Microthrough-Hole Formation in PCBs Using Patterned Electroplating
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Solution Overview
Problem
Current methods for manufacturing microthrough-holes in circuit boards are limited by the size of the laser beam and the metal layer, making it difficult to achieve high circuit density due to the minimum window size of 50 μm and resulting pitch of 140 μm, which restricts the miniaturization and integration of electronic components.
Innovation Solution
A method involving patterned dry film electroplating to form a metal circuit with line width and pitch less than 50 μm, where only the insulation layer is penetrated during laser drilling, allowing the microthrough-hole to match the size of the copper window, and a conductive layer is formed to connect the circuits, thereby reducing the occupied area and increasing circuit density.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If traditional laser drilling process with copper window is used, then the through-hole can be formed, but the minimum window size is limited to 50 μm and the pitch is limited to 140 μm, which reduces circuit density
Solution Approach 1:
The patent applies preliminary action by forming the metal circuit layer with precise pitch (less than 50 μm) before the laser drilling process. The metal circuit is embedded in the insulation layer to define the exact position and size of the microthrough-hole, allowing the laser to drill precisely through the insulation layer only, achieving microthrough-hole sizes matching the metal circuit pitch and enabling high circuit density.
2Productivity
If the copper window size is reduced to increase circuit density, then more circuit area is available, but the laser beam size and metal layer absorption limit further reduction
Solution Approach 1:
The patent segments the drilling process by separating the functions of defining the hole position (metal circuit layer) from the drilling process (laser through insulation layer). The metal circuit layer is formed with precise dimensions using electroplating, and the laser drilling is performed only through the insulation layer, decoupling the limitations of laser beam size from the final microthrough-hole dimensions.
Solution Approach 2:
The patent introduces the metal circuit layer as an intermediary that defines the microthrough-hole position and size. This metal circuit layer acts as a template or mask that guides the laser drilling process, allowing precise control of microthrough-hole dimensions independent of laser beam size, thereby enabling smaller features and higher circuit density.
3Ease of manufacture
If photoresist development and photolithography are used to form the copper window, then the opening can be created, but the minimum size is limited to larger than 50 μm
Solution Approach 1:
The patent replaces the photolithography and photoresist development process with an electroplating process to form the metal circuit layer. Electroplating allows for precise control of the metal layer thickness and pattern dimensions, achieving line widths and pitches less than 50 μm, which is finer than what photolithography can achieve. This substitution eliminates the minimum opening size limitation imposed by photoresist processing.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The method effectively shrinks the microthrough-hole size and reduces its occupied area, enabling higher circuit density and overcoming the limitations of traditional manufacturing processes.
Implementation Method 1
a laser beam easily penetrates insulation material but difficultly through metal material
Implementation Method 2
employing a drilling process to upward drill through the insulation layer corresponding to the copper window and stop at the stop pad to form a microthrough-hole
Implementation Method 3
electroplating a metal layer on the carrier plate, forming a first circuit having copper pads on one surface of the metal layer
Data Source
AI summary
A method for manufacturing microthrough-hole includes electroplating a metal layer on a carrier plate, patterning the metal layer to form a first circuit having copper pads, covering the first circuit with a photoresist layer and not covering the copper window between two of the copper pads, etching the metal layer beneath the copper window and removing the photoresist layer, sequentially forming an insulation layer and a second circuit on the first circuit and the copper window, the second circuit layer having a stop pad corresponding to the copper window, removing the carrier plate, upward drilling through the insulation layer between the stop pad and the copper window to form a microthrough-hole beneath the stop pad, and forming a conductive layer in the microthrough-hole to form the microthrough-hole connecting the first and second circuits. The microthrough-hole and its occupied area is greatly reduced, thereby achieving high circuit density.