A balloon fold design for efficient expansion of a side branch assembly in a bifurcated stent. The design involves forming a cup arrangement by folding the radial end of the side branch balloon structure into the luminal end of the side branch balloon structure and then folding the cup down into an orderly discus arrangement. The folding pattern allows for the side branch balloon structure to inflate in a sweeping rotational manner efficiently pushing the side branch assembly petals out and away from the main body of the stent with a low risk of the balloon becoming entangled or damaged by its contact with the petals. The design also allows for the expansion force to be applied at the appropriate time in the optimally needed direction by initially being oriented in a predominantly circumferential direction which is gradually shifting to a predominantly radial direction. In addition, the fold design reduces the overall volume and profile of the side branch balloon structure.