Testing Todd: Don’t Get Pickled by the Barrel

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. The practical magic, of course, is plated drilled holes. Through the early years, it was all holes and large analog components with 16–18 layers being state of the art. Standard holes for components were usually 0.060” and spaced 0.100”. That was then. Today, the larger holes are left for connectors and hardware, with almost all componentry evolving to SMT.

Now, our plated holes are used for interconnects or vias. Although some may still accept components, they mainly provide the Z-axis connection between layers. Unlike vias of earlier times, these holes have become extremely small. In fact, some vias don’t even go through the board any longer. Some may go from the surface to a layer somewhere in the stack, where others are not visible from either side. Even though the holes have become smaller, the board thicknesses have not. From a plating engineering standpoint, this has become challenging as the aspect ratios have become very high. Each layer can be perfectly developed and etched, all to be scuttled by a bad interconnect or via. The entire board ends up being scrapped. This can be costly (Figure 1)

C_Kolmodin_Nov20_Fig1.jpg

Although some would argue that electrical test (ET), what with all the mystical voodoo that goes on, is not a value-added process; in some aspects, they are correct. However, think of it more as an insurance policy. Having a finished board fail at a customer site or CM is the worst thing that can happen. Not only must you deal with the returned product, but you also take one on the nose for delivered quality. It can be difficult to recover from that in this competitive market. How is ET guaranteeing you the peace of mind that what you are shipping isn’t getting pickled by the barrel?

Well, there are couple things we are doing in addition to the standard continuity and isolation test. Industry standards specify the minimum requirements to which the product must conform. Remember, these are minimums. Higher-reliability products may require more stringent testing. For example, Class 2 Level B products allow the optimization of mid-points during ET, where Class 3 Level C does not. There are some options in ET that can be added to reduce the risk of rejection once the product leaves the manufacturer (Figure 2).
C_Kolmodin_Nov20_Fig2.jpg

Forced Barrel Test

Although Class 3 Level C products do not allow the optimization of mid-points, it is not specific on how the mid-point is tested. Most ET rasterization routines will follow the circuit from end-to-end and place test points at the endpoints. If optimization is not allowed, the system will place test points at all intermediate test points along the net. However, this is based on the accessibility of the mid-points. The drawback is that if a mid-point is a via, it may test one side or the other depending on the accessibility (solder mask).

When one side of the via is covered, it’s straight forward; the open side receives a test point. The lottery here, though, is if both sides are clear most systems will place the test point on one side or the other randomly. The vulnerability here is that if the test point is placed on one side and the assembly house uses the same via as an in-circuit test (ICT) point but probed from the other side, the standard ET at the manufacture can pass, but the ECT test at the assembler can fail. How can this be?

The answer is that the test on the ICT side of the via could be voided. The barrel on the ET side may still be intact and pass the circuit through the interconnect(s) but is voided above the circuit path. This is undetectable in standard ET, even with mid-point optimization removed. The mid-point is tested, and the circuit is valid. However, the ICT test fails.

In reality, the board is fully functional but cannot be verified at the assembler and is therefore rejected. What we can do is force the barrel test. Regardless of the standard test, the barrel test can be added. Once the barrel test is activated, the user can select the drill size or the range of sizes to be checked. Now, there are some requirements for the forced test to be of value.

As I stated previously, both sides of the barrel must be accessible. This is a straightforward continuity test based on the parameters selected for the full test. This option just forces the side-to-side barrel test to capture the possible electric

al null area of a via void escaping. This test is not to be confused with 4-wire Kelvin. This test option will capture full void scenarios and not necessarily thin copper or taper plate conditions.

4-Wire Kelvin
Kelvin 4-wire testing is all the buzz now in printed circuits. One of the most difficult defects to capture is the latent barrel void. It is common for this defect to hide and miss detection during normal ET. Most ET specifications require continuity of circuits to pass at a minimum of 5 ohms continuity at the stricter end of the spectrum (Figure 3).
C_Kolmodin_Nov20_Fig3.jpg

With plated drilled holes, the difference between a conforming barrel and a non-conforming barrel will be in the milli-ohm range. The standard continuity parameters will not be able to detect these issues, as the difference in resistance will not be detected as it will be masked by parasitic resistance and limitations of the standard metering systems being used. The specific detects are taper plate and micro-fractures.

This is where 4-wire Kelvin really shines. The high-resolution measurement is able to capture these minute changes in resistance of the barrel. Many questions arise on how the Kelvin test works. The industry standard is a master comparison test. What we mean here is that a known electrically correct PCB is used to create the Kelvin master. This is done by performing several cycles (user-definable) on the PCB, and when complete, the master values are written.

The subsequent PCBs are then compared to the master values for evaluation. Differing from the forced barrel test, the theoretical values can be programmed in advance. However, due to the variances in plating from lot to lot, the minor differences in resistance can be fatal in repeatability even though fully conforming.

These options are available today to help capture electrical defects in plated barrels, whether they directly affect the electrical profile of the circuit board or are hiding in the functional spectrum of the barrel that does not affect board integrity. Consult with your ET department on how this may help you in the future. If you have questions, you can reach out to me as well.

The holidays are upon us. Be safe, keep your distance, and hug your family.

This column originally appeared in the November 2020 issue of Design007 Magazine.

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2020

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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