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What should be paid attention to in the processing of PCB plug holes

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With the development of electronic products in the direction of lightness, thinness and smallness, PCBs are also developing towards high density and high difficulty, and the requirements of customers are getting higher and higher. The requirements for holes are also getting higher and higher.

For example, there must be no solder resist ink entering the hole, causing tin beads to be hidden in the hole, no oil explosion, making it difficult to mount components, etc.

PCB via hole plug purpose: to prevent tin from passing through the component surface from the via hole to cause a short circuit during PCB over-wave soldering, to avoid flux residue in the via hole, to prevent solder balls from popping out during wave soldering, causing short circuit, and to prevent surface solder paste The flow into the hole causes virtual welding, which affects the mounting, maintains the surface flatness, and meets the customer's characteristic impedance requirements.

PCB plug hole requirements: copper in the via hole, solder mask can be plugged or not; there must be tin and lead in the via hole, there must be a certain thickness requirement (4um), no solder mask ink should enter the hole, causing the hole inside the hole. Hidden tin beads; through holes must have solder resist ink plug holes, opaque, and must not have tin circles, tin beads, and leveling requirements.

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The PCB plug hole is generally after the solder mask layer, and then the second layer of ink (green paint) is used to fill the heat dissipation hole (Termal Pad) with a diameter of less than 0.55mm.
The purpose of the plug hole:
1. When placing parts on DIP, avoid circuit short circuit caused by tin infiltration when passing through the tin furnace, especially in BGA design.
2. Maintain surface flatness.
3. Meet the customer's characteristic impedance requirements.
4. Avoid damage to the line signal, etc.

Things that should be noted:
There must be tin and lead in the via hole, with a certain thickness requirement (4 microns), and no solder resist ink should enter the hole, causing tin beads to be hidden in the hole; the via hole must have a solder resist ink plug hole, which is opaque and must not There are requirements for tin beading and flatness; for surface mount boards, especially BGA and IC mounting, the via holes must be flat, with a convex and concave plus or minus 1 mil, and there must be no red tin on the edges of the via holes.

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