Blog - Screaming Circuits


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

Friday the 13th. Should You Worry? No.

So, here in Oregon, USA, it's Friday the 13th - and, we have a full moon, to boot. In many societies, both of those would portend of doom. Baseball players tend to be a suspicious lot, so if you're a baseball player, you should stop reading now. Everyone else, keep going and I'll explain why there's nothing to worry about.

Well, the first reason that there's nothing to worry about, is that superstitions are really a bunch of hooey.

DFB full moonBeyond that, it's important to note that we speak hexadecimal here. That means it's really not Friday the 13th. It's actually Friday, the 0x0D. It won't be the true 13th until next Thursday, and there's no superstitions that I know of about Thursday, the 13th.

As far as the full moon goes... There does seem to be a certain amount of anecdotal evidence suggesting that there's more looniness when the moon is full. However, looniness isn't necessarily a bad thing. If you're an officer of the law and your job is to protect the world from 2:00 am two-beer-heroes, then most certainly, extra care must be taken.

On the other hand, in fields requiring creativity, a little looniness can actually help the cause. Tesla clearly had his looniness, and look what he did: pretty much invent the modern world. Einstein? Yeah; a good kind of loony too.

So there you go. Revel in the potential for extra creativity. Don't worry about Friday, the 13th, because it's not the 13th. And, don't worry about the full moon either, because, why worry?

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

Panel Rails - What Are They?

I referred to "panel rails" in my blog about V-score panels, but I didn't explain the "whats" and whys" of panel rails. You might find yourself asking "what are panel rails and why would I want to use them?"

Well, first of all, for our Full-Proto service, we don't require panels or panel rails. We'll take just about any old board that's bigger than 0.75" x 0.75" and smaller than 14.5" x 19.5" and run it through our machines. For our short-run production service, we only require panelization for boards less than 16" sq.

That being said, panel rails do have a purpose. They give the machines a spot to grab onto without coming close to components. They're also a convenient place to put fiducials (more fiducial info here).

As you can see in the image below, the panels give a clear area for handling the panel.

Tab routed panel

There are two important things to note about this panel. First, look closely at the four outside corners. You can see the scoring for easy separation of the rails. This designer made sure that there isn't any copper where the scores are. That's the right way to do it. The V-Score blog shows a panel rail done the wrong way - with copper across the cut.

Next, this board has fiducials. Good. But, the fiducials are in a symmetrical pattern. Not so good. IPC-7351b-3-10 specifies a non-symmetrical pattern so that the board can only be processed in one orientation.

Duane Benson
Once I build a panel rail, now it's done
Brother can you spare a diode

The Past and Future of Electronics

Our parent company, Milwaukee Electronics was founded 60 years ago, in 1954. That's quite a long time in terms of electronics.

  • 60 years back

1954 was a big year for transistor electronics. The first commercially produced transistor radio, the Regency TR-1, was put on sale in November 1954, for a price of $49.95. The Bell Labs TRADIC, the first transistorized computer in the U.S. showed up in 1954.

TiconIt was also a big year for nuclear energy. The first civilian nuclear power plant went on line in Russia (whether it was a military research facility or a power generation facility is under debate). The European CERN nuclear research organization was formed.

The first atomic powered submarine, The Nautilus, was commissioned by the U.S. Navy. 1954 also saw the U.S. explode the first hydrogen bomb. The Atomic Energy Act of 1954 paved the way for the civilian use of atomic power in the U.S.

The magazine Popular Electronics debuted in October 1954. That issue covered, amongst other things, a solar "battery" with 6% efficiency, radio control of models, and capacitors.

That was a bit of the past. What will the future of electronics hold? What will technology look like in 2074? Will the world even be recognisable at all?

  • 60 years forward

Well, hopefully, there won't be any new developments in the area of bigger and more powerful bombs, like in 1954. Hopefully, we won't have been enslaved by our new robot overlords. Regardless, electronics will be vastly different in 2074.

The concept of a printed circuits board will have long passed by that year. Electronics will be more of a construction material supplement.

Processing power and sensors will come in a bag, in the form of tiny particles. They'll self-power with energy harvesting. They'll have integrated wireless communications. Each one, won't do much, but when added together, they will essentially form a big piece of programmable logic.

Take aircraft paint as an example. The paint manufacturers will mix in intelligent "dust." The aircraft paint will get a ratio or 40% computational dust, 10% strain gauge dust, 20% rf/temperature/light/moisture sensor dust, 20% actuator dust, and 10% other miscellaneous functionality dust.

Once applied to the aircraft, the paint will manifest itself as a giant programmable logic and sensor array. The paint will cover communications, location and all forms of sensing and maneuvering.

The smart dust will be mixed up in different proportions, based on the application requirements, and added to everything. Even food.

Duane Benson
I think that pill will be ready long before the year 3535

Individual routed boards - not panelized

Some people, especially in the manufacturing industry, refer to PC board panels by the term "palette." I can't seem to avoid thinking of the big wooden thing used for shipping stuff, so it's tough for me to call a panel a palette. It is, however, a correct designation - as is "panel.".

Milled cornerThis post is about individual routed boards, as in not in panels. Last time, it was tab routed, and before that, V-score.

On the right, you can see the relatively smooth edges of an individually routed board.

If panelization is so cool, you might ask "why not always panelize?" For large quantities, or really, really tiny boards, you really should ask that question because it's pretty much always a good idea. There are, however, good reasons not to panelize when in the prototype world.

First, with small quantities, you may not need enough boards to fill up a full panel. You can save quite a bit of money when ordering five individual boards, than if you had to order a panel of 30.

Fab houses tend to gang up board designs from a lot of different customers onto one panel. That allows for less waste and faster Milled edge 2turns for small quantity boards. The end result of that is that many fab companies charge more for panelization when quantity is small.

Our Full-Proto service can take individually routed PC boards down to 0.75" x 0.75". Our higher volume, more economical service, Short-Run requires that PC boards smaller than 16 square inches be panelized.

Duane Benson
Well my buddy Jim Bass he's a-workin' pumpin gas
And he makes two fifty for an hour
That's not very much

Tab Routing panelization

In my prior post, I covered V-sore panelization. The other very common panelization method is called tab-routing, as in routed, but with tabs. (That's "routed" like using a router, not as in Napoleon being chased out of Russia.) Following this paragraph, we have a tab-routed panel. I've obscured the detail of the PCB to protect the innocent.

Tab routed multi panel 1024

You can get it without the perforations, but if you're separating them yourself, you'll most likely be glad to have the perfs there. If we deem that snapping will cause undue stress on the board, we use a special tool to avoid putting that stress on the boards. If 1-Image30you're separating them manually, the perferations can make a big difference. Next, on the right, is a close up of a actual tab. The three holes make it "Tab Routed with Perforations."

A big advantage to tab routing is the ability to make boards in shapes other than rectangles. On the down side, it takes a bit more PCB material and can put a lot of stress on the area near the tab. That being the case, we recommend that you not put components too close to the tabs.

Now, the definition of "too close" is an interesting one. The IPC doesn't seem to have a specific standard covering the subject. 100 mils, or therabout's, is a reasonable target. Larger or stiffer parts might require a little more space.

When you purchase your PCBs in panels, you can separate them before assembly or after. Generally, the reason for panelization is for ease of assembly, so post assembly is the most common approach. Post assembly separation also requires the most care.

As I said, we have a special tool to avoid stressing the boards when nesessary. If you're separating them and don't have a tool, resist the temptation to just snap them apart like a Saltine cracker. Take some time and do your best to avoid much bending.

If snapped carelessly, or if parts are too close to the tabs, parts can break off. Sometimes the solder joint will just crack, leading to intermittent problems or later field failures. Use of some sort of cutting instrument that won't bend the boards is the preferred method.

Duane Benson
Have no fear; Underdog is here!

V-Score panelization

V-score top viewMy last post talked a bit about panelization, in general. Today, I'm taking a look at V-Score panelization. V-score is created by running a V-shaped blade across the top and bottom of the panel without cutting all the way through. The board in the mini-image of my prior post is V-scored. Top left, on this page, is a close up of the V-scoring. [Note that the cross-hatched area is not in the active circuit portion of the panel. It's in the rails. You'd never want to cut through copper like that in part of the board that will be used. Even here, it would be best not to have copper in the path of the v-scoring blade.]

You'll note that it's all straight lines. V-score can only separate rectangular panelized boards. For curves, you'll need to use a different technique.

V-score edge onThe next image down, on the left, shows an edge-on view of the V-score. You can clearly see what I mean by "without cutting all the way through." The cut leaves enough material to hold the boards solidly together during processing, but easy to separate.

V-score de paneled edgeBy the way, we generally don't just snap them apart. We've got a special tool - a bit like a pizza cutter in a fixture - specifically designed to separate them without stressing or bending the board. If we feel there's any risk of over-stressing, we'll use the tool.

The next image, here on the right, shows a board edge after de-panelization. Note that it's not a smooth, flat edge.

In contrast, the next image down, on the right, shows a flat milled edge. Generally, though, you can't visually tell the difference without close examination. You can, however, feel it if you run your finger lightly along the edge. Just be careful to not get slivers.

Next time, I'll examine tab-routing, which will allow for non-rectangular shapes.

Milled edgeDuane Benson
"I saw two Buffalos, two Buffalos,
Buffaloes on my lawn,
Romping all around and stomping on the ground
And all of my grass was gone."