DocumentCode :
2473563
Title :
9D-6 Signal Analysis in Scanning Acoustic Microscopy for Non-Destructive Assessment of Connective Defects in Flip-Chip BGA Devices
Author :
Brand, Sebastian ; Raum, Kay ; Czuratis, Peter ; Hoffrogge, Peter
Author_Institution :
Martin Luther Univ. of Halle-Wittenberg, Halle
fYear :
2007
fDate :
28-31 Oct. 2007
Firstpage :
817
Lastpage :
820
Abstract :
Failure analysis in industrial applications often require methods working non-destructively for allowing a variety of tests at a single device. Scanning acoustic microscopy in the frequency range above 100 MHz provides high axial and lateral resolution, a moderate penetration depth and the required non-destructivity. The goal of this work was the development of a method for detecting and evaluating connective defects in densely integrated flip-chip ball grid array (BGA) devices. A major concern was the ability to automatically detect and differentiate the ball-connections from the surrounding underfill and the derivation of a binary classification between void and intact connection. Flip chip ball grid arrays with a 750 mum silicon layer on top of the BGA were investigated using time resolved scanning acoustic microscopy. The microscope used was an Evolution II (SAM TEC, Aalen, Germany) in combination with a 230 MHz transducer. Short acoustic pulses were emitted into the silicon through an 8 mm liquid layer. In receive mode reflected signals were recorded, digitized and stored at the SAM´s internal hard drive. The off-line signal analysis was performed using custom-made MATLAB (The Mathworks, Natick, USA) software. The sequentially working analysis characterized echo signals by pulse separation to determine the positions of BGA connectors. Time signals originated at the connector interface were then investigated by wavelet- (WVA) and pulse separation analysis (PSA). Additionally the backscattered amplitude integral (BAI) was estimated. For verification purposes defects were evaluated by X-ray- and scanning electron microscopy (SEM). It was observed that ball connectors containing cracks seen in the SEM images show decreased values of wavelet coefficients (WVC). However, the relative distribution was broader compared to intact connectors. It was found that the separation of pulses originated at the entrance and exit of the ball array corresponded to the condition of- the connector. The success rate of the acoustic method in detecting voids was 96.8%, as verified by SEM images. Defects revealed by the acoustic analysis and confirmed by SEM could be detected by X-ray microscopy only in 64% of the analysed cases. The combined analyses enabled a reliable and non destructive detection of defect ball-grid array connectors. The performance of the automatically working acoustical method seemed superior to X-ray microscopy in detecting defect ball connectors.
Keywords :
X-ray microscopy; acoustic microscopy; acoustic signal detection; acoustic signal processing; acoustic transducers; ball grid arrays; crack detection; failure analysis; flaw detection; flip-chip devices; interconnections; scanning electron microscopy; silicon; source separation; wavelet transforms; SEM; Si; X-ray-microscopy; acoustic pulse emission; acoustic transducer; automatic acoustic detection; backscattered amplitude integral; binary classification; connective defects analysis; cracks; custom-made MATLAB software; densely integrated flip-chip ball grid array devices; echo signals; failure analysis; flip-chip BGA devices; frequency 230 MHz; intact connection; internal hard drive; nondestructive assessment; off-line signal analysis; pulse separation analysis; scanning electron microscopy; silicon; size 750 mum; size 8 mm; time resolved scanning acoustic microscopy; void connection; voids detection; wavelet coefficient values; wavelet-analysis; Acoustic devices; Acoustic pulses; Acoustic signal detection; Connectors; Electronics packaging; Scanning electron microscopy; Signal analysis; Silicon; X-ray detection; X-ray imaging;
fLanguage :
English
Publisher :
ieee
Conference_Titel :
Ultrasonics Symposium, 2007. IEEE
Conference_Location :
New York, NY
ISSN :
1051-0117
Print_ISBN :
978-1-4244-1384-3
Electronic_ISBN :
1051-0117
Type :
conf
DOI :
10.1109/ULTSYM.2007.209
Filename :
4409782
Link To Document :
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