Application of the ultrasonic pulse-echo technique for quality control of the multilayered

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1 ULTRAGARSAS Journl, Ultrsound Institute, Kuns, Lithuni For ll ppers of this puliction click: ISSN 9-4 ULTRAGARSAS (ULTRASOUND), Vol.6, No., 7. Appliction of the ultrsonic pulse-echo technique for qulity control of the multilyered electronic components R. Rišutis, L. Mžeik, R. Kžys, A. Vldišusks Ultrsound institute of Kuns University of Technology, Astrct: The ojective of the presented work ws enhncement of qulity of ultrsonic imges of electronic components, otined y the pulse-echo ultrsonic technique. For this purpose novel signl processing method sed on the dptive ultrsonic numericl model of the electronic device nd selection of the pproprite time nd frequency regions hs een proposed. Key words: qulity control, electronic component, delmintion defect, signl processing. Introduction In the production of microelectronic devices, the electronic component encpsultion process hs predominnt role. In fct, the mount of defects in such components depends minly on this phse of mnufcturing nd lso on surfce mounting processes. The defects cn e loclized t the interfce etween the different lyers (delmintions, crcks, voids, metl corrosion) or in the silicon die ffecting oth the electricl ehvior nd the therml dissiption. Mismtch of expnsion coefficients etween the s of micro ssemly, die ckside or solder oxidtion, intermetllic phses, or fst cooling conditions during the reflow process cn induce stresses following die onding. The exceeding of determined level of defectiveness requirements involves low reliility or mlfunction of the devices. Therefore it is necessry to determine the numer, sptil distriution, dimensions nd the depth of the defects in the structure under qulity control test. Different NDT techniques such s visul inspection, rdiogrphy, thermogrphy nd ultrsonic technique re exploited for detection of defects in printed circuit ords nd in the internl structure of electronic components. The consequence is rejection of components where the defects exceed the llowed mximum nd eventully of modifying prmeters of the mnufcturing process to improve reliility [-4]. The ultrsonic technique is ttrctive for NDT ppliction due to one side ccess: lso it enles to detect very thin internl delmintions in printed circuit ords (PCB) nd multi-lyered electronic components, detection of which is more prolemtic y other techniques. Due to requirements of very high sptil resolution of the defect imging, the conventionl ultrsonic methods need essentil improvement. To improve detection nd chrcteriztion of internl defects inside electronic components, vrious testing methods nd signl processing procedures hve een used, including phse imging, the Wiener filtering, the wvelet trnsform, deconvolution nd etc. [-6]. The ojective of the presented work ws to investigte ccurcy of detection of different types of defects nd to select prmeters of the coustic inspection system nd the method of signl processing, which enles to enhnce qulity of ultrsonic imges. Investigtion of high voltge semiconductor device For on-line investigtion of high voltge semiconductor components, the comintion of the pulseecho nd the through-trnsmission ultrsonic techniques hs een exploited. The immersion experimentl set-up used for this purpose is presented in Fig.. The focussed ultrsonic trnsducer with the centrl frequency MHz, the dimeter 6 mm nd the focl distnce 5 mm ws used for investigtion. Mechnicl positioning of the trnsducer nd dt cquisition were performed using the ultrsonic mesurement system developed t the Ultrsound Institute of Kuns University of Technology. During the lignment of the trnsducer to the smple surfce, it ws ssumed tht the mximum mplitude corresponds to the norml incidence ngle to the surfce of the smple. The multilyered electronic component under investigtion consists of molydenum lyer, Al-Si gsket lyer, Si lyer, gold electrode lyer (Fig.). The mechnicl nd coustic properties of ech lyer were known in dvnce. The scnning of the ultrsonic trnsducer hs een performed in the region with dimensions 4 mm long x xis nd 5 mm long y xis. The scnning step ws the mm. The numericl model of the multi-lyered structure under investigtion ws developed nd simultion of the expected wveform, reflected y the whole structure of the electronic component, ws performed. The six reflections from the djcent interfces hve een nlysed: R is reflection from the interfce etween wter nd the molydenum lyer, R is reflection from the interfce etween the molydenum lyer nd the Al-Si gsket, R is the reflection from the interfce etween the Al-Si gsket nd the Si lyer, R 4 is the reflection from the interfce etween the Si lyer nd the gold electrode, R 5 is the reflection from the interfce etween the gold electrode nd wter, R 6 is the reflection from the interfce etween wter nd the flt Plexigls reflector, which is used to mimic the through-trnsmission mode of the ultrsonic wve propgtion through the whole structure of the electronic component. The experimentl nd the simulted A-scn signls otined from different regions of the electronic component re presented in Fig. nd. The multiple reflections from djcent lyers hve een lso tken into ccount, however the pproprite spikes of the sptil

2 ISSN 9-4 ULTRAGARSAS (ULTRASOUND), Vol.6, No., 7. pulse response hve een not presented in the grphs. These results indicte smll devitions of the reflection mplitudes, however it is possile to otin the symptoms of the internl structure nomlies nd non-homogeneities, which re cused y internl delmintions or y presence of the gold electrode. D mechnicl positioning device (scnner) High frequency ultrsonic mesurement system Computer with pproprite softwre for dt cquisition nd processing The C scn imges cn e creted using the reflected or through trnsmitted signls in which informtive segments re selected y the time window (Fig., nd 4). The etter sptil resolution my e otined sutrcting imges otined from the reflected (Fig.6 ) nd the through trnsmitted signls (Fig.6 ). The imge otined in such wy is presented in Fig.6 c. The internl delmintion defects etween the molydenum nd the Al- Si gsket lyers nd lso the presence of the gold electrode cn e oserved. Focused ultrsonic trnsducer, MHz Trnsmitted through structure Reflected from structure R R R R 4 R 5 R Reflected from internl structure of the multi-lyered Trnsmitted through the multi-lyered Wter -.5 l lyer (molydenum) t, μs l l l 4 lyer (Al-Si gsket) lyer (Si) 4 lyer (Gold electrode) Flt reflector) Fig.. The experimentl (solid line) nd the simulted (dshed line) A- scn signls otined from the region in which the gold electrode is present. The expected rrivl times nd mplitudes of the pproprite reflections re denoted y solid circles: the reflection from the interfce etween the molydenum lyer nd the Al-Si gsket, - the reflection from the interfce etween the Al-Si gsket nd the Si lyer,, 4 the reflection from the gold electrode lyer, 5 the reflection from the interfce etween wter nd the flt reflector. Fig.. Experimentl set-up for on-line immersion testing of electronic components sed on comintion of the pulse-echo nd through-trnsmission techniques, hving only one-side ccess to the oject: R is the reflection from the interfce etween wter nd the molydenum lyer, R is the reflection from the interfce etween the molydenum lyer nd the Al-Si gsket, R is the reflection from the interfce etween the Al-Si gsket nd the Si lyer, R 4 is the reflection from the interfce etween the Si lyer nd the gold electrode, R 5 is the reflection from the interfce etween the gold electrode nd wter, R 6 is the reflection from the interfce etween wter nd the flt Plexigls reflector. The simulted wveforms of the ultrsonic signls, which hve een trnsmitted twice (direct trnsmission through the semiconductor component, reflection from the dditionl flt reflector nd trnsmission gin through the component ck to the trnsducer) through the different regions of the electronic component re presented in Fig.5. These results indicte the shdowing effect of the delmintion in the cse of the ultrsonic wve propgting ckwrd from Plexigls reflector to the ultrsonic trnsducer. Such effect reduces mplitude of the pproprite segment of received signl nd cn e oserved in the experimentlly mesured signls trnsmitted through electronic component lso (Fig. nd Fig.4) Reflected from internl structure of the multi-lyered Trnsmitted through the multi-lyered t, μs Fig.. The experimentl (solid line) nd the simulted (dshed line) A- scn signls otined from the region in which the gold electrode is sent. The expected rrivl times nd mplitudes of the pproprite reflections re denoted y solid circles: the reflection from the interfce etween the molydenum lyer nd the Al-Si gsket, - the reflection from the interfce etween the Al-Si gsket nd the Si lyer, the reflection from the interfce etween the Si lyer nd wter, 4 - the reflection from the interfce etween wter nd the flt reflector. 4

3 ISSN 9-4 ULTRAGARSAS (ULTRASOUND), Vol.6, No., Reflected from internl structure of the multi-lyered Trnsmitted through the multi-lyered t, μs Fig.4. The experimentl (solid line) nd the simulted (dshed line) A- scn signls otined from the region of delmintion etween the molydenum lyer nd the Al-Si gsket. The expected rrivl times nd mplitudes of the pproprite reflections re presented y solid circles: - the reflection from the delmintion, - the reflection from the interfce etween the Al-Si gsket nd the Si lyer (the reflection is completely suppressed), - the reflection from the gold electrode (the reflection is completely suppressed), 4 - the reflection from the interfce etween wter nd the flt reflector (the reflection is completely suppressed) t, μs c Fig.5. Wveforms of the simulted ultrsonic signls in the throughtrnsmission mode, which hve een trnsmitted twice nd hs een otined in direct trnsmission through the electronic component, reflection from the dditionl flt reflector nd trnsmission gin through the component ck to the trnsducer (in three different zones of the electronic component): delmintion etween the molydenum lyer nd the Al-Si gsket, the gold electrode is present, - the gold electrode is sent. Fig.6. The C-scn imge of the electronic component otined y comintion (c) of the pulse-echo () nd through trnsmission () modes: delmintion region t the interfce etween the molydenum lyer nd the Al-Si gsket, the region without defects in which the gold electrode is present, - the region without defects in which the gold electrode is sent, 4 - the cross-section of the C-scn selected for dt evlution in the frequency domin. 5

4 ISSN 9-4 ULTRAGARSAS (ULTRASOUND), Vol.6, No., 7. Processing in the frequency domin For more detiled nlysis the reflection nd the trnsfer functions hve een clculted using one dimensionl pproch [5]-[6]. The trnsfer functions of the plne wve propgting through the whole structure of the electronic component re presented in Fig.7. It cn e seen tht the presence of the dditionl thin gold lyer shifts the mximum of the trnsfer function to the lower frequencies. The delmintion chnges the trnsfer function in similr wy, ut dditionlly much higher losses re introduced due to the lmost complete reflection of the ultrsonic wve. The dependencies of the reflection functions for the sme cses re presented in Fig.7. It cn e oserved tht in the cse of the defect when the complete reflection occurs the chrcter of the reflection function is not ffected. Due to this, the sptil distriution of the spectr mgnitude of the signls reflected y the vrious interfces of the semiconductor device long the line 4 in Fig.6, crossing the delminted re, does not give ny dditionl informtion out defective zones. However, the spectr mgnitudes of the reflected nd through trnsmitted segments of the received signls possess more informtion nd re presented in Fig.8. The region A, region B nd region C (Fig.8,) indicte the presence of delmintion type defects which cuse pproprite frequency shifts. In order to increse the contrst of the C-scn the differentil type (difference etween regions A, B nd C) spectr mgnitude C-scn imge hs een creted. The differentil C-scn imge of the electronic component otined y comintion of the three regions of the spectr mgnitude, creted from the reflected (Fig.9 ) nd through trnsmitted (Fig.9 ) prts of the received signl is presented in Fig.9 c. The differentil C-scn imge of the defect free electronic component otined y comintion of the three regions of the spectr mgnitude, otined in reflection nd through trnsmission modes is presented in Fig.. The presented results clerly indicte the enhncement of the defect contrst nd oundries, which enles etter locliztion nd detection of the internl defects. T, db R, db Trnsducer frequency centrl - -4 Trnsducer frequency centrl f, MHz 9 4 Fig.7. Trnsfer () nd reflection () functions of plne ultrsonic wve propgting through the semiconductor device: the region without defects in which the gold electrode is sent, the region without defects in which the gold electrode is present, the region with delmintion t the interfce etween the molydenum lyer nd the Al-Si gsket. f, MHz Region A Region B Region C Fig.8. Sptil distriution of the spectr mgnitudes long the selected cross-section (Fig.6 the dshed line 4), which corresponds to the reflected prt of the received signl wveform () nd to through-trnsmitted prt of the received signl wveform (): the region with delmintion t the interfce etween the molydenum lyer nd the Al-Si gsket, the region without defects in which the gold electrode is present, - the region without defects in which the gold electrode is sent. 6

5 ISSN 9-4 ULTRAGARSAS (ULTRASOUND), Vol.6, No., 7. Fig.. The differentil C-scn imge of the defect free electronic component otined y comintion of the three regions of the spectr mgnitude, otined in reflection nd through trnsmission modes. in the time nd frequency domins hs een proposed. This technique is sed on the dptive ultrsonic numericl model of the electronic device, which enles to optimize the selection of ultrsonic signl segments possessing the informtion out internl defects. Such selection hs een pplied for the pproprite prts (reflected nd trnsmitted) in the reflected signl wveform in the time nd in the frequency domins. The results presented prove tht this pproch enles to get improved contrst nd resolution of internl delmintion type defects of the multi-lyered electronic components. Hence, the proposed pproch gives dditionl informtion for sptil loclistion of the internl defects during qulity control. Fig.9. The differentil C-scn imge (c) of the electronic component otined y comintion of the three regions of the spectr mgnitude, otined in the reflection () nd the through trnsmission () modes: the region with delmintion t the interfce etween the molydenum lyer nd the Al-Si gsket, the region without defects in which the gold electrode is present, - the region without defects in which the gold electrode is sent. Conclusion c The investigtion results of the high voltge semiconductor component y ultrsonic technique were presented. In order to improve the sptil resolution of conventionl C-scn imge, the signl processing technique sed on the selection of the signl components References. Adms T. E. Acoustic microscopy improves internl reliility of IC pckging. Microelectronics nd Reliility Vol. 5. P Moore T. M. C-mode coustic microscopy pplied to integrted circuit pckge inspection. Solid-stte electronics. 99. Vol. 5. P Jhng K., Jng H., Prk B., H J., Prk I. nd Kim K. Wvelet nlysis sed deconvolution to improve the resolution of scnning coustic microscope imges for the inspection of thin die lyer in semiconductor. NDT&Interntionl.. Vol. 5. P Bechou L., Dllet D., Dnto Y., Dponte P., Ousten Y. nd Rpuno S. An improved method for utomtic detection nd loction of defects in electronic components using scnning ultrsonic microscopy. IEEE Trnsctions on Instrumenttion nd Mesurement.. Vol. 5. P Kžys R. nd Svilinis L. Anlysis of dptive imging lgorithms for ultrsonic non-destructive testing. Ultrsonics Vol.. P Kžys R. nd Svilinis L. Ultrsonic detection nd chrcteriztion of delmintions in thin composite pltes using signl processing techniques. Ultrsonics Vol. 5. P R. Rišutis, R. Kžys, L. Mžeik, A. Vldišusks Ultrgrsinių metodų tikyms elektroninių komponentų struktūros vidinių defektų prmetrms mtuoti Reziumė Elektroninių komponentų kokyės kontrolė gmyos proceso metu, tliekm įviriis NDT metodis, vizuliniis, rentgeno, termogrfiniis, ultrgrsiniis. Kontrolės metu siekim nusttyti įvirių tipų defektus, 7

6 ISSN 9-4 ULTRAGARSAS (ULTRASOUND), Vol.6, No., 7. kurių įvirovė endruoju tveju yr li plti. Vieni iš svriusių defektų yr tskirų sluoksnių, sudrnčių elektroninius komponentus, tplyšims. Jie dugiusi sąlygoti tempertūros poveikio gmyinio ciklo metu. Tokie defekti lengviusii ptinkmi ultrgrsiniis metodis. Tčiu tiknt šiuos metodus dug tyrimo liko sugištm preciziški skenuojnt fokusuotą ultrgrsinį keitiklį virš tirimojo ojekto pviršius, kuris prikluso nuo tirimo komponento integrcijos lipsnio. Be to, siekint didelio erdvinio skirimumo reiki nudoti ukštojo džnio ultrgrso ngs (5 MHz). Tigi ultrgrsinii metodi dugiusi nudojmi tyrimms lortorinėmis sąlygomis tlikti ir sunkii pritikomi kokyės kontrolei gmyoje. Ultrgrsinio keitiklio skenvimo greičio pdidinims r ultrgrso ngų džnio sumžinims plogin tyrimo rezulttų kokyę. Pteikto dro tiksls uvo pdidinti ultrgrsinio keitiklio skenvimo greitį ir sumžinti dro džnį, krtu išliknt pknkmą vidinių defektų geometrinių mtmenų mtvimo tikslumą. Buvo psiūlyt tikyti specilizuotus signlų pdorojimo lgoritmus ir kominuotą mtvimo metodiką, įvertinnčią nuo vidinės komponento struktūros tsispindėjusis ir tiesiogii perėjusis ultrgrso ngs. Kd ūtų nusttomi tikslesni vidinių tsisluoksnivimo defektų geometrinii mtmenys, psiūlyt nudoti likinį ir džninį informtyvių ultrgrsinio signlo segmentų išrinkimą, pgrįstą skitmeniniis ultrgrso ngų sąveikos su tirimojo komponento vidine struktūr modeliis. Nudojnt skitmeninius modelius uvo pskičiuotos tirimo dugisluoksnio elektroninio komponento džninės chrkteristikos ultrgrso ngų tspindžio ir perėjimo tvejis, tip pt nusttytos tikėtinos nuo tskirų sluoksnių tspindėtų signlų likinės pdėtys. Atspindžims ptikti uvo mtuojmi signli, tspindėti nuo komponento vidinės struktūros, ir signli, perėję per komponento vidinę struktūrą ir tsispindėję nuo ppildomo reflektorius. Psiūlytoji mtvimo metodik sujungi rezulttus, gutus nlizuojnt iejų tipų signlus. Sukurto metodo veiksmingumą rodo keturių sluoksnių puslidininkinių didelės glios diodų tyrimo rezultti. Či iškii mtomos tsisluoksnivimo sritys. Pteikt spudi