Blog - Screaming Circuits


Top 5 Things to Know When Moving from Hand Assembly to Robotic Assembly

A lot of factors go into the decision to hand build or outsource circuit boards. I hand build my own sometimes, simply because I enjoy the challenge. Of course most of the projects I design are for my own use, so timeliness isn't that important. When I do design something that will go out to a customer, like my electronic business card holder, I will send the board through our shop. In those cases, quality is important, as is delivery, and the quantity is often too high TI TPS62601 front and backto hand build. Machine building also allows me to use smaller and more complex parts.

That same decision - hand build or outsource - takes place in the heads of designers all over the country. When the decision is to outsource, there are a few important things to consider. Some things that work fine when hand soldering may stand in the way of quality, repeatability, and reliability when machine assembling.

Here are five of the most important considerations when changing from hand built to outsourced at a place like Screaming Circuits

1. Use solder mask and silk screen

A good solder joint needs the right amount of solder in the right place. Solder will tend to flow down bare copper, bleeding outside of the area it belongs, and down exposed copper traces and vias.

The main purpose of solder mask is to keep the solder where it belongs. It also protects the traces, but that's a longevity issue. Solder bleeding is a manufacturing and reliability issue. This isn't a problem when hand soldering. In fact, it can even work to your advantage when hand soldering really small parts. It gives you more room for your soldering iron to hit metal.

Not so with solder paste and machine assembly. Use solder mask.

2. Avoid the pseudo panel

Keeping small boards in a panel is the recommended best practice in the manufacturing industry. We appreciate it and, while not always necessary, can reduce your costs. We sometimes see what we call a "pseudo panel." This is a board where multiples of the board are put in the same PCB, like a panel, but unlike a panel, the boards don't have routing or V-score between them. Sometimes the designer will put a bunch of vias to outline the board, or just ask that we use a band saw to separate them.

That's a time consuming, expensive, and potentially damaging process. The vibration of the saw can crack solder joints, and, you're unlikely to get boards that are all the same size. Have small boards panelized by your board house.

3. family panel (pseudo or not)

Similar to the pseudo panel is the family panel. A family panel is a case where a project is made up of several different PC boards, and they are all laid out together, as though they are one design. If the board isn't routed between to designs, you'll have the pseudo panel problem described above.

The bigger problem, though, comes with reference designators. We typically see family panels with duplicate reference designators. Each design, for example, will have its own C1, R1, Q1, etc. We use the reference designators as position identifiers/ If you have three different parts labeled R5, our machine programmers will have a problem with it. It's even worse if the values differ; on one design, C1 is a 0.1uf capacitor, while on another design, it's a 22pf cap.

If you're making a family panel, give each and every placement a different reference designator. One way would be to us extra digits. For example on one design on the family panel could have C100, C101, C102... The next would be C200, C201, C203, and so on.

And - don't forget the routing or V-score between the designs.

4. QFN - hole  in the middle

A common technique in the hand soldering world, for soldering QFNs and other parts with thermal pads underneath is to put a big via in the middle of the center pad. By doing so, you can stick a soldering iron and some solder down through the hole and get a good solder connection on the bottom pad.

This doesn't work with machine assembly. the solder paste will flow down and out the hole in the reflow oven. You'll end up with a poor connection (or no connection) to the thermal pad, and solder slop on the back side of the board.

BOM line items 0055. Parts and the Bill of Materials (BOM)

When I build my hobby projects, I often get a bit carefree with the bill of materials. It's not good practice, but I do. I'll put a part in the BOM that I used before, and not check to see if it's still in stock. I'll put parts in the BOM with just the values and not any part numbers. Things of that sort require tribal knowledge, which only the designer has.

When building, sometimes I'll just grab a part that's close. If I need an 0805 1uf, 10 volt capacitor, I can grab a 16 volt, 25 volt, etc. I can even make an 0603 part work. You as the designer may know that something close will work, but an outside house can't know. You need to tell them exactly what the part is.

Before sending anything through our shop, I do clean up the BOM. In order for us, or any manufacturer, to build the boards, the BOM needs:

  • A unique reference designator for each part placement
  • The quantity of each part used on the board
  • The manufacturer
  • The manufacturer's part number
  • Digikey part numbers can be used as well

Here's our web site page explaining the BOM format in more detail.

The transition from hand building to outsourced machine building can be an intimidating one. But, with a few considerations, it can be an easy and rewarding transition.

Duane Benson
Put the right part in
Put the wrong part out
Put the right part in
But please don't shake it all about

 

Happy Memorial Day

Happy Memorial Day to everyone here in the USA. We will be closed on Monday for the holiday.

POP with dime

 

Fiducials and Odd PC Boards

One of the handy aspects of getting boards assembled at Screaming Circuits is that we don't require fiducial marks for standard process boards. I would say that we build far more boards without fiducials than with. That's cool, but there are sometimes when fiducials really are a good idea. In fact, if you've got room on the PC board, they're always a good idea (just because something isn't required, doesn't mean that it's not a good idea).

Some boards are more in need of the marks than others. For example, not long ago, we got a rigid flex board in. It had three separate rigid boards connected by flex, designed to be folded into a stack. It looked pretty similar to the mock up in this image. Rigid flex mockup

The boards didn't have any fiducial marks. Normally, what we do, is find a via hole, thru-hole pin hole, or some similar feature to use as a fiducial. That usually works, but not always. In this case, the length of the flex varied slightly from board to board. The PCB color was also very low contrast, which made it difficult for the machine to consistently recognize any mark we picked.

That meant our machines had a hard time finding the "home" spot, and we had to reset for each of the connected boards. Finding a spot on one board did not guarantee that we'd know where to place parts on the other two boards in the set.

In this case, it would have been far better if the boards were a consistent distance apart, and if each of the three boards had a set of fiducial marks.

What makes a good fidicual?

Most CAD packages have fiducial marks in their components library. Basically, it needs to be a metal dot surrounded by an area without any copper or solder mask. More than one is best. It should be an asymmetrical pattern that can only be oriented one way.

I've got some more details in this article here.

Duane Benson
Routed up like a fiducial
Another rigid flex in the night

USB Type-C Connectors

It wasn't terribly long ago that pretty much every cell phone came out with its own custom charging cable. It was a major step forward when they all (except Apple) standardized on the USB micro-B connector.

However, there are a number of limitations with the. First, it takes a minimum of three attempts to get the orientation right when trying to plug in a cable. Second, it's limited in maximum current carrying capacity.

Image70

Now, along comes the USB 3.1 Type-C cable and connector. It's similar in size, universally polarized (the connector and the cable can be plugged in any end to any end and in any orientation), it has much higher data thru-put, and it's spec'ed to carry up to 3 Amps. Further, it has alternate modes so other standards, such as DisplayPort and Thunderbolt.

SMT - TH uUSB with PCBThe connectors are larger than the micro-B, as you can see in the comparison photo above: micro-B, Type-C with only surface mount connections, and Type-C with both surface mount and thru-hole wiring, and a US dime. The size difference won't be an issue in most cases, but it could be in really small devices. My guess is that we'll be talking about a smaller, Type-D connector, not long from now.

All three of the shown surface mount connectors have thru-hole mounting tabs. That adds strength, but it does bring one caution with it. Looking at the micro-B connector in the image on the right, you can see that the tabs are formed out of the same sheet metal as the shell.

You can also see that the tabs don't stick all the way through the PC board. This can lead to some deception when soldering. Without the tabs protruding, it's easy to believe that you don't have enough solder in the connection. If you feed more solder in, it will likely wick along the tab, and end up inside the receptacle, preventing the cable from being plugged in. If you're hand soldering or reworking these type of connectors, keep a close watch on the amount of solder you're using.

Duane Benson
Fester Bester Tester is alive and well and living where?

Arduinos Spotted

ESC2016 bage proto 640I've given a few talks at the various Embedded Systems Conferences on the subject of the Arduino as a real prototyping tool. I've designed and built a number of custom Arduino-compatible boards myself. I've become an advocate for the Arduino as a legitimate tool for the commercial engineering world. But sometimes advocating isn't enough. You need to see it in action to believe it.

Here at Screaming Circuits, we build a lot of different types of boards for a lot of different companies and organizations. The are boards being used for R&D, consumer products, education, medical devices, military things, space craft, Kickstarter companies, aviation... You name it, we've probably built it; up into space, down underwater, and anything in between. What's the engineering joke? "Civil Engineers build targets, mechanical engineers build weapons to destroy them." We build the electronics for both.

But, I've gotten off target. The point I wanted to make is that, if we're building it, it's most likely a professional/commercial caliber product. The other day, amongst the many other designs being assembled out on our shop floor, I spotted a shield, full size for the Arduino Mega. I don't see anything close to every job that we build, but it's gotten pretty common for me to see something Arduino compatible - either in form-factor, code compatible, or both, out on our shop floor.

One such example is the electronic badge we built for the upcoming Embedded Systems Conference in Boston. Our partner, Sunstone Circuits provided the PC boards, Synapse-Wireless designed it and provided the wireless modules. We bought the rest of the parts and built it.

With as many as I'm seeing these days, I can only conclude that the Arduino has entered the commercial design world.

Duane Benson
Open source the pod bay doors, HAL

Advanced Technology now available

CCB - Concrete Circuit Board: Rumored for years, scoffed at for even more years, and now available to you - Concrete substrate for circuit boards!
 
The US NCA (National Circuit Agency) recently declassified this new technology, and granted exclusive assembly rights to Screaming CCB layersCircuits, due in large part to our prior work with the revolutionary Cordwood technology.

CCB has many advantages, such as a thermal expansion coefficient of 17, and a density of 18.98 g/cm3, almost as much as depleted uranium, allowing for solid grounding without bolts.

Prior to now, CCB had only been used in the most secret aviation and space applications, such as the still classified KHD-18 spy satellite and the LB3 Keystone light bomber. It's used all over Area-51 and has been identified as the cause of 42% of UFO sightings. (I can't remember if I'm allowed to say that or not)

For the civilian world, CCB is ideal for mobile* and IOT (Internet of things) devices

* CCB circuit board substrate comes in a minimum 1.2" thickness to prevent cracking. Applications subject to thermal variance or vibration may require the addition of rebar. Titanium and beryllium rebar are not available.
 
Duane Benson

Electronic Business Card Holder, Part III

If you haven't yet read part one or two of this series, find them here:

With all of the key design decisions under my belt, it was time to build. I ordered the boards and parts myself, then hopped onto our website quote engine and placed a kitted order. At the time, I hadn't had anything built for a while, so it kind of freaked people out to get an order from within the company. When I do this, I like to go through our web system, just like any other customer, which sometimes causes a bit of a "we traced the call, and it's coming from inside your house..." moment.

20160324_103054Anyway, we didn't have any problems with the build. Fortunately, I took my own advice and carefully labeled the LED polarity. LED polarity marking "standards" are so unstandard, that extra caution is always a good thing. Anything to reduce ambiguity is welcome.

My calculations suggested that I should get six to nine months of battery life with a few cards being pulled per day. After running the blue LED version for about three months, I was satisfied that battery life would be sufficient. That was good timing, because at about the same time, I was down to about two weeks before the show that I was planning for (one of the Embedded Systems Conferences).

Again, I sent an order through our website. This time a full turn-key, using PC boards from Sunstone. And, this time, no one was 20160324_101515surprised by seeing an in house order. I ended up with plenty of time to program the boards before the show, and was ready to give them away for our in-booth contest.

Since that time, I've left a blue/red card holder and a green/red card holder on my desk with the original batteries. After about a year and a half, the battery voltage dropped enough that the blue LEDs no longer show. The red and green, with a lower forward voltage, are still going strong.

Here are the final specs:

  • 1.5" x 3.5"
  • Two CR2032 coin cell batteries
  • Has a Microchip in circuit (ICSP) programming port
  • Has an I2C/SPI port
  • Microchip PIC18F46k22 microcontroller
  • Freescale MMA8452 3 axis accelerometer
  • Recommended capacity, 10 cards

Next time, I tell you what you need to do to get one of these limited edition Screaming Circuits electronic business card holders.

Duane Benson
A farmer is someone out standing in his field

Happy St Patrick's Day!

In honor of St Patrick's day and all things green, I give you the PCB...

Badge800closeup

And some trivia. You may have noticed that the soldermask used on most PC boards is green, as is the paint used on most steel truss bridges. Why is that? And what do the two things have in common? Why green PCBs and why green bridges?

To answer, I brought in color expert expert Patty O'Patrick O'Dell, who stated: "Many bridges and PCBs are green because they absorb red and blue light, only reflecting the green."

That wasn't quite what I was getting at, but close enough. The important thing, is that, generally, in commercial products, the PC boards are hidden, so the color doesn't matter that much. With prototypes and a lot of the hobby or development boards, that is not the case, so many companies have chosen to use a different color as a part of their identity.

Arduino products are blue, as are most boards from Adafruit. SparkFun makes theirs red. Ti Launchpads are red as well. The Beaglebone uses color, essentially, as a model number; Beaglebone black, Beaglebone green. This is possible because major PC board fab houses have made different colors more economical than they used to be.

I've been asked if the color makes any difference electrically. In general, no. If you're dealing with super high speeds, RF, or other exotic conditions, it's always best to ask your board house. In those fringe areas, a lot of things have the potential to make a difference. Other than that, if you can afford it, and want to make a statement, go for it. You can often get different color silk screen legend too. Just make sure there's contrast between the two. White silkscreen on white soldermask would not be the best choice.

Duane Benson
Beware the monsters from Id

Electronic Business Card Holder, Part II

If you haven't yet read it, rush on back and read part one of this series... Done yet? Okay, good.

When I left off, I had promised some design decisions, of which, the power source would be the first. I wanted a long battery life. If the batteries need to be changed every other month, it would just get too expensive, and annoying, so I wanted at least six months. A year would be even better.

20160308_090949I did some estimations and determined that a CR2032 coin cell would give me about that longevity. I decided to use two, for good measure, and to make a stable base, but mostly for stability. The two batteries go on the bottom of the card holder, as shown in the photo on the right, and have enough weight to give decent stability. For testing purposes, I also put in connections to use a two-AAA battery holder.

For my first build, I decided to used red and blue LEDs. The blue have a higher forward voltage, so I could get a sense of battery life faster than with the eventual red and green.

Speaking of battery life, the accelerometer was the bigger challenge of the two ICs. The MCU (microcontroller) and accelerometer need to sleep when not being used. The PIC18F46k22 MCU will be easy. I don't need any peripherals on while sleeping. It just needs to wake on interrupt. Given that, it'll range in the area of a few tens of nano Amps during sleep. The MMA8452 accelerometer, on the other hand, is up in the micro Amps.

At the slowest sample rate, 1.56Hz, it draws 6 micro Amps. At a sample rate of 800 Hz, it draws a whopping 165 micro Amps. The sampling rate is critical - it's the number of times per second the accelerometer check for movement. Too slow, and it will miss a fast hand picking up a card. Too fast, and the battery life will suffer. After some experimentation, I settled on 50 Hz, drawing 14 micro Amps. 50Hz was the slowest sample rate that gave reliable detection.

Stay tuned for my next installment, where I'll cover the first build, programming, and the test period.

Duane Benson
I'm happy I live in a split level head

Behind the Scenes of Screaming Circuits

We love what we do here at Screaming Circuits. As the first dedicated online quick-turn manufacturer, we've worked hard at delivering on our mission to reinvent electronics manufacturing in North America. It's very important to us to make the design engineer's job (your job) easier, and we take that quite seriously.

We couldn't do it without our parent company, Milwaukee Electronics. In fact, Screaming Circuits started out, back in 2002, as an experiment to help a Milwaukee Electronics customer out of a bind. It worked well, and in 2003, ScreamingCircuits.com was brought online.

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Why do I bring that up now? Well, Milwaukee Electronics hasn't stayed in the old-world of manufacturing. It's improved, expanded, and grown, despite the difficulties the US  manufacturing industry has faced.

And, as testament to that, Venture Outsource just named Milwaukee Electronics as one of the Top-10 EMS Providers in USA-West.

Congratulations to Milwaukee Electronics!

ME Logo sm With Tagline 2014