Browse Prior Art Database

IN LINE SOLDER PASTE MONITORING SYSTEM

IP.com Disclosure Number: IPCOM000006667D
Original Publication Date: 1992-Dec-01
Included in the Prior Art Database: 2002-Jan-22
Document File: 3 page(s) / 147K

Publishing Venue

Motorola

Related People

Allen D. Hertz: AUTHOR [+4]

Abstract

Solder paste properties (mesh, viscosity, tackiness, et cetera) play a key role in surface mount production quality; the changes in solder paste properties are related to the changes in the solder flux. The quality of the solder paste can be determined prior to use, but there is no known practical means of continuous monitoring of the solder paste in use. This paper describes a means to monitor solder paste quality while in use without contacting the printed substrate or removing solder paste from the stencil.

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MOTOROLA INC. Technical Developments Volume 17 December 1992

IN LINE SOLDER PASTE MONITORING SYSTEM

by Allen D. Hertz, David A. Tribbey, Gregory I? Watts and Daniel Alvarado

ABSTRACT:

  Solder paste properties (mesh, viscosity, tackiness, et cetera) play a key role in surface mount production quality; the changes in solder paste properties are related to the changes in the solder flux. The quality of the solder paste can be determined prior to use, but there is no known practical means of continuous monitoring of the solder paste in use. This paper describes a means to monitor solder paste quality while in use without contacting the printed substrate or removing solder paste from the stencil.

THEORY:

  Solder paste consists of solder particles (small spheres of solder usually 0.0008"-0.0012" in diameter) and some form of vehicle, generally flux. The viscosity and tacki- ness of the solder is related to the properties and per- centage of the solder flux. The solder flux has properties that can he characterized by color. Since the color of the solder particles remains constant, and the density of the flux changes proportionally with the solder paste vis- cosity, the solder paste viscosity can be. monitored through color recognition.

  The solder paste properties change due to evapora- tion of the volatiles in the solder flux. This occurs at a rapid rate following the printing process. Solder is deposited in a 0.006-0.008" layer as determined by the stencil thickness. Once deposited, the evaporation ofvari- ous ingredients of the solder flux is enhanced. One prop- erty known to degrade due to this phenomena is tacki- ness, or the adhesion force required during placement. Since this degradation is related to the properties of the flux, it can also be monitored through color recognition.

IMPLEMENTATION of SYSTEM:

The color recognition sensor can be integrated with a PC (personal computer) for process control and data

collection as shown in Figure 1. The output from the sensor to the PC is in pixels. A single number can be derived from the pixels through one of two algorithms. This number can then be referenced to some control data point.

  The following demonstrates the correlation between color recognition and solder paste properties (viscosity and tackiness).

  Bare substrates were presented to the sensor and data collected. The initial board was used for reference. The recorded data showed a delta of approximately 156 pixels for six (6) substrates, with an average of 62.6 and a standard deviation of 50.4. The solder deposition must be large enough to till the entire viewing area of the color sensor such that the board color variation is not recognized during data coUection of the solder paste color

MONITOR SOLDER PASTE VISCOSITY:

  Three samples (same lot) of Kester 247-B solder paste were obtained with the viscosity altered to obtain required deviations. The solder paste was measured fol- lowing standard procedures. The solder paste viscositie...