Blog - Screaming Circuits


Screaming Circuits at EE Live

If you're in San Jose, CA this week, stop by and see us at the EELive show. We'll be in booth 927 - just a short walk, and a left turn from the entrance.

Show hours are:

Tuesday, April 1,    10:30 - 5:00
Wednesday            10:30 - 5:00
Thursday                10:30 - 1:30

Map to booth 2014

0.4mm Pitch BGA is Awesome

I recently had a conversation with a friend about 0.4mm pitch BGAs. The specific part is the Freescale FreescaleKL03KL03 ARM Coretex-M0+ microcontroller in a 1.6mm x 2mm, 04.mm pitch package. That's a 20 ball wafer scale BGA form factor.

I don't have an actual part to photograph next to a grain of sand, but trust me (or don't), it's really small.

Ti 0.44 pitch dimensionsThe challenge, and the reason I suggested a QFN form factor instead, is the costs
involved. If you have the extra budget money for more expensive PC boards, then go ahead and use this form factor. You probably won't be able to use this package in cost constrained situations.

The simple reason is that you can't escape route the inner six pins without using super small vias between pads, or in pads and filled and plated over. The page on the left is from a Ti doc, but any variations in geometry will be minor.

You can see that you can't put a trace between the pads. Maybe a 2 mil trace, but maybe not. There just isn't much room. The recommended method is to put micro vias in the pads and have them filled and plated over at the board fab house. Never put a via in a micro BGA pad unless it's filled, plated over, and flat.

Duane Benson
There are more things in heaven and earth, Horatio, 
Than are dreamt of in your philosophy.
But open vias in pads aren't one of them

When is an 0201 Not an 0201?

Metric vs US resistor packageI'm working on a special project here that involves some 0402 LEDs and 0201 resistors. When doing such a thing, you should always check the footprint you're using against the data sheet. When using extra small parts, like this, I recommend making a custom footprint unless the one you picked is exact, and I mean exact. There just isn't an margin for error at these geometries.

Take a look at the table on the right. The dimensions are in mm. Spot anything a bit off? Counter to most data sheets, the sizes listed in the "Type" column are metric sizes. At DigiKey, the package was listed as "0201 (0603 Metric)." I see that all the time, but for some reason, most data sheets Metric vs US resistor package Conversionshow the package name in US size while listing the dimensions in metric.

The first table was at the front of this data sheet (page 5). The second table was on page 35 - the opposite end of the data sheet.

We do occasionally get boards with metric size pads for a US size part, or vice verse. Sometimes we can make it fit, but not always. Bottom line, is to check and double check. I caught this one because the dimension .54 mm is about 21 mils, which is too small for an 0402. That, and the fact that the table doesn't list an 0201 size.

Duane Benson
Is it Bigfoot or Sasquatch?

 

EELive The Show is On it's Way

If you're going to be in San Jose during the first week in April,stop by the EELive show (formerly known as the Embedded Systems Conference). We'll be in booth 972. Stop by and see what we can do for you. Maybe earn a fabulous T-Shirt.

While you're there, check out my two sessions:

"FPGAs - Light at the End of the Learning Curve", at 3:30 on Tuesday. It's not exactly PCB Assembly, but FPGAs are quite cool and getting more useful by the minute. Get some basic knowledge and see how to avoid many beginner traps.

My second session: "Best Practices in Circuit Board Design", part of the "Hardware Startup Engineering Summit," is set for 2:15 on Tuesday. You can watch that one and then run with me to my FPGA session at 3:30. Place bets on whether I can make it in time.

Duane Benson
Ach, Captain. She Canna Go Any Faster

  

 

Possible Weather Caused Delays

Sign on 2-6-14UPDATE Feb 11, 2014

We are back to our usual 40 degrees and drizzling - so business as usual. No more weather delays from this storm. Just dampness. Never... ending... dampness...

 ---------

Yes, we here in the Portland area can get snow too. I know it's not as deep as everywhere else, but it still gets in the way. That means that some parts shipments in to our plant may be late and some finished board shipments going out may be late.

Unfortunately, I have to pop up a reminder that  weather related days do not count toward your turn-time. I'll let you know as soon as I can if anything changes. Unless it gets worse, Bob the cat will attempt to keep on delivering, but may be late.

Duane Benson
Eli The Ice Man says "What?"

 

UPDATE Feb 7, 2014:

We're here. We're working. But we still may have some weather caused delays. I know, Minnesota has ten more feet of snow than we do, but they also have things like snow plows and mittens.

Here's proof positive that Bob the Cat is attempting to get parts in and out of here.

Bob the cat prints

Old and New: 60 Years at Milwaukee Electronics

In 1954, one of my favorite movies, "THEM!", premiered in U.S. theatres. An even more significant (to us, anyway) event took place in Milwaukee, Wisconsin: The founding of Milwaukee Electronics.

We are excited to announce that our parent company, Milwaukee Electronics has been in business for 60 years! After six decades of dedicated service to customers, and several name and logo changes, Milwaukee Electronics is updating it's image. Click here to view more details.

Without Milwaukee Electronics, Screaming Circuits would not be possible. 60 years of expertise, plus our unique perspective, gives us the ability to offer something that no one else can: real-time, on-line turn-key quote and order of quick-turn prototype and small-lot production assembly.

Duane Benson

Open The Pod Bay Doors, HASL

Does anyone use HASL (Hot Air Surface Leveling) anymore? It's also known as HAL.

Prior to the RoHS days, HASL was probably the most common surface finish. You can get it lead free, but most boards seem to use immersion silver or ENIG (Electroless Nickel Immersion Gold). HASL has traditionally come at a lower cost than those other two finishes, but immersion silver can generally be found at the same price now.

Our friends at Sunstone.com, for example, charge the same for silver and tin/lead HASL. ENIG is still more BGA on HASL closeexpensive no matter where you go though.

One of the chief disadvantages of HASL these days, is the lack of planarity on the surface. (Note the bumps on the BGA land pattern in the image on the right.) With thru-hole or large components, an uneven surface doesn't matter so much. With the increasingly smaller BGAs and QFNs, however, surface irregularities can cause big problems.

Both Immersion silver and ENIG have nice flat surfaces. OSP (Organic Surface Preservative) has a pretty flat surface too, but it's not used much except in high volume consumer goods or specialized applications.

By Duane Benson
Oh, the pain! Save me, William.

ODB++ plus, plus, plus

I wrote a bit about ODB++ back in October. Nothing has really changed much since then. I'm just clarifying a few things.

First, I want to put more emphasis on the use of ODB++. In addition to being beneficial to the manufacturing process, it can make your job a little easier. If you send us ODB++, you do not need to send either the Centroid or Gerber files. The ODB++ replaces both.

Eagle CAD does not have an ODB++ export. However, the Eagle .brd file will work too. You can send us the .brd instead of the Centroid and Gerber files.

If you can't send either of those formats, we still need the Centroid and Gerbers (top copper, bottom copper, solder paste stencil, silkscreen and solder mask layers).

Number Six
I am not a number, I am a free man!

Corporate Cats

Here at Screaming CIrcuits, we're all busy making sure to get everyone's assembly orders shipped off on time so here's a picture of one of our corporate kitty cats.

COrporate kitty

We have a pair that live on campus here. They seem to be quite content to buzz about the parking lot and surrounding hedges all day while we build things. That's for the best because we do keep them off our production floor. Cats can cause static electricity and that would be bad.

Duane Benson
Make sure the dip with your chips is lead free before eating it

VLV - Very Large Vias

I recently received a question over on Twitter. Tomaž Šolc, AKA avian2 asked:

"@pcbassembly What is your opinion on the "one big plated drill in QFN ground pad" pattern? pic.twitter.com/M9ZLftpuo0"

From Avian2 Ban_N62IEAAm3acI answered back: "Bad for machine assembly, okay for hand assembly." That's definitely true, but it's worthy of a bit more explanation. Here's the photo avian2 included along with the question. We're looking at the side opposite of where the QFNs are mounted. The two big openings in the square gold pads are the big vias (plated drill).

This is often done when hand soldering QFNs. Somehow you get the little pins on the outside edge of the QFN soldered down. Then you turn the board over and poke your soldering iron into the big opening to solder the pad down.

Generally, there wouldn't be any reason to do this with machine assembly, as we do here in our plant. You put a number of small vias, cap them, and segment the solder paste layer (refer to this post and this post). Thus, we would never recommend using big vias like this for machine assembly.

However, I can envision some situations that might call for this. First, there's the hand solder method I mentioned above. Next, there may be some very specific need to expose a lot of the pad to open air for cooling. In general, this is not the best way to get cooling, but maybe in some special case. Third, perhaps you need access to the pad as a test point and don't have enough room to get access any other way.

You wouldn't do any of those three things in a production environment, but in a prototype world, sometimes things happen differently.

Duane Benson
Hurray! Only one day until Mitten Tree Day!