Screaming Circuits: January 2008

Kitted vs. Turn-key assembly

Which is right for you?

If you're familiar with us, you probably well know what a kitted job is. Most of our orders come in that way. For those of you new to Screaming Circuits:

A kitted job is where you send us your files, all the parts and the empty pc boards. It's the easiest way to go. You quote the assembly only on our handy quote page - that will show you exactly what it's going to cost. Shipping is extra and if you need any non-standard or special services, they will be extra. But, for the vast majority of jobs, what you see in the on line quote is what you pay for the job.

Quote it, answer a few more questions, up load your files and ship us the kit. If everything is in order, we'll start your turn-time clock  then morning we get your kit. (check out our terms for exact information).


The turn-key is easier for you all around, but the quote process is a bit more awkward.

We like you to go through the labor quote process first, just like for a kitted job. Then go ahead and place the order but in the special instructions, clearly note that this is for a turn-key quote and not a kitted order. We'll give you a call, work out all the details and get back to you with a full quote in about a day.

Duane Benson
I need a latte

Library Oopsies Again

Rj1_part_to_pad_size Google is hilarious sometimes. (I'll get to the point of the post in a minute) I've got two more examples of parts-libraries gone wrong. One of the parts is an SO-8 wide but I wanted to do a quick double check just to make sure I'm saying the right thing. So, I went to Google images and searched "wide So8".

Sure enough, I had the right package and there were several examples showing that, but I always get a kick out of some of the other things that show up. In addition to the chips, Google also showed a picture of a pair of socks, a picture of "Floaty white chiffon fairy dresses" and honey cakes. :-)

Anyway, back to the point. Here are two more examples where a bit of extra checking would have Img_3285_2 saved  time and money. I'm not sure there's anything we could do with the RJ1 part on the blue board. Maybe, but forget about reliability or mechanical sturdiness. A quick comparison between the CAD drawing and the part should have caused question here.

On the green board, it was an easy to make mistake. The footprint is for a narrow SO-8 and the part is a wide SO-8. Oops.

My advice to you: double check your footprints if you are at all unsure or are using something easy to switch like wide vs narrow.

Duane Benson
Enjoy the honey cakes, but treat the horses well

Eagle CAD and Sunstone

Imgsunstonelogo Our pcb fab partners up the road just released a set of design rule files (.DRU) files for use with the Eagle schematic and PCB layout editor. The design rules set allows Eagle users to consider Sunstone's manufacturing rules early on in the layout phase and that's a good thing.

Simply download, install and activate the design rule file and then Eagle will automatically let you know if your board layout will work or if specific areas need to be changed.

You can get the design rule file at the Eagle CAD website or directly off the Sunstone website at: You can also download Sunstone's CAD software, PCB123, from the same page. Scroll down to find the design rules.

Duane Benson

Thru-Hole Parts Can Have Footprint Problems Too

It Happens with thru-hole parts too. See what I meant a couple of posts ago. I get on a subject and can't drop it. (see this and this).Sw1_wrong_footprint_2

Usually when I talk about parts library issues or footprint issues, I'm referring to tiny QFNs or new exotic chip scale parts or things like that. I can happen with old things too. As I pointed out the the Omron relay, the other day, even bigger older parts can have library issues. The thru-hole switch is a good example. It looks like the footprint is on a .1 inch pitch and the switch pins are at .09 or a metric pitch. It's interesting that the tabs on the outside of the part are in the right spot, even though the pins aren't.

I have found a lot of both switches and relays with non-standard footprints. So if you don't find the exact part number in your component library and substitute something close, make sure to double check for fit before sending the boards out for fab or assembly.

Duane Benson
Is it "thru-" or "through-"?

New Look for the Blog

It's a new look for the blog, but the same old, tired content... Ah... I mean the same great content. Yeah. That's what I meant.

The blog is now integrated into our website. You can go back and forth using the same navigation as is on our main site. We've updated the blog look a bit too. You may not care so much about that, but I like the pretty colors. Hopefully, things are easier to read and more accessible. That would be cool.

Let me know if you care one way or the other

Duane Benson
Bad Wolf

Library Borken Record

I seem to get on themes and just not let go. This is only my second parts library post lately, but maybe I'm starting a run or something. Who knows.

Relay_footprintAnyway, here's another parts library oopsie. The top two pins on the little 1Amp Omron relay have a different pitch then the rest. The other six almost fit on a standard .1" pitch DIP footprint. Not quite, but close. The part doesn't even really have a metric pitch, at least not an even one. The big gap is 3.2mm or .12 inch. The other gaps are 2.2mm or .09 inch. Nothing standard of any sort.

We did make this work for prototype purposes, but you never know if doing this will work. It wouldn't have been difficult for the part to have ended up with the first two pins not connected to anything. Here's a case where it would have been much better to (and for production you would have to) either hunt down the right library or make a custom one.

Duane Benson
If I borken, I is okay with it.

Is PCB Assembly

Mmmm... Mom's delicious pumpkin pie...

Sorry. No, that's not the delicious that I'm talking about. I'm referring to the social book marking site Do any of you use it? If you're not familiar with it, it's kind of like Internet Explorer's "Favorites" but portable and on steroids, but with out all th heart-damage risks of real steroids.

On of the cool things is that when you save a site to, you add tags, which can then lead you to other similar sites that you've saved. So if you have a bunch of game sites saved and a bunch Screaming Circuits pages saved, you click on the "pcb" tag and it filters and only shows the Screaming Circuits pages.

It also lets you know who else has saved those pages so you can go and see what other interesting and related things they have saved. You can turn off the public sharing of bookmarks, but it's a pretty cool feature. If you want to see what we've saved, you can go to

If you want to save any of our blog articles, we have a "save to" link right at the bottom of every article.

Duane Benson
Delicious and nutritious

Parts Library Strikes Again

Here's a little bit of a parts library or wrong package problem. I'm not exactly sure how it happened. The Qfn_worng_part_library_2 board may have been laid out for a small QFP footprint but then a QFN part was purchased. The footprint looks like that of a QFP, but QFNs are usually smaller, so it may be a custom made part library with some errors in measurement.

It's surprisingly easy to do that; especially if the person making the library part isn't the same person that's using it. Maybe the person drawing the footprint only had part of the dimension information for the QFN. I can easily see how someone could take the outside dimensions of the part and the pitch and then come up with something like this based of years of making QFP footprints.

The lesson is to always double check the component fit before sending a board out for fab. In this case, the lead pads are so long that they would short every connection to the ground pad in the middle. Oh, and there's also that giant open via in the middle of the center pad. That's not a good thing.

Duane Benson
Analysis, Mr Schlock?

5 Basic Steps to a Successful PCB Layout - Part 5

This is the fifth and final of five parts from guest blogger, Stilwell Baker, covering successful PCB layout. Last week they covered pcb fabrication.

Know your Assembler: Why layout a board that’s hard to assemble when you can just ask your assembler?

  • A working prototype that’s hard to build will need modifications for high volume production. What if those modifications impact performance, compliance, or safety?
  • Obtain the design guidelines from the assembler that you pick, and pass that on to the layout resource.
  • Involve your assembler early in the layout of a design. Involving the assembler early in your design can help save you time and money during this process. Assembly can provide input on panelizing, component location and rotation, and the soldering process (ie reflow, wave, selective wave, …)
  • Again, if you are creating a design that will be sent to a different assembler for production level assembly, make sure that you know what their capabilities are, and you are accounting for that in your prototype design.

Here at Screaming Circuits, we handle the assembly for you. It's a very important part of the process, but only one part of it. As discussed by our Friends at Stilwell Baker, there is a lot consider through the design, layout, fab and assembly process. Look carefully at all of the steps as you put your layout together and the whole process will be easier and more reliable for you as well.

Happy New year!

So, I wrote this blog post about the new year and how things went in 2006. Then I blinked and here it is January of 2008 already. I'm sure 2007 had all of the standard 365 days in it but it feels like it only had about a third of that. I watched a show on The Discovery Channel that discussed a theory about the speed of time changing. Maybe that's what happened to the year.

I don't have all of the summary stats yet like I had in last year's New Years post but I'll get them pretty quick. We've worked hard on our on-time delivery and quality and I'll let you know how we did over the year shortly.

Duane Benson
Don't layout your PCB under the influence of alcohol

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