Browse Prior Art Database

Method for Laser Direct Writing of PWB Circuit Patterns Using Thick Film Conductive Pastes

IP.com Disclosure Number: IPCOM000034739D
Original Publication Date: 1989-Apr-01
Included in the Prior Art Database: 2005-Jan-27
Document File: 2 page(s) / 14K

Publishing Venue

IBM

Related People

Massey, DE: AUTHOR [+3]

Abstract

The present method uses laser beam exposure of a thick film paste to circuitize a printed wiring board (PWB) or ceramic substrate for hybrid circuit fabrication. Process simplification, overall cost reduction and increased energy efficiency results from using the selective beam annealing method rather than conventional IR curing to produce the conductive traces. The replacement of the screening step with a laser- writing step introduces enormous flexibility into the circuit design and eliminates the need for expensive and time-consuming stencil or screen photographic work. This method also makes available the use of the thermally sensitive substrates, such as FR-4, which cannot survive the elevated temperatures necessary for IR curing.

This text was extracted from a PDF file.
This is the abbreviated version, containing approximately 52% of the total text.

Page 1 of 2

Method for Laser Direct Writing of PWB Circuit Patterns Using Thick Film Conductive Pastes

The present method uses laser beam exposure of a thick film paste to circuitize a printed wiring board (PWB) or ceramic substrate for hybrid circuit fabrication. Process simplification, overall cost reduction and increased energy efficiency results from using the selective beam annealing method rather than conventional IR curing to produce the conductive traces. The replacement of the screening step with a laser- writing step introduces enormous flexibility into the circuit design and eliminates the need for expensive and time-consuming stencil or screen photographic work. This method also makes available the use of the thermally sensitive substrates, such as FR-4, which cannot survive the elevated temperatures necessary for IR curing. Conventional hybrid circuit fabrication involves the screening of a circuit pattern using a cement thick film conductive paste and curing this pattern at high temperature (800oC) to produce adherent metal patterns on ceramic substrates. The approach to overall process simplification and cost reduction has been to combine the screening and the curing step into a single direct laser-writing step in which the pattern is defined and the annealing of the metal paste occur simultaneously. Because the energy of the laser is localized only to the area of the substrate where the pattern is written, thermal stresses are minimized, and a wider variety of substrates becomes available. Thick film conductor pastes are used in the fabrication of conductive elements in hybrid electronic packages which offer increased performance and reliability in custom-designed circuit applications. These pastes consist of a thixotropic mixture of metal particles in an organic binder which can be applied to a substrate (typically ceramic) by screen printing, and are cured at high temperature (600oC) in an IR or convection furnace. The contribution to the field consists of using the laser as a process tool in the fabrication of PWB's for a hybrid or conventional application where great flexibility at low cost is desired. The present study demonstrates that laser circuitization can be achieved using commercially available thick film pastes; thus the process can be significantly improved with a minimum of development effor...