0.5 mm pitch BGA designs are pushing the limit of conventional (mechanical) Printed circuits board towards laser drilled vias. The advantage of staying with mechanically drilled vias vs laser drill is cost. We offer two options:
Option 1: Laser Drill
With a 4 mil laser drilled via where the via is stacked or blind. A 4 mill laser drill can only penetrate 1 layer of dielectric if not stacked.
Laser drilled via is 4 mil in diameter and add 30% in cost to the tooling and the unit price of the PCB depending on the complexity of the design.
The advantage of using a 4 mil via is that it can give you more freedom with impedance and stack up planning as you can use wider traces when fanning out of the BGA. Additionally it can help reduce layout time through simplification of the routing.
Option 2: Mechanical Drill
Minimum mechanical drill size is 6 mils and therefore it can be drilled into a 10 mil pad with a 2 mil ring on the outer layers.
Using this approach eliminates the cost of laser drilling but because the vias are drilled in pad plugging, polishing and plating copper the BGA pads is required. This adds about 10% to the cost of the PCB.
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