Thixotropy: An Important Solder Paste Property

Folks,

To the SMT process engineer, the second most important thixotropic material in their lives is solder paste. If solder paste was not thixotropic, it would be difficult to print and would likely slump after printing the paste. What is a thixotropic material? It is a material that has a low viscosity when it is shear stressed and a high viscosity when it is not shear stressed. So, when the solder paste is forced through the stencil aperture by a squeegee, its viscosity plummets and allows it to fill the aperture. See Figure 1.

Figure 1. The viscosity of solder paste dramatically decreases as it is forced through the stencil aperatures.

When the stencil is removed, the resulting solder paste deposit experiences no shear stress so the deposit maintains the shape of a “brick.” See Figure 2. So thixotropy is a very helpful property of solder pastes.

Figure 2. After printing, the solder paste viscosity is high, enabling the depost to maintain the brick shape. Figure courtesy of Ron Lasky, Jim Hall, and Phil Zarrow.

If solder paste was dilatant, it would be a disaster. These materials are the opposite of thixotropic materials. They have a low viscosity when not shear stressed and a high viscosity when shear stressed. So they could not be forced through the stencil aperture and, if they could, they would flow all over the board. Cornstarch and water is an example of a dilatant material.

Oh, yes, what is the most important thixotropic material to the SMT process engineer? Their blood. When getting up from lying down, our heart automatically makes a strong “pump” to rush the flow of blood to our head. Since blood is thixotropic, it shear thins and makes it easier for our heart to get the needed blood up to our head. If blood was not thixotropic, we might faint every time we rise from reclining!

Cheers,

Dr. Ron

Zarrow and Hall’s “Board Talk” Becomes a Book

Folks,

There are a few good books that relate to electronics assembly. Ray Prasad’s Surface Mount Technology: Principles and Practice comes to mind. However, few (none?) teach the skills that need to be developed to become an electronics assembly process engineer, so Jim Hall and I collaborated on Handbook of Electronic Assembly and Guide to SMTA Certification a few years ago.

There was still a gap, however. No book existed that discussed troubleshooting everyday assembly defects and challenges. My good friends Phil Zarrow and Jim Hall have addressed this information in their Circuit Insight radio show Board Talk. All that was needed was a little encouragement to assemble it in book form. This task has now been accomplished!

Phil and Jim’s Troubleshooting Electronics Assembly is certainly one of the most useful books available for everyday SMT and though-hole assembly challenges.

Phil and Jim’s Book Can Help with Everyday Assembly Challenges

Check it out.

Cheers,

Dr. Ron

‘The Era of Offshoring US Jobs Is Over’ … or Is It?

That’s what the US Trade Representative says in an editorial in the New York Times today. And he gets the drivers right, mostly. But the results? “The United States lost five million manufacturing jobs. That, in turn, devastated towns and contributed to the breakdown of families, an opioid epidemic and despair.”

That’s just a crazy extrapolation. The US was at 3.1% unemployment prior to Covid-19.

Repeat after me: There. Were. More. Jobs. Than. Qualified. Workers.

For two decades, the no. 1 complaint I’ve heard from US business owners is the lack of manufacturing talent. Even in times of higher unemployment rates (the last two months notwithstanding), managers consistently noted the lack of basic communication and math skills among the workers available.

In his op-ed, USTR Robert Lighthizer adds, “If you want certainty, bring your plants back to America.”

It’s not that simple. You need the whole supply chain. And you need an end-market. The US, at 327 million people, isn’t big enough to sustain a company of any real size; those firms must be able to sell into other (larger) markets too.

And all those other big markets (China, Brazil, EU, etc.) have their own “make local” requirements and incentives.

I wish Lighthizer were right. But I’ll say it again: The US does not have enough worker talent to handle manufacturing at the cost necessary to satisfy the US market.

Covid-19 is Creating a Perfect Storm for Manufacturing

By Rafael Gomez, Director Product Strategy, Bright Machines

The pandemic’s economic impact started as a supply chain shutdown in Wuhan, China, but rapidly became a three-tier global disruption. As the virus spread, worldwide supply chain was interrupted, followed by an unprecedented shift in product demand and most recently by mandated factory shutdowns imposed on non-essential product manufacturing lines.

Let’s discuss the impact of these disruptions and explore how we can mitigate these forces that threaten to destabilize manufacturing.

Disruption #1 – Manufacturing and the supply chain

The first disruption to manufacturing and the associated supply chain was in China. This was due to the outbreak of novel coronavirus (Covid-19) forced workers in that county to stay home rather than return to work after the Chinese New Year holidays. The resulting impact was that a significant amount of the world’s manufacturing capacity was essentially shut down for an extended period, more than two weeks in most of China, and much longer in Wuhan.

This manufacturing and supply chain shutdown turned out to be just the start.  As the virus spread, manufacturing shutdowns rapidly spread throughout Europe and the US. We are now faced with the challenge to scale additional capacity or rapidly move production from one facility to another, neither of which are feasible in the manufacturing industry.

Disruption #2 –Demand volatility

Just as China’s factories started to come back online it became abundantly clear that the challenges were global and that certain products like PPE (Personal Protective Equipment) and medical devices were in unprecedented demand in terms of volumes and urgency. Meanwhile, workers, who are themselves consumers, were staying home and not shopping, sending economic shockwaves around the world, resulting in a dramatic downturn in market demand for non-essential or discretionary products. Add government and administrative intervention, including the loosening of FDA regulations and the use of the Defense Production Act in the USA, and it’s easy to see how the manufacturing industry was suddenly forced to deal with the unprecedented reactionary shift in market demand.

Disruption #3 – Workplace challenges

The third disruption came in the form of government directives to shelter in place and enforcement of workplace social distancing (including new OSHA guidelines).  Furthermore, non-essential factories have been shut down for an extended period. Once factories reopen, manufacturing plants will need to adhere to new and complex regulations. For example, when factories re-opened in China, they were mandated toto demonstrate ten-day supply of face masks for each worker. For example, a factory of 500 operators would need 10,000 masks to be authorized to continue operations. For many factories, an ongoing supply of PPEs in short supply and can be challenging and costly to obtain.

Once manufacturing companies receive authorization to restart operation, workplace social distancing on the factory floor will impact every discrete manufacturing function Traditionally, manual assembly lines are designed with minimum operator to operator spacing to facilitate the passing of product between stations and to minimize required floor space. With the new OSHA directives, these manual lines will need to be redesigned to increase operator spacing.  factories have met these challenges in creative style, like running extra shifts to redeploy staff and keep them distanced.

The data-haves and data-have-nots

Manufacturers that have embraced digital transformation, and the associated software-controlled automation, are best equipped to succeed in light of these disruptions. Real-time data drives visibility, which allows these “digital haves” to see the impacts of disruption sooner. Meanwhile, smart automation provides tools to adapt and adjust course quickly. Not only are these companies able to adapt production to meet increased demand or comply with new regulations, they are able to rise to the challenge of manufacturing the machines, devices, and consumables needed to help fight the virus, perhaps offsetting the loss of orders for ‘non-essential’ products.

The Future is agile and resilient

This perfect storm of disruption has exposed limitations of traditional manufacturing ecosystems and their associated supply chains. It has become clear that manufacturers need to move away from traditional analogue operational models, where production takes significant and costly time to set up on a line and requires constant tweaking or adjustment by experts with tribal knowledge of manufacturing processes.

To minimize the impact of economic disruption, manufacturers need to operate in a new paradigm.  This new version of manufacturing is fully data-enabled and software-driven to deliver an automated solution that provides the resilience to cope with disruption and the agility to react and adapt when that inevitable disruption occurs.

Considering previous viral outbreaks and natural disasters, Covid-19 isn’t the first global event to disrupt manufacturing and the supply chain, and it certainly won’t be the last. One key learning from this unprecedented event is that companies that have embraced digital transformation of manufacturing are the most robustly equipped to survive this economic disruption. These forward-thinking manufacturers will surely reap the prosperous benefits of their proactive digital transformation.

https://www.brightmachines.com/blog/

Make in India?

A colleague asks whether companies are looking at India as a country they can source electronics goods.

Good question. I would say that right now it’s not high on the list. It has a long way to go to develop the infrastructure and mass of supply chain companies dedicated to electronics (component manufacturers, laminate suppliers, chemistry suppliers, etc.). 

But … the bloom is way, way off the rose in China. China is less attractive from a labor rate perspective, and coupled with the tariffs, firms were already looking at alternatives even prior to Covid. See below for the year-over-year changes in electronics imports to the US from certain nations:

US electronics imports from selected nations, 2017-19

India’s electronics imports to the US grew 20%+ year-over-year in back-to-back years. Granted, it was starting from a low base: imports in 2016 (the base year) were just $754 million, and so even with the increase the total is just over $1.1 billion. Vietnam, another big gainer, is at now at $22.7 billion. China, even with the dip in 2019, was at $170 billion.

I do think US companies will to a greater degree be looking at nations outside China as potential manufacturing centers. India’s massive population continues to make it attractive of course. Now it needs to attract a few more assembly companies, which in turn will drive the suppliers to locate there.

Post-Covid, Will Connections Be Scarcer?

A friend writes to say he’s been about the effects of “social distancing” policies. Will they have a permanent effect on our lives, he wondered. And will they impact events such as trade shows?

It wasn’t the first time I have been asked that of late. The subject also came up on a couple of podcasts I’ve had the good fortune to do, one with Judy Warner of Altium and the other with Mike Konrad of Aqueous Technologies.

My short answer is, I think there will be an impact, but it will swing toward more contact, not less. Indeed, after being cooped up for so long, I think people will crave human connections. Moreover, I don’t think it will have an effect on trade shows. In fact, I think this will reveal lots of holes/flaws in inter-/intra-company digital communications, which gives us all something to work on for the next quarantine (heaven forbid). 

We aren’t the only ones contemplating what happens next. The Boston Globe this week published a piece in which several self-styled business futurists and science-fiction writers expect the world will look like next fall/winter.

I can’t say I’m impressed with most of their responses, which if anything feel exaggerated for effect. But see for yourself.

How Does Turnkey PCB Assembly Reduce Turn Times?

You’ve probably heard of turnkey PCB assembly, an all-in-one solution design and specifications are sent to the PCB manufacturer and they return the assembled PCBs to you (or your client) ready to use. It sounds convenient compared to doing all the legwork yourself, or having one of your engineers do it, but did you know that turnkey assembly also offers the shortest possible lead times for PCBs?

Let’s take a look at some of the ways that turnkey PCB assembly can shave time off of the design process and reduce turnaround time.

It Saves Engineers Time

Turnkey assembly saves engineers time in a couple of important ways. First, time spent hunting for components and availability is eliminated. Manufacturers that offer turnkey assembly have teams dedicated to component sourcing. This also extends to component substitution and BoM management. If something isn’t available, your turnkey team will be able to deal with substitutions for you and check that all substitutions are compatible with the overall design.

Second, and maybe an even bigger time savings, is the reduced communication load. When an engineer is organizing multiple component suppliers, a PCB fabricator, an assembler, and shipping among all of them, keeping everything sailing smoothly can eat a lot of time. Keep your PCB designers focused on their main job—designing and revising PCBs.

That will mean that prototypes are designed, tested, and redesigned faster. No time spent following developments with assembly; no logistics work organizing the movement of boards or components between vendors.

With turnkey assembly, engineers have a single point of contact to deal with any and all questions related to the development of the product. They will keep you up-to-date on the process, and any changes that need to be made can be addressed quickly.

It Reduces Transportation Time (and Costs)

When dealing with multiple companies for every aspect of the production process, the time that goods spend moving from one stage to the next can really add up. Compare that with a turnkey assembly solution:

  • The PCB manufacturer already has ties with component suppliers and knows which parts to find from each one.
  • They have a store of common components already on hand and can handle component inventory storage for you.
  • The assembler is either in-house or nearby.

Instead of orchestrating businesses across borders and possibly continents, the entire process is localized, moving quickly from one stage to the next. That leaves shipping the final product as the only major shipping time.

There Are Fewer Quality Concerns

With a turnkey assembly solution, there are fewer quality concerns to deal with, especially when shipping between vendors.

In a multi-vendor scenario, if you instruct your PCB fabricator to ship your bare boards to an assembly house and they arrive with an error or a large percentage of damaged boards, your only option is to make a new order and wait. With turnkey assembly, this situation is impossible.

The company you deal with is responsible for your project from PCB creation to final testing, if they make a mistake with one step, they catch it and fix it in the next. As we mentioned before, you have a single contact or team within the manufacturer overseeing the progress of your order and checking for quality at each stage.

Not to mention, you’re dealing with a single organization. Internal teams are familiar with each other and have experience working together. Miscommunications and mix-ups are reduced and it’s in the manufacturer’s best interest to make sure that each stage supports the next and products move through the process as efficiently as possible.

Of course, it’s possible to run into a bad manufacturer, which could cause you even bigger problems than one bad vendor might. So, it’s important to vet your potential manufacturer carefully, and find reviews or references if possible.

Scale Up Quickly

The benefits go beyond the turnaround time for your initial prototype. Once you’re satisfied with your PCBs, the manufacturer can immediately start to produce them in quantity.

Think about it. Instead of juggling multiple suppliers and manufacturers to finish the prototypes and then searching for a manufacturer for production, you could finish prototyping quickly and move forward immediately with a company with which you have already developed a relationship.

Not all PCB manufacturers that offer turnkey assembly offer large-scale production, but if your needs fit with the manufacturer’s capacity, turnkey assembly could offer a truly seamless production process. Some manufacturers can even ship to clients for you or offer drop-shipping services.

With turnkey PCB assembly, you get a single, devoted team backing you up as you take a design from PCBs to working products. With less time spent on logistics and organization, you can expect much faster results. It could turn the design process around by reducing product turnaround.

Contributed by Chris Dickey, vice president of sales and marketing at SVTronics

UP Media Statement on Covid-19

Like all the companies we serve in the electronics design and manufacturing industry, we are closely watching the world’s response to Covid-19.

All UP MEDIA GROUP staff work remotely, and our operations should continue as normal. As of this notice, our websites, magazine issues, podcast and newsletter will be updated and published per the schedule in our 2020 Media Kit.

We currently intend to hold the PCB2Day workshops scheduled for June in Austin, TX. We will provide regular updates to all sponsors, speakers and registrants as the situation on the ground becomes clearer.

PCB West 2020 at the Santa Clara (CA) Convention Center remains on track to take place in September. Confirmation letters to speakers are being sent this week, and our conference program and registration will be available by early May.

The health of our employees, contributors and customers is paramount. We will take any measures to ensure we do not subject any staff, contributors or customers to unnecessary risks due to the coronavirus.

We are open and ready to serve you during these difficult times. Please contact Mike Buetow (mbuetow@upmediagroup.com) for editorial, Frances Stewart (fstewart@upmediagroup.com) for shows, and Brooke Anglin (banglin@upmediagroup.com) for advertising.

Sincerely,

UP MEDIA GROUP staff

Statistically Significant vs. Practically Significant in SMT Data Collection

Folks,

Let’s assume your company has decided that transfer efficiency (TE) is the key metric in determining solder paste quality. Transfer efficiency is the ratio of the volume of the solder paste deposit divided by the volume of the stencil aperture. While you agree that TE is an important metric, you are a little troubled with the recent results in a solder paste evaluation. Two out of 10 pastes are fighting for the top spot and it looks like TE will be the deciding metric. Paste A had a TE of 99.5% and Paste B had a TE of 99%. So management wants to go with paste A. You are troubled because paste A has a poor response-to-pause. If it is left on the stencil for 15 minutes or more the first print must be discarded. This weakness may result in 30 minutes or so of lost production time in a 3-shift operation.

However, the TE test results showed that the TE of paste A was statistically significantly better than paste B. You think about this situation and something doesn’t make sense — 5% and 99% are quite close.

You dust off your statistics textbook and review hypothesis testing. Then it hits you, with very large sample sizes, means that are closer and closer together can be statistically significantly different.

The data show that paste A has a mean of 99.5% and a standard deviation of 10%, whereas paste B has a mean of 99% and also a standard deviation of 10%. The sample sizes were 10,000 samples each. These large sample sizes are important in the analysis. The standard error of the mean (SEM) is used to compare means in a hypothesis test. SEM is defined as the standard deviation (s) divided by the square root of the sample size (n):

So as the sample size increases, the SEM becomes smaller or in statistics lingo “tighter.” With very large sample sizes, this tightness enables the ability to distinguish statistically between means that are closer and closer together. This situation was not a concern with sample sizes of less than 100, however with the modern solder paste volume scanning systems of today, sample sizes greater than 1000 are common.

Figure 1 shows the expected sampling distribution of the mean for samples with a TE of 99.5% and 99.0% and a sample size of 100, both have a standard deviation of 10%. Note that to your eye you do not see much difference. However, with the means and standard deviations the same and sample sizes of 10,000 the sampling distributions of the mean are clearly different in Figure 2.

The reality though, is that there is no difference in the results in Figure 1 and 2. The tiny difference in the means (0.5%) may be statistically significant with a sample size of 10,000, but is it practically significant? Would this small difference really matter in a production environment? Almost certainly not.

Figure 1. Sampling distribution of the mean for a sample size of 100.
Figure 2 Sampling distribution of the mean for a sample size of 10,000.

So, with large sample sizes, we need to ask ourselves if the difference is practical. For TE, I think we can be confident that a difference of 0.5% is not practically significant. But, what if the difference was 2% or 5%? Clearly, experiments should be performed to determine at what level a difference is significant.

With the case discussed above, I would much prefer the paste that has a 99.0% TE and a good response-to-pause.

Cheers,

Dr. Ron