ocdb/utils/landpatterns

Land patterns (sometimes called footprints) are the geometry associated with a single package that is to be placed on a design. In JITX, they are represented using the pcb-landpattern statement. The package ocdb/utils/landpatterns contains utilities for generating optimized land-patterns from parameters.

Table of Contents

• Helpful References
• Definitions
• Two Pin Land Patterns
  • Chip Land Patterns
  • Through Hole Land Patterns
    • Radial Through Hole Land Patterns
    • Axial Through Hole Land Patterns
• Small Outline (SO) Land Patterns
  • Small Outline Transistor (SOT) Land Patterns
• QFP Land Patterns
• QFN Land Patterns
• BGA Land Patterns
  • Depopulation Modifiers
    • Full Matrix
    • Staggered Matrix
    • Perimeter Matrix
    • Thermally Enhanced Matrix
    • Equilateral Triangle Matrix
    • Custom Depopulation

Helpful References

• JEDEC JESD30E, "Descriptive Designation System for Semiconductor-device packages"
• IPC 7351B, Generic Requirements for Surface Mount Design and Land Pattern Standard

Definitions

• Package: the physical device that will be placed (including the exterior plastic packaging and metal leads or terminations of a component). A package has one or more leads or terminations..
• Lead or Termination: The conductors on the package that interface with the electrical device.
• Land Pattern: the geometry on the layers of the board that sits underneath the package. A landpattern has one or more pads or and zero or more layers.
• Pad: the geometry on the layers associated with a single lead or termination of the component.

Two Pin Land Patterns

Chip Land Patterns

Two pin chip land patterns are commonly used for passive devices. The following generators are used to generate land patterns for these components that are compliant with IPC specifications.

public defn make-two-pin-chip-landpattern (length:Toleranced,
                                           width:Toleranced,
                                           lead-length:Toleranced)

Create a two pin surface mount (chip) non-polarized land pattern.

• length: the length of the component.
• width: the width of the component.
• lead-length: the length of the leads of the component.

public defn make-two-pin-chip-landpattern (length:Toleranced,
                                           width:Toleranced,
                                           lead-length:Toleranced,
                                           polarized?:True|False)

Create a two pin surface mount (chip) land pattern with optional polarization

• length: the length of the component.
• width: the width of the component.
• lead-length: the length of the leads of the component.
• polarized?: true if the land pattern is polarized, false otherwise.

public defn make-two-pin-chip-landpattern (length:Toleranced,
                                           width:Toleranced,
                                           lead-length:Toleranced,
                                           lead-width:Toleranced)

Create a two pin surface mount (chip) land pattern with a lead width that is different from the component width.

• length: the length of the component.
• width: the width of the component.
• lead-length: the length of the leads of the component.
• lead-width: the width of the leads of the component, which may be different than the width of the component.

public defn make-two-pin-chip-landpattern (length:Toleranced,
                                           width:Toleranced,
                                           lead-length:Toleranced,
                                           lead-width:Toleranced,
                                           polarized?:True|False)

Create a two pin surface mount (chip) land pattern with a lead width that is different from the component width and optional polarization.

• length: the length of the component.
• width: the width of the component.
• lead-length: the length of the leads of the component.
• lead-width: the width of the leads of the component, which may be different than the width of the component.
• polarized?: true if the land pattern is polarized, false otherwise.

Example : A Surface Mount Capacitor

The associated datasheet can be found here

pcb-landpattern TH3Axxx : 
  make-two-pin-chip-landpattern(tol(3.2, 0.2), ; package-length, L
                                tol(1.6, 0.2), ; package-width, W
                                tol(0.8, 0.3), ; lead-length, P
                                tol(1.2, 0.1), ; lead-width, Tw
                                true)          ; polarized ?

Through Hole Land Patterns

Radial Through Hole Land Patterns

Supported two-pin through hole land patterns are either axial or radial.

public defn make-two-pin-radial-landpattern (component-diameter:Toleranced,
                                             lead-spacing:Double,
                                             lead-diameter:Toleranced)

Create a two-pin radial landpattern.

• component-diameter: the diameter of the component package
• lead-spacing: the distance between leads.
• lead-diameter: the diameter of the leads.

public defn make-two-pin-radial-landpattern (component-diameter:Toleranced,
                                             lead-spacing:Double,
                                             lead-diameter:Toleranced
                                             polarized?:True|False)

Create a two-pin radial landpattern with optional polarity.

• component-diameter: the diameter of the component package
• lead-spacing: the distance between leads.
• lead-diameter: the diameter of the leads.
• polarized?: true if the land pattern is polarized, false otherwise.

Axial Through Hole Land Patterns

public defn make-two-pin-axial-landpattern (component-diameter:Toleranced,
                                             lead-spacing:Double,
                                             lead-diameter:Toleranced)

Create a two-pin radial landpattern.

• component-diameter: the diameter of the component package
• lead-spacing: the distance between leads.
• lead-diameter: the diameter of the leads.

public defn make-two-pin-axial-landpattern (component-diameter:Toleranced,
                                            lead-spacing:Double,
                                            lead-diameter:Toleranced
                                            polarized?:True|False)

Create a two-pin radial landpattern with optional polarity.

• component-diameter: the diameter of the component package
• lead-spacing: the distance between leads.
• lead-diameter: the diameter of the leads.
• polarized?: true if the land pattern is polarized, false otherwise.

Small Outline Land Patterns

A small outline (SO) package is a package with pins along two sides of the component.

JEDEC symbol to JITX Generator Arguments

The following table may help in converting JEDEC-style dimensions into arguments for the JITX small outline landpattern generator.

public defn make-n-pin-soic-landpattern (num-pins:Int,
                                         pitch:Double,               ; e
                                         lead-span:Toleranced,       ; E
                                         package-length:Toleranced,  ; E1
                                         package-width:Toleranced,   ; D
                                         terminal-length:Toleranced, ; L
                                         terminal-width:Toleranced)  ; b

Create an SO land pattern.

• num-pins: the number of pins of the package (must be even).
• pitch: the pitch of the leads or terminals (mm), e in the table above.
• lead-span: the distance from lead-edge to lead-edge (mm), E in the table above.
• package-length: the size of the package in the same dimension as the lead-span (mm), E1 in the table above.
• package-width: the size of the package in the orthogonal dimension as lead-span (mm), D in the table above.
• terminal-length: the length of terminals or leads in contact with the land pattern (mm), L in the table above.
• terminal-width: the size of the terminals or leads in contact with the land pattern, in the orthogonal dimension to terminal-length (mm), b in the table above.

Example Usage

pcb-landpattern SO8N : 
  make-n-pin-soic-landpattern(8,    ; number of pins
                              1.27 ; pitch
                              min-typ-max(5.8, 6.0, 6.2) ; lead-span
                              min-typ-max(4.8, 4.9, 5.0) ; package-length
                              min-typ-max(3.8, 3.9, 4.0) ; package-width
                              min-typ-max(0.4, 0.8, 1.27) ; lead-length, using average as typical
                              min-typ-max(0.28, 0.38, 0.48)) ; lead-width, using average as typical

See The Model a Land Pattern tutorial for more details on parametric land pattern generation.

SOT Land Patterns

SOT landpatterns can be defined using the more general purpose API call, make-dual-row-smd-landpattern which creates a two-row SMD land pattern with different numbers of pins on either side.

public defn make-dual-row-smd-landpattern (primary-num-pins:   Int,
                                          secondary-num-pins:  Int,
                                          primary-pin-pitch:   Double,
                                          secondary-pin-pitch: Double,
                                          lead-span:           Toleranced,
                                          package-length:      Toleranced,
                                          package-width:       Toleranced,
                                          terminal-length:     Toleranced,
                                          terminal-width:      Toleranced,
                                          polarity-marker?:    True|False)

• primary-num-pins: the number of pins on one side of the land pattern
• secondary-num-pins: the number of pins on the other side of the land pattern
• primary-pin-pitch: the pitch of pins on the primary side of the land pattern
• secondary-pin-pitch: the pitch of the pins on the other side of the land pattern
• lead-span: the lead span across the land pattern
• package-length: the length of the package
• package-width: the width of the package
• terminal-length: the length of the terminals
• terminal-width: the width of the terminals
• polarity-marker?: whether to add a polarity marker to the landpattern or not

Example Usage

pcb-landpattern SOT-23 :
  make-dual-row-smd-landpattern(
      n1, n2, p1, p2, 
      lead-span, package-length, package-width, 
      terminal-length, terminal-width, 
      polarity-marker?: True|False) where :
  val n1 = 2
  val n2 = 1
  val p1 = 1.9
  val p2 = 0.0 ; unneeded for one pin
  val lead-span       = min-typ-max(2.1, 2.37, 2.634) ; E
  val package-length  = tol(1.3, 0.1)                 ; E1
  val package-width   = min-typ-max(2.8, 2.9, 3.04),  ; D
  val terminal-length = tol(0.4, 0.1)
  val terminal-width  = tol(0.5, 0.1)
  val polarity-marker? = false

QFP Land Patterns

A quad flat package (QFP) is a package with pins along all four sides of the component.

JEDEC symbol to JITX Generator Arguments

public defn make-qfp-landpattern (num-pins:Int,
                                  pitch:Double,               ; e
                                  lead-span:Toleranced,       ; E, D
                                  package-size:Toleranced,    ; E1, D1
                                  terminal-length:Toleranced, ; L
                                  terminal-width:Toleranced   ; b
                                  exposed-metal-heat-feature?:Shape ; optional thermal pad

• num-pins: the number of pins of the package (must be even).
• pitch: the pitch of the leads or terminals (mm), e in the table above.
• lead-span: the distance from lead-edge to lead-edge (mm), E in the table above.
• package-size: the size of the package, E1, D1 in the table above. The package is assumed to be square.
• terminal-length: the length of terminals or leads in contact with the land pattern (mm), L in the table above.
• terminal-width: the size of the terminals or leads in contact with the land pattern, in the orthogonal dimension to terminal-length (mm), b in the table above.
• exposed-metal-heat-feature?: an optional parameter for a thermal pad shape.

Example Usage

pcb-landpattern QFP-100 :
  make-qfp-landpattern(
      num-pins, pitch, 
      lead-span, package-size,
      terminal-length, terminal-width,
      thermal-pad) where :
    val num-pins     = 100 ; the total number of pins
    val pitch        = 0.5 ; the distance between pin centers
    val lead-span    = min-typ-max(15.8, 16.0, 16.2) ; the distance between the outer edges of the leads
    val package-size = min-typ-max(13.8, 14.0, 14.2) ; the size of the package, assumed to be square
    val terminal-width   = min-typ-max(0.17, 0.22, 0.27) ; the width of the leads
    val terminal-length  = min-typ-max(0.45, 0.60, 0.70) ; the length of the leads
    val thermal-pad = false

QFN Land Patterns

A quad flat package no-lead (QFN) is a quad landpattern where the terminals are pads on the underside of the component, as opposed to leads that extend outside the component (see QFP Land Patterns).

JEDEC symbol to JITX Generator Arguments

public defn make-qfn-landpattern (num-pins:Int, 
                                  pitch:Double, ; e
                                  package-size:Toleranced, ; E, D
                                  terminal-length:Toleranced, ; L
                                  terminal-width:Toleranced, ; b
                                  corner-pads?:False|[Pad, Pad], ; L1 x b
                                  exposed-metal-heat-feature?:Shape|False) : ; optional thermal pad

• num-pins: the number of pins of the package (must be even).
• pitch: the pitch of the leads or terminals (mm), e in the table above.
• package-size: the size of the package, E, D in the table above. The package is assumed to be square.
• terminal-length: the length of terminals or leads in contact with the land pattern (mm), L in the table above.
• terminal-width: the size of the terminals or leads in contact with the land pattern, in the orthogonal dimension to terminal-length (mm), b in the table above.
• corner-pads?: optional pair of pcb-pad definitions to use to replace the corner pads on the landpattern.
• exposed-metal-heat-feature?, an optional

Example Usage

pcb-landpattern QFN-28 :
  make-qfn-landpattern(
      num-pins, pitch, 
      package-size, lead-length, lead-width
      corner-pads, 
      thermal-pad,) where :
    val num-pins     = 28  ; the total number of pins, must be divisible by 4
    val pitch        = 0.5 ; the pitch of the pins
    val package-size = min-typ-max(3.90, 4.00, 4.10) ; the size of the package, assumed to be square
    val lead-length  = min-typ-max(0.30, 0.40, 0.50) ; the length of the lead terminals
    val lead-width   = min-typ-max(0.20, 0.25, 0.30) ; the width of the lead terminals
    
    ; Optional Corner Pad Modifiers
    val corner-pads  = [
      smd-pad(loc(-0.1, 0.0) * Rectangle(0.45, 0.21))
      smd-pad(loc(-0.1, 0.0) * Rectangle(0.45, 0.21))
    ]

    ; Optional thermal pad
    val thermal-pad = false

Note: some trial and error might be required to find dimensions for corner pad overrides. In this case, the length was found using the max value of L1 in the table, and the width was found empirically by measuring the width of the other pads.

BGA Land Patterns

A ball grid array (BGA) package uses a matrix of solder balls on the bottom of the package, as opposed to exposed metal terminals.

JEDEC symbol to JITX Generator Arguments

                                     num-cols:Int,
                                     pitch:Double,
                                     ball-diameter:Double,
                                     package-length:Toleranced,
                                     package-width:Toleranced,
                                     modifier:BGAModifier) :

• num-rows : the number of rows of package
• num-cols : the number of columns of the package
• pitch : the pitch of the solder bumps
• ball-diameter : the nominal/typical diameter of the solder balls
• package-length : the length of the package
• package-width : the width of the package
• modifier : the depopulation and/or pitch modifier

Example Usage

pcb-landpattern BGA-64 :
  make-bga-landpattern(
      num-rows, num-cols
      pitch, ball-diameter
      package-length, package-width
      modifier
  ) where :
    val num-rows = 8 ; Number of rows in the matrix
    val num-cols = 8 ; Number of columns in the matrix
    val pitch    = 0.50 ; the spacing between ball centers
    val ball-diameter = 0.28 ; the diameter of the solder balls
    val package-length = min-typ-max(4.85, 5.0, 5.15) ; the length of the package
    val package-width  = min-typ-max(4.85, 5.0, 5.15) ; the width of the package

    ; The BGA Modifier. See ocdb/utils/landpatterns for more
    ; modifiers, supported are StaggeredMatrix, EquilateralTriangleMatrix,
    ; PerimeterMatrix, ThermallyEnhancedMatrix.
    val modifier = FullMatrix()

Depopulation Modifiers

The make-bga-package argument uses a special argument named modifier which allows for a variety of depopulation and ball spacing strategies. The currently supported depopulation modifiers are:

FullMatrix

In a FullMatrix (the default) no pads will be depopulated.

defn FullMatrix () -> BGAModifier

StaggeredMatrix

In a StaggeredMatrix, every other pad is depopulated.

defn StaggeredMatrix () -> BGAModifier

PerimeterMatrix

In a PerimeterMatrix, a range of rows and columns in the center will be depopulated

defn PerimeterMatrix (rows:Range, cols:Range) -> BGAModifier

• rows: the range of rows to depopulate
• cols: the range of cols to depopulate

Usage :

  ; rows 3,4,6 and columns 4,5 will be depopulated.
  val modifier = PerimeterMatrix(3 through 6, 4 through 5)

ThermallyEnhancedMatrix

A ThermallyEnhancedMatrix is like a PerimeterMatrix, except with some region in the center remaining populated.

defn ThermallyEnhancedMatrix (perimeter-rows:Range, perimeter-cols:Range
                              interior-rows:Range, interior-cols:Range ) -> BGAModifier

• perimeter-rows : the range of rows to depopulate
• perimeter-cols : the range of columns to depopulate
• interior-rows : the range of rows in the center to remain populated
• interior-cols : the range of columns in the center to remain populated

Usage :

; Pins (5,5) through (6,6) will be populated, while the other
; pins within the range (4,4) through (7,7) will be depopulated.
val modifier = ThermallyEnhancedMatrix(
  4 through 7, 4 through 7,
  5 through 6, 5 through 6,
))

EquilateralTriangleMatrix

An "EquilateralTriangleMatrix" is like a staggered matrix, but where the pads are all equidistant from each other. This means for any three adjacent pads with two in the same row or column, the centers of the pads form an equilateral triangle.

defn EquilateralTriangleMatrix () -> BGAModifier

CustomDepop

The CustomDepop modifier allows the caller to specify which pins are depopulated using a callback.

defn CustomDepop (callback: (Int, Int) -> True|False)

Usage :

  defn depop? (row:Int, col:Int) :
    ; Specify a list of custom depopulated pins
    val depopulated = [
      [0, 2]
      [0, 5]
      [2, 8]
      [3, 0]
      [5, 8]
      [6, 0]
      [8, 3]
      [8, 6]
    ]
    contains?(depopulated, [row, col])

  val modifier = CustomDepop(depop?)