Screaming Circuits: Our website and Process


Freescale KL03 and PCB123 at 0.4mm pitch

Small component packages seem to be a recurring theme with me. It's understandable, I guess. Super tiny packages are becoming more and more common and we build a lot of product with them.

The smallest we've built is 0.3mm pitch. Those aren't common enough to be considered standard - they're still an experimental assembly - but not many chips use them yet. 0.4mm, on the other hand, is something we see on a pretty regular basis.

What's so tough about that?

The biggest challenge with these form-factors seems to be footprint design and escape routing. I can see why. There really isn't room to follow any of the standard BGA practices. You can't fit escape vias between the pads and you can't put vias in the pads, unless they are filled and plated over at the board house. Filled and plated vias are the easiest way to go, but it can make for an expensive board fab.

KL03 WLCSP20 on a US Lincoln Penny

1-DSC_0008One of my side-projects involves trying to make the smallest possible motor driver. For this project, I've chosen the Allegro A3903 driver. It's a 3mm X 3mm DFN (dual flatpack no leads) with 0.5mm pitch pads and a thermal pad in the middle. The microcontroller will be the new Freescale KL03 32-bit ARM in a 1.6mm X 2.0mm WLCSP (wafer level chip scale) package. It also comes in a 3mm X 3mm 0.5mm pitch 16 pin QFN. Without an expensive PCB, that may be my only option.

Pick your CAD package

I'm using the newest version (5.1) of Sunstone Circuit's CAD package, PCB123, but the principles here will apply to any CAD software. If you don't already have a copy, download PCB123 V5.1 here.

If you've got fast Internet, you're done now, so go ahead and install it. You'll need the manual too, which you can get here.

I need to eat now, so stay tuned for Part 2.

Duane Benson
Nerfvana - It's like Nerdvana, but with more foam darts.

Cost Reduction in Design - More Advice for Makers

If you're looking for the absolute, cheapest possible assembly service, you'll need to look outside of North America. If you really need a decent price with good quality and good service, you can keep your gaze West of the Atlantic and East of the Pacific.

Like everything else in the modern world, design decisions can have a pretty big impact on your cost. So, lets take a look at some design decisions that can make your manufacturing more affordable.

  • Accept longer lead times

Lead times are one of the biggest factors in electronics manufacturing. Screaming Circuits can turn a kitted assembly job overnight, but it costs a lot of money to do that. Screaming Circuits also has a 20 day turn-around that is much, much more affordable. Accepting longer lead times on PCB fab will drop your cost as well.

  • Avoid leadless packages like QFNs and BGAs

We build tons of QFN and BGA boards - even down to 0.3 mm pitch micro BGAs. That's great if you need those packages. However, since all of the leads are underneath, we have to x-ray every part. That adds a bit of cost to the process. If you can, stick with TSSOPs and other parts with visible leads.

  • Use reels, or 12" or longer continuous strips

Tab routed multi panel 1024We will gladly assemble parts on strips of almost any size. But, to save costs, use full or partial reels or continuous strips of at least 12" long. It costs us less time to work with reels and continuous strips, and we pass those saving on.

  • Stick with surface mount

These days, thru-hole components tend to be hand soldered. That costs more than machine assembly, so use surface mount wherever possible. Surface mount components tend to be less expensive than thru-hole too. If you do need a few thru-hole parts, this is an opportunity to put in a little sweat equity by soldering the thru-hole yourself and save a bit of money.

  • Panelize small boards

We can work with really tiny boards individually, but sticking with a larger size makes the job easier, and, again, we'll pass those saving on. If your PC board is smaller than 16 square inches, panelize it. We put in less labor and you get a price break.

By sticking with Screaming Circuits, you get the same care and quality that we give to boards going up into space, down into the ocean, and everywhere in between. By sticking with Screaming Circuits, you get a known turn-time; not an "about ..."

By following these guidelines, you get a decent price and really good quality and service.

Duane Benson
That would be telling

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, you're 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 be overkill, 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

Yes, a Maker can get 250 custom-design Arduino-compatible boards built for about $10.00 each at Screaming Circuits.

How can Screaming Circuits, a full-service assembly provider, compete with a low-cost 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

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.

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

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."