March 2020
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March 2020 • VOL. 37 • NO. 3
First Person
6
Time for a showman?
Mike Buetow
money matters
15
Planning for disaster.
Peter Bigelow
Tech Talk
16
Long parallel routing.
John Burkhert
20
The relative permittivity for FR-4 is just that: relative.
Bill Hargin
38
Artificial intelligence in x-ray: a false call?
Nick Koop
40
The benefits of “dye and pry.”
Bob Willis
41
3-D printing solutions.
Robert Alvord and Victor Mendez
42
Buying the business.
Robert Boguski
March 2020 • VOL. 37 • NO. 3
Features
24
Differential Pairs cover story
Much engineering time is spent measuring the final PCBs to ensure the differential impedance specification is met. Is this necessary?
by Lee Ritchey
Up Media March 2020 cover
26
ROUTING
There are several theories about whether a differential pair should be routed with tight coupling or loose coupling. But the best routing rule for differential pairs is a “not closer than” rule.
by Lee Ritchey
29
IPC Apex Expo Recap
As it turns 20, the annual North American trade show is emphasizing youth. But do millennials – or their employers – take coronavirus warnings to heart?
by Mike Buetow
32
Paste Transfer Repeatability
Stencil tension is one of the variables related to defect origination, but surprisingly has not received much attention. An examination of volumetric transfer efficiencies at different aperture locations illustrates the significant influence stencil tension has on PCB assembly, particularly miniaturized, fine-pitch components.
by Prithvi Kotian, Jeff Schake and Martin Anselm, Ph.D.
24
Differential Pairs cover story
Much engineering time is spent measuring the final PCBs to ensure the differential impedance specification is met. Is this necessary?
by Lee Ritchey
Up Media March 2020 cover
26
ROUTING
There are several theories about whether a differential pair should be routed with tight coupling or loose coupling. But the best routing rule for differential pairs is a “not closer than” rule.
by Lee Ritchey
29
IPC Apex Expo Recap
As it turns 20, the annual North American trade show is emphasizing youth. But do millennials – or their employers – take coronavirus warnings to heart?
by Mike Buetow
32
Paste Transfer Repeatability
Stencil tension is one of the variables related to defect origination, but surprisingly has not received much attention. An examination of volumetric transfer efficiencies at different aperture locations illustrates the significant influence stencil tension has on PCB assembly, particularly miniaturized, fine-pitch components.
by Prithvi Kotian, Jeff Schake and Martin Anselm, Ph.D.
IN the Digital Edition
 
The latest happenings of the Printed Circuit Engineering Association.
by STEPHEN CHAVEZ

Departments

ON PCB CHAT (pcbchat.com)

Solder Paste Insufficients
with Chris Nash
IPC Apex Expo Recap
with mike buetow
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Caveat Lector
Mike Buetow Editor in Chief Image
mike
buetow
editor-
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Finding the Spotlight
I

n 2018 the US Department of Commerce conducted an industrywide survey of all the nation’s printed circuit board manufacturers. Fabricators groused about the scale of the paperwork, which was massive, as well as the focus of the questions, which in many cases required extraordinary data mining to provide the sought-after information. Still, the rationale for the Bare Printed Circuit Board Supply Chain Assessment was sound: That American PCB capacity issues extend beyond military needs into the medical, automotive and telecom sectors, and that Washington was largely unaware of the degree the nation’s supply base has degraded relative to the rest of the world over the past two decades.

The findings made it into an interagency report titled “Assessing and Strengthening the Manufacturing and Defense Industrial Base and Supply Chain Resiliency of the United States” and was provided to President Trump that same year, showing bureaucracy is still capable of moving at times. Even better, they correctly summarized the situation:

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Around the World
PCDF People
Rob Coleman Headshot
Bowman XRF named Rob Coleman sales manager for North America, responsible for XRF instrument sales and service. He was most recently Midwest sales manager for Uyemura, and previously vice president of operations for American Standard Circuits.
Kunal Shah, Ph.D., of LiloTree won the IPC Apex Expo best paper award in the domestic paper category for “Reliable Nickel-Free Surface Finish Solution for High-Frequency-HDI PCB Applications.”
Mentor named Mark Forbes product marketing specialist.
Ernest Litynski Headshot
RBP Chemical Technology promoted Ernest Litynski to president. He had been vice president of operations since 2010.
Leigh Allinson Headshot
Ventec appointed Leigh Allinson technical sales manager, UK. He has over 28 years’ technical and sales experience in PCBs with MacDermid Alpha and eXception PCB.
PCDF Briefs
The 2020 International Electronic Circuits (Shanghai) Exhibition, originally scheduled for Mar. 16-18, is postponed in response to China’s coronavirus outbreak.

American Standard Circuits has licensed Averatek’s A-SAP PCB manufacturing technology.

Apex Circuit, a subsidiary of Taiding, the largest PCB manufacturer in Thailand, has approved a 670 million baht ($21.6 million) plant in Sinsakhon Industrial Park.

Atotech is planning to list on the New York Stock Exchange.

Averatek announced Calumet Electronics as its first A-SAP licensee.

Around the World
Printer OEM Inkjets Conductors Inside Via Holes

MIGDAL HA’EMEK, ISRAEL – An inkjet-based conductive digital printer maker announced it has successfully printed and tested a novel method for printing inside vias.

PV Nano Cell said it printed inside vias 0.6mm (0.024") in diameter and 1mm (0.04") high on an FR-4 substrate. The printed vias were measured at a minimal resistance of 0.1Ω.

One side of the substrate is a printed pattern consisting of multiple widths and thicknesses (heights) of conductive features. This pattern forms an accurate resistor that heats to high temperature in less than milliseconds.

The company said it could print smaller-sized vias as well.

“In this special application, we first print inside the via,” explained Dr. Fernando de la Vega, chief executive, PV Nano Cell. “Then we print the first designated pattern on one side of the FR-4. The substrate is then flipped over, and we print the second designated pattern on the other side of the FR-4. The via printed in the beginning of the process electrically connects between the two patterns printed on the two sides of the substrate.

“The unique printing process that we developed cuts approximately 50% of the cost of production compared to the existing manufacturing solution. We are positive we can improve the process even more and print smaller-sized vias.”

Hanan Markovich, chief of business development, added, “The printed parts have gone through intensive, demanding standard testing by the customer, and we expect the production to begin in the near future. Such an achievement demonstrates the feasibility and attractiveness for mass-production applications.”

PV Nano Cell said the technologies allow customers to fully realize the potential of inkjet-based electronics printing for mass production applications. The company also makes silver-based conductive inks. – MB

Around the World
Plexus to Close Colorado Design Center
LOUISVILLE, CO – Plexus is closing its Plexus Boulder Design Center here, eliminating 104 jobs, according to reports. The move comes two years after the firm moved into the facility.

Plexus filed a notice with the Colorado Department of Labor on Jan. 22. The closure is scheduled for Mar. 22.

Layoffs will include engineers, project managers and management/administrative personnel.

Plexus plans to consolidate the Boulder operation with a facility in Boise, ID, and cites certain engineering programs that will cease.

“We are proactively responding to the engineering program pauses by strategically repositioning our Boulder Design Center to colocate with our existing manufacturing facility in Boise, Idaho,” Plexus president and CEO Todd Kelsey said. “This opportunity will allow for the creation of an Aerospace and Defense Center of Excellence. This combination of engineering and manufacturing services will provide the synergies and cost advantages of a campus environment, while delivering a compelling service offering for our customers in the aerospace and defense sector.” – CD

Around the World
TTM to Sell 4 China Manufacturing Plants, Exit Mobility Business
SANTA ANA, CA – TTM Technologies has agreed to divest its four China manufacturing plants comprising substantially all the assets of its Mobility business unit as a separate enterprise for $550 million in cash consideration.

The buyer is AKMMeadville Electronics (Xiamen) Co., a Chinese consortium consisting of Meizhi Investment (Xiamen) Co., Xiamen Semiconductor Investment Group, AKM Electronics Industrial (Panyu) and Anmei Ventures (Xiamen).

The sale does not include certain accounts receivable of the divested business, estimated to be $110 million in cash receivable to TTM.

“After years of double-digit growth, the cellular market has matured, resulting in lower growth rates,” said Tom Edman, CEO of TTM. “However, this market still demands substantial investment and capital commitments. In addition, the cellular market is highly seasonal and is driven by short-term product cycles. The combination of these trends posed increasing challenges to our strategic direction and desired business model. We are pleased to have found a buyer we believe is strategically committed to cellular market leadership, growing the Mobility business and supporting the customers and the approximately 7,500 employees that support this business. We expect after the transaction is complete, the remaining TTM business should be less seasonal and more exposed to longer cycle markets that fit our strategic direction. We remain excited about the anticipated growth opportunities in 5G base stations, cloud data centers, aerospace and defense electronics, and increasing automotive electronic content.”

In the 12 months ended Sept. 30, the Mobility business unit generated revenues of $528 million, non-GAAP operating income of $5.5 million and adjusted EBITDA of $82.5 million. – CD

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Around the World
CA People
Advanced Assembly announced Jorge Ramos as quality assurance manager.
Advanced Instruments named Joe Perault manufacturing engineering manager.
AIM appointed Leopoldo Valdez sales manager for Central and Western Mexico.
Akrometrix promoted Neil Hubble to president.
Automation Engineering named Jean-Marc Peallat general manager and vice president.
BJG Electronics named Kent Smith president.
Brandon Hannaman
BTU named Brandon Hannaman regional sales manager for Arizona, Southern California and Mexico. He has been in the industry for more than 18 years as a field service technician, IT manager, and most recently product manager.
Matt Kelly
IPC named Matt Kelly chief technologist. He will focus on factory of the future standards and technical research; industry intelligence funding; and the creation and launch of an Industry CTO Council. He comes to IPC following a 14-year career at IBM.
Steve Pudles
IPC inducted Steve Pudles into the IPC Raymond E. Pritchard Hall of Fame. Currently president and CEO of Zentech Manufacturing, Pudles has been an active IPC volunteer and leader for more than three decades.
Libra Industries named David Chavez vice president of integrated business development.
Microart Services hired Charles Tonna as executive vice president.
Around the World
CIRCUITS ASSEMBLY Announces 2020 Service Excellence Award Winners
SAN DIEGO – CIRCUITS ASSEMBLY announced the winners of its 2020 Service Excellence Awards (SEAs) for EMS providers and electronics assembly equipment, materials and software suppliers. CIRCUITS ASSEMBLY recognized companies that received the highest customer service ratings, as judged by their own customers, during a ceremony at IPC Apex Expo in San Diego.

In the EMS category, the overall winners were Kimball Electronics (sales over $500 million), Mack Technologies (sales of $101 million to $500 million), Qualitel (sales of $20 million to $100 million), and XLR8 Services (sales under $20 million).

The EMS companies with the highest scores in each of five individual service categories also received awards. (Overall winners were excluded from winning individual categories.) In the small-company category, Silicon Forest Electronics won for dependability/timely delivery and responsiveness. MacroFab took top honors for manufacturing quality and tied Spectrum Assembly for technology and value.

Around the World
CIRCUITS ASSEMBLY, PCD&F Announce 2020 NPI Award Winners
SAN DIEGO – CIRCUITS ASSEMBLY and PRINTED CIRCUIT DESIGN AND FAB announced the 2020 New Product Introduction Award winners for electronics assembly equipment, materials, software, and PCB fabrication.

The 13th annual NPI Awards recognize leading new products during the past 12 months. An independent panel of practicing industry engineers selected the recipients.

The winners are:

  • Air-Vac Engineering: Rework and Repair Tools (AVX250)
  • Anda Technologies: Cleaning Equipment (AP-3P)
  • Anda Technologies: Curing Ovens (VCO Series)
  • ASM Assembly Systems: Component Placement – Accessory Technologies (Siplace SmartFeeder AutoRefill)
  • Cogiscan: Software – Production (Quality Driver Software Suite)
  • CyberOptics: Software – Process Control (CyberCMM)
  • CyberOptics: Test & Inspection – SPI (SQ3000)
  • Data I/O: Device Programming (PSV2800)
  • Hanwha Techwin: Component Placement – High Speed (HM520)
2020 NPI Award Winners group photo
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Around the World
CA Briefs
Amtech is selling its solar unit and will concentrate on its thermal processing businesses, including BTU.

Apple has a goal to become a closed-loop manufacturer.

Apple has asked suppliers to make up to 80 million iPhones over the first half of this year, reports say, up 10% from last year, but suppliers fear fallout from the coronavirus.

BlueRing Stencils acquired Stone Mountain Tool for an undisclosed sum.

BTU now supports the Hermes Standard, officially referred to as IPC-Hermes-9852.

Compal Electronics is planning a second plant in Vietnam, with its first reaching full capacity around the second quarter of this year.

Foxconn’s Terry Gou vows to fire up the company’s plant in Wisconsin this year.

Foxconn invested $26 million in Nanox to produce futurist and affordable x-ray machines.

Laritech opened a new EMS facility in Moorpark, CA.

Mycronic implemented a new group structure.

New Kinpo Group (Cal-Comp) expects many of the group’s subsidiaries will go public beginning this year.

Pegatron plans to set up production facilities in South Vietnam.

Rohde & Schwarz signed a strategic partnership with Benchmark Electronics to improve its production capacity.

Around the World
Libra Industries Acquires Ex-Benchmark Facility in Mexico
GUAYMAS, MEXICO – Libra Industries has acquired a contract manufacturing facility here formerly run by Benchmark Electronics. Libra Guaymas will be Libra’s fifth plant and first international operation.

The 52,000 sq. ft. plant previously was operated by Benchmark Electronics and makes complex assemblies and subassemblies for customers in the aerospace/defense, medical, semiconductor and industrial end-markets. Benchmark had slated the site for closure this year.

“The facility is complementary to our current operations in Ohio and Texas and will help Libra accelerate its growth strategy by providing customers with more technical capabilities,” said Rod Howell, CEO of Libra. “Our goal is to provide customers with a full suite of capabilities and be a trusted partner for all of their outsourced manufacturing needs. This investment further helps us achieve that strategy.”

Financial terms were not disclosed. – CD

Around the World
Prime Technological Buys 2 EMS Firms
ATLANTA – Prime Technological Services has acquired TeligentEMS for an undisclosed sum. TeligentEMS has a plant in Havana, FL, and was founded in 2003.

The acquisition is important in expanding Atlanta-based Prime’s presence in the US market, the firm says.

Separately, in February Prime also bought I. Technical Services for an undisclosed sum. Mike Thompson, president and CEO of ITS, will continue to work with Prime as a strategic advisor.

“The acquisition of TeligentEMS is a key element of our customer-driven strategy of providing the manufacturing services and geographic footprint our customers require,” said CEO Greg Chesnutt. TeligentEMS is strategically located in the Southeast and represents a significant expansion of our value delivery platform for customers in targeted vertical markets.

TS offers quickturn prototype and NPI capabilities, plus testing and after-market services that will “really resonate with customers in our targeted aerospace, defense, medical, industrial and communications markets,” Chesnutt added. – MB

Around the World
Zentech Acquires Trilogy Circuits
DALLAS, TX – Zentech Manufacturing in January acquired fellow EMS Trilogy Circuits, extending its geographic reach into the middle of the US. Following the transaction, Trilogy Circuits becomes Zentech Dallas and joins the Zentech family of companies that also includes Zentech Baltimore (MD) and Zentech Fredericksburg (VA).

Financial and other terms were not disclosed.

Trilogy Circuits is AS9100D certified and provides electronics manufacturing services and support for the defense and other high-reliability industries.

“We are extremely excited to welcome Charlie Capers and the Trilogy Circuits team to the Zentech family,” said Steve Pudles, CEO, Zentech. “The transaction was driven in large part by requests from our established military customers for Zentech to deliver our highly certified, high-complexity processing model to the Southwest region, as they all have significant operations in this vibrant geography. Zentech is on the leading edge of many emerging DoD programs, and the formation of Zentech Dallas will provide seamless engineering collaboration with our customers to support their mission-critical NPI requirements.”

Capers, who founded Trilogy Circuits in 2002, will continue to manage Zentech Dallas. – CD

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Market Watch
EDITED by CHELSEY DRYSDALE
Report: 61% of Mfg. Cos. Need to Reevaluate AI Implementation
PALO ALTO, CA – While manufacturing companies see the value in implementing artificial intelligence, many are struggling to deliver clear results and are reevaluating their strategy, according to a new report commissioned by Plutoshift.

The findings revealed almost two-thirds (61%) of manufacturing companies said they need to reevaluate the way they implement AI projects.

While companies are making progress with AI initiatives, many planning and implementation struggles remain, from defining realistic outcomes, to data collection and maturity, to managing budget scope and more, according to Plutoshift.

A major reason companies are rethinking their AI implementation plans is a lack of data infrastructure needed to fully utilize AI. Eighty-four percent of respondents said their company cannot automatically and continuously act on their data intelligence.

ROI
The Coronavirus Took Industry by Surprise. Why?
Disaster planning should be part and parcel of our business toolkit.
With only two months of the year behind us, it may be prudent to take any and all business plans you had and rip them up.

Entering a new year is always exciting, when embarking on interesting initiatives that will generate greater profits. Regrettably, sometimes disruptions sideline those exciting new thoughts, replaced by triage efforts that were never in your plans. This year that disruptive event is the coronavirus, and businesses are trying to work through a potentially altered global supply chain.

First and foremost, the coronavirus is just that: a virus – a highly contagious disease debilitating thousands around the world who have or will contract it. Our first thoughts must be with the victims who are infected, hoping they recover. And yes, other viruses and diseases over the years have wreaked havoc on various locations, countries and peoples. By itself, the coronavirus should not derail business planning, business plan execution, or business itself. However, sometimes “things” happen!

DESIGNER’S NOTEBOOK
Contrary Routing Schemes
Why you should be mindful of long parallel routing situations.
It was a warm Saturday morning last August when we decided to visit my favorite Swedish flatpack furniture store. We, of course, means me tagging along with my spouse as she chose some stuff to seal the back-to-school deals. (One more year!) We weren’t the only ones with that plan, so it was fortunate I knew the parking lot well.

For the uninitiated, the store layout – including the garage – is a giant maze of hallways. You pass by little rooms of staged furniture on the top floor, then another habitrail running past an assortment of sundry household items on the floor between that one and the parking level. It is supposed to be a treasure hunt, with cheap, bland food at either end.

All along these meandering paths, little projectors built into the ceiling provide arrow-shaped beams showing which way to go so you don’t get disoriented. Lines of yellow tape extend for miles. The tour would probably take about 20 minutes if you weren’t shopping. Walking the crowded habitrail with a shopping cart is easier when everyone is going the same direction. One problem: those renegade shoppers who decide to backtrack. That messes up the flow.

THE ROUTE
The New Printed Circuit Engineering Association
In this month’s column, we’ll take a first look at the new Printed Circuit Engineering Association (PCEA), including an overview of membership and why we established the organization. We’ll also look at the mission of PCEA, and how it will unfold to the industry.

Membership. PCEA is an international network of engineers, designers, and specialists related to printed circuit development. We are a mixed group of individuals that covers the entire product development cycle. There are no limitations or restrictions as to who can become a member. Membership is free and open to all those interested in gaining and sharing their knowledge with others. We will serve the industry as a nonprofit organization.

Why we established PCEA. Several well-organized groups cater to the electronics industry. These organizations tend to feature a specific segment of this industry by hosting highly focused, major conferences for their followers. These conferences tend to be one or two times a year at different locations.

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MATERIAL MATTERS
Preparing for Next-Gen Loss Requirements, Part 3
The relative permittivity for FR-4 is just that: relative.
Ed.: This is Part 3 of a three-part series on preparing for next-generation loss requirements.
Last month, in Part 2 of this series, I outlined the means by which insertion-loss requirements are determined. Here, I’ll suggest a better method for obtaining accurate Df numbers without having to go to the trouble of building test boards.

A longtime PCB industry technologist asked me recently, “What’s a good Dk (dielectric constant) number for FR-4?” As the interest in signal integrity (SI) was growing roughly 25 years ago, it started to interest me that many SI practitioners considered FR-4 to have monolithic properties. The question reinforced that some still hold that view. One might say the relative permittivity (ϵr) of FR-4 is 4.3. Someone else would say 4.1. A third says they always use 4.0. As I read up on it, I realized it varies with frequency, resin content (as a percentage, with the inverse being the glass percentage), and the resin system. At lower frequencies, static numbers for vanilla FR-4 were probably fine for impedance calculations and signal integrity, but those days are far behind us at this point.

ECTC Advertismet
PCB West 2020
Connecting Design to Fab to Assembly
Conference: September 8 – 11
Exhibition: Wednesday, September 9
See you in September!
PCbwest.com
SANTA CLARA CONVENTION CENTER, CA
  • 1-day Free Expo with 100+ suppliers
  • Free Technical Sessions
  • 4-day Technical Conference featuring Eric Bogatin, Rick Hartley, and Lee Ritchey
  • Professional Development Certificates
Who’s Exhibiting

Accurate Circuit Engineering

Aculon, Inc.

Advanced Assembly

Advanced Circuits

AGC Chemicals Americas, Inc.

AGC Nelco America Inc.

All Flex Flexible Circuits & Heaters

Altium, Inc.

American Standard Circuits, Inc.

APCT

Arlon EMD Specialty

Bay Area Circuits, Inc.

Beta LAYOUT

Bittele Electronics Inc.

Bowman XRF

Cadence Design Systems

Cicor Group

Clear Blue Engineering

dalTools

Dino-Lite Scopes (Big C)

Downstream Technologies, Inc.

DuPont

DYCONEX AG

Dynamic Electronics Co., Ltd.

Elgris Technologies, Inc.

Elsyca

EMA Design Automation

EM Solutions Inc.

Firan Technology Group – FTG

Fischer Technology, Inc.

Flex lnterconnect Technologies

Flexible Circuit Technologies

Freedom CAD Services, Inc.

Fujipoly America

Goal Searchers Co., LTD Zhuhai

Green Circuits

GS Swiss PCB AG

GTS Flexible Materials Ltd.

HIE Display Limited

HSIO/lronwood

ICAPE Group

lmagineering, Inc.

lnsulectro/lsola

Integrated Technology Ltd. (ITL Circuits)

IPC-2581 Consortium

JetPCB USA

JS Electronic Co. Ltd.

Kinwong Electronic Co., Ltd.

Krypton Solutions

Kyocera International, Inc.

Leader Tech, Inc.

LPKF Laser & Electronics

Medcadtron GmbH

Mentor, A Siemens Business

MicroConnex

Minco Products, Inc.

Multek Technologies, Inc.

MV Circuit Technology Co., Ltd.

MVINIX Corporation

NTS

Oak-Mitsui Technologies LLC

Ohmega Technologies, Inc.

Oki Printed Circuits Co., Inc.

Optiprint AG

Panasonic Electronic Materials

PCB Power Inc.

PFC Flexible Circuits Limited

Polar Instruments, Inc.

Polyonics

Printed Circuits

Pulsonix PCB Design Software

Quadcept

RelianceCM

Risho

Rogers Corporation

Royal Circuits

San Diego PCB Design

San-ei Kagaku Co., Ltd.

Sanmina Corporation

Screaming Circuits

SEP Co., Ltd.

Shenzhen Danyu Electronics Co. Ltd.

Shenzhen JDB Technology Co., Ltd.

Shin Yi PCB Co., Ltd.

Sierra Circuits, Inc.

Slingshot Assembly

Somacis Inc.

Summit Interconnect

Sunshine Global Circuits

Sunstone Circuits

SVTronics, Inc.

Tempo Automation

Ticer Technologies

Ultra Librarian

Varioprint AG

Vayo Technology

Ventec International Group

Victory GiantTechnology (Huizhou) Co., Ltd.

VYCOM Global Sources Ltd.

Xiamen Bolian Tech. Co., Ltd.

Zuken USA Inc.

Differential Pairs
Does Differential Signaling Require a Differential Impedance?
Or does it distract from the actual need of the signaling protocol?
by LEE RITCHEY
Much engineering time is spent on designing differential signaling circuits to maintain a differential impedance between the two sides of the differential pair. A similar amount of time is spent measuring the final PCBs to ensure the differential impedance specification is met. The most common differential impedance target is 100Ω. A fair question is whether this impedance requirement is necessary. Once differential signaling is understood, it will be seen as unnecessary and distracting from the actual need of the signaling protocol. This article will clear up this confusion.

FIGURE 1 is a schematic of the original emitter-coupled logic (ECL) differential pair as used in early computer rooms to move ECL signals from one large gray box to another. It was not possible to ensure the ground connections between boxes were of enough quality to permit single-ended ECL signals to function properly. Differential signaling compensated for this ground offset as follows:

In Box A, the single-ended logic signal A is converted into two identical but mirror image signals, A and A-. These two signals have two things in common. They are mirror images of each other, and they are tightly timed to each other. That is all they have in common. The designer’s goal is to ensure these two signals (A and A-) arrive at the two transistor bases in Box B with maximum fidelity. This is achieved by sending each on its own 50Ω single-ended transmission line with a parallel termination in Box B to Vtt, the termination voltage. Neither signal knows the other exists. They are two independent single-ended logic signals.

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Routing
Is TIGHT OR LOOSE COUPLING Best for Differential Signaling?
Or should we just isolate noisy signals?
by LEE RITCHEY
There are several theories about whether a differential pair should be routed with tight coupling or loose coupling. There must be some science that can be drawn on to arrive at a rule set that makes best use of layout time, while optimizing the signal integrity of a differential pair. This article explores the advantages of tight and loose coupling.

A known industry speaker says, “Everybody knows tight coupling is best for differential signaling.” This is stated in a tone of voice that implies those who don’t know this might be lacking. I sometimes say I am from Missouri, which is the “Show-Me State.” If the need for tight coupling is true, perhaps there is some proof. I am still waiting to see it. The following discussion will look at a tightly coupled differential pair and the same pair loosely coupled.

The left side of FIGURE 1 is a 3.25Gb/s differential pair routed with the classic 5-mil line, 5-mil space rule set, and the right side is that same differential pair loosely coupled. Clearly, the tightly coupled differential pair eye diagram is not as good as the loosely coupled differential pair. What happened to the tightly coupled pair is that to achieve 50Ω on each of the two transmission lines (100Ω differential, for those who think this is important), they had to be made narrower than those in the loosely coupled pair and spacing set as 5 mils vs. 10 mils. The primary source of degradation on the left side is skin effect loss due to traces half as wide as the traces on the right.

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IPC APEX EXPO RECAP
The Show Must Go On
In the wake of pandemics and travel bans, visitors still turned out for the annual exhibition.
by Mike Buetow
Heading into IPC Apex Expo the first week of February, I wasn’t sure what to expect. The overall market appears to be slowing somewhat. Many EMS companies have reported lower sales for the past quarter. US presidential elections often seem to dampen electronics orders, at least until November, even though a review of the overall GDP disputes any such letup. And fears of the coronavirus in China have clearly spooked the industry, as some firms have reduced or banned employee travel for the time being.

But once the show started, many of those concerns abated. Floor traffic was up and down through the first two days, before grinding to a near halt per usual on the third and final day of the show. Exhibitors took note, reporting mixed reviews of the attendance. But when it was busy, it was really busy. It’s hard to say whether the postponement of overseas shows such as Nepcon China and the International Electronic Circuits (Shanghai) Exhibition (better known as the CPCA Show) boosted attendance an ocean away in San Diego, but it probably didn’t hurt. (As of this writing, IPC has not released official attendance figures.)

The hallmarks of IPC Apex Expo, which celebrated its 20th anniversary this year (some argued that the show is actually older than that, since it’s a combination of Apex, founded in 2000, and Printed Circuits Expo, which launched in 1994), include size and pageantry. The IPC Hall of Fame, keynote addresses and committee luncheons all feature a lot of color and lights and balloons and massive flashy electronic displays. Those are distinct improvements over the shows of yesteryear. And there’s a clear emphasis on younger engineers, even though there aren’t many of that demographic walking the halls.

Paste Transfer REPEATABILITY
Robustness of High Tension, Standard Tension and Mesh Mount Solder Paste Stencils
An examination of volumetric transfer efficiencies at different aperture locations.
by Prithvi Kotian, Jeff Schake and Martin Anselm, Ph.D.
The fishbone diagram associated with stencil printing contains a staggering number of variables, the interdependence of which contributes to the high probability of defect origination.1 Stencil tension is one of the variables and, surprisingly, has not received much attention. This work illustrates the significant influence – particularly with miniaturized, fine-pitch components – that stencil tension has on next-generation PCB assembly results.

This study evaluated the effectiveness of mesh mount, standard clamping tension, and high clamping tension stencils under different parameters, including print quantity and squeegee blades (new/old) by comparing the volumetric efficiencies at the most wear susceptible locations identified on the stencil. The robustness of the stencil is also determined by analyzing the foil for any potential damage at sensitive locations, which includes the components (BGAs and passive devices) within shield enclosure boundaries for printing defects at intervals of 0 (“as received”), 5,000, 10,000, 15,000, and 20,000 print cycles, respectively. Statistical approaches were used to determine how stencil tension influences volumetric efficiencies and which stencil tension provides a more repeatable print. Designing stencil apertures to industry-acceptable area ratios is also of great importance to ensure all the printed solder paste material is deposited on the substrate.2 These sets of experiments illustrate the effectiveness of stencil tension and provide insight on printing improvements that keep pace with miniaturization of electronic products.

IEEC
State-of-the-Art Technology Flashes
Updates in silicon and electronics technology.
Ed.: This is a special feature courtesy of Binghamton University.
Transistors can process and store information. Purdue University researchers have created a feasible way to combine transistors and memory on a chip, potentially bringing faster computing. They used a semiconductor that has ferroelectric properties. This way two materials become one material, and without worry about the interface issues. The result is a so-called ferroelectric semiconductor field-effect transistor, built in the same way as transistors currently used on computer chips. The material, alpha indium selenide, not only has ferroelectric properties, but also addresses the issue of a conventional ferroelectric material usually acting as an insulator rather than a semiconductor due to a so-called wide “band gap,” which means that electricity cannot pass through and no computing happens. (IEEC file #11468, Science Daily, 12/9/19)

Motherboard replacement – Silicon-interconnect fabric. Research shows the printed circuit board (PCB) could be replaced with the same material that makes up the chips that are attached to it. This would lead to smaller, lighter-weight systems for wearables and other size-constrained gadgets, and to powerful high-performance computers. This all-silicon technology (silicon-interconnect fabric), permits bare chips to be connected directly to wiring on a separate piece of silicon. Unlike connections on a PCB, the wiring between chips on fabric is as small as wiring within a chip. Many more chip-to-chip connections are thus possible, and those connections transmit data faster while using less energy. (IEEC file #11382, IEEE Spectrum, 10/1/19)

test and inspection
AI Yi-Yi-Yi-Yi! Electronics X-ray Inspection and Artificial Intelligence
What are the questions we should ask before diving in?
To deliberately misquote and mangle Shakespeare once again, I come to praise AI, not to bury it, but does the potential evil it may do live after and the good oft interred in the dataset?

I apologize, but … discussion of the benefits of AI in all manner of applications has been the flavor of the month for much of the last two years, and there seems no end in sight! It has been one of the drivers of processor manufacture and use in recent times. However, two recent articles from BBC News seemed to highlight some pros and cons regarding use of AI for x-ray inspection and test.

The first1 describes how AI has been trained to best radiologists examining for potential issues in mammograms, based on a dataset of 29,000 images. The second2 is more nuanced and suggests that after our recent “AI Summer” of heralded successes on what could be considered low-hanging fruit, we might now be entering an AI Autumn or even an AI Winter. In the future, it suggests, successes with more complex problems may be increasingly difficult to achieve, and attempts are made only due to the hype of the technology rather than the realities of the results.

defect of the month
Locating BGA Joint Failures
Why “dye and pry” is a fast, workable solution.
This month we show examples of testing BGAs with a “dye and pry,” a simple and cost-effective way of looking at joint failure or their condition after some form of mechanical testing or abnormal assembly practice.

Figure 1 shows a sample BGA joint after dye-and-pry testing. Eighty percent of the separated surface is covered by the red dye. This clearly shows separation occurred before the dye was added.

Figure 2 shows a solder ball separated from the pad on the PCB. There is no evidence of dye present. This indicates no cracks were present before the two surfaces were separated. The image also shows how the solder has formed around the pad during reflow like an upturned plate.

GETTING LEAN
Lean Manufacturing and 3-D Printing
Additive processes are an effective tool toward the single-iteration design goal.
In past columns we’ve discussed the benefits of strong focus on design for manufacturability (DfM) and assembly (DfA) in the design phase and poka yoke or “mistake-proofing” in production. As the cost of 3-D printing technology drops, its usefulness in DfM/DfA and poka yoke activities grows. At SigmaTron International, 3-D printers are used in a variety of ways to improve design for assembly and reduce variation. Here we look at ways this technology is used in design, manufacturing and test processes to solve challenges that otherwise add time, cost or defect opportunities.

In SigmaTron’s design process, the goal is a single iteration wherever possible. One way that gets accomplished is through peer review of a physical sample of the product. The peer review process usually involves all engineering disciplines, including software development, PCB layout, mechanical, hardware, test engineering and the production team on both the contract manufacturing and customer teams. While 3-D modeling software can provide a representation of the product, 3-D printed parts allow participants in this type of peer review to more easily test assumptions on assembly order of parts and the way parts move in the physical product. SigmaTron’s design team frequently uses a 3-D printer to demonstrate how housings and covers will work on new products to help the team visualize the manufacturing and user processes involved.

Another product development benefit is minimalized tooling iterations for designs that aren’t fully locked down. In some cases, SigmaTron’s design team 3-D prints small quantities of parts for designs that are likely to have engineering changes that will impact hard tooling. When balanced against tooling costs, the 3-D parts are a cheaper option. This path also enables greater flexibility in adjustments to design for assembly or user-friendliness in the early stages of product release when tight deadlines for initial build quantities are involved, since no tooling is involved.

seeing is Believing
Swag 4.0
Finding our next customer, one trinket at a time.
Green is sexy. One ignores the wave – in politics, marketing, journalism, social media, commerce – at one’s peril. In 2019, The Economist published an entire edition raising the alarm about climate change and its implications. Three years ago, Pope Francis wrote an encyclical letter (Laudato Si) about the environment, emphasizing care for our neglected “common home.” Self-righteous millennials and impressionable younger people march, advocating immediate, drastic control of greenhouse gases and other toxic emissions. A Swedish teenager cuts school and uses her sudden free time to excoriate industrialized nations and big corporations at the UN General Assembly for favoring economic growth over ecological sustainability and contaminating the world, shaming magistrates and captains of industry alike for their perceived callous indifference to the effects of rising temperatures. It is a good time to be a scold.

To be green is to hate waste. Waste is anathema. Angels recycle. Daily. So say those who are woke.

But we are anachronistic, and this is business. We play for keeps.

Off The Shelf
Off The Shelf
Machines Materials Tools Systems Software
Bergquist Gap Pad TGP 10000ULM
ProcessLens
GNV-720 and GNV-725
Bergquist Gap Pad TGP 10000ULM
High-Power TIM
Bergquist Gap Pad TGP 10000ULM provides thermal conductivity of 10.0W/m-K within ultra-low modulus, low assembly stress formulation. Soft, high-compliance pad conforms to irregular surfaces, fills small gaps to enable interface wet-out and optimal thermal transfer.
Henkel
ProcessLens
5-D SPI
ProcessLens measures solder paste deposits and controls and optimizes printing process autonomously while learning with each print cycle. Determines matching print parameters and runs virtual prints to check parameters for the stencil design. X/y positioning accuracy is 12.5µm.
ASM
GNV-720 and GNV-725
Humidity/Temp. Meters
GNV-720 and GNV-725 are portable, dual-function meters with three environmental sensors. Offer precision capacitance and semiconductor sensors incorporated directly into the remote wand. Thermocouple sensor adds accuracy.
Global Specialties
Off The Shelf
Off The Shelf
Machines Materials Tools Systems Software
i3070 series 6
Prospector that enables full characterization of any device
YRM20 chipshooter
i3070 series 6
IoT/5G ICT
i3070 series 6 supports range of PCBA sizes for applications including IoT and 5G, as well as automotive and energy. Delivers short signal path between measurement circuitry and devices under test to minimize undesired effects from parasitic capacitance, improve immunity to crosstalk, and eliminate stray signal coupling effects. Features improved test efficiency with up to 4x faster boundary scan, silicon nails and dynamic flash programming; minimal downtime for software installation with 100% backwards compatibility.
Keysight Technologies
Prospector that enables full characterization of any device
Micro Materials Tester
Prospector enables full characterization of any device by combining mechanical testing with electrical, thermal, acoustic and optical. Tests across coatings and thin films, medical devices, microelectronics, and more. Gains failure mode insights. New applications include hardness and scratch testing.
Nordson Dage
YRM20 chipshooter
98K CPH Chipshooter
YRM20 chipshooter uses two head types: a high-speed, multi-purpose rotary head that, when combined with the high-speed feeder, delivers performance under optimal conditions of 115,000cph, as well as a one-head solution via inline (HM) head. Mounting accuracy of ±25µm (Cpk ≧ 1.0); supports 0201 (0.25mm x 0.125mm) sized component packages. 98,000cph.
Yamaha Surface Mount Technology
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Technical Abstracts
In Case You Missed It
Low-Power Transistors

“Uniform and Ultrathin High-κ Gate Dielectrics for Two-Dimensional Electronic Devices”

Authors: Weisheng Li, et al.

Abstract: Two-dimensional semiconductors could be used as a channel material in low-power transistors, but the deposition of high-quality, ultrathin high-κ dielectrics on such materials has proved challenging. In particular, atomic layer deposition typically leads to nonuniform nucleation and island formation, creating a porous dielectric layer that suffers from current leakage, particularly when the equivalent oxide thickness is small. Here, the authors report the atomic layer deposition of high-κ gate dielectrics on two-dimensional semiconductors using a monolayer molecular crystal as a seeding layer. The approach can be used to grow dielectrics with an equivalent oxide thickness of 1nm on graphene, molybdenum disulfide (MoS2) and tungsten diselenide (WSe2). Compared with dielectrics created using established methods, these dielectrics exhibit a reduced roughness, density of interface states and leakage current, as well as an improved breakdown field. With the technique, the authors fabricate graphene radio-frequency transistors that operate at 60GHz, and MoS2 and WSe2 complementary metal-oxide-semiconductor transistors with a sup-ply voltage of 0.8V and subthreshold swing down to 60mV dec−1. They also create MoS2 transistors with a channel length of 20 nm, which exhibit an on/off ratio of over 107. (Nature Electronics, December 2019, nature.com/articles/s41928-019-0334-y)

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Thanks for reading our March 2020 issue!