PCB design engineers design several mechanical features that are difficult to manufacture cost-effectively, such as:
Plating through hole consistency
Conventional FR4 plates are pretreated differently from PTFE prior to electroplating, and manufacturers must be aware of the effect of different processes on hole wall quality. Before copper plating, plasma etching is usually used to remove colloidal residue from the pore wall of PTFE materials. Although plasma etching is beneficial to improve the quality of ptfe pore wall, it also erodes FR4 material to a certain extent, leading to uneven surface, which leads to uneven copper plating in the hole, resulting in void or electrical failure.
Control depth sidestep PCB, groove/cavity
For complex rf mixed circuit board designs with grooves/cavities, it can be achieved by multiple pressing or depth control of the gong plate (using the Routing machine or laser cutting machine to create the shape profile). These two processes increase the cost and complexity of hf PCB design.
When making these grooves/cavities using multiple presses, the manufacturer needs to control the depth of the gongs on large panels and semi-cured plates. Once the control deep grooves/cavities are formed, it is important to have no bias in alignment, otherwise the product will not comply with IPC standards due to inter-layer bias, or the semi-cured sheets between layers will overflow and cover the RF components on the PCB board.
For products requiring depth control processes, the tolerance range for depth control is narrow, as the thickness of the insulation between the bottom of the depth control groove/cavity and the copper foil may be only 1mil.
The grotesque shape of the high-frequency board
The shape of the PCB must be suitable for the unique housing or the narrow space that accommodates the PCB, resulting in the zigzag profile of the HF PCB. Although it is usually not difficult to create this type of PCB profile, for high-frequency boards with mixed-voltage designs, specific solutions need to be used. Some PTFE materials are so soft that the feed speed and the speed of the gongs must be slowed down to ensure that the edges are neat and without burrs. In addition, the gongs must be constantly monitored, as the loss of high-frequency materials to the gongs is much greater than that of conventional plates. If the gong knife is worn too much during machining, the shape of the hf plate may be outside the tolerance range.