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Breakthrough in copper-filled HDI micro-vias

gefülltes Microvia 

ANDUS has qualified and released a new internal process for the galvanic filling of micro-vias. With this process, ANDUS is now able to offer closed micro-vias that are no longer visible from the outside.

Compared to other filling methods, these new micro-vias have been improved regarding two decisive aspects:

  • The thickness of the basic copper layer remains unchanged during the process. This is important to be able to create micro-conductors of a width of down to 50 µm also on the outer layer. In the illustration the used 12 µm laminate copper has been made visible by etching.
  • The micro-vias are completely filled with massive copper. On the one hand this makes the connection more reliable and stable towards thermo-mechanic and mechnic stress. On the other hand the high copper content facilitates heat conduction.

Filled micro-vias have been developed so that BGA balls on micro-vias can be soldered more cleanly. There is no problem to solder BGAs with a pitch of more than 0.8 mm on normal micro-vias. Studies have shown that the possibly remaining air bubble does not affect reliability.

ungefülltes Microvias gefülltes Microvia Pad
left: conventional micro-via with BGA ball (cross section). right: filled micro-via in pad (top view)

For µBGAs with a pitch of <0.8 mm the remaining rest rings, however, are relatively narrow so that after levelling the micro-vias a significantly bigger pad area remains.

The above-mentioned fine-pitch components can only be routed with micro-conductors on thin copper foils. Thus, the newly developed micro-via technology and the new direct laser exposure process complement each other ideally.