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Radiographic inspection Of Miniature Components Through Image Magnification
Using Computed Radiography
Sambamurthy E, R Gunasekaran, Cherian Thomas and C R Thomas
Rocket Propellant Plant, Vikram Sarabahai Space Centre, Trivandrum 695022, India
sambamurthy@vssc.gov.in , r_gunasekaran@vssc.gov.in, cherian_thomas@vssc.gov.in
Abstract
Radiography is one of the age old NDT techniques for testing wide range of components. It is
highly effective in revealing internal details of components. However general radiography
technique is inadequate for radiography of miniature components for viewing it's internal
details that are in the order of microns. Techniques like micro-focal radiography and nano-
focal radiography are evolving for such applications. Ironically computed radiography (CR)
is found to be highly promising technique for radiography of miniature components such as
printed circuit boards. The present work is focused on the image magnification applications
of computed radiography. Miniature components viz PCB, MEMS rate sensor, Li-ion cell that are used in launch vehicle/satellite components have been radiographed by CR. In some
of the components the details to be investigated are as low as 50 micron. CR is successfully used for examining these components and image magnification was achieved upto 20X
without deteriorating the image quality.
This paper covers the details of experiments carried out using computed radiography towards inspection of miniature components used in aerospace applications.
Key words: NDT, Radiography, Computed radiography, Image magnification, MEMS rate
sensor, PCB and Li-ion cell
1. INTRODUCTION:
Radiography is a widely used NDT technique for testing various components. Computed
radiography (CR) and digital radiography (DR) are upcoming digital technologies in the field
of radiography. Higher latitude, ability to process the image, easy archival, image quality on
par with the film, elimination of chemicals and darkroom etc are some of the advantages of
digital radiography. The prime component in computed radiography is specialised phosphor
screen called imaging plate (IP) that replaces x-ray film, for capturing images. When exposed
to x-ray Phosphor crystal lattice are excited and become trapped at high energy states. By
scanning laser beam over an exposed screen and detecting the emitted energy at each
location, image stored in the phosphor can be fully converted into digital.
National Seminar & Exhibition on Non-Destructive Evaluation, NDE 2014, Pune, December 4-6, 2014 (NDE-India 2014)
Vol.20 No.6 (June 2015) - The e-Journal of Nondestructive Testing - ISSN 1435-4934www.ndt.net/?id=17883
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Radiography of miniature components is a challenging exercise as the details to be examined
are in the range of few mm to microns. Discerning such miniature details is very difficult in
conventional film radiography. Further, magnification of a digitised film results in reduction
in image quality. Special techniques like micro-focal and nano-focal radiography techniques
are used for this purpose, however CR images are found to be highly useful for discerning the
miniature details. In this current work trials have been carried out on printed circuit boards,
miniature electronic component, MEMS rate sensor and Li-ion cell. Details of the test results
are presented.
2. TEST METHODOLOGY:
In the present study all the components are tested with GE make x-ray machine of focal spot
size 0.4mm (mini focus) with an SFD of 1.5 meter. Exposure parameters are chosen to ensure
the sufficient grey values. CIT make super high resolution imaging plate is used for capturing
image. imaging plate is scanned by CIT make DR HD system with 16 bit scanner at 1200DPI
i.e a resolution of 21micron. 5Megapixel black and white screen is used for visualisation of
the digital image.
With the help of CIT make DR 1200 software images are magnified upto 30X and the
required details are seen. Image processing tools such as edge detection and localised contrast
enhancement also helped in visualising the required features.
Fig 1.1 CR imaging plate Fig 1.2 CR scanner
Fig 1.3 CR image acquisition and image display
process
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The reason for the magnification capabilities of the CR can be explained as follows. When
the image is scanned it is scanned with higher dots per inch(DPI).Scanning at such a higher
DPI gives a resolution of around 21 micron. This image is stored in tif format and the image
size is around 800 MB. Because of such a high resolution scanning, the information in
digitised image is large and therefore the image quality is maintained at higher
magnifications.
3. RESULTS AND DISCUSSION:
i. PCB inspection:
One of the PCBs used in satellite launch vehicle was found shorted during continuity checks.
The PCB is visually inspected and critical areas like pins of the IC's are examined under a
microscope for locating the shorting however no anomaly is noticed.
The PCB is radiographed with CR and the image is magnified to 15X, all the pins were
inspected. It was found that one of the pin was found to be shorted with another. Fig 2.1
shows the digital radiograph of the PCB and fig 2.2 shows the magnified image(15X) of the
shorted IC.
ii. MEMS rate sensor:
MEMS rate sensor is one of the important launch vehicle component. It consists of ball grid
arrays(BGA). Lead ceramic balls of 0.5mm are used for soldering the IC.
BGA joints are radiographed to inspect
i) dry joints/ insufficient solder
ii) bridging/shorting due to surplus solder
Fig 2.1 CR image of PCB (X 1)Fig 2.2 Magnified image of IC
(X15)
Shorting
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iii) voids due to the gas bubble within solder.
iv) misplacement/misalignment due to inaccurate placement of the components.
Among the above mentioned defects bridging between solder joints is more critical defect
because it can directly result in functional disorder of the product.
MEMS rate sensor shown in fig 3.1 is radiographed with CR and the digital image is shown
in fig 3.3.The image is magnified to 24X and at this magnification it is possible to resolve the
required features. Magnified image is shown in fig3.4 All the Ball Grid Array( BGA)s are
found normal and the CR is used as mandatory for inspection of this product.
iii. MEMS based initiators for micro thrusters:
Micro thrusters are important satellite components used for specialised applications like orbit
correction operations. MEMS based initiators are essential for initiation of the micro
thrusters. Initiator hardware is shown in fig 4.1.It is manually filled with 1-2 mg of charge
slurry. Fig 4.2 shows the initiator with charge. For proper initiation the charge should be in
contact with the resistor. In order to ensure no gap between the charge and the resistor
5mm
Fig 3.4 :Region of interest( X 24)
Fig 3.3 :MEMS
rate sensor( X 1)
Fig 3.2 :IC to be
testedFig 3.1 :MEMS rate
sensor
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radiography is felt essential. Initiator is radiographed with CR and for resolving the required
features the image has been magnified to 30X.
Magnified image is shown in fig 4.3 and it shows the improper filling of the charge. Based on
NDT feedback, process changes were introduced and new initiator is processed. The
magnified (X30) image of modified initiator is shown in fig 4.4 where proper filling of the
charge is noticed.
iv. Li-ion cells:
Li-ion cell is another important satellite launch vehicle component. It is radiographed to
inspect the alignment of the stack and to verify the shorting between case and stock. Digital
radiograph of Li-ion cell is shown in fig5.1.It could not reveal the required features. Here the
gap between the case and stock is in the order of few microns. It is magnified to 15X and the
corresponding image is shown in fig 5.2 . Proper stack alignment is noticed and no short is
noticed between the case and stock.
Resistor
Fig 4.1 initiator without charge Fig 4.2 initiator with charge
Fig 4.4 proper charge
filling ( X 30)
Fig 4.3 improper charge
filling ( X 30)
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4.CONCLUSIONS:
From the above mentioned studies, CR is highly usefull in addressing the specific
radiography requirements of miniature components. In all the above mentioned cases
conventional radiography and other digital radiography techniques could not able to reveal
the required features. It is one of the easiest solution for image magnification requirements
however it requires huge computer memory for image archival.
5. REFERENCES:
1.HalmshawR. Industrial radiology, theory & practice. 2nded. London: Chapman & Hall;
1996.
2. L Koen et al, “Computed radiography Exposure Indices in mammography”, SA Journal of
Radiology, 2008
3.Bavendiak et al, “New Digital Radiography Procedure Exceeds Film Sensitivity
Considerably in Aerospace Applications”, ECNDT, 2006
Fig 5.1: image of
Li-ion cell ( X1)
Fig 5.2: image of Li-ion cell (X 15)Gap between
case and stock
Proper stocking
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