PCB mark point making method

- May 21, 2020-

PCB mark point making method

 

Optical positioning point, commonly known as mark point, is an indispensable part in the SMT production process. The mounter determines the exact position of PCB through the visual positioning system, taking mark point as the reference point. Especially in the process of mounting PCBA with the distance less than 0.65mm, it plays an important role in improving the mounting accuracy.

 

Generally, two mark points will be arranged on the diagonal of PCB (but not completely symmetrical, which plays a role of anti daze), and two mark points will be arranged on the diagonal of each close foot component.

 

Generally, the size of mark point is made up of a round pad with a diameter of 1mm ~ 3mm and a resistance weld with a size of two or more pads. Generally, we use a circular pad with a radius of 0.5mm and a resistance weld with a radius of 1.1mm or more to make mark points.

 

The following uses ad20.0 as an application scenario to explain how to make mark point encapsulation:

 

Step 1: create a new device in the PCB package library, and choose any name. However, it is recommended to choose the name beginning with "mark" for easy search.

 

Step 2: create a pad, select "top layer" as the layer, as shown in figure (1):

image 

Figure 1

Step 3: double click the pad to modify its properties:

 

1. Sharp shape: select "round" circle

2. X / y size: 1mm, 1mm, i.e. circle with 1mm diameter

3. Soldermask expansion:

a) Select "manual"

b) Top: input 0.6mm - (0.6mm radius here, plus 0.5mm radius of pad, the total welding resistance radius is equal to 1.1mm) as shown in figure (2):

image 

Figure 2

 

Step 4: take the center of the pad as the center, establish a top-level circular circuit, place arc (Center):

Width: 0.1mm

Radius: 1mm

 

As shown in figure (3):

image 

Figure (3)

 

Step 5: transfer the circuit of top ring to solder ring:

 

Select "convert" in "tools" and "convert selected primitives to keepouts" to convert the selected prototype to solder mask ", as shown in figure (4) and figure (5):

 

After this step is completed, the encapsulation of mark point is completed.

image 

Figure (4)

image 

Figure (5)

verification:

 

1. Place the generated package in the PCB file after the second, fourth and fifth steps are finished, which are "mark1", "Mark2" and "Mark3" in order, and then lay the copper on the PCB, as shown in figure (6):

image 

Figure (6)

 

2. It can be seen from the 3D display effect figure (7):

 

A when laying copper, mark1 filled the original planned welding resistance space, which is not the effect we need.

 

b. Mark2, when laying copper, avoid the welding resistance area, but the circular circuit has a wire diameter of 0.1mm. First, PCB production process causes confusion. Second, even if the wire diameter is modified, the circular line will occupy a part of the space, which is not suitable for the situation where the line is dense. C.mark3 can be used with limited degree. When laying copper, the resistance welding area is completely avoided, which meets our established requirements.

image

Figure 7

Some careful partners may have noticed that in the fourth step, we set a radius of 1mm for the top circular line. Why do we say that the resistance welding is more than 1.1mm? The reason is that when laying copper, the safety distance increases by 0.1mm or more. .


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