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Difference and features of 2 systems

- Multilayer board process method (4 layers)
- Milling samples of a thin Double-Sided Flexible Board
- Processing hard-type Board

Multilayer board process method (4 layers)

This example describes a 4-layer milling procedure in which layers 2 and 3 are
a double-sided board and layers 1 and 4 are thin-pressed copper plating.


Inner Layer Process
(2nd and 3rd layer)
The inner layer (2nd and 3rd layer) is processed both top and bottom side.

Multilayer Press Press the board by placing the prepreg on both side of the inner layer followed by 1st and 4th layer.


Drill holes with PCB Prototyping Machine Drill holes using the PCB Prototyping Machine.

Through Hole Plating Through hole plate the drilled holes.

Process 1st and 4th layer Process the 1st and 4th layer of the board.

Major difference between milling and etching: the process of inner layer

Inner layer (2nd and 3rd layer) example

Milling Method Etching Method
0.2mm pattern processed by 90 degrees milling cutter
Hatching by 90 degrees milling cutter
0.2mm pattern process
Double-Sided Flexible Board of 0.5mm and 35µm-thickness copper

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 Board

The 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.

  Milled depth Remaining thickness
90°Milling cutter 50µm 100µm
60°Milling cutter 85µm 50µm
(For comparison(reference), a thickness of a person’s hair: 60-80µm)

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 Board

As an example of hard-type board, aluminum board is described below.

Milling Method Etching Method

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.

MITS Electronics

5-1-9, Kajino-cho, Koganei-shi,
Tokyo 184-0002 JAPAN TEL.+81 (0) 42 388 1051
FAX.+81 (0) 42 388 1060


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