A processing method for improving the uniformity of copper reduction of a printed circuit board

Abstract

The application provides a processing method for improving the uniformity of copper reduction of a printed circuit board. The technical core is that a composite copper foil is added. In the copper reduction processing, the etching resist layer in the composite copper foil protects the base copper from being corroded by the copper reduction chemical solution. Then the etching resist layer is removed by a chemical method to expose the base copper, so that the uniformity of the copper thickness is ensured. The method comprises the following steps: covering an etching resist layer on the surface of the copper foil to form a composite copper foil; completing the processing of the inner layer pattern of an inner layer core board; stacking the composite copper foil, the copper foil, the adhesive sheet and the inner layer core board according to the order of the stacking structure, and putting them into a high-temperature and high-pressure press to press them into a multilayer circuit board; after the multilayer circuit board is subjected to processes such as drilling, hole metallization, whole board electroplating and resin hole plugging, the copper reduction is performed, then the etching resist layer is removed by a chemical method to expose the base copper, and then subsequent processing processes are performed.

Description

Technical Field

[0001] This invention relates to the field of printed circuit board manufacturing, and more specifically to a processing method for improving the uniformity of copper reduction after multiple electroplating of circuit boards. Background Technology

[0002] In the manufacturing processes of high-end printed circuit boards (PCBs) with high aspect ratios, blind and buried vias, HDI, high-speed signal via back-drilling, and POFV processes, 2 to 5 copper plating processes are often required to meet the demands of these products. However, each copper plating process increases the surface thickness and accumulates thickness deviations, failing to meet the technical requirements of high-precision impedance control, high-density, and precision wiring products. This problem is particularly prominent in high-end PCBs for AI servers. The traditional approach to reducing surface copper thickness and accumulating thickness deviations involves adding a chemical copper reduction process after electroplating. However, this cannot solve the thickness deviation caused by multiple plating processes. The following key technical indicators need to be addressed: 1. The thickness deviation of the surface copper thickness after copper reduction should be ≤ ±2μm; 2. The batch stability of the surface copper thickness after copper reduction should be CPK ≥ 1.33. The two published Chinese invention patents (CN104135825 A copper reduction process for printed circuit boards / CN105392299A A method for improving the uniformity of copper reduction) fail to solve these two technical problems. 1. Patent CN104135825 uses a dry film to cover the hole ring, preventing a chemical reaction between the acidic etching solution and the dry film during the copper reduction step, thus protecting the hole copper and ensuring the reliability of the hole copper thickness. This method cleverly reduces the copper thickness; however, it only reduces the surface copper thickness, but it does not solve the problems of surface thickness deviation and batch stability. 2. Patent CN105392299A forms a first etching resist layer on the portion of the PCB board surface where the hole ring is removed; a second layer is formed on the first etching resist layer and the hole wall; the second copper layer on the first etching resist layer is removed, and then the first etching resist layer is removed again. This can solve the batch stability problem, but it does not solve the problem of surface thickness deviation after electroplating. Summary of the Invention

[0003] The purpose of this invention is to provide a processing method for improving the uniformity of copper reduction on printed circuit boards, which can achieve the above two key technical indicators and enable mass production.

[0004] This invention adds a layer of chemically resistant material to the copper foil surface during the lamination process of multilayer printed circuit boards, called composite copper foil (copper foil + resist layer). The copper foil attached to the printed circuit board is called base copper, forming a sandwich structure of copper foil + resist material + copper foil. The resist material protects the base copper from chemical corrosion. During multiple copper plating processes, the surface copper thickness only increases on the composite copper foil. When reducing copper, the electroplated copper and the copper on the composite copper foil are removed to expose the resist layer. Then, the resist layer is removed by chemical methods to expose the base copper, thereby meeting the technical indicators of thickness deviation and batch stability after copper reduction.

[0005] According to the present invention, a processing method for improving the uniformity of copper reduction on printed circuit boards is provided. The core technology is the addition of a composite copper foil layer. During the copper reduction process, an anti-corrosion substance protects the base copper from corrosion by the copper reduction solution. The method includes the following steps: attaching an anti-corrosion substance to the copper foil; processing the inner layer pattern on the inner core board; stacking the composite copper foil, copper foil and adhesive sheet, and inner core board in sequence according to the stacking structure requirements, and placing them in a high-temperature and high-pressure press to press them into a multilayer circuit board; after the multilayer circuit board undergoes processes such as drilling, hole metallization, full-board electroplating, and resin plugging, copper reduction is performed to remove the copper foil on the composite copper foil and the copper generated by full-board electroplating. Then, the anti-corrosion substance is removed by chemical methods, followed by secondary drilling, secondary hole metallization, secondary full-board electroplating, and subsequent processing.

[0006] Preferably, the inner core board is a copper-clad laminate.

[0007] Preferably, the bonded sheet is laminated under heat and pressure, causing the resin to melt and flow → solidify, firmly bonding the core board, copper foil, and inner layer circuitry, providing interlayer electrical insulation and structural support. Preferably, the chemical method for removing the resist is a nitric acid-based stripping solution, a fluoride-oxygenated stripping solution, or a sodium hydroxide stripping solution. Attached Figure Description Figure 1 This is a flowchart illustrating the present invention.

[0008] In summary, this invention provides a processing method to improve the uniformity of copper reduction. The method of this invention can improve the uniformity of copper reduction and meet the requirements of high-precision impedance control, high-density and precision wiring circuit boards.

Claims

1. A processing method for improving the uniformity of copper reduction on a printed circuit board, the method comprising the following steps: A resist layer is applied to the copper foil to form a composite copper foil; in the lamination process, the composite copper foil is attached to the copper foil, and the resist layer is attached to the copper foil to form a sandwich structure of copper foil + resist layer + copper foil; the composite copper foil, copper foil, prepreg and inner core board are pressed together to form a multilayer board; after the resin plugging is completed, copper reduction is performed to remove the copper on the composite copper foil and expose the resist layer; the resist layer is removed to expose the base copper.

2. The method according to claim 1, characterized in that, The corrosion-resistant layer of the composite copper foil is a tin layer, dry film, resin, or other polymeric substances.

3. The composite copper foil according to claim 2 is used in the manufacturing process of printed circuit boards.

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