The No-Flow Fluxing Underfill adhesive for low cost, high reliability flip chip assembly

Flip chip circuit assembly is an emerging technology providing faster, smaller, and less costly electrical circuitry. The implementation of flip chip electronic assembly, although estimated to be growing at 25%, has not seen widespread market acceptance in all areas of electronic assembly. The primary reasons for this are processing constraints. The addition of a traditional underfill with a direct-attach flip chip process is not fully compatible with today's Surface Mount Technology (SMT) production lines, because of the additional equipment requirements and process steps. Further proof of this incompatibility is the market's obsession with faster underfill times and snap cure (5 minutes or less) characteristics for traditional underfill. However, if the solder fluxing activity can be incorporated into a polymeric material, which goes on to cure within the reflow oven or in a short post bake, providing the protective underfill layer, then this approach would not only be SMT-compatible but would provide additional reduction in process steps and times. Therefore, the Circuit Assembly Polymer Research group of Emerson and Cuming, together with the Advanced Engineering Team at Jabil Circuit have explored the possibility of a No Flow Fluxing Underfill, henceforth referred to as fluxing adhesives, that will cure within the reflow oven or with a short post-bake.