While not generally necessary for 0.5mm pitch, you might be considering VIP technology for small pitch devices. The VIP strategy places the via straight under the solder pad. However, this will demand another step to seal the via. Usually this is performed with either conductive or nonconductive filling of the vias.
For any 10mil solder pad, TI recommends the utilization of 4mil microvias that are laser beam drilled. After drilling, and with respect to the PCB fabricator choices, the vias are copper plated, then filled up with a polymer comprising a mixture of copper and epoxy for a nonconductive option or copper, metallic, and epoxy for a conductive option. It's important to ensure that the PCB merchant utilizes a via fill up materials with a copper particle size below 1 mil to ensure an entire penetration of the via by the fill up material.
After the vias are packed, healed, and planarized, the rest of the plated openings are prepared. This yields a set copper plated cap on the vias which facilitates element connection. The Via-in-Pad technology provides two main benefits: higher component density and improved routing.
For some PCB fabricators, blind, stacked vias should be limited by just a few layers, with three being the maximum. You need to validate your PCB fabricator’s capacity to reliably build with this course of technology.
All vias must be capped or stuffed to avoid voids and out gassing. The images in Determine 18 show the result of the uncapped via. The voids and harm occurs during reflow. The proper picture is a failurecaused by the extreme package motion during reflow, triggered by out gassing
Again, these decisions are best created by working carefully with the PCB fabricator.
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