Method of and apparatus for laser drilling holes with improved taper

A system for forming a blind via in an electronic substrate that includes a conductive layer and a dielectric layer, wherein said blind via has a depth between said top diameter and said bottom diameter, wherein a ratio of said bottom diameter to said top diameter expressed as a percentage defines a taper of said blind via, and wherein said blind via has a volume corresponding with said top diameter, said bottom diameter, said depth, and said taper, the system comprising:

• a Q-switched CO2 laser operative to produce laser pulses that propagate along a laser beam path and that are characterized by a single set of pulse parameters;
• laser beam optics operative to direct said laser pulses to impinge upon said electronic substrate, wherein forming said blind via includes a first via formation phase including top via formation circumstances for removing dielectric material above said conductive layer while maintaining said top diameter for said via, wherein forming said blind via includes a second via formation phase including bottom via formation circumstances for removing remaining dielectric material at and above said conductive layer while maintaining said bottom diameter for said via without causing substantial damage to said conductive layer, wherein said top and bottom via formation circumstances are different, wherein said top diameter is related to fluence bv the equation Dt≈F, where Dt is said top diameter and F is said fluence, wherein said bottom diameter is related to fluence and pulse width by the equation Db≈F/(t1/2), where Db is said bottom diameter and t is said pulse width, wherein said single set of pulse parameters is selected to be within capabilities of said Q-switched CO2 laser and said laser beam optics, wherein said single set of pulse parameters pulse parameters includes a pulse width and a peak power, and wherein said pulse width and said peak power are selected to minimize an amount of time spent forming said blind via;
• and
• a controller operative to calculate said single set of pulse parameters operable for both the first via formation phase and the second via formation phase based on a top diameter and a bottom diameter intended for said blind via, and to direct said Q-switched CO2 laser to produce said laser pulses characterized by said single set of pulse parameters to remove said dielectric material within said volume to form said volume of said blind via without causing substantial damage to said conductive layer at a bottom of said blind via.