The barrels of the vias will still be plated with copper the same as any other via on the board, the only difference is the empty air in barrel is replaced with the fill material. Because of this, conductive filled vias are not recommended for Via In Pad processing where the purpose of the fill is the reinforce the stability of the copper pad that is plated over the hole.Ī common misconception is that a non-conductive fill will either not pass any or only a very weak electrical signal through the via. Metal will heat and expand much more rapidly than the surrounding laminate and this may cause fractures between the pads and hole wall. The main drawback to conductive filled vias is the difference in CTE (Coefficient of Thermal Expansion) between the metallic fill and surrounding laminate. The metallic nature of the fill will naturally wick heat away from the chip to the other side of the board in many ways like a radiator. These can be found under chips that will be giving off a lot of heat where overheating is a concern. Generally, a conductive filled via will be used when heat or a large amount of current needs to be carried from one side of the board to another. You now have a solderable surface mount pad that also passes signal to inner layers eliminating the need to rout the signal to a via on the surface layer.The newly plated copper surface is flattened and smoothed (planarized) to be even with the surrounding copper features.The surface of the plugged via is then plated over with copper.Conductive material can be used but it’s not recommended since conductive material expands much more quickly than the surrounding laminate when heated which can cause cracks and pad failures during the assembly process.
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