Double Sided PCB

Double sided PCB is a printed circuit board with copper on both sides, including Top (top layer) and Bottom (bottom layer). It is the most common and common circuit board. Both sides of the insulating substrate have conductive patterns. Electrical connections are primarily made through vias or pads. The double sided PCB is mainly composed of top line (GTL), bottom line (GBL), pads (PADS), vias (VIA), top solder mask (GTS), bottom solder mask (GBS), outline layer (GKO), top layer Screen printing (GTO), bottom screen printing (GBO) layer, etc. Because both sides of the double sided PCB can be routed, the difficulty of wiring is greatly reduced, so it is widely used.

Double Sided PCB Products

There are wiring on both sides of the double sided PCB, but to use the wires on both sides, there must be a proper circuit connection between the two sides. The "bridge" between the circuits is called a via. A via is a small hole on a PCB, filled or painted with metal, that can be connected to wires on both sides. Because the double sided PCB has twice the area of the single sided PCB, and because the wiring can be interleaved (can be wound to the other side), it is more suitable for use on more complex circuits than single-sided boards.

The wiring of the double sided PCB can be interleaved, which is the biggest difference from the single-sided board; the double sided PCB is more suitable for complex circuits and has a wider range of use. The cost difference between single and double sided PCBs is not significant. If there are no special requirements, all industries will give priority to double sided PCBs; after all, the performance and stability of double sided PCBs are better than single PCBs.

The Difference Between Single and Double Sided PCB

The production method of the double sided PCB is generally made by the inner layer pattern first, and then the single-sided or double sided substrate is made by the printing and etching method, and is incorporated into the designated interlayer, and then heated, pressurized and bonded. As for the subsequent drilling, the hole is the same as the plated-through hole method of the double sided PCB.

The difference between a double sided PCB and a single sided PCB is that the single-sided circuit is only on one side of the PCB, while the double sided PCB can be on both sides of the PCB. line connected. Parameters of double sided PCB in addition to the different production process of double sided PCB and single sided board, there is also a copper sinking process, that is, the process of conducting double sided PCB circuits.

1. The single-sided printed circuit board is normally a single-sided copper-clad laminate, and the etched circuit pattern is made on the copper surface by the screen printing method or photoimaging method, and the excess copper foil is removed by chemical etching to form a conductor pattern.

2. The double sided PCB has upper and lower conductor patterns, and the upper and lower vias are connected by expensive perforations. In the processing of printed circuit boards, the hole walls of the expensive perforations are plated with a copper layer to make the upper and lower layers conduct. The anti-corrosion circuit pattern is made on the copper surface, and the excess copper foil is removed by chemical etching to form a conductor pattern.

Double sided PCB and single-sided PCB can be basically distinguished from the appearance, single-sided is a circuit board with only one layer and a line layer, double sided PCB is a circuit board with two wiring layers, and there are via holes in the middle, so this is difference between single sided board and double sided PCB. The production of double sided PCBs is a bit more complicated than single-sided PCBs for two main reasons:

(1) The top and bottom layers of the copper-clad board should be wired.

(2) The wires on the top layer and the bottom layer should be connected with metallized vias. Among them, metallization is particularly critical, which is also the core process of double sided PCB production. The so-called via metallization is to coat a layer of metal on the inner wall of the via hole in order to connect the printed wires of the top layer and the bottom layer.

At present, the domestic via metallization mainly adopts the electroless copper plating process. There are two types of electroless copper plating processes:

1. Electroless thin copper is firstly plated, then the whole double sided PCB is electroplated to thicken the copper layer, and then the pattern is transferred.

2. Electroless plating of thick copper first, and then direct pattern transfer. Both are widely adopted. However, electroless copper plating is harmful to the environment, and it will be gradually replaced by more advanced black hole technology, tin/palladium direct plating technology, and polymer direct plating technology.

Double Sided PCB Production Process

1) Cutting materials: Cut out the size that is convenient for processing from the whole large material of copper clad laminate with certain plate thickness and copper foil thickness

2) Drilling: Drill conductive holes or plug-in holes on the double sided PCB according to the computer drilling program

3) Immersion copper: deposit a thin layer of chemical copper in the drilled hole. The purpose is to deposit a layer of copper on the non-conductive epoxy glass cloth substrate (or other substrate) by chemical method to facilitate subsequent electroplating conduction to form a circuit;

4) Copper plating on the whole board: mainly to thicken and protect the thin layer of chemical copper to prevent it from oxidizing in the air, resulting in no copper or holes in the holes;

5) Circuit (graphic transfer): paste dry film on the double sided PCB or silk screen with graphic anti-plating ink, after exposure and development, make circuit graphics

6) Graphic electroplating: Thicken copper plating on the double sided PCB with the graphic circuit ready, so that the copper thickness in the hole and the circuit reaches a certain thickness, and a certain current can be loaded

7) Etching: remove the graphic ink or dry film, and etch away the excess copper foil to obtain the conductive circuit pattern.

8) Removal of tin: remove the tin layer on the formed pattern in order to expose the required circuit

9) Screen printing solder mask ink or paste solder mask dry film: print a layer of solder mask ink on the double sided PCB, or paste a layer of solder mask dry film. After exposure, develop a solder mask pattern. The main purpose is to prevent welding short circuit between time lines.

10) Gold/tin spraying: Apply gold or spray a layer of tin on the double sided PCB where it needs to be welded, which is convenient for welding and can also prevent the copper surface from oxidizing there.

11) Legends: some iconic legends are printed on the double sided PCB, which is mainly convenient for customers to install components.

12) Stamping/Forming: Process the shape of the double sided PCB according to customer requirements

13) Electrical test: detect whether there is an open or short circuit in the double sided PCB by means of a closed loop

14) Visual inspection: For the double sided PCBs that pass the test, conduct visual inspection

15) Packing and shipping

How to Maintain the Double Sided PCB?

Although the double sided PCB has a certain self-protection function, it should be avoided in a corrosive environment in daily use, and the corrosive factors should be eliminated as much as possible so that its service life can be greatly extended. When using it, try to keep it in a medium temperature environment to avoid high temperature and low temperature environment.

1. Avoid contact with weak acid substances

Weak acid substances generally do not cause corrosion to items, but due to the different chemical structures of double sided PCBs, it is necessary to avoid contact with acidic substances. Even weak acid substances should be avoided as much as possible to prevent corrosion of veneers.

2. It is forbidden to contact sand and ash substances.

The double sided PCB should not be in contact with sand ash wood, because the surface of aluminum products has a layer of natural aluminum protective film, which is a natural barrier against oxidation and one of the anti-corrosion structures. If the double sided PCB is in contact and rubbed with them for a long time, the protective film will be damaged and its anti-oxidation effect will be affected.

3. Avoid direct sunlight

The double sided PCB should also avoid frequent contact with ultraviolet rays in daily life. Any aluminum products that are often exposed to ultraviolet rays will make the surface oxidized to accelerate the rate of oxidation, and will also make it tarnished, so avoid direct sunlight.

4. Do not hit too hard

Although the double sided PCB has a certain bearing capacity, and has a certain hardness and compression resistance after alloy injection, but combined with its raw material characteristics, it can be seen that aluminum material is not a natural material that is resistant to compression, so the compression resistance is slightly lower than that of other metals. It is weak, so try not to let it have too much impact during daily use to prevent it from breaking.

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