Author Archives: Duane

About Duane

Duane is the Web Marketing Manager for Screaming Circuits, an EMS company based in Canby, Oregon. He blogs regularly on matters ranging from circuit board design and assembly to general industry observations.

Proper PCB Storage — The Top 3 Hazards

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It’s late. Do you know where your printed circuit boards are? Let me rephrase that: Can unused PCBs be stored for future use?

Yes, they can – if stored properly. Keep them wrapped up, or sealed in a bag. Anti-static isn’t necessary in this case, but it won’t hurt. Keep them in a cool, dark place. Keep them clean. Do your best to avoid dropping them on the floor and stepping on them.

The board in this photo was left out on a desk for a while, and then shoved into a desk drawer. The environment took its toll on the immersion sliver finish, making it very much unusable.

What can go wrong:

1. Fingerprints. The oils on your finger can etch fingerprints into ENIG or immersion silver board surfaces. If you plan on committing a crime go ahead and do this so we can catch you. If you aren’t going to start a life of crime be careful to not get your fingerprints on the board surface. Handle on the edges, or at least, don’t touch any exposed metal.

2. Moisture. Moisture is good for your skin but not for your PCBs. Over time, PCBs can absorb moisture, especially in a humid location, or the ocean. If thrown into a reflow oven they then might laminate. Store boards in a dry environment. If stored for a long time, you may want to pre-bake them prior to use.

3. Atmosphere. Sometimes dirty air can contribute to tarnish or corrosion on the exposed land pads. Dust can settle onto the boards as well. Tarnish and dust can usually be cleaned off, but corrosion can’t. Wrap up your boards for long-term storage.

Treat your boards well and you can likely use them at a later date. Don’t treat them well and you may need to replace them, wasting a bunch of money. Often, the damage isn’t as clear as in the above photo, but could still lead to poor solderability.

Duane Benson
Don’t surf on your silver

http://blog.screamingcircuits.com/

What is Personal Manufacturing?

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There’s a lot of buzz floating around these days, about “Personal Manufacturing.” Screaming Circuits has more than a decade of bringing personal manufacturing to engineers. We pretty much started the category in the electronics industry, so we’re quite familiar – but not everyone knows what personal manufacturing is. I’ll do my best to describe it, and what it can do for you.

The short answer, is that personal manufacturing is building your boards on your terms, not on the terms of some nameless, faceless factory.

The longer answer is probably more useful.

Traditional manufacturing is all about statistics and fractions of a penny. Those factors are important; especially if you’re manufacturing millions. But, when you just need a few boards, or a few hundred boards, those factors can make your job nearly impossible.

With personal manufacturing you can decide when you want or need assembled boards on your workbench. You won’t need to beg for time on a busy volume manufacturing line. In the case of Screaming Circuits, it’s cloud-based manufacturing so you can order online from your desktop, when you’re ready, rather than waiting for someone to pick up a telephone.

With personal manufacturing; you design it, get some prototypes, make a few mods, lather, rinse, repeat. Then, you’ll get a few dozen, few hundred, or few thousand, and start selling. You’ll get what your budget allows and don’t need to commit to minimum volumes, or long-term business. You can polish your design faster, with less hassle, and you can get to market faster, with less hassle. Faster to market and less hassle both mean more time and money for you.

NPI (new product introduction) has never been easier than it is with personal manufacturing. Years ago, I was a product manager at a start-up. The entire NPI process was a nightmare. Our engineers couldn’t get anything built without half a dozen support staff. Someone had to make the documentation usable. Someone had to hunt down sample quantities of parts. Someone had to make sure the board would fit on the volume manufacturers’ assembly line. It went on and on like that, taking up months of the design cycle. We were at the mercy or people who only cared about making their part of the process easier.

Rather than producing the quality product we wanted, our new products would be shipped to customers with mod wires. I recall one board that needed 64 mod operations before it could be shipped. Yes, that was on a released, shipping product.

With personal manufacturing, as Screaming Circuits provides, you can get a few prototypes built right away. If need be, you can modify, and get a few more built at your convenience. When the mode wires are gone, you can build up a hundred and get them out to customers without delay. It’s not about what works best for Screaming Circuits; it’s about what works best for you.

Duane Benson
Right now a personal pan pizza delivered to my desktop would work for me.

http://blog.screamingcircuits.com

Manufacturability Index in Practice

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My prior blog covered the Screaming Circuits Manufacturability Index. It’s something I’ll be using from time to time when discussing new components I run across. I’ve got a few examples to put the numbers into context.

On the low side of the index, we have:

1: Just about anyone could hand solder the part
Examples: Through-hole parts

The SN7400 quad NAND Gate, shown on the right, is a good example. It’s big, it’s through-hole, and if someone has trouble hand soldering it, they really need a few more classes. 

Closer to the other end, is a new chip I’ve run across. The Silego GPAK4 is a small FPGA-like mixed signal device. It’s got a number of analog peripherals, a bank of programmable logic, and the ability to configure it up the way you want. Take a look at it below:

This little thing is housed in a 2mm x 3mm QFN package. That’s pretty tiny by the standards of my giant fumble-fingers. I’ve given it a rating of 4.b, on the Screaming Circuits manufacturability index. The number ranking “4” means: “Needs advanced automated assembly technique“, and the letter suffix “b” means: “Typical level of challenge within the number rank.” In other words, right up our alley.

Unless you posses super-human abilities, and maybe lasers in your eyes, you won’t be hand soldering these. You’ll have them assembled by us (or someone with the same technical capabilities as us), where it will be a standard process.

If you do want to put one or more of these in your design, you will want to make (or find) a custom library footprint for your CAD software. Due to the variable length pads, a standard one-size-pad footprint might lead to solder joint reliability issues.

Duane Benson
The chips go marching one by one, hurrah, hurrah
The chips go marching one by one,
The little one stops to suck her thumb
Just to see if the solder is lead-free

http://blog.screamingcircuits.com/

Component Manufacturability Index

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Screaming Circuits’ Manufacturability Index Ranks the difficulty of assembling a component. Index is one to five, with one being easiest, and five being the most complex

Sub index: a, b, c

a: Not a challenge within the number rank
b: Typical level of challenge within the number rank
c: Fits in the ranking, but likely needs special process, fixtures or attention

1. Just about anyone could hand-solder the part
Examples: Through-hole parts

2. Surface mount. Should be machine placed, but big enough to hand solder
Examples: 0805 or larger surface mount passives, SOIC packages

3. Pretty much any grade of surface mount equipment can handle this component
Examples: TSSOP or larger, 0.8mm pitch BGAs

4. Needs advanced automated assembly techniques
Examples: 0.4mm pitch BGAs or QFNs, CSP (chip scale package) or WSP (wafer scale package) BGAs, 0201 size passives, Package on Package (POP)

5. More or less R&D at this point. Few companies have or will assemble this part
Examples: 0.3mm pitch micro BGA, 1,700+ ball BGAs, 01005 passives

Just about everything 4b, and below are routinely within Screaming Circuits standard (guaranteed) process. 4c, 5a, 5b, 5c, are becoming more common here. These are special process (falling outside of our guarantee), but we can usually do a good job with them. You’ll need to speak with a manufacturing engineer before placing the order.

Duane Benson
A colossal negative space wedgie of great power coming right at us at warp speed
Readings are off the scale, captain

blog.screamingcircuits.com

Mark Those Diodes!

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MarcoPOLOLogo5Every 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.

BlackPOLOSo, 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!

blog.screamingcircuits.com

Indicating Polarity on Diodes

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Everyone knows which way current flows through a diode. Right? Of course they do. Diodes only permit 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

Using the Newest Gen Arm, Part III

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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

http://blog.screamingcircuits.com

Using the Newest Gen Arm, Part II

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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 PCBs.
  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 through-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

http://blog.screamingcircuits.com

Component Footprint Rotation, Part II

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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.

20150220_143916
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.

20150220_143650
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.

 http://blog.screamingcircuits.com/

Component Footprint Rotation

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Before we (or any old assembly house) go about putting surface mount parts on a 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. The illustrations below show 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

Package origins

Passives orientation r2

Chip rotation

Quad and BGA

Three-pin parts