The present invention provides chip containing electronic devices such as Multichip Ceramic Modules (MCM's) containing a plurality of chips on a substrate which chips are underfilled with a reworkable composition which allows one or more chips to be removed from the device and replaced. The reworkable compositions contain a base resin which is not cross-linkable and which forms a matrix with a linear curable component or preferably a combination of linear curable components which curable components are cross-linkable and when cured form a cross-linked domain in the base resin matrix. A suitable cross-linking catalyst such as Pt is used and optionally a filler preferably silane surface treated silica. The preferred base resin is linear polydimethylsiloxane and the preferred curable components are vinyl terminated linear poly dimethyl siloxane and hydrogen terminated linear poly dimethyl siloxane.