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66 PCB007 MAGAZINE I SEPTEMBER 2022 expanded over the years. An innovation came about in the mid-1980s with ORMET's devel- opment of the transient liquid phase sinter- ing (TLPS) conductive pastes that would sin- ter into a solid metal structure. is was used for conductive traces, board-to-board multi- layering, and inner layer fabrication, as seen in Figure 1. Many of the metallized pastes were origi- nally used as via connections in the Japanese HDI process created in the early 2000s, such as ALIVH (any layer internal via hole), B 2 IT, or PALUP. ese pastes used conductive parti- cles and were different from nano-technology pastes or TLPS pastes. e advantages of these newer pastes were: • Improved reliability (avoidance of trapped air or liquids) • Improved planarity of multilayer structures (for more reliable surface mount or improved photolithography) • Higher interconnect density (e.g., via in pad vs. dog bone designs) • Better thermal management • Enable stacked microvia structures Fabrication Process e via filling process (Figure 2) is quite common today. Automatic equipment is avail- able as well as simple prototyping apparatus. Screen printing or inkjet is now the most com- mon method. Material Properties e silver-laden conductive pastes have been around since the early 1960s. e introduction of nanotechnologies has revolutionized these Figure 1: Typical applications of conductive pastes board-to-board or inner layer interconnects using the TLPS series 1 . Figure 2: Via fill process flow 2 .