Testing Todd: Homing in on the Target

Although electrical testing provides a beneficial safeguard against an electrically inferior product reaching a customer, it does require adherence to critical processes. One of those processes is the inspection for witness marks or pin marks. The caveat of electrical test is that it needs to be done but at the same time, optimally, there should be no evidence it was performed. This can be a difficult process, especially on some of the more delicate finishes such as immersion silver or soft gold. The horrors of a complex multilayer order scrapping because of one stuck test pin during electrical test keeps sales personnel awake at night. Therefore, a robust inspection process is necessary.

In the past this was not as critical, as bare copper is robust and HASL could easily be reworked. However, as surface finishes have advanced and pad sizes reduced, a stuck fixture pin or overly aggressive flying probe compression can be catastrophic. In Figure 1, we see an example of severe damage caused by a malfunctioning test fixture. In most cases this scenario is fatal to the product.

Kolmodin_Apr21_Fig1.jpg

A live inspection process is the most successful approach to minimizing loss due to test damage. This is not just limited to inspecting the product (which we do) but must include steps prior to that before product is even tested. Although this is more critical with fixture testers, inspection of the test probes, clamping mechanism, and automatic handlers (if applicable) should be inspected prior to testing on flying probes as well. For fixture testers it becomes more in-depth. First, you have the fixture itself which, depending on the scenario, may be a new build or an older repeat part where the fixture was stored for a length of time. This requires inspection of the fixture for missing or bent pins, faulty assembly, or damage incurred during storage. Next is the fixture integration to the fixture tester. The fixture needs to operate freely with no stuck pins. The largest variable contributing to damage is a bent pin or pin side-loading (pin sticking to the side wall of grid stripper plate), which locks the pin from free movement. Once this has been performed the electrical validation should take place. This includes a continuity and isolation test against a copper sheet (continuity) and non-conductive sheet (isolation.) These tests conclude the following:

  1. Continuity: All pins are moving freely and conduct correctly to the fixture tester electronics. This will also identify faulty connections or missing pins.
  2. Isolation: Provides validation that no shorts exist in the test matrix, either pin-to-pin in fixture or faulty test electronics.

It should only be after these critical setup steps are performed that the product be committed to test. When to inspect is now the question, isn’t it? Absolutely. On fixture testers the optimum scenario is to run a test cycle on a pre-scrap board if one is available. However, many times there are none available and a live board must be used.

(Personal note: If the fixture has a diary or log of past performance, do not just use the logged compression values! This can be fatal as mechanical changes may have been made due to maintenance or service repairs.)

Always run at the least possible compression to provide desirable results. Once the board has been tested, regardless of the result, it should be inspected for witness marks. Do not trust your eye alone as with product technology today you will not be able to perform a valid inspection with the naked eye. It should be viewed under a scope.

Kolmodin_Apr21_Fig2.jpg

Now, what to inspect? The examination should cover the entire board, but significant detailed inspection should isolate on the high-density areas and small pads. These areas are more prone to heavy witness marks as the pins are usually quite small and are more susceptible to damage. Figure 2 shows an example of higher density areas that should warrant higher scrutiny. Once the inspection is complete it can be determined whether continuing with testing is allowed or intervention is required. Intervention is usually an adjustment in compression or perhaps replacement of a test pin or two.

Once testing has begun it is recommended that an inspection matrix be created. How often should we inspect the product during the process? Inspecting 100% of a large order is counterproductive, I understand. Therefore, the matrix is necessary. Should we inspect every 10, 20, or 50? Early rules suggest first, middle, and last board of an order. This can work if the order is only 10–15 boards. Worst case scenario if the fixture test causes damage, it would be caught at the inspection interval. If we had 15 boards, we could catch it after board 5, or board 10. Although it could result in a loss of product it would be limited due to the inspection interval. It may be your local process to inspect all boards in that size of order and this is fine. The question really is based on large orders. We should still inspect the first and last board but if we wait until the middle of a large order, we could lose a significant amount of product, especially if the order is 100 pieces or larger. Here is where QMS discretion is advised. The matrix could break down the order by percentage and create an interval for inspection or it could simply state that on orders of X pieces or larger, every X board needs to be inspected. This allows containment quickly should a fatal error occur during test. It must also be noted that there should be a referee inspection done during these inspection intervals. This is simply referred to as a “buddy check.” It is proven that the second set of eyes may capture a witness mark defect that is overlooked by the primary inspector. Repeatedly inspecting small pads and lines can be monotonous and pattern recognition fatigue can cause the visual senses to tire.

So now we have a setup process and a good understanding of the inspection process, and how, where and when to do it. Again, this all is part of the continuous improvement and quality assurance discipline. We need to own our processes and live them as well. Having integral steps in a process where it requires more than one person during a KPI check or inspection is always beneficial. This is by no means a knock to the primary operator but as humans, we can get tired, fall into repetition, and with that comes an increased margin for error.

As newer technologies emerge the ultimate solution would be to add AVI (automated visual inspection) to the final FA process. Even though we are inspecting the boards at regular intervals there remains a margin for error. Using a process where the test is performed and then an AVI is used to scan the surface of the board and sort by “pass” and “fail’ would capture any and all surface defects.

Line = ET Tester + AVI Inspection + Auto sort pass/fail.

Another item to mention is where the mark may be placed. Many specifications call out the probing area “allowed.” Many times, mechanical drawings may state a “pristine area” of the pad. This cannot have any marks whatsoever. It can be difficult many times, but when it’s unavoidable, the absolute lightest contact must be made. In Figure 3, we show very light contact in a high-density BGA.

Kolmodin_Apr21_Fig3.jpg
Today’s extreme densities and small pads are getting to the point that pinned fixtures are no longer the solution and flying probes or high-density wired dedicated fixtures are required.

I close with some finishes (Figure 4) that we come across routinely. By far the most susceptible finishes are the soft gold and immersion silver families.

Kolmodin_Apr21_Fig4.jpg
Stay safe!

This column originally appeared in the March 2021 issue of PCB007 Magazine.

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2021

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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Testing Todd: Getting 'Lean' in 2021

01-26-2021

Many companies and individuals had to make life-altering adjustments in 2020 because of the pandemic, including reduced hours, telecommuting and examining how we do things in this “new normal.” Although the circumstances causing these changes are tragic, it forced us into becoming lean.

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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.

View Story

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.

View Story
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