Abstract: A microelectronic assembly (10) includes an integrated circuit die (12) mounted onto a substrate (14) by solder bump interconnections (32). The die (12) and the substrate (14) are spaced apart by a gap (30) that is filled with a polymeric encapsulant (16). The die (12) includes a die perimeter (24) and a face (27) facing away from the substrate (14). A polymeric reinforcement (18) is disposed onto the die face (27) to protect the die (12) and to reduce the effects of thermally induced stresses on the die (12) and the solder bump interconnections (32). The polymeric reinforcement (18) is spaced apart from the die perimeter (24) to maintain a desired peripheral fillet geometry of the encapsulant (16).

Abstract: A low temperature-wetting solder paste for forming a tin-base solder connection comprises a mixture of compositionally distinct first and second solder powders. The first solder is formed predominantly of tin, preferably at least 90 weight percent. The second powder is formed of a tin alloy containing indium or bismuth and having a melting temperature less than the first powder. During soldering, the second powder melts during the early stages of the heating cycle to initiate wetting of the faying surfaces and promote dissolution of the first powder, thereby reducing the time and temperature required to form the solder connection.

Abstract: A solder connection (30) is formed based upon a tinindium or tin-bismuth alloy, but having a melting temperature greater than the melting temperature of the initial solder alloy. A deposit (26) of solder alloy is placed against a tin plate (24) applied, preferably by electrodeposition, to a first faying surface (18). Following assembling with a second faying surface (22), the assembly is heated to melt the solder deposit, whereupon tin from the tin plate dissolves into the solder liquid to form a tin-enriched alloy having an increased melting temperature.