Comformal Mask Processing
In the Conformal Mask process, the top Cu is removed by chemical etching or UV Laser. The aperture is then used as a mask for CO2 drilling into the dielectric material.
Comformal Mask Drilling Process
Figure 1. Conformal mask drilling process diagram.
- Standard on >12 um Cu thinckness
Process Limitations
- The etching process doesn’t allow the alignment of the vias to the signal layer
- There is no correction of individual shrinkage orstretch possible
- Additional processes/systems required to remove Cu
Advantages
- No oxide treatment necessary
- Thicker outer layer Cu possible
- Typically low overhang
200 um via Example
- System: Geode L
- Stackup: 20/65/35
- Sample size: 106
- OH - μm (µ/σ): 7.6/2.4
- Taper - % (µ/σ): 94.1/5.1
150 um via Example
- System: Geode L
- Stackup: 18/52/13
- Sample size: 20
- OH - μm (µ/σ): 3.6/1.8
- Taper - % (µ/σ): 86.7/4.3
85 um via Example
- System: Geode L
- Stackup: 11/50/16
- Sample size: 60
- OH - μm (µ/σ): 4.09/2.38
- Taper - % (µ/σ): 92.8/0.05
76 um via Example
- System: Geode S
- Stackup: 18/65/18
- Sample size: 20
- OH - μm (µ/σ): 7.99/2.09
- Taper - % (µ/σ): 80.68/3.46