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PCB007-Oct2019

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66 PCB007 MAGAZINE I OCTOBER 2019 composition itself might have an influence on evaporating speed. The solvent concentration itself has an influence on drying speed and evaporating speed of solvents. At the begin- ning of the evaporation process, evaporation speed is high, then falls towards the end of the drying process. In addition, air humidity has a pronounced influence on the evaporation of esters, ethers, and alcohols. The evaporation of ether, esters and alcohols increases with the square of air humidity. Air humidity has almost no influence on the evaporation of hy- drocarbons. As can be seen, the matter is very complex. The mathematical relationship between the drying rate and airflow can be determined em- pirically. The drying rate depends on airspeed on the surface of the ink, vapor pressure of solvent, partial solvent pressure in the air, and is given by the following relation: Where: K = constant, depending on the airspeed, 0.91 if Re < 50; 0,6 if 50< Re > 104 w = airspeed m/s m = constant, 0.4–0.5, depending on the airspeed.; m = 0,385 if Re < 50; m=0,5 if 50< Re < 104 Λp = P v - P air P v = partial pressure of solvent in the diffusion interface at the solder mask surface, vapor pressure of solvent in mm mercury P air = partial pressure of solvent in the air flow in mm mercury; limited to 0.8 Vol% in air BGV D25, less than the lower explosion limit for safety reasons G = evaporating speed g/cm2.h The calculations are not rigorous or exact, but they do illustrate the importance of tem- perature, airspeed, and hold time to the correct tack dry of solder mask. PCB007 References 1. K.F. Pawlow, P.O. Romankow, & A.A. Noskow, Beispiele und Übungsaufgaben zur chemischen Verfahrenstechnik, VEB Deutscher Verlag für Grundstoffindustrie, Leipzig, 1972. 2. P. Mischke, Filmbildung in modernen Lacksystemen, Hannover Vincentz Network, 2007. 3. E.K. Jülke, "Über die Verdunstung von Lösungsmittel aus Lackschichten," TH Zürich, Promotionsarbeit, 1962. Nikolaus Schubkegel retired in February 2019. For the past 12 years, Schubkegel worked at Umicore Galvanotechnik GmbH in Germany as a technical service engineer for Taiyo products. Before that, he worked as a process engineer in the solder mask department at the former IBM-PCB plant (later STP) in Albstadt, Germany. Schubkegel obtained an M.Sc. degree in chemical engineering from the Polytechnic Institute in Timisoara. Nolan Johnson speaks with Graham Naisbitt, chair- man and CEO of Gen3 Systems, and Andy Naisbitt, op- erations director, about how they just signed an agree- ment with a new distributor. Graham also discussed upcoming J-STD-001 changes and Gen3's shift to a more consultative customer model. Click on the image to watch the interview. RTW SMTAI 2019: Company Updates and Future J-STD-001 Changes

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