Monthly Archives: April 2011

Grounded in Reality?

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LED scroller 006 thin trimmed

Looking back, I think I could have done a few things different.

For example, I don’t really need a separate power-on LED. I could either just not populate it, or rev the schematic a little to make it a software controlled indicator rather than hard linked to the power switch. That change would allow me to put the device to sleep. The PIC18F25K20 draws somewhere around a tenth of a microamp while in sleep mode. That being the case, I might just discard the power switch all together. Otherwise, it’s cool.

I cuold have given each LED its own via to the ground plane, too. That’s supposed to reduce noise a bit. Although, this will probably never be clocked high enough to make much difference, nor used in an environment where it matters.

Duane Benson
Only half of 10 the types of people will understand

http://blog.screamingcircuits.com/

Done and Done

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LED scroller 005 trimmed And … (drum roll, please) … it works.

I put in a couple of batteries, programmed the MCU and turned it on. It works.

I’m always surprised when something I design works on the first try. This being such a simple design, I probably shouldn’t be surprised, though. I should at least give myself a little more credit.

The unpopulated lands on the board in the photo are supposed to be unpopulated. I left a few things out because they aren’t needed for what I’m doing with this piece now and leaving them off keeps the cost down.

So, what did I learn from the process?

  • If you have a lot of different parts laying around, it’s pretty easy to grab the wrong one.
  • I ran into some variability in the “zero rotation” position in the CAD library land patterns.
  • The whole process is pretty easy, but start to finish, there are quiet a few steps.
  • It’s a nerve-racking wait after sending off a box of parts.
  • Good communications between designer and assembler are very important.
  • Clear documentation from the designer is very important.
  • This was a WHOLE LOT easier than hand soldering all the SMT parts (I’ve done that before).

That’s a good set of educational results. Next time, I think it will be easier.

Note the large diode polarity indicators on either side of the long row of LEDs and by LED D25. D1, the Schottky on the upper right has the same polarity indicator, but it’s in between the pads, under the part. In case you’re interested, I have a 3V supply. The LEDs drop 1.8V and I’ve got a 150 ohm resistor for each. That gives me a theoretical 8 mA per port for a total maximum of 176 mA with all 22 lit up. That’s within spec in the -40C to 85C temperature range but too much when above 85C. I’m not sticking this in an engine compartment or anything, so no worries there.

Duane Benson
0x45 0x53 0x43 0x20 0x62 0x6F 0x6F 0x74
0x68 0x20 0x38 0x32 0x33 0x20 0x20 0x20

http://blog.screamingcircuits.com/

Time to Co-Opt Co-Design?

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In recent conversations, I’m hearing designers say they are spending enormous amounts of time in meetings. These comments tend to come from folks who work for larger OEMs or ODMs and work on teams spread around the globe.

Certainly there is something appealing to upper management about follow-the-sun design. It maximizes time resources and leverages both the lower labor cost regions of the Pacific Rim and the experienced hands in the West.

But whereas the old model of vertically oriented design and manufacturing had its warts, if designers are getting hung up all day in meetings, as opposed to spending time routing boards, one begins to wonder whether the follow-the-sun model has been taken too far. There’s nothing process-oriented about commiserating with a manufacturing engineer over lunch in the cafeteria, but there is something to be said for being able to talk things over as they occur, rather than being holed up in never-ending CYA sessions.

Is round-the-clock design actually a drag on efficiency and productivity?

Spring Bored

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To those who are tiring of this spring’s back-and-forth between Mentor Graphics and its two largest shareholders, take note: It should only last about three more weeks.

On May 12, the EDA company will hold its annual meeting, at which time shareholders either will affirm their  faith in management by re-electing the current directors, or will try to grab gold via a different channel by voting in favor of dissident shareholder Carl Icahn’s alternate slate.

Icahn and some other investors have claimed, in no uncertain terms, that they feel Mentor spends too much money on itself and not enough flows back to the shareholders. They believe the design software company would be better off run by a group with a greater stake in the outcome — no current Mentor director holds more than a 0.5% share, while Icahn controls nearly 15%. “Over the past 19 years under current management, Mentor’s share price is down 18%, with zero return for shareholders,” Casablanca Capital, another dissident shareholder, wrote in a letter today. “How can we support a board that is responsible for this underperformance?”

For its part, Mentor today responded with its strongest rebuttal yet, saying that Icahn has no plan, short of selling the company, a move it says would jeopardize customer stability; overrates his own nominees’ qualifications; and distorts Mentor’s track record. Mentor further argues that its stock has beaten that of its main rivals over the past five years.

While the battle has been mostly confined to the boardroom — Mentor’s stock price hasn’t yo-yo’d much since Icahn made a $17 per share offer for the company in February — it’s hard to believe that the potential of new management hasn’t been an ongoing distraction to the company’s thousands of employees. They, too, are likely eager for some relief.

It also should be noted that the two investors that are calling for the board’s heads — Icahn and Casablana — own a little more than 20% of the company. The other 79%+ of voting stockholders have been quiet throughout this tennis match. They are the ones who will decide Mentor’s fate, however. At this point, the company is in their hands.

My Mistake — Naturally

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I received my PCBs for this project from Sunstone yesterday at about 10:10. I quickly dropped them into my box of parts and delivered it to the receiving pile-of-boxes in our shipping.receiving department. At 11:40 a.m. yesterday, I received an email from our auditing department informing me of a BoM mismatch.

BOM mismatch Yes. I had made a mistake in my bill of materials. The board has a bunch of yellow LEDs and one red LED. I had mistakenly only packed up yellows. Our audit department caught my mistake and sent me a quick email. If I hadn’t have responded yesterday, I would have received another email at midnight. I could have just told the Downsized_0421110938a manufacturing folks to put a yellow LED in that spot, but the yellows are for a display and the red is a power-on indicator so I got my red LEDs and delivered them to receiving.

This morning I got my assembled boards all nicely wrapped in anti-static bags along with all my leftover parts in their original packaging. Next step, get some batteries and power them up.

Duane Benson
Thor, Dog of Thunder, is not allowed

http://blog.screamingcircuits.com/

Short Cuts Don’t Always Make Long Delays

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The saga continues. I have my parts kit. The PCBs should be here from Sunstone tomorrow. When I placed the order on our website, I estimated that I’d have the parts and PCBs today. I knew it would be tomorrow, but I wanted to see how our communications goes when something is late. Obviously, an assembler can’t start building until the parts have arrived, so the Industry standard is to start the turn-time once everything is in the shop.

If a box is late and the sender doesn’t know it, unintended delays can be added into the process. Knowing this, we recently did a lot of work to improve our communications, on such issues as late parts, to help reduce delays. Sure enough, I dropped on over to the website and right on the top of the home page is a note that I have an issue (late parts) with my job. Tonight at midnight, I should receive an email telling me the same thing too.

On the subject of the PCBs, I sent Gerbers to Sunstone. That works just fine, but I’m always a bit nervous about the accuracy of my layer mapping. They double check, so I’ve never had problems, but I still get nervous.

If I’d waited a few days, like until today, I could have taken a short cut by just sending in my CAD board file — they just started accepting native CAD files. You can still use Gerbers, but if you use Altium, Eagle, OrCAD, National Instruments’ Circuit Design Suite, Ivex Winboard or PCB123, you can just send in the board file and save some time and hassle.

When I get the boards tomorrow, I’ll pack everything up and deliver it to the receiving folks. Then I’ll see how the rest of the build process goes from the other side of the fence, and I’ll see how we deal with extra parts. I did that on purpose also. With a couple of parts, I’m delivering several hundred more than I need. With a few other, just the requisite 5% over. It will be interesting to see just how I get the extras back.

Yes. I know. I work here, so I shouldn’t have any doubt about how all of this stuff works. I do know how it goes, but it’s always a good thing to, every now and then, check and see how well practice matches up with theory.

Duane Benson
Grip, Fang, Wolf! Guard the mushrooms!

http://blog.screamingcircuits.com/

Centroid/XYRLS/Pick-and-Place

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Call it what you may, but surface mount assembly robots need this magic file to determine where to place your components and how to orient them. We call it a centroid. Others may call it something else, but it’s all basically the same. In our case, the basic format is comma delimited, in mils:

Ref designator,     Layer,     LocationX,     LocationY,     Rotation
C1 ,                       Top ,           0.5750  ,       2.1000  ,           90

That’s not too difficult. Most CAD programs will automatically create this file for you. Eagle doesn’t natively, but we have a ULP to do it for you in Eagle (downloaded here). Again, no problems here. Mostly…

I say mostly because, at this point, you are at the mercy of the person who created the CAD library part. Provided they center the origin and follow the IPC for orientation, everything should come out just fine. Unfortunately, we do find parts that don’t follow those rules. We’ll do our best to catch and correct such things here, but for maximum reliability, check you library components to make sure. We find the problem crops up most commonly with passives.

IPC says that zero orientation for two pin passives is horizontal, with pin one on the left. For polarized capacitors, pin one is (+). For diodes, pin one is the cathode. They note that pin one is always the polarity mark pin or cathode. Pin one is also on the left for resistors, inductors and non-polarized capacitors, but left vs. right doesn’t matter so much with non-polarized things. The most common orientation error we see is to have the “zero rotation” 270 degrees off from the IPC standard.

Every now and then we’ll find that someone assumes that since usually the anode on a diode tends to be on the positive side, that the anode should be pin one. Nope. Nope. Nope.

Duane Benson
Is it pulling electrons of pushing holes?

http://blog.screamingcircuits.com/

Cat Chow

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I recently wrote a bit about eating my own dog food relative to a small design I’ve put together. Today, I’m moving along with that process and kitting it all up, so I thought I’d pass on some hints on making a good parts kit. I’m looking at this from the perspective of Screaming Circuits, but my guess is that it would fit for just about anyone assembling your prototypes. Even George’s PCB Assembly and Dry Goods Emporium down past the railroad tracks.

If you’re sending all of the parts, you can leave them in the original package. Just be sure to clearly mark the packages with your reference designators. If you’ve got to cut your strips down, you may need to Downsized_0418110808 re-package the parts, as I am. I got these little handy dandy anti static bags from Digi-Key (part number 16-1032-ND) for less than ten cents each in a pack of 100. You can use the little pink anti-static bags too.

I’ve labeled each bag with the reference designator, the component manufacturer and the manufacturer’s part number. The more ambiguity that you can remove without adding excess clutter, the better. Making the labels was easy. I used Avery #5366 labels and mail merged from my BoM spreadsheet.

You can also put the component value on the label as well, if you can do it without clutter. Maybe line 1, reference designator; line 2, manufacturer and manufacturer part number; line 3, component value. Once you’ve got the bags labeled, go ahead and fill them up with the parts needed for your assembly. Add in 5% extra just in case (50% extra for 0201 passives).

If any of your parts are moisture sensitive either leave them in the original moisture barrier packaging or let us know that they need to be baked prior to assembly. That will prevent popcorn in the reflow oven.

Duane Benson
You’ll like it better or my name isn’t Orville Partenbacher

http://blog.screamingcircuits.com/

Sunstone’s ‘Fab’ Design Tool

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Sunstone is again acting as much like a software company as it is a quickturn PCB fabricator.

The board shop, which over the past few years has developed and honed its free CAD/DfM tool known as PCB123, today rolled out a conversion tool that features native file upload functionality.

In short, customers no longer need to export data in Gerber; instead, they can use one of a series of native data formats, including Altium, Eagle, OrCad, NI, and others (including, of course, PCB123).

It’s the second big development by the PCB maker in the past year, having already rolled out a parts library addition to PCB123 that supports some 500,000 components.

PCB123 won’t replace the big ticket CAD suites, of course, but for the types of prototype boards most designers need, it keeps getting better and better. And with its CAD conversion capability, Sunstone further extends its “ease” factor to those who don’t use the company’s own software.

No Silver Lining

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Many people have been infatuated by the price of gold in recent months, but the price of silver has also skyrocketed. In 2000 silver was about $3 per troy oz. In the eight years that followed, its price grew to $15/oz. Today it is trading at over $41/oz! This price is almost an all time high, except for the time when the Hunt brothers tried to corner the silver market in 1980. The aberration of their efforts jolted the silver price to just short of $50/oz., but it settled down to $11 or so after the Hunts came under margin call and other pressures.

Unfortunately, the dramatic price increase today, does not appear to be an aberration. Although we may hope that it will soon drop to more historic levels, we may not have reason to expect that it will.

Although not as dramatic, tin and copper have experienced significant prices increases as well. The price of tin has doubled in the last year to $15/pound and copper has increased from about $3/lb to $4.50.  These metals are obviously key ingredients in critical electronic materials such as solder pastes, solder bar, and solder preforms.

In addition, oil, which is used for most organic electronic materials such as PWB resins, flip chip underfill, and epoxy fluxes, has increased to $110/bbl – approaching its all time high of $145/bbl.

All of these price increases have a significant impact on the electronics materials supply chain. Although we are used to price decreases in the cost of our mobile phones and PCs, at this point in time, the price of the materials that go into these devices will be increasing.

As one materials supply chain executive commented at Apex: “It’s not like we can be clever and somehow work around the price increase of silver and these other materials, we have to pass it on to our customer, or go out of business.”