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Method for micromechanical drilling of microvias in multilayered, high density organic substrates

IP.com Disclosure Number: IPCOM000022002D
Publication Date: 2004-Feb-18
Document File: 4 page(s) / 107K

Publishing Venue

The IP.com Prior Art Database

Abstract

Disclosed is a method for micromechanical drilling for microvias fabrication in multilayered, high density integration substrates. Benefits include improved performance and improved reliability.

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Method for micromechanical drilling of microvias in multilayered, high density organic substrates

Disclosed is a method for micromechanical drilling for microvias fabrication in multilayered, high density integration substrates. Benefits include improved performance and improved reliability.

Background        

Laser drilled microvia alignment on the Cu pad is conventionally an issue in high-density interconnect (HDI) packaging. Poor alignment control of the microvia limits the ratio of the via diameter to the pad diameter to a very low value (~ 50%). The result is a limitation on the capability to shrink the Cu pad (i.e, increase routing density) and increase the via count. This limitation contradicts the requirements of next-generation packages for higher via counts per layer, smaller pads, and the utilization of padless vias.

Misaligned microvias exhibit significantly higher residual strain distribution at the via bottom diameter than aligned ones, which adversely impacts the reliability of the misaligned vias. Poor alignment control limits the capability of increasing the via diameter at a given pad size. Increasing the via bottom diameter is a potentially important option to improve the strength of the interface between the via bottom and the Cu pad, which improves reliability.

CO2 laser-drilled microvias exhibit a difference between the top and the bottom diameter of ~10 micron (for a typical 30-micron dielectric thickness). In such a tapered micovia, the via bottom diameter is decreased, which decreases the interfacial strength between the via bottom and the underlying capture pad. Approaches to eliminate the via tapering are very important because they enable an increased via bottom diameter at a given top diameter and increase the interfacial strength.

Various experimental and modeling data highlights the deteriorating effect of via tapering and misalignment on CO2 laser-drilled via reliability. Poorly controlled via positioning is currently observed for CO2 drilled microvias due to the misalignment error. In CO2 laser drilling, the misalignment error results mainly from the use of Galvanometer scanners that traverse the laser beam across the panel. At the CO2 wavelength, the scanner mirrors have much higher inertia than those used for shorter wavelengths, namely UV and visible ones, and hence misalignment contribution from Galvanometer are particularly higher for CO2 drilling. Limitation from the alignment capabilities of CO2 drilling technology makes it practically difficult to increase the via bottom diameter at a given pad size. Additionally; CO2 laser has a wide temperature field distribution within the organic material resulting in a tapered microvia .The current tnvention attempts to utilize micromechanical drilling to improve via positioning accuracy and minimize via tapering. Mechanical drilling does not introduce a large temperature field within the dielectric layer during the drilling process. Hence, via tapering can be minimized b...