At the glass transition temperature the resin in the composite softens and significantly increases thermal expansion; exceeding Tg then exerts mechanical overload on the board components - e.g. the joints and the vias. Below Tg the thermal expansion of the resin roughly matches copper and glass, above it gets significantly higher. As the reinforcement and copper confine the board along the plane, virtually all volume expansion projects to the thickness and stresses the plated-through holes. Repeated soldering or other exposition to higher temperatures can cause failure of the plating, especially with thicker boards; thick boards therefore require high Tg matrix. COUNT 5
QSN1 What's the temperature at which resin softens and expands called? ANS1 glass transition temperature QSN2 Along with vias, what makes up the components of a board? ANS2 joints QSN3 What will happen to the components when the temperature of resin goes above that of glass transition? ANS3 mechanical overload QSN4 What do thick boards require to resist plating failure? ANS4 high Tg matrix QSN5 When resin stays below Tg, its thermal expansion is similar to that of copper and what other material? ANS5 glass