Influence of heat flow direction on solder ball interfacial layer

Abstract

This paper deals with the research of an intermetallic layer of SAC305 solder balls soldered from three directions of the heat flow in the ball-attach process for BGA package. From the point of view of the heat flow direction, the samples were soldered by infrared heating. The heat sources were placed on the top, bottom and both lateral sides of the BGA package. After the solder balls-attach process, a metallographic cross-section was performed, followed by selective etching to visualize the relief of the intermetallic layer. Images of the interfacial between the solder and solder pad were taken from the created samples, followed by measurement of the average thickness and root mean square roughness of the intermetallic layer. The results showed changes in the intermetallic layer. The largest thickness of the intermetallic layer was observed on samples soldered from the top and both sides. Soldering with the bottom infrared heater resulted to the smallest thickness of the intermetallic layer. The same trend was in the roughness of the IMC layer. The greatest roughness was found for samples soldered by the top and both side heaters. The top soldered samples exhibit the smallest roughness.

Influence of Flux and Related Factors on Intermetallic Layer Growth within SAC305 Solder Joints

“…However, the heating factor does not always play the decisive role, since it describes only the reflow phase of the soldering process. The IMC thickness is also influenced by the preheat phase, when the flux is activated, as shown in our previous work [25], by the direction of the heat flow [26] and also by the post reflow cooling rate [27].…”

Analysis of solder mask roughness and stencil shape influence on void formation in solder joints

“…Many studies observed and confirmed that the formation of voids strongly depends on the reflow soldering parameters, including preheating zone, peak temperature, and soaking time [7]. The direction of heat flow and cooling can also have an influence on the properties and structure of the resulting solder joints and voids' formation, which was confirmed by [8][9][10].…”