Major difference between milling and etching: the process of inner layerInner layer (2nd and 3rd layer) example
As seen in the above, when the inner layers are processed by milling method, a deep groove will be created between the patterns. When the board is pressed with the groove, the prepreg does not fit in the groove, results an air bubbles after pressed. With the air bubbles, the plated through holes will not function, as a consequence the inner layer to be a defective item.
Milling samples of a thin Double-Sided Flexible BoardThe drawing above shows the milled spaces and lines by milling from the both sides of a thin double-sided flexible board with 90°and 60°milling cutter,
Drawing of a milled sample：a minimum space of a 0.1mm(100µm) track milled with a milling cutter, which is stated in the machine specifications.
In our milling machine catalog, the minimum width line and space is stated as 100µm,
and the milling depth is as below.
However, this reaming thickness of 100µm and 50µm is numerically ideal values. Considering the slight difference in lengths of milling cutters, fluctuation of the axis in machine operation, or machine operator’s error in setting the milling depth etc., the remaining thickness of the board may become “0”.
In milling, the milling cutter can pierce the thin film failing to process.
MITS highly recommends you to use Etching system to process such thin film PCB.
Processing hard-type BoardAs an example of hard-type board, aluminum board is described below.
As shown in the drawing, the prepreg layer is 100µm, and so thin that ,like the thin film board above , the milling cutter may pierce the layer and hit the aluminum material.
The aluminum board gets damaged as PCB and the tip of the milling cutter will be broken.
Therefore, it is also recommended that Etching system be used to process aluminum board.
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