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ubruhin merged 2 commits into from
May 31, 2026
Merged

qfp: Rework footprints & fix too small pads #172

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qfp: Rework footprints & fix too small pads
ubruhin May 31, 2026
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ubruhin May 31, 2026
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149 changes: 87 additions & 62 deletions generate_qfp.py
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Original file line number Diff line number Diff line change
Expand Up @@ -16,7 +16,7 @@
from os import path
from uuid import uuid4

from typing import Iterable, List, Optional
from typing import Dict, Iterable, List, Optional, cast

from common import format_ipc_dimension as fd
from common import init_cache, now, save_cache, sign
Expand Down Expand Up @@ -57,6 +57,7 @@
FootprintPad,
LetterSpacing,
LineSpacing,
MinCopperClearance,
Mirror,
Package,
Package3DModel,
Expand All @@ -79,35 +80,65 @@
text_y_offset = 0.7
silkscreen_offset = 0.150 # 150 µm

# Footprint Expert Guidelines mentions that two separate courtyard values may
# be used for body/leads vs. pads, while by default they are assumed to be
# equal. I think this would lead to too much courtyard, so I'd suggest to use
# a minimal courtyard of 0.1mm around pads.
courtyard_around_pads = 0.1 # 100 µm


# Initialize UUID cache
uuid_cache_file = 'uuid_cache_qfp.csv'
uuid_cache = init_cache(uuid_cache_file)


# Excess as a function of pitch according to IPC-7351C.
# Based on Footprint Expert Guidelines, Chapter 7.0 (Nominal Calculation)
Excess = namedtuple('Excess', 'toe heel side courtyard')
DENSITY_LEVEL_A = { # Most
1.00: Excess(0.35, 0.45, 0.06, 0.40),
0.80: Excess(0.30, 0.40, 0.05, 0.40),
0.65: Excess(0.25, 0.35, 0.03, 0.40),
0.50: Excess(0.20, 0.30, 0.00, 0.40),
0.40: Excess(0.20, 0.30, -0.01, 0.40),
}
DENSITY_LEVEL_B = { # Nominal
1.00: Excess(0.30, 0.40, 0.05, 0.20),
0.80: Excess(0.25, 0.35, 0.04, 0.20),
0.65: Excess(0.20, 0.30, 0.02, 0.20),
0.50: Excess(0.15, 0.25, -0.01, 0.20),
0.40: Excess(0.15, 0.25, -0.02, 0.20),
}
DENSITY_LEVEL_C = { # Least
1.00: Excess(0.25, 0.35, 0.04, 0.10),
0.80: Excess(0.20, 0.30, 0.03, 0.10),
0.65: Excess(0.15, 0.25, 0.01, 0.10),
0.50: Excess(0.10, 0.20, -0.02, 0.10),
0.40: Excess(0.10, 0.20, -0.03, 0.10),
}
DENSITY_LEVELS: List[Dict[str, object]] = [
{
'pitch_above': 1.0,
'C': Excess(0.30, 0.40, 0.08, 0.10),
'B': Excess(0.35, 0.50, 0.10, 0.20),
'A': Excess(0.40, 0.60, 0.12, 0.40),
},
{
'pitch_above': 0.8,
'C': Excess(0.25, 0.35, 0.06, 0.10),
'B': Excess(0.30, 0.45, 0.08, 0.20),
'A': Excess(0.35, 0.65, 0.10, 0.40),
},
{
'pitch_above': 0.65,
'C': Excess(0.20, 0.30, 0.04, 0.10),
'B': Excess(0.25, 0.40, 0.06, 0.20),
'A': Excess(0.30, 0.50, 0.08, 0.40),
},
{
'pitch_above': 0.5,
'C': Excess(0.15, 0.25, 0.02, 0.10),
'B': Excess(0.20, 0.35, 0.04, 0.20),
'A': Excess(0.25, 0.45, 0.06, 0.40),
},
{
'pitch_above': 0.4,
'C': Excess(0.10, 0.20, 0.00, 0.10),
'B': Excess(0.15, 0.30, 0.02, 0.20),
'A': Excess(0.20, 0.40, 0.04, 0.40),
},
{
'pitch_above': 0.0,
'C': Excess(0.10, 0.20, 0.00, 0.10),
'B': Excess(0.15, 0.30, 0.02, 0.20),
'A': Excess(0.20, 0.40, 0.04, 0.40),
},
]


def excess_by_density(pitch: float, level: str) -> Excess:
for table in DENSITY_LEVELS:
if pitch > cast(float, table['pitch_above']):
return cast(Excess, table[level])
assert False


class QfpConfig:
Expand Down Expand Up @@ -188,23 +219,6 @@ def description(self) -> str:
)
)

def excess_by_density(self, density: str) -> Excess:
"""
Return the `Excess` based on the specified density level ('A', 'B' or
'C') and the pitch.
"""
try:
if density == 'A':
return DENSITY_LEVEL_A[self.pitch]
elif density == 'B':
return DENSITY_LEVEL_B[self.pitch]
elif density == 'C':
return DENSITY_LEVEL_C[self.pitch]
else:
raise ValueError('Invalid density level: {}'.format(density))
except KeyError:
raise ValueError('Unhandled pitch: {}'.format(self.pitch))

def __str__(self) -> str:
return self.ipc_name()

Expand Down Expand Up @@ -421,6 +435,7 @@ def _uuid(identifier: str) -> str:
generated_by=GeneratedBy(''),
categories=[Category(pkgcat)],
assembly_type=AssemblyType.SMT,
min_copper_clearance=(MinCopperClearance(0.15) if (config.pitch < 0.5) else None),
)

for p in range(1, config.lead_count + 1):
Expand All @@ -444,7 +459,7 @@ def add_footprint_variant(
uuid_text_value = _uuid('text-value-{}'.format(key))

# Pad excess according to IPC density levels
excess = config.excess_by_density(density_level)
excess = excess_by_density(config.pitch, density_level)

# Lead contact offsets
lead_contact_x_offset = (
Expand All @@ -468,7 +483,18 @@ def add_footprint_variant(
package.add_footprint(footprint)

# Pads
pad_width = config.lead_width + excess.side * 2
# Trim width to maintain 0.15mm clearance, as documented in
# Footprint Expert Guidelines, Minimum pad to pad, page 71.
pad_width = min(config.lead_width + 2 * excess.side, config.pitch - 0.15)
# Increase pad width to a minimum value, because the tolerances
# specified for lead widths are sometimes very wide, possibly
# causing pads thinner than the maximum lead width. This is not
# specified in any standard, but I guess it is good to ensure
# *some* minimum pad width (even though maybe less than the maximum
# lead width).
pad_width = max(pad_width, config.lead_width + 0.03)
# Sanity check that we don't create pads thinner than the leads:
assert pad_width >= config.lead_width
pad_length = config.lead_contact_length + excess.heel + excess.toe
for p in range(1, config.lead_count + 1):
pad_uuid = uuid_pads[p - 1]
Expand Down Expand Up @@ -563,15 +589,15 @@ def add_footprint_variant(

x_min = (
abs(pos_last.x)
+ config.lead_width / 2
+ pad_width / 2
+ excess.side
+ silkscreen_offset
+ line_width / 2
)
x_max = config.body_size_x / 2 + line_width / 2
y_min = (
abs(pos_first.y)
+ config.lead_width / 2
+ pad_width / 2
+ excess.side
+ silkscreen_offset
+ line_width / 2
Expand Down Expand Up @@ -643,19 +669,19 @@ def add_footprint_variant(
footprint.add_circle(pin1_dot)

def _create_outline_vertices(
offset: float = 0, around_pads: bool = False
offset: float = 0, min_pads_offset: Optional[float] = None
) -> List[Vertex]:
x_max = config.lead_span_x / 2
x_mid = config.body_size_x / 2
x_min = abs(pos_last.x) + config.lead_width / 2
y_max = config.lead_span_y / 2
y_mid = config.body_size_y / 2
y_min = abs(pos_first.y) + config.lead_width / 2
if around_pads:
x_max += excess.toe
x_min += excess.side
y_max += excess.toe
y_min += excess.side
x_max = config.lead_span_x / 2 + offset
x_mid = config.body_size_x / 2 + offset
x_min = abs(pos_last.x) + config.lead_width / 2 + offset
y_max = config.lead_span_y / 2 + offset
y_mid = config.body_size_y / 2 + offset
y_min = abs(pos_first.y) + config.lead_width / 2 + offset
if min_pads_offset is not None:
x_max = max(x_max, config.lead_span_x / 2 + excess.toe + min_pads_offset)
x_min = max(x_min, abs(pos_last.x) + pad_width / 2 + min_pads_offset)
y_max = max(y_max, config.lead_span_y / 2 + excess.toe + min_pads_offset)
y_min = max(y_min, abs(pos_first.y) + pad_width / 2 + min_pads_offset)
vertices = [ # Starting at top left
# Top
(-x_min, y_max),
Expand All @@ -682,10 +708,7 @@ def _create_outline_vertices(
(-x_mid, y_mid),
(-x_min, y_mid),
]
return [
Vertex(Position(x + sign(x) * offset, y + sign(y) * offset), Angle(0))
for (x, y) in vertices
]
return [Vertex(Position(x, y), Angle(0)) for (x, y) in vertices]

# Package Outline
footprint.add_polygon(
Expand All @@ -707,7 +730,9 @@ def _create_outline_vertices(
width=Width(0),
fill=Fill(False),
grab_area=GrabArea(False),
vertices=_create_outline_vertices(offset=excess.courtyard, around_pads=True),
vertices=_create_outline_vertices(
offset=excess.courtyard, min_pads_offset=courtyard_around_pads
),
)
)

Expand Down Expand Up @@ -875,7 +900,7 @@ def generate_3d(
configs=configs,
generate_3d_models=generate_3d_models,
pkgcat='3363b8b1-6fa8-4041-962e-5f839cfd86b7',
version='0.4',
version='0.5',
create_date='2019-02-07T21:03:03Z',
)
save_cache(uuid_cache_file, uuid_cache)
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