1. Drilling method
There are two familiar drilling methods:
1.1 Hole-Drilling
It is more trenchant than milling cutter,and advantageous to chip removal upward ,so it have smooth hole wall and good quality of the holes.But only the drill of similar diameter could be chosen and just can drill round hole,because the types of the drill are limited.
1.2 Hole-Milling
Because the milling cutter can transverse shift.It can dig holes of any sizes and shapes by using the manner which is similar to cutting, with no aperture restrictions and high accuracy .But it is less trenchant than drill bit and can’t cut the circuit board smoothly,then the hole wall is more rough . Moreover, milling cutter can’t chip-removal upward, copper sheet interface will be destroyed easily.That can be obviously observed by high-power magnifier, although will not pick out with the naked eye.
Obviously ,judging by the borehole quality , the former is better than the latter.
2. The influencing factors of borehole quality
There are two main factors:
2.1 Drilling rate of the bit
This is the most important factor. The faster the bit drill, the cleaner it cut, and provides the basis for other factors improvement.
2.2 Drilling rate
As the friction produce between bit and hole wall with a lot of heat at the drilling time. When the heat accumulation to definite extent then it will cause hole wall oxidation , goes against hole metallization.
The faster the bit drill ,the shorter the time need and less heat it produce.
3. Other factors
3.1 The through-hole plating tank has thickness to diameter ratio index ,need minimum pore size reach a certain diameter.
3.2 There are several items need drying in the former process of hole metallization, if use other simple tools, the effect must be decreased.
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