A new player is coming in to help make PCB real estate more available on small flex and flex-rigid circuits undergoing microelectronics assembly. It’s called an interposer, and it’s a type of connection that takes connections from one side of the substrate or board or material towards the other side.
Further, it is an electrical interface of connection between one socket to another, with a purpose of spreading the connection to a wider pitch or route connection to a different path. A key benefit of designing an interposer is to increase the density of the package whereby more components can be stacked, thus reducing the overall footprint of the final package.
In Fig. 1, the interposer is used in this semiconductor application, thereby increasing the package density and reducing the size.
Fig. 1 Fig. 1 – Interposer increases BGA package density and reduces size. (Source: Wikipedia.)
There’s more to learn about an interposer in our SMT007 column. But here are some tips and hints that’ll give you a better understanding about associated factors that ensure efficiency and effectiveness.
- Assurances have to be made about the way input/output (I/O) signals are used on both sides of the interposer to make the connections optimal.
- The best signal fanning out method at different board sections and layers has to be determined.
- While designing the interposer, the proper number of blind and buried vias as needed must be used so the interposer is more effective.
- Distribute signals throughout the interposer area so that they flow through properly.
- Keep the length matched for impedance control purposes uniform. Make sure there are no neck downs along the way of dog boning or taking the traces out from the smaller areas of a BGA pad.
- In some cases, different materials like Arlon, Rogers, Teflon or Bismaleimide Triazine (BT) material could be used. Those may be more conducive for making interposers, rather than using FR4 due to thermal, electrical, and mechanical limitations and characteristics.
The PCB microelectronics assembly house must be well up to date on a variety of latest design approaches and nuances associated not only with an interposer design and its application. But it also has to be properly equipped with state-of-the-art systems and equipment along with highly trained engineers and technicians to be able to assemble these interposer designs successfully.