Research on Crucial Manufacturing Process of Rigid-Flex PCB Research on Crucial Manufacturing Process of Rigid-Flex PCB

Research on Crucial Manufacturing Process of Rigid-Flex PCB

  • 期刊名字:中国电子科技
  • 文件大小:313kb
  • 论文作者:WANG Yang,HE Wei,HE Bo,LONG Ha
  • 作者单位:School of Microelectronics and Information Engineering,Zhuhai Topsun Electric Technology Co.,College of chemistry and En
  • 更新时间:2020-11-11
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论文简介

Mar. 2006Jourmal of Electronic Science and Technology of ChinaVol.4 No.1Research on Crucial Manufacturing Processof Rigid-Flex PCBWANG Yang',HE Wei',HE Bo',LONG Hai-rong2,LIU Mei-cai,WU Su31. School of Microelectronics and Information Engineering, University of Electronic Science and Technology of China Chengdu 610054 China2. Zhuhai Topsun Electric Technology Co, LTD. Zhuhai 519060 Guangdong China3. College of chemistry and Environment Protection Engineering, Southwest University for NationalitiesChengdu 610041 ChinaAbstract The main characteristics, applications, the emphases of manufacturing process areintroduced, and the research of new product of rigid-flex Printed Circuit Board (PCB) is alsodescribed. In particular, the plasma desmear process, which is the crucial problems ofmanufacturing process, is discussed in detail. Samsung 4-layer rigid-flex PCB has been developedsuccessfully, and the qualification rate reaches to 89.4%.Key words Printed Circuit Borad (PCB); rigid-flex PCB; manufacturing process;plasma desmear processThe rigid-flex Printed Circuit Borad (PCB) hasthe less it weighs. Because eliminating jumper cablesbeen available for nearly 25 years. And this technologyand connectors or flat cable would be used to connectalmost immediately delivered on its promise of different rigid boards together, it gets a reliabilitysimplifying interconnection and assembly of compleximprovement.rigid-flexinterconnection structures. Because of the superiorlymanufacturers to assemble the product and fold it intomechanical and electrical reliability, the rigid-flexa nice compact package'5 8.PCBs have been used in the fields of military,From an historical perspective, rigid-flexaerospace, .automotive,computer peripherals andapplications were developed primarily as anportable electronics. In recent years, this technologyinterconnect method for military systems. In recenthas been steadily developed. But in China, the researchyears, this technology has been steadily migrating intoabout rigid-flex is in the preparatory stage, and thereApplicationutilizingare no applications produced by civil manufacturers.rigid-flex as interconnect have been subjected to harshCurrently, all rigid-flex PCBs are imported from Japanenvironmental conditions suchthermal shock,and America etctthermal cycling, humidity, and salt spray and it isThis paper introduce main characteristics,found to maintain electrical and mechanical integrity.applications and some new products of rigid-flexFrom early 1980's, rigid flex has been used on everyprinted circuit board. Also Orthogonal Experimentalmajor military aircraft platform including the newlyDesign study been carried out to optimize parameter ofdesigned F-22 fighter. Also because its high reliabilityplasma desmear process.and the ability to reduce weight and volume, manycommercial avionics packaging applications has been1 Characteristics and Applications ofdesigned by utilizing this technology, including theRigid-Flex PCB777 aircraft from Boeing. After 1990, rigid-flex hasThere have always been four drivers that havebeen used in the notebook computer, computer diskcreated the need for rigid-flex: 1) weight reduction;drive, automotive engine control, automotive2) reliability improvement; 3) the need for a compactnavigation system and implantable medical device" .package; 4) easier automatically assemble without2 Research and Development of Newspecial fixturesRigid-flex fits weight reductionProductneeds by using a very thin substrate. Typical rigidboards will be run on 0.1 mm core or thicker. TypicalThe manufacturing processesof rigid-flex PCBflexible circuits are run on 0.05-0.06 mm core material.are very com中国煤化工'ent designs,Obviously, the thinner the core and the the circuit are,there is distinctl:YHCNMH GReceived 2005-07-01_No.1WANG Yang, ct al: Rescarch on Crucial Manufacturing Process of Rigid-Flex PCB25Topsun Electronic Technology Co., LTD had2) The formation of microvia. In this stage, rigiddeveloped several research on Rigid-Flex PCBs.manufacturers have made tremendous strides in theFirst product is shown in Fig.1. It's is a size and quality of driled holes that they can generatedouble-sides rigid-flex PCB. The construction consistswith today's equipment. Flex, however, offers a varietyof a single-side flex and a layer of single-side rigidof methods (mechanical drilling, punching, plasmatogether with a modified epoxy prepreg.etching, laser drilling) for via generation. Thisoperation is very critical, since the rigid-flex is built-upRigid Areawith materials at very different hardness. Whereas therigid material is relatively hard, the polyimide and inCoppeTparticular the adhesive are very soft.Rigid clad3) It uses acrylic adhesive materials that haveFlexAreaPrepreghigh Thermal Coefficient of Expansion (TCE).Flexible base materialBecause of the difference of TCE, the flexible portioncan form groove. A new family of low- and no-flowCopperprepreg epoxies can decrease the tensility, which isinduced by adhesive.Fig.1 Double-sides rigid-flex construction4) After drilling, the polyimide and in particularThe second product is Samsung 4 layer flex-rigidthe adhesive generate some smear which can't beremoved by conventional chemical disposal and canPCB. This construction, which is shown in Fig.2, isinduce low-reliability of rigid-flex PCBs. Ordinarycomprised of a double-side Flexible Printed Circuitdesmearing with potassium permanganate, as used(FPC) with a single-side rigid laminated on each side.in conventional rigid board production, is not feasible,The adhesive is also modified epoxy prepreg.since the adhesive is not compatible with strongRigid areaalkaline chemicals. The plasma surface treatmentsystems are now being used to deal with the problem.Not only removes desmear, but also improves platingadhesion and reduces the likelihood of circuit failure.However, Plasma etching system presents somechallenges to the engineer to decide which attributes ofPI Coverlayervia should be measured and controlled. We can set updesigned experiments to discuss which parameters arecrucial to characterizing the performance of plasmaetching system and how to optimize these parameters,which are our emphases.3 Emphases of ResearchTo characterize the factors of plasma etchingsystem is by conducting a Orthogonal ExperimentalDesign (OED) study. The first stage is to decide theFig.2 4 layer flex- rigid constructioncrucial parameters. There are five variables affectingDuring the research, there are several processesthe performance of plasma etching system. Theshould be noticed.relation between factor and level is shown in Tab.1.1) At the stage of the photochemical patterning ofTab.1 Factor-level listcircuit, the quality of the image depend primarily thethickness of resist and the light source. A highlyFactorcollimated, intenselights source is critical tcLevel Do:/cc:.min-1 DC4/ cminRF/kWTI(F) t/mingenerating a straight, clean image. The thinner the(A)(B)(C)(D)(E)resist is, the easier it is to generate a fine image. In ourAl (400)中国煤化工(110) EI(8)A2 (600) .country, there has been an increase in the availabilityA3 (800)MHCNMHG(I30) E2(10) .D(3uu广10Uw (150) E3 (6)of very thin dry-film resists.26Journal of Electronic Science and Technology of ChinaVol.4Under the same condition, two kinds of materialsweigh (w1) using electronic balance and after plasma(epoxy, polyimide) are tested: the first materialetching weight (w2) again.consists of a layer of adhesive material with single-sideThe equation for the etching rate is D=(w1-w2)t,rigid laminated on each side; the other is comprised bywhere t is time.two layers flex lamination.The experiment scheme and result of experimentSample size: 5 cmx5 cm.are shown in Tab.2.Measurement: before plasma etching weight itsTab.2 The experiment scheme and the related resultsFactorNumber02/c-minDcE/cc minRF/kWT/(°F)t/minEP(epoxy)PI (polyimide)(A)(C)(D)D /mg min~0/ mg min-'1ABC101E110.252.75212.102.95311.173.004C2D28.752.009.501.80AlE35.501.83239.251.69C3D3328.001.957.831.75228.503.194.10126.67EI9.753.63)115.304.703311.503.5816A221)214.635.1317CI17.004.75180212.505.001902(A.0.800.83 .10.133.752:A3B211.705.10c110.834.17D131204.00:39.832.839.156.7412.2611.279.13k111.7110.338.867.8210.60k2E7.397.139.168.52<34.433.452.08R2.192.164.073.402.81<12.932.283.26 |PI中国煤化工2.563.171.922.84CNMHG1.981.242.141.120.45MH_No.1WANG Yang, ct al: Rescarch on Crucial Manufacturing Process of Rigid-Flex PCB274.4.0 -3.5昌P 3.02.5 .2.01.5咖E60 :1mAlA2A3BIB2B3CIC2C3DID2D3E1E2E3reurss mnEEt2EFig.3 Main Effects Plot-PIFig.5 SEM before plasma12-1+0-8AlA2A3BIB2B3CIC2C3DID2D3EIE2E3EFactorFig.4 Main Effects Plot-EPFig.6 SEM after plasmaThe relation between experiment index and factorof OED study is shown in Fig.3 and Fig.4.Theplasma etching optimalparameterA3B3C3D1E1 is obtained by experiment analysis ofOED study.The parameter of plasma etching parameter13:81030m(A3B3C3D1E1) is optimization parameter or noshould set up another experiment to verify. Theacceptance of smear removal by plasma process is noFig.7 Cross section metallography micrographafter thermal stresssmear found under SEM. The contrast between beforeplasma and after plasma is shown in Fig.5 and Fig.6.Base upon all of above checks and standard ofThe final objective of desmear plasma is toIPC, the desirable parameters of desmear plasma isenhance the hole wall adhesion which just be verifiedindeed A3B3C3DIE1(0o2 800 cc/min DCF4 300 cc/minby plating adhesion check. Fig.7 is cross sectionRF 1200kW T 110°F T 8 min) which has been done inmetallography micrograph after check. Fig.7 showsexperiment No.25 in OED studv.that after plating and thermal stress (260 C ,中国煤化工10&20& 30sec), cross section of the hole wall have no4 ConclusYHCNMH Gvoid & hole wall pull away.After the development of 2-layer rigid-flex PCB,28Jourmal of Electronic Science and Technology of ChinaVol.4the experience of production had been accumulated.MultiLayer Flex and Rigid-Flex Technology[Z]. IPC PrintedThe discovery of crucial process and optimization ofCircuits Expo'95/Proceedings, San Diega. CA, 1995.plasma etching system give engineers forethought andinsight. About the Samsung 4-layer rigid-flex PCB,Brief Introduction to Author(S)1200 products had been made, the quantity of certifiedWANG Yang (汪洋) was bom in Anhui Province, China,products is 1 073. High qualification rate (89.4%)in 1980. He is a master student at University of Electronicindicates the success of this project.chemistry. From Sept. 2004 to Jun. 2005, He was a coagent ofhole metallization of rigid-flex PCB project with TopsunReferences[] King J. Rigid-flex bards/looking at a firm future[J]. FPCElectric Technology Co,LTD. His current research fieldsinclude flex PCB and rigid-flex PCB manufacturing process.Fabrication, 1996, 19(9): 26.HE Wei (何为) was borm in Sichuan Province, China, in .[2] McKenney D JCost-eEfective flex/high-volume1957. He received the M.S. degree in applied chemistry frommultilayer flex and rigid-flex technology[J] PC Fabrication,Chongqing University in 1987. He is now a professor and1995, 18(6): 36-37.master advisor at UESTC. His research interests include applied[3] Maynard B, Irvine, Sheldahl, et al. Reliable plated thoughchemistry and electric chemistryholes for rigid flex boards[J]. ElectronicHE Bo (何波) is tchnology manager of Topsun ElectricPackaging&Production, 1988, 28(9): 42-45.Technology Co, LTD. He has a lot of experience and[4] Joseph F. Improving rigid-fex plated through holeprofessional knowledge in flexible printed boards. Now hereliabilit[J],. Circuit Tree, 1997, 10(3): 78.is in charge of the design, manufacturing process, research and[5] Joel Y. Fine-line flex circuitry/A glance into the future ofdevelopment of FPC.flexible circutry[J]. PC Fabrication Asia, 1995, 3(3): 14-17.LONG Hai-rong (龙海荣) received the B.S. degree in[6] Markstein H W. A manufacturing technologyimprovedApplied chemistry from UESTC in 2004. Now he is afabrication technologies have made rigid-lex circuitrysuperintend of Topsun Electric Technology Co, LTD. Hismore reliable and affordable[]. Electronicreserch interests include electroless plating, plasma desmear andPackaging&Production, 1996, 36(2): 61-62, 64, 66.chemical analysis.7] Keating J, Larmouth R. High Volume Applications ofLIU Mei-cai (刘美才) received the B.S. degree in AppliedCommercial Rigid-Flex[Z]. In IPC Printed Circuits Expochemistry from UESTC in 2004. Now he is an engineer of'96/Proceedings, San Jose, Califormia, 1996.Topsun Electric Technology Co, LTD. His research interests[8] Fjelstad J. Improving rigd-flex plated through holeinclude manufacturing process of FPC, lamination, etchingreliability[J]. Circuit Tree, 1997, 10(3): 78.process[9] Forman C. Advances in flex/rigid flex circuit prototypingwU Su (吴苏) was born in Anhui Province, China, intechnology[J]. IPC Printed Circuits, 1995, 7(3):1 245-11983, She is a bachelor student at SouthWest University for248.Nationalities. Her interests include environmental design and10] Mckenney D J. A Cost Effective High Volumeanalysis.中国煤化工MHCNMH G

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