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Mark
Those Diodes!

Every
now and then, I write about ambiguity with diode marking; like here, here, or here. It's a pretty important subject to get right, but what
does it have to do with Marco Polo, you ask? Well, that depends on whether
you're asking about the person or the game.

In the game, people try to find someone, without sufficient information. One
person, designated "Marco" closes their eyes and periodically yells out "Marco."
The other people respond with "Polo", and the Marco tries to find one of those
other people with just the audible cue. For some critters, that's an easy task,
but for the average human it's not always so easy - especially when the diode
doesn't audibly respond to "Marco."

If you're talking about the explorer, Marco Polo; well, he set off on an
adventure, got lost, and either saw a bunch of cool stuff, or made up a bunch of
cool stuff (depending on whom you ask).

Again, you ask... "What does this have to do with hamburgers in a handbag, or
with diodes?"

It has to do with the fact that he didn't know where he was going, and, that
without clear marking, it's not always possible to know which way to point the
diode.

So,
we're celebrating Marco Polo month with our Screaming Circuits Marco Diodo Polo
shirt.

If you place an order with Screaming Circuits during May, 2015, we'll send
you an email with instructions telling you how to get a free Marco Diodo
Polo shirt after your next order (provided the order is placed between May
1, 2015 and on or before June 5, 2015). If you place an order between now and
then, and promptly respond to the email, you can get one for free (a shirt. Not
an order).

Duane Benson
Fifty-four fourty, or fight!

Posted on May 7, 2015 in Announcements
, Circuit
Puns

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Via
in Pad - Why and How

There are many reasons you shouldn’t use via in pad. It’s not good practice,
and those via holes act like little
capillary straws and suck solder off of the pad or the BGA.

That said there are some applications that may require, or seem to require,
via in pad. Here are a few examples of why you might need to use via in
pad:

If there is not enough space on the board.

It can help with thermal management.

Trace routing may be easier with via in pad.

High frequency designs benefit from the shortest possible routing to
bypass capacitors, which may indicate via in pad.

So if you don't have a choice, here are some methods you can try when using
via in pad:

Have
the board fab house plug the via and then plate copper over it. This is
our favorite option. It will give you all of the benefits of via in pad
without causing problems in assembly. It's really our only recommended
via-in-pad method.

Use a micro-via that only goes through one layer of the board. Although
this may be an okay option, the solder can still wander down into the via,
leaving voids.

Cap the underside of the board with solder mask. This is our least
favorite option because sometimes the cap can pop open, and the void may
be big enough to still pull too much of the solder off of the
pad.

For more information on via in pad, check out this video. http://scrm.it/viainpad

Posted on April 17, 2015 in Tips
and tools , Via
in Pad

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Internet
of Things Got Your Tongue?

By now, most of you have heard about the Internet of Things (IOT). If not,
here's a quick summary:

The Internet of Things is the concept of having pretty much everything
connected to the Internet in some way shape or form. At the simplest, it's the
ability to turn a light bulb off and on with your smart phone. At a more complex
point, it is all of the devices in your house, car, recreation, services, and
office connected and talking.

Lights will automatically go on and off as you move through your house or
office. When it's time to get up for work, your coffee will be brewed, your car
will pull up to your door, your house will know when you leave and will lock
down and turn off unnecessary devices - all without any intervention from you.
The streets will talk. Utilities will talk. Everything will talk, coordinate,
and manage.

It won't be enough for your computer to "ding" when an email arrives, or your
phone to "buzz" when a text comes in. No; the IOT wants to control your life.
And, it wants to nag you about all of it too.

The IOT will be good for us, because it will require a lot of super small
parts, which we happen to like. In honor of that, we declared April, 2015 to be
Internet of Things month, and created an "Internet of Things gone Bad" poster.
The poster, by local graphic designer Kyle DeVore, is 18" x 24" and suitable for
framing.

The early birds already have theirs, but we have a few more. If you're a
current customer and would like one, shoot an email to
[email-masked]. We'll give them out until we run out. First come,
first served.

Posted on April 6, 2015 in Announcements
, Circuit
Puns

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Screaming
Circuits introduces new Cordwood assembly service!

Tired of all those small parts? Can't figure out how to route traces to all
1,900 balls on that hot new FPGA? If 0201 passives have you running scared and
the possibility of 01005 parts coming soon has you on the floor, Screaming
Circuits has the answer.

Take a few steps back and use our new Screaming CordwoodTM assembly
process. It'll feel good to put your hands on a honk'n 2-Watt, through-hole
resistor again. No need for fancy, multi-headed SMT assembly robots with
Screaming Cordwood. No need for precision anymore. Just put those parts a
quarter inch apart and you'll be suckin amps just like the good old days. And if
you don't think it's high-tech enough; consider that Cordwood construction has
taken man to the moon and back. You can't say that about surface mount!

Posted on April 1, 2015 in Circuit
Puns , General
interest

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Indicating
Polarity On Diodes

Everyone knows which way current flows through a diode. Right? Of course they
do. Diodes only allow current to flow in one direction.

Well, sort of.

In the case of your garden variety rectifier, barrier diode, or LED, that's
true. That line of thinking leads a lot of people to assume that you can
indicate diode polarity by putting a plus sign "+" next to the anode.

Here's why you can't.

Zener and TVS diodes have a breakdown voltage. They are put in the circuit
with their cathode on the positive side. In that configuration, they don't
conduct unless the voltage rises above their breakdown point. Zeners and TVSs
are used for regulation, transient suppression, and things of that sort.

But wait! There's more!

Regular diodes can be pointed backwards too. Anytime an inductive load is
switched, like a solenoid or motor, you need a flyback diode to protect the
switching logic. A MOSFET switching a solenoid on and off is a good case to look
at.

When
the MOSFET turns off, the current in the solenoid coil starts to drop. As it
starts to drop, the magnetic field generated by the current flow starts to
collapse. The collapsing magnetic field generates an opposite current, referred
to as flyback, or back EMF.

To save your silicon switching device, you put a flyback diode across the
coil, or motor, terminals, pointing backwards from normal current flow - with
the cathode pointed toward +V. Doind so shorts the flyback current back into the
coil, preventing damage to the MOSFET. These are typically Schottky diodes, but
can be ordinary rectifier diodes.

A "+" plus sign alone, doesn't tell anyone anything. For more information on
what to do, read this post. Just for fun, read this post too.

Duane Benson
Diodes. Not just for breakfast anymore

Posted on March 27, 2015 in CAD
Parts Libraries , Layout

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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:

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.):

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

Posted on March 20, 2015 in CAD
Parts Libraries , Circuit
Design , Engineer
stories , Layout
, Partners

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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:

I have three different sets of PC boards.

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)

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:

And, here's the shared escape:

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.

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

Posted on March 5, 2015 in CAD
Parts Libraries , Circuit
Design , Engineer
stories , Layout
, Partners

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Internet
of Things Month

I’m not sure exactly when the term “Internet of Things” (IOT), was
coined, but it’s become one of the hottest topics in the electronics industry.
The IOT is all about connected devices, most small and independent; many from
makers and new start-ups.

In the IOT of the near future, virtually every household, office, and
personal device will be remotely controllable to some degree. And, it’s not just
about control. Most of those devices will also sense conditions, respond, and
communicate appropriately.

If you were to take a tour of our factory floor today, and compare it to a
tour of a few years ago, you’d, of course, see more large boards loaded with
complex components. You’d also see a lot more super small boards crammed with
microcontrollers, wireless communications, sensors, and tiny parts. Many of them
are no larger than a US quarter. Those are Internet of Things devices.

The number of different devices being churned out is staggering, yet is a
trivial number compared to what we’ll see in the next few years. Scoff, if you
must, but there will come a time when your favorite ball-point pen can let you
know just who stole it off of your desk and where they've hidden it.

In honor of the spirit of innovation brought forth with the IOT, Screaming
Circuits has declared April 2015 to be Internet of Things month.

You
too may be able to join in the celebration by placing an assembly order during
March 2015 and requesting our “Internet of Things Gone Bad” poster: a contrarian
view into a possible dystopian world where humans have to argue with their
clothes, coffee pots, and cars, before leaving the house.

If you places an order with us in March 2015, will get an email asking if you
want out Internet of Things poster. Just reply in the affirmative, and we'll
send it out to you.

Duane Benson
All things on the Internet are relative
All my relatives
are things
My relatives took all of my things

Posted on March 3, 2015 in Announcements
, Industry

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Component
Footprint Rotation, Take II

I've noticed that a lot of CAD library footprints for two-pin polarized parts
have pin one pointed up as zero degree rotation. According to IPC, pin 1 pointed
to the left is zero degree rotation.

Why is this such a common error? I can't be certain, but I have a pretty good
idea.

Surface mount parts, as everyone knows, generally come in reels of tape. It
stands to reason, that the parts would be placed into the tape at a standard
zero-degree rotation. They generally do. Before putting a perplexed look on your
face, take a look at the image below.

When looking at the tape, it's a pretty natural thing to pull
it out and hold it horizontally - with pin 1 up - perpendicular to our angle of
vision. Makes sense. It's not a stretch to look at this strip of tape and end up
assuming that pin one is up at zero rotation.

However - the machines are the ones being spoken to. Not humans. The machines
get the parts in line with their line of vision. That puts pin one on the
left.

Makes more sense when you look at it this way. Running into
the machine, pin one, at zero rotation, is on your left.

For more to the part rotation story, tune your browser dial to here. Or just scroll down a little bit. It's right below.

Duane Benson
The long and winding reel leads to your pc board. Not your
door.

Posted on February 20, 2015 in CAD
Parts Libraries

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Component
Footprint Rotation

Before we (or any old assembly house) go about putting surface mount parts on
your board, we need to program our assembly robots. I'm oversimplifying, but
essentially, the machine program needs to know the X / Y coordinates, relative
to the board origin (which is the lower left-hand corner), the part rotation,
and the side of the board.

In years past, we needed a Centroid file (AKA pick-and-place file) containing
all of that information. In some cases, we still need the Centroid, but not
always. Today, we can get the same information from ASCII CAD files, ODB++
CAD files or Eagle .brd files. You only need a Centroid if you send us your
board files in Gerber format.

If you do send us a Centroid file, you no longer need to worry about
rotation. The IPC has defined the zero degree orientation, as well as proper
rotation direction, but too many part footprints set the zero degree at
different angles. We can't rely on the data.

While we have to ignore rotation and figure it out with other means, we still
do strongly recommend that you follow IPC standards when you make your own
footprints. I've got some illustrations below, showing how footprints are
supposed to be oriented.

Duane Benson
There's no earthly way of knowing
which direction we are
going
There's no knowing where we're rowing

Posted on February 13, 2015 in CAD
Parts Libraries , Our
website and Process

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Recent Comments

I agree, that is horrible! I have c

Geoffrey
Hunter

regarding How
NOT to mark a diode

Doh! I hate it when I do that.

Duane
Benson

regarding More
Thoughts on Via Near Pad

I would have to say that I was quit

Duane
Benson

regarding Layout
101 in 1989

With those odd shape type parts, th

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Benson

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Yes. A follow-up is on the way. I h

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regarding Using
the Newest gen ARM Microcontrollers

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