Pads on Ground Plane

Pour-no thermalGenerally, small pads for passive parts are connected  with a single PCB trace of equal size to each pad. That's the right way to do it.

However, sometimes, circumstances dictate a little different approach. The illustration on the upper right here shows something of a worst-case. This is for a snubber (resistor, capacitor pair) between two power planes.

A couple of things will likely happen. The power plane will act as a heat sink, preventing the solder paste on one side from melting, resulting in a poor connection. Or, the unequal melting could lead to surface tension pulling the part up, causing tombstoning.

Pour-with thermalMost designers are aware of that, but sometimes, thermals will be deliberately turned off to allow for better current capacity to and from the large power Mosfets (not shown). If that's the case, make sure that you can turn the thermals (see image on loer right) on or off by the part, rather than just by the plane.

Duane Benson
The rain falls mostly on the ground plane due to static attraction

Geek Week on Youtube

In case you haven't heard, it's Geek Week on Youtube. In honor of that, here are the top ten most incredible pieces of trivia from ancient Geek Mythology. You can scroll down and read them here, or have the questions read to you, by me, over on our Youtube channel. 

 

First question:

F: Everyone has heard the trite phrase: “There are 10 types of people; those who understand binary and those who don’t.” Who’s missing?

E: All your _____ are belong to us. Fill in the blank.

D: Who, in the late ‘70s correctly predicted that by the turn of the century, it would be possible to use our computers to find the answer to any question?

C: And, what name did he give his computer?

 B: Bell is reputed to have said: “Watson, come here. I need you.” What was Charlie Klien’s equivalent statement in 1969?

A: Who caused the “Y2K” problem? And, no, that’s not it. You’re already wrong.

9: Who did business under the name “Traf-O-Data”, starting in 1971?

8: One particular semi-nautically named person wrote the first word processor for the Apple II while in prison. Who was that?

7: And, what was that word processor? Bonus points if you’ve actually used it.

6: Who, in 1995, while on his deathbed, claimed to be DB Cooper? Bonus points if you know why I might know this.

5: How many tubes did a standard superhetrodyne radio have?

4: Name them.

3: When did the first man go into space? Be advised that you’re probably wrong.

2: When someone refers to “scout water”, what are they referring to?

1:  How many instructions did the first CPU have?

Now, drum roll please… ,

0: What is the least known, yet probably the most significant law that enabled the personal computer revolution to happen?

And... This is a contest. The first five people, in North America, to get the correct answers will receive a T-Shirt from us - or the five closest to complete and correct. You have until next Monday (8-12-13), when we post the answers. If you choose to submit answers, send them to dbenson @ screamingcircuits . com with the subject line "Trivia answers"

Duane Benson
According the The Buggles, video killed the radio star
If so, then why do we still have radio telescopes? 

Designing The Future: The Automobile

Here's a small glimpse into the future of the automobile. Granted,these guys had to take the dash off and hard wire in, but imagine this with a not-secure-enough wireless access.

 

Duane Benson
And... some of us here are helping to make this happen...

10th Anniversary Top 10 Traps

A few folks requested my presentation from out 10th anniversary open house.So, without much adieu, here it is.

Download Top 10 traps 7-2013 (PowerPoint format)

Download Top 10 traps 7-2013 (PDF format)

Duane Benson
10 time 10 isn't necessarily equal to 10 times 10.
Especially if you mix bases.

Super Small Via In Pad

Via in pad is an old issue that still pops up now and then. Our standard answer hasn't changed: No open vias in pads. But one of the questions we get related to the subject is: "What if we make the vias really small?"

Beagleboard U6 viasLogically, that makes sense. In fact, in some cases, the via is so small that it's essentially closed. If it's so small that it really is closed, then it's not an open via. But look close - if it's closed with solder, that solder may melt during reflow leading to an open via.

The images here show some pretty small vias. I believe they're 0.3 mm in diameter.

Beagleboard vias back sideIn the first picture, on the left, it appears that the vias are open. They aren't though. This board (an unstuffed Beagleboard) uses soldermask on the back side of the PCB to close off the vias, as shown in the image on the right.

Our recommended method (se more detail here and here) is to plug the via with copper or epoxy and have it plated over at the board fab house. Next, we'd recommend via caps on the component side. FInally, capping the back side with soldermask, like this example can work, but it comes with the risk of voids. The via caps and also pop open, leading to an open via.

Duane Benson
No more open vias-in-pad, I mean it!
Anybody want a peanit?

CAD Data Files

I've spent a fair amount of time researching and writing about the centroid file and about CAD library footprints. One of the challenges in this industry is that somethings that are "standard" really aren't all that standard. That's why we emphasize following IPC guidelines when creating library components.

Well, a few things have changed since we started doing this a decade ago. For one, some of the enhanced manufacturing file formats (as opposed to the 1970's vintage Gerber format) have become more prevelent. Those new formats are a very good thing.

Most CAD packages can now output either ASCII formatted CAD data or ODB++ format data. Those file formats have all of the data that would otherwise be found in the centroid and Gerber files. They also have more accurate data. If you can get one of those formats out, go ahead and send it to us. We can also take plain old Eagle CAD .brd files. If in doubt send one of these newer files along with the centroid and Gerbers. We'll use the file with the best data and, we may be able to simplify the file preparation Centroid snippet rot optyou have to do with future jobs.

And speaking of the Centroid, don't worry so much about the rotation column in the Centroid file. You can consider rotation to be optional now. You don't need to check the rotation, nor do you need to remove it.

Duane Benson
Who will win? Godzilla or Centroid? Maybe the Smog Monster?

 

10 Years of Speedy Prototypes

10th anniversary badgeSN74LS90 years and we're having a party - a party for engineers. Good food & drink, factory tours, door prizes, presentations... You just need to RSVP to: [email protected] or call us at 503-266-9100

July 18, 2013, 3:00pm to 7:00pm.
1140 NW 3rd Avenue, Canby, Oregon 97013

See all the details here.

10 Years of Screaming at Circuits

ladies and gentlemen and engineers of all ages...

Screaming Circuits, A Milwaukee Electronics company, is celebrating ten years of specializing in speedy prototype assembly.In honor of your great support, we're having a party! Come and see where it all happens. Take a tour. Enjoy a come-when-you-can buffet, beer, wine and SMT parts. We promise that the food and drink will all be lead-free.

See more details here:

blog.screamingcircuits.com/10-years-of-screaming-at-circuits.html

July 18, 2013, 3:00pm to 7:00pm. 1140 NW 3rd Avenue, Canby, Oregon 97013

Just RSVP to: [email protected] or call us at 503-266-9100.
  • Food to eat. It will be delicious, but we can't promise it will be nutritious.
  • Wine and beer from Canby's own St Josef's Winery
  • Fabulous door prizes
  • A Google Nexus 7 32GB Wi-Fi tablet for one lucky winner**
  • A $2,500 assembly coupon for another lucky winner**
  • A nice little gift pack from Screaming Circuits for everybody
  • Tables with people to answer any questions about any part of what we do for you
  • Informative presentations***
  • A few examples of fun projects we build for people
  • The "Game room" where you can challenge a Screaming Circuits champion to pool or ping pong

Duane Benson
Come on in and see what's happening
Pay the price*, get your tickets* for the show

* The price is free. just send an email to "[email protected]" and you don't really need tickets.
** We consider you all to be winners, but only one of you will with the tablet.
*** This is supposed to be fun and informative. Sales pitches have been banned from the event.

Push-me Pull-you LEDs

I may never get tired of talking about LED and diode polarities. It's so much fun. Not long ago, I wrote about two LEDs from the same manufacturer, marked with opposite polarities. I recently ran into another one, but at least this one tells you on the same datasheet. This image is an actual unmodified clip from the datasheet.

LED confusing polarityI can't for the life of me understand why this would be done on purpose. I could maybe understand is one was designed in a different building, but it couldn't have been too hard for someone to say: "Hey - wait a minute..." before sending these things off to manufacturing.

Of course, maybe they built a million before noticing and then just decided it would be easier to change the datasheet. Regardless, it's kind of nuts in my opinion.

The other thing here is that, while you can generally get away with the indicators "+/-" on an LED, you can't with all diodes. Thin Zener and TVS.

Duane Benson
Matter + antimatter makes what?
Does it really matter?
Does anybody really know what time it is?

Intergalactic Geek Pride Day Quiz

There was a time when "Geek" was far from a badge of honor. Jr. High School (AKA middle school) was developed specifically for the purpose of making geeks miserable. We were told that lockers were  designed for holding books, lunches jackets, but in reality, the secret anti-geek coalition had lockers installed so geeks could be stuffed inside of them, or could have the doors slammed in their faces.

But, then something happened. While the world wasn't looking, a geek became the richest man in the world. Pro-nerd and pro-geek movies became popular. It became cool to claim to be a geek or a nerd. The problem is that there's a big difference between claiming the title "geek" and being given the title "geek."

Well, May 25th is Geek Pride Day. In honor of Intergalactic Geek Pride Day, I've put together a little quiz on the subject.

Questions:

  1. Is it better to be considered a nerd, a geek or both?
  2. What's the difference between a nerd and a geek?
  3. Does the outside world know the difference between "nerd" and "geek" and thus does it matter which one you're called?
  4. If you've never actually been called a geek, but claim to be a geek anyway, are you really a geek?
  5. If a geek talks in the woods, but there's no one there to hear, did the geek actually speak?
  6. If you can explain what you do for a living (or hobby) to a random stranger and have more than about one in fifty understand, can you still claim to be a geek?
  7. If you don't have enough cables laying around the houses to connect just about any two pieces of computer / electronic equipment together, can you really claim to be a geek?
  8. If you can't assemble a spare PC from parts you have around the house in about an hour, can you still claim to be a geek?
  9. If you can't count in more than one base, can you still claim to be a geek?
  10. If you don't love songs by Tom Lehrer, can you still call yourself a geek? (If you don't know who he is, quick: Youtube)

 Bonus question:

  1.  Tesla or Edison?

Answers:

If you're a true geek, you already know the answers so I don't need to list them.

Duane Benson
The best revenge is not violence or deviousness
The best revenge is to be happier
...and to build robots for world domination