Reminders are Good Sometimes

I was just recently reading an article on another website that caused me to reflect a bit on where we've been and how far we've come in this industry. The article covered a design engineer's experience with modding a board back in the 80's and being required to ship the board with the mods instead of getting new ones made properly.

Back in the late 80's and early 90's, I worked for a company that designed and built business-oriented displays. One of the products was particularly troublesome to get going and the first production versions shipped with something like 24 different mods. If the company had re-spun the boards, we would have added at least a month to the schedule and payed somewhere in the range of $20,000 to $40,000 dollars. If I recall correctly, one of the biggest problem areas was the PLL (phase-locked loop). We were over-driving the parts a bit and that made all of the support passives and the layout that much more critical. Not smart, but I guess that came from one of those "cost-benefit" analysis type things.

Contrast that today where you can get a new set of boards from a PCB fab company like Sunstone.com in a few days for a few hundred dollars, get the parts from Digi-Key overnight and have us (Screaming Circuits) assemble them in a day or two.

Of course, it's a bit of a double edged sword. Like when faxes and later email came along. Written communications cycles that used to be measured in days became measured in hours and minutes. The expectations changed. Can you imagine writing a letter to a company and waiting a couple of weeks to get a response?!! That's the way it used to be.

In the same vein, us here at Screaming Circuits (and some other people too) have changed the prototype cycle expectations. Can you even imagine finishing your layout and having to wait four to six weeks for assembled boards to come back? Yikes! But that's what it used to be like. We're all making things go faster and faster. It keeps getting faster and it won't slow down. But that's good because time = money so less time building = less money spent and more time selling = more money earned. Right?

Duane Benson
I... Just... Need... More... Coffee... NOW!!!!

PCB Edge Clearance

In my continuing saga of answering the question "what are the real limits?", I'll spend a little time giving my thoughts on edge clearance. That makes the question for the day: "how close can I put parts to the edge of a PCB?" It's a good question but, regardless of what IPC says, surprisingly difficult to nail down.

The problem is that there are a number of valid answers all governed by the phrase "it depends." I'm not going to leave it at that though. I could. But I won't. Not today anyway. It really does depend on a number of factors, but I think it can be nailed down a little tighter than that. You've got to start by considering a few things:

  1. First, our old friend IPC-7351A does specify a keep-out area (AKA Courtyard Manufacturing Zone) on the part footprint. Keep stuff out of that area. This includes the board edge. Don't have any part of the component's keep-out area hanging over the edge of the PCB.
  2. Second, look at your PCB mounting arrangement. Make sure the keep-out area does not interfere with any mounting screws, and that includes any washers you may be needing. If your PCB mounts with slots or rails, make sure the keep-out area doesn't interfere with any of the rails or slots or case edges.
  3. Check with your manufacturer about their specific line limits. Many manufacturers have specific edge clearance limits based on their assembly line.

Now, take your application and consider those three items. Whichever gives you the biggest number is the Eagle_corner edge clearance you need to follow. Based on your mounting scheme, you may have different clearance requirements on different parts of the board. Still, make sure that for each section of the board, you use the biggest number from above.

Now, in the world of prototypes, things are a little different. At Screaming Circuits, we sometimes build up boards with parts right up to, and in some cases, over the pc board edge. You just have to ask yourself two questions for your prototype:

  1. Is there enough copper to give a good electrical and mechanical connection to the PCB?
  2. Am I likely to knock the part off the board with my handling?

If the answer the #1 is yes and #2 is no, then go for it. Of course, in the prototype world, you can always accept the risk yourself and go for it whatever the answers are. That's up to you.

Duane Benson
No worries. The green patches will burn off in the reflow oven.

IPC Says What?

I recently wrote about spacing, IPC standards and such. James M. commented on the post with a question:

"I run into this issue all the time. Assembly houses love to say that they can make anything that meets "IPC Standards for Placement" but when pressed no one can provide the exact number that gives this information. I know of IPC7351A, in fact I own a copy. And the keepout is clear there. But that doesn't influence things like component placement grids, how close things can get to the edge of a board, etc.... Are there other specific IPC standards that do?"

After reading James' comment and re-reading my post, I kind of realized that there isn't a lot of actual content in that blog post. Certainly not much actionable data. And, upon further thought, I think perhaps, all of us assembly folks kind of use that phrase "can make anything that meets IPC Standards for Placement" as a bit of a cop out. Not totally - we do have to set some limits on what we can build, but yikes! I've been trying to navigate the morass of different standard numbers (Maybe I should say "plethora" instead of "morass") and I don't know how anyone that doesn't specifically live the standards for a living could easily find those kind of answers. But us manufacturers really do owe it to our customers to come as close as we can to giving definitive limits that don't take a week of reading to interpret. I think I have to do this in stages.

First, we have three things: IPC-7351A for land patterns and IPC-A-600, covering the PC board workmanship. Then, we have IPC-A-610, covering our workmanship when we build and inspect the board assemblies. Those are the key standards that we live by.

There are a few other questions, such as edge clearances and things like that. I'll dig some more into that one later, but one thing to note is that for the Screaming Circuits prototype service, we don't require any edge clearance, nor do we require panels, rails or fiducials on our full-proto service. I hope this helps.

Duane Benson

Circuit Design ECOsystem

Years and years ago, I was a product manager at In Focus, the projector manufacturer. It was a great time to be in the display industry. New technology was being invented left and right (and center and back, and some over in that far corner too). Competition was still reasonably light and we were ahead of most of it.

It was always interesting to take one of the early overhead projector-style displays through airport security. Laptops were rare at the time, let alone a big clear display that looked like a see-through touch-pad computer, but without the computer. But that's not the point.

Back in our engineering department, we had the electronics engineers, a few folks to work on firmware, a layout specialist, documentation specialists to deal with all the documentation (duh), purchasing people to buy the parts and PCBs, technicians build up the prototypes, manufacturing people to get the pre-production and production going. And here,s the contrast today. Quite a few engineers I talk to these days have to do all of those jobs except final production. That wouldn't be too much of a problem except that while all of those jobs were being assigned to the engineer, everything got more difficult. Parts got smaller, timelines shrank, competition got more fierce, clock speed increased and a lot of formerly company functions, got out-sourced. It's a lot of work and a lot of ground for that engineer to navigate.

A couple of companies; Digi-Key, NXP, National Instruments, Sunstone Circuits and Screaming Circuits (my company), have gotten together to form the Circuit Design ECOsystem; a cross-company organization designed to help that design engineer get a design from inside the brain to the market.

NXP makes components and is creating library components for the CAD software made by National Instruments and Sunstone. Sunstone allows quoting and ordering of Screaming Circuits assembly service on their website and Screaming Circuits does the same with Sunstone PCB fab. Digi-Key is working to improve the data-flow to Sunstone's PCB123 CAD and streamline the parts procurement process to Screaming Circuits.

It's still early in the process, but the idea is to take the, now fragmented, design to manufacture process and make it easier for the electrical engineer to get through - to remove roadblocks, add in new services and improve communications to make it easier to produce a quality product.

Controlling the Uncontrolled

A nice coincidence. Recently, I wrote a bit about choosing a microcontroller and some issues that crop up when people not used to microcontroller design are tasked with automating systems.

My supposition is that, traditionally, most folks in the industry concentrate on designing and choosing microcontrollers and tool sets from the perspective of an expert in embedded design. However, the new world has a lot of people tasked with microcontroller hardware and software design that are not electronics or software engineers. Mechanical engineers are tasked with integrating electronic controls into their systems. Pure digital engineers are being tasked with adding analog sections into their designs. Hardware engineers are having to learn microcontroller firmware programming. That changes the ground rules.

Last week, I signed into a virtual conference on motor control (I started writing this post as I was listening to the virtual conference, but didn't get around to finishing it until today). I signed in late to start listening to the keynote address by John Hanks, of National Instruments and John was at that moment, discussing this very subject. As he described it, domain experts in such fields as solar, wind, and other areas are being asked to add additional automation into those systems. As domain experts, they may know more about their field than an EE or SE, but they likely have not been trained in the application of hardware, firmware and software development.

Interestingly, this group has a lot in common with the electronics hobbyist community. In both cases, the concepts and the tools are frequently quite new to them. In both cases, the budget for training and tools is frequently pretty minimal. In both cases, we have smart people who many not be trained in our field.

Those of us that create tools and offer services in this industry need to keep this trend in mind if we want to fully serve the new engineering audience.

Duane Benson
See us at ESC next week in booth 827

Let's Get Small

It never stops. Does it? It never stops, but it does seem to accelerate.

Mcro-csp When I fuddled with my first 7400 series logic chip a bazzilion years ago, it was a 0.1" pitch DIP chip. A few years after that, people were buying Macs with 0.1" pitch DIP 68000 processor chips. ten years after that, the new little PIC microcontrollers were largely 0.1" pitch DIP chips, but SOIC and .65mm pitch QFP packages were becoming more and more popular. Then came the 1mm and .8 and .65mm pitch BGAs. 0.5mm pitch BGAs became popular a few years ago as did the 0.5mm pitch QFNs. Last year, we started building the 0.4mm pitch BGA Ti OMAP processor with a 0.5mm pitch memory BGA on top of it in a package on package form factor.

If you spend any time reading about advanced packaging, you know that 0.3mm pitch CSP chips are near. I haven't heard of any passive form factor smaller than the 01005, but I guess that's where embedded passives will likely take hold. It makes my head swim sometimes.

Duane Benson

Who are your tool sets made for?

I've been thinking a lot lately about who's using microcontrollers and why these days. There's a lot at stake with this question. And, not just in terms of which microcontrollers are and will be the most popular. There's an element of the Toyota question in here too.

Traditionally, I suspect that electronics component manufactures, hardware EDA tool vendors and software tool vendors assume that their customers have been trained in EE, CS or similar discipline. I think to a point, that serves the industry well. But change is afoot in our industry. Because of a number of factors - too many to list here - virtually everything is getting some level of electronic control now. Years ago, that would have resulted in the hiring of a lot of electronics and software engineers. But not today.

The tried and true EE, accustomed to designing with logic and letting someone else worry about firmware, is now often tasked with designing in a microcontroller and then producing the firmware as well. Or a mechanical engineer is tasked with the same thing; something he or she never trained for. From what I can see, all sorts of technical folks that don't have programming experience, or any electronics design experience, are now being given that task. Schematic designers are now responsible for the board layout. Pure digital folks are often being required to add in a few RF sections.

What happens if all of the software tools (CAD packages, compilers & tool changes) are designed for well trained experts, but intelligent but untrained, in that field, folks need to use them?

When cars suddenly accelerate, MRI machines over-radiate or satellites fail, it's all good to look for tin whiskers, cosmic rays, manufacturing defects, software bugs and causes of that sort. But, what if the root cause is simply that someone trained and practiced in pure digital design was tasked with the "simple" function of adding in a few analog sensors and a tiny microcontroller. What if that designer had to learn a new discipline, a new tool set and still make budget and a tight deadline?

Maybe twenty years in digital design didn't prepare that designer for the quirkiness that goes with analog signals from sensors, or for the challenges involved in writing a small, but bullet proof SPI interface code. Maybe the designer is well used to determining spring strength and durability but now has to design a small electronic circuit to replace that spring. What does that do to quality and reliability? Food for thought.

Duane Benson
Thought is hungry today

Allocation

Screaming Circuits is seeing more and more components in short supply or on allocation these days. A while back, we took a survey of our customers and found that on average, an engineer would spend about 16 hours sourcing parts for a prototype design.

Schottky top My question is has that changed? There are a few chip companies with a lot of parts in short supply, but what I hear the most about is the passive components. If you've designed a very specific power or radio chip, for example, I can see how a twelve week lead time can be a very big issue. But if it's just a 47pf, 6volt cap, a resistor or diode, is it really that difficult to find a sub quickly?

How much of an issue is parts availability today - really? Is it something that has a lot of visibility and little impact? Or is it something where the visibility and the impact are both pretty big? How much of a hassle and time sink is it for you now?

Duane Benson
I'll trade you a pair of .022 for one .047

Full Circle - Total Quality Management

A thought occurred to me over the weekend as I was pursuing through some of my recent posts and comments.

Back in the late 80's and early 90's, Total Quality Management with such phrases as "Cross-functional team" was all the rage. Essentially, what that meant was that when time to start developing a product, folks from throughout the process would meet; marketing, sales, engineering, mechanical, purchasing, manufacturing, shipping and any other functional groups would send representatives to the product team. That team would meet throughout the development process to ensure that the product was designable, buildable and sellable. It worked.

But... What happens when three quarters of the process is outsourced to three or four different organizations throughout the world? Unless you are very diligent, that quality process breaks down. Then when you remove some of the experts (such as layout specialists), the process can breakdown further. That's where we are now. Perhaps we need to go back in time again and figure out how to get everyone talking and passing data back and forth again.

Duane Benson
Yes - I successfully resisted the temptation to say "we need to go back to the future..."

8 bit vs. 32 bit Microcontrollers

There's a lot of talk these days about the new generation of 32-bit microcontrollers and the demise of the 8-bit controller. I'm a big fan of the Beagleboard and mbed boards (ARM Cortex A8 and ARM Cortex M3). And the Cortex M0 processor looks to be a very promising low-end 32-bit ARM. By the looks of it, ARM could end up ruling the below-X86 world soon.

SP16-1_layout But, one consideration to the 8 vs. 32 discussion that I haven't heard much about is the start-up effort required and the barriers to entry for non-experts. The new ARM Cortex-M processors look to be a great move toward addressing the low-cost and low-power end of the microcontroller market, but they don't really address the buildability issue and the category-entry issue.

At Screaming Circuits, we run into quite a few designs in industries that are just now beginning to automate. In many of these cases, mechanical engineers, not software or electrical engineers, are tasked with putting the brains into the product. These mech folks have to learn, design, layout, build and code. The PIC and Atmel processors, with their thru-hole or big SMT packages, easy 5V power, low clock-speeds and huge base of community support make an impossible job possible for the new entrants into the embedded world. If a thru-hole part with a 20MHz clock can do the job, novice designers can greatly increase their chances for a successful design than if they have to deal with fine pitch parts and 100MHZ clocks.

In a perfect world, this wouldn't be a concern, but as it is, a lot of companies need these parts that are easy to implement for a new designer. M0's may be priced in the sub-$1.00 range, but piece price is not the only component of "cost".

Duane Benson
"Apple II forever"