Electroplated through-holes are holes in a printed circuit board (PCB) with a copper coating. These holes allow the circuit to pass from one side of the board through the copper in the holes to the other side of the board. For any printed circuit board design with two or more circuit layers, electroplated through-holes form electrical interconnections between the different layers.
To create plated through holes during PCB manufacturing, the manufacturer drills holes into the board laminate and the foil present on either side. The wall of the hole is then electroplated so that it carries the signal from one layer to another.
In order to prepare a circuit board for electroplating, the manufacturer must conduct the circuit board from top to bottom through a chemically bonded unelectroplated copper thin layer that adheres to the inside of the hole and to the edge of the circuit board. This step is called copper deposition.
After deposition, the circuit image is applied and developed. The area where the circuit is present is then plated with a thicker copper layer, which coats the holes and circuit to the final desired thickness (usually about.001in /.025mm). From this point of view, the board will continue to be manufactured until it is complete.
Deposition issues can affect the interconnections within the hole walls and cause PCB failure. The most common deposition defect is the electroplating void in the hole wall of copper lining. If the wall of the hole is not smooth and completely coated, the current cannot pass through. The image above shows a cross section of the through-hole where the copper on the wall is too thin, likely due to deposition and poor plating.
During deposition, when copper is not evenly coated, electroplating voids in electroplating through-holes occur, preventing proper electroplating. This may be due to contamination, air bubbles on the side of the hole and/or rough drilling. All of these can create uneven surfaces on the through-hole walls, which makes it difficult to apply a smooth continuous copper wire.
Prevent plating holes in the circuit board
The best way to prevent PCB plating cavities caused by rough drilling is to ensure that the manufacturer’s instructions are followed during use. Manufacturers usually make recommendations for the recommended number of bits and the rate and speed of the bit feed. Bits with too low ROP may actually shatter the resulting material, creating a rough surface that is difficult to coat evenly during deposition and plating. If the rate of penetration is too low, bit smearing may occur, although it can be corrected during decontamination.
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