Investigating the quality of vapour phase solder joints

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Supervisor:
Dr. Krammer Olivér
Department of Electronics Technology

Abstract

My thesis-work deals with the qualitative analysis of the vapour phase and infrared reflow soldering. By surveying the literature, I preferred the vapour phase soldering method. I have designed a test board and a stencil to the board for the investigations. I have made the stencil with a Nd:Yag laser. I planned 3 different thermal profiles with different heating factors: Qη=750 ºC•s, Qη=1000 ºC•s and Qη=1250 ºC•s. In case of infrared profiles, there were two profiles with the same Qη=750 ºC•s. However one with higher maximum temperature and another one with lower maximum temperature with longer time above liquidus.

The shape and the size of the soldered joints met the requirements in all cases of the IPC-A610D standard. The meniscus formed as concave in all cases. The measured shear strengths were between 21 N and 24 N in all cases. These shear strength values were within the standard deviation of each other.

In case of infrared soldered joints, the thickness of intermetallic layer grew when the heating factor grew. When Qη=750 ºC•s the thickness was 2,4 µm, when Qη=1250 ºC•s it was 3,2 µm. When Qη=750 ºC•s and the maximum temperature was lower the thickness was only 2,1 µm. In case of vapour phase soldered joints, the thickness of the intermetallic layer was about 3 µm in all three cases. Although the standard deviation values of average values increased by increasing the heating factor: in case Qη=750 ºC•s the standard deviation was 9 %, in case Qη=1000 ºC•s the standard deviation was 14 % and in case Qη=1250 ºC•s the standard deviation was 18 %.

Solder joints made by both types of reflow soldering can be considered as good. The recommended value of heating factor for the reflow soldering is 1000 ºC•s in case of infrared soldering and 750 ºC•s in case of vapour phase soldering method.

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