into SMT. The connectors, the power switch, the buzzer, batter holder and fuse clips for the tube stayed through-hole. Although I’m sure I could have all but the battery holder and fuse clips into SMT had I wanted to. I tend to keep switches and connectors that will get a lot of use as through-hole just for the extra staying power. If they aren’t used frequently, then SMT is just fine.

There are a number of things to consider when switching from thru-hole to SMT:

  1. Everything is smaller, so you can fit more in the same space or the same in less space. I took advantage of the extra board area to add in a RS232 line driver so I could connect directly to a serial port. I also added in a power-on LED.
  2. Everything is smaller so your layout is more critical. Most PCB houses will build 8mil trace and space as standard process these days. That gives you a lot of flexibility in squeezing your routing into tight areas, but it doesn’t give complete freedom. You have to be core careful because you frequently do have to route a bunch of traces into a pretty small area. When you get into the really fine pitch parts, like 0.5 or 0.4mm center to center, you have to be extra careful.
  3. Some parts are dimensioned in metric and some in SAE units. If all are one way or the other, it’s easy. But when you’ve got both, you may have to tweak with your grid spacing off and on to make sure your traces are centered in the SMT pads they connect to. It usually isn’t a horrible problem, but it can make even spacing more difficult and can make you more likely to violate a design rule.
  4. You don’t have automatic “vias” on each component leg so routing can be more difficult. You’ll likely have to spend more time tweaking the part locations and the trace routing to get a decent layout. A lot of times everything’s too close so it’s not practical to just plant a lot of vias all over.
  5. Hand soldering is less or not practical. Some people do hand solder some pretty tiny parts, but it’s not practical in more than isolated cases. If you’re a hobbyist or on a tight budget, this might limit you to through-hole or some of the largest SMT parts. For commercial work though, SMT is the way to go.

Some things to think about. But what do you get in return? Typically lower cost – especially if you want your design to go into volume manufacturing. You also get access to the newest parts that only come in SMT packages. And, many designs are space constrained, so you can cram more in while still keeping your board size down.

Duane Benson
I shot a neutrino into the air
And where it landed I already knew

 

Geiger Counter Without the Muller?

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My Geiger counter project has been on holiday for a while. When I originally ordered all of the parts, I ordered fuse clips (to hold the tube) with solder lugs too big to fit in the holes and a trim pot (VR1) too small for the SMT pads. I moved on to other things for a while and just now got around to ordering the correct parts and soldering them in. I’ve verified that everything works except the tube. Apparently, S-13BG GM tubethe specific tube I bought (SI-3BG) is not very sensitive.

Other than not knowing if it will actually detect radiation, everything seems to work just five with Mighty Ohm’s original Atmel code. The only difference from his instructions is that the RS232 is 1200 baud instead of 9600. I’m not entirely sure why that is. The source code specifies 9600 and I have an 8MHz resonator just like his kit. I’ll worry about that later. At least it works.

It will beep if I touch my fingers to each lug of the geiger tube, but I haven’t been able to detect any naturally occurring particles. There are a couple of possibilities.

  • I had to choose a different transistor for Q1 and different diode for D1 because I couldn’t find those specific parts in SMT. Maybe the gain or some other performance spec is too far off.
  • The type of tube I bought is not sensitive enough so I just need to find a stronger radiation source.
  • I don’t have VR1 set right to give a high enough voltage to trigger the tube.

I’m going to try a 100:1 voltage divider to a unity gain current amp to measure the voltage and go on the hunt for a hotter (but still safe – I hope) radiation source. I might go back to eBay and buy a different tube too. Lastly, I’m going to get out some data sheets and look at my subs again. Maybe try to find something even closer to the original. Once I’ve verified that it all works, I’ll make the design files available as open source.

Duane Benson
If the Alpha is the tough guy, why can it be stopped by a single sheet of paper?

http://blog.screamingcircuits.com/

BGA Pads with Vias

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Via eyeballs

No. This isn’t a closeup of an owl face.

There is still some debate on how best to create a land pattern for a 0.4mm pitch BGA. We recommend solder mask defined pads at that pitch. But that’s not really what this post is about. Although this land pattern uses non-solder mask defined pads which can encourage bridges. If you need to cross a river, encouraging bridges is good. If you’re trying to make a board work, they are not.

In the case of the two BGA pads shown, I really doubt you would have to worry about bridging. That’s because the solder ball would most likely be sucked off the BGA due to the capillary action of the via in the middle of the pad. You most likely wouldn’t get bridging. You most likely wouldn’t get any contact of any kind at all. This will not work.

Duane Benson
Hoot. Hoot.

http://blog.screamingcircuits.com/

Speaking of Small Packages …

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T’was a a dark and stormy night when the news came through. Joe Layout had been both dreading and preparing for years. But it had always been little more than rhumors from a far off land. It was a looming threat, always dancing in the distance, but never quite real.

Until now. 1.27mm, 1.0mm, 0.8mm, 0.5mm, 0.4mm … and now … drum roll please 0.3mm pitch.

I just got an email announcing an Amkor 8 x 8mm 368 ball BGA at 0.3mm pitch. Yikes.

There’s still some controversy over the best way to make a 0.4mm pitch BGA land pattern. Some say says you need to use solder mask defined pads. Some say you still need to use the non-solder mask defined pads. Now we throw something 25% smaller into the mix. The image isn’t to exact actual scale — because I don’t know how big your monitor is — but the parts are in relative scale from 1.27 pitch to 0.3 pitch.

Duane Benson

If you can’t see it, you shouldn’t eat it

http://blog.screamingcircuits.com

Open Source: What Is It Good For?

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I’ve written about open source hardware (OSHW) a few times before. Like this and this. I’ve understood open source software for quite some time and over the past few years have been starting to get what open source hardware is all about. It is different than open source software.

With software, your tangible product is essentially intangible. Your acquisition and distribution of an open source project can be virtually free. Not so with hardware. Someone has to physically build something, which costs time and money in parts and labor. Really though, all that means is the proliferation of an open source hardware product just takes a little longer. If you look at it as the design being open source more than the actual product, then it gets to be more and more similar to software.

While open source software has moved into real business, hardware is still more closely associated with the hobbyist community. That is changing though. TI’s Beagleboard is serious stuff from a serious company. Some of the hobbyist catering OSHW companies are growing to or have grown to the point of being serious businesses (Adafruit, Sparkfun).

This all begs the question: “What is open source hardware good for?” Let’s divide and conquer. Or, at least, divide and explain.

  • What does it do for innovation?

History is rife with stories of great inventions that were not commercially successful because the inventor was a good inventor but was a lousy business person, didn’t have access to funding or just didn’t have the drive to build, promote and sell the product.

With OSHW, companies that do have the drive, funding and know-how can pick up an open source project from a developer that doesn’t.  There are none of the IP concerns that sometimes keep big companies from taking on product from independent inventors. Great products that otherwise would stay hidden can make it out in the world.

Some OSHW companies, like Adafruit, compensate the designers whose product they sell. No marketing or selling expense for the designer and yet money comes in to them. Much reduced design expense for the seller, yet they can build a business.

  • What does it do for small companies?

It’s another way to jump-start design or production of products that will fund the small business. It can reduce the barriers to entry. People who are good at designing but not so good at selling can still earn money. People who are not so good at designing but good at selling can earn a living. People who are good at both designing and selling — they have the best of both worlds and can earn a living. Products that would otherwise stay in obscurity can more easily make it to the world.

  • What can it do for big companies?

The answer to this question has been the longest in coming, but there are more and more answers showing up. Take the Beagleboard from Texas Instruments. It got a new processor (the OMAP) out into the hands of their customers quickly. It was a great promotional tool. The software side of an organization could get started with the processor without having to wait for the hardware folks to design, layout and build the hardware. The hardware folks could see how the part and its accessories work in real life.

OMAP users could get a jump-start on complex tasks like escape routing. The manufacturing folks could get some insight and practice into assembling the package on package processor / memory combination. design cycles are short enough as it is. Companies that want to use the TI processor get professionally designed short-cuts. TI gets to sell more processors quicker. Everyone wins.

Duane Benson
It doesn’t mean destruction

http://blog.screamingcircuits.com/

Reference Designators

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A while back, I wrote about reference designators relative to family panels. Family panels can cause problems because often times, each individual circuit layout will have reference designators that start at the same place.

For example, circuit A, down in the lower right corner of the panel, will have resistors R1, R2, R3… Looking at the other three circuits on this hypothetical family panel, all of them also start their reference designators with R1, R2, R3… That’s bad. It can lead to confusion and wrong parts on the board in the wrong spots. If we see this here at Screaming Circuits, we may spend some extra time and sort through it manually or we may ask you to fix it first. Fixing it here is a labor intensive and risky process. It’s bad news.

Anyway, to the point of this post: In the original post, I listed one wrong way and three right ways. There are two other wrong ways not in the original post, which I’ll list here.

Wrong way number one: R1-1, R1-2, R1-3. Bad. Most assembly software will interpret a dash as meaning a range. It will see “R1-3” as equalling “R1, R2, R3”. That can be bad.

Wrong way number two: Leading zeros. Don’t do “R1, R01, R001”. The leading zeros are stripped and that can cause all of those the be seen as “R1”. Just don’t put leading zeros in your reference designators.

Duane Benson
Corrigan says Long Beach is actually in Ireland

PCB West Recap: Still Great After 20 Years

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I’m thrilled to be reporting on PCB West 2011 because for the past few years I haven’t been able to attend. I had almost forgotten what it was like to be among that rare breed of “off-grid” individualism, the Circuit Board Designer.Lately I’ve become more involved in IPC standards development committees and therefore feel obligated to attend those conferences, but since few designers participate in IPC activities, PCB West felt like coming home again. If you are one of the designers working alone out there for your company, or are a lone designer supporting multiple companies, this conference is a great opportunity to meet your peers, get away from the daily grind for a few days and see what the rest of the world is doing …  

20 and counting? This was the 20th anniversery of PCB West? Seriously? How could we have gotten so old already? Now I’m feeling nostalgic … UP Media gave out “20 Years and Still Off-Grid” t-shirts to literally everyone that registered. I thought that was a really nice thing to do. Thanks, Uncle Pete! (and while I’m thinking about it, thanks to K&F for supplying free Starbucks coffee for everyone!)

Continuing education. The conference started off with a bang as I attended a presentation by Kevin Coates where he introduced a new series of devices by Texas Instruments (well, new to me anyway) where fine pitch BGAs are being developed using a pin-out method that leaves room for fan-out vias and decoupling devices. Using these “via channel” devices may enable designers to use conventional board fabrication technology, where an HDI solution was required before. It was nice to hear additional comments by Wayne Pulliam, who works on similar efforts for AMD.

Darren Hitchcock’s “Design for Manufacturing” presentation was very informative, mostly focusing on various board materials and their characteristics.
Gary Ferrari gave a great introduction to HDI technology, the various types of HDI constructions (and the materials required for them) and the use of microvias. He gave some good real-world advice and warned about some common pitfalls, and if you are moving in the direction of HDI I would strongly recommend this course. Gary has done so much work with this type of fabrication at his company (FTG), and with so much related experience in his involvement with IPC, you can pretty much take whatever he says to the bank.
Susy Webb seems like the hardest working gal in the game, and has nearly accomplished a complete curriculum for new board designers.
Starting with the basics in her introductory “Symbols and Schematics” class, and moving from “Parts and Placement” through “Routing and Finishing” and even “PCB Layer Stackups,” finishing with “EMI” and “Signal Integrity” presentations. She is getting close to offering the new designer a start-to-finish introduction to the whole electronics development process.
And the good news? All of her presentations are available on the Proceedings CD.
Finally, many of you may wonder what exactly happens to your Gerber data once it leaves your CAD system, and whether that ubiquitous fabrication note “Data May Not Be Modified” really means anything at all. Well, Mike Tucker’s presentation about CAM departments is a welcome addition to any PCB design program, and thanks go to Colonial Circuits (his new employer) for letting him continue to present it.
This is definitely something any board designer worth his salt should know about.
Feeling left out? I apologize to all of the presenters that I wasn’t able to mention in this review. With multiple events happening in every time slot, I simply wasn’t able to make it to everything this year. Fortunately, the proceedings disk contains most of the information from the conference and is available from UP Media at http://pcbwest.com/2011/proceedings/.
Exhibitionism. Although the exhibit spaces have seemed to be shrinking in size over the last decade or so, UP Media does a great job of bringing folks onto the floor. The time frame was shorter, and I suspect the exhibitors are happy enough with not having the show drag on and on for days, so that now the entire event happens in a single session! I love it.
Everyone is there for one entire day and it seemed downright festive.
The event included free lunch for everyone, bringing a lot of traffic into the space virtually the moment it opened, and ended in the evening with open bar for everyone, so even those who need a little of that old-fashioned “social lubricant” could get into the scene. The vendors I talked to seemed to be getting a lot of worthwhile leads this year, and I sensed a real note of optimism that I haven’t felt lately. Hope it was a worthwhile experience for everyone who participated.
Gossip column: Happy for Happy. Many of you know Happy Holden from his long career at Hewlett Packard, many of you know him from his educational conference presentations while working with NanYa, many of you know him for his most excellent introduction to HDI, The HDI Handbook, many of you know him for his work divining the future for Mentor Graphics, and many of you know him for his “retirement” to become the CTO of Foxconn’s Advanced Technology Division in Taiwan. I might have predicted that we had seen the last of Happy; that he had moved so high up the ivory tower that we would never hear from him again. Not so! Happy is moving back to the states! (hope he doesn’t resent me for this announcement). Maybe we will all benefit from his presence again.
Stay tuned … (Michigan?)

Howdy PODners! OK, how many years ago did we start talking about a Universal Library? How long ago was it that Tom Hausherr started collecting PADS library components, analyzing them, collating them, creating a consensus that eventually turned into the PCBLibrary Viewer and Calculator and Wizard?

And when these tools got linked together with the IPC-7351 Land Pattern Standard, it seemed like we were close to crossing the goal line, from then on into the future the world could have a consistent approach to creating reliable footprints for every major CAD system. So, what happened? Well, the short story is that Valor bought PCBLibraries, which seemed like a good idea since Valor was already supporting every major CAD system, but then Mentor Graphics bought Valor. Uh Oh! would Mentor support the dream? Not exactly … they soon started stripping off the interfaces to the competitor’s products, and the most recent news that is that in July they kicked Tom and his team to the curb. sad, Sad, SAD. But, looking at it another way, it could be the best thing that ever happened to propel us toward the dream of a Universal Library, because Tom and his Partners are back together and working on a monster plan for a new web-based library (which will eventually be at http://PCBpod.com). Right now they are putting together the parameters for a set of new and improved land pattern conventions that address many of the common issues. For example, why should we be screening so much silkscreen underneath components for high-volume products that can’t even be seen after assembly? We are wasting a lot of ink for no reason, folks.
Anyway, that might be a minor issue for many of you and it is just an example, but the good news is that these issues are actively being discussed, hopefully to be resolved with the IPC during some meetings in October, and then these parameters will be public-domain for all to use.
And what will happen to Mentor’s calculator? Who cares…!

PCU for me and you. Also, you’ve probably already heard, but UPMedia is putting together various educational materials which will hopefully evolve into a full curriculum under the banner “Printed Circuit University.”

Registration is free, and once your account is set up you will have access to many free resources, and for a fee you can access the in-depth tutorials such as Eric Bogatin’s Signal Integrity series. Check it out! You might even find some videos there from this year’s conference by Kelly Dack.

The missing piece. Finally, the conference just wasn’t the same without Rick Hartley, one of the educational icons of our industry. Hope you’re feeling better, Rick!

Surfin’ the learnin’ curve,
Jack Olson
http://HowToPCB.net

ESC Robot Attendees

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We’ve been hanging out in Boston at the ESC show. Yesterday was a busy day with lot’s to look at and lot’s of folks at our booth. Some human, some not. The Freescale people, just a few booths down, brought along a tele-presence robot.

The little guy wandered here and there a bit. It’s a cool concept, but I think it didn’t quite live up to it’s potential. They really should have registered it as an attendee. It did have a little card hanging around it’s neck, but I don’t see why it couldn’t have had a genuine show badge. If it were me, I would have had it actually stopping by booths, talking to people and collecting goodies.

Still, it was a fun demo and, presumably, an example of Freescale chips in action.

Duane Benson
I salute our new robot tradeshow overlords

http://blog.screamingcircuits.com/

All’s Well at West

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We really had an outstanding week at PCB West. Preshow registration rose to nearly 2,000 (!) and actual attendance was up more than 30% over last year.

Congratulations to Judy Warner and Michael Ingham, whose talk on RF/microwave design and fabrication drew more than 100 attendees, the most in the conference. Newcomer Jamin Taylor’s presentation on flex construction also drew more than 80 folks. Well done!

I also want to congratulate the winners of the PCD&F NPI Award for best new software tools of 2011. They include:

  • Design Verification Tools: DfR Solutions (Sherlock Automated Design Analysis)
  • Computer-aided Design (CAM) Tools: Downstream Technologies (CAM350)
  • Documentation Tools: Polar Instruments (Professional HDI Stackup Design & Documentation)
  • PCB Design Tools: Altium (Altium Designer 10)
  • System Modeling and Simulation Tools: Sigrity (SystemSI – Parallel Bus Analysis)

We have posted the full announcements on PCD&F’s site. Thanks to all who attended!