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Impedance PCB Production Course

writer: G June 10, 2019

If the impedance requirement is below 50, the tolerance is +/- 5 ohms;

If the impedance requirement is above 50, the tolerance is +/-10%;

Those that are not within the tolerance range are judged as unqualified;

Where the test effective position is 3-7INCH of the test attachment piece, the single point is regarded as qualified within the range.

Impedance design qualification standard +/- 5%

The engineered impedance value shall be within +/- 5% of the impedance requirement and shall not be within the tolerance.

The production of the attached edge The design principle of the impedance board: the impedance value of the attached side of the test board is used to ensure and detect the requirements of the impedance control line in the board, which is generally controlled by the whole board.

About the making of the attached side

The impedance is divided into single-ended and differential. The single-ended requires two test points. One test point is connected to the test line, the other test point is connected to the adjacent electrical (or ground) layer; the differential requires four test points, and the two test points are connected to the test. Line, two test points are connected to the adjacent electrical (or ground) layer.

A. Single-ended: one terminal, one ground, 1.25mm in size, 0.1 inches in XY direction, 7.5 inches in length

B. Differential: two terminals, two ground terminals, size 1.25mm, terminal spacing 0.2 inches, ground terminal and

Adjacent terminals are 0.1 inches apart in the XY direction and approximately 7.5 inches in length.

C. Several principles:

1. All holes are metallized tinned holes

2. The terminal is only connected to the layer where the corresponding test line is located, and is completely isolated from the rest of the inner layer.

3. The ground terminal is only connected to one of the electrical (ground) layers closest to the test layer, and is completely isolated from the remaining inner layers.

4. The character relationship between the character (the number of the layer) marked by the character layer and the corresponding hole position. For example, if the label is "L2", the hole should be only connected to the second layer and isolated from the other inner layers.

5. Pay attention to the principle that the attached side is consistent with the structure inside the board, especially the inner layer of the positive film effect, that is, the inside of the board is a large copper surface, and the attached side is also a large copper surface.

6. One wiring port, one hole, single-ended ground can be shared, such as 6-layer board, L1 and L3 layers are impedance control layer, L2 is ground layer, L1 layer and L3 layer can share L2 layer as ground layer; Cannot be shared; in addition, the same line width has both single-ended and differential on the same layer, and needs to be designed separately.

7. The compensation principle of the attached side line width, no matter whether the board is insufficiently compensated, only need to compensate 0.2 mil.

  • PCB
  • SMT
  • Stencil






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