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Control method for impedance of outer layer

A control and outer layer technology, applied in the chemical/electrolytic method to remove conductive materials, printed circuit components, electrical components, etc., can solve the problem that the finished product does not meet the requirements, the finished product impedance of the first board exceeds the standard and is scrapped, and there is an open circuit risk And other issues

Active Publication Date: 2016-07-27
GUANGZHOU FASTPRINT CIRCUIT TECH +2
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Problems solved by technology

However, there are the following problems in the monitoring. 1. When the impedance of the first board exceeds the set range, the first board cannot be re-etched to adjust the line width when it is protected without tin, and there will be a risk of open circuit during etching, so the finished product impedance of the first board will exceed the standard and be scrapped ; 2. In the existing first board impedance control, the impedance control requirement of semi-finished products is given as a certain fixed value. For example, a company controls that the single end cover is 3ohm larger than the cover after welding resistance, and the differential cover is higher than that before welding resistance. Large 8ohm fixed pattern after cover solder mask
According to the relationship of the microstrip line model, the impedance is affected by many factors, that is, there are differences in the impedance change before and after the solder mask of the lower cover with different line widths. The use of fixed fluctuation range control may cause under some conditions, when the first board meets the requirements, But the finished product does not meet the requirements

Method used

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  • Control method for impedance of outer layer
  • Control method for impedance of outer layer
  • Control method for impedance of outer layer

Examples

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example 1

[0065] Example 1: In a factory, the thickness of copper plating on the outer layer is 35um, the thickness of solder resist is 50um, and the thickness of tin plating is 8um on average. 0 and the impedance value after etching (with tin) is Z 1 , the design line width includes a single-ended line of 3.5mil to 14.5mil. According to statistics, the impedance fluctuation range of the two has the following relationship:

[0066] Table 1-1 Effects of single end cap before and after solder mask

[0067]

[0068] In Table 1-1, w is the line width, the unit is mil; Z is the design impedance value, the unit is ohm; wiring layer: shielding layer, indicating the number of layers where the wiring layer is located and the number of layers where the shielding layer is located; Group 1 to Group 8 represents the data of △Z measured for 8 times, the average value is the average value of △Z of the eight groups of data, △Z / Z% is the percentage of △Z of the average value and the design impedance...

example 2

[0071] Table 1-2 Effects of differential cover before and after solder mask

[0072]

[0073] Similar to Example 1, in Table 1-2, w is the line width, in mil; Z is the design impedance value, in ohm, and the first to eighth groups represent the data of △Z measured 8 times, and the average value is eight groups The average value of △Z of the data, △Z / Z% is the percentage of △Z of the average value and the design impedance value Z, △Z / Z% indicates the percentage of impedance change;

[0074] In Example 2: For the control board with 10% impedance tolerance, the area is divided according to the first board control coefficient a=0.3. When the differential line width of the outer layer is 3-4.5mil, the difference between the impedance of the finished product and the impedance of the semi-finished product is △X 1 =△Z 1 / Z is controlled according to 15%; when the line width is 4.5~7mil, the difference between the impedance of the finished product and the impedance of the semi-fin...

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Abstract

A control method for the impedance of an outer layer comprises the following steps of selecting a circuit board from circuit boards in the same batch, making an initial board according to a certain etching speed, and carrying out an impedance test before tin stripping after etching of the initial board; selecting another circuit board from the circuit boards in the same batch when the actually-measured impedance value of the initial board is greater than a set range, increasing the etching speed to remake a new initial board until the actually-measured impedance value of the new initial board is within the set range, and judging that the new initial board is a qualified initial board; and selecting another circuit board from the circuit boards in the same batch when the actually-measured impedance value is smaller than the set range, reducing the etching speed to remake a new initial board until the actually-measured impedance value of the new initial board is within the set range, and judging the new initial board is a qualified initial board. By the control method, the impedance of the outer layer of a printed circuit board (PCB) can be more accurately controlled, and the impedance qualified rate of the outer layer is greatly improved.

Description

technical field [0001] The invention relates to a method for monitoring and controlling the impedance of an outer layer of a PCB positive film process, in particular to a method for controlling the impedance of an outer layer. Background technique [0002] With the development of the high-speed communication industry, the requirements for the impedance accuracy of the PCB are getting higher and higher, from the ordinary ±10% accuracy to ±5% or even ±3% accuracy requirements, which poses a huge challenge to the PCB manufacturing industry. According to the classic microstrip line impedance formula: [0003] Single-ended model: [0004] Differential impedance model: [0005] Z d i f f = 2 * 87 e r + 1.41 ...

Claims

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Application Information

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Patent Type & Authority Applications(China)
IPC IPC(8): H05K1/02H05K3/06
CPCH05K1/025H05K3/06H05K2203/163
Inventor 范红王红飞陈蓓
Owner GUANGZHOU FASTPRINT CIRCUIT TECH
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