PCB: Current Manufacturing Practices

Technology has undergone changes to meet the needs and expectations of the consumer and the industry over time. With many of them getting obsolete and some facing near getting out of use (e.g. turret boards and double sided PCB), there are still practices that have survived. There are also practices and technologies that are getting popular within a short span of time and those that are in the development stage.

ID FanChemical etching
Chemical etching is a process, that relies on chemicals like ammonium persulfate and ferric chloride. In this process, holes are drilled on the insulating substrate at the desired and predetermined places and then the boards are electroplated to build the thickness on the insulating board. The boards are screened and plated with tin/lead. The tin/lead coating becomes a resist and causes the bare copper to be etched.

Immersion etching is employed by hobbyists to develop their PCB boards. This includes covering part of the board to be protected by etching with materials like sunflower seed oil. The chemical removes the unnecessary copper on the board and leaves behind the copper conducting paths.

Bubble etching includes passing air bubbles through the etching solution to speed up the etching process.

FD fanSplash etching uses a motor driven tray to agitate the tray to speed up the etching process.
The drawbacks of the process lies in the fact that as etching goes on, the ability of the solution to dissolve copper falls.

Another drawback is the “undercut” which occurs when the layer of copper under the resist is attacked by the solution resulting in reduction in the width of the track, which in turn leads to short circuiting.

“Overhang” problem may happen due to unetched copper that may result in short circuiting.

Multilayer printing
A PCB of this type consists of many double sided PCBs glued together with a non conducting lamination. However, a mutual connection between the constituent PCB. This results in high data transfer speeds and effective space utilization. The layers of PCBs to be used may range from a few to 25 or even 100, which depends on the complexity of the circuit.

Quite often one or more boards will be dedicated to a common purpose, particularly, for providing ground supply, for providing power or for the signals.

These type of boards are mainly used in high-end computer and equipment, such as supercomputers.
Pressing of different layers is usually done with the help of a hydraulic press and a non conducting glue and lamination are used to keep them compact.

PCB CAM designing and 2d structures
CAD software is aimed to be used in designing circuits in soft format on layer with a predetermined width and thickness and the number of layers to be used. The following steps important to know.

  • Card dimensions are decided based on the required circuitry, the components and the heat sinks required.
  • Deciding stack layers of the PCB – 1 to 12 layers or more depending on design complexity are used.
  • Line impedance determination is done using dielectric layer thickness.
  • In placement of the components, thermal considerations and geometry are taken into account.
  • Routing the signal.
  • Gerber file generation for manufacturing.

ID FansThe gerber files are fed into the CAM system for a professional manufacturing process of PCB. CAM does the following operations:

Input of the Gerber data

  • Verifies the data; optionally DFM
  • Compensates for deviations in the manufacturing processes (e.g. scaling to compensate for distortions during lamination)
  • Panelizes
  • Checks output of the digital tools.

3D Printed Structure Boards : A step ahead
With the available technologies, 2D and 2.5D PCB have achieved great heights, and they are set to be revolutionized with the advent of the 3D printing technology. This will boost the data transfer speeds and eliminate the use of epoxy resins, conducting links, screws and bolts and the circuit can be designed in a flexible cylindrical shape with circuiting done inside the shape taking the level of the sophistication higher.