Summary
The term "plug hole" is not a new term for the printed circuit board industry. At present, the Via holes of PCB boards used for packaging all require via plug oil, and the current multilayer boards are required to be solder-proof green paint plug holes; but the above process All of them are applied to the plugging operation of the outer layer, and the blind buried hole of the inner layer also requires plugging processing. This article will focus on the advantages and disadvantages of various plug hole processing techniques.
Keywords: Stack Via, CTE, Aspect Ratio, screen printing plug holes, resin
1. Introduction
In the era of HDI high-density connection technology, the line width and line distance will inevitably develop toward the trend of smaller and denser, which also leads to the emergence of different previous types of PCB structures, such as Via on Pad, Stack Via, etc. Under this premise, the inner buried hole is usually required to be completely filled and polished to increase the wiring area of the outer layer. The market demand not only tests the PCB manufacturer's process capability but also forces the original material supplier to develop more Hi-Tg , Low CTE, low water absorption, no solvent, low shrinkage, easy to grind, etc. to meet the needs of the industry. The main processes of the plug hole section are drilling, electroplating, hole wall roughening (pre-processing of the plug hole), plug hole, baking, grinding, etc. Here will be a more detailed introduction to the process of resin plug hole.
At the same time, due to the need for packaging, all Via holes need to be filled with ink or resin to prevent other functional hidden dangers caused by the hidden tin in the holes.
2. Current plug hole methods and capabilities
The current plug hole method generally uses the following techniques:
1. Resin filling (mostly used for inner plug holes or HDI/BGA package board)
2. Printing surface ink after plug hole drying
3. Use blank nets to print with plugs
4. Plug hole after HAL
3. Plug hole process and its advantages and disadvantages
Screen printing plug holes are currently widely used in the industry, because the main equipment required for printing machines are commonly owned by various companies; and the necessary tools are: printing screens, scrapers, and lower pads. , Alignment Pin, etc. are almost always available materials, the operation process is not very difficult to operate, with a single stroke scraper printed on the screen with the position of the inner plug hole diameter, by printing pressure Insert the ink into the hole, and in order to make the ink into the hole smoothly under the inner plug hole plate, you need to prepare a lower backing plate for the hole diameter of the plug hole to vent, so that the air in the hole can be smooth during the plug hole process Discharge and achieve 100% stuffing effect. Even so, the key to achieving the required plug hole quality is the optimization parameters of each operation, which includes the mesh, tension, blade hardness, angle, speed, etc. of the stencil will affect the plug hole quality, and Different plug hole diameter aspect ratio will also have different parameters to consider, the operator needs to have considerable experience to obtain the best operating conditions.