The Multilayer board is the middle layer of medium, and both sides are trace layers. A multi-layer board is a multi-layer wiring layer. There is a dielectric layer between every two layers, and the dielectric layer can be made very thin.

Multilayer circuit boards have at least three conductive layers, two of which are on the outer surface, and the remaining layer is synthesized within the insulating board.

The electrical connection between them is usually achieved through plated through holes in the cross section of the circuit board.

Storage conditions:

1.The PCB circuit board needs to be vacuum-packed in a colorless air bead plastic bag, and the necessary desiccant should be attached to the packaging bag to ensure that the packaging bag is tightly packed. It should not be in contact with wet air to avoid the surface of the PCB circuit board being sprayed with tin, immersion gold and the pad parts to be oxidized and affect the welding, which is not conducive to production.

2. When packing the PCB circuit board, it is necessary to surround a layer of bubble film around the box. Because the bubble film has good water absorption, it can absorb water and moisture. Also, moisture-proof beads can be placed in the box.

3. Put the PCB circuit boards into categories and label them. After sealing, the box must keep a distance from the wall and the ground. The box is stored in a dry and ventilated place, while avoiding direct sunlight.

4. The temperature of the warehouse where the PCB circuit boards are stored is best controlled at 23±3℃, 55±10%RH. Under such conditions, the PCB circuit boards with surface treatments such as immersion gold, electro-gold, tin spraying, and silver plating can generally be stored. 6 months, PCB circuit boards with surface treatment such as immersion silver, immersion tin, OSP, etc. can generally be stored for 3 months.