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

Electrical test today has changed dramatically since the "pin-in-hole" technology of yesteryear. Although you may still find these designs today, predominantly you will run across the mind-altering designs of our current generation. It boggles the brain to think that computers once inhabited entire rooms to process just "bits" and "bytes" of data. Now, your smartwatch processes more data than many of those computers combined! The smartphone that you use every day has more computing power than the computers used in the Apollo 13 spacecraft!

It's no wonder that today's requirements have become immensely important in guaranteeing success in the products produced. Shorts, opens, impedance, capacitance, dielectric breakdown, and resistance are all major factors in the success or failure of today's PCBs.

With that said, 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. So, it is easy to understand that ET has become much more of a science than history remembers.

Probers Versus Fixture Testers Probers

Today's probers (flying probes) are much more advanced than their distant relatives of days gone by. Probers not only provide the standard opens and shorts test but also buried passive, four-wire Kelvin, and HiPot testing. They can still provide the strict, resistive-only test still required by some OEMs and high-reliability applications, but probers can also provide indirect testing by signature comparison. This is accomplished by developing a capacitive master from a test specimen that has gone through and passed the strict resistive test. The subsequent boards have their capacitive signature compared to the master, and any nets that are atypical compared to the master are retested in resistive mode to guarantee they are acceptable.

Historic requirements of PCBs did not allow probers in some military requirements or performance classes. This was due, in part, to the lack of ability to detect defects in the 3D environment. Probers of today have the ability to scan the horizon as well as the third dimension or the Z axis. This is known as “line of sight” horizontal or “Z-axis” vertical adjacency. Statistical probabilities have been accepted that if a defect is going to occur, it will occur in a given window between two adjacent nets. This is referred to as the “adjacency window.” Historically, this was limited to the horizontal axis or the same layer. This window can now be expanded to layers adjacent in the vertical axis. This enhancement in prober technology is one of the main reasons that some military and higher-performance class products can now be tested utilizing flying probes. This has allowed quicker turn time and reduced cost for electrical test.

However, you will not find this technology available in older probers. Software and metering systems in older equipment just didn’t have the capacity to perform some of the required tests of today. One needs to inquire about the capabilities of the given prober versus the requirements you may have. Remember your deliverables. Some equipment may provide only some of your solutions while others may deliver the full package and more!

Fixture Testers

There is still no question that fixture testers provide the ultimate opens and shorts test. The fixture tester still provides the full parametric test. The simultaneous compression and test of all nets will still detect possible defects that no flying probe will ever find. This is because the fixture tester applies stress to the PCB. The simultaneous compression may detect microfractures to traces and/or barrels during the test that a flying probe may not. They also do not have the limitation of the adjacency windows as the flying probes have. The isolation test covers all nets to all nets regardless of proximity. A gross short defect covering a long distance will be detected where on a flying probe, it may be out of the adjacency window and not tested. Although rare and statistically low in occurrence, this type of defect would always be detected on a fixture tester.

Fixture testers are still the answer to high-volume production. Automation and dedicated fixtures process thousands of boards per time segment compared to a much smaller amount with flying probes. Although automation does exist for flying probes, they will never be able to handle the volume per capita compared to the fixture tester.

Conclusion

As you can see, the evolution of the PCB and electrical test have come a long way in the last few decades. The advances in PCB manufacturing and design have forced the evolution of ET and the methods used. ET has become as much of a new science as the new manufacturing designs coming from the OEMs. Just checking for opens and shorts is no longer enough. Requirements now not only include the opens and shorts test but also the guard zones of buried passives that are independent of the IPC performance class continuity requirement. Along comes multiple voltage requirements within the same board, HiPot requirements, and in many cases, time domain reflectometry (TDR.) Again, ET needs to supply all these services as efficiently and cost-effectively as possible, which is why finding the right equipment solution is imperative.

Test requirements continue to change as the designs advance. When searching for the right solution, gauge your requirements against the deliverables of the equipment. The advancements in prober technology will now provide multiple solutions within the same package. Do your homework, and you may find that the science of electrical test is not as ominous as you thought. As a colleague of mine once said, “I can’t even spell ET.” We can find answers to black holes. Whether you are doing electrical test yourself or have a partner to turn-key it for you, I hope this bit of knowledge I’ve passed along helps in decision making and understanding some of the science behind ET. ET is a much bigger process than what it used to be, so give those folks a chance when the delivery heat is on. It takes a little more time nowadays to "git 'er done!"

Todd Kolmodin is VP of quality for Gardien Services USA and an expert in electrical test and reliability issues.

This column was originally published in the May 2019 issue of PCB007 Magazine.

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2019

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.

View Story

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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