Screaming Circuits: Engineer stories


Using the Newest gen ARM, Part III

The continuing saga of the 0.4 mm pitch KL03 ARM microcontroller. If you haven't yet done so, read part I, and part II.

Today, I have a look at the good, the bad, and the ugly - or more accurately, the good, and the bad and ugly. As I expected, I was quite pleased with the job done here in house. The board is nice and clean, the parts are well centered, and the solder joints are solid. No surprise here.

Here's a top-view of one we did here in Screaming Circuits:

4mil top view 800

Next, I've got one that I did at home. It actually surprised me and came out better than I had expected. Here's a top-down view of the one I did at home with home-grade tools (No, I didn't intentionally make it look bad. The board surface is just a bit shinier than the one above.):

Home top view 800

Of course, "better" is a relative term. I didn't say good. I could call this both bad and ugly. I did manage to center the parts quite well - that took a lot of careful nudging with sharp tweezers and and an X-Acto knife blade.

All of those little round shiny spots are solder balls. That's what happens when you get too much solder on the board, get solder off the pads, or have the wrong reflow profile. They might look harmless, but if there are too many under the chip, the connections could be shorted.

The fillets on the 0201 capacitor are a little lean on solder in the one I did, and there's a solder ball on the right side, but, again, it looks better than I expected.

Next time, I'll post the X-rays and show what's under the hood.

Duane Benson
Carburetors, man.
That's what life is all about

USING THE NEWEST GEN ARM, Part II

I'm a bit behind in my blog work - well, way behind, actually. I started this series back in January with the intro post.

Here's where I am right now:

  1. I have three different sets of PC boards.
  2. One set, I took home to see if it's possible to solder a micro BGA at home. (As someone working at a car manufacturer might want to see if they could balance a crankshaft at home, for fun)
  3. Two sets, from our partner, Sunstone Circuits, are here in my desk with parts, ready to go through our machines.

After I've got all three sets built, I'll have them X-rayed to see how they look under the hood. Finally, I'll solder thru-hole headers on and fire up the chips to see if the shared escape system works.

Here's one of the boards without access to the inner pads:

KL03 SunstoneFF 4mil (2)-001

And, here's the shared escape:

KL03 SunstoneFF 4mil (3)-001

The main concern I have is that Reset is on one of the inside pins (B4). I'm not sure if I can get the chip to a state where it will operate properly without unobstructed access to reset.

The routing I've chosen is probably the only possible option for reset. Pin A4, right above, is used for the single-wire debug (SWD) clock. I'm assuming that can't be shared. B5 is Vdd, so that's out. It might be possible to go down. C4 defaults to one of the crystal pins, and D4 defaults to a disabled state.

In the route I've chosen, B3 is an ADC input, so it should start out high-impedance, and therefore not interfere. A3 defaults disabled, so it won't get in the way.

Next step: solder time!

One other thing - The images above show non-solder mask defined (NSMD) pads. Those are standard for BGAs 0.5mm pitch and higher. This part is 0.4mm pitch. Some manufacturers recommend solder mask defined pads (SMD) for 0.4mm and smaller. I'm actually testing several pad styles: SMD, NSMD and solder mask opening = copper.

KL03 footprint contenders

Duane Benson
Run it up the flag pole and see who solders

Using the Newest gen ARM Microcontrollers

KL03 on stampI've written a few times about the new Freescale KL03 ARM Cortex M0+ microcontroller. This particular part comes only in very small packages, with the smallest being a 1.6mm x 2mm WLCSP (wafer level, chip scale package) 0.4mm pitch, 20 bump, BGA. That's a mouthful - albeit a very tiny mouthful. Maybe just a toothful.

On the left, here, I've got a pair of them on a US postage stamp.

For us, it's not a particularly difficult part to assembly; just a garden variety 0.4 mm pitch BGA, as far as we're concerned. We place loads of them. But, it can be a very different story for a designer. Conventional wisdom says that a PCB designer has two choices with a part like this: a very expensive PC board, or don't use the part.

Escape routing becomes very difficult (read: expensive) at 0.4 mm pitch. This part only has six connections that need to be escaped, but that can still be a problem. You can't fit vias between the pads KL03 SunstoneFF 4mil 800to escape out the back side. You can't put vias IN the pads, unless you have them filled and plated over at the board house. That's expensive in small quantities.

This blog post series is going to examine some possible ways to use these parts with more of a standard fab, such as Sunstone quickturn. I've got three different process blank PC boards, each with four different land patterns.

I've been asked about home reflow too, so as a bonus, I've done my best to duplicate hobbyist conditions for one of the board sets.

Check back next week for the first set of results, and be sure to quote your assembly job at Screaming Circuits or your PC boards at Sunstone.com.

Duane Benson
"Screaming Reflowster" not sold here

Do you Need that Part? Or, is it Just Habit?

At the moment, I'm working on an Arduino compatible clock. Like most of my Arduino compatible boards, this one uses an Atmega32U4, with USB built in. With the Atmega32U4, I sacrifice a little in program memory and SRAM, but gain a bit in reduced parts count.

A USB capable Arduino-compatible is, of course, programmed via USB, and can be powered by the USB port. Most Arduino boards also have a 5 volt regulator to be used when being powered by a wall-bug power supply. Naturally, I put the USB connector on the clock board, as well as the 5 volt regulator. With the two different supplies, I also put in circuitry to auto switch sources and protect the USB host when both supplies are connected at the same time.

NeoPowerSupplyMy first PCB revision required a few hand-mods, but not many. Still, I decided to re-spin the board and remove the two mod wires. While doing so, it suddenly occurred to me - a blinding flash of the obvious - that most cell phones and other small devices are charged with a USB-connector 5 volt wall-bug power supply. Why then, would I also need a separate power supply and on-board 5 volt regulator?

By pulling the regulator off of the board, I could eliminate a few capacitors and the supply auto-select / protection circuitry. Not only did I save in component cost, but I was able to reduce the PC board size, and thus cost, by about a third.

  1. I had the 5 volt regulator in the design because Arduinos can be powered by either USB or a non-regulated power supply.
  2. The reverse power protection is necessary to prevent damage to the USB host if the other power is also connected.
  3. The auto-power switching circuit is necessary so that a user doesn't need to flip a switch or change a jumper when changing power sources.
  4. I had two extra LEDs to indicate which supply was powering the clock.

I questioned my original assumptions, found a "because it's always done that way" and eliminated it. Assumptions are meant to be challenged.

Duane Benson
Question authority!
And then get squashed
(or, squash extra space out of your PCB)

Intergalactic Geek Pride Day Quiz

There was a time when "Geek" was far from a badge of honor. Jr. High School (AKA middle school) was developed specifically for the purpose of making geeks miserable. We were told that lockers were  designed for holding books, lunches jackets, but in reality, the secret anti-geek coalition had lockers installed so geeks could be stuffed inside of them, or could have the doors slammed in their faces.

But, then something happened. While the world wasn't looking, a geek became the richest man in the world. Pro-nerd and pro-geek movies became popular. It became cool to claim to be a geek or a nerd. The problem is that there's a big difference between claiming the title "geek" and being given the title "geek."

Well, May 25th is Geek Pride Day. In honor of Intergalactic Geek Pride Day, I've put together a little quiz on the subject.

Questions:

  1. Is it better to be considered a nerd, a geek or both?
  2. What's the difference between a nerd and a geek?
  3. Does the outside world know the difference between "nerd" and "geek" and thus does it matter which one you're called?
  4. If you've never actually been called a geek, but claim to be a geek anyway, are you really a geek?
  5. If a geek talks in the woods, but there's no one there to hear, did the geek actually speak?
  6. If you can explain what you do for a living (or hobby) to a random stranger and have more than about one in fifty understand, can you still claim to be a geek?
  7. If you don't have enough cables laying around the houses to connect just about any two pieces of computer / electronic equipment together, can you really claim to be a geek?
  8. If you can't assemble a spare PC from parts you have around the house in about an hour, can you still claim to be a geek?
  9. If you can't count in more than one base, can you still claim to be a geek?
  10. If you don't love songs by Tom Lehrer, can you still call yourself a geek? (If you don't know who he is, quick: Youtube)

 Bonus question:

  1.  Tesla or Edison?

Answers:

If you're a true geek, you already know the answers so I don't need to list them.

Duane Benson
The best revenge is not violence or deviousness
The best revenge is to be happier
...and to build robots for world domination

 

Canada's Singing Astronaut

If you're going to exit, you may as well exit in style and I can't think of a better example than Commander Chris Hadfield's "good by" from the International Space Station on Monday (May 13). Thank you, Astronaut Hadfield.

Since this is my  electronics blog, I've got to tie it into electronics design and assembly, so, like um... If you're building electronics for space, you might need to better insulate your PCB traces or put wider gaps in because otherwise you might get arcs and stuff. And be sure to shave your tin whiskers.

Duane Benson
Please sir. May I have some more

Unsolicited

I have a question for you. When is the last time that you responded to an unsolicited email? It's been a very long time for me. However, I just did open up and read an unsolicited email that actually seems somewhat relevant to me. The specific subject was an offer to be a guest blogger here on blog.screamingcircuits.com. I don't know that I'll take them up on the offer. It kind of depends on what they might want to write about.

But I did jump over to their website: www.circuitspecialists.com. I've never done business with them, but they do have some interesting products and they started in a garage in 1971. Anyone who started in a garage 40+ years ago and is still around must be doing something right. Their site looks like it's more or less focused on test & measurement, prototyping, robotics and other things electronic. (I think I've heard the term "prototyping" someplace...).

What first caught my eye as relevant was their section on digital panel meters. Why would that catch my eye, you might ask? (Or you might not) The first panel meter I looked at is an "independent power supply version." Ah, the plot thickens. Just last weekend, I exploded a power supply in a robot I'm building. It didn't actually explode, but it certainly did release smoke and stopped releasing electrons at about the same time. Smoke for electrons is not  a fair trade as far as I'm concerned.

I was putting a digital Ammeter on the main power line and couldn't remember if it the meter was designed for high side or low side. Poof! I empirically determined that it was designed for low side. I should have known better because it drew power from the robot power supply without any isolation.

If my meter had an isolated or independent power supply, then I could probably have put it on the high side. Oh well. It wasn't the first time I've traded smoke for electrons, nor will it likely be the last.

Duane Benson
rhythm characterized by regular recurrence of a systematic arrangement of basic patterns in larger figures

The ESD Habbit, or an Unexpected Shock.

Excitement is building here. In a little over two weeks from today, The Hobbit movie will be released to theaters. I'm sure everyone reading here knows the story, but in case you don't I'll spoil it for you.

It's a story about Biblio who is, according to Spock, the bravest little hobbit of them all (google that if you don't get the reference. You'll be glad you did). Biblio is minding his own open source robotics business when the Wizard of Menlo Park (in CA, not NJ) invites 12 MCU designers over for a meal and discussion about the merits of hardware peripherals vs. bit-banged peripherals. The MCU guys convince Biblio to go with them to The Lonely Mountain Chip Fab and help them kill a terrible ESD Spike problem. Actually, it's the Wizard that convinces the MCU guys that Biblio could help. The next day the MCU folks left early and Biblio ran out to catch up with them without even an ESD smock.

The ESD problem came from the North because it's more humid up North and that tends to dissipate ESD. Our Terrible Spike didn't like the idea of being dissipated without having first destroyed a few gold interconnect wires. The MCU guys need those gold interconnects to remain intact, so they brought a secret encryption key and enlisted help from the technician Biblio.

First though, they had to get past the TO-92 packaged parts that wanted to squash them into jelly or tacky flux. Fortunately, despite the bumbling of technician Biblio, the Wizard bought solder with no-clean flux which made the TO-92 parts stop moving once applied. After the TO-92 parts stopped working in daylight, they made a brief stop to inspect the last Homely Chip Fab in the Silicon Valley and see where the light sensitivity came from.

Passing over the Siskiyou Mountains on the way to Oregon and The Lonely Mountain Chip Fab, it started raining so they went into a cave and ate porc for dinner. Biblio ate so much that he fell asleep in the corner behind a chair where no one could see him and his buttons popped off. The missing buttons didn't bother him too much because those ones had a de-bounce problem anyway. Luckily, they weren't Grayhill switches or they would have hates Biblio forever, even if he used an ancient gold Tolkien-ring network to bypass more porcs.

Biblio wasn't the most skilled technician and he caught his pine cones on fire while trying to solder new switches into place, but the wizard was able to re-layout the board using Eagle CAD and an FPGA that could take many forms and would satisfactorily control the machinery and bears at the local honey production facility. But the FPGA brought them all into the murky world of Verilog and VHDL. That would have been fine except that the search engine spiders hadn't crawled the eleven Wikipedia pages they needed to properly map out the clock routing.

The MCU guys got hungry and wouldn't wait for Biblio to come back with pi so they rushed in causing so much in rush current that the lights went out with a snap. After eleven clock cycles in his new hall-effect switch, Biblio knew that the de-bounce problem would be gone except when he plugged the barrel jack into his Apple computer. But with no static guards to wine too, he had no choice but to use the Apple barrel jacks to get power to MCUs and switch open the flip flop made from a streaming-transistor logic gate.

Annoyingly, they split the story in two and the movie will end at this point. We'll have to wait another year to see if Silicon Oakensubstrate is robust enough to kill the terrible ESD spike and pass final QC.

Duane Benson
One oven to reflow them all

Cool Customer Application

It's not all that often that we get to see or can talk about just what is done with the boards we build at Screaming Circuits. In most cases, it's a proprietary product or some government thing. But, recently we built some boards for NTH SYNTH. They have a successful Kickstarter project to produce a music synthesizer. They describe it as: "It is fun to use, sonically-rich, and hackable by design." Go check it out.

Nthsynth-small-007

[This image is from their website] I had wanted to take some photos for them of their PC boards being assembled on our SMT machines, but the boards ended up being built on one of our night shifts and I missed the chance.

Duane Benson
They're the people out there turnin' music into gold
But hopefully makin' more than Jim Bass' two-fifty for an hour

 

Retrospective

The other day, I needed just a few things at the grocery store which, given the small town I'm in, should have been a quick no-stress fifteen minutes. But, some kids were sitting in the middle of the first intersection I came to and didn't seem to want to move out of the way of my five thousand pounds of rolling danger. Traffic at another intersection was backed up due to a train. On the next block, I had to follow someone, likely looking for an address, at about ten miles per hour. Then there were pedestrians crossing the street far slower then human body mechanics are designed for. In the store, it seemed like every isle I tried to go down was blocked by carts or people. The "short line" at check out turned out to be short because a customer and checker were having payment issues. The drive home was much like the drive in. In short, there was nothing short about the trip. Nor was there anything low-stress about it.

But this is a blog about electronics stuff. It's not a shopping blog or a driving blog. The point is, that trip reminded me of projects I've been involved in years ago. Someone changes a spec after that part of the design is complete. The only version of a key component on the approved vendor list has a 12 week lead time. It's Friday, at 4:00pm, the board files have to be shipped off by five, but there's still several hours of double checking left to do. While placing the prototype parts order, you keep getting distracted by loud talking in the background.

Ugh. Not only is such a thing blood pressure raising, but it also can lead directly to problems any of us would never dream of letting out the door. Like these here:

Too little time can cause problems. So can too much stress and distraction. There's not always a good solution, but anything to reduce stress and agravation while doing final checks is probably a good thing.

Duane Benson
Is there "lab rage" like there's "road rage"?