As the current design of portable products is developing toward miniaturization and high density,the difficulty of PCB design is also increasing, which puts forward higher requirements for PcB processing technology. Most of the current portable products use the BGA package with a pitch of less than 0.65mm, and the design process of blind and buried holes is used. So what is a blind and buried hole? UcreatePCB answers for you!

Blind holes are mostly small holes with a diameter of 0.05mm~0.15mm. The hole forming methods of buried blind holes include laser hole formation, plasma etching hole and photoinduced hole formation. Laser hole formation is usually used, and laser hole formation is divided into CO2 and YAG. UItraviolet laser machine (UV).

Blind vias (Blind vias / Laser Vias): Blind vias are a type of via that connects the inner traces of the PCB to the surface traces of the PCB.This hole does not penetrate the entire board.

Buried vias: Buried vias are the type of vias that only connect the traces between the inner layers,so they cannot be seen from the surface of the PCB.

The figure is a schematic diagram of the cross-sectional structure of an 8-layer board:

A: Through hole(L1-L8)

B: buried hole (L2-L7)

C: blind hole (L7-L8)

D: blind hole (L1-L3)

Note: The following examples all take 8-layer board as an example

Blind and buried hole circuit boards, also known as HDI boards, are often used in high-end products such as mobile phones and GPS navigation. The structure of conventional multilayer circuit boards includes inner and outer circuits, and then uses drilling, and the process of metallization in the hole, so as to realize the connection function between the inner layers of the lines. Next, let's learn about its precautions and maintenance.

Precautions

If you want to copy the board with blind and buried holes, it is relatively difficult. Generally, when you copy the board on the mobile phone board and HDI board, you will encounter blind and buried holes, so pay attention to the following:

1. Be careful and make preparations before copying the board;

2. The equipment must be advanced;

3. In the process of copying the board, it must be compared with the original board

4. Pay attention to the inspection and repeat the inspection many times.

Blind and buried via maintenance

In order to ensure that the circuit board with blind buried holes works well and reduce the failure rate of the circuit board, the circuit board should be maintained, including annual maintenance and semi-maintenance. The maintenance methods are as follows:

1. Annual maintenance of blind and buried vias

(1) Regularly check the capacity of the electrolytic capacitor in the circuit board. When the capacity of the electrolytic capacitor is found to be lower than 20% of the nominal capacity, it should be replaced in time; generally speaking, the working life of the electrolytic capacitor is about 10 years, so in order to ensure For the normal operation of the circuit board, all electrolytic capacitors should be replaced in about 10 years;

(2) For high-power devices coated with heat-dissipating silicone grease, check whether the heat-dissipating silicon grease is dry. For dry-solid heat-dissipating silicon grease, remove the dried heat-dissipating silicon grease and apply new heat-dissipating silicon grease to prevent circuit The high-power devices in the board burn out due to poor heat dissipation;

(3) Clean up the dust on the circuit board in time to ensure the dleanliness of the circuit board.

2. Blind buried via semi-maintenance

(1) Clean the dust on the circuit board every quarter, and use a special cleaning solution for the circuit board to clean it. After cleaning the dust on the circuit board, use a hair dryer to dry the circuit board;

(2) Observe whether the electronic components in the circuit board have been subjected to high temperature traces, and whether the electrolytic capacitor has bulged and leaked, and if so, replace it.