via in pad PCB manufacturing

Via in Pad (or POFV) Technology

What is Via in Pad or POFV? via-in-pad plated over (VIPPO) structure or called plated over filled via (POFV) structure. In shortly,via in pad is the via holes are at the SMD pad.The vias are very small,usually under 0.3mm.Why and how? First is there is no enough space to layout,you have to put the vias and holes closer even together.Second it helps thermal management and for high frequency boards,it may help improve signals.
Because the SMD pads are for SMD components loading,so the solder can not flow to inner layer or the other side when assemble.That is the most important for via in pad board.
How PCB manufacturers like us to do via in pad board? We will fill all vias with non-conductive epoxy and plate copper over it ,so the vias are flat same as others. Many PCB factories are unable to do such capability.
The key technology is how we fill vias and guarantee there is no any solder (surface finishing) in the holes.
Filled via in pad is a way to achieve intermediate density with an intermediate cost compared to using blind/buried vias. Some of the key advantages associated with using the via in pad technology are:

Fan out fine pitch (less than .75mm) BGAs
Meets closely packed placement requirements
Better thermal management
Overcomes high speed design issues and constraints i.e. low inductance
No via plugging is required at component locations
Provides a flat, coplanar surface for component attachment

Via in big pads are not a big problem.but for BGA,that is technology.As BGA pads are very small,10mil or 12mil,and there is no enough space.Manufacturing is not easy as other boards.

Here are some examples of what we did.

The vias on BGA must be done as via in pad / plated over filled technology.Otherwise, when loading BAG part on PCB,it will be assembly issues,high cost to repair. ~~

Via in pad in CAM file,BGA pad 10mil,via 0.15mm.
6 layer HDI board,0.1/0.1mm,