Screaming Circuits: February 2008

A Working Power Component Footprint

To263_footprint A couple of days ago, I wrote about a TO-263 footprint that caused the part to slide up almost off of the legs. Here are two examples of a footprints (or should it be "feetprint"?) that will work just fine.

The first picture has a nice big pad that will cover the component thermal pad and keep it centered in all of the right places. The big land might even be a little over-kill but it will work.

The second picture shows another good pad after assembly. The difference between this and the one in the Lt1963 prior post is subtle, but the pad on the board matches the pad on the part closely so that the part ends up in just the right spot.

And, on a side note - in that older post, I complained about the LM1086 pinout. This part, the LT1963 is a good low-dropout regulator and, in it's three-pin configuration, does in fact match the pin-out of the old 78XX. So there!

Duane Benson
in-ground-out forever!

The Next Big Idea?

According to the U.S. Census Bureau, more than half a million new businesses open every year in this country. Granted some of them are pizza parlors and carpet cleaners, but a lot of them are start-ups put together by an engineer with a great idea. Big business is important, but start-ups are what really drive innovation in this country.

So, what do you do if you are one of those engineers with a big idea but don't have a clue as to whether you can build it or sell it, or more importantly, make a living off of it? Some people will just quit their job and go for it. Others will work late into the night so they can keep their day-job while designing and building it. Some go on their own and some gather a team and get some venture capital money.

There are a lot of ways to answer the question in detail, but sometimes a simple rule-of-thumb can help to at least jump start the process.

For example; take your total bill of materials cost. It doesn't have to be exact because we're just getting a rough estimate. Go to Digi-Key and get costs for, say, 100 or maybe 1,000 sets of your parts.Then go to and get an online quote for the same number of pcbs. Add that up for your BOM cost. Then double that. That's your cost to a reseller. Then double it again for the price they will sell it at to an end customer.

That means if your BOM cost is $500.00, it will probably sell to customers for about $2,000. It gets a lot more complicated, but this is usually close enough to give you a "yeah, that could work" or a "hmm. I need to to be more creative."

Duane Benson
Ignore the man behind the curtain

Ouch! Shipping Can Hurt.

Crushed There really isn't much you can say about this other than what I said in the post title. (although, I'll probably end up saying a lot more than just "ouch") I don't know what kind of parts were in here but regardless, this looks seriously squished. Sometimes, though, outside appearances can be deceptive.

If it was a bag full of strips of parts, I could certainly see everything coming though the ordeal okay. Even raw PC boards could have survived, provided that are small enough. And, as it turned out, everything did survive this treatment. The parts and pcbs were fine.

Granted, this was an International shipment and it was not only handled by DHL, but also by our friends at U.S. Customs and probably a broker or other country's inspection station here and there, but it speaks to the value of good secure packaging no matter where you are shipping to or from. The box got crushed handily but there was plenty enough room for compressibility.

Duane Benson
Danger, Will Robinson
Crush, kill, destroy...

Power Components and Surface Tension

Another Parts Library issue

Surface tension can be quite handy. For one thing, without surface tension, water bugs wouldn't be able to skip along the surface of a pond. They'd sink like a rock straight to the bottom and frogs wouldn't be able to eat them. The frog population would plummet and we all know what that means.

Another handy effect of surface tension is that it acts to help BGAs and QFNs to center themselves Ground_pad_pulling_part_2 during reflow. This same effect can backfire on us though. Take a look at the TO-263 packaged regulator in the photo. By the way, the LM1086 really annoys me. Why in the world isn't it pin compatible with the ubiquitous 78XX regulator pinout? Yeah, I know it's a low-dropout but other low-dropout regulators use the standard pin out. What gives?

Anyway, what happened is that surface tension pulled the part up and nearly pulled the three legs off of their land pads. If not reworked, the legs won't be mechanically secure, they may not have sufficient current carrying capacity and if there are and mask imperfections, they are at risk of shorting to the copper fill area.

There are a couple of possible remedies here:

  1. Mask off the top of the thermal pad so the part can't slide up that far.
  2. If the pad needs to be fully exposed for better convection, just use a strip of soldermask as a solder dam. If you use this approach, don't forget to modify the paste layer so that no solder paste is spread above the mask dam.
  3. Extend the thermal pad down so that when the body of the part is centered, the legs will still be appropriately located on their pads.

Duane Benson
What about newts?

LED Via-In-Pad

Darn, darn, darn. More vias in those pads. It kinda makes the LEDs look prettier without any solder on those pads, but it won't make them light up any more reliable - and  light emitting diode that doesn't emit any light isn't very helpful. It's pretty clearly illustrated here what can happen with an open via in the pad, especially if you compare the two via-padded LEDs on the right with the via-less one on the left.


Plug those vias or keep them off of the pads, please. From the looks of this board, space wasn't an issue so the least expensive solution would have been to just move the vias off of the pads.

Duane Benson
The worms crawl in.
The worms crawl out.
The worms play pinocle on my heart

Modules and Daughter Boards.

We ran across an interesting part the other day. Modular sub-components are getting more and morePth05060_on_board  common. You see bluetooth radios in module form, ZigBee radios, GPSs, Power Supplies and other common building blocks showing up like this more and more.

Pth05xx_modules_2These little modules are are non-isolated PTH05060WAS and PTH05050WAZ DC to DC converters; less than $20.00 each from Digi-Key as of this writing. One of the interesting aspects of this product is that they are multi-sourcable. In my experience, most modules of this sort are dramatically different from one manufacturer to another. These ones, though, are offered by at least three manufacturers as part of the "Point-of-Load Alliance" (POLA) with a standard footprint and functionality.

It's also interesting to note that these are essentially BGA packages. It's not quite the same as a standard BGA but the connections use solder balls like a BGA.

Continue reading "Modules and Daughter Boards." »

OSP PCB Finish Problems

Osp_bad_bga_finish800 OSP (Organic Surface preservative, not Oregon State Patrol) isn't all that commonly seen in our shop. It has been a pretty common pcb finish for high-volume, low-cost products for quite a while and I've heard that it's starting to show up more frequently on complex boards these days too. Some of the new formulations are pretty good for RoHS applications.

We got a set of OSP pc boards in just the other day with a lot of fine pitch parts and a few big, honkin BGA lands. Click on the two thumbnails for bigger images that do a good job of illustrating one of the potential pitfalls of OSP boards. In the close-ups, you can clearly see two different colors of copper land pads. That's not normal. It indicates an unsolderable, contaminated finish. If you look at an OSP board and see a pretty multi-colored pattern like that, get on the phone with your pcb fab shop and get the boards re-done.Osp_bad_bga_close

Take a second look at the closer close-up here. This board also does a good job of illustrating the use of NSMD (Non Solder Mask Defined) pads. Most BGA manufacturers recommend the use of NSMD pads. This allows the BGA ball to sag down a little more and grip on the side of the pad too. It also illustrates the proper way to mask the trace between the pad and the via. That's very important too. That mask will keep the solder balls from being sucked off of the BGA.

Duane Benson
Suddenly, State Patrol...

Rain Isn't So Bad

I can get pretty tired of the rain and drizzle out here in Oregon. Sometimes it seems like we spend half the year living through 40 degrees and raining. Yuck. Nothing bad, as you can see in this photo of our parking lot. Just drizzly and annoying.


Every now and then though, someone reminds me that 40 degrees and raining isn't so bad.


Mark from the Milwaukee, Wisconsin office of our parent company, MEC, just sent over some pictures of the place. Here's what one of the company picnic tables looks like about now. Yikes. If we had that much snow here in Oregon, they'd shut the whole state down for a month.

Duane Benson
The grass is greener on this side of the fence

Restoring Immersion Sliver PCBS?

I've written before about immersion silver finished boards and some of the challenges associated with that technology. It's a popular choice for RoHS these days because it's inexpensive compared to some of the others, has a nice planar surface and, conveniently, is, in fact, RoHS compliant.

Silver_sampleIt has a somewhat high nuisance factor though, because of its proclivity to tarnish and susceptibility to fingerprint grease and other surface contaminants. All the board houses will say it doesn't have any of those issues, but it does. Immersion silver pcbs need to be kept clean, dry and dark. Even then they still have a shelf life. A silver board doesn't take solder well if it's been stored too long, poorly or mishandled. Nag, nag, nag. Okay - got that out of my system...

So, what do you do if your boards have surface issues? Do you toss them? Do you send them to a psychologist? Do you turn them into expensive cubicle art? Do you use them like a Frisbee®? One of my manufacturing engineers told me that some board houses will re-plate them for you. For a fee, of course.

Apparently, in some cases, they can dip the boards and etch the old silver surface off and then re-plate them. I don't know if all board fab shops can or will do this, but if you have a couple of hundred dollars worth of unusable PCBs, it would certainly be worth a call to your Board fab shop to see if they can re-plate them for you.

Has anyone already had silver boards replated? Drop me a comment - I'd like to hear how it worked out for you.

Duane Benson
No Tarn-X, please

Turn-Key Prototype Electronic Assembly Order

Tutorial on placing a Turn-Key assembly order with Screaming Circuits:

With a kitted quote, you send us the pcbs and parts and we build up the assembly for you. With a turn-key order, you just send us your files and we quote and then buy the boards and parts as well as build up the assembly.

Placing a turn-key order is not very different from a kitted order. The key difference is that you will not see a materials quote right away. You first place the order, then we will call you about the pcb and components details. In about a day, we will return the full quote and you can decide to proceed or not.

  1. Create a Labor Quote: Start on our quote page and tell us a few details of your project and obtain a price quote. Mostly, you are describing your BOM (bill of materials) to us. After "Generating" the quote, choose quantity and turn time. Then select "Order".
  2. "Place" your Order: For a turn-key order, these details will be used to complete your quote. Give a project name and timeline. In the "Box Details" section, enter "Turn-Key"
    In the "Special Instructions", note that this is for a turn-key quote.
  3. Payment Method: You can select "Other" or give us your credit card information (Visa, Mastercard, or AmEx) so we will have it on file. We will not charge it unless you authorize us to proceed.
  4. File Upload: The last step of the online order process. On this page you can upload your files (in a single .zip file, please).
  5. Call us: To complete your turn-key quote, we need to speak with you first. The online quote will only show labor costs. We will quote the materials manually.


For Turn-key pcb prototype assembly orders, the online
quote will only reflect the labor costs. Call, toll-free,
1-866-784-5887 to quote the pc board fab and other materials costs.

Don't forget to click the blue SUBMIT button at the bottom of the page.

You can also have us do a partial turn-key order for you. We can get the PCBs and you can send us the parts. We can do the opposite. Or we can get some of the parts while you supply the rest. Just use that Special Instructions box or give us a call.

You can get started on our assembly quote page.

We're here to help

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