Analysis On Mechanical Behavior Of BGA Solder Joints Under Shock Loading

Traditionally, the reliability of BGA (ball grid array) packaging refers to solder joint fatigue failure during thermal cycling, but with the increasing application of BGA products in extreme conditions, the reliabilities of IC packages under shock loading becomes critical, especially for aerospace and military electronic equipments. Therefore, it is essential to research BGA reliability under shock loading and design a more robust package.The dynamic response of a BGA assembly under high acceleration shock loading was modeled as a spring-mass system, a beam, and a plate, respectively. The analyses have shown that: (1) the response of the BGA assembly was dominated by the fundamental mode; (2) the response of the BGA assembly depends heavily on the ratio between the frequency of the PCB and the input acceleration pulse.Through the Analytical calculation and ANSYS simulation the solder joint stress was researched and parametric analysis was adopted to compare the levels of the structure parameters and material characteristics of BGA assembly affecting on the stress. The results indicate that: (i) the magnitude of stresses in the solder joint due to the differential flexing between the PCB and BGA is three orders higher than the magnitude of the stresses induced by acceleration and inertia loading the IC package; (ii) the location of the solder joint is the first important factor under shock loading and the outmost solder joint experiences higher stress than the rest, The peak stress occurs at the outer corner at the PCB end of the solder joint. So this area may be most susceptible to break and the outset solder joint turns to be the critical solder joint which is easy to failure. (iii) parametric studies performed suggest that: the modulus of BGA and the modulus of PCB have little effect on the stress; the peak stress can be reduced effectively by increasing the diameter of the solder joints, reducing the modulus of the solder joint materials or using a very thin or a very thick PCB; Unlike temperature cycling, increasing the height of solder joint does not reduce the stress.The finite element models and the results of the paper can be used in the shape optimization and will contribute to increase the fatigue life prediction of BGA solder joints under shock loading.