Browse Prior Art Database

SCREEN PRINT PROCESS CONTROLLER

IP.com Disclosure Number: IPCOM000007014D
Original Publication Date: 1993-Oct-01
Included in the Prior Art Database: 2002-Feb-18
Document File: 2 page(s) / 103K

Publishing Venue

Motorola

Related People

Marc Marini: AUTHOR

Abstract

With the emergence of line pitch SMD technol- ogy, solder paste deposition has become a critical process parameter. The current screen print process relies on statistical process control (SPC) methods to maintain the process in its optimum range. Because of this, the process depends on a static oper- ating condition to generate its output. Thus the sys- tem output is directly tied to the calibration of the equipment.

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MOTOROLA INC. Technical Developments Volume 20 October 1993

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SCREEN PRINT PROCESS CONTROLLER

by Marc Marini

  With the emergence of line pitch SMD technol- ogy, solder paste deposition has become a critical process parameter. The current screen print process relies on statistical process control (SPC) methods to maintain the process in its optimum range. Because of this, the process depends on a static oper- ating condition to generate its output. Thus the sys- tem output is directly tied to the calibration of the equipment.

  In order to prevent downstream defects, such as shorts and opens, that are directly traceable to the solder paste print, an automated inspection device can be used to gather area, height, and volume infor- mation. This information would then be used to determine if a circuit board is acceptable for down- stream processing.

This technique, however, actually just tests in

quality by separating good boards from bad ones, The real solution to the problem is ensuring proc- ess related defects never occur. An implementation of this solution would utilize an in-line, real time feedback mechanism (refer to Figure l), that calcu- lates adjustments to the screen printer setup param- eters based on the current process data. Real time means that the information required to implement the screen print process corrections would be derived horn the most recently processed board and applied to the next board to be screen printed. By perform- ing this analysis in-line,, there would no longer be a requirement for SPC. A specific set of pads on every board will be measured to provide the necessary information for the feedback system to determine any adjustments, if they are required. The feedback rules would then adjust the process parameters to either increase or decrease the deposition of solder paste.

Figwe 1: Screen-Printer Feedback System

60 0 Motorola. 1°C. ,993

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MOTOROLA /NC. Technical Developments Volume 20 October 1993

  A fuzzy logic engine would be utilized to deter- mine the necessary process adjustments, Fuzzy logi...