Detection of PCB Soldering Defects using Template Based Image Processing Method

Transcription

1 International Jornal of Intelligent Systes and Applications in Engineering ISSN: www.atscience.org/IJISAE Advanced Technology and Science Original Research Paper Detection of PCB Soldering Defects sing Teplate Based Iage Processing Method Şaban Öztürk *1, Bayra Akdeir 1 Accepted : 09/12/2017 Pblished: 28/12/2017 DO Abstract: In this stdy, a predefined teplate-based iage processing syste is proposed to atoatically detect of PCB soldering defects that negatively affect circit operation. The proposed syste consists of a scaled inspection strctre, a caera, an iage processing algorith erged with Fzzy and teplate gided inspection process. The prototype is prodced sing a plastic aterial, depending on the focal length of the caera and the PCB size. Iage processing step coprises two steps. Firstly, solder joints are deterined and boxed sing Fzzy C-eans clstering algorith. Then, the center of each joint is deterined. In the next step, a joint teplate is created that contains solder joints inforation. This joint teplate contains inforation abot the joints that incldes possible toching odds to other joints. Teplate accelerates the algorith diverting to closest joint that ay inclde defect. Finally, each joint is only inspected regarding teplate gide that based on neighbor joints. Proposed ethod incldes a scaled inspection strctre related to focal length of caera. Dring the every qery, PCB st be located sae coordinates via echanical giding on the strctre to obtain sae pictre. Ths, taken pictre cold be sae every trying. The proposed ethod is exected 85 ties on sae saple PCB in case of any fake otpt error. In order to obtain coercial sccess, echanical strctre was iproved and for inspected PCB sccess was obtained 100%. Keywords: Printed circit board (PCB), soldering defects, teplate based inspection, solder joint inspection 1. Introdction PCB is a skeleton of a circit to carry crrent, hold the coponents and connects to coponents to each other s. For this reason, it is very iportant in ters of continity of technological developent and operation of electronic circits. With the developent of technology, deands for electronic prodcts to contain ore featres and to be prodced in saller sizes have eerged [1]. This deand cases the PCB area to be saller or contain ore electronic aterial in the sae area. The increase in the nber of electronic aterials leads to a shortening of the distance between the aterials and ths to soldering probles. Soldering probles often lead to ajor probles sch as failre of the circit or daage to circit eleents [2]. Detection of soldering istakes redces the cost by preventing daage to the circit, and increases prodction qality and efficiency. Exaination of soldering defects anally ade by inspectors, varios probles have arisen. These falts, which are related to the han factor, sally lead to slower prodction, lower qality standards and increased cost [3]. In order to overcoe these probles, copter vision systes are sed for PCB soldering defect inspection [4, 5]. The ain coponents of copter vision systes consist of an external coponent, a caera and an iage processing algorith [6]. Copter vision systes coe to the forefront with featres sch as rapid inspection, objective decision aking, working withot fatige, working nder difficlt conditions [7]. Iage processing is the fndaental part of copter vision. So, it is widely sed in literatre and reel world applications to find an effective soltion for sophisticate probles [8, 9]. In the PCB 1 Electrical and Electronics Eng., Selck University, Konya 42002, TURKEY * Corresponding Athor:Eail: sabanoztrk@selck.ed.tr soldering defect detection process, soldering joints st be deterined via iage processing algoriths. For this operation, object detection is applied first. Then, object recognition is perfored to eliinate joint-like isleading objects so that joint regions can be detected correctly. The goal of this stdy is to find short circit probles cased by PCB soldering process. Dring the first testing of electronics device cold be daage in case of solder bridges. Ths, especially soldering joints which are connects each other relctantly case boards daage. For this reason, inspection before the power p has vital iportance. In order to avoid an han-indced falts a copter vision syste is proposed, which detects probles that ay occr if two or ore joints toch each other de to soldering. According to designed PCB soe joints are already short-circited to each other via circit tracks or soldering area and these joints de to soldering istake is not a proble for the operate of circit. The proposed copter vision algorith does not perceive these soldering defects as error. Bt, if joints that are not interconnected by circit paths are shorted to each other de to soldering probles, this creates a proble for the circit and this proble is perceived by the proposed algorith as a soldering defect. As the first step of the soldering defect analysis, the fzzy c-eans algorith [10] is sed to deterine the joints in the iage. Then, the contact between the joints is inspected according to the previosly defined joint teplate according to regarding teplate giding. The organization of the rest of this paper is as follow; Section 2 contains the description of the proble and details of the proposed copter vision algorith. In the Section 3, experients and experiental reslts are discssed. In Section 4, conclsion is sarized. 2. PROPOSED METHOD This jornal is Advanced Technology & Science IJISAE, 2017, 5(4),

2 Short circiting cases probles for electronic circits. A nber of tests are sally done for this. Bt these tests are costly and take a long tie. One of the fastest ethods for short circit inspection is visal inspection. However, it can be qite isleading becase of the PCB coplexity. Becase soldering joints can be in contact with each other sing circit paths that are difficlt to follow. In sch a case, a short circit cased by soldering will not case a proble and reworking this circit will case both oney and tie loss. The two types of probles that this stdy sggests are; the first is the deterination of the joints that do not have a proble with each other, and the second is the deterination of the pixels that will becoe a proble if they are in contact with each other. These two type joints are shown in Figre 1. clstering, each data is assigned to a grop according to its ebership vale. The nber of clsters is deterined by proble. Eqation 1 is sed to iniize the objective fnction with FCM [13]. n c 2, ik i k 2 (1) J U H x h i1 k1 where U is fzzy atrix, H represents clsters, x represents set of objects. Firstly, h is pdated according to sing Eqation 2. h it, n k 1 n k1 ik ik x k (2) Then, the fzzy ebership atrix is pdated according to Eqation 3 Fig.1.Soldering joint types, a) already connected joints with PCB paths, b) nconnected paths To overcoe the soldering proble, a teplate based copter vision techniqe with joint contact inforation is proposed. For this, a prototype is prodced in accordance with the caera field of view and the PCB diensions. The iages obtained with the help of the caera on the prototype are transferred to the copter and processed. Finally, obtained soldering defects are presented to ser via onitor. Proposed copter vision syste is shown in Figre 2(b). ik, t 2/( 1) 1 c xk h i, t1 A (3) j1 xk hj, t1 A where, A is one of the ebers set area, and sb paraeters i,j,k,,n and c are characterized to show nerical vales of ebers. Fig. 3 shows how fzzy akes defzzication to obtain otpt. Fig 3. Fzzy ses eberships to obtain otpt. Fzzy ipleentation is especially sed and focsed to find borders of soldering areas. In order to iprove proposed ethod sccess Fzzy was erged or ai. Especially any error dring the nderstanding the border of a soldering area, redces syste (a) Fig 2.Proposed Prototype Strctre (a) inspected PCB exaple (b) location of caera in the inspection strctre Figre 2 (a) shows inspected PCB that incldes 50 soldering joints. When PCB was located to end of the plastic rails, caera takes sae pictres to evalate. Ths, this trick is very iportant to iprove evalation reslts. (b) 2.1. Fzzy C-Means Clstering for Joint Detection Fzzy C-Means (FCM) grops the data in a data set according to the siilarity rate. Therefore, the siilar data is assigned the sae grop. FCM was originally proposed by Dnn [11] and advanced by Bezdek et al. [12]. Basically it is an iterative clstering algorith that iniizes the sqared error objective fnction. For perforance and ability Joint Teplate Usage for Joint Contact Inspection In order to obtain effective soltion of this proble in real life, the inspection tie and flly sccess are so iportance to obtain robst behavior for inspection created ethod. Technological soltions that akes slow down prodction speed are generally not preferred. For this reason, rather than very heavy and coplicated systes, siple and fast systes are preferred. Fig.4 shows prepared strctre to take photo to scrtinize the PCB. The inspection of soldering defects for a PCB can be done by exaining all joints against all other joints. In this process, the relationship of each joint to all other joints is exained. Even thogh the reslt is qite sccessfl, the inspection tie is qite long for this process. The soltion akes inspection tie longer wold be seless becase of the long tie. Instead, the joints that shold not toch a joint are identified and only the relationship with these joints is exained to redce inspection tie withot losing total sccess. In this stdy, a joint teplate-based inspection This jornal is Advanced Technology & Science IJISAE, 2017, 5(4),

3 ethod has been presented for rapid detection of soldering defects. In order to prepare the teplate, every joint exeinated by anally which joints can connect the other neighbor joints relctantly. Ths, teplate incldes real possible solder defects locations that coe into connect. Dring the inspection, each joint is exained only for dangeros joints. The steps for creating a teplate are as follows; 1- For each joint, the joints cold which are likely to coe into contact relctantly are identified. Becase there is no possibilities a short circit between the target joint and the joints in far regions. 2- If the two joints are connected together by circit tracks, then no inspection is perfored between those joints. 3- Inspections are perfored between close joints that are not interconnected by circit paths. An exaple teplate is shown in Fig. 5. In the Fig. 5, the nbers on the left and above indicate the nbers of the joints. The colors in the sqares where the joints intersect have certain eanings. The red color indicates that the two joints shold not toch each other. Fro Fig. 5, soldering area, nbered 7, cannot toch area 2, on the contrary, even if area 7 toch the area 1, this is not crcial proble to search. Non-colored soldering areas have no possible to toch each others. The ble color indicates that the two joints are already connected to each other via circit tracks. A joint is only inspected with the joints that have the color relationship specified in the teplate. Becase there is no possibilities for soldering defects with other joints. We can explain the inspection sing teplate process for the first joint as follows; the first joint has only a short circit with the second joint and the seventh joint. For this reason, only these two probes st be inspected. between the first joint and the second joint. Ths, instead of eight reviews, only one review process is sfficient for the first joint. 3. EXPERIMENTS AND EXPERIMENTAL RESULTS In experients, PCB iages are converted to gray level iages. The vale of each pixel is assigned to the range This way it is easier to clster each pixel. The raw RGB iage has 1296x780x3 pixels and after gray level conversion iage size trns 1296x780 pixels. The clstering of the pixels is done with FCM. 3 was selected as the clster nber. The first clster represents the epty PCB areas, the second clster represents circit paths, and the third clster represents soldering joints. In order to iprove searching speed, pictre related to PCB is converted to gray scale. Making gray protects all possible featres and abilities in gray ode and cold be exected in one tie to obtain sae resoltion. In order to convert RGB to gray ode eqation 4 is exected. Linosity ethod is sed RGB to Gray ode converting. Linosity ethod is calclation via Eq. 4. G=0.3*R+0.59*G+0.11*B (4) PCB and soldering areas colors have no iportance on searching ethods de to converting gray scale. After clstering, the eleents of each clster can be expressed separately. Coordinates of circit paths and soldering joints are obtained at this point. Using the soldering joint coordinates, each joint is nbered and the area covered by each joint is deterined. A single sided PCB is sed in the experients carried ot. A teplate is fored sing this PCB that does not have soldering defects. Soldering joints are inspected according to this teplate. The controlled PCB has 50 soldered joints. The fll teplate created for PCB is shown in Fig. 6. Fig. 5. Teplate shows joint conditions Bt, according to the teplate, the first joint and the seventh joint are already short-circited with circit paths. For this reason, they do not need to be exained. Only one exaination is perfored This jornal is Advanced Technology & Science IJISAE, 2017, 5(4),

4 Fig. 6. Fll teplate for exeinated PCB Flly teplate related to the exeinated PCB (shown Fig.7) incldes all joints. Teplate akes easier and faster searching de to reslt oriented working. Fig. 7 shows exeinated PCB. Left side (a) is target PCB which has no proble. Middle pictre in Fig. 7b shows that area 24 and joint 25 have connection each other. Bt regarding the teplate this not a proble (ble boxed in the Fig. 7b). On the contrary, area 14 and 22 creates short circit that akes alfnction on the circit (red boxed in Fig. 7c). Ths, red colored toching in Fig.7c right side is a crcial proble that st be aware and be corrected by. The control process is atoatically perfored according to the color boxes in the teplate. In Figre 5, a joint is not inspected by the reaining 49 joints on the teplate. It is only inspected with the joints where the red boxes in the row or coln are fond. Sae PCBs were prepared as target and different soldering defected PCB (created solder defect on soldering areas, intentionally). For different soldering defects exaination exected 85 ties for every kind soldering proble. Soe of these falts do not adversely affect circit operation, and soe of the have adverse effects. Soldering falts with negative effects are enclosed in the red box, while soldering probles withot negative effects are arked with the black box as noral joints. These reslts are presented to ser with a onitor. Soldering joint inspection reslts are shown in Figre 7. Soldering defects detection accracy, calclated based on the catching of soldering errors. All soldering falts in the PCB were detected sccessflly. 4. CONCLUSION In this stdy, a fast and sccessfl copter vision ethod is presented for PCB soldering defect inspection. The prpose of the work is to create a faster and ore sccessfl application for soldering defects in PCBs. Becase slow inspection ethods slow down prodction speed and create onetary loss. In the playgrond, RGB iage is first converted to gray level iage. Then, the iage is clstered with FCM to deterine the soldering joints. A teplate is created anally to qick inspection to qery soldering joints. All joints are inspected efficiently with the joints specified in the teplate. In this way, the process tie is redced by draatically via gided teplate. All soldering defects in experients have been detected correctly. In order to obtain zero errors, inspected PCB checked by anally and powered for rn in real life. Sccess was obtained as 100% for inspected PCB odel. Saple PCB is one side soldered and sit for trogh hole coponents. Fzzy iproves border finding and teplate akes faster the proposed soltion. Reslts encorage s to se the proposed ethod for wide, big and coplex PCB to find soldering probles. 5. References [1] F. W and X. Zhang, An inspection and classification ethod for chip solder joints sing color grads and Boolean rles, Robotics and Copter-Integrated Manfactring, vol. 30, no. 5, pp , [2] S. K. Bhat, R. Deshpande, P. Beck, S. Hegde, Y. S. Upadhyaya, and C. K. Ghosh, Stdy on effect of thero-strctral loading on the PCB dring Selective Soldering process sing finite eleent ethod, 2016 International Conference on Electronics Packaging (ICEP), [3] W.-Y. W, M.-J. J. Wang, and C.-M. Li, Atoated inspection of printed circit boards throgh achine vision, Copters in Indstry, vol. 28, no. 2, pp , [4] N. Cai, J. Lin, Q. Ye, H. Wang, S. Weng, and B. W.-K. Ling, A New IC Solder Joint Inspection Method for an Atoatic Optical Inspection Syste Based on an Iproved Visal Backgrond Extraction Algorith, IEEE Transactions on Coponents, Packaging and Manfactring Technology, vol. 6, no. 1, pp , [5] C. Benedek, O. Kraer, M. Janoczki, and L. Jakab, Solder Paste Scooping Detection by Mltilevel Visal Inspection of Printed Circit Boards, IEEE Transactions on Indstrial Electronics, vol. 60, no. 6, pp , [6] J. A. Garcia-Plido, G. Pajares, S. Dorido, and J. M. de la Crz, Recognition of a landing platfor for nanned aerial vehicles by sing copter vision-based techniqes, Expert Systes with Applications, vol. 76, pp , This jornal is Advanced Technology & Science IJISAE, 2017, 5(4),

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