2005 Sep AdvancedPkg

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SEPTEMBER 2 5

THE INTERN TION L M G ZINE FOR ELECTRONIC P CK GING PPLIC TIONS

www.apmag.comwww.apmag.com

Underfill VoidsEliminating

X-rayInspection

MEMS Update

TemperatureSensors

2005 APARecognitionSection

5 9AP_CV1 CV10509AP_CV1 CV1 8 26 5 12:11:18PM8/26/05 12:11:18 PM

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ADVANCEDADVANCED

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Its rough in the semiconductor jungle

Heraeus is your machete.

Two of the industry's top three SiP assemblers depend

on Heraeus for semiconductor assembly materials thathelp keep their businesses on competitive ground.Because they know our products can help them cutthrough their most demanding challenges, includingcost, size, performance and lead-free implementation.

Heraeus can do the same for you. We have the technicalexpertise to provide you with the right products andsupport for your application. Like conductive adhesives,solder pastes, tack fluxes and more many of them lead-free. All designed to perform exactly the way you needthem to, from superior quality to consistent perform-ance lot after lot.

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CORPORATE OFFICES

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CHAIRMAN

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Communications and

Optoelectronics Group

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Advanced Packagingmagazine is published

by PennWell Corporation. Reproduction of textand illustrations is not allowed without express

written permission. Opinions expressed by authors are notnecessarily those of the publisher, and this publication can

accept no responsibility in connection with any liability which

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Theres a reason people are getting excited. For over 20 years Newport has set

the industry standard for complex die bonding solutions. Today we have taken it

another step forward with the introduction of the next generation assembly work

cell, the new MRSI-M5. Flexible by design, the MRSI-M5 is the right choice for

accuracy, speed and reliability.

The MRSI-M5 system has a large work area and is the best solution for a variety

of die bonding interconnect technologies including eutectic, epoxy die attach and

various flip chip processes. And, with Newport you can rest assured that you are

working with an industry leader who delivers global support, process experience

and manufacturing expertise. To see what all the excitement is about, visit

www.newport.com/workcell18or call 978.667.9449.

Some people just cant wait to see the new

MRSI-M5 assembly work cell.

2005 Newport Corporation

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The Carsem MLP Advantage

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CONTENTS

ONLINEw w w . a p m a g . c o mINDUSTRY NEWS UPDATES . NEW PRODUCT HIGHLIGHTS . EDITORIAL COMMENTARY . SEARCHABLE ARTICLE ARCHIVES

INDUSTRY ASSOCIATION LINKS . CALENDAR OF EVENTS . TRADE SHOW NEWS . LEAD-FREE WEBINARS

T H E back-en d P R O C E S S

S E P T E M B E R 2 0 0 5 On The CoverVoids or air gaps in underfill are a

common problem across underfill

applications, from the smallest die on

flex to the largest BGA. The

consequences of having voids in

underfilled parts depend on thepackage design and use model.

Courtesy of Asymtek.

18A close-up of

plug-and-play

technology

that links the

application to

the calibration

lab.

A top

view of a

thermoplastic

cavitypackage.

22

A diagram of

a typical

X-ray system

for industrial

inspection.

24

FEATURES

14 Troubleshooting Underfill Void Elimination Methods for Gaining Reliability in Underfill Applications BY ALAN LEWIS

18IEEE 1451.4 Facilitating Temperature Sensor Success BY CHRIS SEYMOUR

20 MEMS Packaging Update Providing a Foundation for Future Packaging Advancements BY KEN GILLEO

24 Building on a Basic X-ray Inspection Platform Configuring an X-ray Inspection System BY UDO E. FRANK

DEPARTMENTS

7 Editorial BY GAIL FLOWER

8 In the News

29 Advanced Packaging AwardsSpecial Section

51 IMAPS 2005 Product Preview

55Advertiser Index

56Editorial BoardBY JOSEPH FJELSTAD

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Precious moments. Shared when youre not there.All because smaller, more advanced components canrely on packaging thats durable in even the mostdemanding circuitry. Thats where youll find NuSil.

Our customizable, low-outgassing packagingmaterials are helping opto-electronic systems staycontaminant-free under stressful, heated conditions.While your needs might be very different, fromlarge batches to small, you can count on NuSilto deliver precise, custom formulations and themost complete line of encapsulants, under-fillsand die-attach adhesives available. All backed by

more than 25 years of packaging materials expertise.

What? When? Where? If it s NuSil, its no problem.

Flight delayed.

Early delivery.

Hello Daddy.

NuSil Technology.

Whats your challenge?www.nusil.comEurope +33 (0)4 92 96 93 31US 805/684-8780

2005 NuSil Corporation. All rights reserved. AP0205-E

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EditorialG A I L F L O W E R

www.apmag.com September 2005 ADVANCED PACKAGING 7

EDITORIAL ADVISORY BOARD

Daniel Baldwin, Ph.D.

Engent Corp.

Jeffrey C. Demmin

Tessera Technologies

Joseph Fjelstad

SiliconPipe Inc.

Nasser Grayeli, Ph.D.

Intel Corp.

Bruce Hueners

Palomar Technologies

R. Wayne Johnson, Ph.D.

Auburn University

Stephen Kay

Ultratech Inc.

George Ri ley, Ph.D.

FlipChips Dot Com

Michael Steidl

Amkor Technology Inc.

Rao R. Tummala, Ph.D.

Georgia Institute of Technology

Jim Walker

Gartner-Dataquest

Someone once said thatto do the same thingover and over whileexpecting a different

result is the definition of insan-ity. I thought of this while attend-

ing SEMICON West on July 12 14 in San Francisco. During eachinterview with company leaders,each review of new products, andeach technical session, I lookedfor what was innovative and asource for new ideas. Originalthinkers are keeping the back-end ahead of the recovery curvein the electronics marketplace,and I was on a mission to talk toa few creative leaders.

Tien Wu, Ph.D., AdvancedSemiconductor Engineering,Inc.s (ASE) president, Americas/Europe, presented a fresh perspec-tive on mostly everything involv-ing advanced packages. His back-ground a BSCE degree fromTaiwan University and a MS andPh.D. in mechanical engineeringfrom the University of Pennsylva-nia fits his career choices. Priorto joining ASE, Wu held several

management positions at IBM,including R&D, process develop-ment, manufacturing, applicationand ASIC design, marketing, andsales in the U.S., Europe, and theAsia-Pacific region.

How was ASEs growth out-standing this year? SEMIs mid-year capital equipment consensusforecast for the semiconductorindustry showed a 12% declinefrom 2004 figures, ending at a

predicted $32.6 billion in salesfor 2005. SEMI members antic-ipated cautious spending thisyear, as the expanded capacity in2004 was absorbed. Respondentsto SEMIs survey said that themarket would grow at a single-digit rate in 2006 and reach $44.3billion in 2008. ASE is gainingmarket share among SATS pro-

viders, and their growth showsdouble digits this year, outpac-

ing competitors.Wu sees a tightening of capac-

ity in back-end processing, andexpects 2006 to be especiallyfruitful for this segment of themarket. Back-end is leadingthe industry, and ASE providesback-end services. But theresmore to it than being in the rightmarket segment. There are lotsof reasons for ASEs success, ac-cording to Wu, including:

Flexibility of package assem-bly services, including bump-ing, bonding, testing, supplyingmaterials, and providing turn-key or stand-alone assistance.

Right investments for future

growth. Willingness to meet present

demands or perceive futurecustomer demands.If a customer wants complete-

ly lead-free, ASE provides lead-

free packages. Cost control isone of the biggest problems withlead-free, according to Wu. Thecheapest material that works wellis what a customer will use. How-ever, at present, there are no reli-able standards of material choicesand no recipe. Each bill of mate-rials is different for each OEM.Eventually, lead-free will evolvein the industry, but it will take afew standards and verification of

materials used.We asked Wu where he saw

the boundary between the front-and back-end. He said that it wasmuch more determined by busi-ness than by technology. Mon-ey, not processes, determines thedifference between the front- andback-end, he added. That will beanother topic for a future articleinAdvanced Packaging.

Editor-in-Chief

A Breath of Fresh Air

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NEWSI N T H E

Intel to Build 300-mm Wafer Factoryin ArizonaSANTA CLARA, CALIF. Intel Corp. plansto build a new 300-mm wafer fabrica-tion facility at its Chandler, Ariz. site,and the $3 billion projects constructionis set to begin immediately. DesignatedFab 32, the new factory will begin mi-croprocessor production in late 2007 on

45-nm process technology. This invest-ment positions our manufacturing net-work for future growth to support ourplatform initiatives, and will give us ad-ditional supply flexibility across a rangeof products, states Paul Otellini, IntelsCEO. Once completed, Fab 32 will be-come Intels sixth 300-mm wafer facility,and the structure will be about 1 millionsq. ft. 184,000 sq. ft. of which will becleanroom space.

300-mm wafer manufacturing increas-

es lower-cost semiconductor productionability when compared to 200-mm wa-fers. Total silicon surface area of a 300-mm wafer is 225%, or more than twicethat of a 200-mm wafer, and the numberof printed die increases to 240%. Larg-er wafers lower production cost per chipwhile eliminating overall use of resources 300-mm wafer manufacturing will use

40% less energy and water per chip than

a 200-mm wafer factory.Intel also plans to invest $105 million

to convert an existing, inactive wafer fabin New Mexico to a component tempo-rary test facility. The project will provideadditional test capacity to the companysfactory network for the next 2 years, re-sulting in an additional 300 jobs at theNew Mexico site during that time. AP

SEMI Appoints New Board Chair,Board MemberSAN FRANCISCO, CALIF. SEMI has ap-pointed Ed Segal, senior advisor to Me-tron Technology, as chairman of SEMIsInternational Board of Directors. Segalsucceeds Tetsuro (Terry) Higashi, chair-man and CEO of Tokyo Electron Ltd.,who served as chairman for the pastyear. Also appointed as the Boards new-est member is Michael Splinter, president

and CEO of Applied Materials. ArchieHwang, chairman and CEO of HermesEpitek, succeeds Segal as vice chairmanof the board.

Segal served as CEO of Metron fromJuly 1995 until its acquisition by AppliedMaterials in December 2004. Prior to join-ing Metron, he served as president andCEO of Transpacific Technology Corp., acompany he founded in 1982, which latermerged with Metron. SEMI is a uniqueglobal trade organization serving thesemiconductor equipment and materi-

als industry. In a period when the needsof members are shifting, I am pleased tohave the opportunity to serve as chairmanof the organization, says Segal. AP

SMT ChinaInternationalConference Call for PapersSHANGHAI, CHINA PennWell andChina Electronics Appliance Corpo-ration (CEAC) will sponsor the 2005SMT China International Confer-ence on Emerging Technologies andLead-free Challenges, November 21-22, 2005. This 3rd annual conference

will take place at the Shanghai Inter-national Convention Center, Shang-hai, China, in conjunction with theCEACs 66th China Electronic Fair(CEF). SMTand SMT Chinamaga-zines, sister publications toAdvancedPackaging, announce a call for papersfor this conference on topics such ashigh-density, fine-pitch placement;equipment modular design; processoptimization programming; 0201 and01005 components; chip scale, BGA,

flip chip, and 3-D interconnection;nanotechnology; and MEMS; as wellas several other SMT, emerging tech-nology, and modern assembly topics.

Papers from environmental man-agers and technical experts are soughton relevant subjects. For a completelist of topics, and for the submis-sion form, please visit www.smtmag.com. Abstracts should be 300 wordsin length and include an attached ab-stract submission form and a brief

biography. The deadline for abstractsubmission is September 25, 2005.Presenters will be allotted 40-min-ute time slots for their presentationand discussion. Simultaneous Man-darin/English interpretation willbe provided. Some papers may begrouped together in a forum or pan-el discussion. Speakers will receivediscounted admission to the con-ference, including a copy of pro-ceedings, and any refreshments and

luncheon. For more information onthe event, please e-mail Gail Flowerat [email protected]; or CharlieZeng at [email protected]. AP

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A S S E M B L Y & M A N U F A C T U R I N GLead-Free Webinar Series

www.apmag.com/webcasts

Participatein the discussion.

Talkto the experts.

Registertoday!

Wednesday, October 11TH, 12:00 Noon (Central)



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BY JULIA GOLDSTEIN

SAN FRANCISCO, CALIF. Many compa-nies were eager to share their technol-ogy and business news with the editorsatAdvanced Packaging. Here is some ofwhat we saw:

Test sockets. Kulicke & Soffa (K&S)

introduced a new test socket technol-ogy last year that replaces traditionalspring-loaded pins with a photolithog-raphy-based process. Flexible metal leadsare used as the contacts, providing lowcontact force to minimize pad or bumpdamage. Oded Lendner, senior VP of

Package Test, explained that K&S nowhas a product based on this technology,called Quatrix, which is being tested bycustomers and is expected to go into pro-duction at the end of the year. Contactorlife has been tested up to 2.5 million cy-cles, and will be specified at one millioncycles for production. Standard metal-lization is Au over Ni, with a Pd-basedalloy as an option for probing lead-freesolder bumps. In an effort to improvetime-to-market for their standard prod-

ucts, K&S introduced web-based socketselection software that enables custom-ers to input specifications for BGA testsockets and receive a detailed footprintdiagram and quote within 24 hours. GoldTechnologies has a new product for test-ing lead-free packages that is based ontheir spring-loaded Au-plated probes,but includes a proprietary coating onthe pins, as well as higher spring force.They have also introduced a socket liddesign that can accommodate a range of

package heights.Wafer Dicing. Laser dicing technol-

ogies are coming to the forefront. Onenew player in the semiconductor spacewill be New Wave Research. They in-troduced a compact laser scribing sys-tem for 2- and 3-in. sapphire wafers sixmonths ago, which is now used for high-

volume production by customers in theLED market. A new system for siliconwafer dicing that can accommodate upto 12-in. wafers is in development and

expected to be released in a little over ayear. Synova was showcasing their wa-ter jet-based laser system. Guiding thelaser beam down a 25- to 50-m-widewater jet allows a much larger workingdistance than conventional laser dicingmethods, and the water automaticallycools the area being cut, eliminating theheat-affected zone. CEO Bernold Richer-zhagen noted that customers are usingthe system to cut Si, GaAs, and SiC wa-fers, as well as to remove edge damage

from thinned wafers after backgrinding.Synovas next focus will be on packagedicing, where the variety of materials to


NEWSI N T H E

News from SEMICON West

continued on page 13

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be cut poses many challenges.Materials. Honeywell discussed their

wafer-thinning materials, announced inApril as the first new product line fromtheir Chandler, Ariz. manufacturing fa-cility. By using a bulk etch, a stress reliefetch, and a texture etch to enhance ad-hesion, they are able to completely re-place backgrinding and the wafer dam-age that goes along with it.

Polysciences, Inc. has been manufac-turing encapsulants and adhesives forOEM customers for decades, but this isthe first year they exhibited at SEMI-

CON. One of their products is an en-capsulant that is dispensed in a fineline over wire bonds to lock the wiresin place. It effectively halves the lengthof the long wires used in stacked pack-ages. The encapsulant flows down to un-derlying wires, but does not touch thesubstrate. Standard overmolding ma-terials and processes can then be usedwith minimal risk of wire sweep.

China or Mexico? Manufacturingin China has been a hot topic in re-

cent years, with much of the emphasison reducing manufacturing costs. Key-note speaker Tien Wu, President of ASEAmericas & Europe, gave an interesting

viewpoint. He said, Why you want togo to China [is] to rule the world, notto save 20%, but to be well-positioned tosell products to the Chinese. He also not-ed that the emergence of China could beconsidered as a black hole draining re-sources from the U.S. or as a new growthengine driving the semiconductor indus-

try. Tiens advice to companies consid-ering expanding into China is not to goahead if their only reason is to trim laborcosts. Labor costs are rising in China, asScott Kulicke noted during K&Ss PressLuncheon. High employee turnover, asmuch as 25%, is a problem, and sometechnical and managerial expertise is notavailable in China. Hiring workers fromTaiwan and Singapore to fill the gaps in-creases costs. Still, K&S continues to shiftmore of its manufacturing to China, and

Kulicke said that 90% of its wire bondersales are to Asian customers.

Ron Jones, co-founder of Silicon Bor-der, is looking to greatly expand man-

ufacturing in Mexico and recentlyannounced groundbreaking on a billion-dollar industrial and educational com-

plex in Mexicali, Mexico, just south ofthe U.S. border. Silicon Border has hiredtwo engineering firms, one Americanand one Mexican, to design and buildthe infrastructure and provide supportto tenants building manufacturing fa-cilities. Jones is in negotiations with po-

tential tenants IDMs from the U.S.,Europe, and Asia and expects to signletters of intent by this fall. The long-term

goal is to have manufacturing facilitiescovering all steps of semiconductor fab-rication and assembly, providing a com-plete supply chain in North America. Ifthe first tenants are successful, it is likelymore will come and make Silicon Bordera viable alternative to China. AP

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C O V E R S T O R Y


Voids or air gaps in underfill are a common problemacross underfill applications, from the smallest die onflex to the largest BGA. The consequences of having

voids in underfilled parts depend on the package designand use model. Voids typically result in a loss of reliability. This

article explores strategies for troubleshooting void problems.

Detecting Voids

If you have determined there is a voiding problem, you prob-ably already have a method of detecting the voids; however,different methods can be useful for troubleshooting. Three ofthe most common methods for detecting voids are the use of aglass die substrate, ultrasonic imaging, and destructive testingof a cross section or breaking the die off the part.

Using a glass die or substrate can be helpful. This methodprovides instant feedback during testing and can be used tohelp understand flow patterns to optimize underfill speed. Us-

ing underfill materials of different colors can also help visual-ize the flow. The disadvantage of this method is that flow and

voiding behavior may be slightly different for glass parts thanactual production parts.

Ultrasonic acoustic imaging is a powerful tool. It allows theuser to detect voids in the underfill material on the actual pro-duction part before or after cure. The size of the void to be de-tected can be limited depending on the package and equipmentused, so there is a need to check with the equipment makers to

understand what size void can be detected. These tools are alsouseful in reliability testing to detect delaminating and intercon-nect failures. Figure 1 shows an image of a void in an underfilledpackage taken with an acoustic microscope.

Destructive testing uses a cross-section saw or breaks the dieor package away from the underfill. These methods can be use-ful to better understand the three-dimensional shape and po-sition of the void. The primary disadvantage of this method isthat it cannot be used on uncured parts.

Causes of Voids

There are several potential root causes of voids. Describing them

and their root causes helps devise tests to troubleshoot them.Some causes include: Flow pattern voids. There are several sub-categories here, but all

of these voids occur during the time the material is flowing un-

BY ALAN LEWIS

T R O U B L E S H O O T I N G

METHODS FOR GAINING RELIABILITY IN UNDERFILL APPLICATIONSUNDERFILLV O I D E L I M I N A T I O N

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Straight through hermetic vias

Up to 40 layers

.001"/" flatness

.002" top surface linesand spaces

+/- .2% via position tolerance

Cool Off. Precisely.High thermal conductivity multilayer aluminum nitride packages from AdTechCeramics are manufactured to achieve position tolerances better than +/- 0.2%,hermetic vias and flatness less than 0.001"/". These features allow for thin film of theexternal surfaces with increased density for high performance microwave applications.Metal components may also be added as required.

The AdTech process has provided high quality, 100% dense AlN ceramic withup to 40 layers in complexity for over 15 years. This, along with 30+ years ofHTCC production, makes AdTech Ceramics your prime source for customceramic packages.

AdTech Ceramics

Advanced Technical Ceramics Company

511 Manufacturers Rd. Chattanooga, TN 37405Tel (423) 755-5400 Fax (423) 755-5438Internet:www.AdTechCeramics.comEmail: [email protected]

Meeting your advanced ceramic needs with experience, communication and technology.

ISO 9001:2000 Certified


C O V E R S T O R Y

der the die or package. The leading edgeof the wave front traps a pocket of air.

Moisture voids. This type of void occursduring curing when moisture from thesubstrate outgases. This commonly oc-

curs in organic substrates. Voids caused by bubbles in the fluid. This

is rare in fluids that materials supplierspackaged, as most suppliers are care-ful about packaging materials air-free.However, mishandling the fluid or re-packaging after receipt from the supplercan introduce bubbles. In some cases,suppliers provide samples or experi-mental fluids that may not be properlyde-gassed. If not configured properly,some automated dispensing equipment

can also induce bubbles in the fluid pathduring dispense.

Contamination voids. Contamination ofexcess flux or other sources of contami-nation can occur in a variety of ways.

Void Characteristics

Void characteristics can help match themup with their root causes. These include: Shape Are the voids round or some

other shape? Size Voids are usually described as the

area they cover in the plane of the die. Frequency Do you get about one void

per 10 parts, or 10 voids per part? Dovoids occur during specific times, all thetime, or randomly?

Location Do the voids appear in oneplace of the die or randomly? Do theyappear attached to interconnect bumps?What is the relationship of the void tothe dispense pattern?

Test Strategies

The first step is to determine if the voidsoccur before or after curing. This can behelpful in eliminating some root causes. Ifthe voids are not present after dispensing,but are present after curing, flow pattern

voids, or voids caused by bubbles in thefluid, can be eliminated as a root cause.At this point, it would be good to lookfor moisture problems, contaminationproblems, some source of outgassing dur-ing cure, or problems with cure profiles.Most underfill materials are designed to

shrink during cure to create compressivestress on the interconnect bumps to im-prove reliability. This shrinking can giveany outgassing source the ability to cre-

ate a void. If the voids are present withthe same characteristics before and af-ter cure, it is a good indication that someflow pattern during the underfill processcaused the void. If the number of voidschanges after cure, there could be morethan one root cause. In some cases, con-tamination can cause two different typesof voids; they can create an obstructionduring flow, then outgas during cure.

Flow-pattern Voids

Two or more flow fronts meeting to trapa pocket of air cause flow-pattern voids.One cause of this can be the dispensepattern. Dispensing on multiple sides of

a BGA or die can improve the speed ofthe flow, but increases the probability oftrapping a void. Experimentation with

various dispense patterns or parts witha quartz die or transparent substrate isthe most direct method of understand-ing how the voids are formed and how toeliminate them. The use of underfill ma-terials with different die colors for var-ious dispense passes (Figure 2) can be agood tool to visualize flow.

Temperature can affect the flow front

of the material. Temperature variationson the part can also affect material cross-linking during flow, speed of flow, andflow speed. Therefore, it is prudent toconsider this variable in testing.

Often, multiple dispense passes areused to reduce fillet size, but can also in-crease the probability of trapping voids iftiming between the passes is not carefullyplanned and controlled. The use of jetting

Figure 1. Image taken with acoustic

tomograph shows void in underfilled package.

Photo courtesy of Hitachi Kenki FineTech.

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C O V E R S T O R Y

technology, instead of needle dispensing,to control fillet size can help reduce thenumber of passes.1Figure 3 shows jet dis-pensing of underfill.

Material flowing to other board fea-

tures (passive components or vias), leav-ing the underfill material short, can alsocause flow-pattern voids. The use of jet-ting technology can help control theplacement of the underfill fluid.

Moisture Voids

Moisture in the substrate can outgas dur-ing cure, creating a void during the cureprocess. These voids are often random inplacement and can have finger- or snake-like shapes. They usually are seen in pack-

ages using organic substrates.To test if voids are caused by mois-

ture, one can pre-bake the parts for sev-eral hours at temperatures above 100C,then dispense immediately on the parts.Once it has been established that moistureis the root cause, further testing to estab-

lish optimal pre-bake times, temperatures,and storage protocols can be designed. Agood metric for water content is to trackweight gain of a part with a precision an-alytic balance.

Note that some flux contaminationissues can be remedied with a pre-bakeprocedure and act like moisture-inducedproblems. It is easy to test for the differ-ence. Moisture-induced problems will re-cur if the part is exposed to humidity; fluxcontamination problems will not.

Contamination issues caused by excessflux often create irregular or random flow

variations, particularly at the intercon-nect bumps. If the voids that are occur-ring during flow show this characteristic,it would be prudent to investigate clean-ing or sources of contamination. In somecases, flux contamination can show up af-ter cure in a series of small bubbles on theside of the die opposite the dispense side.

Apparently, fluid flow carries the flux tothe far side of the die.

Material Bubble Voids

As mentioned earlier, most material sup-pliers are very careful about packagingunderfill material with air bubbles. Im-proper handling, repackaging, or dispens-ing technology can induce these issues. Ifair bubbles in the material are suspected,there is a straightforward way to inspectfor this. Dispense the material from thesyringe through a fine needle and drawa fine line in a long pattern, then inspectfor gaps in the dispensed line. If bubblesin the material have been confirmed, con-

tact your material supplier about properhandling and storage of the fluid.

If no bubbles are found, this test can berepeated with the valve, pump, or jet at-tached to the syringe. If voids occur dur-ing this test, and no voids were presentwhen dispensing directly from the sy-ringe, then the equipment induced thebubbles. In this case, contact your equip-ment supplier about proper setup andequipment use.

ConclusionUnderfill voids can be a vexing produc-tion problem. Understanding the charac-teristics of various root causes, and how totest for them, can help engineers resolvethe issues. AP

References

1. Babiarz, Alec J., Paradigm Shift in Applying Un-

derfill, Pan Pacific Microelectronics Symposium,

SMTA, 2005.

ALAN LEWIS, director of application engineering,

may be contacted at Asymtek, 2762 Loker Ave.

West, Carlsbad, CA 92010; 760/930-3379; e-mail:

[email protected].

Figure 2. Use of glass and two colors of un-

derfill can help visualize flow and formation of

flow-pattern voids.

Figure 3. Jet dispensing the underfill, rath-

er than needle dispensing, can avoid some

causes of voiding under the die.

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IEEE 1451.4FACILITATING TEMPERATURE SENSOR SUCCESS

BY CHRIS SEYMOUR

Temperature sensors are usuallyconsigned to supporting roles insemiconductor manufacturingand packaging. But, as in mov-

ies, how supporting roles perform can bethe difference between success and fail-ure. When problems with temperatureaccuracy, repeatability, or stability arise,the spotlight turns and remains fixed ontemperature components.

In recent years, continuous and rapidadvancements in the semiconductor in-

dustry have thrust temperature sensorsinto the spotlight. Traditional sensorshave struggled to keep pace, and oftenhave been the weakest link in new or ad-

vanced processes. For example, many oftodays applications, such as wafer andintegrated circuit (IC) test and bondingapplications, require an extremely tighttemperature tolerance, and therefore,an extremely accurate sensor. Duringthe past decade, the only way to makea sensor more accurate was to rely on

tighter material property controls. Overthe years, this has resulted in the use ofpurer and more homogenous elementalmetals, which are often more costly andless readily available. This approach hasonly taken the industry so far. Processdrift, unachievable levels of accuracy,and increasing costs drove the needto abandon this approach and searchfor more effective ways to improve sen-sor accuracy.

Two recent developments have

emerged and converged to overcomethe limitations of traditional sensors,and perhaps more importantly, to bringadditional options and benefits to pro-

cesses. These developments include theuse of smart-sensing technology andthe development of the IEEE 1451.4smart-sensing technology architecturestandards. Today, many engineers in-

volved in thermal processes are familiarwith both developments, but have only

caught a glimpse of their potential.Smart sensors achieve high-level accu-

racy not through the use of purer mate-rials, but by putting their known charac-

teristics to work. Specifically, four errorvalues, known from sensor calibration,are transferred into a compatible temper-ature controller during installation. Thecontroller takes these four offset points,connects them with three straight-linesegments, and then performs a high-or-der curve fit to correct known errors.This process improves the sensors accu-racy because it knows the error limita-tions at specific temperatures and replac-es previously assumed tolerance windows

with exact information. The result is lessprocess variation, better efficiency, andimproved yield.

The other development, the IEEE1451.4 standards, is also capturing theattention of the industry. The standardsdefine the parameters for plug-and-playanalog sensors, their interface to exist-ing instrumentation, and the use ofembedded transducer electronic datasheets (TEDS) to convey a sensors er-ror values automatically.

IEEE 1451.4 standards contribute tosmart sensing as Fords assembly lineeased automotive production. The stan-dards not only provide a universal for-mat for smart-sensing information andthe hardware it uses, they also propel thequick adoption of smart sensing by elim-inating adaptability concerns makingthe technology mainstream.

Still, users and potential users of smartsensors see only half of the technologyspotential. IEEE 1451.4-compliant in-

strumentation offers previously unob-tainable levels of accuracy. But becausethe sensors no longer rely on the purityor composition of materials to achieve

Figure 1. The plug-and-play technology

provides linking of the application to the

calibration lab.

S

TA

N

D

A

R

D

S

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The jet shoots a fluidstream as small as 100mand achieves wet outareas as small as 250m allowing tighter diespacing. Jetting has beenproven to deliver higherthoughput comparedto needle dispensing

for die sizes fromunder 1 mm toover 20mm.

Dispensing problems typicallyassociated with needles suchas die clipping, broken wires,bent needles and dripping areeliminated with jettingtechnology. With jetting, youhave fewer problems,higher yields and

a better process.

Jetting delivers speedincreases of 400% over

needle dispensing withimproved yields andbetter accuracies withthese fluids:

Underfills Encapsulants Flux Conductive adhesives UV-cure adhesives

FIND OUT MORE NOW:

Americas: +1-760-431-1919Europe: +31-43-352-4466Japan: + 81-3-5762-2801China: +86-21-5899-1879Email: [email protected]

www.dispensejet.com

Get into production

and to the marketfaster with jetting.

Do you need faster, lower cost,better dispensing?Its called,Jetting.


accuracy, the industry is freeto use sensors constructedfrom virtually any alloy. Thatfreedom means alloys canbe selected to achieve other

benefits, such as stability, ro-bustness, homogeneity, or lowprice and availability.

This higher level of smart-sensing technology opensthe door to an unlimited va-riety of new sensors thosethat can meet modern designgoals. If a smart thermocou-ple can carry its entire volt-age table information, andthis information can be com-

municated to a controller tocorrect known errors, it is nolonger forced to be a standard thermo-couple, such as Type J or K. Instead, al-ternative metals that are more accurate,stable, and available can be used. Forexample, engineers specifying a type ofthermistor may have struggled betweenepoxy-coated units and glass-coatedunits. Epoxy-coated thermistors offer the

best accuracy, but also a low-temperaturerating. Conversely, glass-coated thermis-tors arent very accurate, but offer a high-temperature rating. Using smart-sensingtechnology allows the engineer to make aglass-coated thermistor as accurate as anepoxy-coated thermistor.

Smart sensing contributes to diagnostics

and failure prediction. Sensorschange and degrade in a repeat-able and predictable way. There-fore, it is simple to enable sensorsto communicate their status and

health, via instrumentation, tooperators and maintenance of-ficials. This function allows us-ers to ask a sensor if it is func-tioning properly before startinga batch or process, or schedulemaintenance and downtime in amore cost-effective manner.

Conclusion

Combined, the benefits of smartsensing, especially with IEEE

1451.4 standards offering formand function, are transforming

sensors from a limiting factor within newor advanced processes, to an enabling com-ponent worthy of their own spotlight. AP

CHRIS SEYMOUR served as sensor strategic marketing

manager for Watlow. For more information, please con-

tact Watlow Electric Manufacturing Co., 12001 Lackland

Road., St. Louis, MO 63146; 1-800-4-WATLOW.

S T A N D A R D S

Table 1.Calibration information increases accuracy.

See Asymtek at IMAPS Booth 645 and ATE Booth 5623

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M

E

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S

Microelectromechanical sys-tems (MEMS) are alive andwell in 2005 with a grow-ing market now in the bil-

lions of dollars. Motion sensors, todaysfastest-growing commercial segment,continue to see frequent new productlaunches by both established and newsuppliers. While simpler ink-jet chipshave more market share because they aredisposable (part of the ink-jet cartridge),this is a limited market. Inertial sensors,

however, continue to find new applica-tions on a regular basis. While air bagsystems are still the main market for sen-sors, there are many newer applications,such as disk drive free-fall detectors andinnovative consumer applications.

The most popular MEMS fabricationprocess is surface machining where sac-rificial materials, such as SiO

2, are selec-

tively formed and then etched away toleave 3-D structures typically made ofsilicon. This process is also compatible

with CMOS and allows intelligence tobe built into the MEMS chip. MEMS in-ertial devices have moving parts, whichequates to special handling and packag-ing challenges. MEMS parts can be sen-sitive to mechanical shock, especiallyin unpackaged form, and are especial-ly vulnerable to particulate contamina-tion, such as residue from wafer saw-ing. The mechanical motion zone of aMEMS chip must be protected duringsingulation with a temporary mask, or

by wafer-level packaging techniques.However, the most significant pack-aging challenge is to provide environ-mental protection that does not restrict

chip-level motion. Electronic devicesare readily overmolded and the encap-sulant can contact the active side of thechip. But direct contact of the MEMS

surface with molding compound or

other encapsulant would freeze themoving parts. MEMS-specific designsoffer the most suitable solutions tothese special needs.

MEMS Package Requirements

The hermeticity debate continues; do wereally need a full-hermetic package forinertial devices like accelerometers andgyroscopes? We should consider thatmany other types of MEMS products arenot packaged in hermetic enclosures be-

cause they require access to the outsideworld, as is the case with ink-jet chipsand fluidic-MEMS products. But iner-tial sensors are somewhat unique and

require only electrical I/Os. At present,however, inertial devices are being her-metically enclosed with cavity designs somechanical action is allowed. Therefore,

the first MEMS-package requirement is

free space typically achieved with cav-ity-style packaging. Some devices alsorequire internal atmosphere control be-cause moisture and particle contamina-tion can be damaging. Getters (trappedmoisture and particles), lubricants, oranti-stiction agents may also be addedto the package to prevent wear, degra-dation, or stiction. Stiction, a combi-nation of sticking and friction, occurswhen smooth, planar surfaces makecontact and become locked together

permanently by short-range atom forc-es. Because MEMS devices are so small,these moving parts have a high area-to-mass ratio, making stiction likely. More

BY KEN GILLEO

PROVIDING A FOUNDATION FOR FUTURE PACKAGING ADVANCEMENTS

MEMS PackagingUpdate

Figure 1. Packaged MEMS accelerometers.

5 9AP_2 20509AP_20 20 8 26 5 12:5 :59 PM8/26/05 12:50:59 PM



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M E M S

complex MEMS devices, such as gas andfluid analyzers, require selective access tothe environment.

Commercial Package Designs

MEMS inertial sensors are one of theoldest classes of products and one of themost active areas. Production is expectedto exceed 600 million devices for 2005.Cambridge, Mass.-based Analog Devic-

es, Inc. (ADI) did much of the pioneer-ing work in this field and enjoys a leader-ship position in the accelerometer area.ADI reached a milestone earlier this yearwhen they shipped their 200-millionthinertial sensor. But there is substantialcompetition. Freescale also has a longhistory in motion sensors and recently

has launched 3-axis motion-sensor prod-ucts. OKI, MemSense, Hitachi, Kionix,and STMicroelectronics have, or soonwill offer 3-axis accelerometers. Whilesuch devices are useful for the automo-tive market, other applications includecell phone pedometers, game sensors/controllers, and a variety of sports prod-ucts. MEMS can already help improveyour golf game or fly-casting skills.

Most inertial devices are packaged insmall QFN format. The smallest pack-

age is 5 5 1.2 mm, offered by Kionix,but competitors have designs only slight-ly larger. Figure 1 shows several QFNMEMS packages. Most use ceramic her-metic packages, at least for now. The sim-ple QFN has reduced the cost over earli-er ceramic cavity-style packages that hadaccounted for more than half of the totalcomponent cost. But even newer ceramicQFNs are not the lowest-cost packages.The general electronics market enjoyslow-cost plastic packaging that reaches

as low as $0.05 per assembled packagefor low I/O QFNs. This is almost an or-der of magnitude lower than MEMS ce-ramic QFNs.

Plastic vs. Ceramic

Electronics have benefited from low-cost plastic non-hermetic packagingmaterials for the past 50 years. Simpleepoxy overmolding adds little cost, es-

pecially today, with area or flood-mold-ing techniques that produce hundredsof packages per cycle. The main cost forplastic packaging, however, has been at-tributed to the platform, or chip carri-

er. The QFN has reduced cost by sim-plifying the platform and eliminatingsecondary operations, such as solder-ball attachment, making this the lowestcost design in production. Aware of thecost benefits of plastics, the MEMS in-dustry has been seeking ways to adaptcost-reducing plastics. Because a cav-

ity is required, at least around the me-chanical zone, two basic strategies areavailable.

Although epoxy cavity packages arefeasible, transfer molding is not theperfect process here. However, injec-tion molding, a more common plastic-shaping process outside of the pack-age industry, is ideal for producing3-D shapes, including cavities. Injec-tion molding uses thermoplastic resinsinstead of thermosets, and that can be

beneficial. There are several commer-cial high-temperature (>300oC stability)thermoplastics that have better proper-ties than epoxies, especially regardinglow moisture absorption. Whats more,materials such as liquid-crystal poly-mers (LCPs) pass flammability specswithout adding flame retardants. Bro-mine flame retardants are coming underregulatory attack and may be banned, sointrinsic flame retardancy is a plus forpackaging materials. Even better, ther-

moplastics are no-waste materials,since they can be remelted and reused.This also means that thermoplastic elec-tronics could be recycled just like many

other thermoplastic products.Analog Devices has been exploring

plastic-cavity packages for their MEMSgyroscope family. However, ADI firstcaps the MEMS device at wafer level

so that the motion zone is hermeticallyenclosed. Now, the device is protectedfrom both particulate contaminationand moisture. The bonded-silicon capsare specially singulated so that they aresmaller than the chip, allowing bond-ing pad access. The capped MEMS de-

vice can now be handled more like anordinary electronic chip. While someparts can be overmolded with epoxy,chips that are more mechanically sen-sitive are placed inside injection-mold-

ed cavity packages. Overmolding addsstress due to shrinkage that detunes theMEMS sensor, making it undesirable forsome products. Once the capped deviceis attached and wire bonded to the cav-ity package, a lid is sealed using dis-pensed adhesive. The capping adds cost,but solves pre-package problems, suchas contamination from sawing. How-ever, many MEMS devices cannot becapped and these are candidates for in-

jection-molded, plastic-cavity packages.

These thermoplastic packages have bet-ter barrier performance than non-her-metic epoxies, but do not achieve fullhermeticity; the term near-hermeticpackage (NHP) seems appropriate. Fig-ure 2 shows low-cost thermoplastic cav-ity packages.

Future

MEMS will continue to grow at a steady,sustainable rate that will drive low-costpackaging innovation. Plastic packag-

ing is certainly in the future, but ceram-ic dominates for now. MEMS packagingtechnology, because of its high versatility,will also provide the foundation for na-noelectronics devices that could emergewithin the next 5 years. A paradigm shiftis likely within a decade.1 AP

Reference

1. Gilleo, K., MEMS/MOEM Packaging: Concepts, de-

signs, materials and processes, McGraw-Hill, New York,

NY June 2005.

KEN GILLEO, Ph.D., is a consultant at ET-Trends LLC,

38 Cedar Pond Drive, Suite 6, Warwick, RI 02886;

401/965-8019; e-mail: [email protected].

Figure 2. Thermoplastic cavity packages.

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T H E back-end P R O C E S S

emiconductor components, high-density circuitry, wafer-level chip scale packages, stacked assemblies, micro-elec-tromechanical systems (MEMS), and micro-opto-elec-

tromechanical systems (MOEMS) the advantages of X-rayinspection are well recognized and understood for such applica-tions. However, selecting the right X-ray system for each appli-cation can be a challenge.

A variety of factors come into play, in-cluding how equipment will be used andwhere it will be installed (in a production

line or off-line), feature-size capability re-quired, and a host of performance char-acteristics, such as contrast, sharpness,magnification, and acceptable noise level.Applications also can change. Selectingan X-ray inspection system often meanspurchasing equipment that exceeds cur-rent requirements.

An alternative, cost-effective ap-proach is to purchase a basic systemthat is configured to meet current per-formance requirements. What distin-

guishes the system is the versatility ofthe platform concept, which allows thesystems X-ray inspection capabilities tobe tailored to specific inspection needs. In this case, the basicconfiguration includes: Open microfocus tube with a transmission target the tube

features an acceleration range up to 160 kV and a detail de-tectability of 1 m. The tube also incorporates a design thatenables controlled and continuous stable output intensity forX-ray emission, constant image contrast, and brightness.

Geometric magnification up to 2000. 4-axes manipulator capability of accommodating sample sizes

up to 440 550 mm (17 21 in.). 4-in. (102-mm) dual-field image intensifier. Digital-imaging chain with a CCD camera. A 17" (432-mm) monitor, GUI (graphical user interface) and

real-time image processing system.This system provides a basic X-ray imaging capability con-

tained within a radiation-secure cabinet with a 1 1-m footprint.Additional capabilities can be added to the platform. Instead ofa microfocus tube, a multifocus tube can be substituted. Thistube offers three mode capabilities with a single tube: microfo-

cus, nanofocus and high-power. Instead ofa four-axes manipulator, a six-axes subas-sembly can be incorporated. Should theapplication warrant additional costs, add

a high-resolution scientific-grade camera,BGA module, voiding calculation soft-ware and direct digital detectors.

With such a system, the decision comesdown to what level of performance is re-quired. What detail detectability, for in-stance, is necessary? If above 1 m, then amicrofocus tube will suffice. On the otherhand, for improved feature recognition, atube with nanofocus capability is requiredto meet these requirements. The decisionwill impact cost, because a microfocus

tube costs less than a multifocus tube withan additional nanofocus mode. However, acost/performance analysis based upon im-

mediate and near-term application needs could determine thatthe extra, upfront expense of a multifocus tube.

Design and Performance Considerations

X-ray systems primarily consist of three subassemblies: an X-raysource, remote- controlled fixture for holding and manipulat-ing the sample, and a radiation detector (Figure 1). These sub-assemblies are contained in a multiple-fused, radiation-shield-ed cabinet.

The X-ray source for industrial inspection is a tube, whichmay be sealed or open. An open design usually is a stainless-steel tube, in which a continuous vacuum is created, and it can beopened for cleaning and maintenance. However, a sealed tube is

S

BY UDO E. FRANK

Configuring an X-ray Inspection System

Building on a Basic X-rayInspection Platform

Figure 1. Diagram of a typical X-ray system for

industrial inspection.

X-ray tube

Detector

Sample on X-Y-Zmanipulator withrotating/tilting

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T H E b a c k - e n d P R O C E S S

one in which the vacuum is introducedat the time of manufacture, and it cannotbe opened without destroying it.

The manipulator is designed to pro-

vide precise X-Y-Z positioning and ro-tating/tilting of the sample at variedspeeds, depending on whether a quickoverview of the part at low magnifica-tion, or a more detailed examination athigher magnification, is desired. Thefunction of the detector is to convertthe real-time X-ray data into an imageof visible light that can be seen and ex-amined by the human eye. The mostcommon detector is a combination

video camera/image intensifier. Other

types include high-dynamic scientific-grade cameras and flat-panel direct dig-ital detectors (DDDs).

To determine the required configura-tion for a particular application, choicesare required in terms of the subassem-blies to be installed in the cabinet, such astype of mode required: microfocus, nano-focus, or high-power; most appropriatetype of tube: open or sealed; what mo-tion is required of the manipulator; andwhat type of imaging system is most suit-

able. These are a few of the specific designquestions that should be considered:

Contrast. X-rays are generated withina continuously evacuated tube housing.Electrons are emitted from a cathode,accelerated through a high-tension field(typically 10 to 225 kV) and focused ontoa thin layer of target material, usually tung-sten (Figure 2). As electrons col-lide with target-material particles,they are slowed down, and the lossin kinetic energy is converted into

other types of energy, mostly heat,but also X-rays. Acceleration volt-age determines the velocity and

violence of the collisions with thetarget material; and therefore, thepenetration power of the X-raysgenerated. At 30 kV, more soft ra-diation, which is highly absorbedin typical electronics assemblies,is generated. At 160 kV, more hardradiation is generated. The objec-tive in selecting acceleration volt-

age for a particular application isto achieve the highest possible ab-sorption (or attenuation) differ-ence. Thus, in viewing a solder

ball with a void, radiation must penetratethe ball sufficiently to depict the differencein absorption between the solid metal andthe less-dense area of the void. Therefore,finding the optimal contrast is a one-pa-rameter task of determining proper accel-

eration voltage, because all other param-eters in an X-ray system can be adjustedautomatically.

Sharpness. The focal spot, a resolutiontube generally half the diameter of the fo-cal spot, determines image or geometricsharpness. Therefore, a microfocus X-raytube provides a resolution of about 1 m.

Only open tubes can achieve such high-resolution grades, are capable of higher-acceleration voltages than sealed tubes,and provide higher tube power with

higher intensities (dose rates). They arethe standard in X-ray microscopy.

As seen in Figure 3, the near-punc-tiform shape of the focal spot elimi-nates peripheral shadowing in the X-ray image almost entirely, achieving anearly infinite in-depth sharpness. Therequired resolution is important whenselecting tube types for the application.The smaller the focal-spot capability, thehigher the tube cost, and vice versa.

Magnification. All absorbing struc-

tures of the 3-D sample under inspec-tion are projected as a 2-D shadow imageonto the entrance field of the detector.Geometric magnification depends onthe position of the sample between theX-ray source and detector plane on the

relationship of the focus-to-detector dis-tance (FDD) and focus-to-object distance(FOD). Magnification (m) equals FDD di-

vided by FOD. Magnification increases sig-nificantly within the last few millimeterstoward the focal spot of the X-ray source.

Because of this, the X-ray tube must bea transmission-target type, as a transmis-sion target features a thin X-ray window(250 m) located practically at the samelevel with the focal spot and a thin targetlayer sputtered onto the inner side of theX-ray window from which X-rays emit.With a typical FDD of 500 mm, maxi-

mum geometric magnificationof 2000 can be achieved if thesample to be examined touch-es the outer surface of the X-

ray window. This also is calledstamp magnification.

An FOD of 1.25 mm resultsin a geometric magnification of400, while an FOD of 5 mmachieves 100. For a sample thatis 5-mm high, total achievablegeometric magnification can

vary by a factor of 20. In select-ing a tube design for a particularapplication, maximum geomet-ric magnification required must

be taken into consideration.Total magnification is visible

to the operator on the display-ing media. If, for example, the

Figure 2. Microfocus transmission tube showing gen-

eration of X-ray beam.

Figure 3. Relationship of focal spot diameter and geometric sharpness.

Cathode

Grid

Alignment unit

Electron beam

Objective

Objectiveaperture

Target

X-ray beam

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X-ray source

Object

FOD

Image plane

Ug

FDD

a) With punctiform FEINFOCUS X-ray source

b) With extended (conventional) X-ray source

Benefit:Highest featurerecognitioncapability

F: Focal spot size

F F

FDDGeom. magnification: m =FOD

Geometrical unsharpness: Ug = F (m-1)



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T H E b a c k - e n d P R O C E S S

X-ray image is copied from a monitorscreen onto a wall (by an LCD projector),the image on the wall is enlarged visiblycompared to that on the screen. Howev-

er, the resolution remains the same be-cause only the image pixels are displayedlarger in size.

Noise. In addition to image contrastand sharpness, noise is an important fac-tor in determining image quality becauseit affects the observed clarity. For optical

inspection, noise plays an inferior role be-cause sufficient photons are available. ForX-ray inspection, however, the situation isdifferent; X-ray intensity, or dose rate, has

a significant influence on noise. The rela-tion of absorption signal to the gray-valuenoise level (frequently referred to as thesignal-to-noise ratio) doubles with qua-drupled intensity. The objective in X-rayinspection is to achieve the highest pos-sible intensity. An Isowatt function keeps

electrical power applied to the target con-stant and ensures consistent optimal con-ditions independent of the selected accel-eration voltage.

A recursion filter also is an efficient toolfor reducing noise level without losing real-time impressions of an image. It creates anoutput image that is the weighted sum ofprior images in a time sequence. Duringimaging, gray values of individual capturedimages are being added pixel-wise, and av-eraged. Images that were captured earlierwill be less weighted than those capturedmore recently. Noise reduction can beachieved for an unmoved sample. Shouldthe sample be moved; however, the image

would be smeared. This can be avoidedwhen reducing the recursion level dur-ing movement so the image appears to benoisier, while the sample structures remainclearly discernible during motion. An au-tomatic adjustment of the recursion levelto the motion status (moving noise reduc-tion) ensures user-friendly operation.

FDD also influences X-ray intensi-ty. The relation is an inverse square.Therefore, when the FDD is doubled,the captured intensity is reduced to a

quarter of the previous amount. Forthis reason, the sample should be po-sitioned as close to the X-ray tube aspossible, while adjusting the FDD tothe required magnification grade. Thisis possible only with systems enabling a

variable-detector position.Leaving the pixel number constant

where the converted entrance image is im-aged results in useful post-magnificationeffects. This is possible when the detectorunit consists of a combination of an image

intensifier and camera. The image intensi-fier converts X-ray waves into visible lightand amplifies them. The optica

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