Method of sequential laser processing to efficiently manufacture modules requiring large volumetric density material removal for micro-via formation

DETAILED DESCRIPTION The present invention provides an interconnection circuit device having vias and a method for making vias in an interconnection circuit device.
The vias formed by the present invention have smaller entrance diameters, exit diameters, greater aspect ratios and lower average via resistances than vias formed by conventional techniques.
Additionally, the present invention provides an improved high-volume manufacturing yield over conventional approaches because a high degree of manufacturing repeatability is ensured by the present invention.
For example, vias produced according to the present invention have low entrance and exit diameter variances, low average via resistances, and correspondingly low via resistance variances.
The present invention provides a method for laser drilling blind-vias in a laminated substrate, where the blind-vias have via entrances of 75 .
mu.
m or less and aspect ratios of 1:1 and greater.
According to the invention, the laminated substrate has a first conductive layer, a dielectric layer formed on the first conductive layer, and an outer second conductive layer formed on the dielectric layer.
The second conductive layer includes a preformed aperture at each location where a blind-via is to be formed.
The dielectric layer is laser drilled through to the first conductive layer using a plurality of laser pulses that are applied through the preformed apertures in the outer second conductive layer.
Each laser pulse applied to the dielectric layer has an energy density per pulse that is greater than an ablation threshold of the dielectric layer, but is less than an ablation threshold of the first conductive layer.
When the laser emits at a wavelength of 355 nm, the energy per pulse applied to the dielectric material is between 0.
5 J/cm.
sup.
2 and 11 J/cm.
sup.
2, inclusive, for a pulse width that is 100 nanoseconds (ns) or less.
When the dielectric layer is made of an ePTFE matrix containing a mixed cyanate ester-epoxy adhesive, the energy density per pulse applied to the dielectric layer is preferably between 0