We have 0.4mm pitch bga and board thickness have become 280 mills ,we can not drill a 5 mills via with 8 mills pad upto this thickness,what is the solution,any suggestions?
Try using a blind via from TOP-Layer2 which can the size you want and use larger "core"vias that can be drilled through the whole PCB.
Right now we have VIA on pad and drill is just 5 mills with pad of 8 mills,with this pad size we have just 2.374 mils pad to line,how we can increase the via size because it will decrease the pad to line distance which is minimum,if there is any misunderstanding then please explain your idea.
You need to consider using blind and buried vias to enable you to leave the via from top-l2 at the size it is. You can use buried vias and core vias to get the track out.
Having stack vias (BLIND/BURRIED) is a good approach but that is too costly:))
Will you please explain the core vias?
many thanks for your reply
Core vias are used in a blind/buried stack where for example you have an 8 layer board, you use blind/buried (microvias) from l1-l2 an l2-l3 then a core via crossng the core material from l3-l6 then l6-l7 and l7-l8 are microvias again. With the drill diameter you have this type of construction may well be your only option. Try talking to your fabricator who should be able to give you options / costs for this type of design.