Interconnects and Conductive Pastes

Transient Liquid Phase Sintering (TLPS) pastes are similar in form, fit and function to lead-free solder pastes.

However, unlike conventional solder pastes, TLPS pastes comprise a mixture of high melting point metal powders (Cu, Ag, etc.) and lead-free solder powders (SAC305, SnBi, etc.) within an organic flux vehicle. Upon thermal processing above the reflow temperature of the solder powders, the liquid phase alloy reacts with the adherents as well as with the high melting point powders within the paste, driving rapid solidification and the formation of metallurgical connections extending across the bondline.

Since the sintering reaction is assisted by a lead-free solder alloy, the sintering process is achieved using conventional assembly and processing equipment (reflow and/or batch-ovens), and any solderable metallization is suitable. 

When formulated for high-temperature stability with a lead-free, tin(Sn)-alloy (SAC305 or equivalent), intermetallic formation can be driven to consume the entirety of the solder alloy during the sintering process, rendering a metallurgical network with excellent thermomechanical stability beyond 400°C, far higher than the original melting point of the lead-free SAC solder (218°C) and the peak processing temperature (235°C).

This is shown in in the Differential Scanning Calorimetry (DSC) scan below. Initially, the solder alloy is shown to melt at 218°C, however, after a 5-minute dwell at 235°C, no sign of the initial solder is left upon re-heating.
There is no re-melting. Unlike conventional solder pastes, TLPS materials can undergo additional reflows without re-melting and without change in performance.

TLPS formulations are available in a variety of viscosities and rheologies and can be processed via needle-dispense or stencil-printing. In most cases, best-practices utilized for solder pastes can also be applied to TLPS pastes.