Double-layer PCB Production Process

Posted on 2020-07-11

The circuit board is the carrier of electronic design and is the place where all electronic components and circuits are summarized. Now electronic products have more and more functions and more and more components. The circuit design is more and more complicated, the most basic single The panel can no longer be used universally. When the circuit on one side is not enough to provide the connection requirements of electronic parts, the circuit can be arranged on both sides of the substrate, and a through-hole circuit is arranged on the board to connect the circuits on both sides of the board. This type of PCB board is called a double-layer PCB board.

Double-layer PCB production process

The production process of double-layer PCB board can be roughly divided into the following parts:

Printed circuit board – inner layer circuit – pressing – drilling – plated through hole (primary copper) – outer layer circuit (secondary copper)-anti – weld green paint – text printing – contact processing – forming cutting – final inspection packaging.

The detailed process is as follows:

1.After processing the original data of the customer’s original PCB. After confirming that there is no problem and meets the process capability, the first station entered, according to the work order issued by the engineer, determines that the PCB substrate size, PCB material, number of layers…etc. To put it simply, it is to prepare the materials needed for making PCB.


2.Dry film of inner layer: Dry film is a kind of resist that can be sensitive to light, develop, resist plating and resist etching. The photoresist is attached to the clean surface by hot pressing. The water-soluble dry film is mainly because its composition contains organic acid radicals, and it will react with strong alkali to make it become a salt of organic acid, which can be dissolved by water. It forms a water-soluble dry film, developed with sodium carbonate, and stripped with dilute sodium hydroxide Film to complete the development action. This step is about to “stick” the surface of the PCB that is about to be processed to a layer of water-soluble dry film that will undergo a photochemical reaction. It can be photosensitive to show the prototype of all the circuits on the PCB.

3.Exposure: The copper plate after lamination, and the negative film made with the PCB is automatically positioned by the computer and then exposed to light, so that the dry film on the surface of the plate is hardened by the photochemical reaction to facilitate the subsequent copper etching. Exposure intensity and exposure time.

4.Inner layer development: remove the unexposed dry film with a developer solution, leaving the exposed dry film pattern.

5.Acid etching: The exposed copper is etched to obtain PCB wiring.

6.Dry film removal: In this step, the hardened dry film attached to the surface of the copper plate is removed with a chemical solution. The entire PCB circuit layer has been roughly formed.

7.AOI machines with automatic optical alignment inspection: perform alignment inspection based on correct PCB data to detect whether there is a circuit break, etc. If there is such a situation, then inspect and repair the PCB.

8.Blackening: This step is to treat the copper on the surface of the PCB after the maintenance is confirmed to be correct. The copper surface is fluffy and the surface area is increased to facilitate the bonding of the PCB layers on both sides.

9.Pressing: Pressing with a hot pressing machine. Press the steel plate on the PCB, and after a certain period of time, reach the required thickness and determine the complete bonding. The bonding of the PCB layers on both sides is now complete.

10.Drilling: After inputting the computer with the control engineering data. It is automatically positioned by the computer and exchanged for drills of different sizes for drilling. Since the entire PCB is already packed, it needs to be scanned with X-RAY. After finding the positioning hole, drill the necessary holes for the drilling procedure.

11.PTH: Since there is no continuity between the layers in the PCB, it is necessary to plate copper on the drilled holes for inter-layer conduction. However, Resin between layers is not conducive to copper plating. It is necessary to produce a thin layer of chemical copper on the surface, and then carry out the copper plating reaction to meet the functional requirements of the PCB.

12.Outer laminated film: Outer laminate film pretreatment After drilling and through-hole plating, the inner and outer layers are connected. The next step is to make the outer layer circuit to complete the circuit board. Laminating is the same as the previous laminating step, the purpose is to make the outer layer of PCB.


13.Outer layer exposure: same as the previous exposure steps.

14.Outer layer development: same as the previous development step.

15.Line etching: The outer line is formed in this process.

16.Dry film removal: In this step, the hardened dry film attached to the surface of the copper plate is removed with a chemical solution. The entire PCB circuit layer has been roughly formed.

17.Spraying: Spray green paint of appropriate concentration evenly on the PCB. Or use a doctor blade and a screen to evenly spread the ink on the PCB.

18.S/M use light: harden the part that needs to keep the green paint, and the part that is not exposed to light will be washed away in the development process.

19.Imaging: Wash the unexposed hardened parts with water, leaving the hardened parts that cannot be washed away. Bake and dry the good green paint, and make sure that the PCB is firmly attached.

20.Printed text: Print the correct text on the appropriate screen according to customer requirements, such as material number, manufacturing date, part location, manufacturer and customer name and other information.

21.Tin spray: In order to prevent the oxidation of the bare copper surface of the PCB and maintain its good solderability, the PCB needs to be surface treated, such as HASL, OSP, chemical silver immersion, nickel immersion gold, etc.

22.Test: 100% circuit test is performed on the PCB board according to the performance required by the customer to ensure that its functionality meets the specifications.

23.Final inspection: For the board that passes the test, 100% inspection of appearance shall be done according to the customer’s appearance inspection standard.