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How is a PCB board made?

   PCB, which full name is printed circuit board is indispensable for all electronic products. It is actually bonded together by several layers of a resin material, and the inside is made of copper foil. A typical PCB circuit board is divided into four layers. The uppermost and lowermost layers are signal layers. The middle two layers are the ground plane and the power plane. The ground and power layers are placed in the middle so that the signal lines can be easily corrected. Some boards with higher requirements can reach 6-8 layers or more.

  • How is the PCB board manufactured?

 1. Woven glass fiber is unwound from the reel and sent through the processing station. The above figure shows an enlarged portion of the PCB in which the epoxy resin is impregnated or sprayed. The impregnated glass fibers are then passed through a roller which rolls the material to the desired thickness for use in the finished substrate and also removes any excess resin.

2. The substrate is cured. After curing, the material is cut into large panels.

3. These panels are layered and stacked alternately with the copper foil layer of the adhesive backing. The laminate was placed in a press and subjected to a temperature of about 340 °F (170 °C) and a pressure of 1500 psi for one hour or more. This completely cures the resin and tightly bonds the copper foil to the surface of the base material.

  • Drilling and plating holes

4.pieces of the substrate, each large enough to make several printed circuit boards that are stacked one on top of the other and held together to prevent them from moving. The stacked plates are placed in a CNC machine and drilled according to the pattern determined when the plates are laid. The holes are deburred to remove any excess material attached to the edges of the holes.

5. The inner surface of the hole is designed to provide a conductive circuit from one side of the board to the other, which is plated with copper. After cutting the individual panels from the larger panel, non-conductive holes are inserted to prevent them from being plated or drilled.

  • Create a printed circuit pattern on the substrate

The printed circuit pattern can be produced by an "addition" process or a "subtraction" process. In the additive process, copper is plated or added to the surface of the substrate in a desired pattern such that the remaining surface is not plated. In the subtractive process, the entire surface of the substrate is first plated and then the regions that are not part of the desired pattern are etched away or subtracted. We will describe the additive process.

6. The foil surface of the substrate is decreased. The panel passes through a vacuum chamber in which a layer of positive photoresist material is firmly pressed against the entire surface of the foil. A positive photoresist material is a polymer that has properties that become more soluble upon exposure to ultraviolet light. The vacuum ensures that no bubbles are trapped between the foil and the photoresist. A printed circuit pattern mask is placed on top of the photoresist and the panel is exposed to strong ultraviolet light. Since the mask is transparent in the area of the printed circuit pattern, the photoresist in these areas is illuminated and becomes very soluble.

7. The mask is removed and the panel surface is sprayed with an alkaline developer that dissolves the irradiated photoresist in the printed circuit pattern region to expose the copper foil to the surface of the substrate.

8. Then plate the plate with copper. In this process, a foil on the surface of the substrate serves as a cathode, and copper is plated to a thickness of about 0.001-0.002 inches (0.025-0.050 mm) in the exposed foil region. The area still covered with photoresist cannot be used as a cathode and is not plated. Tin or other protective coating is applied to the top of the copper plating to prevent copper oxidation and as a resist for the next fabrication step.

9. The photoresist is stripped from the plate with a solvent to expose the copper foil of the substrate between the plated printed circuit patterns. Spray the plate with an acid solution which will dissolve the copper foil. The copper plating on the printed circuit pattern is protected by a tin-lead coating and is not affected by the acid.

  • Mounting contact

10. A contact finger is attached to the edge of the substrate for connection to a printed circuit. The contact fingers are masked off the rest of the board and then electroplated. Plating is done with three metals: first, tin-lead, then nickel, then gold.

Fusion tin-lead coating

11. The tin-lead coating on the surface of the 11-copper printed circuit pattern is very porous and easily oxidized. To protect it, the panel is melted or reflowed into a shiny surface by a "reflow" oven or hot oil bath.

  • Seal, formwork and cutting panel

12. Each panel is sealed with epoxy to protect the circuit from damage when the components are connected. Instructions and other marks are printed on the board.

13. The panel is then cut into individual panels and the edges are smoothed.

  • Installation component

14.separate boards through several machines, placing electronic components in place in the circuit. If surface mount technology is to be used to mount the components, the board is first placed through an automated solder placement machine with a small amount of solder paste at each component contact point. Very small parts can be placed through the "chip shooter", which quickly places or shoots the part onto the board. Larger components can be placed by the robot. Some components may be too large or weird to place the robot and must be placed manually and soldered later.

15. Then solder the component to the circuit. With surface mount technology, soldering is accomplished by passing the board through another reflow process that melts the solder paste and forms a bond.

16. The flux residue in the solder is washed with water or solvent depending on the type of solder used.

17. Unless printed circuit boards are used immediately, they will be individually packaged in protective plastic bags for storage or shipping.