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28 The PCB Magazine • November 2016 upon these new fabrication processes that are common too other microvia technologies. Definitions of HDI Process Factors In Figure 9, the HDI technologies in use today are made up of four factors: The via stackup, the dielectric materials, the methods of IVH forma- tion, and the method of metallization of those z- axis via connections. In recent years, 14 different advanced HDI processes have been used. Solid Conductive Via Fill The IPC Type VI group of HDI technologies all utilize metallic pastes or a solid sheet of met- al to form the via connections. Table 2 presents these alternatives to copper plating for forming IVH connections. OrmeLink Ormet's innovative metallic paste allowed CTS's co-lamination process with their (Ormet's) transient liquid phase sintering (TLPS) process (OrmeLink) to be similar to the ALIVH process conductive paste. It is a via paste of copper-tin organometallic matrix that sinters into a solid metallurgical via. CTS's process is called ViaPly. Past users, in addition to Sheldahl, included Li- tronics, acquired by Allied Signal/Honeywell in 1997. Up to four layer pairs have been connect- ed (eight metal layers) using OrmeLink. Other uses of the Ormet paste have constructed multi- layers of up to 60 layers. Structure The Ormet structure is made up of poly- imide or FR-4 layer pairs. Different materials can be mixed if a rigid core or heat spreader is required. The conductive paste is a TLPS ink of copper-tin. The structure is shown in Figure 10. Figure 11 shows the cross-sections of two fin- ished circuits with lasered-via polyimide layer pairs, with TLPS solid metallurgical vias con- necting the layer pairs and FR-4 innerlayer cores with buried TLPS vias. Table 2: Alternative HDI technologies utilizing filled, solid IVH [8] . INNOVATIVE USE OF VIAS FOR DENSITY IMPROVEMENTS