Materials and Technological Developement of Screen

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Horvah E. e al. Maerials and echnological Developemen of Screen Prining in ransporaion

MATERIALS AND TECHNOLOGICAL DEVELOPEMENT OF SCREEN

PRINTING IN TRANSPORTATION

Eszter Horvath1, Gabor Henap2, Gabor Harsanyi3

1, 3 Department of Electronics Technology, Budapest University of Technology and Economics, H-1111

Budapest, Goldmann Gy. 3., building V2, Budapest, Hungary2 Department of Applied Mechanics, Budapest University of Technology and Economics,

H-1111Műegyetem rakpart 5., building MM, Budapest, Hungary

Received 21 December 2011; acceped 1 February 2012

Abstract: Screen prining is a widely used echnology in elecronic echnology. Even hough

here were many developmens in he echnology, i is sill being under improvemen. Tispaper deals wih he auomoive indusry relaed screen prining processes. Te processesassociaed wih layer deposiion and he manuacuring process parameers, which affec hequaliy o he prins. As he repair o elecronic conrol uni (ECU) used in road vehicles isnearly impossible he qualiy o prining hereore unquesionable. I is very imporan ha heaccidens caused by mechanical ailure mus be kep as low as possible hereore he avoidanceo ailure in screen prining is no only economical quesion bu in case o ransporaion iis also quesion o road saey. Finally, an overview is given o he ypical ailure effec andpossible causes appearing in screen prining.

Keywords: screen prining, squeegee, layer deposiion, elecronic conrol uni.

1 Corresponding auhor: [email protected]

1. Introduction Auomoive indusry is one o he mosdynamically developing secors. However,every improvemen should be handled verycareully, because an incidenal ailure can akehuman lie. Tereore, qualiy and reliabiliyplays a very significan role in he auomoiveindusry. Someimes hese applicaions

have o sand high power, emperaure ormechanical sress. Tereore, hick film andLCC (Low emperaure Co-fired Ceramics)are acceped echnologies or hese purposes,e.g. in ESP (Elecronic Sabiliy Program) orCU (ransmission Conrol Uni) (Borgees,2008). Tey are suiable or high-perormanceengine conrol uni (Nishigaki e al., 2004),gear conrol unis, ani-blocking breakingsysems and speed conrol devices (Bechold,

2009) or uel cell applicaions (Parsch eal., 2006). Furhermore, polymer hick filmis also uilized in he producion o heaedauomobile mirror (Berg e al., 1983 - Paen)and sea (Ellis, 1961 - Paen). Since herealizaion o elecric inerconnecion andpassive elemens is screen prining, hequaliy o he end produc is condiioned

by his echnology. In order o achievehigher reliabiliy o hese devices, he mosimporan echnological process has o bedeeply undersood.

1.1. History of Screen PrintingTe origin o screen prining can be racedo he Song Dynasy in China. Alhoughhis echnology has been used since he 2nd

UDC: 655.228:656.1



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Inernaional Journal for raffic and ranspor Engineering, 2012, 2(2): 133 – 141

millennium i is sill under developmenand here have been many innovaions wihhe echnology in he las 50 years (Kosloff,1987). Te echnology has a large applicaion

field as varied as decal abricaion, balloonand clohs paerning, exile abricaion,producing signs and displays, decoraiveauomobile rim and ruck signs and las buno leas prined elecronics, including circui board prining and hick ilm echnology.Tese circuis are wildly used in nowadays vehicles. Screen prining echnology offers widespread and inexpensive way o realisehigh-densiy circuis (Horvah, 2008). Manual

screen prining can be carried ou by usingonly a rame, a screen, a squeegee, and paseor ink. While he auomaic varian requiresscreen priner equipmen, i signiicanlyspeeds up he process.

2. Methodology – Applications andMaterials

In he producion o prined wiring boards,he prining is usually based on his screenprining echnology. Each applicaion fieldrequires a horough invesigaion o he screenproperies beore selecion he righ screenype. I can happen ha one ype o screenfis in only wih one applicaion. Firs, hemaerial o he screen has o be deermined.Te mos common maerials used or screensin ransporaion are polyeser and meal.

Polyeser and meal mesh are he mos widespread screen abric because polyeseris widely used or is versailiy and cheapness while meal mesh (made o sainless seel,copper, bronze, or brass) is he mos durableabric uilised or mass producion and alsoappropriae when plasic subsraes areprined wih heaed inks (Board, 2003). Ahe screen selecion, urher parameers haveo be given. wo ypes o hread are available:

mulifilamen or monofilamen. Monofilamen

ype provides beter qualiy han mulifilamenype avoiding prins wih uneven edges buhey are more expensive han mulifilamenhreads. Anoher parameer o he screen is he

mesh coun, which is he number o hreadsper linear inch. Te higher is he mesh counhe iner deails and higher qualiy can beproduced. Te diameer o he hread playsalso a significan role in he screen prining. A larger hread diameer provides highersrengh o he abric, bu he overlayinginduced by he filamens resuls in worse prinqualiy. Neverheless, we canno orge abou weave paterns. Tree ypes o weave paterns

are applied in his echnique (Fig. 1):

• Plain is he simples ype o weave. A single wef is progressively passed over one warpand under he nex warp. I is suiable ormos applicaions.

• will is similar o plain weave in ha he wef passes over and under warp hreads.

However, warp yarns are skipped apredeermined inervals. I is he beschoice i he qualiy is no so imporan because i is he cheapes soluion.

• Gauze is creaed as pairs o warps arealernaively crossed over one anoherand secured in posiion as he wef hreadpasses hrough. I can be used or long runs because o is srengh.

Areas o he screen are blocked wih a non-permeable maerial o orm a negaive masko he image and a he open spaces he pasecan be pressed hrough. his mask can bemade o meal mask or emulsion mask. Teemulsion is a UV polymerized maerial and isadvanage is ha i can be washing ou so i isreusable. However, unorunaely he solvenso he pases usually solve he emulsion as

well, hus he mask can be damaged during



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cleaning. Eched meal mask can be hesoluion o his problem bu i is much moreexpensive bu i is no reusable. Te rame

is also an imporan elemen o he screen-prining process, however, i is viruallyuseless. Screen rames are available in manysizes, shapes, and profiles. Tey are made omany dieren maerials, including wood,aluminium, magnesium, and seel. Despie oheir eaures, all screen rames are requiredo wihsand he orce o he ensioned screenand he addiional orces applied during

prining remaining la and square beingligh enough o handle easily. For example, a30 cm*30 cm screen wih he ension o 30 N/cm has o sand o approximaely 900 N alongeach side or beam o he rame (30 cm*30 N/cm=900 N). Obviously, he load increasesproporionally o he rame size. I he rameis no appropriae bowing or wising, effecso he rame can occur (Kiddell, 2000).

3. Analysis – Variation and Parametersof Screen Printing

Te prining mehod can be carried ou in wo ways: he common flabed prining, which issuiable or fla rigid subsraes and he flabedcylinder prining (Fig. 2) can be applied orlonger runs o flexible subsrae.

Te screen prining process consiss o orcing

ink hrough a mask covered abric or wire

mesh, which has been mouned, in a srongrame.

Tere are wo main echnique o he screenprining:

• off-conac, where he screen is warped wih a given ension above he subsrae;

• conac, where he screen is in ull conac wih he subsrae.

Conac screen-prining is less advanageousin general, because due o he lif off o hescreen i is ofen deeced damage o he highresoluion paern. In case o o-conacscreen-prining, some pase is applied onop o he screen in he ron o he polymer

squeegee. While he squeegee is moving

Fig. 2.

Flabed Cylinder Prining Source: Auhors

Fig. 1.

Differen Weave Paterns in Screen Prining: a) plain b) will c) gauzeSource: Auhors

a) b) c)



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orward, i deorms he screen downwards unil

i comes ino conac wih he subsrae beneah.Te pase is pushed along in ron o he squeegeeand pushed hrough he screen no covered byemulsion patern ono he subsrae. Te screenand subsrae separae a behind he squeegee.Te flabed off-conac screen prining processis demonsraed in Fig. 3.

Te qualiy o he image depends on several

parameers.

Squeegee pressure: A he deerminaion o heopimum squeegee pressure, a ew parameersshould be assumed. Te squeegee orce haso overcome he orce which is necessary opress he pase hrough he screen, whichdepends on he hardness o he squeegeemaerial hardness, he squeegee angle, he warp hickness, spin off heigh, screen ension,

he raio o and he blade lengh and masklayou size. Te squeegee orce has o be highenough o conac whole edge. Alhough as aconsequence o oo high pressure he squeegeedeorms and premaurely desruced. Due ohe large number o acors, he acual valueo he squeegee pressure is no possible odeermine: i can be speciied by rial anderror mehod. By increasing he squeegeepressure, - lengh and – flexibiliy he squeegee

has a definie wave line rom op view. I he

shape o he squeegee line differs rom he

sraigh line such a way, i leads o bulgingprined layer in he middle he prined image –depending on he ype o pase, he flow - andrheological properies o he pase. In order oachieve uniorm pase film in he whole widho he prined layer he squeegee has o be onlymoderaely flexible. Te raio o he squeegeelengh and he mask layou size plays animporan role because he orce agains spin-

off is much higher i he end o he squeegeeis close o he rame. Advanageous siuaioncan be approached i he size o he screen iswice o he mask layou size. Furhermore,changing he squeegee pressure resuls indifferen prined layers and he elongaion ohe screen can cause aligning ailures as well.

Speed o he squeegee: Te finer is he maskresoluion he lower should be he squeegee

speed. I he prining speed is oo high, hesqueegee canno spin ou he pase regularly bu a hin pase film is lef back in he screen, which can cause disorion o he prinedlayou and pase smearing.

Off-conac se: Afer coarse posiioning ohe patern he disance beween he subsraeand he screen should be checked (Jerzy eal., 1990). Incorrec disance adjusmen can

cause he ollowing ailures:

Fig. 3.

Te Squeegee Pushes he Pase on he Screen and Presses i Trough he OpeningsSource: Auhors



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a) conac disance is small:- During screen prining he screen sicksdown, causing a significan hickening o hepase a he sicking place;

- Sicking down can induces prin-disorion,- Due o higher squeegee pressure he prinedpatern is blurred,

b) conac disance is large:- Te prin is incomplee;- Te hickness o he prined layer is unevenand hin;- Te screen is permanenly elongaed due ooo large squeegee pressure;

- Te imprin disors, he posiioning accuracy(reverse direcion) decreases;- Fine adjusmen can no be done properly.

Squeegee shape: Squeegees are usually made opolyurehane or oher elasomers. Firs, heyare cas in liquid orm, hen cu and milledin order o creae sharp edges. Te squeegeemaerial is delivered o he users in rolled orm

or shipping and or he acual applicaion. Inhe process o screen prining he squeegeehas o perorm ew asks bu hese asks are

influenced by many o parameers. Firs, hesqueegee orces he ink ino he mesh, bu iis influenced by he ink viscosiy and meshopening. In order o deposi he ink ono he

subsrae screen has o be in conac wih hesubsrae, however, oo high screen ensionand high off-conac disance can prohibii. Furhermore, squeegee removes excesspase rom he screen so he hickness o nexprined layer and he image qualiy as well.In order o find he righ squeegee or ourprocess hree parameers o he squeegee haveo be seleced:

• hardness,• profile,• edge shape.

In general, we can sae ha hard squeegeesransmi more orce han sof ones while sofsqueegees have higher adapabiliy o hesurace o he subsrae.

By modiying he proile (Fig. 4) o hesqueegee he value o he orce ransmitedo he prining surace can be limied.

Fig. 4.

Differen Profile Edges Provide Sufficien Mechanical Behaviour and Resrain he ransmited ForceSource: Auhors



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Fig. 5.

Sharper Edge Shape Increases he Image Resoluion and Decreases he Pase TicknessSource: Auhors

In addiion, his shape influences he effecivesqueegee angle. he se angle diers romhe eecive squeegee angle, which is heangle beween he screen and he subsrae,

because he squeegee bends due o he load.I he effecive squeegee angle is small, moreink is pushed hrough he screen ahead ohe squeegee and he less ink is scraped romhe surace o he screen. Square profile ishe mos commonly used profile in screenprining which provides medium adapabiliy bu maximal orce and he effecive angle hese angle are abou he same. However, heeffecive angle is always less han he se angle

in case o bevelled edges. Tis consrucionprovides he bes adapabiliy and minimumorce. Te effecive angle o bevelled profilesis always less han he se angle. Round profilesqueegee has low adapabiliy, ransmisminimum orce and he eecive angle isalways very small and hardly affeced by hese angle. Te sharpness o he squeegee can be se by he edge shape (Fig. 5).

Edge shape esablishes he amoun o inkdelivering o he subsrae. Sharper edge

delivers less ink and he amoun o deposiedink influences he resoluion o he prinedimage, because less ink resuls in sharperimage. In order o achieve bes qualiy in

prining he dieren squeegee hardness,proile and edge shape can be combined(Frecska, 1999). Anoher soluion can beso called roller squeegee (Anderson, 2003).Subsiuing he convenional squeegee bya roller squeegee (Fig. 6) higher priningspeed can be achieved and an excellen andconsisen pase hickness is also ensured.

Fig. 6.

Roller Squeegee Provides Consan Conac AngleWhich Promoes Consan Pase TicknessSource: Auhors



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4. Discussion – Typical Failures in ScreenPrinting

I is very imporan o deec and classiy

he differen ailure ypes o screen prinedimage. I we deec he problems and colleche daa or documening ailures occurred inhe process we have good chance o confinehe ailure mode. Prin definiion auls areone o he mos ofen problem (Krammer eal., 2012), (Legén e al., 1986):

1. Ragged edges/sawooh: his aul usuallyshows as saw edge wih pich equal o mesh

spacing.Tis problem can be originaed in poorly madeor worn screen or rough subsrae surace.

2. Smeared edges:

2.a. Smearing on only cerain pars opatern. Irregulariies on screen surace.

2.b. Overall smearing bu mainly indirecion o squeegee ravel. Low screenension or snap-off oo low.

2.c. General overall smearing. Ink viscosiyoo low, rough subsrae surace, badly worn squeegee or angle o atack oo low.oo much squeegee pressure or unwanedscreen or subsrae movemen duringprining.

3. Incomplee patern:

3.a. Areas compleely missing, paricularlynear he railing edge o he paern.Insufficien ink.

3.b. Failures always in same place. Faulyscreen.

3.c. Prin pachy and missing in depressionsin subsrae surace. Down pressure oo low

or incorrec or incorrec down sop seting.

3.d. Tin prin, missing in pars. Squeegeeransverse oo as.

3.e. Prin hin and incomplee near railingedge. Snap-off oo low or squeegee lifingoo soon or screen blocking occurred.

3.. Prin pachy as in 3.c and 3.d. Ink viscosiy oo high, squeegee oo hard,atack angle oo high.

3.g. Fisheye: A small round or oval

imperecion wih a dark cener. hisproblem is usually caused by ink/subsraeincompaibiliy.

3.h. Motling: A ain, irregular patern inhe image area. Ta is caused by eiherdiffering raes o ink absorpion ino hesubsrae or minor differences in subsraehickness.

3.i. Pinholes: Small prined dos in he non-image areas. Caused by a poorly processedsencil.

Prin hickness auls can also appear (Frecska,2002), (Holmes e al., 1976):

1. Prin generally oo hin Incorrec choice oscreen mesh, squeegee ranser speed is oo

high or ink viscosiy oo low (over-hinningor emperaure effec can change he paseheology), angle o atack oo high.

2. Uneven prin hickness

2.a. Prins are consisenly hin on one edgeor a one end. Screen/squeegee/subsraeno parallel.

2.b. End o end variaion in prin hickness. Variaion in squeegee ransverse speed.



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2.c. Tin paches wih pronounced meshmarkings usually near railing edge o prin.Screen ension or snap o oo low, squeegeelifing oo soon.

2.d. Tin in paches, usually in depressionsin subsrae surace. Down pressure oolow, incorrec down sop seting, squeegeeoo hard, insufficien ink.

2.e. Prins locally hick in sreaks whereink railed behind squeegee. Ink behindsqueegee.

3. Prins oo hick.Incorrec choice o screen mesh or squeegeepressure oo high.

3.a. Oen accompanied by smearing oprin edges. Atack angle oo low, snap-offoo large or oo much ink on screen.

5. Conclusion

Screen prining is widely used o realize desiredimages on several suraces while he processparameers and he maerials involved are variedor each process o auomoive producs. Teechnology is sill requiring developmens dueo higher and higher demands. Te ease oconsrucion and he low cos makes screenprining commercial layer deposiion mehodin he field o labels, elecronics and auomoive

indusry. Te highes qualiy ECUs used inransporaion or in road vehicles producedin such a way.

Acknowledgements

his work is conneced o he scieniicprogram o he “Developmen o qualiy-

oriened and harmonized R+D+I sraegyand uncional model a BME” projec.Tis projec is suppored by he SzechenyiDevelopmen Plan (Projec ID: ÁMOP-4.2.1/B-09/1/KMR-2010-0002). Te auhors would like o hank Havan – Rober BoschElekronika Ld. or unding he work.

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M A T E R I J A L I I T E H N O L O Š K AU N A P R E Đ E N J A T E H N O L O G I J E

SITO ŠTAMPE KOJA SE KORISTI U

TRANSPORTUEszter Horvath, Gabor Henap, Gabor

Harsanyi

Sažetak: ehnologija siošampe je širokozasupljena u elekronskoj ehnologiji.Pored dosadašnjeg značajnog razvoja, ovaehnologija se i dalje unapređuje. Ovaj radse bavi procesima ehnologije siošampe u

auomobilskoj indusriji. Ovi procesi su u vezi sa nanošenjem slojeva i paramerimaprocesa izrade koji uiču na kvalie šampe.Kako je popravka elekronske konrolne jedinice (ECU) ugrađene u drumska vozilagoovo nemoguća, kvalie šampe mora biineosporan. Veoma je važno da broj nezgodakoje su nasale kao posledica mehaničkihošećenja siošampe bude šo je moguće

manji, pa zbog oga izbegavanje greškeu siošampi predsavlja ne samo pianjeekonomičnosi već i bezbednosi drumskogranspora. Na kraju ovog rada da je pregleduobičajenih grešaka u siošampi i mogućihuzroka njihovog nasanka.

Ključne reči: sio šampa, špahle za aplikacije,nanošenje slojeva, elekronska konrolna jedinica.

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Materials and Technological Developement of Screen