The backdrilling is a handy way to achieve an electrical connection between outer and inner layer of the printed circuit board in the case when the drill aspect ratio was not sufficient for drilling blind vias.
The manufacturing goes as following – first we drill through the board as for normal plated through hole (PTH) and process it in pre-plating solution to prepare the hole for metallisation. Then the board will enter the drilling device again and holes are re-drilled to partially remove the pre-plating substance. This gives a result when in further plating process the metal is adhering only to this pre-determined depth of the via where pre-plating is still intact.
The penetration of working and cleaning solutions in through vias is significantly better than in blind vias, so the plating result will be better too. If backdrilling is considered, please bear in mind that the drill size for backdrilling has to be at least 0.3 mm bigger than for initial PTH and minimal clearance from backdrilled hole is 0.2 mm. If in doubt, err to the bigger side or consult with our sales assistants at firstname.lastname@example.org.