Screaming Circuits: June 2007


July 4th Holiday Closure

Images We will be closed on Independance day, July 4th. This means that that day won't be counted toward your turn times. For example, if you have asked for a 48 hour turn time and we receive you kit on the afternoon of the 3rd, your 48 hour clock will start on Thursday, the 5th.

We apologize for any inconvenience and wish you a happy holiday.

Sayings

I don't really know if this is a post-worthy post, but I'm having a bit of trouble waking up so I thought I'd pass on a bit of philosophy. I get kind of annoyed by motivational posters, but I have an assortment of sticky notes with little sayings that resonate with me in the way those motivational posters are supposed to.

"What would a customer think of that?"

"Treat the customer like they are giving you money (because they are). If you don't, they won't."

"What kind of chip are you?"

"Stop! You are not thinking."

The last one is my favorite. I think they are all good and they are all perspectives that we like to keep rolling through our heads. Just a little reminder that, while we are all trying to make a living doing this, you folks will only provide us with that living if we do a good job for you.

Duane Benson
Like to think I'm an i.MX31, but probably a CDP1802

Library Parts II

A couple of posts back, I wrote about a shareware tool available on the IPC website that can help you make custom parts for your CAD package. One of our readers commented back with a little more detail and pointed out the company that makes the tool. In addition to the shareware tool, they have a professional version that looks very capable.

Ipc7351a_lpwizard I haven't used it, so I don't know first hand, but it sounds like a pretty useful tool. I've had to make parts in Eagle and in PCB123 and it really is no picnic. I suppose if I did it enough, I'd have it down but I don't. Every time that I need a new part, I have to re-read the instructions. Actually, first I try to make the part. Then after unsuccessfully trying to remember if I need to make the schematic or the package first, I dig up the instructions.

It certainly looks worth checking out. www.pcblibraries.com

Duane Benson

Via in Pad whitepaper PDF

We've collected up a bunch of our Via in Pad hints and published them as a white paper PDF for download on our website. It's in our Services section, in the FAQ on the right side-bar. We keep all of our PDF downloads there.

If you've read our blog regularly, you won't find anything really new in the white paper, but in that form, it's easier to print out and keep handy or pass on.

Duane Benson

Comments From Customers

A good Saturday morning can be used for sleeping in or it can be used for reflecting on the past week. Maybe both. I'll sort of take both. I did sleep in a bit and I'm going to spend some time reflecting on the past. We send out a survey form with each order we assemble. I'm paging through the stack, like I do periodically, to see how we're doing.

The most valuable comments we get are those that come in when something doesn't go as well as we would like. Those are the ones that help us improve our service.

Following are a number of comments taken off of these surveys and some of my related thoughts.

  • "Excellent job over several orders."
  • "Excellent customer service. Thanks Chris."
  • "We are very impressed with you quick turn around and quality work. We'll be using you again in the future."

That's always nice to hear. We get a lot like this, but I'm skipping all of the positive comments except the three above. The rest are about things that we could do to improve the experience or about quality improvements we have needed to make.

  • "More status updates on web would be nice feature."

That would be nice. Right now, we update the web order status (on your MY ACCOUNTS page) when the order is placed and confirmed, when we receive the kit and when the order ships. We've got a system improvement that we are currently working on that will give a lot more detail about where your job is in our shop. I'm not sure when it will be implemented, but probably within the next two months.

  • "The boards weren't very clean, had solder flux on them. The hand soldered parts weren't very straight or even with the board's edge lines."

We use no-clean flux so usually, this isn't a problem. Sometimes, though there is more residue that we or our customers would like to see. We send notes like this back to our floor. They'll take a look and see if there is additional training or process improvements that we can implement. Sometimes though, given that we are working on prototypes, we don't pay as much attention to cosmetics as an individual might. We make sure the function and reliability are there and that the solder joints and things meet up to IPC-A-610.

  • "My only issue was trying to pay with a Purchase Order. It was not clear (on the website) how to do this. I spoke with someone on the phone who explained it in just a few minutes. Its was easy!"

You're right. It isn't very clear on the website. We do tell you about our policy on credit terms, but it's hidden in our FAQ page. That's a bit of trickery. I could just say what our policy on POs and getting Terms is, but I'd rather give you the opportunity to see it in our FAQ and then browse around a bit.

  • "It can be confusing when parts are re-sealed in packaging without updating quantity."

Good point. I'm not sure we've thought of this issue before. Again, this is one I'll pass back to the shop floor. When we get more parts than we need, we do reseal them back into the original bags - especially if they are moisture sensitive parts.

  • "Add a way to reorder from the past 'order summary' page."

Another very good suggestion. This is something we are talking through. We do have the capability to do this when we place an order for you over the telephone. We keep the solder stencil for 30 days, so if you reorder within that time, you can even get a discount for the stencil charge. The caution, of course, is that if anything has changed, it's not the same order and we have to treat it as a new one, including ordering a new stencil.

  • "Some pins on the through-hole connectors were not soldered. Flux was left on the board. Kudos for completing our boards ahead of schedule!"

Gyarrr! I hate it when that happens. There really isn't an excuse for not soldering pins and ahead of schedule is worthless if it isn't right. Again, this note went back to the floor. This comment came in back in February and I don't think we've had this happen since. See my earlier note on the flux.

It is very important to us that we build your boards the way you want them and when you want them. That's why we're here and why we strive to be the best at this. If things don't go as well as you would like, tell us. If it's an immediate problem, call us (866)784-5887 or email us. Otherwise, just fill out the survey form and fax it back to us.

Duane Benson

It Lives!

I think the very first logic gate I got my hands on was the 7408 quad AND gate. Not a 74AC or HCT or anything like that. Just plain old SN7408N - probably made by Texas Instruments. The first actual gate I played with would have been an inverter, but that was a proto board wired single transistor job made with a 2N2222.

7400_2 Yes, the first IC logic gate was the 7408. Well, the first of the 7400 series was actually the 7400 quad NAND gate, but the first one I used was the AND gate. I'm not going to tell you how many million years ago that was, but it was a few.

If you're a regular reader of this blog, you are undoubtedly somewhat familiar with the QFN (Quad Flat pack No lead) package. We see many of the newest components coming out in this package. It has better thermal characteristics than other packages and is a lot smaller. Since much of the really high volume is with cell phones and other hand held devices, "small" is where the volumes and profits are for chip makers. These days it is not uncommon to see chips only come out in a QFN package or at least launch with that package and add larger packages later.

I just read an article in Planet Analog article about Texas Instruments releasing new versions of 7400 series logic in QFN packaging (TI calls it an RGY package). My SN74LVC08A is still a 14 pin device with the exact same pin-out as the original 7408. It's 3.5 x 3.5mm and 1mm thick. Costs $0.50 each in quantity one at Digi-Key.

Every now and then, I'll need a basic logic gate for some robot or motor driver I'm building up. I still have an old proto board and a few of the old '70s vintage chips and they still work. Like you, though, if I wanted to use the new QFN version, I'd have to run it through Screaming Circuits. No hand soldering there.

Duane Benson
Long live the 7400!

The Rest of the Story

Screaming Circuits assembles prototypes and some small volume production pc boards. We put electronic components on printed circuits boards and [Danger Will Robinson: ego alert] we think we are one of the best in the Industry. If you combine our technology with our engineer friendly approach, we think we may even be the best. This post isn't about a possibly over inflated ego though, it's about what is behind our little prototype pcb assembly world.

We have a parent company, Milwaukee Electronics, which has been building mid-volume production for 60 years. They do everything from simple pcb assembly on up to complete box-build.

One of our sister divisions within the Milwaukee Electronics family is our Design Engineering Group. The Design Engineering Group takes on concept-to-production jobs, schematic design jobs, project management jobs and pc board layout. They have a pretty wide range of expertise, but if I had to tag a specialty, it would probably be in industrial control and motion control.

Getting a quote is not in the remotest sense an automated process like assembly is with Screaming Circuits, but if you need help with design or layout, give us a call or shoot us an email and we will connect you up with them. You can also check out our Design Engineering Group directly on their website.

Duane Benson
He's not heavy, he's a division of my parent company

Custom Library Parts

I ran across a resource for those of you that need to make custom parts libraries for your PCB CAD software. In general, the part datasheet is the first place to go for land pattern, dimensions and all of the other key details needed to create a library component.

Ipc_footprints However, sometimes not all of the data is there. Sometimes it isn't complete or is difficult to interpret. If you can't find what you need with the manufacturer, the IPC has something that might help too. It's the IPC-7351A Land Pattern Viewer. I don't know if it shows everything, but it has a lot of different packages with a lot of good information.

Download it and check it out. It might just help.

Duane Benson
In the pattern on short final for landing on runway 7351 right.

Plugged or Capped Via in Pad

One more thing on the plugged or capped via in pad -

If you do this, ask your board fab house about the flatness of the resulting pad. Some manufacturers will plug and plate over or cap a via in a pad but not deliver a flat surface.

The pads might have an indent or a bulge. This can be a problem, especially with the smaller BGA with .5mm or smaller pitch. The flatness of the surface is very critical with these parts. An indent can lead to insufficient solder under that ball and a bump can tilt the part, leading to poor connections under other balls.

Talk with your board fab house and make sure the surface is flat and flush.

PCB Panelization at Screaming Circuits

Most design and manufacturing type folks wouldn’t dream of sending a 2” x 3” pcb out for high-volume manufacturing as a single board. It would generally be replicated up to a panel (also called an array by some) size that would fit the volume manufacturers equipment and would yield the largest number of boards.

In the prototyping world, though, that usually doesn’t make sense. With a prototype, it often makes sense to run just few boards in case there are design errors. That’s why we usually assemble single boards and don’t require any tabs, fiducials or things of that sort.

Sometimes we do get requests to assemble panels and we generally can do that without problem – provided we have the right information at the right time.

If you want us to assemble a full panel of boards, you should still quote the individual board. For example:

  • Your design has 25 different bill of material line items
  • You have two panels, each with ten boards
  • Each board has 45 smt placements on it.

On our website, you would quote the “Desired board quantity” as 20 boards, with 25 “Total # of manufacturer part #s” and 45 “SMT” placements.

Then, in the “Special Requirements / Comments for Assembly” box, tell us that the boards are panelized ten-per-panel and tell us if your Gerbers are panelized or single.

Family panels are another issue altogether and will be discussed in a separate posting.

Duane Benson

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