Via in pad technology
Connect via in solder pads is a big trouble in pcb assembly process.
Especially,when the via in BGA pads,
But the designer often based on its design can not achieved.
In fact,the electronic products is getting smaller,
printed circuit board going to smaller, high density and more layers,
so,many CAD Engineers( PCB Layout engineers) design the via in pads.
In particular,small BGA ball space of BGA Pads,there is no enough place
Could place the via holes.
It is disaster for SMT engineers.
With the improvement of via in pad technology,
The solder problem can be solved.
Via in pad guidelines ：
1. plug via by solder mask.
No cost addition.
The standard LPI solder mask process cannot tent of
Fill vias without the risk of exposed copper inside the hole barrel.
Typically,a secondary screen print operation is used that deposits
Uv or thermally curable epoxy soldermask into the holes to plug them.
This is called via plugging. Via plugging is used to plug via holes with a solerrsist
prevent air leakage during in circuit test, or to prevent shortin from
Components that are close to the board surface.
2. Plug the via by resin and plated it flat by copper.
This process fill the via hole with a conductive or
Nonconductive material and then the via surface is plated over，
To provide a smooth flat solderable surface.
There are used for Via-in-pad designs where component may be
Mounted over the via,or a solder joint will extend over the via connection.
3. Microvias and via in pad plated over.
According to IPC,a microvia is a hole with a diameter of < 0.15mm.
It can be a through viahole (with all respect to a aspect ratio),
But we normally see them as blind vias between 2 layers.
Mostly drilled by laser,but some pcb manufactuers are also drilling mircorvias
with a mechanical drill bit.
It is slower,but the holes have a clean and nice cut.
The microvia copper fill process is an electrochemical depossition
Process applied in the manufacturing of multilayer process,
Also called capped vias.
The process is complex,copper filling of microvias is available from most
PCB manufacturers,that are capable of producing HDI PCB Boards.