No Need to Waste Parts

We love parts on reels. Who doesn’t? But reels aren’t always practical — and it’s not just about cost. Cost is, of course, important, but there may be other factors to consider.

Say, for example, you need 20 2.2K Ohm, 5% 0805 resistors. You could buy a small strip of 25 from Digi-Key for $0.32. That gives the 20 you need, plus a few spares just in case.

Alternately, you could buy a digi-reel ( a custom quantity reel). On the reel, you’ll probably want more parts to keep the strip long enough for the feeder. Let’s go with 250 parts for $1.39. Digi-Key charges $7 extra to create a custom reel, so that’s a total of $8.39. Still peanuts.

For a third choice, you could just buy a full reel of 5,000 for $10.64. Still peanuts. If you’re gong to need the same part for a lot of designs, this might make sense. But, there’s more than just cost to consider. You need to store and ship it. Shipping two dozen reels gets pretty expense. Storing and inventorying several dozen reels can become a hassle too. 6a00d8341c008a53ef01b8d1356272970c-320wi

The beauty of Digi-Key, Mouser and other places that sell cut strips is that they essentially become your parts warehouse. You pay the 32 cents and never have to worry about whether the part is in your inventory, how many are in your inventory, digging it out of wherever you stuffed the reel when you last needed it.

If you do buy and store the whole reel, you don’t need to ship the entire reel to us. Just cut a strip with the number you need, plus about 5% for that “just in case.”

Of course, if you need a few thousand of the parts go ahead and send us the reel. It would make sense then.

Duane Benson
Reel, reel your part
Solder it, solder it, solder it, solder it
Cost is but a factor

Chowing Down

I don’t know how common the phrase “eating your own dog food” is. I know I’ve heard it before in some of those obnoxious business seminars. Not all business seminars are obnoxious. Some are quite helpful and actually, now that I think about it, I’m not really sure if I’ve heard the phrase in the obnoxious seminars or the useful ones. Maybe the so-so ones. Hmm.

Anyway, in case you haven’t heard the phrase (it may be a regional thing), it means to use your own product, or in our case, service. I’m not an engineer, but I play one on the Internet. Still, I design and build little things. Since generally what I build is hobby-related, I tend to solder them up myself, leaving our capacity here at Screaming Circuits for the paying customers. But right now, I’m doing something a little different.

SC Promo 042011 top layer I’ve got a little design that I’m going to use to help some folks better understand how things work around here. At first, I’ll just give it to some writers and editors (writers and editors, feel free to shoot me an email about it), but at some point, I hope to be able to have enough to send out to design engineers that want to get a feel for our process. It’s quite a simple board” a PIC microcontroller (18F25K20 SSOP), some switches, resistors, a bunch of 0603 LEDs and some bypass caps. One Schottky diode too. I’m putting together a sample kit just like the sort of kit we like to receive. The files will be on a Screaming Circuits USB drive. The PCB, fabbed at, will be in there. All the parts, purchased from Digi-Key will be in individual bags; one per BoM line item.

The idea is for someone to take the kit as though it were theirs, create an account on our website, quote the job, place the order (no payment needed), upload the files and send in the kits. Along the way, that person will see what we like to see in a parts kit and how the whole register, quote and order process goes. Once they receive the working board back, all they have to do is decode the secret message it displays.

Back to the dog food. From my side of the Interpipes, it’s easy to say that things are easy. I sit back, drinking lattes and eating oatmeal while everyone else does the real work. But during this process, I’ll get a refresher course on what it’s really like to get a prototype built.

The other day, I sent the Gerber files off to Sunstone to get the PCBs fabbed and the parts order off to Digi-Key. Tomorrow, I’ve got to kit everything up. Stay tuned. Details as events warrant.

Duane Benson
Is this the kind that makes gravy when you pour water on it?

Picking Packages

A long, long time ago, in a place pretty close to here, picking a form factor was easy. Your CPU came in a 40 pin DIP. Your logic came in 14 or 16 bit dips. You picked resistor sizes based on their current carrying needs. Transistors and other power components got a little more difficult, but not much. It was largely a matter of power dissipation requirements.

Different story now, though. First, there’s through-hole vs. SMT. Then there’s a plethora of options beyond that. So, what really matters? A specific resistor size may come in multiple wattages. Chips come in multiple packages — often from big DIPs all the way down to tiny QFN or BGA packages. Let’s look at a few examples.

Here’s a simple microcontroller: the PIC18F25K22. It’s a pretty typical 8-bit PIC. You can purchase it in four different packages:

  • DIP, $2.05 each, Qty 100, Tube
  • SSOP, $1.86 each, Qty 100, Tube
  • SSOP, $1.90 each, Qty 2,100, Tape & reel
  • QFN, $1.86 each, Qty 100, Tube
  • SOIC $1.89 each, Qty 1,600, Tube
  • SOIC $1.93 each, Qty 1,600, Tape & reel

(DigiKey prices as of the posting date. Some are non-stock items.) There’s also the part presentation to consider; e.g., reel, cut tape, tube.

Next, look at a 1K resistor that might be used as a pull-up. (As listed in DigiKey) through-hole resistors range from 1/20W up to multiple watt packages. SMT parts range from 1/32W up to lots. Simplifying a bit and just looking at 1/4W, you can purchase 0402, 0603, 0805 and 1206 packages. For high volumes, price will be a factor, but for lower volumes, the price difference can be trivial.

If you have plenty of space to work with and you need to build by hand or for some reason need a socketed part, your choice is the DIP. If space is a bit of an issue and you may or may not hand build, then an SOIC is probably your pick. Some people will hand build QFNs and SSOP packages, but that’s not realistic in anything but rare cases.

When size, speed, current or performance need to be at maximums, selection is still not that difficult. You’ll often have far fewer options to choose from at the performance edges. But when there’s headroom all over the place, how do you decide? Why an SOIC over an SSOP over an QFN? Why 0603 over 0402, 0805 or 1206?

Duane Benson
Peter Piper picked a peck of pickled PIC packages.

Parts Time

Sunstone this week released v4 of its award-winning PCB123 CAD tool.

The no-cost, license-free tool features parts outlines for 500,000 components, automated BoM and integrated DRC/DfM rules. But what’s most interesting is that users can automatically get availability and pricing info for each component registered in Digi-Key’s database.

This development is fascinating in two respects.

First, that a modest-sized PCB fabricator, not a billion-dollar EDA company, is pushing the envelope on electronics design software.

Second, for engineers who now must not only draw the electrical circuit but also lay out the board and order the prototypes, built-in parts procurement is a huge time saver. Which begs the question, why aren’t the big CAD companies offering this too?

How Fast is Fast? I Mean, Really?

We talk a lot about speed here at Screaming Circuits. Back in 2003, one of the main reasons our parent company started us up was because their customers were telling them that they needed prototypes faster.

So, I know that getting everything built is faster these days – we can ship fully built boards as fast as 24 hours after we receive a kit, and you can get the raw fabbed PCBs in a day too. Certainly, everyone knows that you can place an order with Digi-Key and have the parts on your desk (or in our shop) the next morning. But has the rest of the process gotten faster too? (See if you can find the shameless plug in there. Sorry.)

Whether you’re using Sunstone PCB123, Ultiboard, Eagle, Pads, Altium, Allegro, or any of the common Bb input pwr sect CAD packaged, you’ll probably spend most of your prototyping time in the software. It’s also probably the least predictable segment of the process.

What takes longer? The schematic capture or the layout? Or are both completely variable and totally unpredictable? If your boss came running into your office and said:

Bob! Quick! We just spilled something. We need an underwater temperature sensor with a video camera that can send a real-time temperature data stream and live video feed a mile back a cable to a host computer. And we need it NOW!

How long would “NOW” take for you?

Duane Benson
Changing your reaction to the duration of time since 2003…

Reminders are Sometimes Good

I was recently reading an article on another website that caused me to reflect on where we’ve been and how far we’ve come in this industry. The article covered a design engineer’s experience with modding a board back in the 80s and being required to ship the board with the mods instead of getting new ones made properly.

Back in the late 80s and early 90s, I worked for a company that designed and built business-oriented displays. One of the products was particularly troublesome to get going and the first production versions shipped with something like 24 different mods. If the company had respun the boards, we would have added at least a month to the schedule and payed somewhere in the range of $20,000 to $40,000. If I recall correctly, one of the biggest problem areas was the PLL (phase-locked loop). We were over-driving the parts a bit and that made all of the support passives and the layout that much more critical. Not smart, but I guess that came from one of those “cost-benefit” analysis-type things.

Contrast that today where you can get a new set of boards from a PCB fabrication like in a few days for a few hundred dollars, get the parts from Digi-Key overnight and have us (Screaming Circuits) assemble them in a day or two.

Of course, it’s a bit of a double-edged sword. Like when faxes and later email came along. Written communications cycles that used to be measured in days became measured in hours and minutes. The expectations changed. Can you imagine writing a letter to a company and waiting a couple of weeks to get a response?!! That’s the way it used to be.

In the same vein, we at Screaming Circuits (and some others too) have changed the prototype cycle expectations. Can you even imagine finishing your layout and waiting four to six weeks for assembled boards to come back? Yikes! But that’s what it used to be like. We’re all making things go faster and faster. It keeps getting faster and it won’t slow down. But that’s good, because time = money, so less time building = less money spent and more time selling = more money earned. Right?

Duane Benson
I… Just… Need… More… Coffee… NOW!!!!

Circuit Design ECOsystem

Years and years ago, I was a product manager at In Focus, the projector manufacturer. It was a great time to be in the display industry. New technology was being invented left and right (and center and back, and some over in that far corner too). Competition was still reasonably light and we were ahead of most of it.

It was always interesting to take one of the early overhead projector-style displays through airport security. Laptops were rare at the time, let alone a big clear display that looked like a see-through touch-pad computer, but without the computer. But that’s not the point.

Back in our engineering department, we had the electronics engineers, a few folks to work on firmware, a layout specialist, documentation specialists to deal with all the documentation (duh), purchasing people to buy the parts and PCBs, technicians build up the prototypes, manufacturing people to get the pre-production and production going. And here,s the contrast today. Quite a few engineers I talk to these days have to do all of those jobs except final production. That wouldn’t be too much of a problem except that while all of those jobs were being assigned to the engineer, everything got more difficult. Parts got smaller, timelines shrank, competition got more fierce, clock speed increased and a lot of formerly company functions, got out-sourced. It’s a lot of work and a lot of ground for that engineer to navigate.

A handful of companies — Digi-Key, NXP, National Instruments, Sunstone Circuits and Screaming Circuits (my company) — have gotten together to form the Circuit Design ECOsystem; a cross-company organization designed to help that design engineer get a design from inside the brain to the market.

NXP makes components and is creating library components for the CAD software made by National Instruments and Sunstone. Sunstone allows quoting and ordering of Screaming Circuits assembly service on their website and Screaming Circuits does the same with Sunstone PCB fab. Digi-Key is working to improve the data-flow to Sunstone’s PCB123 CAD and streamline the parts procurement process to Screaming Circuits.

It’s still early in the process, but the idea is to take the, now fragmented, design to manufacture process and make it easier for the electrical engineer to get through – to remove roadblocks, add in new services and improve communications to make it easier to produce a quality product.

Newark Electronics and Eagle CAD — Interesting

I just read that Newark purchased CadSoft, including Eagle CAD. I guess it’s probably old news to everyone but me. The press release about it that Newark posted on its website, Element 14, has a date of Aug. 13. I find this purchase an interesting development and I don’t quite know what it means, or if it means anything.

I guess partnering is becoming a trend. Certainly, we’re involved in some good partnerships (Sunstone, Digi-Key, NXP, National Instruments) and Sunstone’s PCB123 connects up with Digi-Key parts. It does make sense. The engineer’s job has just gotten more difficult with this recession and the ensuing reduction in support staff. That’s pretty much what our ECOsystem partnership is all about — taking the disparate tasks involved in getting a prototype built up and reducing the steps and complexity involved in the process.

The Eagle / Newark deal does have me very curious. For one, I hope the CadSoft folks got a good deal. Their product has done a lot toward lowering the barriers to electronics design and they deserve a lot for that. The big questions are for the future. Will Eagle remain as accessible as it is? Will Newark throw a lot of resources into it and keep it moving forward? Will it get good attention or will it be treated as an impulse buy and not be given focus or direction? Hmmm…

Duane Benson
What about Element 32?

Pin BGA Interconnects

My “Speaking of Art in the Process” post used a photo of a point of load power module as an example. The specifics aren’t really relevant to this post though, but a commenter by the name of “Me” asked about the type of pins connecting the module to the main PCB.

“Do you know where to get those pins to attach two boards like that? I mean, do they sell just the pin for example on Digi-Key and give it a name, or is it just wire. Can’t see if they are pins with a lip to lift board to a set height.”

The part (above) came with the pins already on, so I don’t have a specific part number for the interconnect pins. I have some underside photos (below) that give a better view. They are basically solder-type terminal pins with a solder washer and BGA ball on one side (to attach to the main PCB) and either a press-fit or solder type side to affix to the module PCB.

I wasn’t able to find this exact part from Digi-Key or Mouser. Vector sells the solder washers and lots of interconnect pins of this sort, so they may be able to steer you to them with a phone call. This board uses the BGA style, but we’ve seen other POL modules of a similar type with thru-hole solder pins too. Digi-Key has lots like that. Here’s one example of some through-hole terminal pins from Mil-Max. You could use the solder-washers (like a T124 from Vector) to put some space between the module and the PCB.

Duane Benson