Investigating the effect of board inclination during vapour phase soldering

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Supervisor:
Dr. Géczy Attila
Department of Electronics Technology

In my diploma thesis I investigated the effect of board inclination during vapour phase soldering. I studied the related literature and physical background of the topic. I researched measurement methods of heat transfer and I also get to know adjustability of board inclination. Then I studied the attributes and parameters of used instruments and equipment.

Initially I created adjustable inclination sample holder, whom angle of inclination can be set with a clinometer. I prepared a sample board with 5 thermocouples. The fixing of thermocouples to the board was performed using SMD glue. I used Galden fluid during my work. The boiling point of Galden is 170 oC. I made series of measurements with following inclination angles 0o, 5o and 10o. I recorded the measured values with myPCLab software and for evaluation I used Excel and Matlab.

As a first step I plotted the temperature distribution on the surface of the board in Matlab. At the beginning the board warmed symmetrically in all three cases. On the center of board the temperature was lower and on the edges it was higher. After 8 seconds the temperature was higher on the higher side of board and lower on lower side of board. Higher side of the board was farther from Galden fluid in height. I concluded that the temperature was lower on the right-upper corner of board in case of inclination angle 0o after 8 seconds. In case of inclination angle 5o the temperature was lower on left-down corner of board. The cause of this phenomenon was that the board slightly inclined to the direction of this edge. I found that measured values were lower that the simulated because ideal condition was assumed during simulation.

As a second study I calculated the heat transfer coefficient on sample board from measured temperature values. During the immersion, the average values gave the same result, which was around 770W/(m2K), then heat transfer coefficient decreased. The lowest values of heat transfer coefficient was 479 W/(m2K) in case of inclination angle 0o, after 30 seconds. I found that heat transfer coefficient was higher on edges of board and lower on center. After 8 seconds, the heat transfer coefficient was higher on the higher side of the board and lower on the lower side of board. The rate of the degree depends on inclination. The measured values were similar like the simulated values.

I examined the heating time to 170 oC. The heating time was the shortest in case of angle 10o, then in case of angle 5o and it was the longest in case of angle 0o. I also realized that we increase the angle of inclination more and more, we investigate shorter and shorted heating time.

During the investigation of heat profile, I found that when I increase the angle of inclination, I get shorter temperature difference between the middle of the board and the edges of the board. It’s also then was slower in case of angle 5o and finally it was slowest in case of angle 0o. After 8 seconds the steepness of curve decreased in case of angle 0o on right-upper corner and in case of angle 5o on left-down corner of the board.

I investigated the temperature difference between two points of the board. The temperature difference was the highest between the center and corner measuring points in case of angle 0o, then the difference was lower in case of angle 5o and it was lowest in case of angle 10o. The temperature difference achieves the maximum value about 12 second, after that it’s dependence.

In conclusion it seems that in case of inclined board the temperature and heat transfer coefficient were higher, the heating time was shorter, steepness of curve was larger and temperature difference was lower between two points than in case of angle 0o. The measurement arrangement is very sensitive for the setup of inclination.

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