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."

PCB Panel Routing Technique

Most PCBs we receive are individually routed, i.e., not panelized. That doesn't mean that, sometimes, sending them in a panel isn't a good idea, or required. Generally, we don't require panels (sometimes called a pallet), but there are some cases when we do.

V-score panelIf the individual PC board, destined for Full Proto service, is smaller than 0.75" x 0.75", it needs to be panelized. If a PC board needing Short Run production service is less than 16 square inches, it needs to be in a panel of at least 16 square inches to qualify for Short Run.

So... you ask... why else might I want to panelize my PC boards? Keep reading and I'll tell you why.

  • First, if you've got a lot of small boards, it's easier to handle and protect then when they're in a panel. A few panels can be more safely packed coming and going from our shop here.
  • You may be able to get the through our factory faster. If you have a really large number, and need them super fast, panelizing them may enable that fast turn. With a lot of boards, sometimes, it simply isn't physically possible to put them all on the machine, run them and take them off, in a short turn time. Panelize them and the machine will be running longer for each board change, which reduces the total run time.
  • It may also cost you less. If you use leadless parts like BGAs, QFNs or LGAs, you can usually reduce your cost a bit by panelizing the boards. Leadless parts cost a little extra because of the X-Ray test needed, but the extra handling is mostly per board, rather than per part. One panel of ten boards with ten BGA, in total, will cost a little less than ten individual boards with one BGA each.

Stay tuned for my next few posts where I'll cover the pluses and minuses of different panelization techniques.

Duane Benson
"I looked outside my window and what do you think I saw?
The strangest sight I've ever seen you'll never guess just what I mean,
I can't believe it myself"

ODB++ plus, plus, plus

I wrote a bit about ODB++ back in October. Nothing has really changed much since then. I'm just clarifying a few things.

First, I want to put more emphasis on the use of ODB++. In addition to being beneficial to the manufacturing process, it can make your job a little easier. If you send us ODB++, you do not need to send either the Centroid or Gerber files. The ODB++ replaces both.

Eagle CAD does not have an ODB++ export. However, the Eagle .brd file will work too. You can send us the .brd instead of the Centroid and Gerber files.

If you can't send either of those formats, we still need the Centroid and Gerbers (top copper, bottom copper, solder paste stencil, silkscreen and solder mask layers).

Number Six
I am not a number, I am a free man!

Surface Mount, But Not Really

Sometimes parts labeled as surface mount aren't quite ready for prime time. I've written about this subject before (read here), and I'm going to write about it again - whether you like it or not. This time, however, I'm not talking about components that aren't up to thermal par. Today, it's about components that can take the heat, but aren't set up to be machine assembled.

Surface mount machines need a flat surface to pick on. They use small vacuum nozzles that need to seat on that flat spot. Chips, of course, are flat on top, as are most other components. Connectors, however, are often not flat on top. That doesn't leave any place for the "pick and place" machine to pick.

Single row header with pick and place padGenerally, manufacturers will place a small tab of Kapton® tape or a small snap-in plastic pad on top of the connector, giving the machine a surface to work with. You can see that in the photo on the left. Once the board has been fully assembled, the tape or plastic pad is simply removed.

Every now and then, we'll see connectors come in without that flat pick and place surface (like on the right). That means the machine can't place it, so it will have to be placed by hand. 1.25mm-Wafer-SMT-Connector

When buying your surface mount connectors, if you have a choice between a part with the tape and one without, you're better off picking the one with the tape. No offence intended to all of you humans, but machine assembly is generally preferred over human assembly.

Duane Benson
Only three more days until Mitten Tree Day!

How Do You Know?

This isn't a Thanksgiving blog. It is Thanksgiving day, and if it were a Thanksgiving blog, I would have to be working today, but we're shut down for the holiday, so I'm not working. I just woke up pondering what it would be like to do business with us (or anyone like us) and decided that I wanted to hear myself speak (metaphorically) for a bit. A word of warning though; I'm in a long-winded rambling mood today.

Take an example; the Beagleboard. I use that because it's a complex board that's open source, so I can freely talk about it. It was originally put together by Gerald Coley and Jason Kridner. I don't know how Beagleboard face onlong they spent designing it, but according to a UBM study, a typical product design cycle is about a year.

So, what we're really talking about is a year of a couple of engineer's lives. It can be a lot of cash money too. When ordered in large quantities, the Beagleboard and it's progeny are inexpensive enough to be sold for quite a decent price. However, when purchased in small quantities - say five - it can cost several thousand dollars.

When the Beagleboard was new, we built a few just to kind of show off. We took the open source files and ordered all of the parts. We tried to get some PCBs fabbed, but in that quantity, they would have cost us $1,200. Instead, I posted a request on the Beagleboard.org forum and found someone with some bare Beagleboard fabs.

I got those boards and the parts and ran them through our system. Had a customer quoted the build, it would have cost somewhere (if my memory serves correctly) around $800 per board for assembly. That would be $10,000 for a set of prototypes. That may seem like a lot for a board that retails for $150.00, but that's the difference between ordering hundreds of thousands and ordering five.

That cost comparison isn't the point. If you're in this business you know that getting small quantities of complex stuff in short notice is expensive in direct dollars, but more than worth it in time and effort saved. The point is that, while we build a lot of sub-$1,000 orders, we are frequently given orders that are valued at $10,000 or more. Sometimes CONSIDERABLY more. We've seen projects where parts alone are tens of thousands of dollars. I've seen a single FPGA cost several thousand dollars alone. Yikes!

You've spent a year of hard labor on a design. You hit "Save" for the last time. If you're like me, you want nothing more than to get a working board into your hands. The gap between that save and a fully built board is painful for me. But the prospect of shelling out $20,000 to some unknown company for the purpose of turning that year of my life into a physical product is positively terrifying.

Well, if you don't already do business with us, we are that "some unknown company." That makes me wonder how this all happens. I design boards myself - not the big ones, but I do design a fair number of them. Right now, I have four boards I'm actively working on and about that many that I've shelved for a few months. I understand a bit of the fear of handing a design off. Of course, I have an unfair advantage. I can just send some boards through our shop and get them done just about any time.

It's easy for me to trust us. I got a job here and I know that I take the stewardship of that big check and year of your life very seriously. I treat it like it were my own. I also know that I don't work for companies that don't share that philosophy. I've tried, out of necessity, twice in my career, working for companies that didn't treat customers they way I would and I ended up pushing my agenda so hard that I got fired. It wasn't pretty.

I've established that I (as in me) trust us. How do you get to the point that you can give us (or anyone else) the same trust? The Beagleboard guys didn't know us enough to do so. We built some of their boards on our own. Plenty of people do know us well or are somehow willing to make that leap. We quite literally* have built things that have gone up into space, down into the ocean and everywhere in between. It's pretty fun to look through our customer list and see so many names of companies doing really cool stuff.

All of the marketing mumbo-jumbo I spit out is designed to somehow convince you to let us take care of your design. But those are just words. Words are meaningless without the deeds. It's what all of the other people in my company do that really counts. I spill out glurge. They do their best to treat your project with the same respect and care that you do. I'm thankful for that, because if they didn't do that, I wouldn't want to work here. If they didn't do that, my job would be meaningless and stupid. Hey - this did turn out to be a Thanksgiving post!

Happy Thanksgiving!

Duane Benson
* The word "literally" is terribly misused these days, but I'm actually using it by the correct definition. Well, okay, the "everything in between" isn't quite literal, but "space" and "under water" are. And it's comprehensive a representative sample that I'm in the spirit of "literal."

More Fun File Facts: ODB++

In my last post, I wrote about the up and coming IPC-2581 PCB manufacturing file format. While IPC-2581 may be looked at by PCB fabricators and assemblers as a holy grail of sorts, it's not yet widely adopted by CAD software. But, that doesn't mean that Gerbers are the only option.

ODB++ was developed by Valor in the waning years of the last century as an improved method for getting manufacturing data into their CAM systems. Valor and, hence, ODB++ was purchased by Mentor Graphics in 2010. ODB++ is still widely available, however there's concern in some circles that it's not truly open. That concern is where IPC-2581 came from. In fact, IPC-2581 is somewhat derivative of ODB++.

I can see how a CAD software developer might fear the use of something owned by a rival. However, my understanding is that Mentor does it's best to treat it like an open standard and has made it available more or less as though it is open.

The history isn't really important. What is important is that ODB++ is a more complete format than the Gerber and is widely supported. Pretty much everything good that I said about IPC-2581 in my prior post also applies to ODB++.

The bottom line is that, regardless of whether Screaming Circuits is your fab (through our partner Sunstone) and assembly (through our factory right here) provider, ODB++ is a good thing. It makes the job easier and more accurate than does use of Gerber files. Both "easier" and "more accurate" help keep costs down and keep ambiguities to a minimum. As you know, ambiguity is the bitter enemy of both accuracy and quality.

Unfortunately, for all of you Eagle users, Eagle does not yet support ODB++. If anyone out there is really good with Eagle ULP scripting, you might want to create a on ODB++ and/or IPC-2581 creation ULP.

Duane Benson
I was ionized, but I'm better now. 

Fun Facts About Manufacturing Files

Circuit boards live and die by their manufacturing files. Without complete and accurate information, the board fab house can't fab the boards, the assembly house can't assemble your boards and nobody can buy the parts.

Our old standard, the Gerber file, has been around since about the time King Arthur pulled the inductor out of the solder pot. It's old. We all use it because it's familiar, but it's day is done. It's time to pass the torch.

IPC-2581 is the new standard in manufacturing files. It hasn't been fully adopted, but it's showing up in more and more CAD packages. The IPC-2581 format is much more advanced and has the complete data set in one file. While we still work with Gerbers every day, we can also accept IPC-2581 manufacturing files.

I've been called the champion of bad analogies, but I'll try one out anyway.

Imagine, if you will, a map of the city. All of the streets are there. All of the houses are there. What's missing are all of the street names. No street names, no numbers and no landmarks of any sort are labeled.

Given that information, find John Smith, at 1620 SW 14th Avenue. There is a house at 1620 SW 14th Avenue. There are a dozen or so houses at 1620 something. You just don't know where 14th is, or which direction 14th runs, or where the street numbering starts.

You can physically walk each and every street until you find John's name on his mailbox, but it's not an easy nor error-safe process. And, hopefully, the town only has one John Smith. That's a Gerber file.

IPC-2581, on the other hand, is an electronic map, with everything clearly labeled, and a GPS guiding you. Which would give you more confidence?

Duane Benson
IPC-2581 is like shatter-proof glasses for Henry Bemis