Top 5 Things to Know When Moving from Hand Assembly to Robotic Assembly

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A lot of factors go into the decision to hand build or outsource circuit boards. I hand build my own sometimes, simply because I enjoy the challenge. Of course most of the projects I design are for my own use, so timeliness isn’t that important. When I do design something that will go out to a customer, like my electronic business card holder, I will send the board through our shop. In those cases, quality is important, as is delivery, and the quantity is often too high to hand build. Machine building also allows me to use smaller and more complex parts. 

That same decision — hand build or outsource — takes place in the heads of designers all over the country. When the decision is to outsource, there are a few important things to consider. Some things that work fine when hand soldering may stand in the way of quality, repeatability, and reliability when machine assembling.

Here are five of the most important considerations when changing from hand-built to outsourced at a place like Screaming Circuits

1. Use solder mask and silk screen. A good solder joint needs the right amount of solder in the right place. Solder will tend to flow down bare copper, bleeding outside of the area it belongs, and down exposed copper traces and vias.

The main purpose of solder mask is to keep the solder where it belongs. It also protects the traces, but that’s a longevity issue. Solder bleeding is a manufacturing and reliability issue. This isn’t a problem when hand soldering. In fact, it can even work to your advantage when hand-soldering really small parts. It gives you more room for your soldering iron to hit metal.

Not so with solder paste and machine assembly. Use solder mask.

2. Avoid the pseudo panel. Keeping small boards in a panel is the recommended best practice in the manufacturing industry. We appreciate it and, while not always necessary, it can reduce your costs. We sometimes see what we call a “pseudo panel.” This is a board where multiples of the board are put in the same PCB, like a panel, but unlike a panel, the boards don’t have routing or V-score between them. Sometimes the designer will put a bunch of vias to outline the board, or just ask that we use a band saw to separate them.

That’s a time-consuming, expensive and potentially damaging process. The vibration of the saw can crack solder joints, and, you’re unlikely to get boards that are all the same size. Have small boards panelized by your board house.

3. Family panel (pseudo or not). Similar to the pseudo panel is the family panel. A family panel is a case where a project is made up of several different PCBs, and they are all laid out together, as though they are one design. If the board isn’t routed between the designs, you’ll have the pseudo panel problem described above.

The bigger problem, though, comes with reference designators. We typically see family panels with duplicate reference designators. Each design, for example, will have its own C1, R1, Q1, etc. We use the reference designators as position identifiers: If you have three different parts labeled R5, our machine programmers will have a problem with it. It’s even worse if the values differ; on one design, C1 is a 0.1uf capacitor, while on another design, it’s a 22pf cap.

If you’re making a family panel, give each and every placement a different reference designator. One way would be to us extra digits. For example on one design on the family panel could have C100, C101, C102… The next would be C200, C201, C203, and so on.

And don’t forget the routing or V-score between the designs.

4. QFN — hole  in the middle. A common technique in the hand soldering world, for QFNs and other parts with thermal pads underneath, is to put a big via in the middle of the center pad. By doing so, you can stick a soldering iron and some solder down through the hole and get a good solder connection on the bottom pad.

This doesn’t work with machine assembly. the solder paste will flow down and out the hole in the reflow oven. You’ll end up with a poor connection (or no connection) to the thermal pad, and solder slop on the back side of the board.

5. Parts and the bill of materials (BoM). When I build my hobby projects, I often get a bit carefree with the bill of materials. It’s not good practice, but I do. I’ll put a part in the BoM that I used before, and not check to see it’s still in stock. I’ll put parts in the BoM with just the values and not any part numbers. Things of that sort require tribal knowledge, which only the designer has.

When building, sometimes I’ll just grab a part that’s close. If I need an 0805 1uf, 10V capacitor, I can grab a 16V, 25CV, etc. I can even make an 0603 part work. You as the designer may know that something close will work, but an outside house can’t know. You need to tell them exactly what the part is.

Before sending anything through our shop, I do clean up the BoM. In order for us, or any manufacturer, to build the boards, the BoM needs:

  • A unique reference designator for each part placement.
  • The quantity of each part used on the board.
  • The manufacturer.
  • The manufacturer’s part number.
  • DigiKey part numbers can be used as well.

Here’s our website page explaining the BoM format in more detail.

The transition from hand building to outsourced machine building can be an intimidating one. But, with a few considerations, it can be an easy and rewarding transition.

Duane Benson
Put the right part in
Put the wrong part out
Put the right part in
But please don’t shake it all about

blog.screamingcircuits.com

Using Solder Preforms to Reduce Voiding in BTCs

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Folks,

Let’s see how Patty and the team are doing on their presentation on voiding for Mike Madigan …

Patty was kind of down. Like millions of others, she and Rob watched, in horror, as Jordan Spieth had his meltdown at the 2016 Masters Golf Tournament. Some newscasters considered it the biggest meltdown in golf history, but Patty considered Rory McIlroy’s 2011 and especially Greg Norman’s 1996 meltdowns to be worse. She felt the NY Daily News did the best job of comparing the five worst Masters meltdowns. She agreed that Spieth would surely recover, certainly better than Ken Venturi in his famous collapse in the 1956 Masters. She was surprised that so many newscasters often seemed to not put history in as strong a perspective as it deserved.

As she sat in her office, she was reminded that she needed to finish her part of the presentation that Mike Madigan needed on minimizing voiding. Her topic was, “Using Solder Preforms to Minimize Voiding.” To her, voiding appeared to be the hottest issue in electronics assembly.  Especially voiding under bottom-terminated components, or BTCs. Rob and Pete were coming by in a few minutes to review her progress. Just as she finished, they were at her door.

“Hey, Professor! What’s the scoop on using solder preforms to minimize voiding?” Pete asked, clearly teasing by calling her “Professor.”

They all chuckled a bit and Rob added, “Yes, Professor. Let’s hear it.”

Patty began, “Remember a few years ago the standard approach to using preforms, to minimize voiding under BTCs, was to use a flux-coated solder preform and place it on the thermal pad on the PWB after printing a minimum amount of solder paste?”

“Sure! A great paper was written on it, by some of the folks at Indium Corporation,” Rob said.

Then Pete added, “I gather there is a new approach?”

“Well, think about the motivation to find another technique,” Patty replied.

“A specialized preform needed to be made, it needed flux coating and placing it was a bit of a challenge,” she continued.

“So, what’s the new technique?” Rob asked.

“Well, I chatted with Tim Jensen. Although the original technique is still used, a preferred technique using 0201- or 0402-sized solder preforms has been developed.  The preforms are purposely placed off center so that the BTC is at an angle.  This angle allows the solder paste volatiles to escape.  Since these preforms are a standard size, and not flux-coated, they will typically be less expensive and easier to handle in the assembly process,” Patty elaborated.

“How well do they work?” Pete asked.

“They work quite well. Look at these data,” Patty replied. (see Figure 1).

Figure 1. Preforms of either 0201 or 0402 reduce voiding by up to 50%.  Note that the standard deviation is also tighter by using preforms.

“Looks like the 0402 preforms do a little better than 0201s,” Rob commented.

“Yeah! And using two of them instead of one seems to help a little,” Pete added.

“It’s also striking how the preforms tighten the data up. Look at how much the standard deviation is reduced by using them,” Rob added.

The trio spent the next several hours collating all their PowerPoint slides into one 45-minute presentation. Patty then scheduled a meeting with Mike Madigan to review the entire presentation.

Epilogue: Patty, Rob and Pete reviewed the presentation with Mike Madigan using WebEx.  Mike implemented the recommendations after reviewing them with his critical customers.  By using the best solder paste, making minor modifications to the SMT processes, and using solder preforms where appropriate, ACME was able to reduce voiding to less than 10% in all products and less than 5% in most.

Cheers,

Dr. Ron

 

 

Industry 4.0: The Great Equalizer?

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Gen Consutling Co. (GCC) has issued the Radiant Insights report “Global HDI Printed Circuit Board Market Forecast and Analysis 2016-2021.” The report provides a detailed analysis of worldwide markets for HDI Printed Circuit Board from 2011-2016, and provides market forecasts for 2016-2021 by region/country and subsectors. It covers the key technological and market trends in the HDI Printed Circuit Board market and further lays out an analysis of the factors influencing the supply/demand for HDI Printed Circuit Board, and the opportunities/challenges faced by industry participants. GCC states that the major players in the global HDI market are Unimicron, COMPEQ, AT&S, TTM, Zhen Ding, Ibiden, Tripod and Unitech.

Multek, a wholly owned subsidiary of FLEX, launched its new Zhuhai automotive division on May26 to support its rapidly growing automotive business. The company also announced completion of ISO/TS16949:2009 quality accreditation for its high layer count factory, and now delivers TS16949-grade automotive offerings at all of its manufacturing facilities globally.

Industry 4.0 is advancing rapidly in the Kunshan, China, electronics manufacturing hub. Will Industry 4.0 be enough by itself to make other areas of the world more competitively suitable for  sourcing?

Kunshan in Jiangsu Province near Shanghai attracts much of its investment from Taiwan. It is now accelerating growth by replacing workers with robots. Thirty-five of the 4,800 Taiwan companies in this area, including Foxconn, spent $610 million on artificial intelligence last year. Foxconn reduced  its labor force there from 110,000 to 50,000 by the introduction of robots. AS many as 600 more Taiwanese companies in  Kunshan are reported to have similar  plans.

Reality 4.0 – Are you missing the boat?

Some of our North American smaller fabricators facing difficult times and decisions sit back on their haunches and vociferously state that the IPC does nothing for them. They are missing the boat. The IPC provides the structure and support that allows virtually any group to band together, and work collaboratively to overcome obstacles and handicaps, and succeed in a rapidly changing and challenging environment. The IPC Ambassadors are creating an Executive Forum just for them and their supply chain. It will explore new technologies and trends, support opportunities,  and provide answers to many of the questions posed by these smaller enterprises of which there are more than 100 in the US. Additionally, the IPC will provide a new membership opportunity that will be difficult to refuse. Remember, there is strength in numbers! Stay tuned!

The IPC’s 3rd Reliability Forum held in Dusseldorf this month was a resounding success. The 2-1/2 day event started with a presentation on building in reliability by IPC director and ambassador Mike Carano, vice president of RBP Chemical Technology. Other prominent presenters included DuPont, Fraunhofer Institute, Atotech, and Park Electrochemical. The first full day focused designing for reliability, while the second addressed process. A half day on government relations activities was also included.

The Boston Chapter of the SMTA held its May meeting at Cirtronics, which graciously opened its doors (and factory for a tour) to host the event. Though held in New Hampshire, it attracted IPC and SMTA members from Massachusetts and the Western part of Connecticut. Cirtronics is an employee-owned contract manufacturer founded by its CEO Gerardine Ferlins. The busy facility was up-to-date and spotless. The profitable 176 employee company has progressed to the point where 70% of its business includes box-build. It has just acquired several new screen printers and is evaluating several new 3D AOI systems for purchase.

The meeting program featured Leo Lambert, vice president and technical director of EPTAC Corp. He covered key changes in and amendments to the IPC-A-600, IPC-A610, and J-STD-001 standards and how they affect our industry and the latest training and certification programs. Somehow the live presentation provided a far different result than the typical webinar. Humor was used to highlight specific points, problems, difficulties and the current situation. The result was very effective – at least to me. For example, amendments have been made that are different or in direct opposition to the original document. Yet the certification programs and manuals still contain and teach the unmodified or corrected items. Lambert well presented the need for peer review of training – if not standards – documentation so when the users receive it, they are not confused by any inconsistency.

The first Innovations Forum Hungary: Automation in Electronics Production “– building a competitive advantage in the region” will be held on the 16th of June, 2016 at the prestigious Academy of Sciences in Budapest.

The International Federation of Robotics (IFR), which represents robot manufacturers and research institutes, says China has surpassed Japan to become the world’s biggest market for industrial robots.

There is increasing concern about the secure availability of advanced printed circuits for America’s defense industry. These are needed to provide the platforms for high tech electronics. R&D for new systems seem to be progressing well. However, the US base of smaller fabricators that produce more than half of military boards is hard-pressed to fund the new equipment needed to build these circuits. Costs are often more than 20% of annual turnover. Some fabs in the Northeast as well as in California continue to report difficulty in acquiring the skilled workers needed for production. Others cannot modernize or add capacity due to local (state) “environmental” laws and restrictions. Congress is slow to act and too busy with the election to do much of anything this next year. It has funded some major items but do not consider printed circuits a big item. PWBs’ importance is still not yet well-enough understood. Do you have a comment, recommendation, or solution?

When will 3-D printing for prototyping be at your favorite circuit shop?

Sooner than you think — at least for prototyping. One system utilizing an ink containing nano silver particles for fine line printing will be made available commercially by the end of this year. It will be demonstrated at the CES show in Las Vegas January 2017. The deposited circuit traces may be photonically cured (sintered). HP announced a 3-D new system that is 10 times faster than its predecessors. The insulating substrate may be UV cured epoxy. One such system for epoxy has already been demonstrated in the UK. Get your 3-D circuit printing update at the IPC Ambassador Council Executive Forum for fabricators and their supply chain at IPC Apex Expo in San Diego on Feb. 13, 2017.

Financial news from Taiwan

Chin-Poon Industrial, with more than 70% of its revenues coming from the automotive industry, announced consolidated revenues for April 2016 increased 5.4% over April 2015 to $58.7 million. The company’s cumulative 2016 sales through April increased 9.3% from a year earlier. Consolidated revenues at Tripod Technology’s sales were up 1.1% from a year ago to $107 million in April 2015 Compeq Manufacturing had consolidated revenues of $93.9 million in April 2016, down 0.1% from April 2015 PCB producer Apex International’s April 2016 revenues were $21.4 million a 9.4% increase over last year.

Board maker Zhen Ding Technology Holding’s net profits declined 88% on quarter and 77% on year to $9.52 million in the first quarter of 2016.

The UK’s HK Wentworth, parent company of Electrolube, which supplies sprays and coatings to protect, clean and lubricate electronic circuit boards, switches and sensors, is spending £500,000 to build a new factory to make protective coatings in Bangalore, India.

It’s a new era and all about “the Car”

SEMI and Georgia Tech, in partnership with iNEMI, IMAPS, and IEEE, will launch a new workshop called FUTURECAR: New Era of Automotive Electronics Nov. 9-10, 2016, in Atlanta, GA. The new era of automotive electronics is the most complex electronics technology to date. It includes not only computing and communications electronics, autonomous driving electronics, sensing electronics but also high-power and high-temperature electronics. It is expected to account for a third of the value of “the car”, creating a market of approximately $1 trillion within a decade. The challenges to address this market include: 1) research and development of key technologies, and 2) technology ecosystem stewardship to enable swift and cost-efficient commercialization. The basis of this workshop is the synergy between Georgia Tech in R&D in partnership with its 50 supply-chain companies and SEMI in technology stewardship. This is complemented by the strength of co-sponsors such as iNEMI in roadmaps, and IEEE-CPMT and IMAPS as global electronics societies.

The European Institute of Printed Circuits (EIPC) meeting on “Strategies to maintain profitability in the European PCB Industry” will be held June 9-10 in Glasgow, Scotland.

The European Commission said growth in the euro zone and the wider European Union will be slightly weaker this year than previously forecast, as it warned that the economic slowdown in China and other emerging markets, geopolitical tensions and uncertainty ahead of the U.K. referendum on EU membership could weigh on the economy. Economic growth in Gulf States is forecast to slow to 1.8% this year as the oil dependent region cuts spending to battle fiscal deficits reaching 11.6% of Gross Domestic Product (GDP).

A new China target?

French oil and gas producer Total plans to sell Atotech. “Atotech no longer falls within Total’s strategic vision,” chief executive Patrick Pouyanne was quoted as saying. Total is reported to be seeking a buyer that was “committed to sustaining Atotech’s current strategy.” Berlin-based Atotech, which generates annual sales of about $1 billion, manufactures specialty chemicals and equipment for printed circuit boards and semiconductors. It is Total’s sole remaining specialty chemicals unit.

Apple lost the trademark suit in the Beijing Municipal High People’s Court, which ruled that Xintong Tiandi Technology can continue to use the phrase “IPHONE” on its leather wallets and accessories, according to China-based Legal Daily. Chinese regulators reportedly shut down iTunes Movies and the iBooks Store last month.

Billionaire investor Carl Icahn sold his entire stake in Apple, citing the risk of China’s influence on the stock.

SEMI continues to strengthen and broaden its supply chain reach

SEMI has announced the appointment of Melissa Grupen-Shemansky, Ph.D., as chief technology officer for the FlexTech Group and for SEMI’s Advanced Packaging program. With over 20 years of experience in the semiconductor industry, Grupen-Shemansky will oversee FlexTech’s flexible hybrid electronics (FHE) and Nano-Bio Manufacturing Consortium (NBMC) R&D programs and technology advisory councils. Grupen-Shemansky will also serve as technical advisor to SEMI’s Advanced Packaging initiative and as technical liaison to NextFlex, the Flexible Hybrid Electronics Manufacturing Innovation Institute.

Nepcon China held in Shanghai the last week of April was surprisingly the best in years. Pent up demand for pick-and-place equipment led the surge in active buying interest after a near drought in purchasing the past few years of the economic slowdown there.  The next few weeks will tell just how real the show activity was as stated interest converts to orders.

Firan Technology Group (FTG) is buying the assets of Teledyne Technology’sNew Hampshire’s printed circuit technology business (Teledyne PCT) for $9.3 million in cash. For approximately 50 years, Teledyne PCT has designed and manufactured rigid-flex printed circuit boards and assemblies used in the defense, aerospace and oil and gas industries. For each of the last three years, the unit has generated between $15.0 to $20.0 million of annual revenue. FTG has two operating units: FTG Circuits is a manufacturer of high technology, high reliability printed circuit boards. FTG Aerospace manufactures illuminated cockpit panels, keyboards and subassemblies for original equipment manufacturers of aerospace and defense equipment.

USB Type-C Connectors

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It wasn’t terribly long ago that pretty much every cellphone came with its own custom charging cable. It was a major step forward when they all (except Apple) standardized on the USB micro-B connector.

However, there are a number of limitations with the. First, it takes a minimum of three attempts to get the orientation right when trying to plug in a cable. Second, it’s limited in maximum current carrying capacity.

Now, along comes the USB 3.1 Type-C cable and connector. It’s similar in size, universally polarized (the connector and the cable can be plugged in any end to any end and in any orientation), it has much higher data throughput, and it’s spec’d to carry up to 3A. Further, it has alternate modes for other standards, such as DisplayPort and Thunderbolt.

The connectors are larger than the micro-B, as you can see in Figure 1, micro-B, Type-C with only surface mount connections, and Type-C with both surface mount and through-hole wiring, and a US dime. The size difference won’t be an issue in most cases, but it could be in really small devices. My guess is that we’ll be talking about a smaller, Type-D connector, not long from now.

Figure 1. Micro-B, Type-C with only surface mount connections, and Type-C with both surface mount and through-hole wiring, and a US dime. Figure 2. Micro-B connector with tabs formed from the same sheet metal as the shell.

All three of the surface mount connectors shown above have through-hole mounting tabs. That adds strength, but it does bring one caution with it. Looking at the micro-B connector in the image on the right, you can see that the tabs are formed out of the same sheet metal as the shell.

You can also see that the tabs don’t stick all the way through the PCB. This can lead to some deception when soldering. Without the tabs protruding, it’s easy to believe there’s not enough solder in the connection. If more solder is fed in, it will likely wick along the tab, and end up inside the receptacle, preventing the cable from being plugged in. If hand soldering or reworking these type of connectors, keep a close watch on the amount of solder used.

Duane Benson
Fester Bester Tester is alive and well and living where?

http://blog.screamingcircuits.com

Balancing Cost Savings vs. Offshore Sourcing Risks

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So many purchasing professionals I meet are wary of exposing their company to a supply line risk by buying offshore. With good reason, it often goes wrong.

An article published by Thomas A. Foster of Global Logistics & Supply Chain Strategies highlighted the issues:

Sourcing from offshore suppliers in China, India, Eastern Europe, Latin America and other low-cost regions is so widespread that few manufacturers and retailers can be competitive unless they join in this trend. In fact, the U.S. Federal Reserve Board attributes much of the recent economic growth and low inflation to this offshore outsourcing “best practice.”

However, the downside of offshore sourcing receives far less attention at the Fed or in any boardroom — at least until something goes wrong.

The more a company sources from distant, low-cost lands where financial transparency, operating visibility and reliable logistics are practically unknown, the risk of serious supply chain disruptions increases geometrically.

In a recent supply chain risk assessment study, Aberdeen Group, a Boston-based research firm, said that more than 80% of supply management executives reported that their companies experienced disruptions within the past two years serious enough to negatively impact their companies’ customer relations, earnings, time-to-market cycles, sales, and overall brand perceptions.

Let’s put some real numbers to this.

The cost of establishing a source offshore in time and out of pocket expenses can exceed $50,000. The cost of attempting to resolve an issue by revisiting a supplier, an equal amount, considering the airfare and hotel alone can top $10,000 per person … and there’s no assurance the problem will be resolved.

Not a huge number to you? Now add the cost of disappointing customers: big. The writeoff of bad product: big. And, to pour salt in the wound, making several trips before you realize there will be no resolution.

Real life case in point. One customer of ours had the unfortunate experience of finding 20% of the goods it received from its Asia-based supplier failed in system in the field. The supplier insisted they did not nothing wrong and would not support any reimbursement. This was after scrambling to replace units in the field for customers, and two engineers flying to China for a week. The customer finally turned to us for the rework at a cost essentially equal to the original purchase price. Ouch.

So, what does the OEM with limited resources do to compete on the same level as the big guys which have deep pockets and feet on the ground in Asia?

The answer is to shift the accountability from the offshore supplier to an experienced provider of managed PCB manufacturing services in the US. They can eliminate the risk of poor quality and greatly mitigate the risk of supply line disruption.

They do this through rigorous attention to technical detail on the front end, using only developed, strong, factory relationships, then thorough incoming inspections, and holding the factories accountable for any errors.

Basically, knowledgeable feet on the ground here, with the skills and experience to manage complex Asia-based electronics projects, and perhaps most importantly, financially accountable for the results.

Eliminating risk and capturing the savings from offshore. That is a pretty decent balance.

To Minimize BTC Voiding, Start with the Right Solder Paste

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Let’s see what’s up with Patty ….

Patty was just dropped off at O’Hare airport after finishing a 3 day workshop on Lean Six Sigma statistics, design of experiments, and statistical process control. Interestingly, the students were lawyers. In recent years more and more service-based organizations were adopting lean Six Sigma and it was a long time since Patty had taught such a workshop to engineers. She noted that although the lawyer’s math skills were a bit rusty, they were very good listeners and picked up the math behind lean Six Sigma topics very quickly.

After paying the cab driver, she entered the terminal and went to see an agent. She was early enough to get an early flight home, so she had called the people at the online ticket agency during the cab ride. They said the change fee would be over $300, she felt that was just too much to pay. She was delighted to see that it was only $75 at the terminal.

She looked at her paper boarding pass and saw that she had more than two hours, just enough time for a relaxed lunch at Wolfgang Puck while she read USA Today. Patty was the only person her age that she knew who enjoyed reading a paper newspaper, she guessed that she picked the habit up from her dad.

The two hours went by quickly and she was standing in line waiting to board the flight to Boston’s Logan Airport. She had now been at Ivy U for a few years and traveled much less than when she worked at ACME. She had forgotten how stressful and unpleasant traveling was. As she stood in line, the man in front of her put his smartphone on the scanner and the scanner could not read the QC code. He and the agent fumbled for a while before they got it to work. This was another place where, in her opinion, paper was still king.

Patty got on board and settled into her middle row seat. She groaned a little bit at how uncomfortable and cramped it was. Patty was reminded of what her dad used to say in situations like this; “I know it is a bit uncomfortable, but just think what the 49ers went through to get to California,” he would tease.

After takeoff, she turned on her laptop. She absolutely had to send some emails, so she signed on to the onboard WiFi. She got sticker shock when she saw that it cost $18.95!  Even though Ivy U would pay for it, the high price galled her.

After she finished the emails, a wave of fatigue swept over her and she needed a break.  She chuckled to herself when she thought of a recent event. She had taken two of her best teaching assistants (TAs) to lunch and the conversation somehow came to discussing people who hid Jews from the Nazi’s in World War II. Patty mentioned to her two young protégés about an excellent book and movie she read and saw as a teenager, The Hiding Place. The story is about Corrie Ten Boom and her family and how they hid, and hence saved, many Jews from the Nazis in Holland during WWII. Although the movie was made before she was born, it was shown at Patty’s church every few years, for the new sets of youngsters who came along. Patty mentioned to her two superstar TAs that the film was produced by Billy Graham’s organization.

“Who is Billy Graham?” they both asked in unison.

Patty struggled to keep her composure as she explained who he was. How could they not know this?  She decided to examine the situation a bit further.

“OK, you two. Who was Mickey Mantle?” Patty asked.

The youngster’s both looked at each other.

“We have no clue,” they chuckled.

Patty though she would try a few more, “Nikita Khrushchev?”

Nothing.

“Roy Orbison?”

Nothing.

Patty started humming a few bars of Orbison’s most popular song.

“Oh, Pretty Woman,” the boys said in unison.

Patty thought to herself, “Each of these young lads are the best student in every class that they take and yet they don’t know these ‘celebrities’?”

The next day Patty arrived at her office early to meet with Rob and Pete to discuss how the presentations that they were making for Mike Madigan on voiding were coming. Patty had arrived so late the night before, that Rob was already asleep. She did not see him in the morning as it was her turn to get the boys ready for school and he was off early to get in his 90 minutes of exercising. So, they had no chance to discuss the progress of the presentation.

“Pete, your presentation of BGA voiding is terrific. How is my hubby doing on BTC voiding?” she chuckled as she looked at Rob.

“I feel like I’m going to get yelled at ’cause I didn’t do my homework,” Rob said sheepishly.

“Yikes! We only have a few days,” Patty responded. “And I have yet to do my part on using solder preforms to minimize voiding,” she went on.

“I’m only teasing. I have quite a bit of info,” Rob said.

“We have been out of the mainstream for a while and one thing is for sure, voiding is the number one issue among assemblers today.  So many people are assembling QFNs and are struggling with voiding. Voiding with some solder pastes can be over 50% of the area,” Rob went on.

“Wow! With 50% voids, think of how poorly the heat is being transfer away for the BTCs,” she looked at Rob and chuckled. “Remember, ‘BTC’ not ‘QFN,’ Patty went on.

“Yes ma’am,” Rob jokingly replied.

“Can you imagine the effect on reliability and field issues with so little heat being removed? The ICs inside the BTCs must be frying” Pete added.

“Voiding at this level has got to be really costly,” Patty mused.

“One of the things that really helped me was that I found quite a few experiments on voiding,” Rob added.

“What were some of the key points?” Pete asked.

“Well, as you might expect, the solder paste is typically the most critical part of the process. Some pastes have voiding lower than 10% with others above 50%,” Rob replied.

“What about the process?” Patty asked.

“Well, the reflow profile can be very important, as is controlling the PWBs and components. But, with the best pastes, it has been found that you can control the voiding content even if you can’t change the reflow profile and the PWBs and components have some issues,” Rob responded.

“Look at the x-rays of poor and good voiding between two pastes,” Rob said.

“What a difference,” Patty and Pete said in unison.

“What about the stencil design and venting?” Pete asked.

“Chris said that stencil design for venting is not as critical as once thought, although a window pane design is usually used,” Rob replied.

Figure 1.  The window pane design for the stencil is used to permit venting.

“So it sounds like starting with the best solder paste solves 90% of the problem and adjusting the process, say with the right reflow profile, helps refine the result,” Patty summed up.

With this Rob went off to put the finishing touches on his PowerPoint® slides for his part of the presentation, while Patty started working on her part of the presentation on using solder preforms to reduce voiding.

Two weeks later.

Patty’s mom and dad came for a visit on a Sunday. Her mom had graciously offered to bring a complete Sunday dinner. Patty, Rob and the boys were grateful for the delicious meal. As they began to eat, Patty shared the story of her best students not knowing Billy Graham, et al.

“But, what was even more surprising was that I ended up asking 10 or 20 more students and only one had ever heard of any of these four ‘famous’ people,” Patty sighed.

“It’s your age,” Patty’s mom replied.

Thirty years old was not that far in the rear view mirror for Patty and she really didn’t consider herself old.

“These youngsters were born in the late 1990s, a generation after these people were prominent,” her mom went on.

“Mom’s right.  Do you know Billy Sunday, Ty Cobb, Glenn Miller, and Trotsky?”  her dad asked.

“Who?” Patty asked.  And then she chuckled, getting the point.

After a brief pause, she said, “I do know who Trotsky was; tell me about the others.”

Cheers,

Dr. Ron

As always, this story is based on true events.

 

BGA Voiding in Electronics Assembly

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Patty had to admit that the last few weeks were exciting.  Her talk to US Army Rangers and Navy Seals on critical thinking went really well.  Now, the local newspaper was asking her to comment on political polling in the current presidential primaries.  Patty was just finishing her response to the paper before a meeting with Pete to discuss the voiding presentation that they were working on for Mike Madigan.  Her response follows:

Dear Editor:

My favorite candidate was trailing in the polls by only 1% in my state, but on primary day he lost by 5%.  Why isn’t polling more accurate?

Sincerely,

Disappointed

 

Dear Disappointed,

Pity the pollsters. They have to predict what will happen by sampling a manageable number of people, say 1,000. This situation creates several challenges. The first is that their sample should represent the population as a whole. This challenge is not easy. They need to assure that the 1,000 people represent the population of the entire state. If they get an inappropriate number of old, young, wealthy, lower income, educated, less educated, etc., in these 1,000 people then their prediction will be off. As an example, let’s say that 45% of a state’s residents have a bachelor’s degree or higher, yet their sample has 60% with a bachelor’s degree or more. This difference will likely make their sample non-representative of the population as a whole and will skew the results.

Let’s go back to your candidate, whom we will call candidate A. It ends up that candidate A was supported by only 47.5% of the total population and his opponent, candidate B, by 52.5%, giving the difference of 5% that you mentioned. Let’s assume that the pollsters establish a good sample of 1,000 people that is very close to representing the state as a whole. It is unreasonable to expect that the 1,000 people polled would exactly have 47.5% or 475 supporting candidate A, due to statistical variation.  To show the likelihood of a number different than 475, we have to use the binomial distribution as seen in  Figure 1 below. Note that there is about a 10% (0.1085 in the figure) chance that a population of 1,000 will have 495 or greater supporting candidate A. This uncertainty, added to the difficulty of establishing a perfect sample, makes polling error of 5% or so not uncommon.

Figure 1. Note that, even though 475/1,000 is the most likely, if the larger population has 47.5% supporting candidate A, there is a 10% chance a sample of 1,000 could have 495 or greater favoring candidate A.

 

Just as Patty finished her response, Pete came to her office door.

“Hey kiddo! Can we go over my thoughts on the voiding in BGA balls section on voiding for Mike Madigan?” Pete asked cheerfully.

“Sure. What do you have so far?” Patty asked.

“I’m focusing on the importance of the reflow profile.  Have you seen this graph,” Pete began.

Figure 2. The hot soak profile produces the fewest voids in CSP and BGA balls.

“Wow! That really shows the benefit of a hot soak profile over a cool soak profile. But, I am most surprised at how much benefit a hot soak profile has over a ramp-to-peak profile (RTP),” Patty commented.

“Isn’t the timing of the higher temperatures important, too?” Patty asked.

“My next point precisely. Look at this graph,” Pete said enthusiastically.

Figure 3.  The combination of the reflow profile and flux characteristics that produces outgassing before the solder becomes liquid (the red curve) will minimize voiding.

“The process engineer needs to assure that most of the flux is volatilized before the solder melts, as in the red curve, not as in the black curve where almost all of the flux is outgassing during the melting it the solder (Tm). This situation is assured by the correct combination of flux and reflow profile,” Pete said confidently.

“Anything else, Professor Pete?” Patty asked.

“It is really helpful to work with your solder paste supplier to obtain the red curve. They should be able to tell you what type of reflow profile and solder paste will most likely provide this kind of result,” Pete finished with a chuckle.

And he added drolly. “Right … Professor Pete.”

“Rob’s working on voiding on thermal pads for BTCs right?” Patty asked.

“Yep. He said he will be ready in two days,” Pete answered.

What will Robs plan be for minimizing voiding with BTCs?  Will Patty be happy with it?  Stayed tuned for the details.

Best Wishes,

Dr. Ron

Fiducials and Odd Boards

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One of the handy aspects of getting boards assembled at Screaming Circuits is that we don’t require fiducial marks for standard process boards. I would say that we build far more boards without fiducials than with. That’s cool, but there are sometimes when fiducials really are a good idea. In fact, if you’ve got room on the PCB, they’re always a good idea (just because something isn’t required doesn’t mean that it’s not a good idea).

Some boards are more in need of the marks than others. For example, not long ago, we got a rigid flex board in. It had three separate rigid boards connected by flex, designed to be folded into a stack. It looked pretty similar to the mockup in this image:

The boards didn’t have any fiducial marks. Normally, what we do, is find a via hole, through-hole pin hole, or some similar feature to use as a fiducial. That usually works, but not always. In this case, the length of the flex varied slightly from board to board. The PCB color was also very low contrast, which made it difficult for the machine to consistently recognize any mark we picked.

That meant our machines had a hard time finding the “home” spot, and we had to reset for each of the connected boards. Finding a spot on one board did not guarantee that we’d know where to place parts on the other two boards in the set.

In this case, it would have been far better if the boards were a consistent distance apart, and if each of the three boards had a set of fiducial marks.

What makes a good fidicual?

Most CAD packages have fiducial marks in their components library. Basically, it needs to be a metal dot surrounded by an area without any copper or solder mask. More than one is best. It should be an asymmetrical pattern that can only be oriented one way.

I’ve got some more details in this article here.

Duane Benson
Routed up like a fiducial
Another rigid flex in the night

http://blog.screamingcircuits.com

Voiding: A Critical Issue in Electronics Assembly

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Folks,

Looks like Patty and the team have a new assignment from Mike Madigan. Let’s look in ….

Patty had just waved to her twin boys as they got on the school bus when her mobile phone rang.  The voice was unfamiliar.

“Professor Coleman, this is Mel Ott.  I’m doing some classroom trading for a bunch of Navy Seals and Army Rangers at a location about an hour from Ivy U. I wondered if you could conduct a workshop on critical thinking for these folks?” Ott asked.

Before Patty knew it, she had agreed to do it. As she drove to the university, she kept on thinking,

“Me teaching Army Rangers and Navy Seals!?”

However, a few moments later, an outline for a workshop was forming in her mind. One topic would be: Which animal is implicated in more human fatalities in the US each year?

  1. Bears
  2. Mountain Lions
  3. Horses
  4. Deer
  5. Sharks

A few moments later, Patty was in the Engineering building complex and was rounding the corner to her office. She saw Pete and Rob waiting outside the door.

“By the looks on your faces, I can tell that we must have another assignment from Mike Madigan,” she said with a chuckle.

“This one is a little strange, even for him,” Pete began.

“Yeah! Look at this note he sent us,” Rob chimed in.

Ever since the three of them left ACME to join the ranks of Ivy University, ACME CEO Mike Madigan continued to use their services. They were paid a fair consulting fee, which all agreed more than paid for Christmas presents and vacations. In addition, Madigan convinced the board of directors at ACME to generously contribute to Ivy U’s general fund. In the three times Patty had met Ivy U’s president, he pointed this out to her with his appreciation. So, the bottom line was that the three of them were quite responsive to Mike’s requests.

Together they read his note:

“Team, our biggest customer is concerned with voiding. They claim it to be their number one concern. Since the three of you left, we have drifted a bit in keeping on top of these things. I am away for a week in Eastern Europe and my wife and daughter are joining me after that for a bit of a vacation in Slovakia. My wife’s heritage is from there, steeped in the traditions of the Rusyn peoples. So, she wants to visit the hometown of her great grandfather. Bottom line is that I will be gone for more than two weeks, without reliable Internet access, so I will be out of touch.

I need you to prepare a presentation on voiding that I (with you) will give to the customer’s president the day I get back. The presentation should have recommended actions. The pitch is at 2PM, 20 days from today. Come at 11AM and join us for lunch.”  Mike

“It’s just like Mike to give us an assignment with no details and we can’t ask him any questions and he schedules the meeting without asking if we are available,” grumbled Pete.

“I, for one, think it is great he is going on vacation,” Patty said brightly.

“Good point,” Rob added.  “I can’t recall him ever taking time off.”

“Well, what is our plan?” Patty asked.

“I’m almost certain that they are not interested in champagne voids, Rob pointed out.

“I agree, since they are mostly associated with immersion sliver finish while ACME’s customers mostly use OSP finish,” Pete added.

“I think the big issue today is voiding in quad flat pack no leads (QFN) thermal pads, BGA voiding is sort of passé,” Rob suggested.

A BGA void image, taken by CALCE.

“Oops! We are supposed to call them bottom-terminated components (BTCs), right?” Patty asked.

“OK. You’re right on that one,” Rob chuckled.

“So, let’s focus on BTC thermal pad voids. But, I think, for completeness, we should cover BGA voids, too,” Patty said.

“Pete, if you can cover BGA voids Rob and I will pull together something on BTC voids.  Let’s put it on our calendars to meet one week from today to review our material,” Patty sort of commanded.

“Yes, ma’am,” Pete and Rob said in unison.

Patty was about ready to get annoyed, but they all burst into laughter as they got up to leave her office.  Even though Patty was now a prof, she still had a lot of manager in her!

Cheers,

Dr. Ron