Classification of Holes
The drilled holes classified into Plated Holes (PTHs) and Non-Plated Holes (NPTHs).
The plated holes (PTHs) are the signal carrying conductive vias. that establish interconnection between the different layers in the PCB.
The non-plated holes (NPTHs) are non-conductive. These used to hold the components in position during the PCB assembly process. The component mounting holes are NPTHs. There is no tolerance level for these holes since the components won’t fit in if the hole size is too small or large.
A rule is a rule even for a hole
Non-Plated Through Hole (NPTH)
Finished hole size (mimimum)= 0.006″
Edge to edge clearance (from any other surface element) (minimum)= 0.005″
Plated Through Hole (PTH)
Finished hole size (Smallest) = 0.006″
Annular ring size (Minimum)= 0.004”
Edge to edge clearance (from any other surface element)(minimum) = 0.009″
After repeated usage, the drilling tools tend to wear and break. This leads to the following problems:
The accuracy of the hole location compromised:
When the drill bit fails to hit the preferred spot and shifts away in the same axis. The shifts in the drilled hole will give rise to tangency or breakout in annular rings.
Roughness inside the drilled hole:
Roughness leads to non-uniform plating of copper. This results in blow holes and barrel cracks. It can also result in lower insulation resistance. by penetration copper plating solution to the hole wall.
The resin in the board melts due to the heat generated during the drilling. This resin sticks to the hole walls and called as resin smear. This again results in poor copper plating and leads to conductivity failure. between the via and the interior layers of the circuit. The resin smear removed by a chemical solution.
Presence of entry and exit burrs:
Burr is the unwanted part of copper sticking out of the hole after the drilling process. They seen both on the top surface of highest stacked of printed circuit board. and on the bottom surface of lowest-stacked of the printed circuit board.
Exposed copper of inner layers on through holes. formed the shape of nail heading during drilling. Such a huge burden to hole brings non-uniform surface of. through holes and may cause conductivity failure of plating.
The partial separation of the PCB layers.
All these irregularities ruin the integrity of a PCB. These problems have been a nightmare for the PCB manufacturers. For these reasons our in-house PCB engineers define PCB as, “Problems Come Back!”
To drop these flaws. scholars have researched on drilling process and PCB design structure. and have come up with the following solutions:
It is a chemical process where the melted resin that deposited on the hole walls removed. This process eliminates unwanted resin and enhances electrical conductivity through the vias.
It is a motorized process that. eradicates the elevated ends (crowns) of the metal (copper) called burrs. Any debris that’s left out
CNC pcb drill backing board advantage
• Excellent flatness and thickness tolerance
• Homogeneous high density core provides for good cleaning. and cooling of the drill bit
• offers a smooth surface. providing good face to face contact with the PCB giving good burr control. through a wide range of drill diameters
• Can be ‘flipped’ and used on both sides, maximizing use and material yield