Surface Mount Power Component Footprints

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There was a time when the bison ran free on the plains and power components were easy to design with. Everything, with the exception of an exotic few, used either the TO-220 or TO-3 packages. Even when surface mount came along and cut the bison off from their grazing lands, most power components came in some derivative of the TO-220, with bent leads.

That’s no longer the case. Today, power components come in those TO-220 derivatives, SO-8 packages, QFNs, and down to 0.3 mm pitch wafer scale micro-BGAs. It’s madness.

The advantage of all of that chaos is that it gives more flexibility for sourcing and sizing of components. Which, of course, brings in a few more potential issues. Take the example below:

 

 

 

 

 

 

 

The footprints were originally created for a package with four 1.27 mm (0.05″) pitch leads on one side and a big heat slug on the other. The component selected is a variant in an SO-8 package. It’s not an uncommon occurrence.

As long as pins 5 – 8 all share the same internal connection, there isn’t anything electrically wrong here. However, with that large open copper pad on top, it’s going to be very difficult to get a good solder joint.

The fix is pretty easy. Just add solder mask to separate the pins. Make the mask openings the same size as you would if the pins were on individual pads. You don’t need to cover the whole pad with solder mask — just surround the pins so solder will stay where it’s needed. The mock-up below illustrates what it would look like:

 

 

 

 

 

 

 

Do the same with your solder paste layer. Unless the component has a heat slug underneath, make the paste layer block the big open area.

Duane Benson
Would a bisontennial be a 100 year old, large grazing animal?

Time to Go?

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I spoke today with a longtime friend in the PCB industry who shared that multiple times in the past year his company had made inquiries to various suppliers about various lines of equipment. They specifically asked for quotes on certain machines. And yet this company, which pays its bills and has a long track record, never received the quotes. Followup calls went unanswered for months.

I asked the names of the persons at the suppliers to whom my friend’s company made their inquiries. I’m sorry to say, they were names I recognized. Good, knowledgeable people. Old-timers, all. Hangers on. Definitely folks that no longer initiate contact. What some would call the “working retired.”

I’m no ageist. There’s no question the electronics industry today can sap one’s energy. While the end-product are nothing short of exciting, it’s been a long time since something came along to upend the manufacturing side. And even in good years business isn’t growing so fast that the prospect of making Zuckerberg-like coin is enough motivation to hustle. I get it: Once you get in the rut, it’s tough to get out.

Here’s my plea. If your passion for building, promoting or selling the industry is gone — consider hanging it up. Find a younger person, train them and step aside. If you want to maintain your industry friendships, show up at a trade show once or twice a year. But don’t let your inability to let go impede your company, or your industry.

Out of energy? The PCB industry needs you … to retire!

In Trade War of Words, Huawei Goes on Offensive

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“Huawei won’t move manufacturing to America.”

The headline sounds, well, weird, almost like “Tiffany’s not robbed.”

But the crux of it is a tale of global politics and business tactics growing ever-more-fascinating by the day.

In short, at the Consumer Electronics Show this week, the head of Huawei’s consumer business group issued a statement saying the smartphone maker doesn’t think much of the incoming Trump administration’s habit of calling out companies that build and import product to the US.

While Trump has thus far had mostly automakers in his sights (GM, Toyota, Ford), Apple has been the poster child for the war of words over trade. By speaking out at CES, the world’s largest technology trade show, Huawei is among the first companies, and likely the biggest, to go on the offensive.

“If [companies] move all manufacturing to the U.S., some manufacturing is not good for US companies, because costs will likely increase,” said Richard Yu, who was also a keynote at the show. “If you move all that [low-cost] manufacturing to the US, you’ll damage the US.”

Huawei has an uneasy history with the US. Its head is a former Chinese military officer Ren Zhengfei, and the company was banned from supplying telecom equipment to US government buyers after a Congressional committee accused the firm of spying on behalf of China. It is also the third-largest smartphone OEM in the world, and given the easy nature of using those devices as tools for capturing user habits and data, that is hardly less troubling.

More complex, Huawei, like Apple, depends heavily on Foxconn as a contract manufacturer. Although based in Taiwan, Foxconn founder and chairman Terry Gou is a strong supporter of China. He also is reportedly considering a run for president in his native Taiwan, a move that if successful would likely strengthen the ties between the island and mainland — and potentially further complicate already precarious relations between China and the US.

Until the new administration is officially installed in two weeks, the machinations are mostly bluster. But the chatter shows no signs of abating, and the campaigns for — and now, against — Made in America are just starting to heat up.

Start the Year Right, Without PCB Placement Overlap

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Today’s illustration isn’t a super-bad problem. You can usually make this work — unless  you’ve got to align with a hole in case. I’m talking about the venerable 3.5mm audio jack. They aren’t used all that often these days, but when they are, one of the most common formats has a design detail that makes edge alignment pretty critical.

The part of the connector that receives the jack is a short barrel, with an outside diameter larger than the height of the rest of the connector, as you can see in the image on the right. It comes in thru-hole and surface mount varieties.

This means that you have to have your solder pads or holes just the right distance from the board edge. Too close, and you can violate design rules. Too far inset, and you won’t be able to mount the connector flush.

 

 

 

 

 

This part can cause additional problems if the board is panelized. Like other overhanging connectors, the panel tabs, panel rails or other boards in the panel may make it impossible to mount the part, even if the spacing is correct.

The board shown below has both incorrect spacing, and another board in the panel blocking placement. The surface mount pads allow for more flexibility in positioning — it would have worked if not in a panel.

 

 

 

 

 

I’ve done this myself. Speaking from experience, I can say that it’s easy to avoid, and quite sad when discovered at assembly.

Duane Benson
Down at the edge, close by a panel rail
Close to the edge, round by the routing tab

The Top 10 of 2016 — PCD&F

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As we did with CIRCUITS ASSEMBLY, each year we review the 10 most-viewed features.

Keep in mind that the counts are not adjusted by the date of publication. Therefore, an article published in January has an advantage over one published in December. The month of publication is listed in parentheses.

10. “Designing PCBs for DDR Busses,” by Nitin Bhagwath (June 2016)

9. “Ensuring Reliable Products with New Rigid-Flex Design Rules,” by Jim Frey (September 2016)

8. “Empirical Confirmation of Via Temperatures,” by Doug Brooks, Ph.D. (February 2016)

7. “6 Pillars of PCB DfMA Success,” by John McMillan (March 2016)

6. “Insertion Loss Modeling,” by Jeff Loyer (January 2016)

5. “Price vs. Function in Today’s EDA Software,” by Chelsey Drysdale (December 2016)

4. “IPC-1782: The New Dawn of Electronics Traceability,” by Michael Ford (December 2016)

3. “5 Common Mistakes in Board Design,” by Arbel Nissan (December 2016)

2. “DC Analysis of PDN: Essential for the Digital Designer,” by Jeff Loyer (March 2016)

1. “Via-in-Pad Design Considerations for Bottom Terminated Components on PCB Assemblies,” by Matt Kelly, Mark Jeanson and Mitch Ferrill (March 2016)

Thanks, as always, for reading!

The Top 10 of 2016 — Circuits Assembly

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Each year we review the 10 most-viewed features of PCD&F and CIRCUITS ASSEMBLY. This year, we’ll start with CA. Keep in mind that the counts are not adjusted by the date of publication. Therefore, an article published in January has an advantage over one published in December. The month of publication is listed in parentheses.

10. “New Embeddable Technologies,” by Chris Reynolds. (January)

9. “Applying Lean Philosophies to Supply Chain Management in EMS,” by Wally Johnson. (February)

8. “GHS: The Final Countdown,” by Scott Mazur. (Note: This isn’t his only entry in this year’s top 10.) (January)

7. “Field Performance of pH neutral Cleaning Agents,” by Umut Tosun, Jigar Patel, Kalyan Nukala and Fernando Gazcon. (September)

6. “Online Bath Monitoring,” by Rebecca Dettloff. (March)

5. “Via-in-Pad Design Considerations for Bottom Terminated Components on PCB Assemblies,” by Matt Kelly, Mark Jeanson and Mitch Ferrill. (February)

4. “How to Use the Right Flux for Selective Soldering Applications,” by Bruno Tolla, Ph.D., Denis Jean and Xiang Wei, Ph.D. (April)

3. “Blurred Lines,” by Mike Buetow, a review of the Top 50 EMS companies from 2015. (April)

2. “Extreme Long-Term PCB Surface Finish Solderability Assessment,” by Gerard O’Brien and David Hillman. (July)

1. And the most-viewed article on CircuitsAssembly.com this year (by 35 views) was  “Energy Reduction in the Electronics Facility” by Scott Mazur. (March)

Thanks to everyone to contributed this year, and thanks especially to all our loyal readers!

Don’t Expect Apple to Fall for US Again

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Analysis of the impact of Apple moving its production — or at least some of it — to the US will continue over the next several months but with the imminent change in US administration it could be peaking now.

Back and forth continues among various media sites debating whether Apple can or can’t, and should or shouldn’t, relocate some of its assembly.

Forbes today points to multiple studies, one by Syracuse and another by MIT (from June) that estimate assembly costs for a high-end domestically produced iPhone would rise 5% ($30 to $40). Other estimates peg it at closer to 13% ($100).

To be sure, there will be more of these types of discussions taking place. But much of the chatter disregards that Apple can’t do this alone. We have argued previously that Apple’s mastery of the supply chain has as much to do with its success as the occasionally startling hipness of its designs. The cool factor is subsidizing; keep in mind Apple has only 12% share of the cellphone market, and the tablet market — in which it once commanded a 90% stake — is now absolutely flooded with competitors and shrinking by the year. Apple’s net income has been falling with it, and the Watch Series 2, its latest entrant in the smartwatch sector, is not only losing share, the entire category is diving.

Capacity would not only be a huge issue, but the costs of scaling up are not included in any of the financial analyses I’ve read. The very real costs of $1 million or more per high-volume line would be to be absorbed — and passed on. (Zhengzhou is said to be the largest Foxconn/Apple factory in the world, with 94 lines currently running.) That’s not including the costs of finding and/or greenfielding factories, hiring, training, and so on. By the time all that is done, a new administration could be in place.

And then there’s the issue of taxes, which most reports fail to assess or even discuss. A New York Times article today, however, quotes a former chief of staff of the congressional Joint Committee on Taxation as saying: “US multinationals are the world leaders in tax avoidance strategies. In doing so, they create stateless income — income that has become unmoored from the countries to which it has an economic connection.”

Apple has stashed scores of billions of dollars offshore to avert a ginormous tax bill. The US corporate tax rate is third highest in the world on a top marginal basis, according to the Tax Foundation. This is a bit of a red herring — the lowest listed non-island nations are Uzbekistan and Turkmenistan, and no one is thinking of rushing there. But Ireland is among the lowest 20, a fact Apple has used to its advantage (although that could bite them, if the EU has its way).

All of this adds up to a very unlikely scenario that Apple will be motivated to relocate production. I could see a bit of highly publicized migration to what’s essentially a US showroom as a means to give politicians a “win” and displace some heat, but it would be trivial relative to the overall volume.

Update: Here’s yet another opinion, published on Dec. 29. And other, from the South China Post, asking whether China’s manufacturing is “hollowing out.”

Dec. 30 update: Foxconn’s CEO says will invest $8.8 billion in a new flat-panel display plant in China.

Alloy Metal Weight Fraction Calculation

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Iasad writes,
“Dear Dr. Ron,

I see that you have developed software to calculate the density of an alloy if given the weight fractions of the constituent metals. Is it possible to find the weight fractions of the metals in an alloy given the alloy’s density? Thank you!”
Unfortunately, finding the weight fractions of the metals in an alloy from the alloy’s density can only be accomplished with a two metal alloy. First we must use the equation:

Equation 1

Where x is the weight fraction of metal A and the rhos are the associated densities.  All that has to be done is to solve for x.  The solution is worked out below in Figure 2, the final result is:

Equation 2

As an example, let’s say you have a gold-copper alloy with a density of 18.42 g/cc.  The density of gold (metal A) is 19.32 g/cc and that of copper (metal B) is 8.92 g/cc.   Substituting these values into equation 2 gives the weight fraction of gold as 0.958.  Hence the weight fraction of copper is 1-0.958 = 0.042.

I have developed an Excel-based software tool to perform these calculations. An image of it is shown in Figure 1.  If you would like a copy of this tool send me a note.

 

Figure 1.  A screen shot of the alloy metal weight fraction calculator.

 

Figure 2. The derivation of the weight fraction formula.

Cheers,

Dr. Ron

Top 10 PCB Assembly Tips for 2016

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I’ve already written my top 10 predictions for the coming decade, in this blog post. But, while predictions might be fun to muse upon, they really won’t help you get your job done. My top-ten8 pieces of PCB assembly advice for the coming year should make up for that.

000

Before you even start component selection, give thought to the design scale. What’s more important, board size, cost, or time to layout? A large board will be easier to route, but will cost more for the fab. A smaller board will cost less for the fab in terms of square inches, but may cost more due to extra layers, and may take longer to layout.

001

Factor in the cost of component size. For passives, roughly 0603 size parts will probably be the sweet spot in terms of lowest cost. The 0603 is also a good size for overall handling. We’ll assembly down to 0201 parts, but not all manufacturers will. 0603s are also easy to rework, and are manageable if you feel the need to hand solder a few.

010

Check out any exotic or very new parts. Some parts, these days, are only available in super small wafer scale BGA, or small QFN form factors. Take a look at your integrated circuits and make sure they come in packages that you’re comfortable working with.

011

Check for sole-source parts, or low-availability parts. The last thing you want is a completed design that’s sitting around waiting for one long-lead time, sole sourced part. If a sole-sourced part is at risk for availability, you might want to find something similar and more available.

100

Don’t forget manufacturing thermal concerns when laying out your board. Very large parts next to very small parts can cause problems. The large parts will act a bit like a heat sink and may prevent the solder for the small part from melting properly. The same thing can happen with internal copper planes that overlap on half of a small part, but not the other.

101

Give extra care to the clarity of reference designators and polarity markings. Make sure that it’s very clear which designator goes with which part, and that there isn’t any ambiguity in polarity markings. Take special care with LEDs, as manufacturers sometimes swap polarity markings between the anode and cathode – yes, the exact same mark can mean anode on one LED and cathode on another. Also, do your best to keep reference designators off of vias or any other spots that might break up the text.

110

When you’re ready to send your project our to be built, give your files a double check to makes sure you have the correct versions. bills of materials are especially susceptible to having bits of information out of date that might cause delays.

111

If you’re sending in a parts kit, double check that you have all of the parts, and that you have part number and reference designator on the individual part bags.

Manufacturing is just putting parts on boards, but it’s doing so with a whole lot of variables. A few extra checklist steps can go a long way toward removing variability of those variables.

Duane Benson
I am one with the net force. The net force is with me

Suspect Through-Hole Packaging

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Surface mount components are carefully packaged up in strips, tubes or trays, because they’re machine-assembled. The assembly robots need order and organization to properly do their job.

Through-hole parts, on the other hand, are almost always manually inserted by actual human-type people. That being the case, the manufacturers and distributors are sometimes more lax with their packaging. They assume that, since a human is picking the parts, a jumble is okay. Sometimes it is, but not always.

In the case of these through-hole DB-25 connectors, the jumble was too much and lead to a number of bent pins. Slightly bent pins usually aren’t a problem, but some of these ended up a lot more than “slightly” bent.

To make matters worse, these pins are small thin-wall tubes, which are more susceptible to breakage when bent than are solid wire pins. For the connector on the bottom of the image, some of the most horribly bent pins may not be straightened without breaking. If they are, they’ll certainly be weakened.

The moral of the story is that through-hole parts need care too. We can’t toss them around just because they aren’t the latest technology.

Duane Benson
Spider-Pin, Spider-Pin,
Does whatever a Spider-Pin does