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Simultaneous Line and Via Screening

IP.com Disclosure Number: IPCOM000080768D
Original Publication Date: 1974-Feb-01
Included in the Prior Art Database: 2005-Feb-27
Document File: 2 page(s) / 25K

Publishing Venue

IBM

Related People

Urfer, EN: AUTHOR

Abstract

An idealized sketch of a metallurgy pattern for multilayer ceramic is shown in the figure. The designed line-to-via spacing is as small as 4.5 mils. However, in actual practice there are several tolerances that tend to decrease this gap. These tolerances can be classified into either resolution tolerances or registration tolerances. Examples of resolution tolerances are paste bleed-out, flow-on lamination, metallurgy diffusion, i.e. molybdenum, via hole size and shape, and screening mask dimensional accuracy. Examples of registration tolerances are via hole location, green sheet distortion, screening mask positional accuracy, via mask-to-hole alignment, pattern mask-to-via alignment, and layer-to-layer registration.

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Simultaneous Line and Via Screening

An idealized sketch of a metallurgy pattern for multilayer ceramic is shown in the figure. The designed line-to-via spacing is as small as 4.5 mils. However, in actual practice there are several tolerances that tend to decrease this gap. These tolerances can be classified into either resolution tolerances or registration tolerances. Examples of resolution tolerances are paste bleed-out, flow-on lamination, metallurgy diffusion, i.e. molybdenum, via hole size and shape, and screening mask dimensional accuracy. Examples of registration tolerances are via hole location, green sheet distortion, screening mask positional accuracy, via mask-to-hole alignment, pattern mask-to-via alignment, and layer-to-layer registration.

Obviously, a line-to-via spacing of 4.5 mils does not permit any one of these tolerances to be very large. In practice, line-to-via shorts are the most frequent cause of failure when separate via and pattern screening is used.

A process using simultaneous line and via screening eliminates some of the tolerances (reduce the tendency for line-to-via shorts) and improves screening economics. This process requires a special design of paste, mask and screener. A single paste must be optimized for use on lines as well as vias. With separate and pattern screening, via pastes are optimized for high solids loading and line pastes are optimized for minimum flow or bleed-out. A selective mesh mask is preferred that has open ho...