Backdrilling PCB Technology
Backdrilling technology used in semiconductor industry that ensure the highest fidelity signals can be carried at ever increasing speeds.This will ensure signal stubs are minimized; Stubs are the source of impedance discontinuities and signal reflections which become more critical as data rates increase. It is preferred method in HS designs.
The advantages of back drill via:
- Reduce noise interference
- Improve signal integrity
- Reduce the use of buried blind holes,reduce difficulty of PCB manufacturing
What is the role of back drill?
The purpose of back drill is to drill through hole that does not have any connection or transmission to avoid reflection,scattering, delay of high-speed signal transmission.It is shown that the main factors that affect signal integrity of signal system are that vias have a great influence on the signal integrity except design, board material,transmission line,connector,chip package and so on.
The principle of back drill production working
When the drill bit is drilled, drill tip touches the copper foil of substrate board generates micro-current to sense the height of board surface,and then drill down according to the set drilling depth. It will stop when reach drilling depth.
The process of back drill
1. Providing PCB with tooling hole,and make drilling process.
2. Plating the hole before dry film sealing treatment.
3. Make outer graphics after plating process.
4. Performing pattern plating on the PCB after forming the outer pattern,and performing dry film sealing treatment of the positioning hole before pattern plating.
5. Drilling the tooling hole and then drill back vias on need
6. Remove the residual after drilling back vias and cleaning them.
What the features of back drill via PCB?
*Most of back drill are rigid PCB
*Layer is generally 8 to 50 layer
*Thickness:2.5mm or more
*Large PCB aspect ratio
*Large board dimension
*Outer layer is less trace,mostly for the press-fit holes square array design
*Back drill via is usually larger 0.2mm than vias that need to be drilled
*Back drill depth tolerance:+/- 0.05mm
*The minimum insulation thickness is 0.17mm
In PCB manufacture process,backdrilling is 2nd drill operation that removes the unused plating in vias from a certain side to a certain depth.
The major fabrication points of backdrilling:
- Use new drill tool to reduce chippload.
- Check fabrication capability of depth of backdrilling.
- Control precision of drilling.