Process design of self-replication for micro bump formation

For the bumping of BGA, CSP, and FC packaging, the trade-off of the cost-effectiveness (materials and instrument cost, productivity) and the performance (pitch, fan-out, precision, reliability) arises. To meet both demands, some unique concepts and the flexible methodology by using solder micro-fillers/polymer materials have been proposed. The self-replication phenomena of the twin micro bumps, typically several hundreds micrometers, from a single micro bridge in the resin media was focused. A couple of micro molten droplets-on-lands out of a vertically bridged bump could form in a small parallel gap filled with the resin between two co-planar substrates which are moved apart with the balance of surface tension among molten solder, polymer liquids, and metal traces. In order to optimize the process, the effects of the physical properties of the solder alloys and filler size were examined through the X-ray observations of the formed micro bumps before detachements.