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Corrected footprint for Atmega-48-MHN and Atiny-48-MHN

Rene Poeschl requested to merge github/fork/poeschlr/qfn_28_mcu_atmel into master

Edit: i originally looked at the wrong page of the datasheet. This is now corrected.

The original footprint had the wrong EP size (taken from an unrelated application note)

Datasheets:

Symbol PR: https://github.com/KiCad/kicad-symbols/pull/769

Script PR: https://github.com/pointhi/kicad-footprint-generator/pull/149 Responsible file for the dimension is qfn-2x.yaml

Script params for reference:

QFN-28-1EP_4x4mm_P0.45mm_EP2.4x2.4mm:
  device_type: 'QFN'
  size_source: 'http://ww1.microchip.com/downloads/en/PackagingSpec/00000049BQ.pdf (Page 280)'
  ipc_class: 'qfn' # 'qfn_pull_back'
  body_size_x:
    nominal: 4
    tolerance: 0.05
  body_size_y:
    nominal: 4
    tolerance: 0.05
  lead_width:
    minimum: 0.17
    maximum: 0.27
  lead_len:
    minimum: 0.35
    maximum: 0.45

  EP_size_x:
    nominal: 2.4
    tolerance: 0.05
  EP_size_y:
    nominal: 2.4
    tolerance: 0.05
  EP_num_paste_pads: [2, 2]

  thermal_vias:
    count: [3, 3]
    drill: 0.2
    paste_via_clearance: 0.1
    EP_paste_coverage: 0.75
    paste_avoid_via: False

  pitch: 0.45
  num_pins_x: 7
  num_pins_y: 7
  chamfer_edge_pins: 0.1

Screenshot of the thermal vias version screenshot from 2018-07-17 14-28-09

32 pin version should have 3.1x3.1mm ep instead of 3.8x3.8mm Example datasheet:

Parameters:

QFN-32-1EP_5x5mm_P0.5mm_EP3.1x3.1mm:
  device_type: 'QFN'
  size_source: 'http://ww1.microchip.com/downloads/en/DeviceDoc/8008S.pdf (Page 20)'
  ipc_class: 'qfn' # 'qfn_pull_back'
  body_size_x:
    nominal: 5
    tolerance: 0.1
  body_size_y:
    nominal: 5
    tolerance: 0.1
  lead_width:
    minimum: 0.18
    maximum: 0.3
  lead_len:
    minimum: 0.3
    maximum: 0.5

  EP_size_x:
    minimum: 2.95
    nominal: 3.1
    maximum: 3.25
  EP_size_y:
    minimum: 2.95
    nominal: 3.1
    maximum: 3.25
  EP_num_paste_pads: [3, 3]

  thermal_vias:
    count: [3, 3]
    drill: 0.2
    paste_via_clearance: 0.1
    paste_between_vias: 1
    paste_rings_outside: 1
    grid: [1, 1]

  pitch: 0.5
  num_pins_x: 8
  num_pins_y: 8

screenshot from 2018-07-18 00-05-25

The AVR MCU uses an already existing footprint (3.6x3.6mm EP) it is not added here for this reason.

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