Foil tension variations may create distortion and unpredictable print deposition. A novel method for foil characterization and verification is proposed.

Typical foil mounting methods involve stretching a woven fabric, typically polyester, across an aluminum frame, creating a taut screen (Figure 1). There appears to be no standard for mesh tensioning values, but different sources report a range of 25 to 35 N/cm¹. The thin metal foil is placed and bonded on the bottom of the frame, and the mesh covering the squeegee side is cut away. The mesh tension will suspend the bonded metal foil, holding it taut. IPC-7525B is informative regarding stencil design guidelines and various terminology. In this mounted state the tension of the actual foil is rarely verified due to lengthy verification and specialized tools.

Densely populated printed circuit boards and fine printing features make planarity and consistency from frame to frame important. Variation negates any precision established in the stencil printer design and manufacture.

Among the concerns for mesh mounted stencils:

• Aluminum frame: Planarity variability, bow under tension (different wall thickness).
• Mesh to frame: Variable tension, gluing variability.
• Foil to mesh: Foil flatness, gluing variability.
• Hand-assembled: Operator-dependent.

Alternative stencil mounting technology involves a reusable metal foil mounted to a reusable master frame, tensioning by either pneumatic bladder or a multitude of levers and springs. This technology is targeted at addressing the space and planarity drawbacks of mesh-mounted stencils. Tensioning of the foil in a master frame is created by either air bladders or springs attempting to emulate the mesh mount tensioning characteristics. This technology has been touted as having better tensioning characteristics than mesh-mounted stencils. However, as seen in Figure 2, a different tensioning trait can be seen.

Tension versus elasticity. Within this specific research, we found it difficult to comprehend the use of the term of “tension” in a system that now uses a steel plate or steel membrane for print deposition. Therefore, following definitions are highlighted for clarity and understanding of the correct terms to be used and how this paper will refer to them:

• Tension. Tension is the pulling force exerted by a string, cable, chain, or similar solid object on another object. In the case of today’s stencils it is the lateral force pulling on the foil by either the tension of the mesh in a mesh mount stencil frame or the spring/pneumatic force derived by reusable tensioning frames.
• Elasticity. Elasticity is a physical property of materials that return to their original shape after they are deformed. How this applies to stencil systems of today is it is the characteristic of the foil property returning to its original position after a force has been applied and then removed. The tensioning system applied to the foil/steel plate maintains the plate in a state of planarity. Any force applied will deform the plate by a proportionate amount. This is explained by Hooke’s law, a principle of physics that states the force needed to extend or compress a spring by some distance is proportional to that distance.

From these definitions, it is clear that the true property and characteristic of a stencil system should be measured by the spring constant k. This is a measure of elasticity of a spring that in our specific stencil systems is the stencil foil.

k = ΔF/Δx

where

ΔF = Force applied to the foil to displace
Δx = The distance moved by the force applied.

Area mapping of elasticity across the foil. To understand the characteristics of elasticity across the various stencil mounting technologies, a measurement methodology must be employed. A novel, patent-pending, fast real-time mapping system for foil characteristics utilizes complex resonance algorithms to determine regional characteristics of the foil. The tool used for our initial characterization is an RST Gage SMT Foil Analyzer1. This system consists of a known weight, a floating dial indicator and a gantry mechanism. The gantry system rests on the outer frame, suspending the dial indicator in the selected region. The dial indicator is set to touch the foil and zeroed. Applying the known weight on to the dial indicator will deflect the foil; therefore, a deflection measurement will be displayed.
Each displacement reading is converted into N/cm by the formula k = ΔF/Δx.

Nine points are taken across the foil area² (Figure 3), and for graph smoothing, additional data points are interpolated from the nine point reading. The types of stencils characterized are:

• Standard mesh mounted from different suppliers.
• Space saver mesh mounted frames.
• Mesh-less foil mounted system from manufacturer A.
• Mesh-less foil mounted system from manufacturer B.

Test Readings

The following surface plots represent the plotted regions of each stencil system. These graphs are a visual representation of how the foil is behaving in its relative mounting system. The narrower the lines, the greater the range/deviation.

Mesh mount – standard 29” x 29”. The following outlines the format and characteristic of the mesh mounted stencils under test (Figure 4).

• Vendor A – Range across the foil = 10 N/cm, foil center = 40 N/cm.
• Vendor B – Range across the foil = 5 N/cm, foil center = 38 N/cm.
• Vendor C – Range across the foil = 9 N/cm, foil center = 39 N/cm.

As can be seen by the surface plots, patterns are starting to appear. It is clear that the corners of the foils are undergoing higher stress than their center points, resulting in a dishing effect.

Mesh mount – space saver 29” x 29”. Figure 5 shows surface plots of production stencils from the same vendor.

• Vendor D-a – Range across the foil = 15 N/cm, foil center = 41 N/cm.
• Vendor D-b – Range across the foil = 11 N/cm, foil center = 49 N/cm.
• Vendor D-c – Range across the foil = 22 N/cm, foil center = 23 N/cm.

Once again the dish-shaped patterns are occurring. Surface plot “D-c” was of a stencil that showed delamination around the foil. The data show clear indication of non-normal distribution and need for replacement.

Mesh-less tensioning systems. This test is directed at characterizing the two most popular tensioning systems. One test is to use one master frame with different foils, and one test with two master frames is from the same supplier with one foil. This was based on availability of master frames and foils at the time of the test.

Test 1: Same frame, different foils. With the mesh-less surface plots, pattern characteristics are appearing similar to the mesh-mounted stencils, but clearly the stress intensity is far greater on these tensioning devices (Figure 6). These patterns still reflect the foil corners undergoing higher stress than their center points, and the dishing effect is greatly exaggerated.

• Vendor E-a – Range across the foil = 40 N/cm, foil center = 47 N/cm.
• Vendor E-b – Range across the foil = 16 N/cm, foil center = 28 N/cm.
• Vendor E-c – Range across the foil = 24 N/cm, foil center = 51 N/cm.

Test 2: Same foil, two different master frames by same supplier. See Figure 7.

• Vendor F-a – Range across the foil = 21 N/cm, Foil Center = 47 N/cm
• Vendor F-b – Range across the foil = 24 N/cm, Foil Center = 44 N/cm
• Vendor F-c – Range across the foil = 25 N/cm, Foil Center = 45 N/cm

Summary of Elasticity Results

Although the patterns of both types of mounting technology have similar traits – higher in the corners, lower in the center – the spring/pressure tensioned systems display higher center elastic force and greater range across the whole foil area compared with the mesh-mounted stencils.

The typical stencil central point value is around 40 N/cm of a newer mesh-mounted stencil. The deviation from this value across the foil area is +10 N/cm (25% deviation).

For the mesh-less systems, the typical central point value is 46 N/cm, with a typical range deviation from this value of +20 N/cm (43.5% deviation).

As both systems (mesh mount and tensioning frames) have been in full production worldwide for years, there has been no specific evidence that one works better than the other with regard to print deposition performance. For discussion: If the perceived tension of a stencil is that the higher the better, then would that imply that the corners of each foil system print better than the center? Maybe edge-justified stencils print better than center-justified stencils? Either way, it would make better sense if these values were tightly controlled frame to frame, foil to foil where this consistency would remove variation and doubt from this argument.

The concentrated effort toward higher performance stencils for improving the transfer efficiency on smaller features is attempting to use the higher tension model to achieve better print performance. Given the effects of surface energies of stencil apertures, variations of solder paste chemistries and PCB surfaces/topography, it would also stand to reason that each individual image in the stencil will bring about infinite variables, due to positioning and sizes of the printing features within this image. On a side note, if the foil is to be held in a planar state during board separation for increased paste release performance, the mass of solder paste resting on the top side will clearly deform the stencil during the separation sequence.

In Figure 8, a represents the idealistic yet unrealistic stencil to board during the print separation process; b represents a slack foil and how it will sag based on little to no applied tension, and c represents a taut foil with a paste mass on the squeegee side. As the board separates, the unsupported paste mass will deflect the foil, causing a sag and therefore potentially uncontrolled separation. As the paste mass/bead deteriorates in size, so does its mass; therefore, the effect is lesser on the separation process.

As an exercise using the Catenary curve equation and a paste mass of 500g, it would take a tension force of over 300,000 N/cm to overcome the sag caused by the effect of the paste mass.

Area mapping of resonance across the foil. The Equi-Tone handheld device has been developed as a quick and objective measurement method/device. First phase development results are very encouraging.

Harmonic oscillation. Given Hooke’s law and our perspective that a stencil be viewed as a spring, then pulling the foil and releasing would set it into oscillation about its equilibrium position. However, due to the various mounting system techniques, the foil as a spring will be affected at a location across its area, bringing about different oscillations within these locations.

To test this theory, all the above tested stencils were compared with measuring the frequency responses in each of the nine locations previously selected and tested.

Frequency response across the foil. Moving a frequency recording device around each of the previously selected nine points highlighted not only patterns, but uncovered unwanted overtones. Split frequencies, beat frequencies and other mixed frequencies are noise to our signal. To isolate the primary frequency at each location, the use of Fast Fourier Transform (FFT) Spectrum Analyzer (Figure 9) and sophisticated filtering was required. These techniques would eliminate any false readings and overtones, and a stable primary frequency response could be isolated.

It is clear that the frequencies generated were complex and required various filtering to identify the primary frequency. Once this was achieved, the novel device was able to accurately and repeatedly identify the specific tone.

The testing and comparison study could then take place, with the results plotted below.

Novel device v. displacement. Using the novel device, each of the previously measured stencils was tested for comparison. The frequency data collected were paired and plotted with their respective stencils. As seen below, the patterns generated resemble the N/cm plots fairly closely.

Summary

It is clear from these findings that the steel used in stencils will deflect based on its own elastic properties. The mesh-mounted stencil and newer direct-tensioned frames are shown to have similar patterns. The mesh-mounted stencils have two modes of elasticity: one being the mesh, the other the foil. The lower elastic properties of the mesh permit the foil to be more coplanar under stress than are direct-tensioned foils. Direct-tensioned systems clearly distort the foil and create larger deviations across the foil area. This phenomenon is counterintuitive when it comes to the idea of uniform separation between foil and board post-print. Further increasing the tension applied to the foil in these direct-tensioned systems may create further distortion and is therefore likely to create unpredictable print depositions. This research also points out that there are clear differences not only among vendor-to-vendor master frame technologies, but also different master frames from the same supplier.

Compared to other analyzers, the novel device clearly shows it can plot similar characteristics when area mapping the foil. Therefore, it is a viable alternative tool for fast and convenient foil characterization and verification.

Subsequent research will look at how these technologies and their elastic properties affect print deposition.

References

1. RST Gauge, company website.
2. Murakami Screen, company website.

Ricky Bennett, Ph.D., is founder of Lu-Con Technologies; rbennett@lu-con.com. Richard Lieske is director of applied product development at Lu-Con Technologies. 

Up next for the task group: defining build-intent.

A very large percentage of PCB designs today are sent to manufacturing using a myriad of different file formats. The correlation between the data in these different file formats becomes the responsibility of the manufacturer and their partner at the systems company. Much time and effort is spent in automating this process to ensure that the data provided meet the designer’s fabrication, assembly and test intentions. For small companies it’s typically manual.

IPC-2581 replaces this process of providing multiple files in different formats (that requires an efficient methodology to be successful) and saves millions of dollars wasted by its inadequacies. As with any data format specification, adoption accelerates only after the supply chain produces, consumes and supports such a specification. A consortium of PCB design and supply chain companies was created to bring companies together to enable, facilitate and drive use of IPC-2581. The charter of the IPC-2581 Consortium is to accelerate the adoption of IPC-2581 as an open, neutrally maintained global standard to encourage innovation, improve efficiency and reduce costs.

The consortium is open to any PCB design/supply chain company that is prepared to adopt its goals/objectives and commit to a roadmap for IPC-2581 adoption.

Major milestones. As with any standard that describes the entire PCB data, it is important to ensure it is interpreted correctly by all the software that produces and consumes the data. As such, the consortium set an aggressive goal of validating that the producers and consumers interpreted fabrication data accurately by end of January 2012, with a goal of fabricating the first PCB by September 2012. These goals were met. From the startup in mid 2011 through January 2012, consortium members developed software that produced and consumed PCB design data in IPC-2581 format. During the validation process they identified and addressed specification interpretation issues, discovered, compiled and tracked extensions needed to improve efficiency further.

Throughout 2011 and the first half of 2012, the consortium added new members. Three of the consortium members – Fujitsu Network Communications, Wise Software and CC Electronics – collaborated to build the first PCB using only IPC-2581 data. They discovered that the board was built with no iterations between CC Electronics and Fujitsu and that the fabrication setup time was reduced by 30% over the traditional approach of using multiple files in different formats. This first PCB was demonstrated at PCB West last September.

Today, the consortium has 46 members from the electronics supply chain and continues to grow. Eight software companies have released software that supports IPC-2581, and four others plan to support IPC-2581 in the near future. Complete information on the IPC-2581 support status with software version numbers is listed at ipc2581.com/index.php/validation-status.

Bi-directional build-intent collaboration. More recently, the consortium is on track to extend the standard beyond that which any other approach can do. Members have begun working on extending the standard to enable build-intent collaboration between PCB manufacturers and design houses before layout begins. Consortium members brainstormed this idea and developed a proposal in 2012, then proposed it at an IPC working group meeting hosted by Cadence in Chelmsford, MA. Active participation from the members has made it possible to innovate through improvements in the IPC-2581 standard. In addition to extending the standard to exchange build-intent (stack ordering, material types, etc.) before the layout begins, the next version of IPC-2581 will include the following changes:

• Ability to define build-intent through stack ordering, material types, technology attributes, stack-up composites.
• Expanded BoM section to include stackup.
• Geometry object fill types, line types, user-defined primitives.
• Backdrilling support.
• Pin one, origin/orientation standard criteria, pick-up point for packages.
• Pad stack reference definitions.
• Z-axis definition, V-groove cavity/slot support.
• Ability to add more notes on design intent in the Spec section.

Companies across the entire PCB design and supply chain companies – from software companies that develop PCB design and manufacturing tools to systems companies to manufacturers – are collaborating on the standard. The IPC-2581 Consortium is continuing to accelerate the adoption of IPC-2581 as an open, neutrally maintained global standard to encourage innovation, improve efficiency and reduce costs.

Hemant Shah is product marketing director, Cadence Design Systems (cadence.com); shah@cadence.com.

From components to wrist straps, a look at more than 60 documents that make up ESD control programs.

Industry standards play a major role in providing meaningful metrics and common procedures that permit manufacturers, customers and suppliers to communicate from facility to facility around the world. Standards are increasingly important in our global economy. In manufacturing, uniform quality requirements and testing procedures are necessary to make sure all involved are speaking the same language. In ESD device protection, standard methods have been developed for component ESD stress models to measure a component’s sensitivity to electrostatic discharge from various sources. In ESD control programs, standard test methods for product qualification and periodic evaluation of wrist straps, garments, ionizers, worksurfaces, grounding, flooring, shoes, static dissipative planar materials, shielding bags, packaging, electrical soldering/desoldering hand tools, and flooring/footwear systems have been developed to ensure uniformity around the world.

The EOS/ESD Association, Inc. (ESDA) is dedicated to advancing the theory and practice of electrostatic discharge (ESD) protection and avoidance. The ESDA is an American National Standards Institute (ANSI) accredited standards developer. The association’s consensus body is called the Standards Committee (STDCOM), which has responsibility for the overall development of documents. Industry volunteers participate in working groups to develop new and  update current ESDA documents.

STDCOM is charged with keeping pace with the industry demands for increased performance. The existing standards, standard test methods, standard practices and technical reports assist in the design and monitoring of the electrostatic protected area (EPA), and also assist in the stress testing of ESD sensitive electronic components. Many existing documents relate to controlling electrostatic charge on personnel and stationary work areas. However, with increasing emphasis on automated handling, the need to evaluate and monitor what is occurring inside of process equipment is growing daily. Since automation has become more dominant, the charged device model (CDM) has become the primary cause of ESD failures and thus the more urgent concern. Together, the human body model (HBM) and charged device model cover the vast majority of ESD events that might occur in a typical factory.

The ESDA document categories are:

• Standard (S): A precise statement of a set of requirements to be satisfied by a material, product, system or process that also specifies the procedures for determining whether each of the requirements is satisfied.
• Standard Test Method (STM): A definitive procedure for the identification, measurement and evaluation of one or more qualities, characteristics or properties of a material, product, system or process that yield a reproducible test result.
• Standard Practice (SP): A procedure for performing one or more operations or functions that may or may not yield a test result. Note: If a test result is obtained, it may not be reproducible.
• Technical Report (TR): A collection of technical data or test results published as an informational reference on a specific material, product, system or process.

The ESDA Technology Roadmap is compiled by industry experts in IC protection design and test to provide a look into future ESD design and manufacturing challenges. The roadmap previously pointed out that numerous mainstream electronic parts and components would reach assembly factories with a lower level of ESD protection than could have been expected just a few years earlier. This prediction has proved rather accurate. As with any roadmap, the view of the future is constantly changing and requires updating on the basis of technology trend updates, market forces, supply-chain evolution and field return data. An updated roadmap was published in March, and industry experts extended the horizon beyond the 2013 predictions. It contains, for the first time, a roadmap for the evolution of ESD stress testing. This includes forward-looking views of possible changes in the standard device level tests (HBM and CDM), as well as the expected progress in other important areas, such as transmission line pulsing (TLP), transient latch-up (TLU), cable discharge events (CDE), and charged board events (CBE). A view of work on electrical overstress (EOS) has also been included. EOS is an area that has long been overlooked by the industry, not because it was not important but because it could be a difficult threat to define and mitigate. Recently, a working group has been focusing on this area and will soon be publishing a technical report (TR) that helps establish some fundamental definitions and distinctions between various EOS threats. The TR will be followed by a “best practices” document outlining ways to mitigate EOS threats. Another development has been a request by the aerospace industry for an ESD control document that defines more definitively what ESD controls need to be in place in aerospace manufacturing factories. This document will be predicated on ANSI/ESD S20.20 but will introduce further limits and controls.

The ESDA Standards Committee is continuing several joint document development activities with the JEDEC Solid State Technology Association. Under the memorandum of understanding, the ESDA and JEDEC formed a joint task force for the standardization work. This collaboration has paved the way for development of harmonized test methods for ESD, which will ultimately reduce uncertainty about test standards among manufacturers and suppliers in the solid state industry. At the time of this publication, ANSI/ESDA/JEDEC JS-001-2012, a third revision of the joint HBM document, has been released for distribution. This document replaces ANSI/ESDA/JEDEC JS-001-2011, the current industry test methods and specifications for human body model device testing. A second joint committee is currently working on a joint charged device model (CDM) document with a goal of publishing in 2014. These efforts will assist manufacturers of devices by providing one test method and specification instead of multiple, almost – but not quite – identical, versions of device testing methods.

The ESDA is also working on a process assessment document. The purpose of this document is to describe a set of methodologies, techniques and tools that can be used to characterize a process where ESD-sensitive items are handled. The goal is to characterize the ability of a process to safely handle ESD-sensitive devices that have been characterized by the relevant device testing models. The document will apply to activities that manufacture, process, assemble, install, package, label, service, test, inspect, transport, or otherwise handle electrical or electronic parts, assemblies, and equipment susceptible to damage by electrostatic discharges. At the present time, this document will not apply to electrically initiated explosive devices, flammable liquids or powders.

The ESDA standard covering the requirements for creating and managing an ESD control program is ANSI/ESD S20.20, “ESD Association Standard for the Development of an Electrostatic Discharge Control Program for – Protection of Electrical and Electronic Parts, Assemblies and Equipment (Excluding Electrically Initiated Explosive Devices).” ANSI/ESD S20.20 is a commercial update of and replacement for MIL-STD-1686 and has been adopted by the US Department of Defense. In addition, the 2007-2008 update of IEC 61340-5-1 edition 1.0 “Electrostatics - Part 5-1: Protection of Electronic Devices from Electrostatic Phenomena General Requirements” is technically equivalent to ANSI/ESD S20.20. A five-year review of ANSI/ESD S20.20 has begun, and technical changes are being made to the document based on industry changes and user requests. Unique constraints with the revision must be taken into account, including facility certification and continued harmonization with other standards: IEC 61340-5-1 and newly revised JEDEC 625B. A target date of September 2013 has been given for the release of a draft document.

In order to meet the global need in the electronics industry for technically sound ESD control programs, the ESDA has established an independent third-party certification program. The program is administered by the EOS/ESD Association through country-accredited ISO 9000 certification bodies that have met the requirements of this program. The facility certification program evaluates a facility’s ESD program to ensure that the basic requirements from industry standards ANSI/ESD S20.20 or IEC 61340-5-1 are being followed. More than 519 facilities have been certified worldwide since inception of the program. The factory certification bodies report strong interest in certification to ANSI/ESD S20.20, and consultants in this area report that inquiries for assistance remain at a very high level. Individual education also seems of interest once again, as 46 professionals have obtained Certified ESD Program Manager status, and many more are attempting to qualify as Certified ESD Control Program Managers. A large percentage of the certification program requirements are based on standards and the other related documents produced by the ESD Association Standards Committee.

Current ESD Association Standards Committee Documents

Charged Device Model (CDM). ANSI/ESD S5.3.1-2009 Electrostatic Discharge Sensitivity Testing - Charged Device Model (CDM) - Component Level: Establishes the procedure for testing, evaluating, and classifying the ESD sensitivity of components to the defined CDM.

Cleanrooms. ESD TR55.0-01-04 Electrostatic Guidelines and Considerations for Cleanrooms and Clean Manufacturing: Identifies considerations and provides guidelines for the selection and implementation of materials and processes for electrostatic control in cleanroom and clean manufacturing environments. (Formerly TR11-04)

Compliance verification. ESD TR53-01-06 Compliance Verification of ESD Protective Equipment and Materials: Describes the test methods and instrumentation that can be used to periodically verify the performance of ESD protective equipment and materials.

Electronic design automation (EDA). ESD TR18.0.01-11 – ESD Electronic Design Automation Checks: Provides guidance for EDA industry and ESD design community for establishing a comprehensive ESD electronic design automation verification flow satisfying the ESD design challenges of modern ICs.

ESD control program. ANSI/ESD S20.20-2007 Protection of Electrical and Electronic Parts, Assemblies and Equipment (Excluding Electrically Initiated Explosive Devices): Provides administrative and technical requirements for establishing, implementing, and maintaining an ESD Control Program to protect electrical or electronic parts, assemblies, and equipment susceptible to ESD damage from Human Body Model (HBM) discharges greater than or equal to 100V.

ESD TR 20.20-2008—ESD Handbook (Companion to ANSI/ESD S20.20): Produced specifically to support ANSI/ESD S20.20 ESD Control Program standard, this 132-page document is a major rewrite of the previous handbook. It focuses on providing guidance that can be used for developing, implementing, and monitoring an ESD control program in accordance with S20.20.

Flooring. ANSI/ESD STM7.1-2012 Resistive Characterization of Materials – Floor Materials: Covers measurement of the electrical resistance of various floor materials, such as floor coverings, mats, and floor finishes. It provides test methods for qualifying floor materials before installation or application, and for evaluating and monitoring materials after installation or application.

ESD TR7.0-01-11 Static Protective Floor Materials: This technical report reviews the use of floor materials to dissipate electrostatic charge. It provides an overview on floor coverings, floor finishes, topical antistats, floor mats, paints and coatings. It also covers a variety of other issues related to floor material selection, installation and maintenance.

Flooring and footwear systems. ANSI/ESD STM97.1-2006 Floor Materials and Footwear – Resistance Measurement in Combination with a Person: Provides test methods for measuring the electrical system resistance of floor materials in combination with person wearing static control footwear.

ANSI/ESD STM97.2-2006 Floor Materials and Footwear – Voltage Measurement in Combination with a Person: Provides for measuring the electrostatic voltage on a person in combination with floor materials and footwear, as a system.

Footwear. ANSI/ESD STM9.1-2006 Footwear – Resistive Characterization: Defines a test method for measuring the electrical resistance of shoes used for ESD control in the electronics environment (not to include heel straps and toe grounders).

ESD SP9.2-2003 Footwear – Foot Grounders Resistive Characterization: Provides test methods for evaluating foot grounders and foot grounder systems used to electrically bond or ground personnel as part of an ESD Control Program. Static Control Shoes are tested using ANSI/ESD STM9.1.

Garments. ESD DSTM2.1-2013 Garments - Resistive Characterization: Provides test methods for measuring the electrical resistance of garments. It covers procedures for measuring sleeve-to-sleeve resistance and point-to-point resistance. This is a draft document.

ESD TR2.0-01-00 Consideration for Developing ESD Garment Specifications: Addresses concerns about effective ESD garments by starting with an understanding of electrostatic measurements and how they relate to ESD protection. (Formerly TR05-00)

ESD TR2.0-02-00 Static Electricity Hazards of Triboelectrically Charged Garments: Intended to provide some insight to the electrostatic hazards present when a garment is worn in a flammable or explosive environment. (Formerly TR06-00)

Glossary. ESD ADV1.0-2012 Glossary of Terms: Definitions and explanations of various terms used in Association Standards and documents are covered in this Advisory. It also includes other terms commonly used in the electronics industry.

Gloves and finger cots. ANSI/ESD SP15.1-2011 In-Use Resistance Testing of Gloves and Finger Cots: Provides test procedures for measuring the intrinsic electrical resistance of gloves and finger cots.

ESD TR15.0-01-99 ESD Glove and Finger Cots: Reviews existing known industry test methods for the qualification of ESD protective gloves and finger cots. (Formerly TR03-99)

Grounding. ANSI/ESD S6.1-2009 Grounding: Specifies parameters, materials, equipment and test procedures necessary to choose, establish, vary, and maintain an Electrostatic Discharge Control grounding system for use within an ESD Protected Area for protection of ESD susceptible items, and specifies the criteria for establishing ESD Bonding.

Handlers. ANSI/ESD SP10.1-2007 Automated Handling Equipment (AHE): Provides procedures for evaluating the electrostatic environment associated with automated handling equipment.

ESD TR10.0-01-02 Measurement and ESD Control Issues for Automated Equipment Handling of ESD Sensitive Devices below 100 Volts: Provides guidance and considerations that an equipment manufacturer should use when designing automated handling equipment for these low voltage sensitive devices. (Formerly TR14-02)

Hand tools. ESD STM13.1-2000 Electrical Soldering/Desoldering Hand Tools: Provides electric soldering/desoldering hand tool test methods for measuring the electrical leakage and tip to ground reference point resistance, and provides parameters for EOS safe soldering operation.

ESD TR13.0-01-99 EOS Safe Soldering Iron Requirements: Discusses soldering iron requirements that must be based on the sensitivity of the most susceptible devices that are to be soldered. (Formerly TR04-99)

Human body model (HBM). ANSI/ESDA/JEDEC JS-001-2012 ESDA/JEDEC Joint Standard for Electrostatic Discharge Sensitivity Testing – Human Body Model (HBM) – Component Level: Establishes procedure for testing, evaluating, and classifying the electrostatic discharge sensitivity of components to the defined human body model (HBM).

ESD JTR001-01-12, ESD Association Technical Report User Guide of ANSI/ESDA/JEDEC JS-001 Human Body Model Testing of Integrated Circuits:
Describes the technical changes made in ANSI/ESDA/JEDEC JS-001-2011 (contained in the new 2012 version) and explains how to use those changes to apply HBM (Human Body Model) tests to IC components.

Human Metal Model (HMM). ANSI/ESD SP5.6-2009 Electrostatic Discharge Sensitivity Testing - Human Metal Model (HMM) - Component level: Establishes procedure for testing, evaluating, and classifying the ESD sensitivity of components to the defined HMM.

ESD TR5.6-01-09 Human Metal Model (HMM): Addresses the need for a standard method of applying the IEC contact discharge waveform to devices and components.

Ionization. ANSI/ESD STM3.1-2006 Ionization: Test methods and procedures for evaluating and selecting air ionization equipment and systems are covered in this standard test method. The document establishes measurement techniques to determine ion balance and charge neutralization time for ionizers.
ANSI/ESD SP3.3-2012 Periodic Verification of Air Ionizers: Provides test methods and procedures for periodic verification of the performance of air ionization equipment and systems (ionizers).

ANSI/ESD SP3.4-2012 Periodic Verification of Air Ionizer Performance Using a Small Test Fixture: Provides a test fixture example and procedures for performance verification of air ionization used in confined spaces where it may not be possible to use the test fixtures defined in ANSI/ESD STM3.1 or ANSI/ESD SP3.3.
ESD TR3.0-01-02 Alternate Techniques for Measuring Ionizer Offset Voltage and Discharge Time: Investigates measurement techniques to determine ion balance and charge neutralization time for ionizers. (Formerly TR13-02)

ESD TR3.0-02-05 Selection and Acceptance of Air Ionizers: Reviews and provides a guideline for creating a performance specification for the four ionizer types contained in ANSI/ESD STM3.1: room (systems), laminar flow hood, worksurface (e.g., blowers), and compressed gas (nozzles & guns). (Formerly ADV3.2-1995)
Machine Model (MM). ANSI/ESD STM5.2-2012 Electrostatic Discharge Sensitivity Testing - Machine Model (MM) - Component Level: Establishes procedure for testing, evaluating, and classifying the ESD sensitivity of components to the defined MM.

ANSI/ESD SP5.2.1-2012 Human Body Model (HBM) and Machine Model (MM) Alternative Test Method: Supply Pin Ganging – Component Level: Defines an alternative test method to perform Human Body Model or Machine Model component level ESD tests when the component or device pin count exceeds the number of ESD simulator tester channels. (Formerly ANSI/ESD SP5.1.1-2006)

ANSI/ESD SP5.2.2-2012 Human Body Model (HBM) and Machine Model (MM) Alternative Test Method: Split Signal Pin - Component Level: Defines an alternative test method to perform Human Body Model or Machine Model component level ESD tests when the component or device pin count exceeds the number of ESD simulator tester channels. (Formerly ANSI/ESD SP5.1.2-2006)

ESD TR5.2-01-01 Machine Model (MM) Electrostatic Discharge (ESD) Investigation - Reduction in Pulse Number and Delay Time: Provides procedures, results and conclusions of evaluating a proposed change from 3 pulses (present requirement) to 1 pulse while using a delay time of both 1 second (present requirement) and 0.5 second. (Formerly TR10-01)

Ohmmeters. ESD TR50.0-02-99 High Resistance Ohmmeters – Voltage Measurements: Discusses a number of parameters that can cause different readings from high resistance meters when improper instrumentation and techniques are used and the techniques and precautions to be used in order to ensure the measurement will be as accurate and repeatable as possible for high resistance measurement of materials. (Formerly TR02-99)

Packaging. ANSI/ESD STM11.11-2006 Surface Resistance Measurement of Static Dissipative Planar Materials: Defines a direct current test method for measuring electrical resistance, replacing ASTM D257-78. This test method is designed specifically for static dissipative planar materials used in packaging of ESD-sensitive devices and components.

ANSI/ESD STM11.12-2007 Volume Resistance Measurement of Static Dissipative Planar Materials: Provides test methods for measuring the volume resistance of static dissipative planar materials used in the packaging of ESD sensitive devices and components.

ANSI/ESD STM11.13-2004 Two-Point Resistance Measurement: Measures the resistance between two points on a material's surface without consideration of the material's means of achieving conductivity. This test method was established for measuring resistance where the concentric ring electrodes of ANSI/ESD STM11.11 cannot be used.

ANSI/ESD STM11.31-2012 Bags: Provides a method for testing and determining the shielding capabilities of electrostatic shielding bags.

ANSI/ESD S11.4-2012 Performance Limits for Bags: Establishes performance limits for bags that are intended to protect electronic parts and products from damage due to static electricity and moisture during common electronic manufacturing industry transport and storage applications. This is a draft document.

ANSI/ESD S541-2008 Packaging Materials for ESD Sensitive Items: Describes the packaging material properties needed to protect ESD-sensitive electronic items, and references the testing methods for evaluating packaging and packaging materials for those properties. Where possible, performance limits are provided. Guidance for selecting the types of packaging with protective properties appropriate for specific applications is provided. Other considerations for protective packaging are also provided.

ESD ADV11.2-1995 Triboelectric Charge Accumulation Testing: Provides guidance in understanding the triboelectric phenomenon and relates current information and experience regarding tribocharge testing as used in static control for electronics.

Seating. ESD DSTM12.1-2013 Seating – Resistive Measurement: Provides test methods for measuring the electrical resistance of seating used for the control of electrostatic charge or discharge. It contains test methods for the qualification of seating prior to installation or application, as well as test methods for evaluating and monitoring seating after installation or application. This is a draft document.

Socketed device model (SDM). ANSI/ESD SP5.3.2-2008 Electrostatic Discharge Sensitivity Testing – Socketed Device (SDM) – Component Level: Provides a test method for generating a Socketed Device Model (SDM) test on a component integrated circuit (IC) device.

ESD TR5.3.2-01-00 Socket Device Model (SDM) Tester: Helps user understand how existing SDM testers function, offers help with the interpretation of ESD data generated by SDM test systems, and defines the important properties of an “ideal” socketed-CDM test system. (Formerly TR08-00)

Static electricity. ESD TR50.0-01-99 Can Static Electricity Be Measured? Overview of fundamental electrostatic concepts, electrostatic effects, and most important, of electrostatic metrology, especially what can and cannot be measured. (Formerly TR01-99)

Susceptible device concepts. ESD TR50.0-03-03 Voltage and Energy Susceptible Device Concepts, Including Latency Considerations: Contains information to promote an understanding of the differences between energy and voltage susceptible types of devices and their sensitivity levels. (Formerly TR16-03)

Symbols. ANSI/ESD S8.1-2012 Symbols – ESD Awareness: Three types of ESD awareness symbols are established by this document. The first one is to be used on a device or assembly to indicate that it is susceptible to electrostatic charge. The second is to be used on items and materials intended to provide electrostatic protection. The third symbol indicates the common point ground.

System level ESD. ESD TR14.0-01-00 Calculation of Uncertainty Associated with Measurement of Electrostatic Discharge (ESD) Current: Provides guidance on measuring uncertainty based on an uncertainty budget. (Formerly TR07-00)

ESD TR14.0-02-13 System Level Electrostatic Discharge (ESD) Simulator Verification: Developed to provide guidance to designers, manufacturers, and calibration facilities for verification and specification of the systems and fixtures used to measure simulator discharge currents. (Formerly ANSI/ESD SP14.1)

Transient Latch-up. ESD TR5.4-01-00 Transient Induced Latch-Up (TLU): Provides brief background on early latch-up work, reviews the issues surrounding the power supply response requirements, and discusses the efforts on RLC TLU testing, transmission line pulse (TLP) stressing, and the new bipolar stress TLU methodology. (Formerly TR09-00)

ESD TR5.4-02-08 Determination of CMOS Latch-up Susceptibility - Transient Latch-up - Technical Report No. 2: Intended to provide background information pertaining to development of transient latch-up standard practice originally published in 2004 and additional data presented to the group since publication.

ESD TR5.4-03-11 Latch-up Sensitivity Testing of CMOS/Bi CMOS Integrated Circuits – Transient Latch-up Testing – Component Level Supply Transient Stimulation: Developed to instruct the reader on the methods and materials needed to perform Transient Latch-Up Testing.

Transmission Line Pulse. ANSI/ESD STM5.5.1-2008 Electrostatic Discharge Sensitivity Testing – Transmission Line Pulse (TLP) – Component Level: Pertains to Transmission Line Pulse (TLP) testing techniques of semiconductor components. The purpose of this document is to establish a methodology for both testing and reporting information associated with TLP testing.

ANSI/ESD SP5.5.2-2007, Electrostatic Discharge Sensitivity Testing - Very Fast Transmission Line Pulse (VF-TLP) - Component Level: Pertains to Very Fast Transmission Line Pulse (VF-TLP) testing techniques of semiconductor components. It establishes guidelines and standard practices presently used by development, research, and reliability engineers in both universities and industry for VF-TLP testing. This document explains a methodology for both testing and reporting information associated with VF-TLP testing.

ESD TR5.5-01-08 Transmission Line Pulse (TLP): A compilation of information gathered during the writing of ANSI/ESD SP5.5.1 and information gathered in support of moving the standard practice toward re-designation as a standard test method.

ESD TR5.5-02-08 Transmission Line Pulse Round Robin: Intended to provide data on the repeatability and reproducibility limits of the methods of ANSI/ESD STM5.5.1.

Workstations. ESD ADV53.1-1995 ESD Protective Workstations: Defines minimum requirements for a basic ESD protective workstation used in ESD sensitive areas. It provides a test method for evaluating and monitoring workstations. It defines workstations as having the following components: support structure, static dissipative worksurface, a means of grounding personnel, and any attached shelving or drawers.

Worksurfaces. ANSI/ESD S4.1-2006 Worksurface - Resistance Measurements: Provides test methods for evaluating and selecting worksurface materials, testing of new worksurface installations, and the testing of previously installed worksurfaces.

ANSI/ESD STM4.2-2012 ESD Protective Worksurfaces - Charge Dissipation Characteristics: Aids in determining the ability of ESD protective worksurfaces to dissipate charge from a conductive test object placed on them.

ESD TR4.0-01-02 Survey of Worksurfaces and Grounding Mechanisms: Provides guidance for understanding the attributes of worksurface materials and their grounding mechanisms. (Formerly TR15-02)

Wrist straps. ESD DS1.1-2013 Wrist Straps: A successor to EOS/ESD S1.0, this document establishes test methods for evaluating the electrical and mechanical characteristics of wrist straps. It includes improved test methods and performance limits for evaluation, acceptance, and functional testing of wrist straps. This is a draft document.

ESD TR1.0-01-01 Survey of Constant (Continuous) Monitors for Wrist Straps: Provides guidance to ensure that wrist straps are functional and are connected to people and ground. (Formerly TR12-01)

This column is written by The ESD Association (esda.org); info@esda.org.

Changing economics is moving contract assembly to North America.

In which direction do the economies of electronics production push the manufacturing location? What is the history of the situation and assumptions? And when is it time to reevaluate those assumptions?

In the 1950s and ’60s, US and other Western-based companies moved manufacturing to Japan, where labor was cheap and factories were being rebuilt using enormous investments from the US and its allies. Japan’s quality was initially poor but rapidly improved, and the nation became an economic powerhouse. Along with this increased sophistication came increased cost, and Western companies relocated to Korea where, again, investment poured in after a cease-fire in hostilities.

The Koreans were mindful of the Japanese experience and from the start emphasized quality. This made Korea a better source for electronics assemblies, but their smaller population (25 million Koreans vs. 95 million Japanese in 1960) prompted rapid increases in labor costs. Next stop Taiwan.

The very Western-leaning government in Taipei, combined with a large, educated workforce, made Taiwan an easy fit for American companies. This writer’s personal experience was that working there was much like Bayonne or Bayport: The locals might have displayed a “funny” accent, but followed the same Yankee Doodle drummer. Sophistication and profits escalated, followed by costs. By the turn of the 21st Century, even Taiwanese companies read the kanji on the wall and began to open subsidiaries in mainland China, where land and labor were cheap.

These lower costs coupled with loosening governmental control in mainland China made for fertile ground where companies could expect to grow quickly and dramatically cut costs. There was a scarcity of university-educated engineers and experienced managers, so most startups were not Chinese-based but rather staffed and managed by Japanese, Koreans, and finally the entrepreneurial Taiwanese.

Part of the competitive nature of the Chinese model was based on low labor costs, where human labor was usually more cost-effective than automation. This meant startup capital was low but also made quality difficult to control. When output varied because of the human interface, the parts not-to-specification were simply culled out during inspection and discarded, or sometimes just ignored as being “close enough.”

As the world demanded higher quality, producers in China invested in more automation and higher caliber staff, with increased training and product flow responsibility. Inevitably costs began their upward climb. The price of fuel increased globally and, with it, the cost to ship to customers halfway around the globe, so the competitiveness of China began to wane.

North American sources for contract assembly, having watched their markets shrinking, see a ray of hope. They could compete on the world stage and indeed win the economic struggle, not only against the historical competitors, but also against any of the new, smaller (Vietnam, Thailand) and potentially larger (Brazil, India) low-cost regions.

But we should put off blue sky guestimating and instead review the actual history and trends in China and what has happened to the cost savings that were envisioned just a few years ago.

Supporting data. Five to seven years ago the push to offshore contract assembly was at its peak, and with good reason. US demand was up, and volumes were increasing. US labor and raw material costs had risen dramatically. Cheap knockoffs from Chinese companies were flooding the market. To compete, the US companies chose to join them, not fight them, and began moving first simple subassemblies and then more complete products to LCRs (low-cost regions) like China and Vietnam.

The American consumer cannot blame US companies for migrating east. We wanted more, and we wanted it cheaper. We accepted lower quality because ours was a throwaway society – use it for a while and when it breaks, just buy a cheap replacement. We went from buying just the most basic components offshore to buying completed goods, all made in the world’s LCR.

Today the tide is turning. Changes in currency values have made this a different world. US dollars just do not buy as much offshore as they once did (Figure 1).

Moreover, the environmental mantra of “reduce, reuse, recycle” has taken hold. Americans are willing to pay a bit more for things of a higher quality that might last longer. Would we pay double? Probably not. So where is that tipping point, and how close to it are we? When should producers in this hemisphere investigate onshore contract assembly? Let’s look first at recent changes in cost in the Pacific Rim:

Chinese labor costs have doubled and are expected to rise another 50% in four to five years.
Chinese currency is 30% more expensive; it has surged from RMB 8.11 per $1 to RMB 6.21.
Shipping costs have also increased, some rates by 43%, others by more (Figure 2).



If you left Western shores for contract assembly in the Far East, and you then saved one-half of your production cost, how much of that savings remains today? 15%? 10%? Less (Figure 3)? Even just 10% might be a reason to let the business remain there because, after all, why incur an avoidable cost increase? But are there other issues to consider? The answers might be in the less obvious areas.

Doing business around the world has obvious hurdles, like language. There are also less obvious obstacles like business mindset and ethics. We in the West have standards that differ even on a single continent. We should not be surprised to discover that there is a greater difference between cultures with less history in common. That is not to say that one is better than the other, only that they are different and must be taken into account in negotiations and daily business transactions.

What other practical issues impact an OEM’s business when considering off- vs. onshoring?

• Should you invest in an overseas manufacturing scenario today if there are major aspects over which you have limited control, and there are forecasts of increasing economic pressure (Figure 4)?
• The 12-hr. time difference: How easy is it to have a phone or video conference if one group is just arising, while the other is getting ready for dinner? Is everyone really at the top of their game?
• The 24-hr. trip to have an onsite roundtable discussion: How many staff could you spare at the same time to make the meeting truly productive? And what happens back home while they are gone?
• What are the background, ability and availability of the LCR staff? Do they have the skillset you are used to encountering? Do they smile and nod because they agree or because they do not understand?

Are your quality standards something that they are just willing to accept, or do they wholeheartedly embrace the concept? Are they committed to protect product quality and hence the good name of their clients, or would they walk away from a situation and move on to another client from a different industry or different country? After all, their name is shielded from notoriety by secrecy agreements.

And speaking of secrecy, is intellectual property protected, and how? Agreements for nondisclosure are easy to sign but difficult to enforce when the parties are separated by 8,000 miles, different legal systems and centuries of tradition.

Quantifying these non-monetary aspects is difficult, but we know they exist. When do they, added to the direct cost, warrant moving contract assembly to North America?

The question could be answered with the use of a supercomputer and the services of many an expensive consultant. Or you could bid your next job here and there, compare the economic results, factor in the ease of dealing locally, and make your first onshore placement.

Robert Simon is a veteran of technology development and marketing, having worked R&D and marketing for electronics, polymer, and metal companies, including Bayer AG of Leverkusen Germany and Battelle Memorial Institute of Columbus, Ohio, before founding USTEK Inc.; r.simon@ustek.com.