After a printed circuit board has been laminated and grouped as a panel, the PCB fabrication will shift into the PCB’s external features.
This article discusses PCB fabrication procedures companies employ in developing the board’s external features. These techniques are already quite complicated to do at home or in a small business. It is therefore recommended to partner with experts to help you with your needs.
1.Drill to interconnect the boards
A PCB panel or multiple layers of PCB are ready to be drilled. By using the software data from the Gerber files, the physical drilling of holes, or vias, can now start. These holes are used to interconnect the boards from different layers. The drilling process allows for physical and electrical communication between boards.
Different sizes of holes are drilled through the recently bonded copper materials. The size and location of the holes are determined through the customer-submitted data. These holes are also subjected to the standard measurements of the specific components. Their sizes are usually 5mils larger than the finished standard size. This must be done to accommodate additional copper fillings from the copper electroplating process.
2.Clean the Drilled Holes
If there’s debris, then another procedure is introduced. This is called “hole cleaning”. This procedure removes any physical obstruction that may obscure the board’s external and internal connections.
A blockade can either be scraped (deburr) or just be cleaned (desmear):
•Deburr is a mechanical process that removes raised and sharp edges of the copper through abrasion. The burrs are the sharp residues around the drilled hole. Any debris left inside the hole are also removed
•Desmear is a chemical process that removes the resin’s coating from the inner layers’ copper connections. These thin coatings were usually produced when the drill heat up the holes, thus, the plastic coatings melt from constant motion and high temperatures. The resin smear should effectively improve the inner layer’s electrical conductivity.
3.Prepare a Plated Connection
The cleaning solution that was previously used is also necessary to prepare the internal layer’s holes and walls for copper plating. “Plating” procedures are essential in PCB fabrication.
In order to create a copper plated hole, a procedure called electroless copper deposition is used. It is a chemical procedure that plates the holes with thin layers of copper, therefore creating a copper “hole wall”. The hole effectively connects all the layers thru just one conductive plate. The thickness of the deposit is between 45 and 60 millionths of an inch.
4.Prepare the Outer Features of the PCB
After the initial layers have been created, merged and drilled together (typically, resulting to a sandwiched copper board wafer), the next step is to prepare for the outer and visible layers of the board. Another major PCB fabrication step has been completed.
To prepare for the outer features: the outer layers of the multi-layered PCB should be cleaned, coated with photoresist, and exposed to UV light. The photoresist coat can also vary in thickness.
5.Photo Exposure Process for the Outer PCB
This basic concept of exposure from the inner layers is applied here. The only difference is the objective. The exposure will harden the areas where the copper is to be removed later.
The development process, therefore, will expose the copper areas where the PCB patterns are found. This may be dumbfounding at first, but the main reason for this move is to open the copper for additional plating and thickening.
6.Pattern plate the visible connections
The exposed copper from the previous step will be copper-plated once again. This procedure is called pattern plating. Additional copper is deposited, through electroplating, to the cavities or openings. This will ensure the PCB holes’ sizes and surface thicknesses to be at par with the customer needs. Copper can be plated to as thick as 1mil, or 0.001”.
Aside from the above plating procedures, a tin-plating procedure is also done. This process is done to protect the copper surfaces from chemical etching. Tin is used to shield the copper traces, holes, and even the walls from the etch procedure.
This article discussed about various plating techniques done to improve the external appearance of the board. These techniques require you to have specialized machines that deposit metals into the board. Always make sure that your PCB fabrication partner also has these machines. It will help you obtain professionally-created electronics that can be easily sold to the market.