Laurent Barreau

Crack-free laser dicing of glass in the microelectronics industry

This paper investigates laser dicing of glass (commercial Borofloat®33) for backend packaging in the microelectronics industry. An ultraviolet (355 nm) diode-pumped solid-state nanosecond laser was used in this investigation. Laser processing of glass is challenging as glass is transparent for most available wavelengths. Nonlinear absorption can be obtained but produces undesirable effects (chipping, cracks) in the nanosecond regime. In the present study, an absorptive polymer layer was spin coated on top of the substrate and acts as a heat incubator during laser irradiation. This paper shows that preheating the substrate produces clean scribe. Laser dicing is qualitatively and quantitatively more efficient than blade sawing. 1 × 1 mm2 dice have been separated by laser scribe/break method that allows a throughput increase of 18%versus blade sawing.

Laser micro-cutting of wide band gap materials

This paper investigates laser micro cutting of wide band gap materials for semiconductor industry purposes. Laser is an alternative to blade sawing for hard materials such as sapphire (α-Al2O3) and silicon carbide (SiC) which are useful for new functions. An ultraviolet (355 nm) diodepumped solid-state (DPSS) nanosecond laser is used in this investigation. The properties of the materials are analyzed by the means of ellipsometry and X-ray diffraction in order to understand laser/matter interaction physics. The effect of pulse energy and feed rate (scanning speed) is studied on the depth of the cutting street of α-Al2O3 and SiC. The depth of the grooves increases with laser energy (10 to 147.5 μJ/pulse with typical frequencies of 40 to 160 kHz) It decreases with the feed rate (10 to 150 mm/s) until saturation except for certain conditions for α-Al2O3. Indeed, results show periodic patterns produced by phase explosion that can influence on the achieved depth. The shape, size and periodicity of the recast ma...

Optimization of diode pumped solid state ultraviolet laser dicing of silicon carbide chips using design of experiment methodology

This paper investigates the laser micromachining of SiC-4H wafers with an ultraviolet (355 nm) nanosecond source. The design of experiment methodology was used to study the effect of pulse energy, number of passes, defocus, and scanning speed on scribing depth and was modeled with Design Expert® software. Pulse energy and scanning speed were found to have a significant effect on scribe depth (by a factor of 10 compared to defocus), while the effect of the number of passes varied with pulse energy and scanning speed. The model predicted a narrow set of processing parameters to scribe half of the wafer thickness (180/360 μm). A more fundamental study was also conducted in order to validate literature observations on the ablation mechanism. A brief comparison between conventional blade dicing and the laser scribe-break method was performed on a 3 in. diameter wafer. It was discovered that a possible gain of gross die (number of usable chips per wafer) of 7% could be achieved which could provide a useful econ...

Shock test evaluation for electronic packages

The need for continuously integrated and miniaturized microelectronics packages for mobiles applications has promoted and will amplify the development and the industrialization of wafer level chip scale packages (WLCSP). Some assembly challenges have already been overcome and some others will need to be validated with the trend to smaller interconnections associated with reduced pitches. In parallel with these challenges, the printed wiring board (PWB) assembly performances of such WLCSP is essential to their extension. In some cases, it is considered as a limiting factor because the shocks that the package can withstand during the assembly process are more critical on bare silicon compared to plastic packages.