Fabrication of Barrier Ribs for PDP by Capillary Infiltration Process and Their Sintering Behavior

JOURNAL OF RARE EARTHSVol.22, Suppl., Aug. 2004, p. 098Fabrication of Barrier Ribs for PDP by Capillary Infiltration Process andTheir Sintering BehaviorTae Jung Tang'，Hak Nynu Choil , Chan Hyoung Kang2*，Yong Seog Kim'(1. Department of Materials Science and Engineering，Hongik University, Seoul 121-791, Korea; 2. Departmentof Aduanced Materials Engineering , Korea Polytechric University Shihung-City, Kyonggi-Do , Korea)Abstract: Closed-cell type barrier ribs such as meander, honeycomb , SDR, and wafle types were produced using capil-ary molding process . Sintering of the ribs revealed that the ribs with asymmetric geometry such as meander and SDR typebecame distorted severely by the sintering process, but the ribs with symmetric geometry such as honeycomb and waffletype maintained their green state morphology . After sintering, the ribs were coated with green phosphor using osmosis coat-ing process and its luminance characteristics were evaluated . The results indicated that the luminance and its fficiency isimproved by using closed-cell type ribs with the new phosphor forming technology .Key words: PDP; close celled barrier ribs ; sintering distortionCLC number: TG146.4Document code: AArticle ID: 1002 - 0721(2004)- 0098 - 04Recently, PDP has been considered as a primein the distortion of the sintered ribs. In this study,candidate for large-area information display. The pro-therefore, the effect of parameters such as solid load-cessing costs, luminance efficiency, and resolutioning in the paste，presintering temperature, and asym-of PDP must be improved more to expand the wide-metric design of the barriers ribs on the sinteringspread use for wall-hanging TV applications. For thatshrinkage of the barrier ribs were investigated.purpose, a new processing route for closed-cell typeL nannnnnnojbarrier ribs needs to be developed. Currently, barierribs of PDP are being produced using powder blasting出processl2J. This process has merits of low cost, ex-pandability to large area device, and high processingspeed . This process ，however, has difficulties in pro-ducing barrier ribs of closed-cell type, such as SDR,DelTA，and honeycomb .Ln易The authors have demonstrated the possibility ofLon_o_n_o__ Rilbw for PDPQReko=e the mold)using capillary molding route in producing the closed-b)cell type barrier ribsb3l. In this process, a soft work-Fig.1 Master mold preparation (a) and Capillany molding pro-ing mold is placed on the top of a paste coated on thecess (b)glass substrate and let the capillary pressure developedbetween the mold and paste to fill the cavities of the1 Experimentalmold (Fig.1)l4J. The mold is released after the pasteis thermally cured. This process can reduce the pro-Master molds for the capillary molding processcessing steps and loss of the materials. In addition,were prepared using a photoresist resin (SU-8 2075,the dimension of the ribs produced can be refined andMicro-Chem，USA). A resin film of 200 μm thick wascontrolled more precisely than those produced by theformed on a silicon wafer by spin coating. The filmpowder blasting process.was patterned after the barrier ribs in cells of stripe，Sintering of the closed-cell type barrier ribs[5] .DelTA、and SDR arraneements using a conventionalproduced by the capillary molding process, however,UV中国煤化Iittem was used as arevealed asymmetric shrinkages of the ribs, resultingm.TYHC N M H G plydimethylsiloxaneReceived date: 2004 -06 - 10; revised date: 2004- 06 -20Foundation item: Project supported by 2003 Hongik University Researth Funding+ Corresponding authorTae Jung Tang et al. Fabrication of Barrier Ribs for PDP by Capillary Infilration Process9(PDMS, Dow Corming, USA) mixed with a curing agent (Sylgard 184, Dow Corning, USA), was cast on(athe top of the master mold and cured in a vacuum ovenat 120 9C for 30 min. The PDMS mold was used asthe working mold for capillary molding process. Thprocessing step of the mold preparation is schematical-ly ilustrated in Fig. 1(a). For the paste to fll-up themold cavity, a thermally curable paste was used. The)aste consisted of epoxy resin of biphenol A type,amine type hardener, dispersant, and ceramic pow-200 umders ( glass frit and alumina powders) .6)The paste prepared was printed on a glass plate(PD-200，Asahi Glass Co. , Japan) and the thicknessof the layer was ~ 40 μm. Subsequently, the PDMSmold was placed on the top of the paste and kept in adrying oven at 120 C for 1 h for curing of the paste.After the sample is taken out of the oven, the moldwas removed from the sample. A schematic ilustration300umof the capillary molding process is shown in Fig.1(b).After the molding process, the sample was heated at aFig.3 Morphology of closed-cell type ribs after sintering: (a)rate of 5 C. min ~ 1 to prefiring temperatures and keptasymmetric type Barrier ribs (SDR) and (b) symmetricfor 1 h. The prefiring temperature was varied from 450type Barrier ribs (Wafle)to520 C. After the prefiring stage, the sample washeated at the same rate to 570 C for sintering. Thepitch was 150 μm. Especially， the closed cell typeholding time at the sintering temperature was 30 min.ribs were fabricated without any defect with this prcThe sintering was conducted in air atmosphere.cess. The results indicate that the capillary moldingprocess might be applicable for the processing of barri-2 Discussioner ribs of PDP, especially high-definition and closed-Fig.2 shows the master mold and working moldcell type ribs .fabricated by replication process. As noted from the3 Resultsshapes，the master molds were replicated precisely .Fig. 3 shows waffle and honeycomb type of barierFig .4 shows the morphology of meander type bar-ribs formed via the capillary infiltration process. Arier ribs in (a) cured and (b) sintered states. Anoted in the figure, sidewalls of mold are very smoothshown in the figure, the morphology of the ribs wasand uniform. The closed-cell type cells were formedseverely distorted such that the rectangular cells werevery uniformly over the large area. The width of thechange to octagonal type cells after the sintering.ribs was 40 μm and the height was 120 μm and cellThis distortion is believed to occur mainly due toa)an anisotropic shrinkage of the barrier ribs during sin-tering. As ilustrated in schematic diagram (Fig.5),the sintering stress from crossing ribs during sinteringshould pull the horizontal ribs together, resulting in50mm转38mm”60mmthe distortion. Similar phenomenon was observed withb)SDR type cells as in Fig.3(a). In this case, the ribswere distorted such that the rectangular cells weretransformed to semi-hexagonal cells. With the sym-metric ribs such aq hnnevcnmh, and waffle type ribs,500 μmS00μmthe sint中国煤化工ts balances eachother,YHCNMHGn.Fig.0 shows the microstructure of the barier ribsFig.2 Master mold fabricated by photo lithography method (a)in a cured state. In the cured state ，the ceramic pow-and Polymeric working mold by replication of the masterders are separated from each other by the binder poly-mold (b)mers. Upon sintering process, the binder are evapora-100JOURNAL OF RARE EARTHS, Vol. 22, Suppl., Aug. 2004(b15 umFig.6. SEM micrograph of barrier ribs in cured stateFig.7, the ratio was 1.38 with the cells prefired at400 C. This means that the width of the cell at thecenter is larger than that at the barrier ribs by 38% .As the prefiring temperature is increased to 520 C,Fig.4 SEM micrographs of meander type in (a) cured andthe ratio was slightly increased to 1.42. In other(b) sintered stateswords, the distortion was not affected significantly withthe prefiring temperature . This indicates that a signifi-(a)cant fraction of the distortion occurred during the den-sification of the powders .Fig.8 shows the effect of powder content in the .paste on the distortion of meander type cells. Thepowder content in the paste was changed from 54% to60% (mass froction). The content could not be in-creased over 60% (mass fraction) due to increased500 umviscosity of paste with the powder content. As noted(b)from the figure, the distortion became less with the in-crease in the solid loading, suggesting that the shrink-age associated with densification is the main cause ofthe distortion.One of the ways to reduce sintering distortion is toincrease alumina content in the barrier ribs. The in-creased alumina content should decrease the densifica-tion of the ribs ，thereby reducing the sintering distor-tion. Fig. 9 shows the barrier ribs of SDR type conta-Fig.5 Schematic ilustration of sintering stress on (a) meandertype and (b) honeycomb barrier ribs1.5ted and powders are aggregated each other to form ful-ly dense barrier ribs. The distortion of the ribs, there-fore, may be caused either by evaporation of the or-ganic components during the prefiring step or by thedensification of the powders during the sintering steps .In order to examine the effect of the shrinkage oC-中国煤化工curring during the binder evaporation， the ratio ofYHCNMHG00350maximum cell width at its centerd2) to crossing riblength (di) of SDR type cell was measured as a func-Prefiring tempernturerCtion of prefiring .temperature. The value should in-Fig.7 Effect of prefring temperature on the degree of sinteringcrease with the sintering distortion. As shown in thedistortion on the SDR type barrier ribsTae Jung Tang et al. Fabrication of Barrier Ribs for PDP by Capillary Ifilration Process101remaining in the ribs. The pores should degrade themechanical properties of the barrier ribs and out-gassing from the ribs during operation of the PDP.The distortion of barrier ribs of asynmetricalshrinkage poses a significant linitation for the processing of the cells such a SDR and DelTA via the sinter-ing route. In other words , symmetrical cells such ashoneycomb and wafle type cells might be. more suit-able for the processing of barier rib via sintering routeas the distortion associated with densification can be51525459 57minimized.Solid loadingvo1l%Fig.8 Efect of solid loading in paste on the sintering distor-4 Conclusiontion of barier ribs of meander typeClosed-cells with barrier ribs such as meander,honeycomb, waffle and SDR type were prepared viamolding process by action of capillary molding of pastecontaining ceramic powders of barrier ribe. Sinteringof meander and SDR cells resulted in distortion andtwisting of cell morphologies, but that of honeycomband waffle type cells maintained their original morphologies . Asymmetric sintering stress on the barrierribs generated during densification of the ceramic pow-231 um，ders seemed to cause the distortion of such cells . Thissuggests that symmetric cell would be more preferredFig.9 Morphology of SDR type barrier ribs containing 30% a-in the manufacturing of plasma display panel. .luminaReference:ining 30 wt% of alumina. As shown in the figure, thedistortion of the barrier ribs was minimized . The addi-[1] Byung Hak Lee, Eun Gi Heo, Cha Keun Yoon, et al.IMID03' , 347.tion of alumina should have retarded the viscous sin-[2] Bouzid-s, Bouaouadia-N. Journal of the European Cetering of barrier ribs and reduced the distortion of theramic Society, 2000, 481.ribs . The observation of the microstructure of the ribs,[3] TJChang, YH Kim, KS Yoo, et al. SID'03 B0OK2,however, revealed that a significant amount of pores1011.中国煤化工MYHCNMHG