Testing Todd: Breaking the Void

Electrical test is best known for identifying routine opens and shorts. But what has plagued ET, and manufacturers in general, is the barrel void. These voids are breaks in the plating of the drilled barrel that result in circuitry “opens” that pass through the stackup from one layer to another. In some cases, the break in plating is severe and results in an immediate open condition that is detected during electrical test.

However, certain plating anomalies can be present that will go undetected during standard ET. What we must remember is that electricity must follow Ohm’s Law no matter what conditions exist. That is: V = I x R, where V = Voltage, I = Current, and R = Resistance.

Todd_Aug_Fig1_cap.jpgThe most significant hidden plating anomaly to barrels is thin copper, sometimes known as “taper plate” as shown in Figures 1 and 2. This is a condition where copper may be acceptable close to the outer layers of the PCB but may become thinner as distance increases to the center of the depth of the barrel. Although copper exists, it is a dangerous anomaly that can routinely go undetected. Now I can hear the gallery saying, “Todd, how is this possible? The thin copper should blow like a fuse under the formula of Ohm’s Law.” Well, if Ohm’s Law were to be applied straight away, you would likely be correct, along with most circuitry in the board. The reason? Most small trace widths could not stand up to the abuse.

ET vs. Ohm’s Law
This law cannot be broken. However, we can adapt to the law while still maintaining safety to the PCB and underlying circuitry. Many specifications call for test voltages to be applied during test. Industry and military requirements are 40V minimum, so let’s use that. Calculators ready? Okay, we see 40V. Let’s say the continuity resistance threshold is 20 ohms. Now plug those into Ohm’s Law: 20V = I x 20. Ohm’s Law can be simplified for solving any variable. For instance, V/R = I or V/I = R. Anyway, we have 40 volts and 20 ohms. Solving, V/R = I we see 40/20 = I, or 2 amps. Not many 3- to 5-mil traces are going to survive that let alone the electronics in the test machine.

Todd_Aug_Fig2_cap.jpg

Now, what many may not understand about ET and how machines check for opens and shorts is that the “test voltage” requirement is not applied to the opens, or continuity test. The simple fact is that, as shown above, the excessive current would be devastating. Two different processes are in place during the opens test. First, the voltage is limited to a low value, typically 12–20V regardless of the test voltage requirement. This is simply because an open will be present at 10 volts, or the low voltage, thus the high voltage is not required. The second is that during the continuity test the machines use bypass circuitry to limit the current that is applied to the circuit under test. Parallel resistive networks in the machine will shunt the current away from the circuit, allowing only enough to safely take the continuity measurements. Pretty sneaky, huh? Indeed.

The higher voltages are applied during the shorts or discontinuity test. Once circuits are validated for opens, the higher voltage is applied to circuits to identify shorts. Again, Ohm’s Law is at play. However, with testing for shorts, we don’t just apply the voltage and hope for the best. In this case, we know the voltage applied but the other variables are unknown. As we are testing network-to-network for possible shorts, the resistance value is expected to be very high to infinite. Using V = I x R, V is known, so in my example, I will use 100V. We don’t know I or current, but we do know the theoretical resistance R. However, we cannot use “0” or infinite as the law will not allow us. 100 = I x 0? It cannot work when we know we have a known voltage value of 100. So, the shorts threshold must have a value in resistance. Most times it is 10 meg ohms or higher. Now the law works again. 100 = I x 10M or 10,000,000 ohms. Solving, 100V/10M ohms = 0.00001 amps or 10 micro-amps. Now that is still way too much current to allow to pass between circuits if a short may exist. Current limit triggers are in place during the shorts test that effectively stop the test on the network when any current is detected between the nets. Therefore, it is relatively rare that a standard automatic electrical test can result in damage to the circuitry. In other words, don’t rely on ET to blow up shorts as, in general, we do not apply enough current to cause shorts to burn. The test can heat up the short momentarily before the fault trigger but usually will not cause the short to go away.

I digressed to theories, so let me come back to voids. Based on my long-winded explanation regarding how the opens and shorts tests work, we cannot lean on ET to detect all types of barrel voids. We limit current flow so that we are not blowing fuses (thin traces.) Furthermore, the difference in resistance of a network with an acceptable signature compared to a network with a taper plate or thin copper wall will not be that different. These changes in resistance are usually in the milli-ohms. Most electrical test machines use a threshold with a tolerance of plus or minus a percentage. For example, 20 ohms ±5%. That is like 1 ohm. A taper plate void scenario may only change the overall resistance of the network by 5–10 milli-ohm. This will not trigger a fault in the continuity test and thus go undetected.

Todd_Aug_Fig3_cap.jpg

William Thompson to the rescue. If you are familiar with 4-Wire Kelvin testing, you might know that Thompson invented this test in about 1861. This high-resolution measurement system is based on the Kelvin Bridge which Thompson (later known as Lord Kelvin) invented (Figure 3). Using this theory, high resolution measurements can be taken while eliminating the stray or parasitic resistance of the leads and electronics. 4-Wire Kelvin can detect finite differences in resistance in the milli- and micro-ohm ranges. This test will detect taper plate anomalies and poor bonding of micro-vias.

It is common to perform destructive analysis on plated barrels during the manufacturing process. These potted micro-sections can identify plating anomalies if they are a systemic or gross error to the entire order. Remember that these sections are a sample of just a few holes and a PCB may have many thousands of holes. Therefore, this is not always a good indicator of an isolated issue such as a low voltage flight bar in plating or a bad agitation cycle which results in an isolated set of suspect panels. This is where 4-Wire Kelvin can save time and money by detecting these types of issues. If 4-Wire Kelvin is integrated into your manufacturing theatre, a sampling of product with high aspect ratio drilled and plated holes is indicated. A random sample of panels from different flight bars should be tested to identify any possible anomalies. If an anomaly is found, that flight bar can be isolated and the panels fully tested under 4-Wire Kelvin guidelines to validate integrity. Conforming groups can be released for further processing. What this does is remove the threat of latent defects in the field due to poor barrel plating or bonding of the micro-vias. Although this might take some time in the manufacturing process, it far outweighs the cost of returned product and reputation damage with your customer base. Here, the cost of quality has a valuable argument against the cost of non-conforming product and loss of customers. This is especially true today when time to market is crucial and PCBs are increasingly more expensive to manufacture.

This column originally appeared in the August 2022 issue of PCB007 Magazine.

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2022

Testing Todd: Breaking the Void

09-07-2022

Electrical test is best known for identifying routine opens and shorts. But what has plagued ET, and manufacturers in general, is the barrel void. These voids are breaks in the plating of the drilled barrel that result in circuitry “opens” that pass through the stackup from one layer to another. In some cases, the break in plating is severe and results in an immediate open condition that is detected during electrical test. However, certain plating anomalies can be present that will go undetected during standard ET. What we must remember is that electricity must follow Ohm’s Law no matter what conditions exist. That is: V = I x R, where V = Voltage, I = Current, and R = Resistance.

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Testing Todd: ET and the DoD

07-12-2022

Building printed circuits can be a tricky business. There are many attributes that go into the production process. Initially the sales interface with the customer, the receipt of the data for the initial quotation. Then there is the procurement process for raw materials. This has to be done to the customer specifications. The list goes on. Now if that isn’t enough, throw in DoD or aerospace specifications. This month lets dive into the DoD and how this effects electrical test.

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Testing Todd: What's in the Electrical Test Crystal Ball?

06-13-2022

We live in an everchanging environment of evolution. From analog, carburation-driven automobiles and tube televisions to the fully electronic fly by wire automobiles and UHD televisions of today. We had to evolve. Today you can speak to your car, speak to your home, and even execute commands by just your voice. Not just any voice, but your voice alone. Pretty slick, especially thinking back to the computers of Apollo 13 that now could be powered by your latest generation of cellphone.

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Testing Todd: Optimize Your Training Time

05-03-2022

Today’s training has become an essential part of any operation, especially because most Quality Management Systems (QMS) require this. To be compliant with ISO9001 you must maintain a competence and training system. However, there are a few things to keep in mind when taking on the competence and training mission.

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Testing Todd: Has Universal Fixture Testing Gone the Way of the Dodo?

04-04-2022

Although flying probe testers have become common place in today’s manufacturing theatre, one must wonder if the fixture tester, specifically the universal grid or “pin in hole” fixture has any valuable use in the electrical test arena? The advancements in flying probe technology are undisputed with the new abilities to do many of the tests that benchtop testing historically required.

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2021

Testing Todd: Why, Why, Why—Never Stop Questioning

12-29-2021

If you have been around young children, I’m sure you have fallen into the “Why” game or “Why” loop with the young’un. I’m now a grandfather and the game started again a long time ago. “Grampa? Why is that man limping?” “Well, he has a cast on his foot.” “Why, Grampa?” “Well, it looks like he was injured.” “Why?” And so it goes. These brilliant young children have mastered root cause analysis and they don’t even know it.

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The New Electrical Test—Riding the Wave

11-22-2021

Many years ago, when electrical test (ET) was necessary on a bare printed circuit board (PCB) you would build a dedicated fixture with spring pins and mount the box fixture to a machine interface and perform the test. However, back then there were no preconfigured netlists, and the machines were only capable of “learning” the board. This was known as the “self-learn” or “learn comparison” test. At the time, all you could do is prove that all the boards of the test lot were the same. The risk was that if there was a film defect and all boards had the same fault, the test would still pass even though all boards were defective.

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Testing Todd: Is Your Process Cluttered? Supercharge It!

09-30-2021

Recently I came across a posting on social media regarding process development in the eyes of Elon Musk. Although there are many philosophies with regard to process development, I found Elon’s insight particularly interesting. Let’s design a process, shall we?

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Testing Todd: Design for Manufacturing? Don't Forget Test!

09-07-2021

Design for manufacture (DFM) is a great discipline for creating designs that provide optimum performance while still maintaining affordability. However, what can be, and does get overlooked is the DFT (Design for Test) variable. As greater manufacturing demands are put to the manufacturer it also creates challenges to validate the electrical deliverables that may be required.

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Testing Todd: The PCB Limbo—How Low Can You Go?

07-26-2021

Columnist Todd Kolmodin takes a stinging look at the price of printed circuit boards over the past 30 years. What caused this "downward spiral" in the industry?

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Testing Todd: Meet Mr. Henry and Do Not Blow a Fuse

06-18-2021

Columnist Todd Kolmodin explains the connection between electrical test and Joseph Henry. Can you figure it out?

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Testing Todd: Keeping the Tools Sharp

05-18-2021

Quality is not just an action; it is a way of life. We can say we are quality conscious but as the days pass the discipline can fade. The tools become worn, dull and finally discarded. So, we must revisit the tool shed periodically to make sure our tools are razor sharp and at the ready.

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Testing Todd: A Point of Order—Do Not Just Rearrange the Pencils!

04-28-2021

In our concentration on continuous improvement, we should look in to the order of things. Efficiency comes from streamlining processes, effective training, and the ability to monitor success through KPIs and feedback on deliverables.

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Testing Todd: Homing in on the Target

03-30-2021

Although electrical testing provides a beneficial safeguard against an electrically inferior product reaching a customer, it does require adherence to critical processes.

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Testing Todd: Owning Your Processes

02-23-2021

It’s extremely common to write a process or work instruction and let it loose in the wild to thrive. The problem is, if there is a problem or a glitch it may never get noticed. Why you ask? It’s simple. Humans have an extraordinary ability to adapt.

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2020

Testing Todd: Training the Force or the Few

12-31-2020

As with any business, the quality of goods and/or services is of the utmost importance. Company reputations are gauged by the success or failure in maintaining high-quality outputs. Todd Kolmodin explains how maintaining high-quality and on-time delivery depends on multiple factors: first, equipment and tools to produce the product or service, and second, the power of the workforce behind the product.

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Testing Todd: Don’t Get Pickled by the Barrel

11-25-2020

Whether you have two layers or 50 layers, it all comes down to how the layers communicate. Otherwise, you just have a bunch of two-dimensional layers, and that isn’t practical. Todd Kolmodin describes how the practical magic, of course, is plated drilled holes.

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Testing Todd: Roadmap? First, Find the Road!

10-22-2020

Todd Kolmodin originally thought of discussing roadmaps and how they pertain to our industry and analyzing trends. However, it’s difficult to work with the roadmap when you cannot find the road. Todd shares his thoughts and experiences regarding the wildfires in Oregon and the West Coast of the U.S.

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Testing Todd: Don’t Be a Boss—Be a Leader

08-26-2020

Leader, boss, follower, collaborator, teammate. These are terms we have heard many times during our travels through this thing called life. Todd Kolmodin explores the difference between a boss and a leader and shares his observations on leadership.

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Testing Todd: Too Much Automation?

08-03-2020

The last six months have brought monumental changes to commerce, manufacturing, recreation, and almost every aspect of our daily lives. Todd Kolmodin shares his thoughts on how much automation is enough?

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Testing Todd: Down-shifting to the New Normal

05-17-2020

Today, we find ourselves in a place none of us even thought could happen due to the global COVID-19 outbreak. Todd Kolmodin encourages readers to be heroes and shift down to the new normal for a bit.

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Testing Todd: It’s Not Easy Being Green (or Is It?)

04-24-2020

“It’s not easy being green,” are well-spoken words from our amphibian friend, Kermit the Frog. Now, more than ever, there is a focus on being green. Todd Kolmodin explains how one of the largest—if not the largest—contributor to waste is paper, but the difficulty is letting go of it in the consumer and manufacturing segments. For the workplace, this can be more difficult, or is it?

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Testing Todd: Waste Not, Want Not

03-15-2020

Any time we overestimate our projects, we lose costs. For individuals, it may not be as monumental, but for manufacturing, it can be painful.

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Testing Todd: Looking at Digital With 11111100100 Vision

02-12-2020

Todd Kolmodin explores how far technology has come, from the challenge to "plug in" in the '80s, to how difficult it can be to "unplug" in this digital age.

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2019

Testing Todd: Go To Bed Hungry

12-19-2019

Another decade is coming to an end, so, forward thinkers, let's take this time to review the past, evaluate past decisions, and hopefully make prudent decisions to move forward in the ever-changing marketplace in which we exist. There has never been a Magic 8 Ball to predict what is going to happen, so we all do our best to calculate, look over the fences, and aim to remain in this competitive meat grinder we call “the market.”

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Testing Todd: Staying in Your Lane

12-15-2019

As 2019 comes to a close, Todd Kolmodin addresses the importance of standardization, which comes down to an agreement that we are to perform a task or set of tasks the same way every time. Putting your engineering hat on, this provides predictability with a high degree of accuracy.

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Testing Todd: Understanding the Fine Print

10-08-2019

New technologies are emerging each day with more stringent requirements than the past. Also, reversals in obsolescence programs bring products back to the market for which the original documentation and/or requirements are ancient compared to today’s standards; in some cases, this documentation is even lost. Further, it is not uncommon to find that original artwork isn’t available or that the part must be recreated from a finished circuit board sample.

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Testing Todd: What Do You Mean 'Passed' Isn't Enough?

08-05-2019

From a reliability standpoint, we need to quickly assess what risk we may have uncovered when faults are detected during electrical test (ET). "Passed" is not always passed. We must be diligent to scrutinize the failures found during routine ET as a high yield may not indicate high reliability.

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Testing Todd: The Evolution of Probers and Fixture Testers: Blinded by Science

06-26-2019

The evolution of the PCB has come a long way in the last 30 years. The science of electrical test has had to travel that road as well. It's not just a question of screening for opens and shorts. Today, the library extends to interrogating passive components, efficiently and cost-effectively evaluating dielectrics with multiple planes and pairs involved, and adhering to strict requirements from the military, export regulations, and OEMs alike.

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Confidence in Inspection

04-12-2019

The job of third-party inspection is to provide an unbiased review of the customer requirements versus the final product manufactured. This inspection can include both physical and functional criteria. Read on to understand the growing acceptance and requirement of third-party inspection in many areas of the manufacturing industry, including military, aerospace, and medical.

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2018

Testing Todd: What’s in your ET?

07-13-2018

With all the buzz around automation, paperless operation, and integrated processes, it’s time to think about how the connected systems work within an electrical test department. We are all familiar with computer-aided design (CAD) and computer-aided manufacturing (CAM), but with electrical test we can also add computer-aided test (CAT) and computer-aided repair (CAR).

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Testing Todd: How are the Ratings?

05-24-2018

Hello, readers! Thank you for stopping by again. Let’s talk about ratings. No, I’m not talking about the latest Facebook likes or Twitter retweets, but a topic that confuses many final QA technicians the world over. I’m talking PCB voltage ratings.

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Testing Todd: AVI—Your Tireless Friend in Final Inspection

05-01-2018

The “automation vs. human” debate continues. There are experts with many years of experience -performing final inspection with precise detail. This is not debated. However, in the course of human events, circumstances change with unpredictable results. This presents challenges to manufacturers striving to deliver product on-time and within specification guidelines.

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2017

Testing Todd: No Missed Steps—5S Methodology

08-22-2017

In today’s work environment, a company should strive to produce quality product, maximize margins and reduce cost as much as possible. At times, this can be very difficult. Work ethics and methodologies of “how to do things” have developed over many years and can be deeply rooted in many manufacturing theatres. We find at times the “way we have always done it” may not be the most practical way today. This is apparent with the advances in automation, labor force reduction and shifting market demands.

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Flying Probe Testing vs IPC-9252B

05-30-2017

Flying probe testing is extremely popular in today’s manufacturing theatres. The main factor is cost reduction in contrast to dedicated fixtures and fixture testing. However, there are some limitations in flying probe testing when gauged against industry specifications—specifically, the use of indirect vs direct testing in Test Level C.

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Testing Todd: Go With the Flow

04-18-2017

In today’s testing theatre, the flow of information from the OEMs and manufacturers to the independent contractors is mission-critical. Missing information can cause delays, incorrect processing and ultimately scrap or end user rejection of the product. The buzz term being used a lot today is “flow-down.” It pretty much describes itself: It is the flow of information down the supply chain.

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Testing Todd: Plating and Surface Finish—The Challenges to Electrical Test

01-23-2017

Plating and surface finish applications are not without their own set of challenges but these manufacturing processes also affect the electrical test theatre. Microvias, high-aspect ratio plate quality, and surface finish all have their own challenges in ET.

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2016

Testing Todd: Are You a Leader or a Manager?

10-21-2016

The question can be asked, are you a manager or a leader? Can you be both? Is there even a difference? The answer to this latter question is, yes. In a successful organization there are many people performing different tasks all in harmony to make the business successful. Some individuals can be phenomenal leaders while others can be excellent managers. Some can actually be both. How do we define a leader from a manager?

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Test & Measurement—The Case for Validation

07-15-2016

Test and measurement (T&M) are terms that can strike fear into the most robust of minds. Many engineers create designs and products of the future with specific results predicted for performance.

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Testing Todd: Quality Management and the Hidden 'I' in Team

05-24-2016

Today, businesses of all types are jumping on the quality bandwagon. The more critical the product, the more the consumer/customer wishes the highest possible quality in the goods or services requested.

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Quality Management and the Hidden 'I' in Team

05-06-2016

Today, businesses of all types are jumping on the quality bandwagon. The more critical the product, the more the consumer/customer wishes the highest possible quality in the goods or services requested. Customers send surveys with buzzwords like ISO, QMS, and AVL for their suppliers to complete so they have confidence that what they receive is of the highest quality.

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Testing Todd: Process Management: Doing It Right

04-27-2016

Simply put, process management is the idea of figuring out how to do something, documenting it and then monitoring the effectiveness of the steps you created for the end result. Simple, right? Unfortunately, many who take on this endeavor fall short due to missing some key attributes to creating and maintaining a robust process. This article features eight steps in building and maintaining a robust process.

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2015

Flex and Rigid-Flex Circuit Testing: Challenges & Solutions

06-24-2015

Although flex circuits are nothing new in today’s technology roadmap, the testing of unpopulated flexible circuits can be challenging. In this article, columnist Todd Kolmodin writes about the different methods available to test these circuits.

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Electrical Test: Surface Finish vs. Water Marks

05-20-2015

New finishes have come to market; some allow better conductivity, while others reduce the overall cost of precious materials. Regardless of the finish, electrical test must be performed on these circuits. With that comes the caveat of how much of a witness mark can be left on any given landing pad and still be acceptable to the CM or the final OEM user. Todd Kolmodin explains.

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Challenges of Electrical Test

01-28-2015

In our arena today, we can solve pitch and density with flying probe machines, and volume with our grid testers, but the catalyst that is in the mix is that pesky soldermask! Here's why I bring up that necessary process as a problem for electrical test.

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2014

What is 4-Wire Kelvin?

12-05-2014

"I've been asked many times, 'What is 4-Wire Kelvin?' So, this month I will explain the 4-Wire Kelvin Test and how it can help uncover defects that normally would go undetected in standard electrical test methodology," writes Columnist Todd Kolmodin.

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Where Do We Go From Here?

12-01-2014

In this installment of "Testing Todd," Gardien's resident expert Todd Kolmodin answers questions from Dan Beaulieu concerning the future of electrical test. His focus is on the future of testing technologies, testing equipment, and E-test.

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Testing Todd: Where Do We Go From Here?

12-01-2014

In this installment of "Testing Todd," Gardien's resident expert Todd Kolmodin answers questions from Dan Beaulieu concerning the future of electrical test. His focus is on the future of testing technologies, testing equipment, and E-test.

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Flying Probe - Indirect Testing vs. Military

08-19-2014

The use of flying probe testers has become increasingly popular in recent times, mainly due to the affordability of the equipment and also the reduced cost of testing, as no dedicated or "bed of nails" fixture is required. When using flying probes to test military product, one must be diligent to make sure the test method is allowable.

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Testing Todd: Flying Probe - Indirect Testing vs. Military

08-19-2014

The use of flying probe testers has become increasingly popular in recent times, mainly due to the affordability of the equipment and also the reduced cost of testing, as no dedicated or "bed of nails" fixture is required. When using flying probes to test military product, one must be diligent to make sure the test method is allowable.

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Everything You Wanted to Know, But Were Afraid to Ask

07-30-2014

This month, "Testing Todd" author Todd Kolmodin of Gardien Services USA presents readers' questions about the basics of electrical test, including the different types of testing available today.

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Testing Todd: Everything You Wanted to Know, But Were Afraid to Ask

07-30-2014

This month, "Testing Todd" author Todd Kolmodin of Gardien Services USA presents readers' questions about the basics of electrical test, including the different types of testing available today.

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Seven Tips for Choosing the Right Test Service

06-12-2014

Do you need to go outside your company for your testing service? Maybe you have capacity issues, maybe your equipment is down, or maybe you just want an established back-up plan? Whatever the reason, it is very important to choose the right outside testing service because, ultimately, you're not just choosing an objective service provider; you're choosing a partner.

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A Summary of Various Test Requirements

06-03-2014

The PCB industry has advanced significantly in the recent millennium. OEM specifications and requirements have also advanced due to the maturing of technologies, which has caused the requirements of electrical test of these higher technology products to advance and increase in intensity.

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Testing Todd: A Summary of Various Test Requirements

06-03-2014

The PCB industry has advanced significantly in the recent millennium. OEM specifications and requirements have also advanced due to the maturing of technologies, which has caused the requirements of electrical test of these higher technology products to advance and increase in intensity.

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