Monthly Archives: October 2014

Freescale KL03 and PCB123 at 0.4mm Pitch

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Small component packages seem to be a recurring theme with me. It’s understandable, I guess. Super tiny packages are becoming more and more common and we build a lot of product with them.

The smallest we’ve built is 0.3mm pitch. Those aren’t common enough to be considered standard — they’re still an experimental assembly — but not many chips use them yet. 0.4mm, on the other hand, is something we see on a pretty regular basis.

What’s so tough about that? The biggest challenge with these form-factors seems to be footprint design and escape routing. I can see why. There really isn’t room to follow any of the standard BGA practices. You can’t fit escape vias between the pads and you can’t put vias in the pads, unless they are filled and plated over at the board house. Filled and plated vias are the easiest way to go, but it can make for an expensive board fab.

KL03 WLCSP20 on a US Lincoln penny. One of my side projects involves trying to make the smallest possible motor driver. For this project, I’ve chosen the Allegro A3903 driver. It’s a 3 x 3mm DFN (dual flatpack no leads) with 0.5mm pitch pads and a thermal pad in the middle. The microcontroller will be the new Freescale KL03 32-bit ARM in a 1.6 x 2.0mm WLCSP (wafer level chip scale) package. It also comes in a 3 x 3 x 0.5mm pitch 16 pin QFN. Without an expensive PCB, that may be my only option.

Pick your CAD package. I’m using the newest version (5.1) of Sunstone Circuit’s CAD package, PCB123, but the principles here will apply to any CAD software. If you don’t already have a copy, download PCB123 V5.1 here.

If you’ve got fast Internet, you’re done now, so go ahead and install it. You’ll need the manual too, which you can get here.

I need to eat now, so stay tuned for Part 2.

Duane Benson
Nerfvana – It’s like Nerdvana, but with more foam darts.

http://blog.screamingcircuits.com/

Wilk the Winner

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Congratulations to Edward Wilk of Facts Engineering, who won the incentive prize for filling out a recent survey of PCB West 2014 technical conference attendees.

Edward, a $50 AMEX gift card is headed your way. Thanks for your support, and thanks to everyone who took the time to respond!

Pin-in-Paste Aperture Calculations Using Solder Preforms

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Folks,

The pin-in-paste (PIP) process is often the best choice when the PCBA is a mixed SMT and through-hole board with a small number of through-hole components. However, ensuring that the correct volume of solder paste is printed to ensure an adequate amount of solder for a reliable thorough-hole solder joint can be a challenge. One tool to help in this regard is the Pin-in-Paste Aperture Calculator. This calculator is now online at http://software.indium.com/. The solder volume equations were developed by good friend Jim McLenaghan of Creyr Innovation.

To estimate the right amount of solder paste, we need to calculate the volume of the plated though-hole, subtract the volume of the component pin, and add the volume of the solder fillet. See Figure 1.

Figure 1. Solder volumes in the pin-in-paste process.

Let’s assume we have the PCB and component pin metrics, as seen in the left hand column of Figure 2, under the header “Input.” Blue cells are inputs, green cells are calculations by StencilCoach. Notice that, if you have a rectangular pin, the software will calculate the equivalent pin diameter for entry into the “Input” cells. The “paste reduction factor” is the fraction of the paste volume that is solder. Most pastes are about 50% by volume flux, so, typically, this metric would be about 50% or 0.50.

Figure 2. PIP metrics.

The “Output” calculations are not really necessary for the task at hand, which is determining the stencil aperture dimensions, but may be of interest. The important stencil dimensions are shown in the “Stencil Metrics” section. Note that in our example, even though we have a 7-mil thick stencil, we would need a square aperture with a side dimension of 93-mils to get enough solder paste. With a circular aperture the radius must be >50-mils, if the pin spacings were 100-mils, there would not be enough spacing between the printed deposits, they would overlap. So we must use square apertures.

As in this case, it is a common problem with the PIP process to deliver adequate solder volume. If the PCB and component metrics are such that obtaining enough solder paste is an issue, it can be helpful to use solder preforms to increase the solder volume. The next post will cover this topic.

Cheers,

Dr. Ron

Optimal at Optimum

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As corporate models go, Optimum Design Associates isn’t unique. Several firms have launched as design shops only to add EMS capability as they matured.

But one thing ODA does that I really like is provide a much greater level of detail about its financials on its website.  See below:

Financial Disclosure

Financials through 12/31/2013

Ownership Private
Annual Revenue $19 million
Credit Access $5 million
Loan Balance $133,000
Principal Payments $3,700
Access to additional financing Yes
Executive changes last 90 days No
Ownership changes last 90 days No
Return on Assets (last quarter) 3.6%
Current Ratio 2.2
Quick Ratio 1.21
Capitalization 23%
Cashflow 5.45
Debt to Equity Ratio .003

 

For a privately held company, that level of public disclosure is unusual. For a small business, it’s unheard of. Certainly any OEM worth its salt would ask for verification of financial stability prior to engaging, but having that data on hand upfront makes determining whether ODA is the right fit a little easier for potential customers (which could also be a time-saver for ODA), and moreover offers a high degree of confidence that ODA will be above board.

Perhaps that’s willingness to break the mold is why ODA is again on the Inc. list of the fastest-growing companies. (It also made the 2007 and 2008 rankings.)

Congratulations to Nick and the gang at ODA.

VTP: Very Tiny Parts

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A while back, I wrote about a new ARM Cortex M0+ chip from Freescale. It’s not the first M0+, but I do believe that it’s the smallest. I’ve been checking stock off and on and finally found the smallest package to be in stock and available to ship. 

I actually bought a couple of different types. First, there’s the WLCSP 20. It’s got 32K Flash, 2K SRAM and an 8K bootloader. The real kicker is that the package is only 1.6 X 2.0 mm. I also got a few in the QFM-16 package, which is a bit more workable at 3 X 3mm.

Finally, I bought a Freedom development board with the 4 X 4mm QFN-24 package. The dev board is hardware compatible with Arduino shields, so that will make for some interesting possibilities.

Anyway, here at Screaming Circuits, I’m most interested in that 1.6 X 2.0mm package to see how easy (or difficult) it is to use – see if there are any particular layout challenges. The other stuff is just for after hours play time.

Duane Benson
I’m not a number. I’m a free development board!
(Free, as in named “Free…”, not free as in “don’t cost nothin”)

http://blog.screamingcircuits.com/

The HP Split

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Those wondering how the HP split might shake out should read this piece in Bloomberg today. In summary, HP’s PC group just lost some of its pricing advantage, as the servers and other business-oriented gear are going with the new Hewlett-Packard Enterprise company. HP is currently Intel’s largest customer, but that will change as the two primary hardware lines are separated. (HP’s server gurus have been working on a competitive line using Applied Micro chipsets, so that ranking might eventually have been in jeopardy either way.)

On the other hand, given HP’s deservedly stodgy reputation in tablets and handheld PCs — despite, or perhaps because of, its acquisition of Palm in 2010 — the shakeup could enable the new HP Inc. to focus on trendier designs for the mobile market.

What’s not clear is whether each group will retain a certain number of chip designers. This is an area of strength for Apple, and HP Inc. will need to ensure it has the internal talent to advance in the hypercompetitive PC space.

Cost Reduction in Design — More Advice

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If you’re looking for the absolute, cheapest possible assembly service, you’ll need to look outside of North America. If you really need a decent price with good quality and good service, you can keep your gaze West of the Atlantic and East of the Pacific.

Like everything else in the modern world, design decisions can have a pretty big impact on your cost. So, lets take a look at some design decisions that can make your manufacturing more affordable.

  • Accept longer lead times

Lead times are one of the biggest factors in electronics manufacturing. Screaming Circuits can turn a kitted assembly job overnight, but it costs a lot of money to do that. Screaming Circuits also has a 20 day turn-around that is much, much more affordable. Accepting longer lead times on PCB fab will drop your cost as well.

  • Avoid leadless packages like QFNs and BGAs

We build tons of QFN and BGA boards – even down to 0.3mm pitch micro-BGAs. That’s great if you need those packages. However, since all of the leads are underneath, we have to x-ray every part. That adds a bit of cost to the process. If you can, stick with TSSOPs and other parts with visible leads.

  • Use reels, or 12″ or longer continuous strips

We will gladly assemble parts on strips of almost any size. But, to save costs, use full or partial reels or continuous strips of at least 12″ long. It costs us less time to work with reels and continuous strips, and we pass those saving on.

  • Stick with surface mount

These days, through-hole components tend to be hand-soldered. That costs more than machine assembly, so use surface mount wherever possible. Surface mount components tend to be less expensive than through-hole too. If you do need a few through-hole parts, this is an opportunity to put in a little sweat equity by soldering the through-hole yourself and save a bit of money.

  • Panelize small boards

We can work with really tiny boards individually, but sticking with a larger size makes the job easier, and, again, we’ll pass those saving on. If your PCB is smaller than 16 square inches, panelize it. We put in less labor and you get a price break.

By following these guidelines, you get a decent price and really good quality and service.

Duane Benson
That would be telling

http://blog.screamingcircuits.com/