In PCB manufacturing, the key points of the buried and plugged hole process involve multiple aspects such as material selection, process flow, equipment accuracy, and quality control. The following is a detailed introduction:
Material selection
Resin materials: Resin materials with low dielectric constant (Dk) and low dielectric loss factor (Df) should be selected to reduce impedance mismatch and dielectric loss during signal transmission and improve signal quality.
Ink material: If ink is used to fill the holes, ink with high hardness, small resin shrinkage change and strong adhesion to the hole wall should be selected to ensure the flatness and reliability of the hole filling.
Technological process
Drilling: According to the design requirements, the buried holes are made by using laser drilling or mechanical drilling technology. Laser drilling is suitable for situations with smaller diameters and can ensure the accuracy and consistency of the diameters.
Hole wall treatment: After drilling, the hole wall needs to be treated to remove glue residue and oil, etc., to enhance the adhesion between the hole wall and the subsequent filling material.
Fill:
Resin filling: Pour low dielectric constant materials such as epoxy resin into the buried holes to ensure uniform filling and no voids. Vacuum filling technology can be adopted during the filling process to improve the filling quality.
Ink filling: If ink is used to fill the holes, an aluminum mesh plate or ink blocking net should be used to accurately fill the ink into the buried holes to ensure that the ink is full and opaque.
Curing and grinding: After filling is completed, the resin or ink needs to be cured to achieve a certain hardness. After curing, the board surface still needs to be ground to ensure its flatness.
Electroplating: Electroplating treatment is carried out on the surface of the filling material to form a conductive path and ensure the conductivity of the buried holes.
Equipment accuracy
Drilling equipment: High-precision drilling equipment should be selected to ensure the accuracy of the hole diameter and position of the buried holes.
Filling equipment: During the filling process, it is necessary to ensure the uniformity and consistency of the filling material to avoid the formation of voids and bubbles.
Curing and grinding equipment: The curing equipment needs to be capable of precisely controlling temperature and time to ensure the curing quality of the filling material. The grinding equipment needs to be able to precisely control the grinding depth and accuracy to ensure the flatness of the plate surface.
Quality control
Visual inspection: Check the appearance quality of the buried holes after filling the holes, such as whether there are any cavities, bubbles, ink contamination, etc.
Electrical testing: Conduct electrical testing on the buried holes to ensure that their conductivity meets the requirements.
Reliability testing: Conduct reliability tests such as thermal shock and wet heat cycling to evaluate the long-term stability of buried and plugged holes.
