A Microvia is defined as a blind construction with a maximum aspect ratio of 1:1 in the new IPC-T-50M standard. terminating on a targeted land with a total depth from the structure’s capturing land foil to the targeted land of no more than 0.25mm. The construction of a Microvia PCB is also outlined in the IPC-6012.
Microvia has a conical frustum structure; the slope inwards as it crosses from one layer to the next, ending at a pad. Microvia PCB should ideally only cross one layer for best dependability. Designers can use stacked Microvia to form connections across multiple layers, where blind and buried Microvia is built up into a stack to reach across multiple layers.
The vias can be physically drilled, plated, stacked, and then pressed, depending on their size, or they may be created using a strong laser. Due to its high productivity and ongoing improvement, the latter method is preferred in the production of big-volume PCBs. Microvia sizes are now being drilled down to as small as 15 m thanks to new developments in laser drilling technology. The via hole is coated using a sputtering, electrolytic deposition, and electroless metal plating technique after drilling and cleaning. Preventing the production of voids, dimples, irregularities, or other structural flaws in the filled via is the aim of the plating procedure.
All Microvia have two common characteristics
- Low aspect ratio: Microvia has a lower aspect ratio compared to through-hole vias found in standard PCBs. These vias should have an aspect ratio of 0.75:1. It is possible to create greater aspect ratios of 1:1 or even higher. But they raise questions about dependability. They often only connect to one layer as a result. It should be noted that the IPC specification of a Microvia does not apply to Microvia with aspect ratios larger than 1.
- Susceptible to neck fractures: The center of the via barrel is typically where high aspects ratio through-hole vias (10:1) are most prone to fracture. Copper curved inward toward the barrel region in Microvia due to the plating technique utilized there, which causes stress to concentrate there. As a result, with repeated temperature cycling, intense vibration, or mechanical shock, Microvia is most prone to shatter in the neck region.