Abstracto

Development of crumb rubber reinforced elastomeric/semielastomeric thermally conductive composite materials to be used as permanent ball grid array stencils in printed circuit board rework

Panagiotis Frantzis, Panagiotis Karydopoulos, Sotiris Villiotis

Thiswork relates to the development of a newfamily ofmaterials to be used for the rework (removal, repair, and replacement) of BGA(BallGridArray) components that can be found on a PCB (Printed Circuit Board). The rework involves the use of stencils to solder an array of micro-balls arranged in a grid manner belowthe BGA.Astencil is a membrane consisting of arrays of perforations (micro-holes or apertures) arranged in a grid manner. The new stencils, with the balls fitted into the apertures, are initially attached below the BGA, and finally are fixed between the soldered balls, the BGA, and the PCB. Similarmethods employ polymer stencils that are initially fixed between the soldered balls and the PCB, and finally are fixed between the resoldered balls, the BGA, and the PCB. The development of the new stencils may uniquely provide a new, easier, repeatable, predictable, low cost, rework method eliminating resoldering of the balls that also gives the benefit of one fewer thermal cycle for the BGA component. Other benefits include reinforcementwith crumb rubber, increase in thermal conductivity, inhibition of whisker formation/growth, no need to use adhesives, and recycling of discarded stencils.