6L Hybrid PCB

In the development of high-frequency Hybrid PCBs, several technical challenges and process bottlenecks commonly encountered in the industry have been faced. Through continuous technological improvement and process optimization, significant advancements have been achieved in the following areas:

Production Challenges

High-frequency high-speed PCBs are primarily used in high-speed information transmission applications such as computers and supercomputers. These products demand high-precision signal lines with extremely strict impedance requirements. Typically, general PCB products have an impedance control tolerance of 10%. However, some high-speed PCB products require an impedance control tolerance of 5%-8%. The conventional production methods, which utilize DES etching for the inner layer pattern, exhibit poor etching uniformity, with discrepancies of up to 15µm in different positions. Furthermore, there is no control over the line width during the brownizing process, resulting in uncontrolled inner layer impedance line widths and only achieving a 10% impedance control tolerance. Consequently, products with impedance control values of 5%-8% have a very low impedance test pass rate.

Improved 6L Hybrid PCB Production Process

To address these challenges, the following improved production process has been implemented:

1.Opening-cutting an inner layer pattern

2.Soaking etching (bubble etching)

3.Line width measurement

4.Inner layer Automatic Optical Inspection (AOI)

5.Brownizing

6.Line width measurement

7.Lamination

8.Post-process

Improved production process: opening-cutting a inner layer pattern- soaking etching (bubble etching)-line width measurement- inner layer AOI- brownizing- line width measurement- lamination- post-process.

Key process description:

1.Immersion Etching Method: By switching to an immersion etching process and closing the etching liquid spray (Hz copper thickness) parameter to 2.7 m/min, the differences in impedance line width caused by the water tank effect and uneven spray are eliminated, achieving etching uniformity of >95%.

2.Line Width Measurement Adjustment: By correcting the standard control during the line width measurement process, the differences in line width (Hoz copper thickness, line width effect 8-10µm) during the brownizing process are accounted for. The line width standard is controlled by L+10µm as the median with a tolerance of 5µm.

3.Post-Brownizing Line Width Measurement: Increasing the line width measurement after brownizing allows for final line width control with a target value of L5µm. Through process control point corrections, the impedance line width tolerance is reduced from the original 10% to 5%, significantly improving impedance control capability and internal impedance pass rates.

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