POGO® Spring Probe Considerations for PCB In-Circuit and Functional Test

How do I select the optimum POGO® spring probe for my PCB test application?
PCB test fixture designers have many factors to consider when selecting the proper spring probe for their application. In the world of spring probes, choices and trade-offs abound when it comes to selecting tip geometry, spring force, probe base material and plating.  Choosing the right combination of options greatly impacts test yields, probe life and cleaning frequency. Read more

Trends in Testing of Analog ICs

“There is a lot of development in op amps,” said Christopher Lemoine, product marketing director in Xcerra’s ATE group in an interview with Semiconductor Engineering. “There are always higher-performance op amps, lower bias currents, getting closer to the rails, you now have zero-headroom op amps where you can operate right down to the ground rail. At the same time, a lot of the performance hasn’t changed a whole lot.”

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Xcerra Kestrel/X-Series Measures Automotive Radar Chirp Linearity

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Collision avoidance radar devices generate bursts of RF energy called ‘Chirps’. Which are transmitted (TX) to be reflected and ultimately received (RX). A Chirp is a sinusoid that increases its frequency linearly. The linearly changing frequency of each chirp can be used to extract vector speed information about the target. EBand Radar devices produce chirps over a bandwidth of 1GHz and, as in this example, near 76GHz.

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Combining Grid and Flying Probe test to achieve higher pass rates and better test quality

In the past, there was a strict separation between testing unpopulated circuit boards on a Universal Grid tester and Dedicated tester (both fixture based test systems) and a Flying Probe Test system (FPT) (i.e. fixtureless test system).  While high-volume productions were tested using a Universal Grid tester or Dedicated tester, the Flying Probe Tester was mainly used for prototypes or small series production. New developments let PCB manufacturers rethink the role of the FPT.

Over the time, the Flying Probe Test systems became faster and more automated. With that the lot sizes for which a FPT can efficiently be used increased, avoiding the cost and the lead times of fixture building. But apart from this, there are also other factors which let PCB manufacturers rethink the role of the FPT:
Due to the increasing density of PCBs and Substrates and also due to the smaller pad sizes, it becomes ever more difficult to test the products with fixtures. Especially in areas with BGAs, the required deflections on the universal grid are testing the limit. There is also an increase in the number of false faults due to a misalignment of test pads and the test pins of the fixture (e.g. resulting from distortions in the printed circuit board). Next to these contacting problems, also measurement capabilities limit the application of fixture based tests. Small structures can require resistance tests down to a few µOhm while a fixture based tester barely can test values of a few mOhm reliably.

Two ideas arose.  On the one hand, to perform a kind of split test: to test on a fixture based tester all the parts of a PCB or Substrate which safely can be tested on such a system and to make all other measurements on a FPT. The latter measurements are predominantly those which require higher mechanical accuracy, better alignment or higher measurement resolution.

On the other hand, to perform a verification of the reported faults of the fixture based tester on the FPT. While this was in the past only feasible for small quantities, with highly automated FPTs, this can now be done on a large scale. An enabling factor for this is also the integration of data between systems and platforms which is advancing rapidly with the spread of Industry 4.0.

With all these options, the PCB manufacturer now has the possibility to set up a far more cost-efficient and more effective test environment than it was possible a few years ago.

Connector Design Considerations for the Demanding Medical Market

Challenging environmental conditions and high reliability requirements create the need for can’t fail connectors.   This article explores some of the more critical design factors that go into designing a new connector for the medical market.

The medical industry requires connectors to reliably operate in a variety of harsh environments.  This drives the connector design to be custom, specifically addressing each application’s unique challenges.  There are many attributes that must be considered when laying out a connector’s specifications, but they typically fall into 1 of 3 categories: material selection, mechanical properties and electrical specifications.   All 3 categories must be considered concurrently to yield a successful connector design.

Material selection

Proper material selection will be determined by the environmental conditions the connector must operate in and is often driven by regulatory acceptance requirements.  These factors must be considered from project inception and throughout the entire development process.   Factors can range from flame rated plastics (UL, Vx rated) to chemical resistance.  Chemical sensitive applications may require plating structures that resist harsh chemicals and balance contact life on both sides of the connection system with the electrical requirements.  Base metal selection can also affect connector reliability.  Compliant contact designs with a capability to self-clean by implementing a scrubbing action can also influence material selection.  The development process must also consider materials that are favorable for prototyping, and that can later be scaled into molded form factors when the project reaches high volume production.  Using the proper materials in the prototyping phase can allow design validation prior to the expense of fixed tools, reducing technical risks, and the commercial risks from a delayed program.

A healthcare application with a portable device dock provides an example where all the considerations will play a role.  The stability of the insulator and reliability of the contacts in such a device can be stressed by common field processes such as using beach wipes to clean, or real-world threats like a spilled beverage.   Planning, design and validation provide the best path to avoid a failure or costly pattern of failures.

Mechanical properties

Choosing the contact element type is probably the single most important decision for any connector design.  Spring probes, also known as or Pogo® pins, have proven to be the most reliable means of making contact when thousands of cycles are needed.   The compliance aspect of spring probes also compensates for non-planarity challenges between the contact surfaces as well as blind mate applications.  For portable, wearable or base charging applications, the challenge can simply be maintaining continuity in a dynamic environment.  Shock and vibration tolerant connectors are necessary for rugged environments.   Spring probes are offered in a variety of spring forces and tip geometries, tailored to the application.

Probe architecture is critical when designing the optimum solution.  Probes with a deliberate bias offer the most stable design to transmit power and data.  The mechanics of how to achieve the bias affect; contact resistance, cycle life, signal stability as well as cost are essential elements to a successful probe design.  The available space and required usable stroke of a probe will also dictate internal probe design.

Electrical specifications

The number of signal contact points and layout pattern is typically the first design parameter to consider.  If the signals operate at high frequencies (>500MHz), then multiple ground pins may be needed to ensure proper signal integrity through the connector. With the advent of increasing data streams, and more capable transmission standards like USB2.0, it is more important than ever to understand the influence of an electrical contact.  A qualified solutions provider must be able provide design, simulation, and then validate data transmission through extensive testing.  Many of today’s medical connectors operate at high voltages and high currents.     Contacts must be designed to the electrical specifications needed to achieve the products functions such as cut and cauterize, or micro fluidic control.

In summary, when designing a connector for medical applications it is important to equally consider the materials, mechanical properties and electrical characteristics of the design to ensure a successful product.

Learn more about Xcerra’s connectors solutions: click here

Test Floor Automation – is it finally due, after years of talking?

Semiconductor front end automation took place decades ago. The sensitivity of the front end process was requiring it and the always equal form factor of the wafers was supporting it nicely with a standardized transport media, the FOUP (front opening universal pod). It provided a standardized interface for all material handling and processing equipment and the wafer handling is, in general, very reliable and jam free. Automation companies were therefore able to address all technical requirements of the flexible automated material handling between standalone equipment in the fab.

On the other hand the semiconductor back end has had to deal with all kinds of different package types and form factors, resulting in different transport media, such as bulk, tube, metal magazine, tray and reel. Even though SEMI has started to standardize this media, there are still many different form factors to consider. This has made it impossible to come up with a global material loading and unloading type for all equipment. It was therefore less costly to move backend into low labor countries to be able to manage and reduce the handling cost.

In addition the packages often have very loose tolerances making it very difficult to handle the devices reliably and jam free through the backend equipment once they were singulated. This leads to a test floor operation with many human machine interactions for clearing jams. But a test floor with frequent human and robotic interaction can lead to a less safe factory operation and may infringe on existing safety standards.

However, over the last 30 years two automation approaches were attempted in the backend. Only one was successful. Fifteen years ago strip test, and its integration in back end production lines seemed to be the Holy Grail solution to automate the test floor. While strip test is still around, the lines disappeared pretty quick again from the test floors with some exceptions. The integration of trim & form assembly equipment with test handlers and final packaging equipment was not successful because of the typically different speeds of the integrated pieces of equipment, causing the OEE to drop significantly compared to a flexible standalone operation.

The only successful backend automation ‘line’ that survived and found its justification is the turret handler. These handlers combine test and final packaging. These handlers are a fast and reliable solution for simple devices, and applications, when long setup times and limited parallelism and temperature test capability are acceptable. Turret handlers are the dominant solution for the discrete jelly bean test market.

Why is the backend getting serious in the move into automation? What boundary conditions changed? Who are the drivers?

With the new generation of collaborating robots there is the ability to get AGVs (autonomous guided vehicles) with robots onto the test floor in parallel with human operators and technicians without any safety concerns. This was not possible before and is now opening options that used to be prohibited due to safety concerns. The automated material handling of standalone gravity, pick & place, strip test and turret test handlers is becoming feasible and manageable.

Historically the transition of test floors into low labor countries used to be one of the answers to manage and reduce the backend cost. However, these low labor countries are now getting into significant cost pressure themselves. And European semiconductor companies, that want to keep backend operations in Europe, are forced to get even more efficient and go for the next evolutionary automation step to reduce the cost of the equipment idle times during material exchange. Because of this effect, Europe has been at the forefront of factory automation efforts with its so called ‘Industry 4.0’.

Singapore has a different reason for embracing factory automation. One of the first low cost manufacturing bases in Asia is now quite expensive with regards to operational costs. In addition it has a people problem as it cannot source enough production workers. Singapore has limited living space, and with the country’s economic and industrial evolution, more high skilled jobs are required putting a squeezing the ability of production workers being able to afford to live in the country. The Singapore government therefore is funding development projects for factory automation and is subsidizing companies’ automation projects.

With these changed boundary conditions, and the mentioned driving factors, the first automation implementation projects began in Europe, Singapore and Korea. Once they get effective in HVM, it is expected, that the cost pressure will force its implementation in the lower cost countries. The automation race is on.

Please contact us if you are interested, how we prepared our handling equipment for test floor automation.
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Flat Probe Technology for RF Test

Today the semiconductor test market is very competitive. This is especially true in the consumable contactor market.
Low operating costs and low average selling prices create low barriers to entry. Micro-organizations plants themselves next to their sole customer and provides fast turn times at competitive prices and onsite support. Although this is acceptable for some it is a risky business model. Furthermore the depth of knowledge of the product and therefore the value add from these micro-organizations is limited.
Outsourcing components can diminish the value add of the end product and lead to finger pointing and delivery delays. These factors push organization toward more stable and established vendors that can not only provide fast turn times and good support but they can focus on R&D and new product development.  The ability of these organizations to fund R&D has resulted in revolutionary “flat probe” technologies that combine both electrical and mechanical performance at a significantly lower cost point than traditional radial spring probe technologies.

Larger spring diameters allow more force with less spring length allowing shorter and narrower probes than possible with radial technology. Furthermore the external plunger surfaces allow superior plating than in the internal surfaces of a barrel. Hard base materials offer longer life with lower contact resistance. Finally, with proper attention to the “guts” of the probe design, flat probe technologies can be used for high frequency semiconductor test applications. This presentation will introduce various flat probe technologies and compare and contrast their designs against other flat probe technologies as well as against radial probe technologies.

Download the presentation of Jason Mroczkowski, Director RF Product Development and Marketing IPG, which was awarded “Best Tutorial” at BiTS 2017:

Download the full presentation

 

MEMS sensor testing challenges and requirements

Andreas Bursian, Director InStrip & InMEMS Products, authored an article for Chip Scale Review Magazine, in which he elaborates on the question of what the test requirements for MEMS sensor devices will be in the future. Before he goes into detail, he describes in general what our world will look like in the future shaped by IoT and Industry 4.0., and how this will drive MEMS and sensor technology. Industry 4.0 and IoT are small components of a rapid global change that experts tend to call the 4th Industrial Revolution. This revolution will change all aspects of today’s living, such as cash flow, data handling, job structure, and the political and social structures of society and the industrial production of goods.

Download the full article published in Chip Scale Review March 2017

What, when, where – the move to 5G

We recently attended the MWC in Barcelona. It is clear 5G is going to happen; it is just not clear on when it will arrive, and what it will actually consist of when it does.

5G Progress

In terms of when, some industry players stated 5G will be earlier than 2020, while others stated later than 2020. Those that ‘want’ it earlier, justified it as ‘the technology that is being used is well understood’; i.e Defense/Mil/Aero have used these technologies, in most cases having either invented or made the technology(ies) viable to manufacture and deploy – albeit in smaller quantities and much higher price points and footprint than what the consumer market for Wireless can support.

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2.5D Adds Test Challenges: Advanced packaging issues in testing interposers, TSVs

OSATs and ATE vendors are making progress in determining what works and what doesn’t in 2.5D packaging, expanding their knowledge base as this evolves into a mainstream technology. Most experts believe that full 3D packaging is at least five years away from mainstream deployment. 2.5D, in contrast, already has made inroads in markets where price sensitivity is low and demand for throughput to memory is extremely high, such as networking, server and graphics applications. Andy Nagy, Senior Director Marketing HG & TCI Operations at Xcerra, recently highlighted the challenges in test handling in an interview with Jeff Dorsch, Semiconductor Engineering. The article compiles thoughts of the key players in this market.

Read the full article here: http://semiengineering.com/2-5d-adds-test-challenges/