A kind of LGA device assembly process and its reliability analysis

LGA(Land Grid Array), also referred as pad array package, similar to BGA, but has no solder ball at the bottom of the body. Standards in the field of domestic military, such as QJ3011 and Q/QJA20080-2012, just claim that there should be appropriate distance between the device body and the Printed Circuit Board(PCB) to release heat mismatch, and have no specific instructive soldering process methods and parameters in detail. In this paper, we set LTM8033V device with LGA package from LINEAR company as an example to provide a practical process for its assembly. Specifically, we raise the LGA device to some appropriate height by planting solder ball on the bottom pad of LGA device. The experience of our experiment shows that, special pretreatment must be performed before ball planting. Then, the whole process involves: Cleaning, Pre-dry, Planting balls, Reflow and Inspect. In addition, we analyze the stress and strain changes of the solder joints under thermal cycling condition, and predict the life of solder joints by Finite Element Simulation method. The result shows that it is workable by planting balls onto the bottom pad of LGA device to match the industry standard and achieve high reliability solder joint.