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