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Oct 8, 2025
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Unify + document default stackups #61

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74 changes: 63 additions & 11 deletions board_config.zen
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Original file line number Diff line number Diff line change
Expand Up @@ -292,10 +292,32 @@ BASE_PREPREG = Material(
loss_tangent=0.025, # Standard prepreg material
)

# Stackup Design Philosophy
#
# Layer convention for 4L/6L/8L stackups:
# - First 3 layers: SIG/GND/PWR (always)
# - Last layer: SIG (always)
#
# This enables module reusability - a 4L module can be ported to 6L/8L by using the
# same top 3 layers and bottom layer. Internal layers provide additional routing.
#
# Impedance Control:
# - GCPW (Grounded Coplanar Waveguide) for all impedance-controlled routing
# - L1 (top) is primary impedance-controlled layer
# - L6/L8 (bottom) serve as backup impedance-controlled layers on 6L/8L
# - 8L also provides L6 as symmetric stripline (GND/SIG/GND)
Comment on lines +297 to +308
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smart

#
# Selection:
# - 2L: Simple, low speed
# - 4L: Standard, L1 impedance-controlled
# - 6L: More routing, L1 + L6 impedance-controlled
# - 8L: High density, L1 + L6 (stripline) + L8 impedance-controlled

# Common stackup configurations

# Base 2-layer stackup (1.6mm, 1oz outer)
# SIG/SIG
# Use case: Simple designs without dedicated power/ground planes
BASE_2L_STACKUP = Stackup(
materials=[FR4_CORE],
thickness=1.6,
Expand All @@ -312,6 +334,14 @@ BASE_2L_STACKUP = Stackup(

# Base 4-layer stackup (1.6mm, 1oz outer/0.5oz inner)
# SIG/GND/PWR/SIG
#
# Layers:
# L1: Mixed + impedance-controlled (GCPW, ref L2, 0.21mm coupling)
# L2: GND plane
# L3: PWR plane
# L4: Mixed signal
#
# Use: Standard stackup with dedicated GND/PWR planes. L1 for high-speed routing.
BASE_4L_STACKUP = Stackup(
materials=[FR4_CORE, BASE_PREPREG],
thickness=1.6,
Expand All @@ -322,7 +352,7 @@ BASE_4L_STACKUP = Stackup(
layers=[
CopperLayer(thickness=0.035, role="mixed"), # Top layer (1oz)
DielectricLayer(thickness=0.21040, material="Prepreg", form="prepreg"),
CopperLayer(thickness=0.0152, role="power"), # Inner L2 (0.5oz)
CopperLayer(thickness=0.0152, role="ground"), # Inner L2 (0.5oz)
DielectricLayer(thickness=1.065, material="FR4-Core", form="core"),
CopperLayer(thickness=0.0152, role="power"), # Inner L3 (0.5oz)
DielectricLayer(thickness=0.21040, material="Prepreg", form="prepreg"),
Expand All @@ -331,7 +361,17 @@ BASE_4L_STACKUP = Stackup(
)

# Base 6-layer stackup (1.6mm, 1oz outer/0.5oz inner)
# SIG/GND/(SIG/PWR)/(SIG/PWR)/GND/SIG
# SIG/GND/PWR/SIG/GND/SIG
#
# Layers:
# L1: Primary impedance-controlled (GCPW, ref L2, 0.099mm coupling)
# L2: GND plane
# L3: PWR plane
# L4: Mixed signal
# L5: GND plane
# L6: Backup impedance-controlled (GCPW, ref L5, 0.099mm coupling)
#
# Use: More routing space than 4L. Two ground planes for return paths.
BASE_6L_STACKUP = Stackup(
materials=[
FR4_CORE,
Expand All @@ -354,20 +394,32 @@ BASE_6L_STACKUP = Stackup(
layers=[
CopperLayer(thickness=0.035, role="mixed"), # Top layer (1oz)
DielectricLayer(thickness=0.09940, material="3313", form="prepreg"),
CopperLayer(thickness=0.0152, role="power"), # Inner L2 (0.5oz)
CopperLayer(thickness=0.0152, role="ground"), # Inner L2 (0.5oz)
DielectricLayer(thickness=0.55, material="FR4-Core", form="core"),
CopperLayer(thickness=0.0152, role="mixed"), # Inner L3 (0.5oz)
CopperLayer(thickness=0.0152, role="power"), # Inner L3 (0.5oz)
DielectricLayer(thickness=0.11640, material="2116", form="prepreg"),
CopperLayer(thickness=0.0152, role="mixed"), # Inner L4 (0.5oz)
DielectricLayer(thickness=0.55, material="FR4-Core", form="core"),
CopperLayer(thickness=0.0152, role="power"), # Inner L5 (0.5oz)
CopperLayer(thickness=0.0152, role="ground"), # Inner L5 (0.5oz)
DielectricLayer(thickness=0.09940, material="3313", form="prepreg"),
CopperLayer(thickness=0.035, role="mixed"), # Bottom layer (1oz)
],
)

# Base 8-layer stackup (1.6mm, 1oz outer/0.5oz inner)
# SIG/GND/SIG/PWR/GND/SIG/GND/SIG
# SIG/GND/PWR/SIG/GND/SIG/GND/SIG
#
# Layers:
# L1: Primary impedance-controlled (GCPW, ref L2, 0.116mm coupling)
# L2: GND plane
# L3: PWR plane
# L4: Mixed signal
# L5: GND plane
# L6: Secondary impedance-controlled (symmetric stripline, L5/L7 refs)
# L7: GND plane
# L8: Backup impedance-controlled (GCPW, ref L7)
#
# Use: High routing density. Three ground planes. L6 symmetric stripline for EMI control.
BASE_8L_STACKUP = Stackup(
materials=[
FR4_CORE,
Expand All @@ -390,19 +442,19 @@ BASE_8L_STACKUP = Stackup(
layers=[
CopperLayer(thickness=0.035, role="mixed"), # Top layer (1oz)
DielectricLayer(thickness=0.1164, material="2116", form="prepreg"),
CopperLayer(thickness=0.0152, role="power"), # Inner L2 (0.5oz)
CopperLayer(thickness=0.0152, role="ground"), # Inner L2 (0.5oz)
DielectricLayer(thickness=0.3, material="FR4-Core", form="core"),
CopperLayer(thickness=0.0152, role="mixed"), # Inner L3 (0.5oz)
CopperLayer(thickness=0.0152, role="power"), # Inner L3 (0.5oz)
DielectricLayer(thickness=0.0764, material="1080", form="prepreg"),
DielectricLayer(thickness=0.0764, material="1080", form="prepreg"),
CopperLayer(thickness=0.0152, role="power"), # Inner L4 (0.5oz)
CopperLayer(thickness=0.0152, role="mixed"), # Inner L4 (0.5oz)
DielectricLayer(thickness=0.3, material="FR4-Core", form="core"),
CopperLayer(thickness=0.0152, role="power"), # Inner L5 (0.5oz)
CopperLayer(thickness=0.0152, role="ground"), # Inner L5 (0.5oz)
DielectricLayer(thickness=0.0764, material="1080", form="prepreg"),
DielectricLayer(thickness=0.0764, material="1080", form="prepreg"),
CopperLayer(thickness=0.0152, role="mixed"), # Inner L6 (0.5oz)
DielectricLayer(thickness=0.3, material="FR4-Core", form="core"),
CopperLayer(thickness=0.0152, role="power"), # Inner L7 (0.5oz)
CopperLayer(thickness=0.0152, role="ground"), # Inner L7 (0.5oz)
DielectricLayer(thickness=0.1164, material="2116", form="prepreg"),
CopperLayer(thickness=0.035, role="mixed"), # Bottom layer (1oz)
],
Expand Down