HDI and BGA PCB Design

Flux is an AI hardware engineer. It plans dense PCB stackups and routes fine-pitch parts with the via types the board uses.

Set up an HDI stackup

Ask Flux to define the layer count, microvia layers, and via spans for the board.

Set up a six-layer HDI stackup with microvias between the outer layers and layer 2.
Plan an HDI stackup with two sequential microvia spans for the processor BGA.
Set the layer count and via spans for this fine-pitch memory board.
Use microvias to connect the top layer to layer 2 and layer 2 to layer 3.

Name the layer count and the layer transitions that the routing needs. Flux configures through-hole, blind, buried, or microvia options in the stackup.

Review the available via types and their spans in the Stackup Editor. For the via settings, see Vias in PCB Design and Smart Vias.

Choose via types and spans

Ask Flux to use via types that reach the required layers.

Use a blind via from the top layer to layer 2 for this BGA escape.
Connect layers 2 and 3 with a buried via.
Use a microvia from the top layer to the adjacent inner layer for the fine-pitch pads.
Set the through-hole via for connections that pass from the top layer to the bottom layer.

Through-hole vias connect the two outer layers and the layers between them. Blind vias connect an outer layer to an inner layer. Buried vias connect internal layers without reaching an outer layer. Microvias connect adjacent layers.

Flux uses the via types configured in the board stackup. See Vias in PCB Design for via configuration and Smart Vias for layer transitions.

Fan out BGA connections

Ask Flux to escape the BGA pads with the configured via types and routing rules.

Fan out the SoC BGA using the microvia spans from the stackup.
Escape the memory BGA with blind and buried vias, and group the DDR lanes.
Fan out this BGA and use a neckdown at each fine-pitch pad where needed.
Route the connections from the inner BGA rows to the assigned signal layers.

Flux routes BGA and fine-pitch connections with the via types available in the stackup. It can use neckdowns at pads to connect fine-pitch terminals to wider traces.

For DDR escape routing and timing, see DDR and PCIe PCB Design.

Route QFN and dense connector pads

Ask Flux to route QFN and connector pads with short escape paths.

Route the QFN pads with neckdowns where the pad pitch requires them.
Escape the inner rows of this fine-pitch connector to the assigned layers.
Route the high-density connector signals and keep the pair groups together.
Connect the fine-pitch pads with the via spans in the board stackup.

Flux can route QFN, dense connector, and other fine-pitch connections. Ask for neckdowns where pads need narrower trace widths.

Repair acid traps near vias

Ask Flux to repair an acid trap with a short dogbone trace.

Repair the acid trap at the escape via beside U3 with a short dogbone trace.
Add a short dogbone to remove the acute copper corner at the BGA via.
Fix the acid trap on this fine-pitch connection and keep the route on its current layer.

Flux repairs via acid traps with short dogbone traces. You can name the part or select the affected connection in the PCB editor.

Check the rules against manufacturing capabilities

Ask Flux to check the HDI design against a manufacturing profile.

Check the via spans and clearances against the selected fabricator profile.
Review the BGA fanout against the manufacturing rules for this board.
Run DRC with the active manufacturing profile and list the HDI issues.
Adjust the stackup and via choices to match this fabricator's capabilities.

Manufacturing profiles define the fabricator's capabilities and rules. Flux can check the board's design rules against the selected profile. See Manufacturing Profiles and Design Rule Check (DRC).

Check manufacturing files before ordering

Ask Flux to check the manufacturing files for the HDI board before you order.

Check the manufacturing files for the HDI board before I order.
Review the exported files for the BGA escape and via layers.
Check the fabrication outputs against the board and its manufacturing profile.
List any manufacturing-file issues that need changes before ordering.

Flux checks manufacturing files before you order. See Check manufacturing files before you order.


Next to read:
PCB Layout Object Tree: Organizing and Managing Design Elements
On This Page
HDI and BGA PCB DesignSet up an HDI stackupChoose via types and spansFan out BGA connectionsRoute QFN and dense connector padsRepair acid traps near viasCheck the rules against manufacturing capabilitiesCheck manufacturing files before orderingRelated pages