IPC 4761明确规定PAD上有通孔需要做特殊处理，通孔里面需要用树脂填充上面再盖一层铜片
MicroVias and Via in Pad
According to IPC, a microvia is a hole with a diameter of < 150um. It can be a through viahole (with all respect to aspect ratio), but we
normally see them as blind vias between 2 layers. Mostly “drilled” by laser, but some manufacturers are also drilling microvias with a mechanical drill bit. It is slower, but the holes have a clean and nice cut. We normally recommend to use fan out vias where possible, but components with a increased pitch and pad size forces the via to be part of the component pad. These vias shall be filled and over plated. Filling can be by paste, but also cu‐filling is requested and available.
The microvia copper fill process is an electrochemical deposition process applied in the manufacturing of multilayer process. The process chemistry is complex, including the interactions of several additive chemicals in addition to the underlying basic electrochemical processes of copper electrodeposition.
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