QFN? QFP? QFwhat?

The QFN (quad flat pack, no leads) has become my favorite integrated circuit package. It's very compact, yet is easier to use than a micro BGA.

Micro BGAs of 0.5mm and smaller pitch become a bit more difficult and costly with more than two rows of pins. At those geometries, escape routing can involve plugged and plated vias which adds complexity and cost to the board fab. QFNs can be almost as small, but have all of the pins exposed around the edges - so, no need for escape routing.

One thing that's important to note, is that despite sharing the first two letters (Q and F), the QFP and QFN footprints are not interchangeable. We do, from time to time, see boards laid out for one along with the other form packaged part. Arduino w QFN and QFP

Take a look at this PCB layout clip from the Arduino Leonardo. It has both footprints on the board. You can see how much bigger the QFP package is.

They put down both footprints because the Atmega32U4 chip used in the Leonardo sometimes has supply issues in one package or the other. This gives them the flexibility to use either without making any changes on the board.

You might consider this as an option if you have the space for a QFP and are concerned about the available of one package variant or the other.

If you do, there are some very important things to check out:

  • Make sure the pin-outs match. Some parts will vary the pin-out a bit between packages or have extra pins on one or the other.
  • Make sure the extra space won't cause noise problems. Generally, you want bypass caps as close as possible to the supply pins. This amount of extra space probably won't be a problem when using a QFN, but in some designs, it might.
  • Make sure the board won't be in an environment where unsoldered pads will be a problem. Some harsh environments could attack the unsoldered pads. If that's the case, consider conformal coat.

Duane Benson
We're always being pushed and shoved by people trying to beat the clock
But we like it - it's what we do

Does Anybody Really Care?

The upside of a visible identity is that people see you can might possibly care and understand. The downside, is that people can find you. Today, I'm sort of treading the line between the two.

I'm testing out some Twitter ads right at the moment. As someone that has a service to present, I have to do things like that. Ideally, it won't be intrusive and will just give information, but that's not the point.

One of the steps in putting together a Twitter ad is to select categories of Twitter users that might be interested in what I do. The process of picking those categories reminded me of something that's almost always annoyed me when I have to pick my categories for anything. Namely, my categories aren't there.

This particular ad, is sending people to eBay to buy (hopefully) a coffee mug with the Sputnik 1 transmitter schematic on it. We're doing it to help out our local FREE GEEK place. (Yikes! Three links in a row) Again, that's not the point here.

I'm thinking that electrical engineers would be interested, as would space fans. Well, those categories don't really exist. The have a major category: "Business." The closest sub category in Business is "Technology." That's somewhat close, but do engineers really want to be classified as in the business world?

 "Careers"; nothing close in the sub categories. "Education"; nothing close. "Events" has "Tech Tradeshows" as  a sub-category, but as with business, it's not really where I'd look.

"Hobbies and Interests"? Nope. They have "Astrology", but no hobby electronics.

There's the category "Science", but its subs look like chapter headings in a sixth-grade science book.

Wait! There's "Technology and Computing"! That looks promising... But... No. It's pretty much software and IT.

And, that's it. I see this sort of thing all over the place. Software, IT and businessy stuff get categories, but electronics design, embedded computing, robotics... Other than in the direct EE press, these types of categories just don't seem to exist.

Duane Benson
What time it is?

PART 2, SCREAMING CIRCUITS AND THE MAKER COMMUNITY

My last post mused on the affordability of assembly at Screaming Circuits for the maker/very small business/kickstarter community. My hypothetical Arduino-compatible dual motor driver Kickstarter came out to $9.81 per board at a quantity of 250. That's probably more than a cheap off-shore assembler, but we'll get you 100% yield. They probably won't.

TI TPS62601 front and backIt's more than just cost though. Many of the budget manufacturers won't do the most complex parts. For example, I could shave about a square inch off of the board size - maybe two - by using 0402 or 0201 passive parts. That's about $.50 - $.75 less per board for the blank PC board. Most discount assembly shops won't assemble 0201 parts. Many won't assemble 0402 parts. Screaming Circuits will assemble 0201s, and your little micro BGAs too!

The part on the right is a tiny wafer scale BGA next to the edge of a U.S. dime. We can build that.

If you're just designing the board and not hand assembling, putting in 0402 or 0201 parts is no big deal. You just design it and let the robots build it. If your assembly house can't deal with those small parts, your stuck. You've lost some freedom of choice.

Now, you would expect me to be biased, because I work here, but more than bias, it's a matter of picking the right tool for the job.

If time is your key driver and cost isn't an issue, you'd want quick-turn Full-Proto; our Short-Run production would be the wrong tool.

If cost is your key driver, you have more time, you need predictability, and need good yields, our 24 hour Full-Proto service might bankrupt you, but our 20 day Short-Run can do all of the hard work for you, and you'd know exactly what you're getting, and when: 250 working boards in 20 days, for a decent price.

Here's a Kickstarter project we built earlier this year.

Duane Benson
Don't use a Marten64 0-dot-19 Freembulator when you really need a Model B Mitchel Warbler brand size 32.125 green Sackcombobulator.

 

Part 1, Screaming Circuits and the Maker community

Can Screaming Circuits, a full-service assembly provider, compete with a “no-frills” assembly house?

Upon first thought, it might seem like Screaming Circuits, would be too expensive for anything but well-funded big-business and big-education. In reality, that may not at all be the case. Like so many other things in life, there are trade-offs between time, effort, and money. The nice thing about Screaming Circuits is that, unlike the low-cost small volume manufacturers, we can cover both ends of the spectrum.

Our least expensive service is not as cheap as the lowest-cost assemblers. We don’t sell on price, but when you start to add in reality and practicality, the cost difference gets much smaller.

OpenHardware logoIf you need that maximum performance, “I need it now, now, now!” service, there’s no question that you need a premium manufacturer, like Screaming Circuits. But let’s do some compare and contrast on the other end of the spectrum. Can Screaming Circuits be a good deal for a maker?

I’ve got an open source Arduino-compatible robot motor board that I designed a while back. I’ve hand-built a few, because I enjoy soldering, but for this exercise, we’ll pretend I’m a maker with a Kickstarter and I need more built up.

I’ll need 250 for the hypothetical Kickstarter project. The 1.5” x 3.5" board uses an ATMEGA32U4 processor with the Arduino Leonardo bootloader. From a software perspective, it looks just like a Leonardo. It uses a different hardware form-factor than the standard Arduino to better fit a mobile robot.

1-DSC_0001It’s got 26 different components (26 line items in the Bill of Materials). Due to some part types being used in multiple places, that’s a total of 48 surface mount (SMT) placements. I’ll ignore the few thru-hole parts. As a Kickstarter, I would supply the board with all of the SMT parts installed and let the customer solder in the thru-hole parts. That’s pretty common practice in the hobby, maker and Open Source world.

You can quote the assembly on the Screaming Circuits website without registering, so let’s do just that. It’s got:

  • 250 desired board quantity
  • 26 unique parts (BOM line items)
  • SMT on 2 sides? Yes
  • Lead-Free? No (If you’re shipping into Europe, you’ll need lead-free)
  • Class III? No
  • ITAR? No
  • 48 SMT parts
  • 0 thru-hole
  • 0 BGA/QFN

For 20 day, Short-Run production service, this comes out to $9.81 per board - less than $10.00 each.

Soldering by hand, I can do about two an hour. Some folks are faster than me, but some are slower. At two per hour, I’d spend 12 ten-hour days hand soldering the 250 boards. Ouch!

You can most likely find a cheap overseas manufacturer that would build 250 them for less, but they may not want such a small job. You may end up with concerns about intellectual property theft, and you may not get the yields you need.

At Screaming Circuits, we treat every job as proprietary, we’re happy with a run of 250 without any commitments for more, and we promise 100% assembly yield. Finally, a job like this, that totals out to $2,452.48, gets the same process and care as does a $10,000 quick-turn complex prototype.

Food for thought.

Duane Benson
Here's a Kickstarter we built back in 2012

National Low Earth Orbit (LEO) Month

Sputnik 1Coming soon, on the heals of National High Voltage AC month, Screaming Circuits has declared October 2014 to be National National Low Earth Orbit (LEO) Month in honor of the October 4, 1957 launch of Sputnik.

This month, rather than T-shirts, we're offering a custom coffee mug sporting the schematic diagram of Sputnik 1's transmitter. The first 100 customers who place an order in September, 2014, will have the opportunity to get one of these mugs for free.

After your order is confirmed, we'll send you instructions explaining how you can get yours and what the deadlines are.

If you don't have anything to order, you can still get your mug by buying one (through ebay) for a measly $10.00. The whole price, less ebay/PayPal fees will be donated to FREE GEEKs. From the FREE GEEK website: "a Portland-based
NLEO month mockup501(c)(3) nonprofit offering free computers, technology and education powered by reuse & recycling in association with Oregon E-Cycles."

We think that's pretty cool, so the money from these mug sales will go to them.

Also, the first person to build a working copy of the transmitter will get another mug free. It could be hard, though. You might have to fabricate the tubes yourself (People do that, you know). If you can get it working and into ordit, you'll get one more for free.

Duane Benson
WARNING! This is a plot complication!
WARNING! This is a plot complication!

Remote ESD

ESD, or electrostatic discharge, is of great concern to anyone who deals with electronics. That's obvious. What's not necessarily so obvious, is that some times, you don't even need to be all that close to the circuit board or component to damage it.

This article by Douglas C. Smith illustrates why sometimes, just a wrist strap isn't enough.

That's why we don't only use wrist straps, but also have a grounded conductive floor and use ESD jackets and conductive foot straps to protect the boards and components out on our manufacturing floor.

Here's a video showing the dreaded ESD monster and us protecting your gear from him: 

Duane Benson
Greased lightning is an interesting concept
Would it reduce power line transmission losses?

Warped PC boards

So... You just got a nice big PC board back from the fab shop. You set one on your desk to admire only to discover that it's warped. What do you do?

There are two primary types of causes of board warping: process related at the fab or assembly shop, and layout related issues. If it's warped before assembly, it's between fab and layout. If it's flat before assembly and warped, after, it's most likely between layout and assembly - although, sometimes a fab problem won't show up until a pass through the reflow oven at your assembly partner.

Determining the root cause is generally a bit of an iterative process. It's tempting to start right off with your fab or assembly partner, but you need some information before giving them a call. You'll need such things as the amount of warpage per inch, board size, and thickness. With that, you need to take a good look at your design and consider copper pours, component size, and component placement.

With that information in hand, you can make your phone call. If the board is warped before assembly, call your fab shop. If it's flat pre-assembly and warped post assembly, call your assembly house.

The shop you call will want to talk over your design to help you pinpoint the cause. If you can rule out a design issue,then you need to talk with your partner to determine whether it's a fab or assembly issue and next steps to take care of you.

 Here are a few design issues that could contribute to warping:

  • Uneven copper pour. Copper and FR4 are a good match relative to thermal expansion, but they aren't exact. A large pour on one side or corner of your board can lead to warping due to dissimilar expansion characteristics. This could cause warpage either at the fab shop or the assembly house.
  • Components with large thermal mass grouped together on the board. This would be more likely to cause problems during assembly than during fab. The thermal mass will act as a heat sink for that area on the board, which can lead to uneven expansion and uneven soldering.
  • A board that's too thin for the size or number of components could lead to warping at any stage.
  • Odd shapes or large cut-outs could also lead to warping at any point.

There may be other, more obscure causes, but those are the main design related causes. If it's none of those, talk with your partner.

Occasionally, design requirements lead to a board that is essentially non-manufacturable. Hopefully, you never have this situation, but if you do, make sure that thickness, component location, pours, or cut outs really, really, really, need to be the way they are.

If you absolutely, positively can't change anything, go back and try again. Then you can to look for heroic means to get the board fabbed and built.

Slight warpage might go away when the board is mounted. Just be careful with that. Some components may not stay securely soldered when you flatten it.

The board may need a special fixture during assembly to prevent warping. This will likely cost extra, but if you can't change your design, and still need it built, it may be your best option.

Finally, if nothing works, you may need to look harder at the design, or look for a new fab or assembly house. We all like to think we can do just about anything, but every shop has its limits, and on rare occasion those limits can be difficult to spot.

Duane Benson
What if Godot was late because he was waiting for John Galt?

BGAs and Package on Package

POP with dimeTake a look at the closeup of one of our Beagleboards here on the right. That's what package on package (POP) looks like up close. The bottom chip is a Texas Instruments OMAP processor, in BGA form with 0.4mm pitch solder balls. It has a land pattern on its top for the top layer, which is a Micron memory chip in 0.5mm pitch BGA form.

A few years back, we built a small handful of Beagleboards ourselves, just to showcase our POP capabilities. It's hard to believe that we did that back in 2009. The Beagleboard has undergone a few iterations and spawned the Beaglebone since then, but 0.4 mm pitch is still pretty small.

Small, but not really all that uncommon anymore. "Smaller" is on the way. In fact, though it's a special process, we've even built a few 0.3mm pitch BGAs.

If you're joining the fun and starting to use on of the Ti 0.4mm pitch BGAs, you might want to take a look at what we learned from the Beagleboard folks about the land pattern.

Duane Benson
The sandwich needs pickles.

National High Voltage AC month

N_TeslaIn honor of Nikola Tesla, hero to engineers', birthday (July 10, 1856), Screaming Circuits has declared this to be National High Voltage AC Month.

For those of you who don't know Nikola Tesla... Never mind. If you don't know who he is, you're probably not an actual engineer. If you are an engineer, but still don't know, I challenge you to use your powers of self-education, and spend a little time learning about the person who pretty much made the modern world possible.

Part of our homage comes in the form of a free T-shirt. Every customer who places an order before August 10, 2014, 5:00 PM, PST, will have the opportunity to get a Free "National High Voltage AC Month" T-Shirt, designed by local graphic artist, Kyle DeVore.

T-shirtLook for instructions via email on how to get a free T-shirt after your next order (provided the order is placed between today and on or before August 10). If you place an order between now and then, and promptly respond to the email, you can get one for free.

But, what if you don't have anything to order? Well, you can still celebrate life threatening high voltage induction by buying a T-shirt from our page on teespring.com. (link here).

Any profits from the sale of the shirts will be donated to the Tesla Museum at Wardenclyffe.

How Teespring works: Orders can go in during a 21 day window. If you buying one, you don't get charged until the closing date. After that, they send you the shirt about a week or so after. They send any profits we made on the shirt directly to Tesla Science Center at Wardenclyffe; a 501(c)3 not-for-profit organization registered with the State of New York.

If you're a recipient of one of the free shirts, you won't pay anything. Your shirt will be mailed at about the same times as the paid shirts.

Born of Fire

There are a lot of places suitable for running an electronics manufacturing plant. Ours is in Oregon, USA – the Silicon Rain forest, if you will. The slower pace of life here, the proximity to recreation and wilderness, the rain soaked green hills; all help to create a healthy and invigorating environment. That’s a healthy environment for those of us that work here and that helps us to deliver dedicated service and quality product on time.

Deep in the woods of Oregon - up at an elevation of about 3000 feet, tucked behind soaring trees in a remote corner of the West-central Cascade foothills lays an alluring, mystifying volcanic remnant, known as Clear Lake.

Snow melt from nearby Mt. Washington and many of its Western hillsides, plus a series of complex underground springs, fill it with extremely cold, ultra-pure water. This creates an average temperature in the lake that is so low that comparatively little algae growth, or other biological activity that would otherwise obscure entering sunlight is able to thrive. Scuba divers are drawn to the exceptionally clear waters to see, with their own eyes, the remains of the ancient forest dispersed along its bed, still preserved in frigid stasis from the time the lake was formed.

Clear_Lake_with_Mount_Washington 500Just to stand on the shoreline and gaze into the slowly rippling turquoise-blue waters, which allow for visibility of up to of 100 feet below the surface, can create a dreamlike feeling of wonder in the observer. Don’t get too comfortable, however… because a miles-long sleeping giant who carries the secret of how the lake originally formed rests motionless, just a few miles to the East.

The Sand Mountain Volcanic Field towers another 2000 further vertical feet above Clear Lake’s shoreline, yet is just a few miles away. It is a massive alignment of 23 cinder cones, sitting dormant, interspersed with 42 distinct vents.

Around 3000 years ago, lava eruptions from vents within this volcanic field flowed downhill and blocked a river, drowning its valley. This immense flow of lava formed Clear Lake and created the relic of standing trees still visible in its depths today.

Porous volcanic rock and soils within these hillsides capture snow melt and other moisture for a gigantic naturally occurring filter. It will be an estimated 2-10 years before it reemerges at Great Spring, on the North East end of Clear Lake.

When the lake water exits over the centuries-old lava flow, the cascading deluge becomes the headwaters of the McKenzie River - and the highest permanent source of its clean, fresh water. The river then flows downhill towards the cities of Springfield and Eugene nearly 75 miles away, providing over 200,000 with their sole source of drinking water.

For 8,000 years – until the early 1800’s – peoples of the Molalla, Sahaptain, Chinook and Kalapuya tribes traveled, hunted, and lived along the McKenzie River. Very little has survived from their culture, but it’s interesting to wonder about what they contemplated when standing on the beautiful shores of Clear Lake, and as they witnessed firsthand the extraordinary events which created it.

You can find this gem for yourself, on Oregon state highway 126 (The McKenzie highway) - just two hours and 20 minutes from your pc boards being assembled at Screaming Circuits. 

Audie Stoehr