594
Y. Li and D. Goyal
Fig. 18.20 TSAM of a PCB with embedded chips showing defects in one embedded chip (Adapted
from Ref. [34])
of the beam is interrupted by a crack or an air gap, which significantly attenuates the
amplitude of the transmitted pulse, thus gives a “dark contrast” in the TSAM image.
Newly designed high power TSAM emission transducers [34] (directly focused
without lenses) in the range of 20–50 MHz along with a focused 10 MHz reception
transducer can improve the TSAM spatial resolution to 50 μm, and have been used
to study a PCB having embedded chips. Figure 18.20 shows a TSAM image taken
from a test vehicle with embedded chips, defects around the four die corners of an
embedded chip are disclosed by non-destructive TSAM technique.
18.3.2.2 Infrared (IR) Imaging
Si is transparent at infrared wavelengths longer than 1.1 microns, which provides
opportunity to examine die active side circus from the back side of the die or wafer
[35]. Doped silicon is much less transparent than un-doped silicon because of bandgap shifts and free carrier absorption or scattering [35]. Depending on Si doping level,
non-destructive IR imaging from die back side is feasible using near-IR imaging [36],
shortwave-infrared (SWIR) imaging at longer wavelengths–for example, the 1300–
1500 nm range [37], or infrared confocal imaging with improved signal to noise
ratio [38]. Non-destructive die backside IR imaging enables real time inspection of
die front side circus, and is very efficient to detect internal die crack, die active side
crack, and die active layer circus defects, which otherwise are invisible using optical
microscope at die backside.
Y. Li and D. Goyal
Fig. 18.20 TSAM of a PCB with embedded chips showing defects in one embedded chip (Adapted
from Ref. [34])
of the beam is interrupted by a crack or an air gap, which significantly attenuates the
amplitude of the transmitted pulse, thus gives a “dark contrast” in the TSAM image.
Newly designed high power TSAM emission transducers [34] (directly focused
without lenses) in the range of 20–50 MHz along with a focused 10 MHz reception
transducer can improve the TSAM spatial resolution to 50 μm, and have been used
to study a PCB having embedded chips. Figure 18.20 shows a TSAM image taken
from a test vehicle with embedded chips, defects around the four die corners of an
embedded chip are disclosed by non-destructive TSAM technique.
18.3.2.2 Infrared (IR) Imaging
Si is transparent at infrared wavelengths longer than 1.1 microns, which provides
opportunity to examine die active side circus from the back side of the die or wafer
[35]. Doped silicon is much less transparent than un-doped silicon because of bandgap shifts and free carrier absorption or scattering [35]. Depending on Si doping level,
non-destructive IR imaging from die back side is feasible using near-IR imaging [36],
shortwave-infrared (SWIR) imaging at longer wavelengths–for example, the 1300–
1500 nm range [37], or infrared confocal imaging with improved signal to noise
ratio [38]. Non-destructive die backside IR imaging enables real time inspection of
die front side circus, and is very efficient to detect internal die crack, die active side
crack, and die active layer circus defects, which otherwise are invisible using optical
microscope at die backside.