Available online at www.sciencediect.com Pocedia Engineeing 41 (2012 ) 1360 1366 Intenational Symposium on Robotics and Intelligent Sensos 2012 (IRIS 2012) Modal Chaacteistics study of CEM-1 Single-Laye Pinted Cicuit Boad Using Expeimental Modal Analysis M.A.Anua a, *, A.A.Mat Isa a, Ummi Z.A.R a a Depatment of Mechanical Engineeing, Univesiti Teknologi MARA, UiTM Shah Alam, 40450 Selango, Malaysia. * Coesponding autho: Azhan788@salam.uitm.edu.my Abstact Since the level of vibation always depends on the natual fequencies of the system, it is impotant to know the modal paametes of such system to contol failue and povide pevention actions. The demand fo stuctually eliable Pinted Cicuit Boads (PCB) has inceased as moe functions ae equied fom electonic poducts along with less weight and smalle size. This imposes cetain limitations and citical equiements. The applications of Expeimental Modal Analysis (EMA), togethe with Finite Element Method (FEM) allow stuctual modification and optimization of the PCB. Howeve, the pupose of this pape will only investigate the dynamic chaacteistics of CEM-1 Single-laye PCB using Expeimental Modal Analysis (EMA) method. The dynamic chaacteistics ae extacted fo fee-fee end condition. In EMA, a model is developed using ME Scope and modal testing is caied out using dbfa Suite 4.9 to obtain the expeimental natual fequencies and mode shapes. The undestanding on dynamic behavio of this stuctue povides valuable insight into the natue of the esponse and emakable enhancement of its model, stength and vibation. Keywods: Dynamic Chaateistics, Expeimental Modal Anal;ysis, Pinted Cicuit Boad Nomenclatue [F] Excitation matix [X] Output matix [H] Tansfe function matix q Mode shape (modal mode) { o } k ω ξ 1. Intoduction Modal stiffness Modal fequency Modal damping Vibation is an unwanted epetitive, peiodic o oscillatoy esponse of a system. In geneal, it is classed into two categoies which ae fee and foced vibations. Fee vibations occu when small displacement o defomation is given to a system and then eleased while foced vibation will occu if a system is applied by a cyclic foce [1]. Inceasing demand fo safety and eliability on a stuctue o machine esult in a lot of study elated to vibation. System identification is used as to define mathematical model of a systems using the measued input-output data whee the majo pat is to estimate dynamics paametes fo paametic model [2]. Modal identification is a banch of system identification fo systems which the dynamics popeties of the stuctues such as fequency, damping and mode shape ae measued as it povides useful infomation fo enginees to update and/o validate analytical model of stuctues. Besides, it also helps to get infomation fo actual bounday conditions and also stuctues popeties [3]. In ode to undestand the 1877-7058 2012 Published by Elsevie Ltd. doi:10.1016/j.poeng.2012.07.322
M.A.Anua et al. / Pocedia Engineeing 41 ( 2012 ) 1360 1366 1361 dynamics popeties and behaviou of the stuctues, analytical, numeical o expeimental appoaches wee used individually o combination of them. In geneal the modal paametes ae obtained by modal identification methods and this pape will be discussing the Expeimental Modal Analysis (EMA) method on the Pinted Cicuit Boads (PCB). Expeimental Modal Analysis (EMA) epesents an intedisciplinay field that bings togethe the signal conditioning and compute inteaction of electical engineeing, the theoy of mechanics, vibations, acoustics, and contol theoy fom mechanical engineeing, and the paamete estimation appoaches of applied mathematics [4]. Pinted cicuit boad (PCB) is one of the majo components in electical devices like computes, disc dives, mouse, etc. It is made eithe fom an inoganic mateial such as a ceamic and fibe glass, o fom an epoxy o othe oganic mateial. Some examples of PCB mateial ae FR-4, CEM-1 ad CEM-3. These mateials can also be of a single laye o multi laye stuctues. CEM-1 single laye PCB is a boad made of cellulose epoxy mat with single laye of coppe on one side. Duing vaious opeations, the pinted cicuit boad will be subjected to mechanical shocks. This vibation sometimes can be excessive to its stuctue and may esult in vaious failues. Futhemoe, a PCB is often identified fo efinement in ode to design o develop electical devices with impoved size, cost and weight. Papes by Robin Alastai Amya, G.S.Agliettia, Guy Richadson [5] and Ying-Chih Lee, Bo-Tsuen Wang, Yi-Shao Lai, Chang-Lin Yeh [6] ] descibes a modal testing which is pefomed on a PCB with well-defined modal paametes. They coelate FEM and EMA to impove the design of the Pinted Cicuit Boad (PCB). The coelation between EMA & FEA has been visualized in fom of Modal Assuance Citeion (MAC) matices. The iteative updating pocedue has bought emakable enhancement of the FE model, even fo a limited numbe of modes. One possible appoach is to ceate an accuate model of the PCB dynamic esponse; subsequently, the failue pobability can be detemined by compaing the esponse model with coesponding failue citeia fo the electonic components. In pinciple the esponse model can be achieved by a vey detailed FE model of the PCB which would include the mass and stiffness of all components pesent on the PCB. The accuacy of these simplified models has not yet been quantified ove a ange of possible design cases [5]. This study pesents Expeimental Modal Analysis (EMA) to investigate the dynamic chaacteistics of CEM-1 Singlelaye PCB. The dynamic chaacteistics (modal fequency and mode shape) ae extacted unde fee-fee end condition. Pactically, an EMA [7] can detemine modal paametes, including natual fequencies, mode shapes, and damping atios, of the specific PCB without the need of peequisite infomation of mateial popeties and layouts of its individual constituent components [8], [9] and [10] 1.1. Expeimental Modal Analysis (EMA) Expeimental Modal Analysis (EMA) is the pocess of detemining the modal paametes; natual fequencies, mode shapes and damping atios, of a linea, time invaiant system by way of an expeimental appoach. Pedominately, EMA is used to explain a dynamics poblem, vibation o acoustic, which is not obvious fom intuition, analytical models, o pevious simila expeience. Expeimental modal analysis methods involve the theoetical elationship between measued quantities and the classic vibation theoy. All moden methods tace fom the matix diffeential equations yield a final mathematical fom in tems of measued data. This measued data can be aw input and output data in the time o fequency domains o some fom of pocessed data such as impulse esponse o fequency esponse functions [11]. Mathematically, the fequency esponse function (FRF) is defined as the Fouie tansfom of the output divided by the Fouie tansfom of the input. The measuements taken duing a modal test ae FRF measuements. The paamete estimation outines ae, in geneal, cuve fits in the Laplace domain and esult in the tansfe functions [12]. Theoetically, when a stuctue is excited by extenal excitation matix [F], the output matix [X] (such as displacement, velocity and acceleation) can be tested in an expeiment [13]. The tansfe function matix [H] is descibed as the following equation: [ ] [ X ] [ F] H = (1)
1362 M.A.Anua et al. / Pocedia Engineeing 41 ( 2012 ) 1360 1366 Expession fo elationship between modal paametes (modal fequency, modal damping, mode shapes and modal stiffness) and tansfe function of such stuctues will povide the following equation: [ H ] = n = 1 { q } { q } o 2 ω k 1 ω T o ω + i2ξ ω (2) } o Whee{ q, k, ω, ξ ae mode shapes, modal stiffness, modal fequency and modal damping, espectively. In expeiment, to obtained modal paametes only one ow o column in the tansfe function matix is needed fo testing and nomalizing due to the othogonality of the modal mass matix and modal stiffness matix. 2. Measuement Pocedue and Expeimental Appaatus 2.1. Expeimental Appaatus In this study, the measuements wee made on the CEM-1 single laye PCB using modal analysis softwae and equipment (dbfa Suite 4.9 and ME Scope) (see Fig. 1). The size of the tested PCB is 308mm x 184mm x 1.7mm made of Cellulose epoxy mateial with single laye of coppe on one side (Fig.2). Fig. 1. Expeimental equipment including Modal Analysis Softwae (dbfa Suite 4.9 and ME Scope), Impact Hamme, 4-Channel Spectum Analyze, Acceleomete Type 3714, Toggle Key and Hamonie Cad. Fig. 2. Test specimen (CEM-1 single laye PCB)
M.A.Anua et al. / Pocedia Engineeing 41 ( 2012 ) 1360 1366 1363 2.2. Measuement Pocedue fo EMA The basic test setup equied fo making fequency esponse measuements depends on a few majo factos. These include; the excitation mechanism the tansduction system, to measue the vaious paametes of inteest the analyse, to extact the desied infomation The heat of the test system is the contolle, o compute, which is the opeato s communication link to the analyze. It can be configued with vaious levels of memoy, displays and data stoage. The modal analysis softwae such as dbfa Suite 4.9 and ME Scope eside hee. In ode to obtain the modal paametes, expeimental pocedues fo modal testing need to be followed as illustated in Fig. 3. Fo test specimen pepaation, the dimension of CEM-1 is measued and lines ae dawn on the PCB so that it has 15 nodes. CEM-1 is then hanged using vey light ubbe band to get a fee condition (Fig. 4). By 'fee' is meant that the test object is not attached to gound at any of its coodinates and is effectively, feely suspended in space. The expeimental model is developed using ME Scope. Basic plate stuctue is selected and the nodes on the plate ae numbeed. Afte pepaing the test specimen, toggle key and Hamonie Cad ae inseted to the laptop. Hamme and Acceleomete 3714 ae connected to the 4-Channel Spectum Analyze at channel 1 and 2 espectively. Then dbfa Suite 4.9 with Tansient/Impact Hamme Acquisition is activated. Fig. 3. Flowchat of Expeimental Modal Testing
1364 M.A.Anua et al. / Pocedia Engineeing 41 ( 2012 ) 1360 1366 3. Result and Discussion Fig. 4. CEM-1 unde fee condition. The challenge of EMA technique is to be able to sepaate natual fequencies which having eal physical defomations fom focing components, hamonics, o uncoelated noise pesents in the analysis. Fom all the natual fequencies that ae obtained fom this analysis, thee ae only seveal eal natual fequencies fo this expeiment. Thus to choose these selected natual fequencies, the natual fequencies need to be finalized based on its mode shape. In this study, modal paametes (natual fequency and mode shape) ae extacted fom the expeimental data. Fo PCB, the main concen fo the analysis is at the lowe modes as accoding to the woking envionment of a compute. As a esult, five natual fequencies ae obtained as illustated in Table 1. As mentioned ealie, the modal testing is caied out unde fee condition. Pactically, it is impossible to povide a tuly fee suppot condition but geneally feasible to povide a closely appoximates to this condition. This is achieved by hanging the stuctue with vey soft 'spings' suppot such as light elastic bands (see Fig. 4). Howeve, unlike theoetical appoach, the igid body modes no longe having zeo natual fequencies but values which ae vey low in elation to the flexible modes. As that can be seen in Table 2, each mode shape will coespond to each paticula natual fequency. The ange fo natual fequency is in between 43.7 Hz to 548 Hz epesenting eithe bending modes o tosion modes. It can be seen that bending mode is dominant fo the fist thee modes (43.7 Hz to 241 Hz) while tosion mode can be seen in the fouth and fifth mode (363 Hz and 548 Hz). Based on the esult obtained fom Expeimental Modal Analysis (EMA), it is poposed that the esonant should be avoided as such failue may occu at the key components of PCB. The obtained natual fequencies as well as the mode shapes suggested that the vibation is citical at this condition and such PCB design should look upon at the attain data fo consideation. Mode Table 1. Expeimental natual fequency 1 43.7 2 143 3 241 4 363 5 548 Natual Fequency (Hz)
M.A.Anua et al. / Pocedia Engineeing 41 ( 2012 ) 1360 1366 1365 Table 2. Expeimental mode shape Mode Natual Fequency (Hz) Mode Shape 1 43.7 2 143 3 241 4 363 5 548
1366 M.A.Anua et al. / Pocedia Engineeing 41 ( 2012 ) 1360 1366 4. Summay Expeimental Modal Analysis (EMA) is caied out unde fee-fee end condition and the expeimental modal paametes of CEM-1 single laye Pinted Cicuit Boad (PCB) ae successfully obtained. The best expeimental models is developed in ME Scope. The eliability of the CEM-1 single laye PCB depends on the fee vibation of its stuctue. The fee vibation is chaacteized by the inheent modal paametes of the PCB. Theefoe, it is cucial to study the inheent modal paametes (natual fequency and mode shapes) of the PCB. EMA ae common appoach to chaacteize the inheent dynamic chaacteistics of a system. Futhemoe, it is advisable fo futue wok to model the PCB using Finite Element Analysis (FEA) as this is anothe appoached used fo modal analysis. Compaison between the esults obtained in this study with the suggested appoach (FEA) is vital in ode to get the good ageement (well coelated) fom both appoaches. Bette coelation of FEM and EMA can be obtained via model updating and the coelation validation is best done using Modal Assuance Citeion (MAC). Acknowledgements The authos ae pleased to acknowledge the Malaysian Ministy of Highe Education (MOHE) and Reseach Management Institute (RMI) of Univesiti Teknologi MARA (UiTM) fo poviding financial suppot fo this study though a eseach gant FRGS. Refeences [1] C. Muthy. Intoduction to Mechanical Vibation. Bangalaoe: R V College of Engineeing, 2002. [2] L. Zhang, "An Oveview of Majo Developments and Issues in Modal Identification," in Poceedings of the 22nd Intenational Modal Analysis Confeence (IMAC) Detoit, Michigan, 2004. [3] D. M. Siingoingo and Y. Fujino, "System identification of suspension bidge fom ambient vibation esponse," Engineeing Stuctues, vol. 30, pp. 462-477, 2008. [4] Bian J. Schwaz & Mak H. Richadson, Expeimental Modal Analysis, Vibant Technology, Inc. Jamestown, Oct 1999 [5] Robin Alastai Amya, G.S.Agliettia, Guy Richadson, Simplified Modeling of Pinted Cicuit Boads (PCB) fo Spacecaft Applications, (Dec 2006), Astonautical Reseach Goup, School of Engineeing Sciences, Univesity of Southampton. [6] Ying-Chih Lee, Bo-Tsuen Wang, Yi-Shao Lai, Chang-Lin Yeh, Rong-Sheng Chen, Finite element model veification fo packaged pinted cicuit boad by expeimental modal analysis, Micoelectonics Reliability, Volume 48, Issues 11 12, Novembe Decembe 2008, Pages 1837-1846. [7] Ewins DJ. Modal Testing: Theoy, pactice and application, 2nd ed., Reseach Studies Pess, Baldock, Hetfodshie, UK; 2000. [8] Yang QJ, Lim GH, Lin RM, Yap FF, Pang HLJ, Wang ZP. Expeimental modal analysis of PBGA pinted cicuit boad assemblies, In: Poceedings of the fist electonic packaging technology confeence, Singapoe; 1997. p. 290 6. [9] R.F. Gibson. Modal vibation esponse measuements fo chaacteization of composite mateials and stuctues. Compos Sci Technol, 60 (15) (2000), pp. 2769 2780 [10] He X, Fulton R. Modeling and simulation of the dynamic esponse of the electonic packaging, In: Poceedings of the 50th electon components and technology confeence, Las Vegas, NV, USA; 2000. p. 1535 47. [11] Expeimental Modal Analysis, UC-SDRL-RJA, CN-20-263-663/664, and Revision: June 7, 1999 [12] The Fundamentals of Modal Testing, Application Note 243-3, Agilent Technologies. [13] Yating Y, Pingan D, Ezhong G. Stuctual obustness study of a compute motheboad, In: Poceedings of the IEEE intenational confeence on industial technology; 2006. p. 2370 4