Browse Prior Art Database

ROLL BACK SQUEEGEE

IP.com Disclosure Number: IPCOM000008143D
Original Publication Date: 1997-Jun-01
Included in the Prior Art Database: 2002-May-21
Document File: 2 page(s) / 98K

Publishing Venue

Motorola

Related People

Roger Callanan: AUTHOR

Abstract

In the solder paste printing industry of the early 90's, the aim of the process was to apply solder paste in a specific pattern to the printed wiring board (PWB). The pattern was to be created by using a stencil or screen (referred to as stencil for the rest of this article) which has openings that match the PWB pad pattern.

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m MO-LA Technical Developments

ROLL BACK SQUEEGEE

by Roger Callanan

INTRODUCTION

  In the solder paste printing industry of the early 90's, the aim of the process was to apply solder paste in a specific pattern to the printed wiring board (PWB). The pattern was to be created by using a stencil or screen (referred to as stencil for the rest of this article) which has openings that match the PWB pad pattern.

  The screen printing operation takes place by putting solder paste onto the stencil and sweeping the paste across the hole pattern. The action of moving the paste across the screen (by an angled blade called a squeegee) creates hydrodynamic pressures within the paste, pushing it through the stencil holes and onto the PWB pad surface.

  This sounds rather simple but it is in fact a complicated process as there are many variables at work (including the paste condition, squeegee speed, squeegee direction, stencil condition, paste volume).

PROBLEM(S) TO BE SOLVED

  If the paste condition is not correct, e.g. there are excess volatiles that have evaporated off or dry material clumps contained in the mass of paste or paste has been insufficiently worked (incorrect viscosity or flow characteristics), there can be incorrect quantities applied. Dry clumps of material can be created by paste spreading out of the squeegee blade area during printing, then to dry out on the sides and be later gathered back in during a cleaning activity. Incorrect viscosity can occur as the paste mass dries out in the fee air of the printer or if it has just been taken from a jar without the appropriate level of working (the trixotopic nature of paste is that it's viscosity varies as it is sheared and it'd immediate history of shearing). If there is too little paste there can be gaps, if there is excess the paste can stick to the squeegee and not print.

SOLUTION TO THE PROBLEM(S)

  The object of this proposed solution is to ensure there is sufficient volume of paste, that it is suf...