Soldering on gold plated substrates-solder joint reliability and integrity of surface components

With the tendency towards smaller printed circuit sizes in the manufacturing industry, the number of components per square area on the PCB increases. With this component increase, tight tolerances come into play, and the requirement for gold plating on PCB tracks and pads then becomes a necessity in order for tolerances to be met and for the ease of solderability. The use of gold rather than tin-lead in tight tolerances is common as the plating of gold over copper tracks and pads offers better control over that of conventional tin-lead plating. Soldering of surface mount components to this gold plated substrate thus becomes a requirement. With the dissolution of gold as an impurity in the liquidus solder forming a tin-gold intermetallic compound, the joint integrity and ductility are severely affected. It is therefore critical that an understanding and control of this dissolution of gold in an eutectic solder joint is achieved