PCB production process five: the third step of PCB production process, the classification and purpose of drilling
The content of today's fifth issue is to describe in detail the third step of the PCB process flow-drilling. For those who forgot the second step, look here at the second step of the PCB process flow. How much do you know?
The purpose of drilling
Drill through holes on the board to connect the lines between layers.
main raw material
Drill bit: Combination of tungsten carbide, cobalt and organic adhesive.
Cover plate: mainly aluminum sheet, which plays the role of positioning the drill bit during the manufacturing process; dissipating heat; reducing burrs; preventing pressure feet from being crushed.
Backing plate: It is mainly a composite board, which protects the drilling rig table during the manufacturing process; prevents export burrs; reduces the temperature of the drill needle and cleans the slag in the groove of the drill needle.
Types of PCB Drilling
Via (via): It is only for electrical conduction and does not need to be inserted into the device for welding. Its surface can be windowed (the pad is exposed), covered with oil or plugged with oil.
Plug-in hole (Pad hole): The pin hole that needs to be inserted into the device for soldering, and the surface of the pad must be exposed.
Copper-free mounting hole (Npth): screw hole or plastic fixing foot of the device, has no electrical performance, and plays a role of positioning and fixing.
hole properties
There are two types of properties for plate factory hole definition, metal and non-metal. Most of the metal holes are device pin holes, and some are metal screw holes, which can be electrically connected up and down. A non-metallic hole is a hole where there is no copper on the inner wall of the hole and it is not conductive, also known as a mounting hole. The difference between the properties of metal holes and non-metal holes is whether "Plated" is checked. If "Plated" is checked, the property of the hole is metal. If it is not checked, it is a non-metal hole. Normally, a non-metal hole has no outer diameter. .
Via spacing
The spacing between vias (Via) and vias (Via):
The distance between the edges of the vias in the same network is ≥8mil (0.2mm), and the distance between the edges of the vias in different networks is ≥12mil (0.3mm).
Spacing between plug-in hole and plug-in:
Hole edge spacing ≥ 17mil (0.45mm), the limit is 12mil. When the plug-in hole PCB is made, the drill hole will be pre-drilled by 0.15mm, and the copper will be sunk after drilling, and finally the hole diameter after the copper sinking will be as large as the finished hole when the PCB is designed. (hole edge spacing 0.45=0.15 hole compensation + 0.1 hole ring + 0.1 hole ring + 0.1 safety distance, unit mm)
The impact of near hole on production:
Two holes too close will affect the PCB production drilling process. If the two holes are too close, the material on one side will be too thin when the second hole is drilled, the force on the drill tip will be uneven and the heat dissipation of the drill tip will be uneven, which will lead to the breakage of the drill tip, resulting in unsightly PCB holes or missing drill holes. Not conducting.
