Back-Drilled PCB Hole Copper Protection via Resin Filling
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Solution Overview
Problem
The existing methods for fabricating back-drilled holes on PCBs, particularly for high-speed electronic products with small holes, face challenges such as complexity, low productivity, stringent copper thickness requirements, and difficulty in plating tin due to excessive surface copper, leading to potential rejection of small holes due to copper absence.
Innovation Solution
A method involving forming a metal layer on the inner walls of through-holes, filling the holes with resin, back-drilling, and removing metal scraps through acidic etching, which simplifies the process, protects hole copper, and avoids aperture reduction and copper loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If alkaline etching flow process is used to remove copper wires in back-drilled small holes, then copper wires can be removed, but the process becomes very complicated and productivity decreases
Solution Approach 1:
The patent changes the etching parameter from alkaline to acidic environment. By using acidic etching solution instead of alkaline etching, the process simplifies significantly while maintaining the ability to remove copper wires. The acidic environment selectively removes copper without requiring the complex multi-step alkaline etching flow process, thereby improving productivity while ensuring reliable copper wire removal.
2Manufacturing precision
If base copper thickness is controlled within 50 micrometers for alkaline etching, then fine lines can be etched properly, but the process becomes more difficult to control
Solution Approach 1:
The patent changes the etching parameter from alkaline to acidic environment, which fundamentally alters the etching characteristics. Acidic etching provides more predictable and controllable etching rates, reducing the stringency of base copper thickness requirements. This parameter change simplifies process control while maintaining the ability to etch fine lines with high precision, eliminating the need for strict 50 micrometer thickness control.
3Reliability
If surface copper is plated twice to ensure sufficient copper, then copper coverage is improved, but surface copper becomes excessive and hole diameter decreases making tin plating difficult
Solution Approach 1:
The patent applies preliminary protection action by filling the through-holes with resin before back-drilling. This preliminary resin filling protects the hole copper during the back-drilling process, eliminating the need for excessive copper plating. The resin acts as a protective barrier that prevents copper loss during drilling, thereby maintaining adequate copper coverage without requiring twice-plating, and preserving the original hole aperture for subsequent tin plating.
4Reliability
If resin filling is performed before back-drilling, then hole copper is protected from loss, but the process steps increase
Solution Approach 1:
The patent merges the resin filling step with the existing back-drilling process flow. Rather than adding a completely separate process, the resin filling is integrated into the preparation phase before back-drilling. This merging approach protects hole copper effectively while minimizing the increase in process complexity, as the resin filling can be performed using existing dispensing equipment and integrates smoothly with the subsequent back-drilling operation.
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
This method simplifies the fabrication process, ensures accurate hole size, and prevents copper loss by protecting hole copper with resin, allowing only metal scraps to be removed in acidic etching, thereby reducing production time and board rejection rates.
Implementation Method 1
filling the holes with resin so that only metal scraps remained in the back-drilled small holes can be removed in acidic etching without affecting the part of the hole copper protected by the resin
Implementation Method 2
removing metal scraps remained in the through-holes
Data Source
Figure 1a~1c
Figure 1d~1e
Figure 1f~1g
AI summary
A method for manufacturing a back drilling hole in a printed circuit board (PCB) and PCB are provided. The method for manufacturing the back drilling hole comprises: forming a through hole in the PCB (1); forming a metal layer (12) with prescribed thickness on an inner wall of the through hole; filling resin in the through hole which has been formed with the metal layer (12); performing back drilling machining on the through hole which has been filled with the resin; removing metal scraps remained in the through hole. The manufacturing method protects the hole wall copper by filling the hole with the resin, so that acid corrosion process only removes the remained metal scraps after back drilling of the small hole, does not affect on the hole copper of the resin protecting portion, and the manufacturing process is simple.