నైరూప్య

Development of semi-elastomeric thermally conductive crumb rubber reinforced cementitious composites to be used as permanent ball grid array stencils in printed circuit board rework

Panagiotis Frantzis, Panagiotis Karydopoulos, Nikolaos Karagiannis

This work relates to the development of a new family of cementitious composites to be used as the material of permanent stencils for the rework (removal, repair, and replacement) of BGA(Ball Grid Array) components that can be found on a PCB (Printed Circuit Board). The rework involves the use of stencils to solder an array of new micro-balls arranged in a grid manner below the BGA. A stencil is a membrane that consists of arrays of perforations arranged in a grid manner. The membrane is produced from a composite that ismade bymixing synthetic rubber latex, cement, and crumb rubber. The thermal conductivity of the composite was measured by a method also developed in this work. The new family of stencils transfers knowledge fromthe field of composites to the field of PCB rework and may uniquely provide the subsequent development of a new, easier, repeatable, predictable, low cost, rework method. Other benefits include increase in thermal conductivity, reinforcementwith crumb rubber, inhibition ofwhisker formation/growth, no cleaning is necessary, and no need to use adhesives.